Wafer-Level Packaging of Micromechanical Resonators

An approach to low-cost, wafer-level packaging of microelectromechanical systems (MEMS), e.g., microresonators, is reported. The process does not require wafer-to-wafer bonding and can be applied to a wide range of MEMS devices. A sacrificial polymer-placeholder is first patterned on top of the MEMS component of interest, followed by overcoating with a low dielectric constant polymer overcoat. The sacrificial polymer decomposes at elevated temperature, and the volatile products from the sacrificial material permeate through the overcoat polymer leaving an embedded air-cavity around the MEMS structure. Thus, the device is released from the sacrificial polymeric material, housed in a protective overcoat. The protected MEMS device can then be handled and packaged like an integrated circuit. The electrical characteristics of the microresonators before and after packaging were essentially the same, showing the packaging scheme does not alter the device performance. This approach is applicable to both surface and bulk micromachined devices