The temperature dependency of power leakage in LST-cut quartz surface acoustic wave filters

Although the LST cut of quartz offers better frequency-temperature stability than the regular ST cut, LST-cut SAW (surface acoustic wave) filters show a greater increase of insertion loss as temperature rises than do regular ST-cut devices of the same frequency (see C.S. Lam and D.E. Holt, 1988). This additional increase of insertion loss for LST-cut filters was attributed to an increase of power loss caused by leakage of the leaky wave. The authors present calculations that indicate that the earlier assertion is indeed correct. They also show that this leakage-temperature dependency varies in magnitude near the LST-cut region. By changing the thickness of the interdigital finger metallization of the LST-cut filters, it is possible to improve the frequency-temperature stability while maintaining an acceptable increase of insertion loss due to the leakage-temperature dependency