Impact of adjacent dielectrics on the high-frequency performance of graphene field-effect transistors
Doktorsavhandling, 2021

Transistors operating at high frequencies are the basic building blocks of millimeter wave communication and sensor systems. The high velocity and mobility of carriers in graphene can open ways for development of ultra-fast group IV transistors with similar or even better performance than that achieved with III-V based semiconductors. However, the progress of high-speed graphene transistors has been hampered by limitations associated with fabrication, influence of adjacent materials and self-heating effects.

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.

diamond

high-frequency electronics

maximum frequency of oscillation

transit frequency

drift velocity

saturation velocity

Graphene

contact resistance

field-effect transistors

Kollektorn, MC2, Kemivagen 9, Gothenburg
Opponent: Professor Deji Akinwande , University of Texas at Austin, USA.

Författare

Muhammad Asad

Chalmers, Mikroteknologi och nanovetenskap (MC2), Terahertz- och millimetervågsteknik

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Transistors operating at high frequencies are the basic building blocks of millimeter wave communication and sensor systems. The high velocity and mobility of carriers in graphene can open ways for development of ultra-fast group IV transistors with similar or even better performance than that achieved with III-V based semiconductors. This 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). State-of-the-are high-frequency performance of GFET are presented. This work paves the ways of future developments depicted in this work for enhancing the high-frequency performance of GFETs up to the level or even higher than that of the modern III-V semiconductor counterparts.

Styrkeområden

Informations- och kommunikationsteknik

Nanovetenskap och nanoteknik (SO 2010-2017, EI 2018-)

Materialvetenskap

Infrastruktur

Kollberglaboratoriet

Nanotekniklaboratoriet

Ämneskategorier

Nanoteknik

Annan elektroteknik och elektronik

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

Utgivare

Chalmers tekniska högskola

Kollektorn, MC2, Kemivagen 9, Gothenburg

Online

Opponent: Professor Deji Akinwande , University of Texas at Austin, USA.

Mer information

Senast uppdaterat

2021-05-05