Surface-acoustic-wave bandpass filters on ZnO/Pyrex substrate with zero temperature coefficient

Thick layers of ZnO (5¿10 ¿m) deposited on Pyrex glass have been investigated in order to realise low-cost and temperature-stable surface-acoustic-wave bandpass filters. We describe the sputtering method used to grow the ZnO layer and we give the measured results of the acoustical and thermal properties for different film thicknesses. A high coupling coefficient (10%) and very good temperature stability (zero first-order and 1 × 10¿8/(°C)2 second-order temperature coefficient) are reported. In addition we show results obtained on an 8% 1 dB relative bandwidth filter operating around 110 MHz which demonstrate that this new piezoelectric substrate leads to filters with better properties than those achieved on ST-cut quartz substrate.