Surface acoustic wave device, and mobile communication device and sensor both using same
View Patent ↗In a surface acoustic wave (SAW) device, such as a SAW resonator or a SAW filter, loss is minimized and steep characteristics are improved. IDT electrodes and a reflector are provided to a piezoelectric substrate cut out at a cut-angle which allows the substrate to excite a leaky surface acoustic wave (LSAW). The IDT electrodes have a given film thickness and a given pitch “p” of finger-electrodes. A phase velocity of the SAW is reduced to slower than a phase velocity “vb”of a slow shear wave propagating on the piezoelectric substrate, and a resonance frequency “f” satisfies a relation of 2×p≦vb/f. This structure allows the use of a Rayleigh surface acoustic wave (RSAW) which does not produce propagation loss, and improving insertion-loss and steep characteristics from those of a conventional SAW device using the LSAW.
1. A surface acoustic wave (SAW) device comprising:
a piezoelectric substrate cut out at a cut-angle allowing excitation of a leaky surface acoustic wave (LSAW); and
an electrode pattern formed of an inter-digital transducer (IDT) electrode prepared on said piezoelectric substrate, said IDT electrode having at least a pair of finger-electrodes meshing with each other,
wherein
a pitch p (m) of said finger-electrodes satisfies a relation of 2×p≦vb/f, where vb (m/s) is a phase velocity of a slow shear wave propagating on said piezoelectric substrate, and f(Hz) is a resonance frequency of said SAW device, and
said piezoelectric substrate has a step and said finger-electrodes of said electrode pattern are formed on a top of said step on said piezoelectric substrate, said step having a pitch similar to the pitch p.
2. The SAW device of claim 1 , further comprising a dielectric film disposed over said electrode pattern for covering at least said electrode pattern.
3. The SAW device of claim 1 , wherein said finger-electrodes are made of one of aluminum (Al) and a metal comprising mainly Al, and a relation of hL≦hr is satisfied, where hL is a film thickness of an IDT electrode of another SAW device using the LSAW and said piezoelectric substrate, and hr is a film thickness of said IDT electrode of said SAW device of which a resonance frequency is equal to that of the another SAW device.
4. The SAW device of claim 3 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
5. The SAW device of claim 4 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
6. The SAW device of claim 3 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
7. The SAW device of claim 6 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
8. The SAW device of claim 1 , wherein at least said finger-electrodes are made of a metal having a larger density than Al.
9. The SAW device of claim 6 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
10. The SAW device of claim 9 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
11. The SAW device of claim 8 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
12. The SAW device of claim 11 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation the LSAW.
13. The SAW device of claim 1 , wherein at least said finger-electrodes are formed of at least two layers, a first layer being made of a metal having a greater density than Al, and a second layer being formed of one of Al and a metal comprising mainly Al.
14. The SAW device of claim 13 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
15. The SAW device of claim 14 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 , has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
16. The SAW device of claim 13 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
17. The SAW device of claim 16 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
18. The SAW device of claim 1 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
19. The SAW device of claim 18 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
20. The SAW device of claim 1 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
21. The SAW device of claim 20 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
22. A surface acoustic wave (SAW) apparatus comprising at least two of said SAW devices, as defined in claim 1 , combined to each other and formed on one chip.
23. A mobile communication apparatus employing said SAW device as defined in claim 22 .
24. A sensor employing said SAW device as defined in claim 1 .
25. A mobile communication apparatus employing said SAW device as defined in claim 1 .
26. A method of manufacturing a surface acoustic wave (SAW) device, said method comprising:
forming an electrode pattern of an inter-digital transducer (IDT) electrode prepared on a piezoelectric substrate cut out at a cut-angle allowing excitation of a leaky surface acoustic wave (LSAW), the IDT electrode having at least a pair of finger-electrodes meshing with each other; and
disposing a dielectric film over the electrode pattern for covering at least the electrode pattern,
wherein the electrode pattern, the cut-angle and a material of the dielectric film satisfy a relation of
2 ×p×f before ≦vb≦ 2 ×p×f after,
where f before (Hz) is a resonance frequency of the SAW device before the dielectric film is formed, f after (Hz) is a resonance frequency of the SAW device after the dielectric film is formed, p (m) is a pitch of the finger-electrodes of the electrode pattern, vb (m/s) is a phase velocity of a slow shear wave propagating on the piezoelectric substrate.
