@article{Meister2022.MMM.2021.3136684,

title = {Flexible Electronics for Wireless Communication: A Technology and Circuit Design Review With an Application Example},

author = {Tilo Meister and Koichi Ishida and Corrado Carta and Niko M\"{u}nzenrieder and Frank Ellinger},

doi = {10.1109/MMM.2021.3136684},

issn = {1557-9581},

year  = {2022},

date = {2022-04-01},

journal = {IEEE Microwave Magazine},

volume = {23},

number = {4},

pages = {24-44},

abstract = {There is a practical gap between conventional rigid electronics and bendable items from daily life, such as paper, tape, textiles, and the human body. This space can be bridged by flexible transistor technologies, which typically offer bendability, a light weight, ultrathin dimensions, transparency, some stretchability, suitability for large areas, and a low cost. Thanks to the continuous increase of the maximal operation frequency of flexible electronics, wireless communication is becoming one of the promising enablers for many new applications and is widely studied. For a long time, electronics have advanced in terms of speed, power consumption, integration density, and cost. In particular, reductions in feature sizes, which lead to improvements in integration density, are expected to keep slowing down, e.g. due to thermal noise constraints. This trend has long been predicted, and it has motivated the investigation of multiple alternative electronic technologies, including mechanically flexible ones.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9704875,

title = {Modeling the Short-Channel Effects in Coplanar Organic Thin-Film Transistors},

author = {Jakob Pruefer and Jakob Leise and James W Borchert and Hagen Klauk and Ghader Darbandy and Aristeidis Nikolaou and Benjam\'{i}n I\~{n}\'{i}guez and Thomas Gneiting and Alexander Kloes},

doi = {10.1109/TED.2022.3145779},

issn = {1557-9646},

year  = {2022},

date = {2022-03-01},

journal = {IEEE Transactions on Electron Devices},

volume = {69},

number = {3},

pages = {1099-1106},

abstract = {We have developed models for three different short-channel effects [subthreshold-swing degradation, threshold-voltage roll-off, and drain-induced barrier lowering (DIBL)] in coplanar organic thin-film transistors (TFTs) and verified them against the measured current\textendashvoltage characteristics of TFTs having channel lengths as small as $0.5 mu textm$ . To derive the models, the Schwarz\textendashChristoffel transformation was applied to obtain a complex mapping function that links the coplanar device geometry to an equivalent geometry in a different coordinate system in order to solve Laplace’s equation of the 2-D potential problem. The solution to this potential problem serves as the basis for the definition of the short-channel models, which can be incorporated into any compact dc models for coplanar TFTs that use the TFTs’ threshold voltage and subthreshold swing as input parameters. To verify the model, the channel-length-dependent effects were extracted from technology computer-aided design (TCAD) simulations (transfer characteristics and surface-potential profile) and from measurements performed on organic p-channel TFTs fabricated using high-resolution stencil lithography.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1126/sciadv.abm9845,

title = {Nanoscale flexible organic thin-film transistors},

author = {Ute Zschieschang and Ulrike Waizmann and J\"{u}rgen Weis and James W. Borchert and Hagen Klauk},

url = {https://www.science.org/doi/abs/10.1126/sciadv.abm9845},

doi = {10.1126/sciadv.abm9845},

year  = {2022},

date = {2022-01-01},

journal = {Science Advances},

volume = {8},

number = {13},

pages = {eabm9845},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.202101215,

title = {Subthreshold Swing of 59 mV decade−1 in Nanoscale Flexible Ultralow-Voltage Organic Transistors},

author = {Michael Geiger and Robin Lingst\"{a}dt and Tobias Wollandt and Julia Deuschle and Ute Zschieschang and Florian Letzkus and Joachim N Burghartz and Peter A van Aken and Thomas R Weitz and Hagen Klauk},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202101215},

doi = {https://doi.org/10.1002/aelm.202101215},

year  = {2022},

date = {2022-01-01},

journal = {Advanced Electronic Materials},

volume = {8},

pages = {2101215},

abstract = {Abstract Organic thin-film transistors (TFTs) that provide subthreshold swings near the theoretical limit together with large on/off current ratios at very low operating voltages require high-capacitance gate dielectrics with a vanishingly small defect density. A promising approach to the fabrication of such dielectrics at temperatures sufficiently low to allow TFT fabrication on polymeric substrates are hybrid dielectrics consisting of a thin metal oxide layer in combination with a molecular self-assembled monolayer (SAM). Here, the electrical and surface properties of titanium oxide produced by the plasma-assisted oxidation of the surface of vacuum-deposited titanium gate electrodes and its use as the first component of a hybrid TiOx/SAM gate dielectric in flexible organic TFTs are investigated. These transistors have a gate-dielectric capacitance of about 1 µF cm−2, a subthreshold swing of 59 mV decade−1 (within measurement error of the physical limit at room temperature) for a wide range of channel lengths as small as 0.7 µm, and an on/off current ratio of 107 for a gate-source-voltage range of 1 V.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D1TC04230K,

title = {Photopatternable solid electrolyte for integrable organic electrochemical transistors: operation and hysteresis},

author = {Anton Weissbach and Lukas M Bongartz and Matteo Cucchi and Hsin Tseng and Karl Leo and Hans Kleemann},

url = {http://dx.doi.org/10.1039/D1TC04230K},

doi = {10.1039/D1TC04230K},

year  = {2022},

date = {2022-01-01},

journal = {J. Mater. Chem. C},

volume = {10},

pages = {2656-2662},

publisher = {The Royal Society of Chemistry},

abstract = {Organic electrochemical transistors (OECTs) have gained increasing attention during the last decade due to their potential for bioelectronic applications, mainly attributed to their mixed conductivity of both electrons and ions as well as their stability in electrolytic environments. Recent advances opened up new areas of applications for OECTs that range from traditional integrated circuits to unconventional brain-inspired devices. This progress is accompanied by comprehensive developments of new polymeric materials for the active channel. Meanwhile, very little effort has been devoted to the design of materials for the electrolyte \textendash a key element for the performance of OECTs. Here, we present a photopatternable solid electrolyte based on the ionic liquid [EMIM][EtSO4] in a polymer matrix. This solid electrolyte can be patterned with standard photolithographic techniques down to a resolution of 10 μm, allowing minimal leakage current and the avoidance of device crosstalk, which is essential for integrated circuits. When employed for PEDOT:PSS-based OECTs, we achieve excellent performance with on\textendashoff ratios of 105, a threshold voltage of 200 mV, and a sub-threshold swing of 61 mV dec−1. We characterize the solid electrolyte in detail and investigate the stability of OECT operation in ambient and inert atmosphere. Finally, we examine the pronounced hysteresis found in the transfer characteristics of these devices, for which we provide a way of quantification. This method allows revealing that the hysteresis saturates with the gate voltage range and that its extent is controllable through the scan rate, rendering it a highly appealing feature for integrated circuits and neuromorphic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{C.Strobel2022.DOISTART,

title = {Improved graphene-base heterojunction transistor with different collector semiconductors for high-frequency applications},

author = {C Strobel and C A Chavarin and S Leszczynski and K Richter and M Knaut and J Reif and S Voelkel and M Albert and C Wenger and J W Bartha and T and Mikolajick},

year  = {2022},

date = {2022-01-01},

journal = {Adv. Mater. Lett.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1021/acsami.2c10634,

title = {Novel Graphene Adjustable-Barrier Transistor with Ultra-High Current Gain},

author = {Carsten Strobel and Carlos A Chavarin and Karola Richter and Martin Knaut and Johanna Reif and Sandra V\"{o}lkel and Andreas Jahn and Matthias Albert and Christian Wenger and Robert Kirchner and Johann W Bartha and Thomas Mikolajick},

url = {https://doi.org/10.1021/acsami.2c10634},

doi = {10.1021/acsami.2c10634},

year  = {2022},

date = {2022-01-01},

journal = {ACS Applied Materials \& Interfaces},

volume = {0},

number = {0},

pages = {null},

abstract = {A graphene-based three-terminal barristor device was proposed to overcome the low on/off ratios and insufficient current saturation of conventional graphene field-effect transistors. In this study, we fabricated and analyzed a novel graphene-based transistor, which resembles the structure of the barristor but uses a different operating condition. This new device, termed graphene adjustable-barriers transistor (GABT), utilizes a semiconductor-based gate rather than a metal\textendashinsulator gate structure to modulate the device currents. The key feature of the device is the two graphene-semiconductor Schottky barriers with different heights that are controlled simultaneously by the gate voltage. Due to the asymmetry of the barriers, the drain current exceeds the gate current by several orders of magnitude. Thus, the GABT can be considered an amplifier with an alterable current gain. In this work, a silicon\textendashgraphene\textendashgermanium GABT with an ultra-high current gain (ID/IG up to 8 × 106) was fabricated, and the device functionality was demonstrated. Additionally, a capacitance model is applied to predict the theoretical device performance resulting in an on\textendashoff ratio above 106, a swing of 87 mV/dec, and a drive current of about 1 × 106 A/cm2.},

note = {PMID: 35993449},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pruefer2021.TED.2021.3088770,

