Characterisation and modelling of graphene FET detectors for flexible terahertz electronics
Doctoral thesis, 2020

Low-cost electronics for future high-speed wireless communication and non-invasive inspection at terahertz frequencies require new materials with advanced mechanical and electronic properties. Graphene, with its unique combination of flexibility and high carrier velocity, can provide new opportunities for terahertz electronics. In particular, several types of power sensors based on graphene have been demonstrated and found suitable as fast and sensitive detectors over a wide part of the electromagnetic spectrum. Nevertheless, the underlying physics for signal detection are not well understood due to the lack of accurate characterisation methods, which hampers further improvement and optimisation of graphene-based power sensors. In this thesis, progress on modelling, design, fabrication and characterisation of terahertz graphene field-effect transistor (GFET) detectors is presented. A
major part is devoted to the first steps towards flexible terahertz electronics.

The characterisation and modelling of terahertz GFET detectors from 1 GHz to 1.1 THz are presented. The bias dependence, the scattering parameters and the detector voltage response were simultaneously accessed. It is shown that the voltage responsivity can be accurately described using a combination of a quasi-static equivalent circuit model, and the second-order series expansion terms of the nonlinear dc I-V characteristic. The video
bandwidth, or IF bandwidth, of GFET detectors is estimated from heterodyne measurements. Moreover, the low-frequency noise of GFET detectors between 1 Hz and 1 MHz is investigated. From this, the room-temperature Hooge parameter of fabricated GFETs is extracted to be around 2*10^{-3}. It is found that the thermal noise dominates above 100 Hz, which sets the necessary switching time to reduce the effect of 1/f noise.

A state-of-the-art GFET detector at 400 GHz, with a maximum measured optical responsivity of 74 V/W, and a minimum noise-equivalent power of 130 pW/Hz^{0.5} is demonstrated. It is shown that the detector performance is affected by the quality of the graphene film and adjacent layers, hence indicating the need to improve the fabrication process of GFETs.

As a proof of concept, a bendable GFET terahertz detector on a plastic substrate is demonstrated. The effects of bending strain on dc I-V characteristics, responsivity and sensitivity are investigated. The detector exhibits a robust performance for tensile strain of more than 1% corresponding to a bending radius of 7 mm. Finally, a linear array of terahertz GFET detectors on a flexible substrate for imaging applications is fabricated and tested. The results show the possibility of realising bendable and curved focal plane arrays.

In summary, in this work, the combination of improved device models and more accurate characterisation techniques of terahertz GFET detectors will allow for further optimisation. It is shown that graphene can open up for flexible terahertz electronics for future niche applications, such as wearable smart electronics and curved focal plane imaging.



scattering parameters

broadband characterisation


terahertz detectors

field-effect transistors

flexible electronics

The defense will be held online
Opponent: Prof. Wojciech Knap, Center for Terahertz Technology Research and Applications, Polish Academy of Sciences, Warsaw


Xinxin Yang

Chalmers, Microtechnology and Nanoscience (MC2), Terahertz and Millimetre Wave Laboratory

Describing broadband terahertz response of graphene FET detectors by a classical model

IEEE Transactions on Terahertz Science and Technology,; Vol. 10(2020)p. 158-166

Journal article

Wide Bandwidth Terahertz Mixers Based On Graphene FETs

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz,; (2019)

Paper in proceedings

Low-frequency Noise Characterization of Graphene FET THz Detectors

2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz),; (2018)

Paper in proceedings

A 400-GHz Graphene FET Detector

IEEE Transactions on Terahertz Science and Technology,; Vol. 7(2017)p. 614-616

Journal article

Test structures for evaluating Al2O3 dielectrics for graphene field effect transistors on flexible substrates

Proceedings of the 2018 IEEE International Conference on Microelectronic Test Structures,; Vol. 31(2018)p. 75-78

Paper in proceedings

A flexible graphene terahertz detector

Applied Physics Letters,; Vol. 111(2017)

Journal article

A linear-array of 300-GHz antenna integrated GFET detectors on a flexible substrate

IEEE Transactions on Terahertz Science and Technology,; Vol. 10(2020)p. 554-557

Journal article

Areas of Advance

Information and Communication Technology

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)


Kollberg Laboratory

Nanofabrication Laboratory

Subject Categories

Electrical Engineering, Electronic Engineering, Information Engineering

Nano Technology



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4732


Chalmers University of Technology

The defense will be held online


Opponent: Prof. Wojciech Knap, Center for Terahertz Technology Research and Applications, Polish Academy of Sciences, Warsaw

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