Indirect Excitation of micro-HRG Using Segmented Piezoelectric ALD PHT Actuator

This paper presents, for the first time, an indirect excitation method for three-dimensional fused quartz dual-shell micro-scale Hemispherical Resonator Gyroscope μHRG. The μHRG was fabricated using three wafer bonding and high-temperature micro-glassblowing processes, providing a sensing element (device shell), a self-aligned fixed-fixed anchor for increased immunity to mechanical shocks and vibrations, and a housing (cap shell) for vacuum encapsulation. The novel actuation technique uses piezoelectric actuation to transfer energy from the cap shell to the device shell to excite the resonant element, where the piezoelectric material is deposited and shaped on the outer cap shell. Using the proposed indirect excitation method, the metal coating of the device shell is eliminated, preserving the high quality factor of the pristine fused quartz material. In this paper, we first introduce the mechanism of excitation, supported by Finite Element Analysis (FEA). We then describe the Atomic Layer Deposition (ALD) method of PbHf˟Ti1-˟O3 (PHT) piezoelectric material, followed by the fabrication process of a dual-shell μHRG prototype co-fabricated with an 80 nm layer of ALD PHT actuator. Finally, we experimentally demonstrated the indirect excitation, showing the feasibility of the method as a possible alternative to capacitive or direct piezoelectric actuation. Though early in development, the reported excitation approach may offer a preferable method for excitation of μHRGs, allowing to achieve the ultra-high mechanical quality factor, on the level of the TED-limit of fused quartz.