MEMS scanning micromirrors have been proposed to steer a modulated laser beam in order to establish secure optical links between rapidly moving platforms. An SOI/SOI wafer-bonding process has been developed to fabricate scanning micromirrors using lateral actuation. The process is an extension of established SOI technology and can be used to fabricate stacked high-aspect-ratio structures with well-controlled thicknesses. Fabricated one-axis micromirrors scan up to 21.8/spl deg/ optically under a dc actuation voltage of 75.0 V, and have a resonant frequency of 3.6 kHz. Fabricated two-axis micromirrors scan up to 15.9/spl deg/ optically on the inner axis at 71.8 V and 13.2/spl deg/ on the outer axis at 71.2 V. The micromirrors are observed to be quite durable and resistant to shocks. Torsional beams with T-shaped cross sections are introduced to replace rectangular torsional beams in two-axis MEMS micromirrors, in order to reduce the cross-coupling between the two axial rotations. Fabricated bidirectional two-axis micromirrors scan up to /spl plusmn/7/spl deg/ on the outer-axis and from -3/spl deg/ to 7/spl deg/ on the inner-axis under dc actuation.

/pdf/scanning-micromirrors-fabricated-by-an-soi-soi-wafer-bonding-47d3z7esme.pdf

Scanning micromirrors fabricated by an SOI/SOI wafer-bonding process

This paper reports a novel capacitive detection method, called the sideband-ratio (SBR) detection, which is robust to variations of such critical parameters as the nominal capacitance, frequency, and amplitude of the probing voltage and gain of the transimpedance amplifier. The approach constructively utilizes the inherent nonlinearity of parallel-plate sense capacitors in order to measure the amplitude of sinusoidal motion. In the case of parallel-plate detection signal, multiple harmonics exist and each carry information about the amplitude of mechanical motion. The SBR method robustly extracts the amplitude of motion from the ratio of multiple sidebands. This paper presents theoretical background and analysis of this nonlinear measurement method. A real-time measurement algorithm is implemented in software and simulated. Feasibility of the developed approach is demonstrated experimentally.

http://www.alexandertrusov.com/uploads/pdf/2007-jmems-trusov-shkel.pdf

A Novel Capacitive Detection Scheme With Inherent Self-Calibration

We report on a position sensing system for quasistatic MEMS mirrors using a point source LED imaged onto the backside of the mirror. The position signal is detected by a 4-quadrant-diode and can be used for digital closed-loop control. The resulting resolution is about 13 bit at a sampling frequency of 500 ksps. The whole detection system is integrated in a package enclosing the MEMS mirror, the optical beam path as well as the amplifier circuit of the 4-quadrant-diode. Based on similar control principles, a laser steering system for searching and tracking of moving objects, marked by retro-reflectors, will be presented. During an initial search, the laser steering system identifies objects by their initial position within a detection range between 1.5 m and 5 m distance and a maximum detection angle between 20 degrees and 72 degrees. The system follows the detected object on random trajectories by minimizing the zero-position error of the back reflected beam on a 4- quadrant-diode. Angular velocities of more than 100 degrees per arcsec have been measured.

Position sensing and tracking with quasistatic MEMS mirrors

In this paper, we demonstrate a novel control strategy for the drive mode of a microgyroscope using ascending frequency drive (AFD) with an AGC-2DOF PID controller, which drives a resonator with a modulation signal not at the resonant frequency and senses the vibration signal at the resonant frequency, thus realizing the isolation between the actual mechanical response and electrical coupling signal. This approach holds the following three advantages: (1) it employs the AFD signal instead of the resonant frequency drive signal to excite the gyroscope in the drive direction, suppressing the electrical coupling from the drive electrode to the sense electrode; (2) it can reduce the noise at low frequency and resonant frequency by shifting flicker noise to the high-frequency part; (3) it can effectively improve the performance of the transient response of the closed-loop control with a 2-DOF (degree of freedom) PID controller compared with the conventional 1-DOF PID. The stability condition of the whole loop is investigated by utilizing the averaging and linearization method. The control approach is applied to drive a lateral tuning fork microgyroscope. Test results show good agreement with the theoretical and simulation results. The non-ideal electrical antiresonance peak is removed and the resonant peak height increases by approximately 10 dB over a 400 Hz span with a flicker noise reduction of 30 dB within 100 Hz using AFD. The percent overshoot is reduced from 36.2% (1DOF PID) to 8.95% (2DOF PID, about 75.3% overshoot suppression) with 15.3% improvement in setting time.

https://iopscience.iop.org/article/10.1088/0960-1317/21/9/095020/pdf

Electrical coupling suppression and transient response improvement for a microgyroscope using ascending frequency drive with a 2-DOF PID controller

In this paper, a MEMS mirror driver ASIC that operates a 1D MEMS mirror with accurate amplitude is presented. It provides a set of position signals, precisely aligned to the MEMS mirror that enables a beam forming and laser shooting scheduling for LiDAR (Light Detection and Ranging) applications. The proposed architecture exploits a capacitive sense method and integrated control loops to sense, actuate and control the movements of the MEMS mirror. The implemented mixed-signal ASIC is fabricated in 130 nm CMOS technology, and can attain an RMS pointing error of less than 4m°for any tested MEMS mirror amplitude.

A MEMS mirror driver ASIC for beam-steering in scanning MEMS-based LiDAR

This paper describes a feedback control system for a MEMS dual-axis scanner, which consists of two single-axis torsional mirrors. The mirror position is measured electronically with the sense capacitors and the EAM technique. The feedback system provides electronic damping and improves the dynamic performance of the high Q (~50) mirrors. Closed-loop controlled device achieves 400µs settling time. Due to the feed-through, drive signal mixes with the sense and limits the control bandwidth. Band-pass filtering and pseudo-differential sense attenuates the feed-through in the sense circuit.

/pdf/capacitive-sense-feedback-control-for-mems-beam-steering-125cg5irj9.pdf

Capacitive sense feedback control for mems beam steering mirrors

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Capacitive sense feedback control for mems beam steering mirrors