Surface acoustic wave substrate

Abstract

A surface acoustic wave substrate includes: a diamond layer; a piezoelectric layer of aluminum nitride; and a titanium nitride-based buffer layer sandwiched between the diamond layer and the piezoelectric layer. The titanium nitride-based buffer layer includes a graded structure or includes a first sub-layer of titanium and a second sub-layer of titanium nitride sandwiched between the first sub-layer and the piezoelectric layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of the first preferred embodiment of a surface acoustic wave substrate according to this invention;

FIG. 2 is a schematic view of the second preferred embodiment of the surface acoustic wave substrate according to this invention;

FIG. 3 is a scanning electron microscopy (SEM) photomicrograph of an aluminum nitride (AlN) layer of the second preferred embodiment, with the layer thickness of a second sub-layer of titanium nitride of a buffer layer being 30 nm;

FIG. 4 is a SEM photomicrograph of an aluminum nitride (AlN) layer of the second preferred embodiment, with the layer thickness of the second sub-layer of the buffer layer being 150 nm;

FIG. 5 is a SEM photomicrograph of an aluminum nitride (AlN) layer of the first comparative example which has no buffer layer between a piezoelectric layer and a diamond layer;

FIG. 6 is a SEM photomicrograph of an aluminum nitride (AlN) layer of the second comparative example which has a titanium layer between a piezoelectric layer and a diamond layer;

FIG. 7 is a X-ray diffractometer (XRD) graph for the first and second preferred embodiments and the first comparative example;

FIGS. 8 and 9 are loading test graphs for the first and second preferred embodiments and the first and second comparative examples;

FIG. 10 is a SEM photomicrograph of a cross-section of an aluminum nitride (AlN) layer of the second preferred embodiment, with the layer thickness of the second sub-layer of the buffer layer being 150 nm;

FIG. 11 is an atomic force microscopy (AFM) image of the second preferred embodiment, with the layer thickness of the second sub-layer of the buffer layer being 150 nm;

FIG. 12 is a photomicrograph of a transducer-forming surface of the aluminum nitride layer of the second preferred embodiment, with the layer thickness of the second sub-layer of the buffer layer being 150 nm; and

FIG. 13 is an insertion loss vs. frequency graph for the second preferred embodiment, with the layer thickness of the second sub-layer of the buffer layer being 150 nm.

Claims

1. A surface acoustic wave substrate, comprising: a diamond layer;a piezoelectric layer of aluminum nitride; anda titanium nitride-based buffer layer sandwiched between said diamond layer and said piezoelectric layer.

2. The surface acoustic wave substrate of claim 1, wherein said titanium nitride-based buffer layer includes a first sub-layer of titanium.

3. The surface acoustic wave substrate of claim 2, wherein said titanium nitride-based buffer layer further includes a second sub-layer of titanium nitride sandwiched between said first sub-layer and said piezoelectric layer, said first sub-layer being sandwiched between said diamond layer and said second sub-layer.

4. The surface acoustic wave substrate of claim 3, wherein said first sub-layer has a layer thickness ranging from 10 to 300 nm.

5. The surface acoustic wave substrate of claim 3, wherein said second sub-layer has a layer thickness ranging from 30 to 300 nm.

6. The surface acoustic wave substrate of claim 3, wherein said second sub-layer has a layer thickness ranging from 100 to 200 nm.

7. The surface acoustic wave substrate of claim 3, wherein said aluminum nitride on said titanium nitride based-buffer layer has a (002) oriented crystal structure.

8. The surface acoustic wave substrate of claim 1, wherein said titanium nitride-based buffer layer has a graded structure of titanium nitride.

9. The surface acoustic wave substrate of claim 1, further comprising a N-type silicon layer, said diamond layer being formed on said N-type silicon layer.