Operating channel temperature in GaN HEMTs: DC versus RF accelerated life testing

Abstract

Abstract-Channel temperature is a key parameter for accelerated life testing in GaN HEMTs. It is assumed that selfheating is similar in RF and DC operation and that DC test results can be applied to RF operation. We investigate whether this assumption is valid by using an experimentally calibrated, combined electrical and thermal model to simulate Joule heating during RF operation and compare this to DC self-heating at same power dissipation. Two cases are examined and the implications for accelerated life testing are discussed: Typical (30 V) and high (100 V) drain voltages.

A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

“…This technique is based on measuring the thermal radiation emitted from the surface of a device, typically detected in the 3 -10 µm spectral range, depending on the detector used. The radiated light intensity (radiance) scales as T 4 , following the Stephan-Boltzmann law, where T is the surface temperature in Kelvin. Therefore, temperature can be determined by measuring radiance, after calibrating the surface emissivity of the device under test (DUT) to take into account that the measured surface is not a perfect black body (emissivity = 1).…”

“…Fig. 8: Simulated temperature rise in a packaged GaN HEMT on a 100μm-thick SiC substrate, shown as a function of number of gate fingers at a constant power dissipation density of 11W/mm; using a model adapted from [4]. The ratio between the peak gate temperature rise and spatially averaged temperature rise, equivalent to a Raman thermography measurement, is shown.…”

“…A more precise device thermal modelling approach is to combine the Joule heating distribution derived from a 2D drift diffusion simulation with a 3D FE transistor model [4,63]. Figure 9 illustrates the simulated Joule heat distribution in the channel of a GaN HEMT operated over a range of drain bias voltages.…”

“…At less than or equal to 30V DS the Joule heating distribution can be approximated by a block heater, as previously described. Above a certain threshold voltage the field plate increasingly spreads the electric field, and the resulting heating, away from the gate [4,64], protecting the gate against damage. The Joule heat dissipation spreading illustrated in Figure 9 lowers the peak channel temperature and also shifts the peak temperature location away from the gate foot towards the drain, as has been observed experimentally in [62].…”

“…However, an ever increasing power dissipation density has resulted in thermal management challenges. It is critically important to be able to accurately determine device temperatures in order to assess the reliability of new technologies, because temperature is one of the dominant drivers of device degradation and influences device performance [2][3][4][5][6][7]. Phonon transport at the nanoscale and at interfaces impacts how waste heat is transported away from the active region in devices.…”