Design and Analysis of A Four Beam MEMS Piezoelectric Accelerometer

Piezoelectricity is a phenomenon in which applied mechanical stress produces a electrical polarization and reciprocally an applied electric field produces a mechanical strain. The piezoelectric micro accelerometers have wide applications in the field of auto mobiles, inertial navigation and bio medical instrumentation. A bulk - micro machined quad beam piezoelectric accelerometer is proposed, designed and analyzed. The main application of this proposed accelerometer is in Bio Medical field. The most important specifications for medical applications are amplitude range +/-5g. resolution 10 -3g, bandwidth d.c.-50 Hz, off axis sensitivity < 5%, dimensions < 2 mm x 2 mm× 2 mm, low drift and power consumption < 1mW. The accelerometer design employs a single silicon seismic mass suspended by four beams. The beams of the accelerometers use the bimorph structure with two PZT films of piezoelectric material and poly silicon as the supporting layer. As the mass moves relative to the anchor, the beams deflect causing the piezoelectric layers to deform and hence a charge is induced. .The amount of charge generated depends upon the piezoelectric properties of PZT material, and many dimensional design considerations. This design is proved to get very high sensitivity, good frequency response and low cross axis sensitivity.

The Z-Axis sensitivity is found to be 4.4X10-14 Col/m/sec2 and X-/Y Axis sensitivities are found to be1.4X10-14Col/m/sec2 with very low cross axis sensitivity.