CN115699176A - Multilayer PZT micro-actuator with active PZT constraining layer for DSA suspension - Google Patents

Abstract

PZT micro-actuators (e.g., for use in hard disk drives) have a constraining layer bonded to the side of the PZT opposite the side on which it is mounted. The constraining layer comprises a rigid and resilient material such as stainless steel. The constraining layer may cover most or all of the top of the PZT, making electrical connections to the PZT where it is not covered by the constraining layer. The constraining layer reduces the bending of the PZT during installation, thereby increasing the effective stroke length, or reverses the sign of the bending, thereby further increasing the effective stroke length of the PZT. The constraining layer may be one or more layers of active PZT material with a direction of action opposite to that of the primary PZT layer. The constraining layer may be thinner than the primary PZT layer.

Description

Multilayer PZT micro-actuator with active PZT constraining layer for DSA suspension

Cross Reference to Related Applications

This application claims priority to U.S. patent application No. 16/857,133, filed on 23/4/2020, which is hereby incorporated by reference in its entirety.

Background of the invention

1. Field of the invention

The present invention relates to the field of suspensions for hard disk drives. More particularly, the present invention relates to the field of multilayer piezoelectric microactuators having one or more active piezoelectric constraining layers for dual-stage actuated suspensions.

2. Background of the invention

Magnetic hard disk drives and other types of rotating media drives, such as optical disk drives, are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension to which the present invention is applicable. The prior art disk drive unit 100 includes a rotating magnetic disk 101 having a pattern of magnetic 1's and 0's thereon, thereby constituting data stored on the disk drive. The disk is driven by a drive motor (not shown). The disk drive unit 100 further includes a disk drive suspension 105, and a head slider (not shown) is mounted near the distal end of the load beam 107. The "proximal end" of the suspension or load beam is the end supported, i.e., closest to the base plate 12, which is welded or otherwise attached to the actuator arm. The "distal end" of the suspension or load beam is the end opposite the proximal end, i.e., the "distal end" is the cantilevered end.

Suspension 105 is coupled to actuator arm 103, and actuator arm 103 is coupled to voice coil motor 112, which voice coil motor 112 moves suspension 105 arcuately to position the head (head) slider over the correct data track of data disk 101. The head slider is carried by a gimbal that allows the slider to pitch and roll in order to follow the correct data tracks on the rotating disk, allowing variations in disk vibration, inertial events (such as bumps), and irregularities in the disk surface.

Single stage drive disk drive suspensions and dual stage Drive (DSA) suspensions are known. In a single stage drive suspension, only the voice coil motor 112 can move the suspension 105.

In DSA suspensions, such as in us patent 7,459,835 to Mei et al, and many others, at least one additional micro-actuator is located on the suspension in addition to the voice coil motor 112 that moves the entire suspension to achieve fine movement of the head slider and proper alignment on the data tracks on the rotating disk. Micro-actuators provide finer control and higher servo control loop bandwidth than voice coil motors alone, which produce only relatively coarse motion of the suspension and head slider. Piezoelectric elements (sometimes referred to simply as PZT) are often used as microactuator motors, although other types of microactuator motors are possible.

Fig. 2 is a top view of the prior art suspension 105 of fig. 1. The two PZT micro-actuators 14 are attached to a micro-actuator mount 18 on a suspension 105, which is formed in the base plate 12 such that the PZT spans a corresponding gap in the base plate 12. The micro-actuator 14 is attached to a mounting bracket 18 at both ends of the micro-actuator by epoxy 16. The positive and negative electrical connections may be made from the PZT to the flex traces of the suspension and/or to the board by various techniques. When the micro-actuator 14 is activated, it expands or contracts, thereby changing the gap length between the mounting brackets, and thereby producing fine movement of the read/write head mounted on the distal end of the suspension 105.

