Piezoelectric cantilever pressure sensor

• US 20050193822A1
• Filed: 03/05/2004
• Published: 09/08/2005
• Est. Priority Date: 03/05/2004
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Amano, Jun, Unkrich, Mark A.
• Granted Patent: US 7,104,134 B2
• Time in Patent Office: Days
• US Class Current: 73/704
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: H04R 17/02 Microphones

Abstract

A piezoelectric cantilever pressure sensor has a substrate and a piezoelectric cantilever having a base portion attached to the substrate and a beam portion suspended over a cavity. The piezoelectric cantilever contains a piezoelectric layer sandwiched between two electrodes and generates a measurable voltage when deformed under pressure. The piezoelectric cantilever pressure sensor can be manufactured at low cost and used in various applications including fingerprint identification devices.

Claims

1. A piezoelectric cantilever pressure sensor, comprising:

a substrate; and

an elongate piezoelectric cantilever mounted at one end on the substrate and extending over a cavity, the piezoelectric cantilever comprising;

a first electrode;

a second electrode; and

a piezoelectric element between the first electrode and the second electrode and electrically connected thereto.

2. The piezoelectric cantilever pressure sensor of claim 1, additionally comprising an access transistor electrically connected to the piezoelectric cantilever.

3. The piezoelectric cantilever pressure sensor of claim 2, wherein:

the access transistor comprises a source contact, a gate contact and a drain contact;

the drain contact is connected to the first electrode;

the source contact is connected to receive a reference voltage; and

the gate contact is connected to receive an activation signal.

4. The piezoelectric cantilever pressure sensor of claim 1, wherein the piezoelectric cantilever additionally comprises an elastic element between the piezoelectric element and the substrate.

5. The piezoelectric cantilever pressure sensor of claim 4, wherein the elastic layer comprises one of silicon and silicon nitride.

6. The piezoelectric cantilever pressure sensor of claim 4, wherein:

the substrate has a top surface on which the piezoelectric cantilever is located; and

the cavity is located between the elastic element and the top surface of the substrate.

7. The piezoelectric cantilever pressure sensor of claim 4, wherein the elastic element is shaped to define a pedestal.

8. The piezoelectric cantilever pressure sensor of claim 1, wherein the piezoelectric element comprises one of PZT, PMN-PZT, PZN-PZT, AlN and ZnO.

9. The piezoelectric cantilever pressure sensor of claim 8, wherein the piezoelectric element comprises PZT with a zirconate to titanate molar ratio of about 0.4 to about 0.6.

10. The piezoelectric cantilever pressure sensor of claim 1, wherein at least one of the first electrode and the second electrode comprises one of gold, silver, platinum, palladium, copper, aluminum, and alloys thereof.

11. The piezoelectric cantilever pressure sensor of claim 1, wherein at least one of the first electrode and the second electrode comprises a layer of platinum and a layer of one of titanium and titanium oxide.

12. The piezoelectric cantilever pressure sensor of claim 1, wherein:

the piezoelectric element is a first piezoelectric element; and

the piezoelectric cantilever additionally comprises;

a third electrode; and

a second piezoelectric element between the second electrode and the third electrode and electrically connected thereto.

13. The piezoelectric cantilever pressure sensor of claim 1, wherein the substrate comprises glass.

14. The piezoelectric cantilever pressure sensor of claim 1, wherein the cavity is defined in the substrate.

15. The piezoelectric cantilever pressure sensor of claim 11, wherein:

the substrate has a top surface and a bottom surface opposite thereto; and

the cavity extends through the substrate between the top surface and the bottom surface.

16. The piezoelectric cantilever pressure sensor of claim 11, wherein:

the substrate has a top surface on which the piezoelectric cantilever is located; and

the cavity extends into the substrate from the top surface.

17. The piezoelectric cantilever pressure sensor of claim 1, wherein:

the substrate has a top surface on which the piezoelectric cantilever is located; and

the cavity is located between the piezoelectric cantilever and the top surface of the substrate.

18. The piezoelectric cantilever pressure sensor of claim 17, wherein:

the piezoelectric cantilever additionally comprises an elastic element between the piezoelectric element and the substrate; and

the cavity is located between the elastic element and the top surface of the substrate.

19. The piezoelectric cantilever pressure sensor of claim 1, additionally comprising a protective layer covering the piezoelectric cantilever.

20. The piezoelectric cantilever pressure sensor of claim 19, wherein the protective layer comprises flexible material.