Effective Thermal Resistance at Diamond Boundaries in MEMS

The high thermal conductivity and large bandgap of chemical-vapor-deposited (CVD) diamond make it a very attractive material for use in Micro-Electro-Mechanical Systems (MEMS), such as high-temperature thermistors and fast thermal radiation detectors. Unfortunately, diamond deposition on non-diamond materials in MEMS yields a highly-imperfect structure near the boundary. The imperfection strongly scatters phonon heat carriers, resulting in an effective thermal boundary resistance that must be considered in the thermal design of MEMS. This work develops a model for the effective boundary resistance as a function of temperature and the size of diamond grains near the boundary. Room-temperature predictions of the resistance are consistent with experimental data and indicate that it can increase the time constant of a diamond-metal thermistor structure by a factor of three. The model developed here facilitates the thermal design of MEMS containing diamond. This work motivates research on tailoring the diamond deposition process to reduce the effective resistance at diamond boundaries.