4J-3. Temperature Compensation of Longitudinal Leaky SAW Waves with Silicon Dioxide Overlay

Longitudinal Leaky Surface Acoustic Wave (LLSAW) is attracting considerable attention for its high velocity and reasonable coupling coefficient [1]. The intrinsic temperature coefficient of frequency (TCF) for these waves for different longitudinal cuts with metal gratings is in the range of -110 to -90 ppm/0C. However, for filter applications the TCF of the LLSAW waves must be quite low in the range of -10 ppm/0C. The introduction of a positive TCF overlay material (generally SiO2) alters the LLSAW wave characteristics. The modified LLSAW mode retains the same high velocity characteristics with an estimated improved TCF. Thus, a systematic study has been attempted by us to evaluate the effect of SiO2 on some interesting longitudinal cuts, such as, Y-Z and 128 Y-Z Lithium Niobate. Measurement data for the frequency-Temperature (f-T) behavior of different longitudinal cuts with metal gratings is first obtained. Based on these measurement data a three dimensional periodic Finite Element (FE) model using the Lagrangian Temperature Coefficients [2] is developed. The temperature coefficients of both the substrate and the metal gratings are incorporated in the FE model. A very good agreement between the FE model and measurement data for different longitudinal cuts is obtained. Based on these validations the effect of SiO2 on the f-T behavior of the modified LLSAW for different longitudinal cut angles is predicted using the FE model. The predicted results are then compared with the measurement data which shows a very good improvement in the f-T behavior of the modified LLSAW mode. [1] T.Makkonen, Victor P. Plessky, Valeri I. Grigorievski, Laurent Kopp, Marc Solal, William Steichen and Martti M. Salomaa, “FEM/BEM Simulation and Experimental Study of LLSAW Resonator Characteristics on YZ-LiNbO3”, Proceedings of the 2002 IEEE Ultrasonics Symposium, 2002, Pg. 317-320. [2] Y-K.Yong and S. Kanna, “IDT Geometry and Crystal Cut Effects on the Frequency-Temperature Curves of A SAW Periodic Structure of Quartz”, Proceedings of the 1998 IEEE Ultrasonics Symposium, 1998, pp. 223-228.