Micromachined Piezoelectric Accelerometers via Epitaxial Silicon Cantilevers and Bulk Silicon Proof Masses

Abstract

Deep reactive ion etch (DRIE) processes are performed on both sides of a silicon-on-insulator (SOI) wafer to realize piezoelectric accelerometers consisting of 20- μm-thick epitaxial silicon cantilevers with bulk silicon masses at the tip. Sol-gel deposition of lead-zirconate-titanate (PZT) is used to realize an 800-nm-thick film on the top surface of the beams. Prior to accelerometer characterization, a system identification procedure based on laser Doppler vibrometry is performed, providing a complete description of the devices and predicted sensitivities. Frequency response measurements confirm device sensitivities in the 3.4-50 pC/g range in the flat-band (depending on device geometry), and resonance frequencies in the 60-Hz-1.5-kHz range. The self-noise for the longest beam of 8.5 mm is measured as 1.7 μg/√{Hz} at 30 Hz and is limited by dielectric loss of the PZT film which is estimated to have a tanδ of 0.02. Scaling relationships for this particular device geometry are presented to provide insight into possible future design directions.