title = {Compact Modeling of Nonlinear Contact Effects in Short-Channel Coplanar and Staggered Organic Thin-Film Transistors},

author = {Jakob Pruefer and Jakob Leise and Aristeidis Nikolaou and James W Borchert and Ghader Darbandy and Hagen Klauk and Benjam\'{i}n I\~{n}\'{i}guez and Thomas Gneiting and Alexander Kloes},

doi = {10.1109/TED.2021.3088770},

issn = {1557-9646},

year  = {2021},

date = {2021-08-01},

journal = {IEEE Transactions on Electron Devices},

volume = {68},

number = {8},

pages = {3843-3850},

abstract = {We present analytical physics-based compact models for the Schottky barriers at the interfaces between the organic semiconductor and the source and drain contacts in organic thin-film transistors (TFTs) fabricated in the coplanar and the staggered device architecture, and we illustrate the effect of these Schottky barriers on the current-voltage characteristics of the TFTs. The model for the source barrier explicitly considers the field-dependent barrier lowering due to image charges. Potential solutions have been derived by applying the Schwarz-Christoffel transformation, leading to expressions for the electric field at the source barrier and for the contact resistance at the source contact. With regard to the drain barrier, a generic compact-modeling scheme based on the current-voltage characteristics of a barrier-less TFT is introduced that can be applied to any compact dc model. Finally, both models are incorporated into an existing charge-based compact dc model and verified against the results of measurements performed on coplanar and staggered organic TFTs with channel lengths ranging from 0.5 to 10.5 μm.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9329125,

title = {Three-Terminal Floating-Gate Cell for Threshold-Voltage Control of Organic Thin-Film Transistors},

author = {Kareem Mansour and Samar Elsaegh and Ute Zschieschang and Hagen Klauk and Ghada H Ibrahim},

doi = {10.1109/TED.2021.3050138},

issn = {1557-9646},

year  = {2021},

date = {2021-03-01},

journal = {IEEE Transactions on Electron Devices},

volume = {68},

number = {3},

pages = {1088-1092},

abstract = {A floating-gate (FG) cell as a circuit-level approach to control the threshold voltage of organic thin-film transistors (TFTs) operated in the transdiode configuration is presented. Charging and discharging of the FG are achieved by controlling the charge leakage through the gate dielectric of one of the organic TFTs that constitute the FG cell. Using programming voltages not exceeding 4 V, systematic tuning of the threshold voltage to values between -0.5 and 2.6 V was achieved. The versatility of the concept is demonstrated by employing organic-TFT-based FG cells as transdiodes with programmable threshold voltage in passive rectifiers and diode-load inverters fabricated on flexible, transparent plastic substrates. Rectifiers with programmable FG cells show flatter frequency response, improved 3-dB point, and reduced ripple compared to conventional rectifiers. Inverters with programmable FG-transdiode load have larger small-signal gain, larger output-voltage swing, and larger noise margins than conventional diode-load inverters.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nikolaou2021.JEDS.2020.3046301,

title = {Noise-Based Simulation Technique for Circuit-Variability Analysis},

author = {Aristeidis Nikolaou and Jakob Leise and Jakob Pruefer and Ute Zschieschang and Hagen Klauk and Ghader Darbandy and Benjamin I\~{n}iguez and Alexander Kloes},

doi = {10.1109/JEDS.2020.3046301},

issn = {2168-6734},

year  = {2021},

date = {2021-01-01},

journal = {IEEE Journal of the Electron Devices Society},

volume = {9},

pages = {450-455},

abstract = {An accurate and efficient noise-based simulation technique for predicting the impact of device-parameter variability on the DC statistical behavior of integrated circuits is presented. The proposed method is validated on a source follower, a diode-load inverter and a current mirror based on organic thin-film transistors. Taking advantage of the standard noise analysis of a circuit, after translating the statistical variation of the electrical parameters of the transistors into equivalent-noise circuit components, the proposed technique yields results identical to those obtained from a Monte Carlo simulation, but in a significantly shorter amount of time.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/5.0062146,

title = {Flexible megahertz organic transistors and the critical role of the device geometry on their dynamic performance},

author = {Jakob Leise and Jakob Pruefer and Ghader Darbandy and Aristeidis Nikolaou and Michele Giorgio and Mario Caironi and Ute Zschieschang and Hagen Klauk and Alexander Kloes and Benjamin I\~{n}iguez and James W Borchert},

url = {https://doi.org/10.1063/5.0062146},

doi = {10.1063/5.0062146},

year  = {2021},

date = {2021-01-01},

journal = {Journal of Applied Physics},

volume = {130},

number = {12},

pages = {125501},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Geiger2021.DOISTART,

title = {Optimizing the plasma oxidation of aluminum gate electrodes for ultrathin gate oxides in organic transistors},

author = {Michael Geiger and Marion Hagel and Thomas Reindl and J\"{u}rgen Weis and Thomas R Weitz and Helena Solodenko and Guido Schmitz and Ute Zschieschang and Hagen Klauk and Rachana Acharya},

url = {https://doi.org/10.1038/s41598-021-85517-7},

issn = {2045-2322},

year  = {2021},

date = {2021-01-01},

journal = {Scientific Reports},

volume = {11},

number = {1},

pages = {6382},

abstract = {A critical requirement for the application of organic thin-film transistors (TFTs) in mobile or wearable applications is low-voltage operation, which can be achieved by employing ultrathin, high-capacitance gate dielectrics. One option is a hybrid dielectric composed of a thin film of aluminum oxide and a molecular self-assembled monolayer in which the aluminum oxide is formed by exposure of the surface of the aluminum gate electrode to a radio-frequency-generated oxygen plasma. This work investigates how the properties of such dielectrics are affected by the plasma power and the duration of the plasma exposure. For various combinations of plasma power and duration, the thickness and the capacitance of the dielectrics, the leakage-current density through the dielectrics, and the current-voltage characteristics of organic TFTs in which these dielectrics serve as the gate insulator have been evaluated. The influence of the plasma parameters on the surface properties of the dielectrics, the thin-film morphology of the vacuum-deposited organic-semiconductor films, and the resulting TFT characteristics has also been investigated.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kublitski2021.DOISTART,

title = {Reverse dark current in organic photodetectors and the major role of traps as source of noise},

author = {Jonas Kublitski and Andreas Hofacker and Bahman K Boroujeni and Johannes Benduhn and Vasileios C Nikolis and Christina Kaiser and Donato Spoltore and Hans Kleemann and Axel Fischer and Frank Ellinger and Koen Vandewal and Karl Leo},

url = {https://doi.org/10.1038/s41467-020-20856-z},

issn = {2041-1723},

year  = {2021},

date = {2021-01-01},

journal = {Nature Communications},

volume = {12},

number = {1},

pages = {551},

abstract = {Organic photodetectors have promising applications in low-cost imaging, health monitoring and near-infrared sensing. Recent research on organic photodetectors based on donor-acceptor systems has resulted in narrow-band, flexible and biocompatible devices, of which the best reach external photovoltaic quantum efficiencies approaching 100%. However, the high noise spectral density of these devices limits their specific detectivity to around 1013 Jones in the visible and several orders of magnitude lower in the near-infrared, severely reducing performance. Here, we show that the shot noise, proportional to the dark current, dominates the noise spectral density, demanding a comprehensive understanding of the dark current. We demonstrate that, in addition to the intrinsic saturation current generated via charge-transfer states, dark current contains a major contribution from trap-assisted generated charges and decreases systematically with decreasing concentration of traps. By modeling the dark current of several donor-acceptor systems, we reveal the interplay between traps and charge-transfer states as source of dark current and show that traps dominate the generation processes, thus being the main limiting factor of organic photodetectors detectivity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wu2021.DOISTART,

title = {Efficient and low-voltage vertical organic permeable base light-emitting transistors},

author = {Zhongbin Wu and Yuan Liu and Erjuan Guo and Ghader Darbandy and Shu-Jen Wang and Ren\'{e} H\"{u}bner and Alexander Kloes and Hans Kleemann and Karl Leo},

url = {https://doi.org/10.1038/s41563-021-00937-0},

issn = {1476-4660},

year  = {2021},

date = {2021-01-01},

journal = {Nature Materials},

volume = {20},

number = {7},

pages = {1007--1014},

abstract = {Organic light-emitting transistors, three-terminal devices combining a thin-film transistor with a light-emitting diode, have generated increasing interest in organic electronics. However, increasing their efficiency while keeping the operating voltage low still remains a key challenge. Here, we demonstrate organic permeable base light-emitting transistors; these three-terminal vertical optoelectronic devices operate at driving voltages below 5.0 V; emit in the red, green and blue ranges; and reach, respectively, peak external quantum efficiencies of 19.6%, 24.6% and 11.8%, current efficiencies of 20.6 cd A-1, 90.1 cd A-1 and 27.1 cd A-1 and maximum luminance values of 9,833 cd m-2, 12,513 cd m-2 and 4,753 cd m-2. Our simulations demonstrate that the nano-pore permeable base electrode located at the centre of the device, which forms a distinctive optical microcavity and regulates charge carrier injection and transport, is the key to the good performance obtained. Our work paves the way towards efficient and low-voltage organic light-emitting transistors, useful for power-efficient active matrix displays and solid-state lighting.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Guo2021.DOISTART,

