6 MHz BAW resonators fabricated using new piezoelectric crystals PrCa 4 O(BO 3 ) 3 and NdCa 4 O(BO 3 ) 3

Abstract Thickness shear mode Bulk Acoustic Wave (BAW) resonators with frequency of 6 MHz, were fabricated using monoclinic piezoelectric crystals PrCa 4 O(BO 3 ) 3 (PrCOB) and NdCa 4 O(BO 3 ) 3 (NdCOB). Zero temperature coefficient of frequency (TCF) characteristics were achieved over the temperature range of –140 °C to 200 °C for ( YXt )–1.5° cut PrCOB and ( YXt )15° cut NdCOB, with the turnover temperature at 20 °C. The electromechanical coupling factor k 26 and the piezoelectric coefficient d 26 were determined to be 30.2% and 15.8 pC/N for PrCOB, 29.0% and 15.1 pC/N for NdCOB resonators, respectively. The temperature independent frequency behavior, large coupling factor, high piezoelectric coefficient, together with noticeable mechanical quality factors ( Q > 2,500), make PrCOB and NdCOB crystals good candidates for sensing applications with expanded temperature usage range. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)