FlexMEMS-enabled hetero-integration for monolithic FBAR-above-IC oscillators

In this work, a monolithic oscillator chip is heterogeneously integrated by a film bulk acoustic resonator (FBAR) and a complementary metal-oxide-semiconductor (CMOS) chip using FlexMEMS technology. In the 3D-stacked integrated chip, the thin-film FBAR sits directly over the CMOS chip, between which a 4 μm-thick SU-8 layer provides a robust adhesion and acoustic reflection cavity. The proposed system-on-chip (SoC) integration features a simple fabrication process, small size, and excellent performance. The oscillator outputs 2.024 GHz oscillations of −13.79 dBm and exhibits phase noises of −63, −120, and − 136 dBc/Hz at 1 kHz, 100 kHz, and far-from-carrier offset, respectively. FlexMEMS technology guarantees compact and accurate assembly, process compatibility, and high performance, thereby demonstrating its great potential in SoC hetero-integration applications.