Large-signal RF Reliability Modeling for GaN Power Amplifiers

Prof. John Albrecht
Michigan State University

Abstract
Technical progress at the transistor level, through significant research to scale devices for high-frequency performance [1] and for higher power [2], has enabled practical and competitive GaN HEMT based mm-wave power amplifier (PA) circuits suitable for EHF communications. As foundry offerings emerge and mature, there is a compelling need to predict reliability and safe operating conditions before using this emerging technology in systems. Reliability challenges have emerged related to the appropriate testing conditions and the relevant analysis for large signal mm-wave operation that are not consistent with existing methods at lower frequencies. Simulation capabilities will be discussed that can be used to understand whether test conditions are stressing and accelerating the physical processes that occur in a PA under operating conditions, class of PA, and signals of sufficient complexity. Outputs of the simulation include high resolution maps of electron energetics and transport, thermal effects, and electric field conditions. Exhaustive forensic analysis to deconstruct pristine and failed devices to provide a conclusive standard for reliability testing is not only expensive in time and money, but may not be relevant across PAs designed for different operating requirements. The span of expected operating requirements and circuit approaches is large and diverse, and a single test definition is unlikely to capture the operational stresses of different circuit architectures without extensive modeling.

[1] J.D. Albrecht, et al., "DARPA's Nitride Electronic NeXt Generation Technology Program," Compound Semiconductor Integrated Circuit Symposium (CSICS), 2010 IEEE pp.1-4, 3-6 Oct. 2010.
[2] M.J. Rosker, et al., “DARPA’s GaN Technology Thrust,” Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International, 1214-1217 (2010).

Bio:
Dr. Albrecht is an Associate Professor of Electrical and Computer Engineering at Michigan State University.  Prior to that (2009-2012) he led the NeXt, WBGS-RF, and MPC programs in the field of GaN electronics at DARPA, among other programs in RF electronics. Dr. Albrecht spent many years with the Air Force Research Laboratory’s Sensors Directorate working with emerging devices and subsystems for RF sensing in the areas of radar, communications, and electronic warfare. His research interests are in the area electrical and thermal transport properties of devices under extreme operating conditions such as high electric fields, temperature, and frequencies. He has a PhD in Electrical Engineering from the University of Minnesota (1999).