title = {Integrated complementary inverters and ring oscillators based on vertical-channel dual-base organic thin-film transistors},

author = {Erjuan Guo and Shen Xing and Felix Dollinger and Ren\'{e} H\"{u}bner and Shu-Jen Wang and Zhongbin Wu and Karl Leo and Hans Kleemann},

url = {https://doi.org/10.1038/s41928-021-00613-w},

issn = {2520-1131},

year  = {2021},

date = {2021-01-01},

journal = {Nature Electronics},

volume = {4},

number = {8},

pages = {588--594},

abstract = {Lateral-channel dual-gate organic thin-film transistors have been used in pseudo complementary metal-oxide-semiconductor (CMOS) inverters to control switching voltage. However, their relatively long channel lengths, combined with the low charge carrier mobility of organic semiconductors, typically leads to slow inverter operation. Vertical-channel dual-gate organic thin-film transistors are a promising alternative because of their short channel lengths, but the lack of appropriate p- and n-type devices has limited the development of complementary inverter circuits. Here, we show that organic vertical n-channel permeable single- and dual-base transistors, and vertical p-channel permeable base transistors can be used to create integrated complementary inverters and ring oscillators. The vertical dual-base transistors enable switching voltage shift and gain enhancement. The inverters exhibit small switching time constants at 10 MHz, and the seven-stage complementary ring oscillators exhibit short signal propagation delays of 11 ns per stage at a supply voltage of 4 V.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D0TC04554C,

title = {Stability of organic thin-film transistors based on ultrathin films of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)},

author = {Rachana Acharya and Darius G\"{u}nder and Tobias Breuer and Guido Schmitz and Hagen Klauk and Gregor Witte},

url = {http://dx.doi.org/10.1039/D0TC04554C},

doi = {10.1039/D0TC04554C},

year  = {2021},

date = {2021-01-01},

journal = {J. Mater. Chem. C},

volume = {9},

pages = {270-280},

publisher = {The Royal Society of Chemistry},

abstract = {Organic thin-film transistors (TFTs) based on ultrathin semiconductor films are potentially useful as highly sensitive physical, chemical or biological sensors and may also help in the development of a better understanding of the relations between structural and charge-transport characteristics of thin films of organic semiconductors. A particularly promising small-molecule organic semiconductor is dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT). However, it was recently reported that ultrathin DNTT films spontaneously undergo dramatic morphological changes within minutes after deposition that lead to the disaggregation of the initially closed (or at least connected) single-monolayer films into disconnected multilayer islands. Here, we investigate how this spontaneous structural reconfiguration affects the characteristics of TFTs based on ultrathin DNTT films and explore the extent to which it can be prevented by cryogenic cooling or in situ encapsulation. We fabricated inverted coplanar TFTs with a hybrid aluminum oxide/alkylphosphonic acid self-assembled monolayer gate dielectric and vacuum-deposited DNTT films with nominal thicknesses of 2.5 or 25 nm. Using atomic force microscopy (AFM) we monitored the spontaneous changes in the DNTT morphology in a quasi-continuous manner over a period of 12 hours after deposition. The charge-carrier mobility of the ultrathin DNTT TFTs was found to decrease rapidly, while the mobility of the TFTs with the thicker DNTT films is far more stable. We also found that the initial closed-monolayer morphology of the ultrathin DNTT films is preserved when the substrates are cooled to cryogenic temperatures immediately after the DNTT deposition, but that the morphological changes resume upon returning the substrates to room temperature. Furthermore, we fabricated TFTs in which the ultrathin DNTT films were encapsulated in situ with a vacuum-deposited film of polytetrafluoroethylene, C60 or titanyl phthalocyanine immediately following the DNTT deposition and found that the encapsulation decelerates the structural reorganization of the ultrathin DNTT films and the concurrent degradation of the carrier mobility.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D1DT01634B,

title = {A study on the influence of ligand variation on formamidinate complexes of yttrium: new precursors for atomic layer deposition of yttrium oxide},

author = {Sebastian M J Beer and Nils Boysen and Arbresha Muriqi and David Zanders and Thomas Berning and Detlef Rogalla and Claudia Bock and Michael Nolan and Anjana Devi},

url = {http://dx.doi.org/10.1039/D1DT01634B},

doi = {10.1039/D1DT01634B},

year  = {2021},

date = {2021-01-01},

journal = {Dalton Trans.},

volume = {50},

pages = {12944-12956},

publisher = {The Royal Society of Chemistry},

abstract = {The synthesis and characterization of a series of closely related Y(iii) compounds comprising the formamidinate ligands (RNCHNR) (R = alkyl) is reported, with the scope of using them as prospective precursors for atomic layer deposition (ALD) of yttrium oxide (Y2O3) thin films. The influence of the side chain variation on the thermal properties of the resulting complexes is studied and benchmarked by thermal analysis and vapor pressure measurements. Density functional theory (DFT) studies give theoretical insights into the reactivity of the compounds towards water, which was targeted as a co-reactant for the deposition of Y2O3via thermal ALD in the next step. Among the four complexes analyzed, tris(N,N′-di-tert-butyl-formamidinato)yttrium(iii) [Y(tBu2-famd)3] 1 was found to possess enhanced thermal stability and was selected for Y2O3 ALD process development. A broad ALD window ranging from 200 °C to 325 °C was obtained, yielding films of high compositional quality. Furthermore, with a film density of (4.95 ± 0.05) g cm−1 close to the bulk value, polycrystalline fcc Y2O3 layers with a smooth topography resulted in promising dielectric properties when implemented in metal insulator semiconductor (MIS) capacitor structures.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D1TC02417E,

title = {Sensing and electrocatalytic activity of tungsten disulphide thin films fabricated via metal\textendashorganic chemical vapour deposition},

author = {Jan-Lucas Wree and Jean-Pierre Glauber and Denis \"{O}hl and Alessia Niesen and Aleksander Kostka and Detlef Rogalla and Wolfgang Schuhmann and Anjana Devi},

url = {http://dx.doi.org/10.1039/D1TC02417E},

doi = {10.1039/D1TC02417E},

year  = {2021},

date = {2021-01-01},

journal = {J. Mater. Chem. C},

volume = {9},

pages = {10254-10265},

publisher = {The Royal Society of Chemistry},

abstract = {The unique structural and electronic properties of transition metal dichalcogenides (TMDs) and in particular tungsten disulphide (WS2) make them interesting for a variety of applications such as the electrocatalytic hydrogen evolution reaction (HER) for water splitting devices and chemiresistive gas sensors. The key parameter for the realisation of these devices is the controlled large-area growth of WS2 combined with tuning the surface morphology and electronic properties which is achieved by bottom-up fabrication methods such as chemical vapour deposition (CVD). In this study, 2H-WS2 films are fabricated by a new metal\textendashorganic CVD (MOCVD) process resulting in the growth of crystalline, pure, and stoichiometric films which was accomplished at temperatures as low as 600 °C as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS)/nuclear reaction analysis (NRA), and Raman spectroscopy. The surface morphology of WS2 layers was investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). Following successful process development, the WS2 layers were deposited on conducting FTO/glass substrates and their catalytic activity for the HER was evaluated in a linear sweep voltammetry (LSV) experiment. Furthermore, the temperature-dependent sensor response towards NO2, CO, and NH3 was investigated for WS2 films deposited on special sensor chips, revealing a p-type response towards NO2 and NH3 and sensitivities of around 20% for NO2 and NH3 concentrations of 1.5 ppm and 7.6 ppm, respectively. These promising results demonstrate the effectiveness of scalable CVD-grown WS2 and pave the way for practical applications by modulating the properties of materials to achieve enhanced electrocatalytic and sensing performances employing WS2 layers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.3389/felec.2021.797308,

title = {Mechanical Stress Stability of Flexible Amorphous Zinc Tin Oxide Thin-Film Transistors},

author = {Oliver Lahr and Max Steudel and Holger von Wenckstern and Marius Grundmann},

url = {https://www.frontiersin.org/article/10.3389/felec.2021.797308},

doi = {10.3389/felec.2021.797308},

issn = {2673-5857},

year  = {2021},

date = {2021-01-01},

journal = {Frontiers in Electronics},

volume = {2},

abstract = {Due to their low-temperature processing capability and ionic bonding configuration, amorphous oxide semiconductors (AOS) are well suited for applications within future mechanically flexible electronics. Over the past couple of years, amorphous zinc tin oxide (ZTO) has been proposed as indium and gallium-free and thus more sustainable alternative to the widely deployed indium gallium zinc oxide (IGZO). The present study specifically focuses on the strain-dependence of elastic and electrical properties of amorphous zinc tin oxide thin-films sputtered at room temperature. Corresponding MESFETs have been compared regarding their operation stability under mechanical bending for radii ranging from 5 to 2 mm. Force-spectroscopic measurements yield a plastic deformation of ZTO as soon as the bending-induced strain exceeds 0.83 %. However, the electrical properties of ZTO determined by Hall effect measurements at room temperature are demonstrated to be unaffected by residual compressive and tensile strain up to 1.24 %. Even for the maximum investigated tensile strain of 1.26 %, the MESFETs exhibit a reasonably consistent performance in terms of current on/off ratios between six and seven orders of magnitude, a subthreshold swing around 350 mV/dec and a field-effect mobility as high as 7.5 cm^{2}V^{−1}s^{−1}. Upon gradually subjecting the transistors to higher tensile strain, the channel conductivity steadily improves and consequently, the field-effect mobility increases by nearly 80 % while bending the devices around a radius of 2 mm. Further, a reversible threshold voltage shift of about −150 mV with increasing strain is observable. Overall, amorphous ZTO provides reasonably stable electrical properties and device performance for bending-induced tensile strain up to at least 1.26 % and thus represent a promising material of choice considering novel bendable and transparent electronics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vahland2021.acsaelm.1c00872,

