| 摘要 |
PROBLEM TO BE SOLVED: To improve the steepness of a pass frequency band end part, to reserve sufficient frequency margin on both sides of a shave factor part and to improve the yield at the time of production by making a standard film thickness of serial and parallel SAW resonators which constitute a ladder-type surface acoustic SAW filter having different specific values. SOLUTION: Serial SAW resonators 11a to 11c which have a pair of comb- shaped electrodes are connected to a serial distribution on a piezoelectric substrate, and parallel SAW resonators 12a and 12b which have a pair of comb- shaped electrodes are connected to a parallel distribution between the serial distribution and the ground. When the electrode film thickness of the resonators 11a to 11c is Hs, the electrode film thickness of the resonators 12a and 12b is Hp and the wavelength of SAW isλ, and when a piezoelectric substrate is LiTaO3 , Hp/λ, Hs/λare set such that 0.01<=|Hp/λ-Hs/λ|<=0.1. Also, when a piezoelectric substrate is LiNbO3 , Hp/λ, Hs/λare set such that 0.01<=Hp/λ-Hs/λ<=0.2. As a result of this, the control of film thickness and the matching to an external circuit are facilitated.
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