ELASTIC WAVE DEVICE

• US 20070296528A1
• Filed: 08/23/2007
• Published: 12/27/2007
• Est. Priority Date: 04/08/2005
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: KANDO, Hajime
• Granted Patent: US 7,501,916 B2
• Time in Patent Office: Days
• US Class Current: 333/195
• CPC Class Codes: H03H 9/0071 the balanced terminals being on the same side of the tracks
• CPC Class Codes: H03H 9/0222 of interface-acoustic, boundary, pseudo-acoustic or Stonely wave devices
• CPC Class Codes: H03H 9/02559 of lithium niobate or lithium-tantalate substrates
• CPC Class Codes: H03H 9/02858 of wave front distortion
• CPC Class Codes: H03H 9/02881 of diffraction of wave beam
• CPC Class Codes: H03H 9/1452 by finger overlap length, apodisation
• CPC Class Codes: H03H 9/14532 Series weighting; Transverse weighting
• CPC Class Codes: H03H 9/14544 Transducers of particular shape or position weighting H03H9/14517
• CPC Class Codes: H03H 9/64 using surface acoustic waves

Abstract

An elastic wave device includes at least one IDT electrode provided on a piezoelectric substrate. The at least one IDT electrode includes first and second electrode fingers arranged next to each other in a propagation direction of elastic wave. The side edges of at least the electrode finger of the first and second electrode fingers are provided with projections. The position of the projections in the longitudinal direction of the electrode fingers substantially corresponds with the position of a gap in the longitudinal direction of the electrode fingers, the gap being provided at the tip end of the electrode finger of the first and second electrode fingers.

Claims

1. An elastic wave device comprising:

a piezoelectric member; and

at least one IDT electrode;

wherein

said at least one IDT electrode has first and second electrode fingers that are arranged next to each other in a propagation direction of elastic waves and are connected to different electric potentials;

gaps are provided external to tip ends of the first and second electrode fingers in a longitudinal direction of the electrode fingers; and

a projection is provided in at least one of a position on a side edge of the first electrode finger and a position on a side edge of the second electrode finger, the position on the side edge of the first electrode finger corresponding to that of the gap located external to the tip end of the second electrode finger in the longitudinal direction of the electrode fingers, the position on the side edge of the second electrode finger corresponding to that of the gap located external to the tip end of the first electrode finger in the longitudinal direction of the electrode fingers.

2. The elastic wave device according to claim 1, wherein the electrode finger having the gap that is adjacent to the projection in the propagation direction of elastic wave and that is located at the tip end of the electrode finger is tapered toward the tip end of the electrode finger.

3. The elastic wave device according to claim 2, wherein a distance between a periphery of the first electrode finger and a periphery of the second electrode finger arranged next to the first electrode finger is substantially fixed.

4. The elastic wave device according to claim 1, wherein the projection is arranged such that an effective propagation distance in a case where an elastic wave propagates through the gaps in an area provided with the first and second electrode fingers is substantially equal to an effective propagation distance in a case where an elastic wave propagates through a section without the gaps in the area provided with the first and second electrode fingers.

5. The elastic wave device according to claim 1, wherein the projection projects from the side edge of one of the first and second electrode fingers towards the gap provided at the tip end of the other electrode finger, the side edge from which the projection projects being one of the side edges that faces the gap.

6. The elastic wave device according to claim 1, wherein the projection has a trapezoid shape in plan view such that a lower base of the trapezoid is defined by the side edge of the electrode finger that is provided with the projection, and wherein an internal angle formed between the lower base and sides of the trapezoid that connect an upper base and the lower base of the trapezoid is about 90°

or less.

7. The elastic wave device according to claim 6, wherein if the lower base of the projection has a midpoint in the longitudinal direction of the electrode fingers and the gap at the tip end of the other electrode finger has a center in the longitudinal direction of the electrode fingers, a position of the midpoint substantially corresponds with a position of the center in the longitudinal direction of the electrode fingers, and the lower base has a length that is larger than a gap width, the gap width being a dimension of the gap in the longitudinal direction of the electrode fingers, and wherein the upper base has a length that is smaller than the gap width.

8. The elastic wave device according to claim 7, wherein the projection has an isogonal trapezoid shape in plan view.

9. The elastic wave device according to claim 6, wherein the projection has a plurality of rounded corner portions.

10. The elastic wave device according to claim 1, wherein the projection has a planar shape that has a bottom side that continues from the side edge of the electrode finger and a periphery edge that is curved except for the bottom side.

11. The elastic wave device according to claim 10, wherein if the bottom side of the projection has a midpoint in the longitudinal direction of the electrode fingers and the gap is bisected by a line with respect to the longitudinal direction of the electrode fingers, a position of the midpoint substantially corresponds with a position of the bisecting line in the longitudinal direction of the electrode fingers, and the bottom side has a length that is larger than the gap width.

12. The elastic wave device according to claim 1, wherein the projection is also provided on the other one of the first and second electrode fingers.

13. The elastic wave device according to claim 1, wherein said at least one IDT electrode is crossing width weighted.

14. The elastic wave device according to claim 1, wherein the elastic wave comprises a surface acoustic wave.

15. The elastic wave device according to claim 1, wherein the elastic wave comprises a boundary acoustic wave.

16. The elastic wave device according to claim 14, further comprising a medium layer that covers said at least one IDT electrode provided on the piezoelectric substrate, wherein said at least one IDT electrode has a density that is equal to or higher than a density of the piezoelectric substrate and a density of the medium layer, and a ratio of the density of said at least one IDT electrode to the density of the medium layer is higher than about 1.22.

17. The elastic wave device according to claim 15, further comprising a medium layer that covers said at least one IDT electrode provided on the piezoelectric substrate, wherein said at least one IDT electrode has a density that is equal to or higher than a density of the piezoelectric substrate and a density of the medium layer, and a ratio of the density of said at least one IDT electrode to the density of the medium layer is higher than about 1.22.

18. The elastic wave device according to claim 15, further comprising a medium layer stacked on said at least one IDT electrode provided on the piezoelectric substrate so as to cover said at least one IDT electrode, wherein said at least one IDT electrode has a density that is equal to or higher than a density of the piezoelectric substrate and a density of the medium layer, and a ratio of the density of said at least one IDT electrode to one of the higher densities of the piezoelectric substrate and the medium layer is higher than about 1.22.