Surface acoustic wave filter and multiplexer
AssigneeMurata Manufacturing Co., Ltd.
InventorsYuichi TAKAMINE, Hideki IWAMOTO
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Abstract
A filter includes a LiTaO3 piezoelectric layer having a cut angle, a high acoustic velocity support substrate, a low acoustic velocity film, and an IDT electrode. A cut angle θB of the piezoelectric layer at which a Rayleigh wave spurious response is locally reduced or minimized is determined from a wavelength of the IDT electrode, a film thickness of the IDT electrode, a specific gravity of the IDT electrode, an electrode duty, a thickness of the piezoelectric layer, and a film thickness of the low acoustic velocity film. The Cut angle of the piezoelectric layer satisfies a relationship of θB−4≤θ≤θB+4.
Claims20
A surface acoustic wave filter comprising:
- a LiTaO3 piezoelectric layer having a cut angle θ°;
- a high acoustic velocity support substrate in which a bulk wave propagates at a higher acoustic velocity than an acoustic wave propagating in the LiTaO3 piezoelectric layer;
- a low acoustic velocity film between the high acoustic velocity support substrate and the LiTaO3 piezoelectric layer, and in which a bulk wave propagates at a lower acoustic velocity than the acoustic wave propagating in the LiTaO3 piezoelectric film;
- and
- an InterDigital Transducer (IDT) electrode on the LiTaO3 piezoelectric layer;
- wherein a repetition period of a pair of comb-shaped electrodes defining the IDT electrode is denoted by a wavelength λ (μm), a film thickness of the pair of comb-shaped electrodes is denoted by TIDT (μm), a specific gravity of the IDT electrode is denoted by ρ (g/cm3), an electrode duty of the pair of comb-shaped electrodes is denoted by D, a thickness of the LiTaO3 piezoelectric layer is denoted by TLT (μm), a film thickness of the low acoustic velocity film is denoted by TVL (μm), and a cut angle θB(°) of the LiTaO3 piezoelectric layer at which a Rayleigh wave spurious response is locally reduced or minimized is specified by:
- θ
- B
- =
- 43.09
- -
- 27.5
- ×
- {
- (
- T
- IDT
- λ
- )
- ×
- ρ
- -
- 0.1956
- }
- -
- 19.2
- ×
- (
- D
- -
- 0.5
- )
- +
- 17.4578
- ×
- {
- (
- T
- LT
- λ
- )
- -
- 0.35
- }
- +
- 5.619
- ×
- {
- (
- T
- VL
- λ
- )
- -
- 0.3
- }
- +
- 32.66
- ×
- [
- {
- (
- T
- LT
- λ
- )
- -
- 0.35
- }
- 2
- -
- 0.0125
- ]
- +
- 24.63
- ×
- {
- (
- T
- LT
- λ
- )
- -
- 0.35
- }
- ×
- {
- (
- T
- VL
- λ
- )
- -
- 0.3
- }
- and, the cut angle θ(°) of the LiTaO3 piezoelectric layer satisfies a relationship of:
- θB−4≤≤θB+4.
Dependencies are inferred from the claim text.