Computational Modeling of Extreme Heat Flux Microcooler for GaN-Based HEMT

Abstract

This study explores an extreme heat flux limit of microcooler for GaN-based HEMTs (high electron mobile transistors) which have local power densities exceeding 30 kW/cm2 using both solid conduction simulation and single-phase/two-phase conjugate simulations. Solid conduction simulation models are developed for full geometry of the microcooler to account for the overall thermal resistances from GaN HEMT to working fluid. This allows investigating the temperature distribution of the suggested microcooler. Parametric studies are also performed to investigate the impact of geometries and heat transfer coefficients on the junction temperature. The solid conduction simulation results using COMSOL Multiphysics agree well with single-cell ANSYS Fluent simulation results. Separately, fluid-solid conjugate CFD (Computational Fluid Dynamics) simulation models provide the detailed flow information in the microchannel using a single-channel geometry with symmetry boundary conditions. Single-phase CFD simulations obtain the lower bound of total pressure drop and heat transfer coefficient at the microchannel walls for a mass velocity range of G = 6000–24000 kg/m2-s. The local temperatures and velocity distributions are reported that can help with identifying the locations of the maximum velocity and recirculation regions that are susceptible to dryouts. Two additional alternative tapered inlet designs are proposed to alleviate the significant pressure loss at the entrance of the SiC channel. The impact of the tapered inlet designs on pressure drops and heat transfer coefficients is also investigated. Two-phase simulations in microchannel are conducted using Volume-of-Fluid (VOF) method embedded in ANSYS Fluent to investigate two-phase flow patterns, flow boiling, and temperature distributions within the GaN HEMT device and SiC etched mircochannels. A user-defined function (UDF) accounts for the phase change process due to boiling at the microchannel walls. The results show that the time relaxation factor, ri has a strongly influence on both numerical convergence and flow solutions.

Thermal management of GaN HEMT devices using serpentine minichannel heat sinks

“…The standard -turbulence model has been used to solve the governing equations, as this model has been shown to capture the physics well for other similar heat transfer studies [31,42,43]. Themodel introduces two additional variables: the turbulent kinetic energy, ), and specific dissipation (12) rate, . The transport equations for and used in the CFD model are based on those given by Wilcox [44]:…”

“…For example, Calame et al [10] used experiments and numerical simulations to study the dissipation of 4 kW/cm 2 over a 1.2 × 5 mm 2 active area of a GaN on SiC semiconductor using water-cooled microchannel coolers, while the experimental study of Lee et al [11] investigated how to dissipate a heat flux of 11.9 kW/cm 2 over eight heat sources of size 350 × 150 µm 2 on a 7 × 7 mm 2 silicon (Si) die with a maximum hotspot temperature of 175°C. Recently, Lee et al [12,13] used 3-D numerical simulations to analyse the thermal conditions when a total power of 92.4 W is applied to 40 multiple gates (a heat flux of 330 kW/cm 2 is applied to each gate) located on GaN HEMTs on a SiC-based microchannel heat sink using water and methanol as a coolants in single and two phase flow conditions. Other relevant studies have focused on the effect of using very high thermal conductivity substrates to enhance heat spreading for GaN and a number of these have analysed diamond heat spreaders [14 -16] since diamond's thermal conductivity is 2200 W/m.K -5.5 times greater than copper [17].…”

Inductive Coupled Plasma Etching of High Aspect Ratio Silicon Carbide Microchannels for Localized Cooling

“…Thus, the addition of microchannels and cooling fluid into the SiC substrate is one solution for decreasing device temperatures during operation. This approach allows the use of both convective and conductive heat transfer to reduce overall temperature of the system and increases the overall heat flux of the system and local cooling [5]. It is approximated that channel temperatures can remain below 110°C using this integrated cooling architecture [6].…”