Piezoelectric actuator with wrap-around electrode on inactive constraining layer

• US 9,330,699 B1
• Filed: 05/24/2015
• Issued: 05/03/2016
• Est. Priority Date: 03/18/2013
• Status: Active Grant

• Current Assignee: Magnecomp Corporation (TDK Corporation)
• Original Assignee: Magnecomp Corporation (TDK Corporation)
• Inventors: Hahn, Peter, Ee, Kuen Chee, Dunn, Christopher
• Primary Examiner(s): Garcia, Carlos E
• Application Number:
  US14/720,827
• Time in Patent Office: 345 Days
• Field of Search: 360/294.4
• US Class Current: 1/1
• CPC Class Codes: G11B 5/4806 specially adapted for disk drive assemblies, e.g. assembly prior to operation, hard or flexible disk drives G11B5/488 - G11B5/54 take precedence
• CPC Class Codes: G11B 5/483 Piezoelectric devices between head and arm, e.g. for fine adjustment
• CPC Class Codes: G11B 5/4873 the arm comprising piezoelectric or other actuators for adjustment of the arm
• CPC Class Codes: G11B 5/5552 using fine positioning means for track acquisition separate from the coarse (e.g. track changing) positioning means
• CPC Class Codes: G11B 5/56 with provision for moving the head support for the purpose of adjusting the position of the head relative to the record carrier, e.g. manual adjustment for azimuth correction or track centering G11B5/52, G11B5/54, G11B5/58 take precedence

Abstract

A piezoelectric actuator such as for a hard disk drive or other application has a restraining layer on its side that is opposite the side on which the PZT is mounted. The restraining layer is a stiff material. The restraining layer reduces bending of the PZT as mounted and hence increases effective stroke length, or reverses the sign of the bending which increases the effective stroke length of the PZT even further. For simplicity of construction and assembly to the suspension, the PZT actuator may be a multi-layer PZT with the top layer being unpoled or otherwise inactive PZT material, and having a wrap-around electrode so that the actuator can be mechanically and electrically bonded to the suspension or other environment using a single adhesive dispense and cure step.

Claims

1. A piezoelectric actuator assembly having a top side, a bottom side, and at least a first end, the assembly comprising:

a first layer comprising a single active piezoelectric layer, the first layer having a bottom face thereof;

a first electrode disposed on the first layer;

a second electrode having at least a bottom electrode portion disposed on the bottom face of the first layer; and

a second layer on the first electrode, the second layer comprising a stiff material, the second layer acting as a constraining layer to constrain expansion or contraction of the first layer when the first layer is activated by application of a voltage across the first and second electrodes;

the first electrode having a wrap-around portion that extends onto at least one of the first end of the assembly, the top side of the assembly, and the bottom side of the assembly;

wherein the constraining layer comprises unpoled piezoelectric material.

2. The piezoelectric actuator assembly of claim 1 wherein the constraining layer comprises a single layer of inactive piezoelectric material.

3. The piezoelectric actuator assembly of claim 1 wherein both a driving voltage and a ground are supplied to said electrodes at the assembly'"'"'s bottom side.

4. A piezoelectric actuator assembly comprising:

a first ceramic layer comprising piezoelectric material;

a second ceramic layer comprising piezoelectric material, the second ceramic layer being disposed on the first ceramic layer; and

first and second electrodes comprising respective conductive layers, the first and second electrodes being arranged such that when a voltage is applied across the electrodes;

a first region of the first ceramic layer expands or contracts, said first region defining a piezoelectrically active region of the first ceramic layer; and

a second region of the first ceramic layer substantially does not expand or contract, the second region defining a piezoelectrically inactive region of the first ceramic layer;

wherein;

the second ceramic layer has a greater horizontal extent than does the piezoelectrically active region;

when a voltage is applied across the first and second electrodes, the second layer substantially does not expand or contract as does the piezoelectrically active region of the first layer, such that the second layer acts as a constraining layer to resist expansion or contract of the first layer; and

both the first and second electrodes are electrically accessible from a bottom surface of the assembly, the first electrode extending between the first and second layers and to said bottom surface.

5. The piezoelectric actuator assembly of claim 4 wherein the piezoelectrically inactive region comprises unpoled piezoelectric material.

