Diamond Thin Film Micro-package for MEMS Resonator

This paper reports the development of a polycrystalline diamond (poly-C) thin film encapsulation packaging process which is integrated into the MEMS cantilever resonator fabrication. The high Young's modulus and chemical stability of poly-C make it an excellent candidate material for a thin film package. A test chip is fabricated using a 4-mask process. First, poly-C cantilever beam resonator is fabricated using a 2-mask process, while PECVD SiO₂ serves as sacrificial layer material. Then, another sacrificial PECVD SiO₂ layer with a thickness in the range of 4-5 mum is deposited at 350 degC and is patterned to create package anchor. A 4-mum-thick poly-C film is grown and patterned to provide fluidic access ports for the releasing of the package. Then, the fluidic access ports are 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 piezoelectric actuation and laser detection method before and after poly-C packaging process. Resonance frequencies measured before and after are in the range of 240-320 KHz, which is consistent with theoretical calculations. The application of diamond for thin film packaging is being reported for the first time