The Impact of Nongray Thermal Transport on the Temperature of AlGaN/GaN HFETs

Abstract

The hotspot temperature in AlGaN/GaN heterostructure FETs has been of great interest due to its effect on the reliability of these devices. Both the nanoscale heat transfer effects and complex energy transfer mechanism from electrons to lattice are factors affecting the hotspot temperature, which is not accounted for in continuum level thermal simulations. The effects of heat generation zone size and the energy transfer mechanism from electrons to the lattice on the hotspot temperature were analyzed using electrical and nongray ballistic-diffusive thermal transport simulations for devices operated at a fixed power, but different biasing conditions. Results show that hotspot temperatures are impacted from nanoscale effects but the complex energy scattering mechanisms from electrons to the lattice do not have a significant impact on the hotspot temperature due to the scattering and redistribution of the energy within the phonon population.Index Terms-AlGaN/GaN heterostructure FETs (HFETs), electrothermal modeling, hotspot, nongray phonon transport.

Applications and Impacts of Nanoscale Thermal Transport in Electronics Packaging

“…According to fully coupled electrothermal simulation [158,175,178] shown in Fig. 12(a), the domain size of the peak heat generation zone can be less than 10 nm  50 nm, which is in agreement with theoretical predictions in literature [172,179].…”

“…Currently, industrial practices for device thermal analysis and accelerated direct current operational life tests [157,169] rely on simulation data based on the simple and widely accepted Fourier's law of heat conduction. However, a limited number of pioneering theoretical studies [170][171][172][173][174] have suggested that a nanoscale temperature spike or a so-called hot-spot forms in GaN HEMTs, which can be significantly hotter than predictions based on purely diffusive thermal transport models (i.e., the Fourier's law of heat conduction). This unanswered question has inhibited the use of GaN devices for high power RF applications where demonstrated long product lifetimes are required [158,175].…”

“…This local depletion region with high electrical resistance causes spatial confinement of the 2DEG Joule heating. This leads to formation of a nanoscale hotspot [170,[172][173][174] subject to extreme local heat flux (>1 MW/cm 2 ). According to fully coupled electrothermal simulation [158,175,178] shown in Fig.…”

“…This device model was developed to validate the near-UV thermoreflectance results. The coupled modeling scheme self-consistently solved, for each mesh point, the Poisson, current continuity, and electrohydrodynamic equations (for electronic transport), and the BTE [170,172] (for thermal transport) to derive the electrostatic potential, electron/hole concentration and their energy/temperature distributions, heat generation, and electron/hole/lattice temperature rise. Consequently, the model accounted for the nanoscopic heat source size effect.…”

Transient Simulation for the Thermal Design Optimization of Pulse Operated AlGaN/GaN HEMTs

“…Meanwhile, the interface of GaN/SiC is a thick AlN nucleation layer with 20 nm thickness that involves intricate resistance mechanisms, including defects, dislocations, and interfacial disorders, these mechanisms seriously damage the thermal property, therefore heat spreading capacity of this interface of GaN/SiC was represented as a single effective interface thermal resistance in our model. Finally, to reduce the total computing time, only a quarter of device was simulated, because of their structural symmetry [3,[12][13][14][15][16][17][18][19][20][21].…”