DARPA – Threads – Thermal Analysis and Design of High Power GaN RF Devices

The integration of high thermal conductivity dielectric materials with GaN RF transistors will be a key in the reduction of device thermal resistance and improvement in operational power density. This will ultimately require an understanding of the thermophysical properties of the integrated materials, thermal interface resistances, and eventually temperature measurements to verify device performance. Temperature and thermal resistance of materials, interfaces and devices will be measured with a suite of techniques in Hopkins’ and Graham’s labs at UVA and UMD, respectively. Broadly, these labs house a variety of thermoreflectance and micro-Raman-based measurement capabilities that can measure the pertinent thermal properties of materials (in plane and cross plane thermal conductivity of thin films, thermal resistance at interfaces, temperature distributions in devices) as a function of temperature and in operando during operation of devices subjected to loads up to 200 V and 1.2 A. An additional power of the specific experimental techniques are the custom-built optical trains on each system allowing for variable focus and position control of the lasers used in these systems, permitting local measurements (on the order of 1 micron) or more global resistance measurements via use of increased spot sizes. The ability to tightly focus the beams allows for position sensitive measurements of thermal properties and the ability to create thermal resistance and temperature maps of operating devices, a key thermal diagnostic to evaluate material and device design via feedback of the thermal measurements to our predictive models. In addition to optical techniques, we will employ gate resistance thermometry to measure the average temperature across the channel width for additional metrology and device verification. In this project, we are working with Prof. Samuel Graham (UMD), Prof. Patrick Hopkins (UVA), and Qorvo.