title = {Quasi-Self-Aligned Organic Thin-Film Transistors in Coplanar Top-Gate Configuration},

author = {J\"{o}rn Vahland and Karl Leo and Hans Kleemann},

url = {https://doi.org/10.1021/acsaelm.1c00872},

doi = {10.1021/acsaelm.1c00872},

year  = {2021},

date = {2021-01-01},

journal = {ACS Appl. Electron. Mater.},

volume = {3},

number = {11},

pages = {5131--5137},

publisher = {American Chemical Society},

abstract = {Besides charge carrier mobility and contact resistance, parasitic overlap capacitance is a key factor limiting the dynamic behavior of organic thin-film transistors. The most effective away to reduce parasitic overlap capacitances between source/drain and gate electrode is to employ self-aligned transistor architectures. However, so far, self-alignment in organic transistors has only been achieved using nonscalable or complex fabrication processes. Here we demonstrate quasi-self-aligned OTFTs in a coplanar top-gate architecture fabricated with reliable and scalable state-of-the-art fabrication techniques such as wet-chemical etching. Self-alignment is achieved by carrying out a wet-chemical etching process on top of the channel interface. We prove that for the proper choice of etchant, the charge carrier transport properties of the channel interface are not deteriorated. The benefit of the self-aligned design lies in the reduction of the specific overlap capacitances which are 2 orders of magnitude (0.13 nF cm-2) lower than for nonself-aligned devices (15 nF cm-2). Furthermore, we highlight the potential of this approach for high-frequency operation of organic transistors and quantify the gain in cutoff frequency compared to non-self-aligned devices. 

Besides charge carrier mobility and contact resistance, parasitic overlap capacitance is a key factor limiting the dynamic behavior of organic thin-film transistors. The most effective away to reduce parasitic overlap capacitances between source/drain and gate electrode is to employ self-aligned transistor architectures. However, so far, self-alignment in organic transistors has only been achieved using nonscalable or complex fabrication processes. Here we demonstrate quasi-self-aligned OTFTs in a coplanar top-gate architecture fabricated with reliable and scalable state-of-the-art fabrication techniques such as wet-chemical etching. Self-alignment is achieved by carrying out a wet-chemical etching process on top of the channel interface. We prove that for the proper choice of etchant, the charge carrier transport properties of the channel interface are not deteriorated. The benefit of the self-aligned design lies in the reduction of the specific overlap capacitances which are 2 orders of magnitude (0.13 nF cm-2) lower than for nonself-aligned devices (15 nF cm-2). Furthermore, we highlight the potential of this approach for high-frequency operation of organic transistors and quantify the gain in cutoff frequency compared to non-self-aligned devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/advs.202003519,

title = {Doped Highly Crystalline Organic Films: Toward High-Performance Organic Electronics},

author = {Michael F Sawatzki and Hans Kleemann and Bahman K Boroujeni and Shu-Jen Wang and Joern Vahland and Frank Ellinger and Karl Leo},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/advs.202003519},

doi = {https://doi.org/10.1002/advs.202003519},

year  = {2021},

date = {2021-01-01},

journal = {Advanced Science},

volume = {8},

number = {6},

pages = {2003519},

abstract = {Abstract Today's organic electronic devices, such as the highly successful OLED displays, are based on disordered films, with carrier mobilities orders of magnitude below those of inorganic semiconductors like silicon or GaAs. For organic devices such as diodes and transistors, higher charge carrier mobilities are paramount to achieve high performance. Organic single crystals have been shown to offer these required high mobilities. However, manufacturing and processing of these crystals are complex, rendering their use outside of laboratory-scale applications negligible. Furthermore, doping cannot be easily integrated into these systems, which is particularly problematic for devices mandating high mobility materials. Here, it is demonstrated for the model system rubrene that highly ordered, doped thin films can be prepared, allowing high-performance organic devices on almost any substrate. Specifically, triclinic rubrene crystals are created by abrupt heating of amorphous layers and can be electrically doped during the epitaxial growth process to achieve hole or electron conduction. Analysis of the space charge limited current in these films reveals record vertical mobilities of 10.3(49) cm2 V−1 s−1. To demonstrate the performance of this materials system, monolithic pin-diodes aimed for rectification are built. The f3db of these diodes is over 1 GHz and thus higher than any other organic semiconductor-based device shown so far. It is believed that this work will pave the way for future high-performance organic devices based on highly crystalline thin films.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{C.Strobel2021.DOISTART,

title = {A novel graphene base heterojunction transistor with saturated output current},

author = {C Strobel and Alvarado C Chavarin and K Richter and M Knaut and J Reif and S Voelkel and A Jahn and M Albert and C Wenger and R Kirchner and J W Bartha and T and Mikolajick},

year  = {2021},

date = {2021-01-01},

journal = {Vid. Proc. Adv. Mater.},

volume = {2},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gotthardt2021.acsaelm.0c00957,

title = {Molecular n-Doping of Large- and Small-Diameter Carbon Nanotube Field-Effect Transistors with Tetrakis(tetramethylguanidino)benzene},

author = {Jan M Gotthardt and Severin Schneider and Maximilian Brohmann and Simone Leingang and Eric Sauter and Michael Zharnikov and Hans-J\"{o}rg Himmel and Jana Zaumseil},

url = {https://doi.org/10.1021/acsaelm.0c00957},

doi = {10.1021/acsaelm.0c00957},

year  = {2021},

date = {2021-01-01},

journal = {ACS Appl. Electron. Mater.},

volume = {3},

number = {2},

pages = {804--812},

publisher = {American Chemical Society},

abstract = {The guanidino-functionalized aromatic compound 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) has been shown to be an efficient n-dopant for field-effect transistors (FETs) with gold contacts and networks of semiconducting single-walled carbon nanotubes (SWCNTs) with small diameters and large band gaps. Here, we investigate the broader applicability of ttmgb as a molecular n-dopant by fabricating bottom-contact/top-gate FETs with different air-stable, high work function metals as electrodes and with both small- and large-diameter polymer-sorted SWCNTs. Kelvin probe measurements indicate a reduction of the work functions of gold, palladium, and platinum by about 1 eV after ttmgb treatment and, correspondingly, gated four-point probe measurements show orders of magnitude lower contact resistances for electron injection into SWCNT networks. FETs based on networks of (6,5) SWCNTs with large band gaps as well as mixed semiconducting plasma torch SWCNTs with small band gaps can thus be transformed from ambipolar to purely n-type with no hole injection or increased off-currents by applying optimized ttmgb concentrations. Carrier concentration- and temperature-dependent measurements reveal that ttmgb treatment does not impact the electron transport and maximum mobilities in SWCNT networks at high carrier densities, but greatly improves the subthreshold slope of nanotube FETs by removing shallow electron trap states. This effect is found to be particularly pronounced for small-diameter nanotubes with large band gaps. 

The guanidino-functionalized aromatic compound 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) has been shown to be an efficient n-dopant for field-effect transistors (FETs) with gold contacts and networks of semiconducting single-walled carbon nanotubes (SWCNTs) with small diameters and large band gaps. Here, we investigate the broader applicability of ttmgb as a molecular n-dopant by fabricating bottom-contact/top-gate FETs with different air-stable, high work function metals as electrodes and with both small- and large-diameter polymer-sorted SWCNTs. Kelvin probe measurements indicate a reduction of the work functions of gold, palladium, and platinum by about 1 eV after ttmgb treatment and, correspondingly, gated four-point probe measurements show orders of magnitude lower contact resistances for electron injection into SWCNT networks. FETs based on networks of (6,5) SWCNTs with large band gaps as well as mixed semiconducting plasma torch SWCNTs with small band gaps can thus be transformed from ambipolar to purely n-type with no hole injection or increased off-currents by applying optimized ttmgb concentrations. Carrier concentration- and temperature-dependent measurements reveal that ttmgb treatment does not impact the electron transport and maximum mobilities in SWCNT networks at high carrier densities, but greatly improves the subthreshold slope of nanotube FETs by removing shallow electron trap states. This effect is found to be particularly pronounced for small-diameter nanotubes with large band gaps.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.202000883,

title = {All-Amorphous Junction Field-Effect Transistors Based on High-Mobility Zinc Oxynitride},

author = {Anna Reinhardt and Holger von Wenckstern and Marius Grundmann},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202000883},

