Elastic wave device with a dielectric layer on the comb-shaped electrodes

1. An elastic wave device comprising:

a piezoelectric substrate;

comb-shaped electrodes having teeth electrodes facing each other on the piezoelectric substrate;

a non-overlapping area in which the teeth electrodes of the comb-shaped electrodes do not overlap each other;

an overlapping area in which the teeth electrodes overlap each other and the velocity of sound is higher than that in the non-overlapping area; and

a dielectric layer formed on the comb-shaped electrodes, wherein the dielectric layer comprises silicon oxide (SiO 2 ), and a portion thereof that covers the non-overlapping area of the comb-shaped electrodes is larger in thickness than a portion thereof that covers the overlapping area,

wherein the dielectric layer has a portion thereof that covers the comb-shaped electrodes, wherein the portion is larger in thickness than the comb-shaped electrodes.

2. The elastic wave device according to claim 1 , wherein the comb-shaped electrodes have portions which are different in overlap width.

3. The elastic wave device according to claim 1 , wherein the electrode width in the non-overlapping area is larger than the electrode width in the overlapping area.

4. The elastic wave device according to claim 1 , wherein a film comprising a material having a sound velocity higher than that of SiO 2 film is formed on the overlapping area of the comb-shaped electrodes.

5. The elastic wave device according to claim 1 , wherein a film comprising a material having a sound velocity lower than that of SiO 2 film is formed on the non-overlapping area of the comb-shaped electrodes.

6. An elastic wave device comprising:

a piezoelectric substrate;

comb-shaped electrodes formed on the piezoelectric substrate;

a reflector adjacent to the comb-shaped electrodes, having a portion in which an overlap width of the comb-shaped electrodes varies, the comb-shaped electrodes have a non-overlapping area in which adjacent electrodes do not overlap each other and an overlapping area in which adjacent electrodes overlap each other, and wherein the reflector has an area having a sound velocity that is lower than the sound velocity of the overlapping area of the comb-shaped electrodes; and

a dielectric layer formed on the comb-shaped electrodes, wherein the dielectric layer comprises silicon oxide (SiO 2 ), and a portion thereof that covers the non-overlapping area of the comb-shaped electrodes is larger in thickness than a portion thereof that covers the overlapping area,

wherein the dielectric layer has a portion thereof that covers the comb-shaped electrodes, wherein the portion is larger in thickness than the comb-shaped electrodes.

7. The elastic wave device according to claim 6 , wherein the elastic wave device comprises a Love wave device.

8. The elastic wave device according to claim 7 , wherein the Love wave device includes a piezoelectric substrate comprising a lithium niobate (LiNbO.sub.3) substrate.

9. The elastic wave device according to claim 6 , wherein the elastic wave device comprises a boundary wave device.

10. A filter equipped with an elastic wave device comprising:

a piezoelectric substrate;

comb-shaped electrodes having teeth electrodes facing each other on the piezoelectric substrate;

a non-overlapping area in which the teeth electrodes of the comb-shaped electrodes do not overlap each other;

an overlapping area in which the teeth electrodes overlap each other and the velocity of sound is higher than in the non-overlapping area; and

a dielectric layer formed on the comb-shaped electrodes, wherein the dielectric layer comprises silicon oxide (SiO 2 ), and a portion thereof that covers the non-overlapping area of the comb-shaped electrodes is larger in thickness than a portion thereof that covers the overlapping area,

wherein the dielectric layer has a portion thereof that covers the comb-shaped electrodes, wherein the portion is larger in thickness than the comb-shaped electrodes.

11. A communication module having a filter equipped with an elastic wave device comprising:

a piezoelectric substrate;

comb-shaped electrodes having teeth electrodes facing each other on the piezoelectric substrate;

a non-overlapping area in which the teeth electrodes of the comb-shaped electrodes do not overlap each other;

an overlapping area in which the teeth electrodes overlap each other and the velocity of sound is higher than that in the non-overlapping area; and

a dielectric layer formed on the comb-shaped electrodes, wherein the dielectric layer comprises silicon oxide (SiO 2 ), and a portion thereof that covers the non-overlapping area of the comb-shaped electrodes is larger in thickness than a portion thereof that covers the overlapping area,

wherein the dielectric layer has a portion thereof that covers the comb-shaped electrodes, wherein the portion is larger in thickness than the comb-shaped electrodes.

12. A communication device including a communication module having a filter equipped with an elastic wave device comprising:

a piezoelectric substrate;

comb-shaped electrodes having teeth electrodes facing each other on the piezoelectric substrate;

a non-overlapping area in which the teeth electrodes of the comb-shaped electrodes do not overlap each other;

an overlapping area in which the teeth electrodes overlap each other and the velocity of sound is higher than in the non-overlapping area; and

a dielectric layer formed on the comb-shaped electrodes, wherein the dielectric layer comprises silicon oxide (SiO 2 ), and a portion thereof that covers the non-overlapping area of the comb-shaped electrodes is larger in thickness than a portion thereof that covers the overlapping area,

wherein the dielectric layer has a portion thereof that covers the comb-shaped electrodes, wherein the portion is larger in thickness than the comb-shaped electrodes.