Thermal Design Rules of AlGaN/GaN-Based Microwave Transistors on Diamond

Thomas Gerrer*, James Pomeroy, Feiyuan Yang, Daniel Francis, Jim Carroll, Brian Loran, Larry Witkowski, Marty Yarborough, Michael J. Uren, Martin Kuball

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


Reliable operation of high power GaN amplifiers at maximum performance relies on the mutual optimization of several design parameters constrained by a defined thermal budget. On high thermal conductivity, substrates, such as SiC and diamond, undergo small changes within the design that can lead to drastic changes in channel temperature. We utilize finite element simulations to provide design rules for device structures for GaN-on-diamond amplifiers, benchmarked against GaN-on-SiC. At 8 W/mm power density, a 13μm gate pitch GaN-on-diamond design compared to a commonly employed 40μm gate pitch GaN-on-SiC design results in 40 °C and 20 °C cooler peak channel temperature, i.e., 182 °C for single and 201 °C for polycrystalline diamond (PCD) substrates despite the 3× larger areal power density. The simulations were validated with 1.25 mm wide, 10-finger GaN-on-diamond high-electron-mobility transistors (HEMT) devices of 13 and 40μm gate pitch, with good electrical performance in pulsed I - V measurements and Raman thermography measurements. The commonly used Au-Sn die-attach is determined as the next limiting factor for GaN-on-Diamond technologies which require the development of new die-attach materials.

Original languageEnglish
Article number9372136
Pages (from-to)1530-1536
Number of pages7
JournalIEEE Transactions on Electron Devices
Issue number4
Publication statusPublished - 8 Mar 2021

Bibliographical note

Funding Information:
Manuscript received November 26, 2020; revised February 8, 2021; accepted February 10, 2021. Date of publication March 8, 2021; date of current version March 24, 2021. This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) under the program Grant GaN-DaME (EP/P00945X/1). The review of this article was arranged by Editor S. Chowdhury. (Corresponding authors: Thomas Gerrer; Martin Kuball.) Thomas Gerrer, James Pomeroy, Feiyuan Yang, Michael J. Uren, and Martin Kuball are with the H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, U.K. (e-mail:;

Publisher Copyright:
© 2021 IEEE.

Copyright 2021 Elsevier B.V., All rights reserved.

Structured keywords

  • CDTR


  • Finite element analysis
  • GaN-on-diamond
  • high-electron-mobility transistors (HEMT)
  • Raman thermography
  • simulation

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