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, polymC 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 mu m is deposited at 350 degrees C and is patterned to create package anchor. A 4-mu m-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 240320 KHz, which is consistent with theoretical calculations. The application of diamond for thin film packaging is being reported for the first time.