doi = {https://doi.org/10.1002/aelm.202000883},

year  = {2021},

date = {2021-01-01},

journal = {Advanced Electronic Materials},

volume = {7},

number = {4},

pages = {2000883},

abstract = {Abstract This report is on the electrical properties of all-amorphous junction field-effect transistors (JFETs) based on n-type zinc oxynitride (ZnON) as a channel material and room-temperature deposited p-type ZnCo2O4 (ZCO) as a heterojunction gate. Devices with different channel thicknesses are thereby compared. Best devices with 48 nm channel layer thickness achieve drain current on/off\textendashratios of 105 and low subthreshold swing of 134 mV dec−1 within a gate voltage sweep of less than 2 V. The channel mobility extraction is reliable for 90 nm-thick channels yielding saturation mobility values over 50 cm2 V−1 s−1. For JFETs with 48 nm-thick channels an overestimation of the saturation mobility due to deviations from the ideal transistor characteristics is determined.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.202100082,

title = {A Fully Integrated Ferroelectric Thin-Film-Transistor \textendash Influence of Device Scaling on Threshold Voltage Compensation in Displays},

author = {David Lehninger and Martin Ellinger and Tarek Ali and Songrui Li and Konstantin Mertens and Maximilian Lederer and Ricardo Olivio and Thomas K\"{a}mpfe and Norbert Hanisch and Kati Biedermann and Matthias Rudolph and Varvara Brackmann and Shawn Sanctis and Michael P M Jank and Konrad Seidel},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202100082},

doi = {https://doi.org/10.1002/aelm.202100082},

year  = {2021},

date = {2021-01-01},

journal = {Advanced Electronic Materials},

volume = {7},

number = {6},

pages = {2100082},

abstract = {Abstract Thin-film transistors (TFTs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) have attracted vast attention for use in organic light-emitting diode (AMOLED) displays due to their high electron mobility and large current on\textendashoff ratio. Although amorphous oxide semiconductors show considerably less threshold voltage (Vth) variation than poly-silicon, large-area processing and degradation effects can impede the characteristic parameters of a-IGZO TFTs, which manifests in an uneven brightness distribution across the display panel. Such Vth variations are usually reduced by additional compensation circuits consisting of TFTs and capacitors. Herein, a new approach to compensate such variabilities is demonstrated: the integration of a programmable ferroelectric (FE) film in the gate stack of the TFT. This simplifies the complexity of the pixel cell and potentially minimizes the need for compensation circuits, which is crucial for transparent displays. To test this new approach, fully integrated FE-TFTs (i.e., with vias contacting a structured bottom gate electrode from the top) based on a-IGZO and FE hafnium-zirconium oxide (HZO) are developed. A single low-temperature post-fabrication treatment at 350 °C for 1 h in air is used to simultaneously crystallize the HZO film in the FE phase and to reduce the number of defects in the a-IGZO channel. The structural and electrical characterizations provide comprehensive guidance for the design of effective FE-TFT gate stacks and device geometries. An accurate control of the polarization state and linear switching between multiple intermediate states is shown by using programming pulses of various amplitudes and widths. Furthermore, a direct correlation between the channel length and the applied pulse width for programming is observed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Costa2020.TED.2020.3026613,

title = {Long-Term Aging of Al2O3 Passivated and Unpassivated Flexible a-IGZO TFTs},

author = {Julio C\'{e}sar Costa and Arash Pour Yazdan Panah Kermani and Giuseppe Cantarella and Luisa Petti and Christian Vogt and Alwin Daus and Stefan Knobelspies and Gerhard Tr\"{o}ster and Niko S M\"{u}nzenrieder},

doi = {10.1109/TED.2020.3026613},

issn = {1557-9646},

year  = {2020},

date = {2020-11-01},

journal = {IEEE Transactions on Electron Devices},

volume = {67},

number = {11},

pages = {4934-4939},

abstract = {Amongst the new materials studied for the fabrication of high-performance flexible thin-film transistors (TFTs), amorphous indium-gallium-zinc-oxide (a-IGZO) exhibits a combination of advantages that enables its application in commercial electronics. Hence, it is crucial to understand the electrical stability of a-IGZO TFTs over long periods of time. In this work, we present the effects of long-term aging on Al2O3 passivated and unpassivated flexible a-IGZO TFTs over a period of 80 months (≈ 6.5 years). It is found that although remaining functional, these devices are influenced by different instability effects. More specifically, positive gate bias stress experiments indicate that the Al2O3 passivation layer contributes to the degradation of the devices' performance. These results show that the Al2O3 passivation, although beneficial to the initial device stability, does not prevent the degradation of the passivated devices in comparison with their unpassivated counterparts after long periods of storage.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9198932,

title = {Compact Modeling of Short-Channel Effects in Staggered Organic Thin-Film Transistors},

author = {J Pruefer and J Leise and G Darbandy and A Nikolaou and H Klauk and J W Borchert and B I\~{n}\'{i}guez and T Gneiting and A Kloes},

doi = {10.1109/TED.2020.3021368},

issn = {1557-9646},

year  = {2020},

date = {2020-11-01},

journal = {IEEE Transactions on Electron Devices},

volume = {67},

number = {11},

pages = {5082-5090},

abstract = {This article introduces analytical compact models of short-channel effects in staggered organic thin-film transistors (TFTs). The effects of subthreshold-swing degradation, threshold-voltage roll-off, and drain-induced barrier lowering (DIBL) on the static current-voltage characteristics of staggered TFTs are extracted from an analytical potential solution of the 2-D problem of the staggered geometry. This solution is derived by using the Schwarz\textendashChristoffel transformation that leads to a complex mapping function linking the staggered geometry to an equivalent in another coordinate system for which an analytical potential solution exists. The technology CAD (TCAD) Software Sentaurus is used to verify the compact models. Finally, the closed-form and physics-based equations are incorporated into an existing compact current model and verified by measurements on staggered organic TFTs with channel lengths as small as 0.4 $mu textm$ fabricated on flexible plastic substrates by stencil lithography.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9184253,

title = {Macromodel for AC and Transient Simulations of Organic Thin-Film Transistor Circuits Including Nonquasistatic Effects},

author = {J Leise and J Pruefer and A Nikolaou and G Darbandy and H Klauk and B I\~{n}iguez and A Kloes},

doi = {10.1109/TED.2020.3018094},

issn = {1557-9646},

year  = {2020},

date = {2020-11-01},

journal = {IEEE Transactions on Electron Devices},

volume = {67},

number = {11},

pages = {4672-4676},

abstract = {A charge-based macromodel for small-signal ac and transient analyses of organic thin-film transistors (TFTs) is presented. Due to the comparatively small charge-carrier mobility in organic TFTs, the dynamic behavior of the gate-field-induced carrier channel is greatly affected by the frequency of the applied gate\textendashsource and drain\textendashsource voltages. The model presented here is, therefore, based on the transmission-line model and shown to reproduce the results of frequency-dependent admittance measurements and numerical simulations of the transient switching behavior of organic TFTs fabricated in the staggered architecture with good accuracy. The model has been implemented in the hardware description language Verilog-A.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9186799,

title = {Charge-Based Model for the Drain-Current Variability in Organic Thin-Film Transistors Due to Carrier-Number and Correlated- Mobility Fluctuation},

author = {A Nikolaou and G Darbandy and J Leise and J Pruefer and J W Borchert and M Geiger and H Klauk and B I\~{n}iguez and A Kloes},

doi = {10.1109/TED.2020.3018694},

issn = {1557-9646},

year  = {2020},

date = {2020-11-01},

journal = {IEEE Transactions on Electron Devices},

volume = {67},

number = {11},

pages = {4667-4671},

abstract = {In this study, a consistent analytical charge-based model for the bias-dependent variability of the drain current of organic thin-film transistors is presented. The proposed model combines both charge-carrier-number-fluctuation effects and correlated-mobility-fluctuation effects to predict the drain-current variation and is verified using experimental data acquired from a statistical population of organic transistors with various channel dimensions, fabricated on flexible polymeric substrates in the coplanar or the staggered device architecture.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9098061,

title = {Low-Power Organic Light Sensor Array Based on Active-Matrix Common-Gate Transimpedance Amplifier on Foil for Imaging Applications},

author = {S Elsaegh and C Veit and U Zschieschang and M Amayreh and F Letzkus and H Sailer and M Jurisch and J N Burghartz and U W\"{u}rfel and H Klauk and H Zappe and Y Manoli},

doi = {10.1109/JSSC.2020.2993732},

issn = {1558-173X},

year  = {2020},

date = {2020-09-01},

journal = {IEEE Journal of Solid-State Circuits},

volume = {55},

number = {9},

pages = {2553-2566},

abstract = {This article presents a 57.6-μW mechanically flexible active-matrix imaging system based on a 4 × 5 array of light sensors, each composed of a photodetector (PD) using a light-sensitive organic polymer and a transimpedance amplifier (TIA) based on organic thin-film transistors and integrated thin-film carbon resistors. The PDs and the electronics are fabricated on separate plastic films and integrated into a system. Two different topologies for the TIA are designed, implemented, and characterized. The first topology is a self-biased TIA based on a gain-boosted operational amplifier (op-amp), providing an open-loop dc gain of 41.3 dB. This op-amp-based TIA, with a feedback resistor, provides stable current-to-voltage conversion (0-100 μA and 2.0-3.7 V) at frequencies up to 300 Hz. The second topology is a low-power gain-boosted common-gate (GB CG) TIA that performs current-to-voltage conversion with a nonlinearity as small as ±0.3% within a bandwidth of 1 kHz. The output voltages of the light sensors are read and converted into a 4 × 5 pixel gray-scale image displayed on a computer monitor to visualize the functionality of the system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9091819,

