Dielectric characterization of microwave assisted chemically vapor deposited diamond

Freestanding polycrystalline diamond films produced by Microwave Plasma Chemical Vapor Deposition (MWCVD) were investigated for high power and high temperature electronic applications. The diamond films were deposited on polished tungsten substrates using 5000 W to I500 W power, 15.33 kPa pressure, methane-hydrogen-oxygen precursor gas between 0.5% CH₄ and 95% CH₄, oxygen/carbon ratio between 0 and 0.33, and temperature from 600°C to 900°C. The diamond film parted from the substrate as the samples cooled after deposition due to the difference in the thermal expansion coefficients of diamond and tungsten. Cohesive freestanding films of randomly oriented polycrystalline diamond were obtained ranging from 10 μm to 150 μm thick Either aluminum or tungsten metal contacts were deposited on the diamond to form parallel plate capacitors. Electrical measurements were performed before and after annealing. The dielectric constant and the loss tangent at temperatures from 23°C to 300°C were determined from capacitance measurements over a 20 Hz to 1 MHz frequency range. The effect of methane concentration, oxygen concentration, deposition temperature and annealing on the frequency and temperature stability of the dielectric properties of CVD diamond capacitors was investigated. Dielectric constants ranging between 8.0 and 4.2 and resistivities between 1×10⁸ ohm-cm and 5×10¹⁴ ohm-cm were obtained for the diamond samples