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Multi-band radio-frequency filters fabricated using polyimide-based membrane transfer bonding technology

In this paper, we present a polyimide-based Si membrane transfer bonding technology and its application to CMOS-compatible integration of different modes of AlN/Si composite piezoelectric MEMS resonators. The thermosetting polyimide, which has excellent chemical resistance and thermal stability, is used as a bonding adhesion, and is successfully removed as a sacrificial layer by O2 plasma to release free-standing MEMS devices. The whole process temperature is below 350 °C and compatible with CMOS LSI. Using this technology, different modes of AlN/Si resonators, which are film bulk acoustic wave resonators and wine-glass mode disk-type resonators, have been co-fabricated on the same wafer. We also fabricated a ladder-type FBAR filter with a center frequency of 7.71 GHz and a mechanically coupled disk-array filter with a center frequency of 292.8 GHz.