Boundary acoustic wave device and method for manufacturing boundary acoustic wave device
A boundary acoustic wave device has a small thickness, which is suitable for thin apparatuses, and can be manufactured at low cost. The boundary acoustic wave device includes a first IDT electrode disposed on a first surface of a substrate, a first insulating film covering the first IDT electrode, a second IDT electrode disposed on a second surface of the substrate, and a second insulating film covering the second IDT electrode. Either the substrate or the first and second insulating films have piezoelectric characteristics.
1. A boundary acoustic wave device comprising:
a substrate having a first surface and a second surface opposed to the first surface;
a first IDT electrode disposed on the first surface;
a second IDT electrode disposed on the second surface;
a first dielectric film extending over the first surface so as to cover the first IDT electrode; and
a second dielectric film extending over the second surface so as to cover the second IDT electrode; wherein
either the substrate or the first and second dielectric films have piezoelectric characteristics;
the velocity of a slow transverse wave propagating in the substrate is greater than at least one of the velocity of a slow transverse wave propagating in the first dielectric film and the velocity of a slow transverse wave propagating in the second dielectric film; and
the substrate has a thickness of about 3λ to about 100λ so as to prevent boundary acoustic waves propagating along the first surface from being combined with boundary acoustic waves propagating along the second surface.
2. The boundary acoustic wave device according to claim 1 , wherein at least one of the first and second dielectric films has a surface which is opposed to the substrate and which has at least one of a recessed portion and a projecting portion, or both.
3. The boundary acoustic wave device according to claim 1 , further comprising a sound-absorbing film disposed on one of the first and second dielectric films.
4. The boundary acoustic wave device according to claim 1 , wherein the substrate is piezoelectric and the first and second dielectric films are insulative.
5. The boundary acoustic wave device according to claim 1 , wherein the substrate is dielectric and the first and second dielectric films are piezoelectric.
6. The boundary acoustic wave device according to claim 1 , wherein the substrate has a thickness of about 20λ to about 70λ.
7. A method for manufacturing a boundary acoustic wave device, comprising:
a step of preparing a wafer, having a first surface and a second surface opposed to the first surface, for forming a plurality of boundary acoustic wave devices;
a step of forming a plurality of first IDT electrodes on the first surface of the wafer;
a step of forming a plurality of second IDT electrodes on the second surface of the wafer;
a step of forming a first dielectric film over the first surface of the wafer such that the first dielectric film covers the first IDT electrodes;
a step of forming a second dielectric film over the second surface of the wafer such that the second dielectric film covers the second IDT electrodes; and
a step of dicing the wafer subsequently to the formation of the first and second dielectric films to prepare each boundary acoustic wave device; wherein
the velocity of a slow transverse wave propagating in the substrate is greater than at least one of the velocity of a slow transverse wave propagating in the first dielectric film and the velocity of a slow transverse wave propagating in the second dielectric film; and
the substrate has a thickness of about 3λ to about 100 so as to prevent boundary acoustic waves propagating along the first surface from being combined with boundary acoustic waves propagating along the second surface.
8. The method for manufacturing a boundary acoustic wave device according to claim 7 , wherein the substrate has a thickness of about 20λ to about 70λ.