Piezoelectric element and touch screen utilizing the same

• US 7,176,903 B2
• Filed: 02/20/2004
• Issued: 02/13/2007
• Est. Priority Date: 10/07/2003
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Takahashi, Yuji, Katsuki, Takashi, Sano, Satoshi, Nakazawa, Fumihiko
• Primary Examiner(s): Patel; Nitin
• Application Number:
  US10/781,791
• Publication Number:
  US 20050073505A1
• Time in Patent Office: 1,089 Days
• Field of Search: 178/18.01, 178/18.04, 178/19.02, 310/313, 310/311, 310/363, 345/156, 345/173, 345/174, 345/177
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate
• CPC Class Codes: H03H 3/08 for the manufacture of resonators or networks using surface acoustic waves
• CPC Class Codes: H10N 30/87 Electrodes or interconnections, e.g. leads or terminals
• CPC Class Codes: H10N 30/877 Conductive materials

Abstract

A piezoelectric element includes a substrate, a lower electrode on the substrate, a piezoelectric layer on the lower electrode, and an upper electrode on the piezoelectric layer. The upper electrode includes a common base and a plurality of parallel branches extending from the base. The branches are arranged at a regular interval or pitch λ₁. The lower electrode faces the branches of the upper electrode via the piezoelectric layer. The thickness h of the piezoelectric layer and the branch pitch λ₁ are determined to satisfy an inequality 0.005≦h/λ₁≦0.1. The lower electrode has a hillock occurrence rate which is no greater than 0.1%.

Claims

1. A touch screen comprising:

a substrate including a detection region and a marginal region surrounding the detection region;

a wave generator arranged in the marginal region for generating a surface acoustic wave in the substrate; and

a wave receiver arranged in the marginal region for receiving the surface acoustic wave;

each of the wave generator and the wave receiver comprising;

a piezoelectric layer having a first surface facing the substrate and a second surface opposite to the first surface, the piezoelectric layer having a thickness h;

a first electrode arranged between the substrate and the first surface of the piezoelectric layer; and

a second electrode held in contact with the second surface of the piezoelectric layer;

wherein one of the first electrode and the second electrode includes a common base and a plurality of parallel branches extending from the base, the branches being spaced from each other by a pitch λ

, the other of the first electrode and the second electrode including a portion that faces the branches via the piezoelectric layer,

wherein the thickness h and the pitch λ

are determined to satisfy an inequality 0.005≦

h/λ

≦

0.1,

wherein the first electrode has a hillock occurrence rate which is no greater than 0.1%.

2. The touch screen according to claim 1, wherein the common base and the branches belong to the first electrode.

3. The touch screen according to claim 1, wherein the first electrode is formed of an aluminum alloy containing 0.1˜

3.0 wt % of a metal selected from a group consisting of Ti, Cr, Ni, Cu, Zn, Pd, Ag, Hf, W, Pt and Au.

4. The touch screen according to claim 3, wherein the piezoelectric layer is formed of ZnO doped with Mn.

6. The piezoelectric element according to claim 1, wherein the common base and the branches belong to the first electrode.

7. The piezoelectric element according to claim 1, wherein the first electrode is formed of an aluminum alloy containing 0.1˜

3.0 wt % of a metal selected from a group consisting of Ti, Cr, Ni, Cu, Zn, Pd, Ag, Hf, W, Pt and Au.

8. The piezoelectric element according to claim 7, wherein the piezoelectric layer is formed of ZnO doped with Mn.

5. A piezoelectric element comprising:

a substrate;

a piezoelectric layer having a first surface and a second surface opposite to the first surface, the first surface facing the substrate, the piezoelectric layer having a thickness h;

a first electrode arranged between the substrate and the first surface of the piezoelectric layer; and

a second electrode held in contact with the second surface of the piezoelectric layer;

wherein one of the first electrode and the second electrode includes a common base and a plurality of parallel branches extending from the base, the branches being spaced from each other by a pitch λ

, the other of the first electrode and the second electrode including a portion that faces the branches via the piezoelectric layer,

wherein the thickness h and the pitch λ

are determined to satisfy an inequality 0.005≦

h/λ

≦

0.1,

wherein the first electrode has a hillock occurrence rate which is no greater than 0.1%.