Sc0.2Al0.8N Lamb wave filter with a high temperature stability using the strategy of double-layer SiO2 and groove structure

Abstract

The Lamb wave filter (LWF) has a moderate bandwidth, and the conventional temperature compensation method with one layer of SiO2 on the Lamb wave resonator (LWR) will significantly reduce its effective electromechanical coupling coefficient. This, in turn, narrows the bandwidth of the LWF and limits its application range. This paper achieves high temperature stability for both the LWR and LWF by employing a strategy that combines a double-layer SiO2 and a groove structure based on a Sc0.2Al0.8N film. Finite element analysis is employed to investigate the effect of adding single or double layers of SiO2 films on the temperature stability of the Sc0.2Al0.8N LWR. The simulation results show that applying SiO2 to both the top and bottom of the Sc0.2Al0.8N film can mitigate the reduction in k2 while enhancing temperature stability. The groove structure in the piezoelectric layer can simultaneously improve the temperature coefficient of frequency (TCF) and k2 by altering the electric field distribution and boundary conditions. Measurement results show that the double-layer SiO2 improves the TCF of the LWR to approximately –10 ppm/°C. The grooves can further improve the TCF toward 0 ppm/°C and increase the k2 of LWR.