Fig. 3 is a side cross-sectional view of the prior art PZT micro-actuator and mounting of fig. 2. The pico actuator 14 includes the PZT element 20 itself and top and bottom metallization layers 26, 28 on the PZT defining electrodes for driving the PZT. The PZT14 is mounted across a gap on both its left and right sides by epoxy or solder 16 as shown.

In DSA suspensions, it is generally desirable to achieve a high stroke distance, or simply "stroke length," per unit input voltage on the PZT.

Many DSA suspension designs in the past mount PZT on a mounting plate. In such a design, the linear motion of the PZT is amplified by the arm length between the center of rotation of the PZT and the read/write sensor head. Thus, a small linear motion of the PZT results in a relatively large radial motion of the read/write head.

Other suspension designs mount the PZT on or near the gimbal. One example of a gimbal mounted PZT is the DSA suspension shown in co-pending U.S. application 13/684,016, which is assigned to the assignee of the present invention. In gimbal mounted DSA suspensions ("GSA" suspensions), achieving high stroke lengths is particularly important because these designs do not have nearly as long arms between the PZT and the read/write sensor head. Because of the shorter arm length, the amount of movement of the read/write head is correspondingly smaller. Therefore, achieving large stroke lengths is particularly important in GSA design.

Disclosure of Invention

The inventors of the present application have found that in suspensions mounted with PZT micro-actuators according to the prior art, there are factors that cause a loss in the stroke length of PZT, and have developed a PZT micro-actuator structure and production method to eliminate the loss in the stroke length.

Figure 4A is a side cross-sectional view of the PZT micro-actuator 14 mounted on the suspension of figure 2 when driven by a driving voltage applied to it to expand the PZT, according to the prior art. Because the bottom layer 22 of PZT is partially constrained by adhesion to the suspension 18 on which it is mounted, the bottom layer 22 does not expand as much in a linear direction as the top layer 24. Since the top layer 24 expands more than the bottom layer 22, the PZT14 bends downward and takes on a slightly convex shape when viewed from the top. The resulting linear stroke length loss is shown in the figure as δ 1.

Figure 4B shows the PZT micro-actuator 14 of figure 4A when the PZT is driven by a driving voltage applied to it to contract the PZT. Since the bottom layer 22 of PZT is partially constrained by adhesion to the suspension 18 on which it is mounted, the bottom layer 22 does not contract as much in the linear direction as the top layer 24. Since the top layer 24 contracts more than the bottom layer 22, the PZT14 bends upward and takes on a slightly concave shape when viewed from the top. The resulting linear stroke length loss is shown in the figure as δ 2.

Thus, while it is desirable for the PZT to exhibit a purely linear expansion and contraction when actuated, in conventional installations the PZT may experience an upward or downward bending, resulting in a stroke length loss.

Figure 5 is a graph of the amount of effective linear travel increase or loss due to PZT bending and related equations. When Liang Rutu a is bent upward as shown, the bottom point will have a positive displacement δ in the x-direction when the bend angle is small.

Figure 6 is a graph of travel loss versus bend angle for bending of three different thicknesses of PZT. As shown, for PZT of 1.50mm length and 45 μm thickness, bending causes a positive x displacement δ when the bend angle is less than 5 degrees. For this amount of bending, it can also be seen that thicker beams produce a greater x displacement than thinner beams. Likewise, when the PZT contracts under an applied voltage, the right half of the PZT bends downward and the bottom end of the PZT, which is bonded to the suspension, will experience a negative x-displacement. In other words, in the conventional way of mounting PZT on the suspension, the component δ of the linear displacement due to bending is opposite to the driving direction of PZT. It is therefore desirable to reduce or eliminate the δ, and even reverse the sign of the δ, so that the net result is that the total amount of linear expansion or contraction is actually increased.