27. A method of manufacturing the SAW device as defined in claim 26 , wherein the finger-electrodes of the SAW device are made of one of aluminum (Al) and a metal comprising mainly Al, and the electrode pattern and the cut-angle satisfy a relation of hL≦hr, where hL is a film thickness of an IDT electrode of another SAW device using the LSAW and the piezoelectric substrate, and hr is a film thickness of the IDT electrode of the SAW device of which a resonance frequency is equal to that of the another SAW device.
28. A surface acoustic wave (SAW) device comprising:
a piezoelectric substrate cut out at a cut-angle allowing excitation of a leaky surface acoustic wave (LSAW);
an electrode pattern formed of an inter-digital transducer (IDT) electrode prepared on said piezoelectric substrate, said IDT electrode having at least a pair of finger-electrodes meshing with each other; and
a dielectric film disposed over said electrode pattern for covering at least said electrode pattern,
wherein a pitch p (m) of said finger-electrodes satisfies a relation of 2×p×f before ≦vb≦2×p×f after , where f before (Hz) is a resonance frequency of said SAW device before said dielectric film is formed, f after (Hz) is a resonance frequency of said SAW device after said dielectric film is formed, and vb (m/s) is a phase velocity of a slow shear wave propagating on said piezoelectric substrate.
29. The SAW device of claim 28 , wherein said finger-electrodes are made of one of aluminum (Al) and a metal comprising mainly Al, and a relation of hL≦hr is satisfied, where hL is a film thickness of an IDT electrode of another SAW device using the LSAW and said piezoelectric substrate, and hr is a film thickness of said IDT electrode of said SAW device of which a resonance frequency is equal to that of the another SAW device.
30. The SAW device of claim 29 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
31. The SAW device of claim 30 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
32. The SAW device of claim 29 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
33. The SAW device of claim 32 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
34. The SAW device of claim 28 , wherein at least said finger-electrodes are made of a metal having a larger density than Al.
35. The SAW device of claim 34 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
36. The SAW device of claim 35 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
37. The SAW device of claim 34 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
38. The SAW device of claim 37 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
39. The SAW device of claim 28 , wherein at least said finger-electrodes are formed of at least two layers, a first layer being made of a metal having a greater density than Al, and a second layer being formed of one of Al and a metal comprising mainly Al.
40. The SAW device of claim 39 , wherein said piezoelectric substrate is made of a single crystal of LiTaO 3 .
41. The SAW device of claim 40 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
42. The SAW device of claim 39 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
43. The SAW device of claim 42 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
44. The SAW device of claim 28 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
45. The SAW device of claim 44 , wherein said piezoelectric substrate made of the single crystal of LiTaO 3 has a cut-face cut out at a rotation angle of not less than 26° and not more than 50° from a Y-axis to a Z-axis with respect to an X-axis of the single-crystal of LiTaO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
46. The SAW device of claim 28 , wherein said piezoelectric substrate is made of a single crystal of LiNbO 3 .
47. The SAW device of claim 46 , wherein said piezoelectric substrate made of the single crystal of LiNbO 3 has a cut-face cut out at a rotation angle of not less than 50° to not more than 80° with respect to an X-axis of the single-crystal of LiNbO 3 , and said piezoelectric substrate allows for excitation of the LSAW.
48. A surface acoustic wave (SAW) apparatus comprising at least two of said SAW devices, as defined in claim 28 , combined to each other and formed on one chip.
49. A mobile communication apparatus employing said SAW device as defined in claim 48 .
50. A sensor employing said SAW device as defined in claim 28 .
51. A mobile communication apparatus employing said SAW device as defined in claim 28 .