Experimental Demonstration of Thermal Management of High-Power GaN Transistors with Graphene Lateral Heat Spreaders
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Experimental Demonstration of Thermal Management of High-Power GaN Transistors with Graphene Lateral Heat Spreaders Zhong Yan, Guanxiong Liu, Javed Khan, Jie Yu, Samia Subrina and Alexander Balandin Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, University of California - Riverside, Riverside, California 92521 USA ABSTRACT Graphene is a promising candidate material for thermal management of high-power electronics owing to its high intrinsic thermal conductivity. Here we report preliminary results of the proofof-concept demonstration of graphene lateral heat spreaders. Graphene flakes were transferred on top of GaN devices through the mechanical exfoliation method. The temperature rise in the GaN device channels was monitored in-situ using micro-Raman spectroscopy. The local temperature was measured from the shift in the Raman peak positions. By comparing Raman spectra of GaN devices with and without graphene heat spreader, we demonstrated that graphene lateral heat spreaders effectively reduced the local temperature by ~ 20oC for a given dissipated power density. Numerical simulation of heat dissipation in the considered device structures gave results consistent with the experimental data. INTRODUCTION Self-heating is a severe problem for high-power GaN electronics. A possible method for improving heat removal from GaN/AlGaN heterostructure field-effect transistors (HFETs) is introduction of an additional heat escape channel using materials with high thermal conductivity. Graphene is a promising candidate material for heat removal and thermal management applications. In 2008, our group discovered that the intrinsic thermal conductivity of single-layer graphene is extremely high and can exceed that of bulk graphite [1]. The defects and coupling to the substrate reduce thermal conductivity of graphene. However, the bulk graphite limit, K ~2000 W/mK, achieved in few-layer graphene (FLG) of certain thickness [2] is still much higher than thermal conductivity of conventional semiconductors or metals (e.g. K~145 W/mK for bulk crystalline Si or K~400 W/mK for bulk copper). In this study, we report preliminary results, which suggest a possible use of graphene flakes for heat removal. For the proof-of-concept demonstration, mechanical exfoliated graphene flakes were transferred on top of GaN/AlGaN HFETs. We measured the temperature rise in GaN HFETs using a micro-Raman spectrometer. The Raman peak position in the spectra of GaN depends on temperature [3]. Knowing the temperature coefficients of the Raman peaks we could monitor the temperature rise from the shifts in the position of Raman peaks. By comparing the Raman spectra for the GaN HFETs with and without graphene heat spreaders on top, it was demonstrated that graphene layers reduced the local temperature by ~20 oC for the power densities involved. The numerical simulations of heat dissipation in the considered device
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structures were carried out with the help of COMSOL software and the results were consi
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