SURFACE-ACOUSTIC-WAVE CHARACTERISTICS OF A ZNO QUARTZ SUBSTRATE STRUCTURE HAVING A LARGE ELECTROMECHANICAL COUPLING FACTOR AND A SMALL TEMPERATURE-COEFFICIENT/

A substrate having a suitable electromechanical coupling factor (k(s)) value and a good temperature coefficient of frequency (TCF) is requir ed for an applications of resonator surface acoustic wave (SAW) filter s and rudder-type SAW filters requiring a specific bandwidth, because their bandwidth largely depends on the coupling factor of the substrat e. Although a quartz substrate for SAW devices provides a good TCF, th e electromechanical coupling factor obtained is small. The author spec ulated that an excellent TCF and an appropriate electromechanical coup ling factor could be realized by combination of a quartz substrate hav ing a positive TCF and a ZnO film having a negative TCF. As a result o f theoretical and experimental investigations performed using a 29 deg rees 45' rotated Y and a 42 degrees 45' rotated Y 35 degrees X propaga ting quartz substrate, an excellent TCF (approximate to 0 ppm/degrees C) and an appropriate coupling factor (k(s) = 0.1-0.11; k(s)(2) = 0.01 -0.0121) were realized with a zero degree power now angle on the struc ture of IDT/ZnO/quartz or IDT/ZnO/shorted-plane/quartz for the first l ime.