Ultrasonic Micro Array Sensors Using Piezoelectric Thin Films and Resonant Frequency Tuning

摘要

Air-borne ultrasonic micro array sensors for three-dimensional imaging have been developed using sol-gel derived PZT (Pb(Zr,Ti)O{sub}3) thin films on silicon-micromachined diaphragms. The array sensor just after fabricated has scattered resonant frequencies of its elements due to non-uniformity of element size and material properties. The sensor having scattering range of 12 in resonant frequency could not realize three-dimensional measurement. Adjustment methods for the resonant frequency after the fabrication have been developed; electrical poling to the piezoelectric layer and additional mass using inkjet printing. Resonant frequency shifts up to 8 by electrical poling of less than 10 V, or shifts up to 7.5 by printing ink of less than 4μm thick. The resonant frequency scattering was reduced within 2 ～ 0.5 using the tuning methods. Finally, three-dimensional object position measurement was successfully performed using the tuned array sensor.