Elastic wave device, high-frequency front-end circuit, and communication apparatus

1. An elastic wave device comprising:

a supporting substrate;

an acoustic reflection layer disposed on the supporting substrate;

a piezoelectric layer disposed on the acoustic reflection layer; and

an interdigital transducer electrode disposed on the piezoelectric layer; wherein

the acoustic reflection layer includes:

three or more low acoustic impedance layers; and

two or more high acoustic impedance layers;

a film thickness of a low acoustic impedance layer of the three or more low acoustic impedance layers closest to the piezoelectric layer is larger than a film thickness of a low acoustic impedance layer of the three or more low acoustic impedance layers closest to the low acoustic impedance layer that is closest to the piezoelectric layer; and

the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is about 1.38 times or less than the film thickness of the low acoustic impedance layer closest to the low acoustic impedance layer that is closest to the piezoelectric layer.

2. An elastic wave device comprising:

a supporting substrate;

an acoustic reflection layer disposed on the supporting substrate;

a piezoelectric layer disposed on the acoustic reflection layer with no conductor layer disposed therebetween; and

an interdigital transducer electrode disposed on the piezoelectric layer; wherein

the acoustic reflection layer includes:

three or more low acoustic impedance layers; and

two or more high acoustic impedance layers; and

a film thickness of a low acoustic impedance layer of the three or more low acoustic impedance layers closest to the piezoelectric layer is larger than a film thickness of a low acoustic impedance layer of the three or more low acoustic impedance layers closest to the low acoustic impedance layer that is closest to the piezoelectric layer.

3. The elastic wave device according to claim 2 , wherein the three or more low acoustic impedance layers and the two or more high acoustic impedance layers are alternately stacked.

4. The elastic wave device according to claim 2 , wherein the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is in a range of about 0.7 times to about 0.8 times a component of a wavelength of a transversal elastic wave in a thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the low acoustic impedance layer closest to the piezoelectric layer.

5. The elastic wave device according to claim 4 , wherein

a film thickness of each of the three or more low acoustic impedance layers except the low acoustic impedance layer closest to the piezoelectric layer is in a range of about 0.2 times to about 0.3 times the component of the wavelength of the transversal elastic wave in the thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the low acoustic impedance layers; and

a film thickness of each of the two or more high acoustic impedance layers is in a range of about 0.2 times to about 0.3 times the component of the wavelength of the transversal elastic wave in the thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the high acoustic impedance layers.

6. The elastic wave device according to claim 2 , wherein the elastic wave device is structured to generate an S 0 -mode plate wave.

7. The elastic wave device according to claim 2 , wherein

a spurious response of a mode different from a fundamental mode used occurs; and

denoting a resonant frequency of the spurious response as F s , denoting a resonant frequency of the fundamental mode as F m , and denoting a resonant frequency ratio of the spurious response to the fundamental mode as F s /F m , the resonant frequency ratio F s /F m is outside a range of about 1.45 to about 1.55.

8. The elastic wave device according to claim 2 , wherein each of the low acoustic impedance layers is made of silicon oxide.

9. A high-frequency front-end circuit comprising:

the elastic wave device according to claim 2 ; and

a power amplifier.

10. The high-frequency front-end circuit according to claim 9 , wherein the three or more low acoustic impedance layers and the two or more high acoustic impedance layers are alternately stacked.

11. The high-frequency front-end circuit according to claim 9 , wherein the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is about 1.38 times or less the film thickness of the low acoustic impedance layer closest to the low acoustic impedance layer that is closest to the piezoelectric layer.

12. The high-frequency front-end circuit according to claim 9 , wherein the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is in a range of about 0.7 times to about 0.8 times a component of a wavelength of a transversal elastic wave in a thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the low acoustic impedance layer closest to the piezoelectric layer.

13. The high-frequency front-end circuit according to claim 12 , wherein

a film thickness of each of the three or more low acoustic impedance layers except the low acoustic impedance layer closest to the piezoelectric layer is in a range of about 0.2 times to about 0.3 times the component of the wavelength of the transversal elastic wave in the thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the low acoustic impedance layers; and

a film thickness of each of the two or more high acoustic impedance layers is in a range of about 0.2 times to about 0.3 times the component of the wavelength of the transversal elastic wave in the thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the high acoustic impedance layers.

14. The high-frequency front-end circuit according to claim 9 , wherein the elastic wave device is structured to generate an S 0 -mode plate wave.

15. The high-frequency front-end circuit according to claim 9 , wherein

a spurious response of a mode different from a fundamental mode used occurs; and

denoting a resonant frequency of the spurious response as F s , denoting a resonant frequency of the fundamental mode as F m , and denoting a resonant frequency ratio of the spurious response to the fundamental mode as F s /F m , the resonant frequency ratio F s /F m is outside a range of about 1.45 to about 1.55.

16. The high-frequency front-end circuit according to claim 9 , wherein each of the low acoustic impedance layers is made of silicon oxide.

17. A communication apparatus comprising:

the high-frequency front-end circuit according to claim 9 ; and

an RF signal processing circuit.

18. The communication apparatus according to claim 17 , wherein the three or more low acoustic impedance layers and the two or more high acoustic impedance layers are alternately stacked.

19. The communication apparatus according to claim 17 , wherein the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is about 1.38 times or less the film thickness of the low acoustic impedance layer closest to the low acoustic impedance layer that is closest to the piezoelectric layer.

20. The communication apparatus according to claim 17 , wherein the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is in a range of about 0.7 times to about 0.8 times a component of a wavelength of a transversal elastic wave in a thickness direction of the piezoelectric layer, the transversal elastic wave propagating through the low acoustic impedance layer closest to the piezoelectric layer.