6. The piezoelectric actuator assembly of claim 4 wherein the first electrode extends on a top and a bottom of the piezoelectrically inactive region of the first layer, and a side thereof.

7. A piezoelectric actuator assembly comprising:

a first piezoelectric layer having a horizontal extent thereof, the first piezoelectric layer being disposed adjacent a bottom side of the assembly, said bottom side defining a bottom face of the assembly;

a second piezoelectric layer disposed over the first piezoelectric layer, the second piezoelectric layer having a horizontal extent thereof;

a first electrode comprising;

a first conductive layer disposed between the first and second piezoelectric layers, the first conductive layer having a horizontal extent thereof that is substantially coextensive with the horizontal extents of the first and second piezoelectric layers; and

a wrap-around portion suitable for making an electrical connection thereto, comprising at least one of an end portion on an end of the assembly, a bottom portion on said bottom face of the assembly, and a top portion on a top face of the assembly; and

a second electrode comprising a second conductive layer extending over a majority of said bottom face of the assembly;

wherein;

when a voltage is applied across the first and second electrodes, the second piezoelectric layer substantially does not expand or contract as does the first piezoelectric layer, such that the second layer acts as a constraining layer to resist expansion or contract of the first layer.

8. The piezoelectric actuator assembly of claim 7 wherein the first piezoelectric layer includes:

an active piezoelectric region that is disposed between the first and second electrodes, such that a voltage across the first and second electrodes produces an electric field therethrough and produces piezoelectric expansion or contraction thereof; and

an inactive piezoelectric region that is not disposed between the first and second electrodes, such that a voltage across the first and second electrodes does not produce a significant electric field therethrough and therefore does not produce a significant piezoelectric expansion or contraction thereof.

9. The piezoelectric actuator assembly of claim 8 wherein the first electrode at least partially wraps around to a top and a bottom of the inactive piezoelectric region.

10. The piezoelectric actuator assembly of claim 7 wherein the first electrode has a portion that substantially covers the first piezoelectric layer.

11. The piezoelectric actuator assembly of claim 7 wherein the first piezoelectric layer does not have an electrode over a majority thereof.

12. A piezoelectric actuator assembly having top, a bottom side, and at least one end, the assembly comprising:

a poled piezoelectric material, the poled piezoelectric material having opposite first and second faces;

a first electrode extending over the poled piezoelectric material, the first electrode also being electrically connected to at least one of the bottom side of the assembly and the end of the assembly;

a restraining layer affixed to the first electrode above the second face of the poled piezoelectric material such that the first electrode is sandwiched between the poled piezoelectric material and the restraining layer, the restraining layer comprising the same material as said piezoelectric material but being unpoled;

a second electrode extending on the bottom side of the assembly, such that the assembly can be activated by applying a voltage across the second electrode on the bottom side of the assembly and the first electrode on said at least one of said bottom side of the assembly and said end of the assembly;

wherein the restraining layer alters the bending behavior of the assembly so as to increase the effective stroke length of the assembly compared to what the stroke length of the assembly would be in the absence of the restraining layer.

13. The piezoelectric actuator assembly of claim 12 wherein the first electrode substantially completely covers the poled piezoelectric material.

14. The piezoelectric actuator assembly of claim 12 wherein the first electrode is electrically connected to the bottom side of the assembly, such that the assembly can be activated by applying a voltage across the first and second electrodes on the bottom side of the assembly.

15. The piezoelectric actuator assembly of claim 12 wherein a majority of a top side of the restraining layer is uncovered by metallization.

16. The piezoelectric actuator assembly of claim 12 wherein the poled piezoelectric material is integrally formed as a sheet of ceramic material, and the ceramic was poled such that a first part thereof is now poled piezoelectric material and a second part thereof remains substantially unpoled.

17. The piezoelectric actuator assembly of claim 16 wherein the first electrode extends to at least one of an end of the second and unpoled part of the ceramic material and a bottom side of the ceramic material.

18. The piezoelectric actuator assembly of claim 17 wherein:

the first electrode extends over at least a portion of the bottom side of the ceramic material on the bottom side of the assembly, such that the assembly can be activated by applying a voltage across the first and second electrodes on the bottom side thereof.