Surface acoustic wave filter with multiple ground terminals

摘要

In a surface acoustic wave (SAW) filter, on a 36 DEG Y-cut X-propagation lithium tantalate substrate, series branch SAW resonators, which are connected in series between an input terminal and an output terminal, and parallel branch SAW resonators, which are connected between respective pairs of the series branch resonators by wirings and which are grounded, are provided. Two series branch resonators and one parallel branch resonator are connected in a T shape, so as to form a fundamental unit. In the SAW filter, three fundamental units are serially connected. An interdigital transducer (IDT) included in each resonator is made of a metal film containing aluminum as the main component. The thickness of the metal film is in the range of 8% to 10% of the electrode pitch of the IDT of the parallel branch resonator.