Fabrication of Ultrasonic Transducers Using Epitaxial Pb(Zr,Ti)O_3 Thin Films on Epitaxial γ-Al_2O_3/Si Substrates for Smart Sensors

摘要

Ultrasonic transducers using epitaxial Pb(Zr,Ti)O_3 (PZT) thin films on epitaxial γ-Al_2O_3/Si substrates were successfully fabricated for the first time. The characteristics of PZT thin films on the γ-Al_2O_3/Si substrates were investigated. 240-nm-thick PZT films with various compositions were formed by the conventional sol-gel method. All PZT films were epitaxially grown on the substrates and exhibited ferroelectric and piezoelectric characteristics. Ultrasonic transducers were fabricated on the epitaxial γ-Al_2O_3(001)/ Si(001) substrates with transducer element of 1 mm square. The transmission and reception characteristics of the ultrasonic transducers were observed in water by a hydorophone. Fabricated transducers can transmit and receive an ultrasonic wave with frequency of 2.5 MHz at distances of 15 and 20 mm. From these results, ultrasonic transducers with the epitaxial PZT/Pt/γ-Al_2O_3/Si structure can be applied to Si monolithic ultrasonic smart sensors.