The present invention is a PZT element having one or more rigid constraining layers or elements bonded to at least one of the sides or faces of the PZT opposite to that on which it is mounted on the suspension to reduce, eliminate, change the direction of bending of the PZT when driven or otherwise control its bending. An unexpected result is that even though a rigid layer is added to the PZT that at least nominally inhibits expansion and contraction of the PZT, the effective linear travel distance achieved is actually increased. In accordance with the present invention, PZT with a constraining layer may be used as a micro-actuator in a hard disk drive suspension, although it may be used in other applications as well.

In a preferred embodiment, the constraining layer acts to actually change the direction of the bend. Thus, for PZT bonded to the suspension at its bottom surface, the presence of the constraining layer has the effect of: when the piezoelectric element is driven by a voltage that causes the piezoelectric element to expand, the piezoelectric element bends in a direction that causes the topside to become net concave; and when the piezoelectric element is driven by a voltage that causes the piezoelectric element to contract, the piezoelectric element bends in a direction that causes the top side to become net convex. The effect is therefore to actually increase the effective linear expansion in the expansion mode and increase the effective linear contraction in the contraction mode. Thus, the presence of the constraining layer actually increases the effective stroke length.

PZT with constraining layers can be made by various techniques including laminating the constraining layer to an existing PZT element, or one of the PZT element and the constraining layer can be formed on top of the other by additive processes. Such additive processes may include depositing a PZT thin film onto a substrate, such as Stainless Steel (SST). The constraining layer may be stainless steel, silicon, ceramic, such as a substantially unpolarized (unactivated) ceramic material, or the same ceramic material as the ceramic material comprising the PZT element, or other relatively hard material. If the constraining layer is non-conductive, one or more electrical vias containing columns of conductive material may be formed through the constraining layer to conduct an activation voltage or ground from the surface of the microactuator to the PZT element on the inner side.

The constraining layer may be larger (larger surface area) than the PZT element, the same size as the PZT element, or smaller (smaller surface area) than the PZT element. In a preferred embodiment, the constraining layer is smaller than the PZT element, thereby providing the micro-actuator with a stepped structure, wherein the step's platform is not covered by the constraining layer and is the location where the PZT element is electrically connected. One benefit of this configuration including a stage to make the electrical connections is that the complete assembly including the electrical connections has a smaller profile than if the constraining layer covered the entire PZT. A smaller profile is advantageous because it means that more hard drive platters and their suspensions can be stacked together within a given platter stack height, thereby increasing data storage capacity within a given volume of the disk drive assembly.

Simulations indicate that a micro-actuator constructed in accordance with the present invention exhibits enhanced stroke sensitivity, and also exhibits reduced rocking mode gain and torsional mode gain. These are advantageous in increasing the head (head) positioning control loop bandwidth, which reduces data search time and reduces sensitivity to vibration.

Another advantage of adding constraining layers or elements to the PZT according to the present invention is that in current hard disk drives, the suspension and its components, including the PZT, are typically very thin. The thickness of the microactuator (where the PZT is mounted on the mounting board) used in current DSA suspension designs is about 150 μm. In gimbal mounted DSA suspension designs, the PZT is even thinner, typically less than 100 μm thick. Thus, the PZT material is very thin and brittle and is prone to cracking during manufacturing/assembly, including the manufacturing process of the PZT microactuator motor itself and automated pick and place operations in the suspension assembly process. It is expected that PZT in future generation hard disk drives will be 75 μm thick or thinner, which will make the above problem more serious. Such thin PZT is expected to be susceptible to not only damage during manufacturing/assembly, but also to cracking or breaking when the disk drive encounters shock (i.e., g-forces). In accordance with the present invention, the additional rigid, resilient constraining layer provides additional strength and resilience to the PZT, thereby helping to prevent cracking or other mechanical failure of the PZT during manufacturing/assembly and in the event of impact.

In another aspect of the invention, the microactuator assembly is a multi-layer PZT device wherein the plurality of active PZT layers, including one or more active PZT layers, act as constraining layers tending to counteract the effect of the primary active PZT layer.

