Our approach is a two-step approach: first to design the microaccelerometer, and second to use parameteric module generator to translate the design into masks. The first step can also be used to aid the system-level designer in exploring the micromechanical design issues and objectives, as you will soon see.

• Major Parameters For Microaccelerometers 

The accelerometer consists of a movable proof mass, suspended by two U-shape spring beams on both sides. External acceleration causes the proof mass to move relative to the substrate, subject to restoring spring forces and the damping provided by the motion of air around the device. The suspension is designed to be compliant in the x direction of motion and to be stiff in the orthogonal direction (y) to keep the comb fingers aligned. Movable comb (rotor) fingers are attached to the proof mass. They are combined with the fixed comb (stator) fingers to form the sensing and force functional units. The applied voltages on the force unit causes a net electrostatic force to pull the proof mass in the desired direction. These force fingers can be used for either self-test or force-feedback control. The sensing fingers form a capacitive bridge, which is modulated with voltage Vm during sensing. The output voltage is proportional to the difference in the capacitances, and therefore to the proof mass position. This voltage passes through a buffer and is then demodulated to generate the final output voltage. At two ends of the proof mass there are four small rectangular cantilever beams, which act as limit stops on the x and y displacement to prevent contact between rotor and stator fingers. 

This work was supported by the Defense Advanced Research Projects Agency under agreement number F30602-96-2-0304.

For more information about other projects funded by DARPA in the Composite CAD area, visit the DARPA site.