Fabrication of Bulk Acoustic Wave Resonators using Sol-Gel Derived Lead Zirconate Titanate Thin Films

This paper reports the first piezoelectric application of sol-gel derived lead zirconate titanate (PZT) in thin film bulk acoustic wave (BAW) resonators. Using a new sol-gel route based on a 1,3-propanediol solvent developed by Tu and Milne¹⁾, sol-gel PZT films 0.5¿m thick are obtained for a single coating deposited on Pt/Ti coated, passivated Si substrates. Films annealed at 700°C for 30 minutes crystallize fully into the perovskite phase and show excellent ferroelectric behaviour as reported elsewhere¹⁾. A fabrication procedure has been developed which allows the resonator input impedance to be measured using Cascade Microtech wafer probes in conjunction with an HP 8510C Network Analyzer. Fundamental acoustic resonances at 0.3 GHz with unloaded Q values of the order of 700 have been observed for substrates which had been polished down to a thickness of 12¿m. The impedance response of the devices was found to be enhanced by poling.