The idea of increasing the overall net stroke length by adding one or more layers that resist the motion of the primary PZT layer is unforeseeable. Even more unforeseeable, the overall net stroke length can be further increased by adding one or more active layers acting in the opposite direction to the main PZT layer. However, this is the result demonstrated by the present inventors.

Exemplary embodiments of the invention will be further described with reference to the accompanying drawings, in which like reference numerals refer to like parts. The figures may not be drawn to scale and certain features may be shown in generalized or schematic form and identified by commercial designations in order to facilitate clarity and conciseness.

Drawings

FIG. 1 is a top perspective view of a prior art magnetic hard disk drive;

FIG. 2 is a top view of the suspension of the disk drive of FIG. 1;

FIG. 3 is a side cross-sectional view of the prior art PZT micro-actuator and mounting of FIG. 2;

FIG. 4A is a side cross-sectional view of a PZT micro-actuator mounted on the suspension of FIG. 2 when a voltage is applied to the PZT to expand it according to the prior art;

FIG. 4B is a side cross-sectional view of a PZT micro-actuator mounted on the suspension of FIG. 2 when a voltage is applied to the PZT to cause it to contract, according to prior art;

FIG. 5 is a schematic diagram of the amount of linear travel added or lost due to PZT bending and related equations;

FIG. 6 is a graph of travel loss versus bend angle for bending of three different thicknesses of PZT;

FIG. 7 is a side cross-sectional view of PZT with a constraining layer bonded thereto in accordance with the present invention;

FIG. 8A is a side cross-sectional view of the PZT micro-actuator of FIG. 8 when a voltage is applied to the PZT to expand it;

FIG. 8B is a side cross-sectional view of the PZT micro-actuator of FIG. 8 when a voltage is applied to the PZT to cause it to contract;

FIG. 9 is a graph showing stroke length per unit input voltage in nm/V versus constraining layer thickness for PZT of 130 μm thick;

FIG. 10 is a side view of a PZT having a constraining layer bonded thereto in accordance with the present invention;

FIG. 11 is a graph of stroke length versus PZT thickness for the PZT of FIG. 10, with the combined thickness of the PZT and constraining layer held constant at 130 μm;

FIG. 12 is a graph of GDA stroke sensitivity versus constraining layer thickness for suspensions of PZT with stainless steel constraining layers of different thicknesses;

FIGS. 13 (a) -13 (h) illustrate a fabrication process by which PZT with constraining layers according to the present invention may be produced;

FIGS. 14 (a) and 14 (b) are oblique views of a GSA suspension assembled with a thin film PZT micro-actuator motor according to the present invention;

FIG. 15 is a cross-sectional view of the micro-actuator region of FIG. 14 (B) taken along section line B-B';

FIG. 16 is a graph of stroke sensitivity versus SST substrate thickness for the micro-actuator of FIG. 15 from simulations;

FIGS. 17 (a) -17 (f) illustrate a process for fabricating a thin film PZT structure with a stainless steel substrate in accordance with the present invention;

FIG. 18 is a top view of a thin film PZT structure with a silicon substrate in accordance with the present invention;

FIG. 19 isbase:Sub>A side cross-sectional view of the thin film PZT structure of FIG. 18 taken along section line A-A';

FIG. 20 is a graph of stroke sensitivity versus silicon substrate thickness for the micro-actuator of FIG. 19 obtained from simulations;

FIGS. 21 (a) -21 (e) illustrate a process for fabricating the thin film PZT structure of FIG. 18;

FIG. 22 is a top view of a thin film PZT having a base and a side hole in accordance with one embodiment of the present invention;

FIG. 23 isbase:Sub>A cross-sectional view of the micro-actuator of FIG. 22 taken along section line A-A';

FIG. 24 is a cross-sectional view of a PZT micro-actuator according to another embodiment of the present invention;

