Haoran Wen

Substrate-decoupled silicon disk resonators having degenerate gyroscopic modes with Q in excess of 1-million

This paper details a center-supported solid disk resonator in <;100> single-crystalline-silicon (SCS) that uses a novel substrate decoupling feature to achieve ultra-low dissipation gyroscopic modes with small frequency split. The secondary bulk acoustic wave (BAW) elliptic modes (m = 3) of a 2mm diameter substrate-decoupled disk resonator exhibit quality factor (Q) of ~1.3 M with 40 ppm frequency split (as fabricated) at 2.745 MHz. Q-factor remained in excess of 1 million at pressure levels as high as 500 mTorr. The measured temperature behavior of the Q, which is mostly limited by thermoelastic damping (TED), is in very close agreement with FEM predictions.

Resonant pitch and roll silicon gyroscopes with sub-micron-gap slanted electrodes: Breaking the barrier toward high-performance monolithic inertial measurement units

This paper presents the design, fabrication, and characterization of a novel high quality factor (Q) resonant pitch/roll gyroscope implemented in a 40 μm (100) silicon-on-insulator (SOI) substrate without using the deep reactive-ion etching (DRIE) process. The featured silicon gyroscope has a mode-matched operating frequency of 200 kHz and is the first out-of-plane pitch/roll gyroscope with electrostatic quadrature tuning capability to fully compensate for fabrication non-idealities and variation in SOI thickness. The quadrature tuning is enabled by slanted electrodes with sub-micron capacitive gaps along the (111) plane created by an anisotropic wet etching. The quadrature cancellation enables a 20-fold improvement in the scale factor for a typical fabricated device. Noise measurement of quadrature-cancelled mode-matched devices shows an angle random walk (ARW) of 0.63° √h−1 and a bias instability of 37.7° h−1, partially limited by the noise of the interface electronics. The elimination of silicon DRIE in the anisotropically wet-etched gyroscope improves the gyroscope robustness against the process variation and reduces the fabrication costs. The use of a slanted electrode for quadrature tuning demonstrates an effective path to reach high-performance in future pitch and roll gyroscope designs for the implementation of single-chip high-precision inertial measurement units (IMUs).

A 0.5MHz mode-matched pitch or roll annulus gyroscope with nano-gap slanted electrodes for quadrature cancellation

This paper presents, for the first time, the effective quadrature cancellation in a high-frequency pitch or roll bulk acoustic wave (BAW) gyroscope to enable perfect mode-matching for sensitivity improvement and noise reduction. The presented gyroscope has a high operation frequency of 0.5MHz and high translational stiffness for shock and vibration robustness. Quadrature cancellation, which is the biggest challenge in high-performance pitch or roll gyroscopes, is achieved by incorporating nano-gap slanted electrodes through the new HARPSS+ fabrication process, which combines anisotropic wet-etching of silicon with conventional DRIE-based HARPSS process. The HARPSS+ process enables precision capacitive transduction and tuning in all desired orientations, providing tuning coverage over typical process corners and significantly improving the yield of pitch or roll gyroscopes. Quadrature cancellation is verified on fabricated devices, allowing a perfectly mode-matched operation with a scale factor of 95.2pA/(°/s) and an open-loop bandwidth of 15Hz. The HARPS S+ process also enables simultaneous fabrication of single-chip tri-axial BAW gyroscopes: high-frequency (0.5–5MHz) gyroscopic modes with high quality factors (10,000s–100,000s) are measured on both yaw and pitch/roll BAW gyroscopes on the same wafer.