The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device

Abstract

The present work uses finite element thermal simulations of Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) to evaluate the impact of device design parameters on the junction temperature. In particular the effects of substrate thickness, substrate thermal conductivity, GaN thickness, and GaN-to-substrate thermal boundary resistance (TBR) on device temperature rise are quantified. In all cases examined, the TBR was a dominant factor in overall device temperature rise. It is shown that a TBR increase can offset any benefits offered through a more conductive substrate and that there exists a substrate thickness independent of TBR which results in a minimum junction temperature. Additionally, the decrease of GaN thickness only provides a thermal benefit at small TBRs. For TBRs on the order of 10 -4 cm 2 K/W or greater, decreasing the GaN thickness can actually increase the temperature as the heat from the highly localized source is not sufficiently spread out before crossing the GaN-substrate boundary. The tradeoff between GaN heat spreading, substrate heat spreading, and temperature rise across the TBR results in a GaN thickness with minimum total temperature rise. For the TBR values of 10 -4 cm 2 K/W and 10 -3 cm 2 K/W these GaN thicknesses are 0.8 µm and 9 µm respectively.Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it Same asReport (SAR) 18. NUMBER OF PAGES 9 19a. NAME OF RESPONSIBLE PERSON a. REPORTunclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98)

Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern

“…The GaN thickness is known to influence the heat spreading and associated temperature variations when GaN/substrate interface has large TBR 45 . However, the cross-sectional scanning electron microscopy images evidenced no major thickness difference between the samples grown simultaneously on planar sapphire and rGO buffer layer.…”

A Hybrid Multi-gate Model of a Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) Device Incorporating GaN-substrate Thermal Boundary Resistance

“…As in the previous numerical study, our GaN HEMT model accounts for the highly localized heat originating in the Al x GaN 1-x and spreading through the device layers, including crossing the GaN-substrate TBR (14). This model takes a hybrid approach by combining 2-D analytical YMC heat spreading models with extracted numerical models of the parameter-dependent heat spreading behavior.…”

“…Figure 12. FEA extracted single-gate GaN HEMT temperature distribution (table 1 parameters and no TBR) (14).…”

“…The University of Bristol recently reported that this TBR in commercial devices on silicon carbide (SiC) substrates can reach levels greater than 60 m²K/GW, which can increase the device's maximum temperature by up to 40%-50% (11)(12)(13). In fact, previous work by the authors numerically modeled several single-gate GaN HEMT devices and demonstrated significant TBR influences on junction temperature trends (14). Yet, evaluating a large parameter space with this numerical approach to fully understand device design tradeoffs would require significant computational resources.…”

“…Thermal spreading resistance models like those developed by Yovanovich, Muzychka, and Culman (hereafter referred to as YMC models) that solve heat diffusion using separation of variables while accounting for geometric, heating, and convection cooling boundary conditions (15,16) can provide accurate temperature distributions within the layers if the TBR is ignored. However, as our previous analysis showed, the TBR must be integrated into these solutions to provide an accurate parametric tool for designers (14).…”