► Flexible Graphene-Base Heterojunction Transistor for Several Hundred Gigahertz Operation


Professor Dr. Johann-Wolfgang Bartha

Technische Universität Dresden
Institut für Halbleiter- und Mikrosystemtechnik (IHM)

Dr. Christian Wenger

Innovations for High Performance Microelectronics (IHP)
Leibniz-Institut für innovative Mikroelektronik
Abteilung Technologie                                                   

Project Summary

In this project a highly innovative vertical graphene/silicon based heterojunction transistor, called GBHT, for very high operation frequencies (several hundreds of Gigahertz) will be realized on flexible substrates. This is an absolutely new device concept, combining both n-type silicon thin-film layers and monolayers of graphene as base material of the transistor. This novel concept is based on a vertical arrangement of emitter (n-silicon), base (graphene monolayer) and collector (n-silicon). Up to now there are only simulations available for this transistor concept showing very promising output characteristics and RF performance with cutoff frequencies fT up to the THz range. These high frequencies are possible due to the monatomic thickness of the monolayer graphene base (very short base transit time) and due to the very fast unipolar transistor design. In this proposal the outstanding RF performance of the GBHT should be transferred to flexible devices. The use of flexible substrates opens the way to a unique feature of future electronics. The challenge is to design high speed devices (fT) on flexible substrates without deterioration of the device functionality at high bending radii. These aspects will be investigated in this project on the example of the novel vertical GBHT technology. Therefore flexible substrates like polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polyimide (PI) will be characterized concerning their suitability for high speed flexible transistor devices. In this project the n-type silicon layers of the GBHT are made of high quality amorphous and microcrystalline silicon layers deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). This deposition method is a key element of the proposal as it allows for a very soft deposition of amorphous silicon because of low ion energies in the plasma. Therefore no degradation of the electronic properties of the underlying graphene is expected by the applied deposition method. Actually, using plasma excitation frequencies higher than 100 MHz is a worldwide unique feature of the applicants. The strong VHF expertise is very beneficial to reach the scientific objectives within the project.