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Diamond Thin Films with Tailored Microstructures for Thermal Management of Power Electronics
Keywords: Nanocrystalline diamond, Thermal management, Power electronics
Thin film diamond possess exceptional properties such as large energy bandgap, high thermal conductivity (20 W/cmK), high resistivity, chemical inertness, and high dielectric breakdown strength making it well suited for applications in thermal management, power electronics, optoelectronics,and microelectromechanical systems (MEMS) among others (Gruen, 2001; Krauss et al., 2001; Miskys et al., 2003; Ralchenko et al., 2007; Willander et al., 2006). To date, two different diamond morphologies have dominated the landscape of diamond thin film research – microcrystalline (MCD) and nanocrystalline diamond films (NCD). MCD films, with grain sizes typically in micrometer regime possess high electrical resistivity and high thermal conductivity. However, the surfaces of MCD films are rough with RMS roughness values in the micrometer regime making them unsuitable for device applications. NCD films, on the other hand, possess low surface roughness but exhibit low electrical resistivity and thermal conductivity values. Therefore, there is a need to develop diamond films with smooth surfaces and superior thermal and electrical properties. We have developed process conditions which enable us to seamlessly switch between MCD and NCD morphologies within a single diamond film. It will be shown that it is possible to alternate between NCD and MCD morphology and vice-versa to produce high quality diamond films (with more than 80% diamond content) even when the individual NCD and MCD layers are less than 3 microns thick. The microstructure of the diamond films evaluated by scanning electron microscopy is correlated with film phase purity quantified using Raman spectroscopy. The effect of process conditions vis-à-vis the microstructure and phase purity will be delineated using optical emission spectroscopy and quadrupole mass spectroscopy. This research lays the foundation for the development of smooth “composite” diamond films with tailored structure, phase purity and materials properties. It is envisaged that these composite diamond films will find applications in thermal management of power electronics, by enabling the direct extraction of heat from devices.
Nirmal Govindaraju, Research Assistant Professor
Oklahoma State University
Tulsa, OK

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