Settings of a monolithic piezoelectric filter on bulk acoustic waves by ion-beam etching

Abstract

The process of tuning of the piezoelectric filter consists in lowering the frequencies of the resonators as a result of removing the electrode layer by means of ion-beam etching (IBE) in an inert gas atmosphere. It is necessary to control frequencies of the first and second resonators, as well as the frequency spacing (distance between frequencies of the upper and lower resonances of the piezo system), dynamic impedance of partial resonators and insertion attenuation. We present the results of using ion-beam etching in tuning monolithic piezoelectric filters on volumetric acoustic waves. It is shown that tuning should be performed using frequencies of the upper and lower resonances of the piezo system under control of the insertion attenuation. It is also necessary to exclude the control operations for the frequencies of the first and second resonators. The optimum parameters of ion-beam etching electrodes of the resonators are determined: working pressure — 1.33 × 10–5 Pa, working gas flow — 1.75 m3 · Pa/sec, ion beam energy — 1 keV, ion current density — 6 mA/cm2. Moreover, the dependence of the insertion damping and dynamic resistance on the frequency of the resonator was revealed. Characteristics of the obtained monolithic quartz filter are presented: nominal frequency — 21400.681 MHz, bandwidth by –3 dB — 32.66 kHz, insertion loss 0.5 dB. The obtained results can be used when tuning sections with smaller electrodes for filters at higher frequencies.