Thermal performance of high-temperature stable die-attachments for GaN HEMTs

This work focuses on the thermal performance of high-temperature stable die-attachments for GaN HEMTs. For mounting of GaN HEMTs, three die-attachment technologies i.e. Ag-sintering, TLP bonding and Au80Sn20 eutectic soldering, were investigated. For comparison purposes, the thermal resistance of GaN assemblies, with different die-attachments was measured. The surface temperature of the devices was measured with the Infrared (IR) thermography and in-built temperature sensors. It was found that built-in temperature sensors measure the temperature of the device higher than the surface temperature by 10%. The sensor on the chip was aimed at measuring temperature values close to the transistor channels. The channel temperatures are usually measured using Micro-Raman spectroscopy. Our investigations have shown that channel temperature measurements, using Raman spectroscopy are by 40 to 50% higher than surface temperature readings from IR thermography. In comparison with Raman measurements, the integrated temperature sensor values 30% lower than actual junction temperatures. It was found that both Ag-sintering and TLP bonding give better thermal performance in comparison with Au80Sn20 soldering. Our earlier investigations prove, that both Ag-sintering and TLP bonding are stable up to 480 deg C, which is well above the operating limits of AuSn solder. Moreover, both sintering and TLP bonding have good electrical and thermal properties as compared to AuSn solder. It can be stated that both Ag-sintering and TLP bonding are better die-attachments in terms of electrical and thermal performance than AuSn solder joints