title = {High-Frequency Rectifiers Based on Organic Thin-Film Transistors on Flexible Substrates},

author = {G H Ibrahim and U Zschieschang and H Klauk and L Reindl},

doi = {10.1109/TED.2020.2989730},

issn = {1557-9646},

year  = {2020},

date = {2020-06-01},

journal = {IEEE Transactions on Electron Devices},

volume = {67},

number = {6},

pages = {2365-2371},

abstract = {Rectifier circuits featuring low threshold voltages and high cutoff frequencies based on p-channel organic thin-film transistors (TFTs) have been designed, fabricated and characterized. The TFTs and circuits were fabricated by shadow-mask lithography on flexible plastic substrates using the vacuum-deposited small-molecule organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b] thiophene (DNTT). The TFTs have a gate dielectric with a thickness of 5.3 nm and a channel length of 10 μm. The study considers the frequency characteristics of diode-connected transistors (transdiodes) and adopts circuit techniques from silicon CMOS technology, namely single-stage and multistage dynamic-threshold-compensated differential rectifiers. The characterization of the rectifier circuits indicates cutoff frequencies up to 4.75 MHz at a peak-to-peak input voltage of 3 V for transdiodes, up to 32 MHz at a peak-to-peak input voltage of 1.5 V for single-stage differential rectifiers and up to 7.5 MHz at a peak-to-peak input voltage of 1.5 V for two-stage rectifiers. The efficiency is 25% for a load of 10 MΩ and below 1% for a load of 1 MΩ.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Meister2020.LSSC.2020.3008027,

title = {3.93-MHz/328-μW Dynamic Frequency Divider in Flexible a-IGZO TFT Technology},

author = {Tilo Meister and Koichi Ishida and Antony Sou and Corrado Carta and Frank Ellinger},

doi = {10.1109/LSSC.2020.3008027},

issn = {2573-9603},

year  = {2020},

date = {2020-01-01},

journal = {IEEE Solid-State Circuits Letters},

volume = {3},

pages = {134-137},

abstract = {The implementation of a dynamic frequency divider in a fully flexible amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) technology on a sub-15 μm polyimide substrate is presented. This frequency divider is regenerative and is also known as a Miller divider. In this letter, it is implemented using only a Gilbert cell with minimum-size LO transistors. Including the bias network, it has only eight transistors. Using a 6-V supply voltage, it operates up to 3.93 MHz, consumes 328 μW, and has a speed over power Figureof-Merit (FOM) of 12.0 MHz/mW. To the best of our knowledge, this FOM is the highest reported for circuits in this class of flexible TFT technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cantarella_2020,

title = {Review of recent trends in flexible metal oxide thin-film transistors for analog applications},

author = {Giuseppe Cantarella and J \'{u} and Tilo Meister and Koichi Ishida and Corrado Carta and Frank Ellinger and Paolo Lugli and Niko M\"{u}nzenrieder and Luisa Petti},

doi = {10.1088/2058-8585/aba79a},

year  = {2020},

date = {2020-01-01},

journal = {Flexible and Printed Electronics},

volume = {5},

number = {3},

pages = {033001},

publisher = {IOP Publishing},

abstract = {Thanks to the extraordinary advances flexible electronics have experienced over the last decades, applications such as conformable active-matrix displays, ubiquitously integrated disposable flexible sensor nodes, wearable or textile-integrated systems, as well as imperceptible and transient implants are now reachable. To enable these applications, specialized analog circuits able to transmit and receive data, condition sensors’ parameters, drive actuators or control powering devices are required. High-performance sensor conditioning, driving and transceiver circuits on a wide range of flexible substrates are therefore extremely important to develop. However, the currently available materials and processes compatible with mechanically flexible substrates impose massive limitations in terms of large-area uniformity, device dimensions’ shrinkability and circuit design, challenging the realization of flexible analog systems. Among state-of-the-art technologies employing low-temperature fabrication processes, thin-film transistors (TFTs) based on metal oxide semiconductors represent the potentially best compromise in terms of prize, performance, technology maturity and capacity to realize complex systems. This is why metal oxide TFTs are nowadays widely used for flexible, light-weight, transparent, stretchable and bio-degradable analog circuits and systems. Here, we review the current trends of flexible metal oxide TFTs for analog applications. First, an introduction is given, where current challenges and requirements related to the realization of flexible analog circuits and systems are analysed. Additionally, TFT performance parameters and configurations are briefly revised. Then, the recent advances in the field of flexible metal oxide TFTs for analog applications are summarized. In particular, all reported approaches to reduce the channel length and improve the AC performance are shown. Next, the current state of flexible metal oxide TFT-based analog circuits is shown, discussing n-type only and complementary circuit configurations. The last topic of the review covers systems based on flexible metal oxide analog circuits. Finally, a conclusion is drawn and an outlook over the field is provided.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Guo2020.DOISTART,

title = {Vertical organic permeable dual-base transistors for logic circuits},

author = {Erjuan Guo and Zhongbin Wu and Ghader Darbandy and Shen Xing and Shu-Jen Wang and Alexander Tahn and Michael G\"{o}bel and Alexander Kloes and Karl Leo and Hans Kleemann},

url = {https://doi.org/10.1038/s41467-020-18576-5},

issn = {2041-1723},

year  = {2020},

date = {2020-01-01},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {4725},

abstract = {The main advantage of organic transistors with dual gates/bases is that the threshold voltages can be set as a function of the applied second gate/base bias, which is crucial for the application in logic gates and integrated circuits. However, incorporating a dual gate/base structure into an ultra-short channel vertical architecture represents a substantial challenge. Here, we realize a device concept of vertical organic permeable dual-base transistors, where the dual base electrodes can be used to tune the threshold voltages and change the on-currents. The detailed operation mechanisms are investigated by calibrated TCAD simulations. Finally, power-efficient logic circuits, e.g. inverter, NAND/AND computation functions are demonstrated with one single device operating at supply voltages of <2.0 V. We believe that this work offers a compact and technologically simple hardware platform with excellent application potential for vertical-channel organic transistors in complex logic circuits.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D0DT02471F,

title = {A new metalorganic chemical vapor deposition process for MoS2 with a 1,4-diazabutadienyl stabilized molybdenum precursor and elemental sulfur},

author = {Jan-Lucas Wree and Engin Ciftyurek and David Zanders and Nils Boysen and Aleksander Kostka and Detlef Rogalla and Maren Kasischke and Andreas Ostendorf and Klaus Schierbaum and Anjana Devi},

url = {http://dx.doi.org/10.1039/D0DT02471F},

doi = {10.1039/D0DT02471F},

year  = {2020},

date = {2020-01-01},

journal = {Dalton Trans.},

volume = {49},

pages = {13462-13474},

publisher = {The Royal Society of Chemistry},

abstract = {Molybdenum disulfide (MoS2) is known for its versatile properties and hence is promising for a wide range of applications. The fabrication of high quality MoS2 either as homogeneous films or as two-dimensional layers on large areas is thus the objective of intense research. Since industry requirements on MoS2 thin films can hardly be matched by established exfoliation fabrication methods, there is an enhanced need for developing new chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes where a rational precursor selection is a crucial step. In this study, a new molybdenum precursor, namely 1,4-di-tert-butyl-1,4-diazabutadienyl-bis(tert-butylimido)molybdenum(vi) [Mo(NtBu)2(tBu2DAD)], is identified as a potential candidate. The combination of imido and chelating 1,4-diazadieneyl ligand moieties around the molybdenum metal center results in a monomeric compound possessing adequate thermal characteristics relevant for vapor phase deposition applications. Hexagonal MoS2 layers are fabricated in a metalorganic CVD (MOCVD) process with elemental sulfur as the co-reactant at temperatures between 600 °C and 800 °C. The structure and composition of the films are investigated by X-ray diffraction, high resolution transmission electron microscopy, synchrotron X-ray photoelectron spectroscopy and Raman spectroscopy revealing crystalline and stoichiometric MoS2 films. The new MOCVD process developed for MoS2 is highly promising due to its moderate process conditions, scalability and controlled targeted composition.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{9004602,

title = {An Iterative Extended Kalman Filter for Coherent Measurements of Incoherent Network Nodes in Positioning Systems},

