Wafer-level-packaged HARPSS+ MEMS platform: Integration of robust timing and inertial measurement units (TIMU) on a single chip

This paper presents a nano-precision high aspect-ratio poly- and single-crystal silicon DRIE plus wet-etching fabrication platform, also known as HARPSS+, which enables single-chip integration and wafer-level-packaging of robust high-frequency timing and inertial sensors. The HARPSS+ platform is the first highly developed process providing scalable deep submicron gaps in vertical, horizontal, and 54°-slanted orientations for efficient transduction and dynamic control of high-Q single crystalline silicon resonators. The platform also provides wafer-level-packaging of MEMS devices in cavities with different cavity pressures in a single bonding step. Single-chip timing and inertial measurement units (TIMU) are fabricated with high yield through the HARPSS+ platform, which features 3-axis high-frequency resonant gyroscopes with complete quadrature cancellation enabled by the slanted electrodes. High-bandwidth 3-axis accelerometers are used on the TIMU with high sensitivity provided by the nano-gaps. A high-Q BAW resonator is included as internal frequency reference for self-contained timing and inertial measurement, along with on-chip heaters for ovenization capability. Each device is packaged in cavities with different pressure levels ranging from atmosphere to sub-10Torr for optimized operation through one single bonding step. The nano-gap-enabled high-frequency devices have high environmental robustness and small form-factor with the overall TIMU being 4.5mm×5.5mm×1mm. Fabricated TIMU demonstrates high-performance with sub-10°/h gyroscopes and sub-100μg accelerometers. Low power chip-level ovenization is achievable with on-chip heaters owing to small size and vacuum packaging.