Automated measurement and CAD analysis technique for accurate determination of UHF acoustic resonator equivalent circuit parameters

Many measurement techniques have been reported for accurate determination of equivalent electrical circuit parameters of HF and VHF acoustic resonators. Recent technological advances in the fabrication and processing of conventional bulk- and surface-wave resonators, and in the development of monolithic sputtered film resonators, have extended device operating frequencies into the UHF range. At UHF, resonator package and bond-wire parasitic reactances are nonnegligible and can significantly mask the impedance characteristics of the resonator itself and result in inaccurate determination of device equivalent circuit. This paper describes an automated resonator measurement and data analysis technique that has been developed for accurate determination of UHF acoustic resonator equivalent circuit parameters. The procedure consists of computer-controlled measurement of resonator input reflection coefficient using an HP4191 RF impedance analyzer. Subsequent automatic data transfer, in the form of a circuit analysis file, is used in conjunction with the Super Compact
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RF analysis/optimization software for determination and “removal” of effects of packaged resonator parasitic reactances from the measured data, based on device out-of-band impedance characteristics. The residual resonator motional arm impedance characteristic is calculated from which equivalent circuit element values are readily determined. The HP4191 RF analyzer control software enables determination and identification of individual resonator desired and spurious (anharmonic) resonances in specified search bands. This is extremely helpful when the resonator exact operating frequency is unknown as is often the case for sputtered, thin-film, monolithic devices. Examples will be given showing the results of measurement of UHF resonators including conventional surface acoustic wave (SAW), bulk-wave quartz and lithium niobate resonators, and monolithic sputtered aluminum nitride and zinc oxide and ZnO film resonators.