Monitoring the Self-Heating in a High Frequency GaN HFET

Self-heating in GaN HFETs is a consequence of the high power and current levels common in such devices, and the limited ability of the substrates to conduct heat away from the devices. Most high frequency test devices are usually composed of 2 separate devices, laid out in a parallel electrical configuration but spatially symmetric with shared gate and drain contacts. The self-heating at high current densities causes the drain current to decrease as a function of drain bias, as the temperature of the active area increases above that of the substrate and device mount. Since a high frequency device is essentially 2 devices, one can bias the two parts to have different currents. Effectively one can then use one side of the device to monitor the self-heating and heat flow from the other side, if they are biased differently. This paper describes such experiments