Improvement in temperature characteristics of plate wave resonator using rotated Y-cut LiTaO3 / sin structure

Realization of a high frequency resonator for 3.6 GHz-band filter in the International Mobile Telecommunication Advanced (IMT-Advanced) system is desired. It is difficult to accomplish such a high frequency resonator using conventional surface acoustic wave (SAW) technology, because the strip width of the inter-digital transducers (IDT) becomes too narrow. Although anti-symmetry 1st (A1) mode Lamb type plate wave is known to have a high propagation velocity, however it has a problem such as large temperature coefficient of frequency (TCF). This paper reports an improved technique for TCF in A1 mode Lamb type plate wave resonator with air-gap type membrane by using rotated Y-cut single crystal LiTaO₃ thin plate. The fabricated plate wave resonator has excellent characteristics such as a zero TCF, a large electromechanical coupling coefficient (k²) of 7 % and a high acoustic wave velocity of 12,142 m/s.