Intrinsic characteristics of thermally stable AlN Lamb wave resonators at high temperatures

Abstract —The thermal compensation at high temperatures for aluminum nitride (AlN) Lamb wave resonators utilizing the lowest symmetric (S 0 ) mode is theoretically and experimentally demonstrated in this work. The turnover temperature can be designed at high temperatures by changing the normalized AlN film thickness ( h AlN / λ ) and the normalized silicon oxide (SiO 2 ) layer thickness ( h SiO2 / λ ) in the AlN/SiO 2 composite layer. The AlN Lamb wave resonators were well temperature-compensated at 214°C and 430°C, respectively, by using different ratios of h AlN / λ to h SiO2 / λ . Even though the intrinsic quality factor ( Q ) degrades and the intrinsic motional impedance ( R m ) increases at high temperatures, a Lamb wave resonator shows a Q of 760 at its turnover temperature, 430°C. These results demonstrate that thermally stable AlN Lamb wave resonators have the great potential for harsh environment applications. Keywords – Lamb Wave Resonator, Aluminum Nitride, Silicon Dioxide, Thermal Compensation, Zero First-order TCF, Harsh Environment