author = {Markus Hehn and Erik Sippel and Martin Vossiek},

doi = {10.1109/ACCESS.2020.2975290},

issn = {2169-3536},

year  = {2020},

date = {2020-01-01},

journal = {IEEE Access},

volume = {8},

pages = {36714-36727},

abstract = {Many positioning and tracking applications use spatially distributed sensor stations, each equipped with coherent measurement channels. The coherent data set of each node is incoherently measured to the data sets of all other nodes, avoiding expensive synchronization procedures between the stations. Usually, the measurements are evaluated by mapping the incoherently measured complex valued data on real valued data like angle of arrival or received signal strength. After this preprocessing step, recursive filters fuse the real valued data to estimate a system state. Unfortunately, even though the original measurements are performed in additive white Gaussian noise environments, the preprocessing step can result in correlated, noise shaped errors, whose variance is system state dependent. Hence, the additive white Gaussian noise assumption, which is commonly drawn in Kalman filters, is violated. Therefore, this paper proposes an iterative extended Kalman filter, which estimates the state of a nonlinear real valued system via a complex valued measurement model that consists of incoherent sensor stations, each with several coherent measurement channels. Since the proposed iterative extended Kalman filter is well suited for distributed positioning systems with several stations, a transmitter is localized in a simulation via two sensor stations, each measuring the received signal's amplitude and phase at four channels. To illustrate the advantages of the proposed algorithm, the direct measurement evaluation using the proposed algorithm is compared to a Kalman filter that evaluates the received signal strengths and angle of arrivals at each sensor station. Finally, a reflecting wall is incorporated into the simulation scenario to demonstrate the flexibility of the proposed Kalman filter.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{M_nzenrieder_2020,

title = {Focused ion beam milling for the fabrication of 160 nm channel length IGZO TFTs on flexible polymer substrates},

author = {Niko M\"{u}nzenrieder and Ivan Shorubalko and Luisa Petti and Giuseppe Cantarella and Bajramshahe Shkodra and Tilo Meister and Koichi Ishida and Corrado Carta and Frank Ellinger and Gerhard Tr\"{o}ster},

url = {https://doi.org/10.1088/2058-8585/ab639f},

doi = {10.1088/2058-8585/ab639f},

year  = {2020},

date = {2020-01-01},

journal = {Flexible and Printed Electronics},

volume = {5},

number = {1},

pages = {015007},

publisher = {IOP Publishing},

abstract = {The quest for short channel length transistors is an important challenge in the semiconductor industry. A similar trend is observed in the field of flexible electronics where sensor conditioning circuits and transceivers have to be realized on plastic foils. Here the use of a focused Ga+ ion beam (FIB) to structure the channel of a flexible InGaZnO-based thin-film transistor (TFT) is presented. The resulting flexible TFT exhibits a channel length of and an effective field effect mobility of 4 cm2 V−1 s−1. Furthermore, the optimized Ga+ beam milling does not damage the Al2O3 gate insulator underneath, leading to a gate leakage current of <. The extreme channel length demonstrates that focused ion beams can complement conventional fabrication approaches, overcoming current limitations imposed by flexible substrates. While the dimensions result in short channel effects and a drain conductance of limiting the DC applicability of the FIB TFT, the device also exhibits a high internal gain of . Consequently, a transit frequency of ≈ and a maximum frequency of oscillation of ≈ is measured for supply voltages . This shows that highly scaled flexible TFTs for analog circuits can be fabricated by ion beam milling.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.202000230,

title = {Unraveling Structure and Device Operation of Organic Permeable Base Transistors},

author = {Ghader Darbandy and Felix Dollinger and Petr Form\'{a}nek and Ren\'{e} H\"{u}bner and Stefan Resch and Christian Roemer and Axel Fischer and Karl Leo and Alexander Kloes and Hans Kleemann},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202000230},

doi = {https://doi.org/10.1002/aelm.202000230},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Electronic Materials},

volume = {6},

number = {7},

pages = {2000230},

abstract = {Abstract Organic permeable base transistors (OPBTs) are of great interest for flexible electronic circuits, as they offer very large on-current density and a record-high transition frequency. They rely on a vertical device architecture with current transport through native pinholes in a central base electrode. This study investigates the impact of pinhole density and pinhole diameter on the DC device performance in OPBTs based on experimental data and TCAD simulation results. A pinhole density of NPin = 54 µm−2 and pinhole diameters around LPin = 15 nm are found in the devices. Simulations show that a variation of pinhole diameter and density around these numbers has only a minor impact on the DC device characteristics. A variation of the pinhole diameter and density by up to 100% lead to a deviation of less than 4% in threshold voltage, on/off current ratio, and sub-threshold slope. Hence, the fabrication of OPBTs with reliable device characteristics is possible regardless of statistical deviations in thin film formation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1021/acsami.9b21691,

title = {Electron Transport across Vertical Silicon/MoS2/Graphene Heterostructures: Towards Efficient Emitter Diodes for Graphene Base Hot Electron Transistors},

author = {Melkamu Belete and Olof Engstr\"{o}m and Sam Vaziri and Gunther Lippert and Mindaugas Lukosius and Satender Kataria and Max C Lemme},

url = {https://doi.org/10.1021/acsami.9b21691},

doi = {10.1021/acsami.9b21691},

year  = {2020},

date = {2020-01-01},

journal = {ACS Applied Materials \& Interfaces},

volume = {12},

number = {8},

pages = {9656-9663},

abstract = {Heterostructures comprising silicon, molybdenum disulfide (MoS2), and graphene are investigated with respect to the vertical current conduction mechanism. The measured current\textendashvoltage (I\textendashV) characteristics exhibit temperature-dependent asymmetric current, indicating thermally activated charge carrier transport. The data are compared and fitted to a current transport model that confirms thermionic emission as the responsible transport mechanism across devices. Theoretical calculations in combination with the experimental data suggest that the heterojunction barrier from Si to MoS2 is linearly temperature-dependent for T = 200\textendash300 K with a positive temperature coefficient. The temperature dependence may be attributed to a change in band gap difference between Si and MoS2, strain at the Si/MoS2 interface, or different electron effective masses in Si and MoS2, leading to a possible entropy change stemming from variation in density of states as electrons move from Si to MoS2. The low barrier formed between Si and MoS2 and the resultant thermionic emission demonstrated here make the present devices potential candidates as the emitter diode of graphene base hot electron transistors for future high-speed electronics.},

note = {PMID: 31999091},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1021/acsphotonics.0c00361,

title = {Highly Responsive Flexible Photodetectors Based on MOVPE Grown Uniform Few-Layer MoS2},

author = {Daniel S Schneider and Annika Grundmann and Andreas Bablich and Vikram Passi and Satender Kataria and Holger Kalisch and Michael Heuken and Andrei Vescan and Daniel Neumaier and Max C Lemme},

url = {https://doi.org/10.1021/acsphotonics.0c00361},

doi = {10.1021/acsphotonics.0c00361},

year  = {2020},

date = {2020-01-01},

journal = {ACS Photonics},

volume = {7},

number = {6},

pages = {1388-1395},

abstract = {Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are seen as promising candidates for flexible electronic and optoelectronic devices due to their high tensile strength and favorable optical properties. Molybdenum disulfide (MoS2) is a benchmark material for TMDCs, which has already been studied extensively. Here, we report on highly responsive flexible few-layer MoS2 photodetectors based on MoS2 synthesized uniformly for full coverage of 2 in. sapphire wafers using metalorganic vapor-phase epitaxy (MOVPE). Device performance is studied by electro-optical characterization. Electrostatic gating allows tuning both the responsivity between 150 and 920 A/W and the specific detectivity between almost 1012 and 1010 Jones. The measured spectrally resolved responsivities of the detectors suggest applications in the blue-light range, with opportunities for fine-tuning the most sensitive wavelength through gating, as shown through optical simulations. Finally, the flexible devices were bent to demonstrate their suitability for flexible electronics in fields of future Internet of Things and medical devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Illarionov2020,

title = {Insulators for 2D nanoelectronics: the gap to bridge},

author = {Yury Yu. Illarionov and Theresia Knobloch and Markus Jech and Mario Lanza and Deji Akinwande and Mikhail I Vexler and Thomas Mueller and Max C Lemme and Gianluca Fiori and Frank Schwierz and Tibor Grasser},

url = {https://doi.org/10.1038/s41467-020-16640-8},

issn = {2041-1723},

year  = {2020},

date = {2020-01-01},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {3385},

abstract = {Nanoelectronic devices based on 2D materials are far from delivering their full theoretical performance potential due to the lack of scalable insulators. Amorphous oxides that work well in silicon technology have ill-defined interfaces with 2D materials and numerous defects, while 2D hexagonal boron nitride does not meet required dielectric specifications. The list of suitable alternative insulators is currently very limited. Thus, a radically different mindset with respect to suitable insulators for 2D technologies may be required. We review possible solution scenarios like the creation of clean interfaces, production of native oxides from 2D semiconductors and more intensive studies on crystalline insulators.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/5.0022975,

title = {Ultrahigh-performance integrated inverters based on amorphous zinc tin oxide deposited at room temperature},

