Ultrasonic micro array sensor using piezoelectric PZT thin film and resonant frequency tuning by poling

Arrayed ultrasonic microsensors using piezoelectric PZT (Pb(Zr,Ti)O₃) thin films on micromachined silicon diaphragms have been fabricated. The sensor is designed to compose an electrical phased array for three-dimensional object detection in air. The resonant frequencies of the elements were scattered in the error range of 12% and the objects could not be detected due to the beat in the sum of delayed element waveforms. Each element has been tuned by adequate poling less than 10 V to make its resonant frequency equal to a center value. The frequency scattering was reduced within the range of 2% and the tuned array could give the objects by summing up of the delayed signals. Three-dimensional object detection has been demonstrated using the tuned sensor of eight-element crossed linear array.