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3D Graphene for Next Generation Thermal Management of GaN MMICs
Keywords: Graphene, Thermal, MMIC
As the power dissipation requirements for both commercial and military products become more stringent, conventional heat sinking methods become very challenging. TPG (Thermal Pyrolytic Graphite) is a unique form of synthetic graphite manufactured from thermal decomposition of hydrocarbon gas in a high temperature chemical vapor deposition reactor. This proprietary process produces a 3D highly oriented graphene stack which exhibits a thermal conductivity 4x of copper but only ¼ of the weight. TPG along with its metal and ceramic encapsulated products makes it very attractive for high power and low weight applications. Early reported study of thermal simulation and reliability tests such as thermal cycle, shock and vibration is very encouraging. In this study, we have designed a TPG thermal spreader as a test vehicle for die attaching GaN MMICs to substrates utilizing the highest TPG conductive path. Our studies have shown that the thermal conductivity of the TPG spreader is 609 W/m-K, a 5x improvement compared to commercially available Cu-Mo 131 W/m-K. The CTE of the thermal spreader is dominated by the low CTE metal encapsulant and has a measured value of 5-8 ppm, suitable for most MMIC packages used in defense industry. Further, the CTE can also be modified to sub-optimize other commercial applications. In addition, the TPG thermal spreader reduces the weight of the incumbent metal significantly. Thermal simulations revealed 55% reduction in device operating temperature, which will have significant impacts on device performance and reliability. DC and RF testing results along with IR imaging results of GaN MMICs attached to the TPG thermal spreader will be reported.
Ramesh Varma, Consulting Engineer
Northrop Grumman MIssion Systems
Linthicum, MD

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