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Doolittle, William Alan

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Heat dissipation in high-power GaN electronics on thermally resistive substrates

2005-08 , Christensen, Adam , Doolittle, William Alan , Graham, Samuel

The heat dissipation in GaN devices grown on low thermal conductivity lithium gallate (LGO) substrates was investigated. The thermal conductivity of single-crystal LGO was measured utilizing the 3ω technique for temperatures ranging from 100 K–500 K. For the GaN layer, the thermal conductivity was estimated using a phonon transport model which included dislocation density and temperature dependence. These data were then used in a finite element program to determine the thermal behavior of a heterojunction field-effect transistor. Based on a maximum junction temperature of 500 K, it was found that devices with a power dissipation of 1W/mm were possible if the primary heat dissipation path was through the low thermal conductivity substrate. However, in using a front side cooling scheme, results suggest that it may be possible to develop devices with power dissipation in the range of 10 W/mm.

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Leaky surface acoustic waves in Z-LiNbO ₃ substrates with epitaxial AlN overlays

2004-10 , Bu, G. , Ciplys, D. , Shur, M. S. , Namkoong, G. , Doolittle, William Alan , Hunt, William D.

The properties of leaky surface acoustic waves (LSAW) in MBE grown AIN layer on Z-cut LiNbO₃ structures have been studied by numerical simulation and experimental measurements and compared with those of Rayleigh waves in the same structure. In the range of AIN layer thicknesses studied (0

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