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New GaN Power-Electronics Packaging Solutions: Thermal Analysis
Keywords: Thermal management, Raman thermography, Thermal simulation
Thermal management of GaN-based power electronics has become a crucial design step. Indeed, long-term reliability of GaN devices is essentially limited by self heating and associated stresses. In this view, the use of innovative high performance materials for packages is required. Silver diamond composite is a very promising candidate with excellent thermal conductivity and a CTE matching that of the semiconductor materials. In this work, micro-Raman thermography measurements were performed on AlGaN/GaN multi-finger HEMTs (power bars) grown on SiC substrates to determine their temperature at various power levels. The devices were mounted on both silver diamond composite and CuW baseplates, in order to benchmark the thermal performance of diamond composite baseplates compared to traditional materials. Since package machining requires high roughness tolerances for the baseplate, silver diamond composite baseplates with copper metallisation were assessed as well. We show that AlGaN/GaN HEMT devices mounted on silver diamond composite baseplates with and without metallisation exhibit peak temperatures which are, respectively, 30% and 50% lower than the peak temperatures exhibited by devices mounted on traditional CuW baseplates. This is a dramatic improvement in terms of heat extraction leading to much longer device life-times and better performances. In additional, time-resolved Raman measurements were carried out on devices mounted on the silver diamond composite in order to obtain thermal dynamics of devices and heat diffusion response during pulsed operation. This time-dependent information is of great importance for reliability and failure analyses, as pulsed operation of a HEMT is the standard operation condition. When the devices are initially switched on, time evolution of device temperature is dominated by adiabatic heating within the initial few nanoseconds, followed by a slower heat diffusion which reaches the steady state at about 1ms. Finite-element thermal simulations were performed for comparison with the experimental results, and a good agreement was obtained.
Mustapha Faqir, Postdoctoral Research Assistant
University of Bristol
Bristol BS8 1TL,

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