Thermal resistance measurements and reliability of GaAs power MESFETs

Summary form only given. Thermal resistance measurements have been carried out on more than 50 devices with an in-house developed instrument, using the well-known electrical method based on temperature dependence of the Schottky junction forward voltage. The selected MESFETs, intentionally chosen with completely different layout and heat-sinking solutions, such as via-hole or air-bridge source contacts and flip-chip or backside mounting, have been measured at several temperatures and power levels. Present experimental results have been related to the different device structures available and have been compared with theoretical values coming from simplified models proposed in the literature. The results show that the exact location of heat-source areas and the description of heat transfer processes cannot be easily handled with a simple model without a considerable loss of accuracy. The quality of die-attach also has a relevant influence on the value of thermal resistance, essentially due to the presence of voids in the die-attach alloy.<>