In-line wafer level hermetic packages for MEMS variable capacitor

In this paper, we report in-line wafer level hermetic packages (WLP) for MEMS variable capacitors. The beam structure of MEMS vibrates strongly under decompression. Since this vibration causes RF noise, it is necessary to set the pressure around the beam structure at 40000Pa or greater. Therefore, a structure that carries out a resin seal of the hole for etching the cap of a formed in the sacrificial layer process, at atmospheric pressure (101300Pa) is crucial for what. To prevent moisture permeation inside a cap, the resin was coated with a PECVD SiN layer. The developed packages become a hybrid hermetic encapsulation, which consists of PECVD SiN layers. Moreover, the deformation of the cap by external pressure was reduced using a corrugated cap. The developed package is comparatively large (340 times 1100 mum). Nevertheless, after the 265degC reflow test (5 times) and -55degC/125degC thermal cycle test (20 cycles), no cracks were observed in the packages. Since all of such processes and materials are compatible with the CMOS process, this package has very low cost. We present a summary of several aspects of our development activities in this MEMS variable capacitor packaging technology.