A digital output piezoelectric accelerometer for ultra-low power wireless sensor node

We have developed a novel piezoelectric accelerometer with digital output for ultra-low power wireless sensor nodes. The accelerometer is composed of an array of piezoelectric parallel-plate capacitor structures that are joined together in series and connected to a CMOS switch array. This composition makes it possible to realize a digital output accelerometer in which the number of on-state CMOS switches increases with increasing acceleration. The switches can be turned on by the voltage generated due to the piezoelectric effect and then the acceleration can be directly converted to digital output without an A/D converter. In this study, we have designed this type of accelerometer and developed its fabrication process utilizing SOI wafer and solgel derived PbZrTiO₃ (PZT) thin films. And a wireless sensor node integrated with the fabricated accelerometer device has been demonstrated. Evaluating the devices, it has been shown that an ultra-low power accelerometer can be realized with improving the piezoelectric property of the piezoelectric thin film.