Abstract
Temperature dependence has been proved to be a significant design parameter for the development of SAW devices. It is well known that many design parameters are temperature dependend, e.g. velocity, reflection coefficient, trans- duction coefficient, electro-static capacitance and resistance. Thus the performance of SAW filters, in particular center frequency, insertion loss, group delay, and input and output impedance vary with temperature. However, the temperature behavior is even more complicated since it is not only dependent on material constants but also on the filter structure itself, e.g. type of configuration, film thickness to wavelength ratio, mark to period ratio, as well as the acoustic wave (Rayleigh wave, leaky SAW, STW, ...) and mode (transverse or longitudinal modes) utilized. This paper reports on the determination of the temperature coefficient of frequency of high frequency SAW devices. We present experimental data for impedance element filters on leaky materials like LiTaO3 and derive an empirical dependency of the temperature coefficient of frequency (TCF). We found that the TCF mainly dependends on the film thickness to wavelength ratio and frequency. Different resonator modes show different TCF. The agreement between the measured and the calculated values is within about ±2 ppm/K.
Published Version
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