Characterization and Compensation of Thermal Effects in GaN HEMT Technologies
Licentiatavhandling, 2020

Further advancements with GaN based technologies relies on the ability to handle the heat flux, which consequently arises from the high power density. Advanced cooling techniques and thermal optimization of the technology are therefore prioritized research areas. Characterization techniques play a key role in the development of new cooling solutions, since these rely on accurate measurements of e.g. the temperature of the device. This thesis covers techniques to electrically characterize the lateral and vertical heat properties in GaN, and a temperature compensation technique for GaN MMICs.

The first part outlines a methodology to electrically extract the thermal resistance of a GaN resistor without risking distortion from field induced electron trapping effects, which are exhibited by GaN heterostructures. The technique uses differential resistance measurements to identify a suitable resistor geometry, which minimizes trapping effects while enhancing the self-heating. Such conditions are crucial for electrical methods since these exploit the self- heating for a thermal analysis.

Furthermore, a test structure and measurement method to electrically characterize the lateral heat spread was designed and evaluated. The structure is implemented with a thermal sensor, which utilizes the temperature-dependent IV characteristics of a GaN resistor, making it suitable for integration in GaN MMICs. The transient response can be obtained to extract the thermal time constants and propagation delay of the heat spread. At higher ambient temperatures, the propagation delay increases and the thermal coupling is increased. Lastly, a biasing technique to compensate for thermal degradation of the RF performance of an LNA was developed. By utilizing the gate- and drain voltage dependence of the RF performance, a constant gain against increasing temperature can e.g. be achieved.

thermal coupling

thermal effects

thermal resistance


temperature compensation.



Kollektorn (A423), Kemivägen 9
Opponent: Dr. Peter Melin, Ericsson AB, Sweden


Johan Bremer

Chalmers, Mikroteknologi och nanovetenskap, Mikrovågselektronik

Compensation of Performance Degradation Due to Thermal Effects in GaN LNA Using Dynamic Bias

2018 48th European Microwave Conference, EuMC 2018,; (2018)p. 1213-1216

Paper i proceeding

Analysis of Lateral Thermal Coupling for GaN MMIC Technologies

IEEE Transactions on Microwave Theory and Techniques,; Vol. 66(2018)p. 4430-4438

Artikel i vetenskaplig tidskrift

Johan Bremer, Ding Yuan Chen, Aleksandra Malko, Manfred Madel, Niklas Rorsman, Sten E. Gunnarsson, Kristoffer Andersson, Torbjörn M. J. Nilsson and Mattias Thorsell, "Thermal Characterization of GaN HEMTs Affected by Trapping Effects Using Electrical Measurements"






Elektroteknik och elektronik

Annan elektroteknik och elektronik

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: Technical report MC2-429



Kollektorn (A423), Kemivägen 9

Opponent: Dr. Peter Melin, Ericsson AB, Sweden

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