FIG. 25 is an oblique view of a GSA suspension having a pair of the PZT micro-actuators of FIG. 24;

fig. 26 isbase:Sub>A cross-sectional view of the GSA suspension of fig. 25 taken along section linebase:Sub>A-base:Sub>A';

FIG. 27 is a graph of PZT frequency response function for the suspension of FIG. 25, according to a simulation;

FIGS. 28 (a) -28 (j) illustrate an exemplary process for fabricating the PZT micro-actuator assembly of FIG. 24;

FIG. 29 is a side cross-sectional view of a multi-layer PZT micro-actuator assembly in accordance with another embodiment of the present invention, where the PZT is a multi-layer PZT;

FIG. 30 is a side cross-sectional view of a multi-layer PZT micro-actuator assembly in accordance with another embodiment of the present invention with the ultra-thick electrode acting as a constraining layer;

FIG. 31 is a cross-sectional view of an embodiment wherein the constraining layer of the microactuator assembly comprises one or more active PZT layers that tend to act in the opposite direction as the primary active PZT layer;

FIG. 32 illustrates the polarization of the microactuator assembly of FIG. 31 including the polarization directions of the resulting layers of active PZT material;

FIG. 33 is an exploded view of the micro-actuator assembly of FIG. 31, conceptually illustrating electrical connections;

FIG. 34 is a graph showing the stroke sensitivity (in nm/V) of a micro-actuator with one or more active confinement layers according to simulations for various configurations;

FIG. 35 is a cross-sectional view of another embodiment in which the microactuator assembly includes multiple active PZT layers and conceptually illustrates the poling process and the resulting poling direction;

FIG. 36 is an isometric view of one embodiment of a single layer micro actuator PZT assembly according to one embodiment of the present disclosure;

FIG. 37 is a cross-sectional view of FIG. 36 taken along section line C-C';

FIG. 38A is a plan view of a gimbal of a suspension including the single layer micro-actuator PZT assembly of FIG. 36 according to one embodiment of the present disclosure;

FIG. 38B is a cross-sectional view of FIG. 38A taken along section line D-D' according to an embodiment of the present disclosure;

FIG. 39 is a graph of PZT frequency response function for the suspension of FIG. 38, according to a simulation;

FIG. 40 is a plan view of a gimbal mounted dual stage drive (GSA) suspension including the single layer micro-actuator PZT assembly of FIG. 36 according to an alternative embodiment of the present disclosure;

FIG. 41 is a graph of PZT frequency response function for the suspension of FIG. 40 based on simulation;

FIG. 42 is a plan view of a gimbal of a suspension including a single layer micro-actuator PZT assembly according to an alternative embodiment of the present disclosure;

FIG. 43 is a cross-sectional view of FIG. 42 taken along section line E-E' according to an embodiment of the present disclosure;

FIG. 44A is an oblique view of the gimbal of the suspension at which the single layer micro-actuator PZT assembly of FIG. 37 is rotated;

FIG. 44B is a cross-sectional view of FIG. 44A taken along section line F-F' according to an embodiment of the present disclosure;

FIG. 44C is a cross-sectional view of FIG. 44A taken along section line G-G' according to one embodiment of the present disclosure;

FIG. 45A is a plan view of a gimbal of a suspension assembled with a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 45B is a cross-sectional view of FIG. 45A taken along section line H-H' according to an embodiment of the present disclosure;

FIG. 45C is a graph of PZT frequency response function for the suspension of FIG. 45A, according to a simulation;

FIG. 46A is a plan view of a gimbal of a suspension including a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 46B is a cross-sectional view of FIG. 46A taken along section line J-J', according to an embodiment of the present disclosure;

FIG. 46C is a graph of PZT frequency response function for the suspension of FIG. 46A based on simulations;

FIG. 47A is a plan view of a gimbal of a suspension assembled with a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 47B is a cross-sectional view of FIG. 47A taken along section line K-K', according to one embodiment of the present disclosure;

