The application of polycrystalline diamond in a thin film packaging process for MEMS resonators

This paper reports the design, fabrication and testing of a polycrystalline diamond (poly-C) thin film packaging process for a MEMS cantilever type resonator using a 4-mask fabrication process, which integrates chemical vapor deposition (CVD) diamond thin film technology with an encapsulation packaging process. After poly-C cantilever beam resonators were fabricated using the first two masks, a sacrificial PECVD SiO2 layer with a thickness in the range of 4–5 μm was deposited at 350 °C and patterned to create the package anchor. Then, a 4-μm-thick poly-C film was grown and patterned to create the thin film packaging structure containing fluidic access ports for the removal of the sacrificial layer. The fluidic access ports were finally sealed with an additional poly-C growth. To evaluate the efficacy of the poly-C encapsulation process, poly-C cantilever beam resonators were tested using a piezoelectric actuation and laser detection method before and after the poly-C packaging process. Resonance frequencies measured before and after are in the range of 240–320 kHz, which is consistent with predicted calculations. A modified fabrication process was designed to test the fluidic hermiticity of the thin film package.