SUBJECT: Ph.D. Proposal Presentation
BY: Nicholas Hines
TIME: Tuesday, June 7, 2022, 12:30 p.m.
TITLE: Device-Level Thermal Management and Reliability of Gallium Nitride and Aluminum Gallium Nitride High Electron Mobility Transistors
COMMITTEE: Dr. Samuel Graham, Chair (ME)
Dr. Satish Kumar (ME)
Dr. Vanessa Smet (ME)
Dr. Sukwon Choi (ME)
Dr. Brianna A. Klein (SNL)


The fields of power and RF electronics are experiencing tremendous growth due to the ongoing development of gallium nitride (GaN) high electron mobility transistor (HEMT) technology. However, GaN HEMTs suffer from acute self-heating that limits their performance in high-power and high-frequency applications. The most recent advancements in GaN HEMT device-level thermal management consist of integrating high-thermal conductivity CVD diamond to GaN HEMT device layers. While the thermal merits for CVD diamond integration are clear, the processes for integrating diamond to GaN HEMTs introduce residual stress to the device layers that can detrimentally affect the performance and reliability of GaN HEMTs (Problem Statement 1).

Alternative to GaN HEMTs, ultra-wide bandgap aluminum gallium nitride (AlGaN) HEMTs have been recently developed that have the potential to exceed the performance limitations of GaN HEMTs. While AlGaN HEMTs are structurally similar to GaN HEMTs, the low thermal conductivity of AlGaN suppresses local heat spreading near the hotspot of AlGaN HEMTs and exacerbates acute self-heating that is detrimental to device performance and reliability (Problem Statement 2). Holistically, this proposed work seeks to advance thermal management solutions for mitigating the excessive self-heating of GaN and AlGaN HEMTs by answering several research questions that address critical research problems.

Problem Statement 1: (i) How do various CVD diamond integration processes affect the accumulation of residual biaxial stress in GaN HEMTs? (ii) How can non-contact optical stress metrology techniques be used to improve diamond integration processes for GaN HEMTs? The research methodology will primarily consist of Raman and photoluminescence spectroscopy experiments to measure the residual biaxial stress within various diamond-integrated GaN films.

Problem Statement 2: (iii) How can localized heat spreading be implemented near the hotspot of AlGaN HEMTs? (iv) How do novel device-level thermal management approaches affect the transient thermal behavior of AlGaN HEMTs and how do these transient thermal effects compare to the transient thermal behavior of GaN HEMTs? The research methodology will consist of experimentally validated thermal finite element analysis to identify novel thermal management approaches that achieve local heat spreading and to analyze the transient thermal behavior of AlGaN HEMTs under pulsed-mode operation.