Elastic boundary wave substrate and elastic boundary wave functional element using the substrate
The structure of the patent is a substrate wherein a metal electrode, a dielectric thin film, and a further dielectric thin film are adhered onto a piezoelectric substrate. A substrate wherein elastic wave energy is confined in the piezoelectric substrate can be obtained. In particular, when a SiO 2 thin film and an AlN thin film are used as thin films 4 and 5 , respectively, a substrate excellent in an electromechanical coupling coefficient (k 2 ) and a temperature characteristic of frequency can be yielded by making the film thicknesses of electrodes 2 and 3 and those of the thin films 4 and 5 into optimal values.
1. An elastic boundary wave functional element comprising:
a LiNbO 3 substrate;
a film electrode formed above the LiNbO 3 substrate;
a SiO 2 film formed above the film electrode; and
a thin film formed above the SiO 2 film, the thin film having a transverse wave velocity larger than that of SiO 2 film,
wherein the film electrode has a ratio H 2 /λ or H 3 /λ that is 0.05 or more, symbol H 2 representing a film thickness of the film electrode, symbol λ representing the wavelength of the central frequency of the boundary wave,
wherein the SiO 2 film has a ratio H 4 /λ that is 0.4 or more and 1 or less, symbol H 4 representing a film thickness of the SiO 2 film,
wherein the thin film has a ratio H 5 /λ, symbol H 5 representing a film thickness of the thin film,
wherein the functional element is structured and arranged such that when an energy radiation exists in the thickness direction of the substrate, and
an energy exists in the surface of the thin film,
the energy radiation in the thickness direction of the substrate is ⅛ or less of the whole energy, and the energy of the surface of the thin film is ⅛ or less of the whole energy, and
wherein SV wave energy is larger than SH wave energy at a boundary between the LiNbO 3 substrate and the SiO 2 film.
2. The elastic boundary wave functional element according to claim 1 , wherein the film electrode is made from copper.
3. The elastic boundary wave functional element according to claim 1 , wherein the LiNbO 3 substrate is a 120-136° rotated Y—X propagation LiNbO 3 substrate.
4. The elastic boundary wave functional element according to claim 1 , wherein the ratio H 5 /λ is 1 or more and 2 or less.