Search

In nature, hair typically exists in large-scale arrays, offering improved sensitivity and dynamic range. In this paper, we present a new high aspect-ratio (HAR) hair biomimetic microstructure used as an accelerometer and it consists of a vertically anchored hair-like spring with a proof-mass attached to the top of it and made from thick silicon. Silicon structures mimicking hair, fabricated by MEMS technology, have the potential to greatly improve sensor performance by combining large and dense arrays of HAR microstructures with efficient transduction mechanisms and local interface circuits. Signal processing of the MEMS array outputs (hundreds or thousands) can eventually provide multiplicity of functions, including high sensitivity, greater dynamic range, reduced parasitics, fault-tolerance, and reconfigurability. We present a thick silicon capacitive MEMS accelerometer and accelerometer arrays with a small-footprint based on this microstructure. Multiple electrodes surrounding the core hair structure form differential capacitive pairs and enable fully symmetric readout as well as force-feedback closed-loop operation for sensing acceleration. Arrays of 64 accelerometers each with a footprint of $200\times 200 \,\,\mu \text{m}^{2}$ and $500~\mu \text{m}$ thick have been demonstrated. [2018-0215]

In this paper, we introduce a novel on-chip capacitive sensor design and a motion estimation method for measuring multi-axis out-of-plane tilting motion of a micro-stage that is used for in situ calibration of an integrated MEMS gyroscope. On-chip sensing and motion estimation is critical for this application, since precision in measuring high frequency tilting motion of the micro-stage determines how accurately an on-stage MEMS gyroscope can be calibrated in the field with respect to this motion. To obtain decoupled sensing signals from multi-axis out-of-plane tilting motion, a capacitive sensing layout with high off-axis signal rejection capability is introduced. With the proposed design specifications and range of tilting motion, a dual axis capacitive sensor model is developed, and simulation results show that the sensor is able to reject more than 99.90% of the off-axis signal. The sensor also permits detection of perturbations to stage geometry due to ambient temperature variation through the effects of nonlinear behavior on signal timing. To measure tilting motion with the obtained sensing signal, a motion estimator with extended Kalman Filter (EKF) is also developed. With assistance of a laser Doppler vibrometer (LDV), experiments are performed to identify the parameters of the motion estimator and validate its performance. The experimental results demonstrate a 286 ppm error in scale factor calibration of a commercial MEMS gyroscope by the micro-stage with moderate temperature variation.

We report record-high performance from a fused-silica micro Precision Shell Integrating (PSI) gyroscope. The PSI gyroscope uses a fused-silica resonator with a diameter of 1 cm and a mechanical quality factor (Q) of 5.2 million. The gyroscope has an angle random walk (ARW) of 0.00016 deg/√hr and short-term in-run bias instability of 0.0014 deg/hr without any temperature compensation. This performance for such a small shell gyroscope compares well with the larger mHRG and HRG devices reported previously. This performance, in a device this small, is achieved by optimizing the fabrication of the shell resonator so it provides high Q, large mass, high frequency resonance, and low as-fabricated frequency mismatch.

This paper reports the design, fabrication technology and initial testing results of an all fused-silica 3D shell (hemispherical) resonator and capacitive drive/sense electrodes made from a second shell, for use in high-performance gyroscopes. A single fused-silica shell is patterned to form multiple electrodes that follow the curvature of the shell resonator. 10 mm diameter Shell resonator is then integrated inside a larger Shell electrode (SiS). Our approach enables, for the first time, the fabrication of curved electrodes at the micro-scale. The SiS device provides large overlap area and nearly uniform gap with large capacitance for better frequency tuning capability, reduced operating voltages, improved capacitive sensitivity and reduced temperature sensitivity as compared to other electrode architectures. Successful fabrication and testing of two prototype SiS devices are demonstrated. Quality factor as high as of 0.4 Million and frequency split as low as 1.3 Hz is obtained at operating frequency of ~ 6000 Hz.

A high Q-factor and mode-matched silicon MEMS gyroscope composed of a ladder structure has been developed. The ladder structure that is capable of suppressing energy dissipation has allowed the Q-factors of drive and sense modes to reach 120,000, which is a great value as a Si-tuning fork gyroscope. Moreover, the mode-matched high Q-factor ladder gyroscope shows an angle random walk (ARW) of 0.020 deg/√h and a bias instability (BI) of 0.20 deg/h. These measured results demonstrate that the ladder structure has enabled this silicon gyroscope to achieve high performance that is required for autonomous driving systems.

In this paper, we report a low-cost, fast, and high-throughput process for releasing molded fused-silica 3D micro-shell resonators from their original flat substrate. 49% Hydrofluoric Acid is used to selectively etch the flat part of the substrate to release the resonator shell. Nine resonators are released using this approach and the quality factor is measured and compared with 22 shells singulated using our standard lap/CMP method. In addition, the frequency mismatch of another four devices released using each method is compared. All the resonators exhibited high-Q (as high as 5.8M) and low frequency mismatch comparable to those processed using lap/CMP method.

This paper reports measured results for a fused-silica precision shell integrating (PSI) micro gyroscope employing out-of-plane drive/sense transduction mechanism. The PSI gyroscope is made with a 5 mm radius shell resonator operating in $n=2$ wine-glass mode at a frequency ( $f_{n=2}$ ) of 5.803 kHz with as-fabricated frequency split ( $\Delta f$ ) of 2.1 Hz. Large and reasonably uniform capacitance (∼0.25 pF) is achieved with flat surface electrodes. The gyroscope is operated in the force-rebalance mode by interfacing with an ultra-low-noise transimpedance amplifier (TIA). Near-navigation grade angle random walk (ARW) of $0.0062\ \deg/\sqrt{\mathrm{h}}\mathrm{r}$ , in-run bias instability (BI) of 0.027 deg/hr and scale factor of 158 mV/deg/s without any temperature compensation are achieved.

This paper reports an advanced deep reactive ion etching (DRIE) process for realizing ultra-deep (>500- $\mu \text{m}$ ) and ultra-high aspect-ratio (UHAR) silicon structures (AR > 40 for 1-mm through-trench etch, $\text {AR}\approx 80$ for 500- $\mu \text{m}$ through-trench etch, and AR > 20 for 500- $\mu \text{m}$ through-hole etch), with straight sidewalls across a wide range of feature sizes. The challenges of making such structures are overcome by continuously ramping critical parameters of the Bosch DRIE process throughout the process, including the 380-kHz bias power during etch step, the etch/passivation step duration, and the chamber pressure. The masking material capable of enduring the long DRIE process is also discussed; 10- $\mu \text{m}$ and 25- $\mu \text{m}$ wide trenches are etched to a depth of >750- $\mu \text{m}$ and >1000- $\mu \text{m}$ , respectively, in 1-mm-thick silicon wafers with straight sidewall profiles and flat trench bottoms. Deeper trenches are expected to be etched beyond a 1-mm thick wafer with thicker and/or higher selectivity masking materials. We have also demonstrated etching of circular holes of diameters as small as 25- $\mu \text{m}$ to a depth of >500- $\mu \text{m}$ , and potentially with 10–15 $\mu \text{m}$ diameter holes. This advanced DRIE process offers opportunities for applications ranging from through-silicon via in 3-D CMOS integration to emerging micro- and meso-scale microelectromechanical system applications that demand ultra-deep and UHAR DRIE. [2017–0298]