Study of crosstalk effects on the packaged SAW by the FDTD method

The purpose of this study is to estimate the complete crosstalk effects, including the package and the pads on the surface acoustic wave (SAW) substrate. The coupling influence from the SAW pattern is investigated by the full-wave approach. In order to combine the electromagnetic effects with the surface acoustic wave response, a new approach based on finite difference time domain (FDTD) with equivalent current source method is applied. The resistive voltage source model is carefully used to simulate the situations of measurement by the vector network analyzer more accurately. Two kinds of patterns of one-port SAW resonators with the same package structure and interdigital transducer (IDT) design are studied. From the simulated electromagnetic field distributions over the substrate, it can be seen that, as the pattern on the SAW substrate becomes closer, more input energy will be coupled directly to the parallel pads by crosstalk without filtering. This will lead to more coupling loss and therefore, the insertion loss becomes universally lower by about 2 to 3 dB. Furthermore, it can be observed that the coupling interference from the SAW pattern is more serious than from the package in this case. Verification with the measurement results shows that our method is able to obtain good agreement and can be used to observe the influence from the SAW pattern that can seriously affect the performance of the SAW device.