Surface acoustic wave device and electronic apparatus

Abstract

A surface acoustic wave device includes: (a) a substrate; (b) a piezoelectric film formed on top of the substrate; (c) an electrode for generating a surface acoustic wave formed on top of the piezoelectric film; (d) a first covering film formed on the electrode to cover the electrode, and made of the same material as that of the piezoelectric film; and (e) a second covering film formed on the first covering film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are sectional views showing the steps in a method for manufacturing a surface acoustic wave device according to embodiment 1.

FIGS. 2A and 2B are sectional views showing the steps in a method for manufacturing a surface acoustic wave device according to embodiment 1.

FIG. 3 is a plan view illustrating a pattern example of comb-toothed electrodes 15a according to embodiment 1.

FIG. 4 is a diagram illustrating an example where the invention is applied in a cellular phone.

FIGS. 5A and 5B are diagrams illustrating an example where the invention is applied in a communication system.

FIG. 6 is a chart showing a KH value for the SiO₂, a KH value for the ZnO above the IDTs, and the ratio between the two.

FIG. 7 is a graph showing the phase velocity for each device (Types 1(a)-1(d) and Types 2(a)-2(d)).

FIG. 8 is a graph showing the frequency-temperature coefficient (TCF) for each device.

FIG. 9 shows a formula indicating the frequency-temperature characteristics of a device.

FIG. 10 is a chart showing the (S21) characteristic of a two-port resonator based on Type 2(c).

FIG. 11 is a diagram showing a circuit for evaluating S21.

FIG. 12 is a chart showing the relationship of insertion loss (ΔIL [dB]) with time.

FIG. 13 is a chart showing a KH value for the SiO₂ and a KH value for the ZnO above the IDTs in Types 1(a)-1(f).

FIG. 14 is a graph showing the phase velocity for each device (Types 1(a)-1(f).

FIGS. 15A-15C are sectional views showing the steps in a method for manufacturing a surface acoustic wave device according to embodiment 3.

FIGS. 16A and 16B are sectional views showing the steps in a method for manufacturing a surface acoustic wave device according to embodiment 3.

FIG. 17 is a chart showing the thermal conductivity for each material.

Claims

1. A surface acoustic wave device comprising: (a) a substrate;(b) a piezoelectric film formed on top of the substrate;(c) an electrode for generating a surface acoustic wave formed on top of the piezoelectric film;(d) a first covering film formed on the electrode to cover the electrode, and made of the same material as that of the piezoelectric film; and(e) a second covering film formed on the first covering film.

2. The surface acoustic wave device according to claim 1, wherein the piezoelectric film and the first covering film are made of any of zinc oxide, lithium tantalate, lithium niobate, and aluminum nitride.

3. The surface acoustic wave device according to claim 1, wherein the substrate has a hard layer on its surface, and the piezoelectric film is formed on the hard layer.

4. The surface acoustic wave device according to claim 3, wherein the hard layer is made of any of diamond, boron nitride, and sapphire.

5. The surface acoustic wave device according to claim 1, wherein the product kh of the thickness h of the covering film and the wavenumber k of a surface acoustic wave on the surface acoustic wave device is greater than or equal to 0.003 and less than or equal to 0.2.

6. The surface acoustic wave device according to claim 1, wherein the substrate has a polycrystalline hard layer, and the piezoelectric film is formed on the polycrystalline hard layer.

7. A surface acoustic wave device comprising: (a) a substrate with a hard layer;(b) a piezoelectric film formed on the hard layer;(c) an electrode for generating a surface acoustic wave formed on top of the piezoelectric film;(d) a first covering film formed on the electrode to cover the electrode, and having a thermal conductivity greater than that of amorphous SiO2; and(e) a second covering film formed on the first covering film.

8. The surface acoustic wave device according to claim 7, wherein the piezoelectric film is made of any of zinc oxide, lithium tantalate, lithium niobate, and aluminum nitride.

9. The surface acoustic wave device according to claim 7, wherein the first covering film has a thermal conductivity of 10 W/mK or greater.

10. The surface acoustic wave device according to claim 7, wherein the first covering film is zinc oxide or aluminum nitride.

11. The surface acoustic wave device according to claim 7, wherein the product kh of the thickness h of the first covering film and the wavenumber k of a surface acoustic wave on the surface acoustic wave device is greater than 0, but less than or equal to 0.4.

12. An electronic apparatus having the surface acoustic wave device according to claim 1.