Presentazioni e Articoli Tecnici

SAW devices, in which acoustic wave travels along the surface of a material, are used as filters, oscillators and delay lines in electronic circuits. However, recent research [1] revealed that bulk acoustic waves (BAW) can be nonlinearly generated in LiNO₃ SAW device if the drive level is high enough. Nonlinear harmonic generation of spurious modes is one of several nonlinear phenomena in piezoelectric SAW and BAW devices. The energy leakage from a main mode to spurious modes of higher harmonic frequencies is due to its nonlinear material constants, and its nonlinear f-2f-3f  harmonic generation effects are still not well understood and usually ignored in the design using the linear theory.

In this paper we presented a method for solving nonlinear harmonic f-2f-3f  generation in the piezoelectric SAW and BAW devices using COMSOL Multiphysics^® simulation software. Three sets of coupled frequency domain complex equations were derived and solved using the Piezoelectric Devices multiphysics interface. These f-2f-3f  equations could be solved simultaneously to study the nonlinear interactions of the main mode with the spurious modes of higher harmonic frequencies. Specifically, we studied the characteristics of BAW modes harmonically generated in 128° YX LiNO₃ TC-SAW devices. We compared the results with those recently published experimental observations in [1]. The f-2f-3f  BAW modes were identified. The BAW modes propagated longitudinally along the substrate thickness direction. The effects of the substrate thickness, and effects of the bottom surface roughness on these BAW modes were studied. Consistent results were obtained between the model and the experimentally observed results of Ref.[1].

Reference

1. Solal, M., Kokkonen, K., Inoue, S., Briot, J. B., Abbott, B. P., & Gamble, K. J. (2017). “Observation of nonlinear harmonic generation of bulk modes in SAW devices”. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 64(9), 1361-1367.