Acoustic wave element and acoustic wave element sensor
View Patent ↗An acoustic wave element includes a piezoelectric body, an input IDT electrode, an output IDT electrode, a propagation path provided between the input IDT electrode and the output IDT electrode, a first dielectric layer provided on the piezoelectric body so as to cover the input IDT electrode and the output IDT electrode, and a reactive portion provided on the propagation path and configured to react to a substance to be detected or a binding substance configured to bind with the substance to be detected. The main acoustic wave becomes, in the input IDT electrode and the output IDT electrode, a boundary acoustic wave that propagates between the piezoelectric body and the first dielectric layer, and becomes, in the propagation path, a surface acoustic wave that propagates on an upper surface of the propagation path.
1. An acoustic wave element comprising:
a piezoelectric body;
an input IDT electrode provided on the piezoelectric body and configured to excite a main acoustic wave;
an output IDT electrode provided on the piezoelectric body and configured to output a signal by being configured to receive the main acoustic wave;
a propagation path provided between the input IDT electrode and the output IDT electrode;
a first dielectric layer provided on the piezoelectric body so as to cover the input IDT electrode and the output IDT electrode; and
a reactive portion provided above the propagation path and configured to react to a substance to be detected or a binding substance configured to bind with the substance to be detected,
wherein the first dielectric layer has a film thickness equal to or greater than 0.8 times a wavelength of a main acoustic wave, and
wherein the main acoustic wave is configured to become, in the input IDT electrode and the output IDT electrode, a boundary acoustic wave that is configured to propagate between the piezoelectric body and the first dielectric layer, and become, in the propagation path, a surface acoustic wave that is configured to propagate on an upper surface of the propagation path.
2. The acoustic wave element according to claim 1 , wherein:
the first dielectric layer includes a dielectric layer A formed of silicon oxide and structured so as to cover the input IDT electrode and the output IDT electrode, and a dielectric layer B provided on the dielectric layer A, and
the dielectric layer B is structured to cover a side surface of the dielectric layer A in a boundary portion between the propagation path and the input IDT electrode or the output IDT electrode.
3. The acoustic wave element according to claim 1 , wherein
the first dielectric layer includes a taper portion narrowed in a direction from the input IDT electrode or the output IDT electrode to the propagation path.
4. The acoustic wave element according to claim 1 , wherein
the first dielectric layer is provided on the input IDT electrode, the output IDT electrode, and the propagation path.
5. The acoustic wave element according to claim 1 , wherein the reactive portion is provided directly on the piezoelectric body.
6. The acoustic wave element according to claim 1 , further comprising:
a second dielectric layer provided between the reactive portion and the piezoelectric body.
7. The acoustic wave element according to claim 6 , wherein
a film thickness of the second dielectric layer is not greater than the film thickness of the first dielectric layer.
8. The acoustic wave element according to claim 7 , wherein
the second dielectric layer has a film thickness equal to or smaller than 0.4 times the wavelength of the main acoustic wave.
9. The acoustic wave element according to claim 1 , wherein
the film thickness of the first dielectric layer is equal to or greater than 2.0 times the wavelength of the main acoustic wave.
10. The acoustic wave element according to claim 1 , wherein
the reactive portion is not disposed above the input IDT electrode and the output IDT electrode.
11. The acoustic wave element according to claim 1 , wherein
the input IDT electrode has a first portion which is nearest to the propagation path and a second portion which is farthest from the propagation path in a cross sectional view,
the output IDT electrode has a third portion which is nearest to the propagation path in the cross sectional view, and
a length between the first portion and the third portion is larger than a length between the first portion and the second portion in the cross sectional view.
12. The acoustic wave element according to claim 1 , further comprising:
a dielectric material disposed on a boundary portion between the reactive portion and the input IDT electrode.
13. The acoustic wave element according to claim 1 , wherein
the first dielectric layer comprises a first portion and a second portion spaced apart from the first portion; the first portion being provided on the piezoelectric body so as to cover the input IDT electrode, and the second portion being provided on the piezoelectric body so as to cover the output IDT electrode.
14. A method for operating an acoustic wave element comprising a piezoelectric body; an input IDT electrode provided on the piezoelectric body; an output IDT electrode provided on the piezoelectric body; a propagation path provided between the input IDT electrode and the output IDT electrode; and a dielectric layer provided on the piezoelectric body so as to cover the input IDT electrode and the output IDT electrode, the method comprising;
exciting a first boundary acoustic wave that propagates between the piezoelectric body and the first dielectric layer in the input IDT electrode;
propagating a surface acoustic wave that is transformed from the first boundary acoustic wave in the propagation path; and
receiving a second boundary acoustic wave that is transformed from the surface acoustic wave and propagates between the piezoelectric body and the first dielectric layer in the output IDT electrode.