Multi-layer PZT microactuator with active PZT constraining layer for a DSA suspension
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.
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, the first piezoelectric layer being closest to a surface to which the microactuator assembly is electrically bonded;
a first electrode on a bottom side of the first piezoelectric layer;
a second electrode on a top side of the first piezoelectric layer and disposed underneath the second piezoelectric layer, there being no electrode between the first and second electrodes such that a distance between the first and second electrodes defines a thickness of the first piezoelectric layer, and such that a voltage applied across the first and second electrodes induces an electric field across the first piezoelectric layer thereby causing the first piezoelectric layer to expand or contract; and
a third electrode on a top side of the second piezoelectric layer, there being no electrode between the second and third electrodes such that a distance between the second and third electrodes defines a thickness of the second piezoelectric layer, and such that a voltage applied across the second and third electrodes induces an electric field across the second piezoelectric layer thereby causing the second piezoelectric layer to expand or contract;
wherein the second piezoelectric layer comprises the same material as the first piezoelectric layer and is thinner than the first piezoelectric layer; and
wherein the first and second piezoelectric layers are poled such that when a microactuator activation voltage is applied to the microactuator assembly, the first and second piezoelectric layers tend to act in opposite directions.
2. The microactuator assembly of claim 1 wherein when the microactuator activation voltage is applied to the microactuator assembly, the microactuator assembly acts in the direction of the first piezoelectric layer a greater overall distance than if the second piezoelectric layer were not present.
3. The microactuator assembly of claim 1 further comprising:
a third piezoelectric layer adjacent the second piezoelectric layer on a side thereof opposite the first piezoelectric layer; and
a fourth electrode on a top side of the third piezoelectric layer, with the third electrode separating the second and third piezoelectric layers, there being no electrode between the third and fourth electrodes such that a distance between the third and fourth electrodes defines a thickness of the third piezoelectric layer, and such that a voltage applied across the third and fourth electrodes induces an electric field across the third piezoelectric layer thereby causing the third piezoelectric layer to expand or contract;
wherein in response to the microactuator activation voltage, the second and third piezoelectric layers both tend to act in an opposite direction from an action of the first piezoelectric layer.
4. The microactuator assembly of claim 3 wherein the second and third piezoelectric layers are each thinner than the first piezoelectric layer.
5. The microactuator assembly of claim 3 wherein the second and third piezoelectric layers each have a thickness in the range of 5-15% of a thickness of the first piezoelectric layer.
6. The microactuator assembly of claim 1 wherein the second piezoelectric layer is less than 50% as thick as the first piezoelectric layer.
7. The microactuator assembly of claim 1 wherein the second and third piezoelectric layers are each less than 20% as thick as the first piezoelectric layer.
8. The microactuator assembly of claim 1 wherein the second piezoelectric layer has a higher coercivity than does the first piezoelectric layer.
9. The microactuator assembly of claim 1 further comprising means for reducing an electric field strength across the second piezoelectric layer but not the first piezoelectric layer.
10. The microactuator assembly of claim 1 wherein two of said electrodes are electrically ganged by conductive adhesive that bonds the microactuator assembly to said surface.
11. A multi-layer piezoelectric microactuator assembly for effecting fine positional movements, the microactuator assembly comprising:
a first piezoelectric layer adjacent a surface to which the microactuator assembly is electrically bonded; and
a plurality of restraining piezoelectric layers bonded to the first piezoelectric layer, each of the restraining piezoelectric layers being farther away from said surface, each of the piezoelectric restraining layers having an associated pair of electrodes with one electrode disposed between adjacent restraining piezoelectric layers, 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.
12. The microactuator assembly of claim 11 wherein when the microactuator activation voltage is applied to the microactuator assembly, 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.
13. The microactuator assembly of claim 11 wherein each of the restraining piezoelectric layers is thinner than the first piezoelectric layer.
14. The microactuator assembly of claim 11 wherein each of the restraining piezoelectric layers is less than 50% as thick as the first piezoelectric layer.
15. 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, the first piezoelectric layer being disposed closer to a surface to which the microactuator assembly is bonded; and
conductive electrode layers disposed between respective pairs of said piezoelectric layers including between pairs of adjacent opposing piezoelectric layers;
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.
16. The microactuator assembly of claim 15 further comprising 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.
17. The microactuator assembly of claim 15 wherein two of said conductive electrode layers are electrically ganged by conductive adhesive that bonds the microactuator assembly to said surface.
18. 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; and
conductive electrode layers disposed between respective pairs of said piezoelectric layers;
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; and
wherein two of said conductive electrode layers are electrically ganged by conductive adhesive that bonds the microactuator assembly to a surface therebelow.
19. The microactuator assembly of claim 18 wherein said opposing piezoelectric layers are thinner than the first piezoelectric layer.
20. The microactuator assembly of claim 18 wherein said opposing piezoelectric layers are, taken together, thinner than the first piezoelectric layer.