Piezoelectric thin films for saw applications

Abstract

Piezoelectric films of ZnO, AIN and KLN have been fabricated by rf planar magnetron sputtering. The sputtering deposition rate (≃10μm/h) of the c-axis oriented ZnO films has been increased by one order of magnitude by using planar magnetron sputtering compared to a usual rf sputtering. The film is evaluated as of good quality using X-ray diffraction, scanning electron microscopy, reflection electron diffraction, optical measurement, and electromechanical measurement. The ZnO/glass and ZnO/metal composites have been successfully used as SAW TV-IF filters and electronic watch oscillators. An epitaxial AIN film has been grown onto a basal plane sapphire substrate and also a c-axis oriented AIN film has been grown on a glass or metal-film substrate at substrate temperatures as low as 20–500°C. Because of this low substrate temperature, AIN films have become available for bulk wave transducers, SAW transducers with the IDT's between A1N films and substrates, and SAW transducers on low melting point materials. K₃Li₂Nb₅O₁₅ (KLN) films sputtered on sapphire, Si and glass substrates have also preferential c-axis orientation property, and piezoelectrically active to show SAW responses.