Impact of adjacent dielectrics on the high-frequency performance of graphene field-effect transistors
Doctoral thesis, 2021
This thesis work presents results of the comprehensive analysis of the influence of material imperfections, self-heating and limitations of the charge carrier velocity, imposed by adjacent dielectrics, on the transit frequency, fT, and the maximum frequency of oscillation, fmax, of graphene field-effect transistors (GFETs). The analysis allowed for better understanding and developing a strategy for addressing the limitations.
In particular, it was shown that the GFET high-frequency performance can be enhanced by utilizing the gate and substrate dielectric materials with higher optical phonon (OP) energy, allowing for higher saturation velocity and, hence, higher fT and fmax. This approach was experimentally verified by demonstration of enhancement in the fT and fmax in GFETs with graphene channel encapsulated by the Al2O3 layers. As a further step, GFETs on diamond, material with highest OP energy and thermal conductivity, were introduced, developed and fabricated, showing the extrinsic fmax up to 50 GHz, at the gate length of 0.5 µm, which is highest reported so far among the best published graphene and semiconductor counterparts.
The main achievements of this thesis work are as follows: (i) comprehensive study of correlations between graphene-dielectric material quality, small-signal equivalent circuit parameters and high-frequency performance of the GFETs; (ii) experimental verification of the concept of improving the GFET high- frequency performance via selection of adjacent dielectric materials with high OP energy; (iii) introducing the diamond as a most promising dielectric material for high-frequency GFETs; (iv) development of technology and demonstration of fully integrated X and Ku band GFET IC amplifiers with state-of-the art performance.
In conclusion, the routes of future development depicted in this thesis work may allow for enhancing the high-frequency performance of GFETs up to the level or even higher than that of the modern III-V semiconductor counterparts.
maximum frequency of oscillation
Chalmers, Microtechnology and Nanoscience (MC2), Terahertz and Millimetre Wave Laboratory
Enhanced high-frequency performance of top-gated graphene FETs due to substrate-induced improvements in charge carrier saturation velocity
IEEE Transactions on Electron Devices,; Vol. 68(2021)p. 899-902
Mobility degradation and series resistance in graphene field-effect transistors
IEEE Transactions on Electron Devices,; Vol. 68(2021)p. 3091-3095
Does carrier velocity saturation help to enhance fmax in graphene field-effect transistors?
Nanoscale Advances,; Vol. 2(2020)p. 4179-4186
The dependence of the high-frequency performance of graphene field-effect transistors on channel transport properties
IEEE Journal of the Electron Devices Society,; Vol. 8(2020)p. 457-464
Graphene field-effect transistors with high extrinsic fT and fmax
IEEE Electron Device Letters,; Vol. 40(2019)p. 131-134
Areas of Advance
Information and Communication Technology
Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)
Other Electrical Engineering, Electronic Engineering, Information Engineering
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie
Chalmers University of Technology
Kollektorn, MC2, Kemivagen 9, Gothenburg
Opponent: Professor Deji Akinwande , University of Texas at Austin, USA.