ACOUSTIC WAVE DEVICE WITH REDUCED HIGHER ORDER TRANSVERSE MODES

• US 20130249647A1
• Filed: 03/05/2012
• Published: 09/26/2013
• Est. Priority Date: 03/25/2011
• Status: Active Grant

• Current Assignee: Skyworks Filter Solutions Japan Co., Ltd. (Skyworks Solutions Incorporated)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Nakanishi, Hidekazu, Nakamura, Hiroyuki, Tsurunari, Tetsuya, Fujiwara, Joji
• Granted Patent: US 9,065,424 B2
• Time in Patent Office: Days
• US Class Current: 333/186
• CPC Class Codes: H03H 9/02559 of lithium niobate or lithium-tantalate substrates
• CPC Class Codes: H03H 9/02834 of temperature influence cut angles H03H9/02543
• 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 9/02984 Protection measures against damaging
• CPC Class Codes: H03H 9/02992 Details of bus bars, contact pads or other electrical connections for finger electrodes
• CPC Class Codes: H03H 9/54 comprising resonators of piezoelectric or electrostrictive material H03H9/64 takes precedence
• CPC Class Codes: H10N 30/87 Electrodes or interconnections, e.g. leads or terminals

Abstract

In an acoustic wave device, a high-order transverse mode wave which is an unnecessary wave is suppressed. The acoustic wave device includes: a piezoelectric substrate; at least one pair of IDT electrodes formed on the piezoelectric substrate; and a dielectric film which covers at least a part of the piezoelectric substrate and the IDT electrodes, and the IDT electrodes each has a plurality of electrode fingers. The dielectric film covers at least an area in which the electrode fingers are arranged interleaved with each other. An acoustic velocity of an acoustic wave in an intersection area, within the region, which is a portion from ends of the electrode fingers to a predetermined length or more inward from the ends, is greater than an acoustic velocity of an acoustic wave in an edge area including end portions of the electrode fingers.

Claims

1. An acoustic wave device comprising:

a piezoelectric substrate;

at least a pair of IDT electrodes formed on the piezoelectric substrate; and

a dielectric film which covers at least a part of the piezoelectric substrate and the IDT electrodes, wherein

the pair of IDT electrodes each include a bus bar and a plurality of electrode fingers which extend from the bus bar, and the respective electrode fingers of one of the IDT electrodes are arranged interleaved with the respective electrode fingers of the other IDT electrode,

the dielectric film covers at least a region in which the electrode fingers are arranged interleaved with each other, and

an acoustic velocity of an acoustic wave in an intersection area, within the region, which is a portion from ends of the electrode fingers to a predetermined length or more inward from the ends, is greater than an acoustic velocity of an acoustic wave in each of edge areas which are portions adjacent to the intersection area, including end portions of the electrode fingers.

2. The acoustic wave device according to claim 1, wherein

each of the pair of IDT electrodes is connected to the bus bar and includes a plurality of dummy electrode fingers which are not arranged interleaved with the electrode fingers of the other IDT electrode.

3. The acoustic wave device according to claim 1, wherein

an area, adjacent to the edge area, from the ends of the electrode fingers to the bus bar of the other of the pair of the IDT electrodes is a gap area, and

the acoustic velocity in each of the gap areas is greater than the acoustic velocity in each of the edge areas.

4. The acoustic wave device according to claim 2, wherein

an area, adjacent to the edge area, from the ends of the electrode fingers to ends of the dummy electrode fingers which face the electrode fingers is a gap area, and

the acoustic velocity in each of the gap areas is greater than the acoustic velocity in each of the edge areas.

5. The acoustic wave device according to claim 1, wherein

a material of the piezoelectric substrate is lithium niobate,

a material of the dielectric film is silicon dioxide, and

a film thickness of the dielectric film in the intersection area is thinner than a film thickness of the dielectric film in the edge areas.

6. The acoustic wave device according to claim 5, wherein

the dielectric film has a lamination structure including two kinds of silicon dioxide films or a lamination structure including a silicon dioxide film and a dielectric film that further covers the silicon dioxide film.

7. The acoustic wave device according to claim 1 comprising:

a first dielectric film which covers at least the area in which the electrode fingers are arranged interleaved with each other and a second dielectric film which is formed on the first dielectric film and further covers the intersection area, as the dielectric film, wherein

an acoustic velocity of the second dielectric film is greater than an acoustic velocity of the first dielectric film.

8. The acoustic wave device according to claim 7, wherein

a material of the first dielectric film is silicon dioxide, and

a material of the second dielectric film is any of silicon nitride, silicon oxynitride, and aluminium nitride.

9. The acoustic wave device according to claim 1 comprising:

a first dielectric film which covers at least the area in which the electrode fingers are arranged interleaved with each other and a third dielectric film which is formed on the first dielectric film and further covers the edge areas, as the dielectric film, wherein

an acoustic velocity of the third dielectric film is less than an acoustic velocity of the first dielectric film.

10. The acoustic wave device according to claim 9, wherein

a material of the first dielectric film is silicon dioxide and a material of the third dielectric film is tantalum(V) oxide.

11. The acoustic wave device according to claim 1, wherein

the intersection area of the dielectric film is covered with a passivation film having a moisture resistance higher than a moisture resistance of the dielectric film.

12. The acoustic wave device according to claim 1, wherein

a region including the intersection area of the dielectric film is covered with a passivation film having a moisture resistance higher than a moisture resistance of the dielectric film, and a film thickness of the passivation film in the intersection area is thicker than a film thickness in the region other than the intersection area.

13. The acoustic wave device according to claim 1, wherein

at least a part of an electrode film thickness of the bus bar is thicker than an electrode film thickness of the electrode fingers.

14. The acoustic wave device according to claim 1, wherein

the dielectric film covers the dummy electrode fingers or the area in which the bus bar is arranged with a film thickness thinner than a film thickness with which the dielectric film covers the intersection area.

15. The acoustic wave device according to claim 1, wherein

the piezoelectric substrate has a cut angle and a propagation angle of, when they are represented by the Euler angle (phi,theta,psi) of right-handed orthogonal coordinates, theta being equal to or greater than 36 degrees but equal to or less than 41 degrees.

16. The acoustic wave device according to claim 1, wherein

the IDT electrode has a lamination structure including a first metal layer mainly composed any of platinum, tungsten, and molybdenum and a second metal layer laminated on the first metal layer having a higher conductivity than the first metal layer.

17. The acoustic wave device according to claim 1 further comprising

two reflectors formed on the piezoelectric substrate, wherein

a plurality of pairs of the IDT electrodes are formed between the two reflectors, and

the two reflectors and the plurality of pairs of the IDT electrodes are arranged along a propagating direction of a main acoustic wave, thereby constituting a longitudinally coupled filter.

18. The acoustic wave device according to claim 1, wherein

a tapered portion forms a portion of each of ends of the intersection area and/or the edge areas of the dielectric film where a film thickness of the dielectric film changes, in a manner such that the film thickness of the dielectric film continuously changes at the tapered portion.