Surface micromachined piezoelectric accelerometers (PiXLs)

The design, fabrication, and characterization of surface micromachined piezoelectric accelerometers are presented in this paper. The thin-film aecelerometers employ zinc oxide (ZnO) as the active piezoelectric material, with different designs using either polysilicon or ZnO bimorph substrates, Sensitivity analyses are presented for two specific sensor designs. Guidelines for design optimization are derived by combining expressions for device sensitivity and resonant frequency. Two microfabrication techniques based on SiO2 and Si sacrificial etching are outlined. Techniques for residual stress compensation in both fabrication processes are discussed. Accelerometers based on both processes have been fabricated and characterized. A sensitivity of 0.95 fC/g and resonant frequency of 3.3 kHz has been realized for a simple cantilever accelerometer fabricated using the sacrificial SiO2 process. Sensors fabricated in the sacrificial Si process with discrete proof masses have exhibited sensitivities of 13.3 fC/g and 44.7 fC/g at resonant frequencies of 2.23 kHz and 1.02 kHz, respectively.