John D. Grade

Design of large deflection electrostatic actuators

Electrostatic, comb-drive actuators have been designed for applications requiring displacements of up to 150 /spl mu/m in less than 1 ms. A nonlinear model of the actuator relates the resonant frequency and the maximum stable deflection to the actuator dimensions. A suite of experiments that were carried out on deep reactive ion etched (DRIE), single-crystal silicon, comb-drive actuators confirm the validity of the model. Four actuator design improvements were implemented. First, a folded-flexure suspension consisting of two folded beams rather than four and a U-shaped shuttle allowed the actuator area to be cut in half without degrading its performance. Second, the comb teeth were designed with linearly increasing lengths to reduce side instability by a factor of two. Third, the folded-flexure suspensions were fabricated in an initially bent configuration, improving the suspension stiffness ratio and reducing side instability by an additional factor of 30. Finally, additional actuation range was achieved using a launch and capture actuation scheme in which the actuator was allowed to swing backward after full forward deflection; the shuttle was captured and held using the backs of the comb banks as high-force, parallel-plate actuators.

Widely tunable external cavity diode laser based on a MEMS electrostatic rotary actuator

A C-band continuously tunable external cavity diode laser based on a MEMS electrostatic rotary actuator provides 15 ms tuning time with +7 dBm output power across a 40 nm tuning range and 55 dB side mode suppression.

External cavity diode lasers tuned with silicon MEMS

In summary, silicon deep reactive ion etched (DRIE) MEMS actuators have enabled a small form factor, tunable laser source ideal for many DWDM applications. The performance of the MEM-ECL meets telecommunications requirements for optical power, side mode suppression, polarization extinction ratio, relative intensity noise, and linewidth. Frequency accuracy of /spl plusmn/1.25 GHz is obtained with closed loop control of the MEMS actuator voltage. Substantial immunity from external temperature fluctuations and vibrations can be achieved through a combination of thermo-mechanical design and servo control.

MEMS electrostatic actuators for optical switching applications

Electrostatic actuators providing linear and angular deflection have been developed using deep reactive ion etching (DRIE). Optical switches with 0.5 dB loss at 1550 nm have been made showing switching times less than 5 ms.

Characterization of a high-sensitivity micromachined tunneling accelerometer

We have fabricated successfully and tested a new micromachined tunneling accelerometer. This accelerometer is a prototype intended for underwater acoustics applications, and is required to feature micro-g resolution at frequencies between 5 Hz and 1 kHz. This paper will focus on the experiments carried out in our laboratory to test the tunneling transducer as well as on the experimental determination of accelerometer resolution. The goal of this paper is to outline the measurements which are necessary to verify that the sensor is actually tunneling, and to confirm that the accelerometer performance is consistent with what should be expected from a tunneling accelerometer.

An integrated controller for tunnel sensors

Micromachined tunnel sensors require electronic circuitry to servo control their tunnel gap width. In this paper, we present the first integrated and complete tunnel sensor controller. This self-contained CMOS controller provides all necessary controller functions; it generates a tunnel junction bias, senses the tunnel current by dropping it across a diode-connected transistor, compares the voltage across this diode to an internally generated proportional to-absolute-temperature reference, derives a feedback signal with an externally configurable frequency response, generates a high-voltage electrostatic drive, and provides a low-voltage output for external circuitry. The chip requires -5 and -40-V power supplies and a compensation RC network, consumes 0.9 mW power, has a power supply rejection ratio of 30 dB, and has a total die area, exclusive of bond pads, of 0.35 mm/sup 2/. The circuit compensates for tunnel junction nonlinearity and contributes less signal noise than the sensor that it controls.

A drive comb-drive actuator with large, stable deflection range for use as an optical shutter

A comb-drive actuator has been developed with new features that increase the static deflection range to 175 /spl mu/m without sacrificing die area or switching speed. An optical shutter for a tunable laser has been made by attaching a large-deflection actuator and mirror to opposite ends of a pivoting lever. A 2.5:1 lever ratio allows the smaller mass of the mirror to balance the relatively large actuator mass to reduce vibration sensitivity. The shutter routinely achieves over 50 dB attenuation in production laser modules, with a switching speed of less than 1 ms. A bidirectional actuator with similar design features has 350 /spl mu/m of total travel with less than 3% nonlinearity.

Mechanical Brakes for Electrostatic Actuators

New DRIE actuator systems have been developed which use a high-force, linear actuator to wrap a flexible brake band around the rigid brake shoe of a large-deflection, rotary actuator. The brake can hold the rotary actuator at any arbitrary location within its full range of travel. A third actuator may be used to engage a pair of locking pins in order to keep the brake motor extended in the event of a power failure. The 100x increase in rotational stiffness after the brake is applied raises the fundamental resonant frequency by more than an order of magnitude, enabling precision optical adjustments over a large tuning range in the presence of external shock and vibration. Consistent braking accuracies of 1 mdeg, or 0.025% of the full-scale deflection, have been demonstrated across the entire rotational rangeCopyright