Multi-layer PZT microactuator with active PZT constraining layer for a DSA suspension

• US 10,074,390 B1
• Filed: 02/29/2016
• Issued: 09/11/2018
• 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, Zhang, Long
• Primary Examiner(s): Garcia, Carlos E
• Application Number:
  US15/055,633
• Time in Patent Office: 925 Days
• Field of Search: 360 7716, 3602944
• 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 5/596 for track following on disks G11B5/5526, G11B5/5552, G11B5/5565, G11B5/5582 take precedence
• CPC Class Codes: H10N 30/2042 Cantilevers, i.e. having one fixed end

Abstract

A PZT microactuator such as for a hard disk drive has a restraining layer bonded on its side that is opposite the side on which the PZT is mounted. The restraining layer comprises a stiff and resilient material such as stainless steel. The restraining layer can cover most or all of the top of the PZT, with an electrical connection being made to the PZT where it is not covered by the restraining layer. 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. The restraining layer can be one or more active layers of PZT material that act in the opposite direction as the main PZT layer. The restraining layer(s) may be thinner than the main PZT layer.

Claims

1. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising:

a first piezoelectric layer and a second piezoelectric layer; and

a plurality of electrodes arranged to apply first and second electric fields, respectively, across the first and second piezoelectric layers when a microactuator activation voltage is applied across the electrodes thus activating both the first and second piezoelectric layers;

wherein the first and second piezoelectric layers are poled such that when the microactuator activation voltage is applied to the microactuator assembly, the first and second piezoelectric layers tend to act in opposite directions; and

wherein the piezoelectric layers were poled using at least three voltages applied to three separate electrodes, and then after poling selected ones of the electrodes were electrically ganged.

2. The microactuator assembly of claim 1 wherein the second piezoelectric layer has a higher coercivity than does the first piezoelectric layer.

3. The microactuator assembly of claim 1 wherein:

the assembly further comprises a third piezoelectric layer, the piezoelectric layers being vertically stacked in the order of the first piezoelectric layer, the second piezoelectric layer, then the third piezoelectric layer, the second and third piezoelectric layers tending to act in a common direction;

the plurality of electrodes comprises;

a first electrode on an underside of the first piezoelectric layer; and

a second electrode extending partly on an underside of the first electrode, on a side of the microactuator assembly, and between the second and third piezoelectric layers; and

the electrodes that were electrically ganged after poling are the first and second electrodes.

4. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising:

a first piezoelectric layer and a second piezoelectric layer;

a plurality of electrodes arranged to apply first and second electric fields, respectively, across the first and second piezoelectric layers when a microactuator activation voltage is applied across the electrodes thus activating both the first and second piezoelectric layers; and

means for reducing an electric field strength across the second piezoelectric layer but not the first piezoelectric layer, the means for reducing the electric field strength is integrally formed with the microactuator assembly;

wherein the first and second piezoelectric layers are poled such that when the microactuator activation voltage is applied to the microactuator assembly, the first and second piezoelectric layers tend to act in opposite directions.

5. The microactuator assembly of claim 4 wherein the means for reducing the electric field strength comprises a pattern of voids in an electrode that is operationally associated with the second piezoelectric layer but not with the first piezoelectric layer.

6. The microactuator assembly of claim 4 wherein the means for reducing the electric field strength comprises a voltage reducer disposed between adjacent piezoelectric layers.

7. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising:

a first piezoelectric layer, the first piezoelectric layer tending to act in a first linear direction when a voltage is applied across a pair of electrodes of the microactuator assembly;

a plurality of opposing piezoelectric layers bonded to the first piezoelectric layer, the first piezoelectric layer and the plurality of opposing piezoelectric layers being disposed in stacked planar relationships to one other;

conductive electrode layers disposed between respective pairs of said piezoelectric layers; and

means for reducing an electric field strength across at least one of the opposing piezoelectric layers, the means for reducing electric field strength being integrally formed with the piezoelectric microactuator assembly;

wherein the opposing piezoelectric layers are poled so that they act in a linear direction generally opposite the first linear direction when said voltage is applied across said pair of electrodes.

8. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising:

a first piezoelectric layer adjacent a bottom side of the assembly;

a plurality of restraining piezoelectric layers bonded to the first piezoelectric layer and disposed above the first piezoelectric layer, the restraining piezoelectric layers tending to act in an opposite direction as the first piezoelectric layer when a microactuator activation voltage is applied to the microactuator assembly;

three electrodes all of which are at least partially on a bottom side of the microactuator assembly, the three electrodes comprising;

a first electrode covering a majority of the bottom side of the assembly;

a second electrode extending partially onto the bottom side of the microactuator

assembly and also extending between two of the restraining piezoelectric layers;

a third electrode extending partially onto the bottom side of the microactuator assembly and also extending between the first piezoelectric layer and an adjacent restraining layer; and

wherein the first piezoelectric layer and the plurality of restraining piezoelectric layers are poled using at least three voltages applied to the three electrodes, and selected ones of the three electrodes are configured to be electrically ganged.

9. The microactuator assembly of claim 8 wherein when the microactuator activation voltage is applied across the third electrode and a combination of the first and second electrodes, the microactuator assembly acts in the direction of the first piezoelectric layer a greater overall distance than if the plurality of restraining piezoelectric layers were not present.

10. The microactuator assembly of claim 8 wherein each of the restraining piezoelectric layers is thinner than the first piezoelectric layer.

11. The microactuator assembly of claim 8 wherein each of the restraining piezoelectric layers is less than 50% as thick as the first piezoelectric layer.

12. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising;

a first piezoelectric layer;

a second piezoelectric layer disposed over the first piezoelectric layer;

a first electrode disposed underneath the first piezoelectric layer on a bottom side of the assembly; and

a second electrode that extends between the two piezoelectric layers;

a third electrode that extends over the second piezoelectric layer;

such that layers of the assembly are stacked in a vertical order from top to bottom of;

the third electrode;

the second piezoelectric layer;

the second electrode;

the first piezoelectric layer; and

the first electrode on the bottom side of the assembly; and

wherein the first electrode, the second electrode that extends between the two piezoelectric layers, and the third electrode that extends over the second piezoelectric layer, are all electrically accessible from the bottom side of the assembly; and

wherein the first piezoelectric layer and the second piezoelectric layer are poled using at least three voltages applied to the first electrode, the second electrode, and the third electrode.

13. The microactuator assembly of claim 12 wherein the two piezoelectric layers are oppositely poled such that a voltage applied across the second electrode and a combination of the first and third electrodes, causes either the first piezoelectric layer to tend to expand while the second piezoelectric layer tends to contract, or the first piezoelectric layer to tend to contract while the first piezoelectric layer tends to expand.

14. The microactuator assembly of claim 12 wherein:

the second electrode is electrically accessible from the bottom side of the assembly via a wrap-around portion of the second electrode that extends onto the bottom side at a first end of the microactuator assembly; and

the third electrode is electrically accessible from the bottom side of the assembly via a wrap-around portion of the third electrode that extends onto the bottom side at a second end of the microactuator assembly opposite said first end.

15. The microactuator assembly of claim 12 wherein:

the second electrode is electrically accessible from the bottom side of the assembly at a second electrode bottom portion;

the third electrode is electrically accessible from the bottom side of the assembly at a third electrode bottom portion;

a first gap separates the second electrode bottom portion from the first electrode; and

a second gap separates the third electrode bottom portion from the first electrode.

16. The microactuator assembly of claim 15 wherein the first electrode, the second electrode bottom portion, and the third electrode bottom portion all comprise deposited metal layers.

17. The microactuator assembly of claim 12 wherein the second electrode extends between the piezoelectric layers such that the second electrode separates most of the first piezoelectric layer from most of the second piezoelectric layer, but does not completely separate said piezoelectric layers.

18. The microactuator assembly of claim 12 wherein the first, second, and third electrodes are all electrically isolated from one another.