author = {Oliver Lahr and Holger von Wenckstern and Marius Grundmann},

url = {https://doi.org/10.1063/5.0022975},

doi = {10.1063/5.0022975},

year  = {2020},

date = {2020-01-01},

journal = {APL Materials},

volume = {8},

number = {9},

pages = {091111},

abstract = {Recent advances in the field of integrated circuits based on sustainable and transparent amorphous oxide semiconductors (AOSs) are presented, demonstrating ultrahigh performance operating state-of-the-art integrated inverters comprising metal\textendashsemiconductor field-effect transistors (MESFETs) with amorphous zinc tin oxide (ZTO) as a channel material. All individual circuit layers have been deposited entirely at room temperature, and the completed devices did not require undergoing additional thermal annealing treatment in order to facilitate proper device functionality. The demonstrated ZTO-based MESFETs exhibit current on/off ratios of over 8 orders of magnitude a field-effect mobility of 8.4 cm2 V−1 s−1, and they can be switched within a voltage range of less than 1.5 V attributed to their small subthreshold swing as low as 86 mV decade−1. Due to adjustments of the circuit layout and, thus, the improvement of certain geometry-related transistor properties, the associated Schottky diode FET logic inverters facilitate low-voltage switching by exhibiting a remarkable maximum voltage gain of up to 1190 with transition voltages of only 80 mV while operating at low supply voltages ≤3 V and maintaining a stable device performance under level shift. To the best of our knowledge, the presented integrated inverters clearly exceed the performance of any similar previously reported devices based on AOS, and thus, prove the enormous potential of amorphous ZTO for sustainable, scalable low-power electronics within future flexible and transparent applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.5143217,

title = {Low voltage, high gain inverters based on amorphous zinc tin oxide on flexible substrates},

author = {P Schlupp and S Vogt and H von Wenckstern and M Grundmann},

url = {https://doi.org/10.1063/1.5143217},

doi = {10.1063/1.5143217},

year  = {2020},

date = {2020-01-01},

journal = {APL Materials},

volume = {8},

number = {6},

pages = {061112},

abstract = {Deposition of semiconductors on bendable substrates is a crucial step toward flexible circuitry and deposition by a roll-to-roll process. Since most bendable substrates have limited temperature stability (normally degradation starts between 150 °C and 300 °C), processing temperatures are typically below that of rigid substrates. Amorphous oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) can be fabricated at room temperature (RT) and exhibit electron mobilities >10 cm2 V−1 s−1 being a pre-requisite for application in backplanes of displays. While IGZO is already commercially exploited, the search for alternative materials is highly relevant because indium and gallium are rare and expensive. Zinc tin oxide (ZTO) is a promising AOS since zinc and tin are highly abundant and cheap. In this letter, we discuss RT-fabricated n-type ZTO thin films used as the channel material in flexible inverter circuits based on junction field-effect transistors. RT-fabricated nickel oxide is used as a semitransparent p-type gate material. The devices are fabricated on flexible polyimide and exhibit an excellent peak gain magnitude of 464 and uncertainty level as low as 130 mV at a supply voltage of only 3 V. They are characterized before and after bending at various radii. Even after bending at 2 mm radius, the inverters behave still very well.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.202000423,

title = {All-Oxide Transparent Thin-Film Transistors Based on Amorphous Zinc Tin Oxide Fabricated at Room Temperature: Approaching the Thermodynamic Limit of the Subthreshold Swing},

author = {Oliver Lahr and Michael S Bar and Holger von Wenckstern and Marius Grundmann},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202000423},

doi = {https://doi.org/10.1002/aelm.202000423},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Electronic Materials},

volume = {6},

number = {10},

pages = {2000423},

abstract = {Abstract Thin-film transistors (TFTs) based on transparent amorphous oxide semiconductors (TAOSs) have become essential building blocks for a broad range of electronics, since TAOSs facilitate large-scale fabrication at moderate temperatures and hence feature compatibility with flexible substrates. An emerging indium-free alternative to the widely commercially exploited indium gallium zinc oxide (IGZO) is amorphous zinc tin oxide (ZTO); however, according to previous reports, achieving acceptable performance of ZTO-based devices fabricated at temperatures below 300 °C is still challenging to date. Here, key properties of the first all-oxide and fully transparent metal-semiconductor field-effect transistors (MESFETs), metal-insulator-semiconductor field-effect transistors (MISFETs) and junction field-effect transistors (JFETs) based on amorphous ZTO are compared, employing PtOx, HfOy, and p-type NiO as gate, respectively. All individual layers have been deposited exclusively at room temperature and do not require any additional postdeposition annealing to obtain sufficient device functionality. Demonstrated TFTs exhibit reasonable current on/off ratios of over six orders of magnitude with subthreshold swings as low as 61 mV dec\textendash1 at room temperature. Transistor characteristics have been recorded for several weeks to study performance consistency over time and are further investigated regarding their stability under bias stress.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/aelm.201901066,

title = {Metal\textendashSemiconductor Field-Effect Transistors Based on the Amorphous Multi-Anion Compound ZnON},

author = {Anna Reinhardt and Holger von Wenckstern and Marius Grundmann},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.201901066},

doi = {https://doi.org/10.1002/aelm.201901066},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Electronic Materials},

volume = {6},

number = {4},

pages = {1901066},

abstract = {Abstract Electrical properties of metal\textendashsemiconductor field-effect transistors (MESFETs) based on the amorphous n-type multi-anion compound zinc oxynitride (ZnON) comprising reactively sputtered platinum as Schottky gate are presented. The Schottky barrier diodes reveal a rectification ratio of 4 × 103 at ±2 V and an ideality factor of 1.43. The investigated MESFETs show good switching characteristics with a switching voltage below 2 V, low subthreshold swing of 112 mV dec−1 and reasonable current on/off ratios up to 5 × 105. Additionally, the stability of the devices under visible light illumination is proven.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/admi.201902145,

title = {Effect of the Degree of the Gate-Dielectric Surface Roughness on the Performance of Bottom-Gate Organic Thin-Film Transistors},

author = {Michael Geiger and Rachana Acharya and Eric Reutter and Thomas Ferschke and Ute Zschieschang and J\"{u}rgen Weis and Jens Pflaum and Hagen Klauk and Ralf Thomas Weitz},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.201902145},

doi = {https://doi.org/10.1002/admi.201902145},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Materials Interfaces},

volume = {7},

number = {10},

pages = {1902145},

abstract = {Abstract In organic thin-film transistors (TFTs) fabricated in the inverted (bottom-gate) device structure, the surface roughness of the gate dielectric onto which the organic-semiconductor layer is deposited is expected to have a significant effect on the TFT characteristics. To quantitatively evaluate this effect, a method to tune the surface roughness of a gate dielectric consisting of a thin layer of aluminum oxide and an alkylphosphonic acid self-assembled monolayer over a wide range by controlling a single process parameter, namely the substrate temperature during the deposition of the aluminum gate electrodes, is developed. All other process parameters remain constant in the experiments, so that any differences observed in the TFT performance can be confidently ascribed to effects related to the difference in the gate-dielectric surface roughness. It is found that an increase in surface roughness leads to a significant decrease in the effective charge-carrier mobility and an increase in the subthreshold swing. It is shown that a larger gate-dielectric surface roughness leads to a larger density of grain boundaries in the semiconductor layer, which in turn produces a larger density of localized trap states in the semiconductor.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Borcherteaaz5156,

title = {Flexible low-voltage high-frequency organic thin-film transistors},

author = {James W Borchert and Ute Zschieschang and Florian Letzkus and Michele Giorgio and Thomas R Weitz and Mario Caironi and Joachim N Burghartz and Sabine Ludwigs and Hagen Klauk},

url = {https://advances.sciencemag.org/content/6/21/eaaz5156},

doi = {10.1126/sciadv.aaz5156},

year  = {2020},

date = {2020-01-01},

journal = {Science Advances},

volume = {6},

number = {21},

publisher = {American Association for the Advancement of Science},

abstract = {The primary driver for the development of organic thin-film transistors (TFTs) over the past few decades has been the prospect of electronics applications on unconventional substrates requiring low-temperature processing. A key requirement for many such applications is high-frequency switching or amplification at the low operating voltages provided by lithium-ion batteries (~3 V). To date, however, most organic-TFT technologies show limited dynamic performance unless high operating voltages are applied to mitigate high contact resistances and large parasitic capacitances. Here, we present flexible low-voltage organic TFTs with record static and dynamic performance, including contact resistance as small as 10 Ωtextperiodcenteredcm, on/off current ratios as large as 1010, subthreshold swing as small as 59 mV/decade, signal delays below 80 ns in inverters and ring oscillators, and transit frequencies as high as 21 MHz, all while using an inverted coplanar TFT structure that can be readily adapted to industry-standard lithographic techniques.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/adfm.201903812,

title = {Roadmap to Gigahertz Organic Transistors},

author = {Ute Zschieschang and James W Borchert and Michele Giorgio and Mario Caironi and Florian Letzkus and Joachim N Burghartz and Ulrike Waizmann and J\"{u}rgen Weis and Sabine Ludwigs and Hagen Klauk},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201903812},

doi = {https://doi.org/10.1002/adfm.201903812},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Functional Materials},

volume = {30},

number = {20},

pages = {1903812},

abstract = {Abstract Despite the large body of research conducted on organic transistors, the transit frequency of organic field-effect transistors has seen virtually no improvement for a decade and remains far below 1 GHz. One reason is that most of the research is still focused on improving the charge-carrier mobility, a parameter that has little influence on the transit frequency of short-channel transistors. By examining the fundamental equations for the transit frequency of field-effect transistors and by extrapolating recent progress on the relevant device parameters, a roadmap to gigahertz organic transistors is derived.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}