FIG. 47C is a graph of PZT frequency response function for the suspension of FIG. 47A according to a simulation;

FIG. 48A is a plan view of a gimbal of a suspension assembled with a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 48B is a cross-sectional view of FIG. 48A taken along section line L-L', according to an embodiment of the present disclosure;

FIG. 48C is a graph of PZT frequency response function for the suspension of FIG. 48A, according to a simulation;

FIG. 49A is a plan view of a gimbal of a suspension assembled with a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 49B is a cross-sectional view of FIG. 49A taken along section line M-M' according to one embodiment of the present disclosure;

FIG. 49C is a graph of the PZT frequency response function for the suspension of FIG. 49A according to a simulation;

FIG. 50A is a plan view of a gimbal of a suspension assembled with a single layer micro-actuator PZT assembly in accordance with an alternative embodiment of the present disclosure;

FIG. 50B is a cross-sectional view of FIG. 50A taken along section line N-N' according to one embodiment of the present disclosure;

FIG. 50C is a graph of PZT frequency response function for the suspension of FIG. 50A, according to a simulation;

figure 51 is a cross-sectional view of one embodiment of a single layer micro-actuator PZT assembly according to one embodiment of the present disclosure.

Detailed Description

Figure 7 is a side cross-sectional view of PZT micro-actuator assembly 114 having a constraining layer 130 bonded thereto, in accordance with one embodiment of the present invention. To remain consistent with the orientation shown in the figures, the side of the PZT to the suspension will be referred to as bottom side 129 of PZT 114, while the side of the PZT away from the side to which it is bonded will be referred to as top side 127. In accordance with the present invention, one or more constraining layers or constraining elements 130 are bonded to the top side 127 of the microactuator PZT element 120. The constraining layer 130 preferably comprises a hard and resilient material (e.g., stainless steel) and is preferably bonded directly to the top surface 127 of the PZT element 120, the PZT element 120 including its top electrode 126 on the top surface 127, or the SST material itself can serve as the top electrode, thereby eliminating the need for separate metallization of the top surface. The constraining layer 130 is sufficiently rigid to substantially reduce, eliminate, or even reverse the bending of the PZT when actuated (activated). The SST layer 130 preferably has a layer of gold or other contact metal 131 to ensure a good electrical connection to the SST.

Alternatively, the constraining layer 130 is not stainless steel, but may be a ceramic, such as an unactivated (nonpolarized or unpolarized) layer of the same ceramic material as the piezoelectric layer 120, and may be integrated into the assembly by bonding or deposition. The ceramic material is unpolarized, meaning that the ceramic material exhibits piezoelectric properties that are substantially lower than those of the polarized ceramic defining piezoelectric layer 120, e.g., less than 10% thereof. Such an assembly defining a bottom-up stack of electrode/polar PZT/electrode/non-polar PZT is easier to manufacture than a stack of electrode/PZT/electrode/SST.

In the discussion that follows, the top and bottom electrodes 126, 128 are sometimes omitted from the figures and discussion for simplicity of discussion, it being understood that PZT micro-actuators almost always have at least some type of top and bottom electrodes.

A layer of copper or nickel may be deposited on SST layer 130 prior to application of gold layer 131 to increase the adhesion of gold to SST, as discussed in us patent 8,395,866 to Schreiber et al, owned by the assignee of the present application, the teachings of which are incorporated herein by reference with respect to electrodeposition of other metals onto stainless steel. Likewise, the electrodes 126, 128 may include a combination of nickel and/or chromium and gold (NiCr/Au).

124-167 (fig. 5). In one illustrative embodiment according to the simulation, the thicknesses of the layers are:

130PZT 3μm

126、128、131NiCr/Au 0.5μm

the length of the thin film PZT was 1.20mm, the width of the two ends of the PZT bond was 0.15mm, and the piezoelectric coefficient d31 was 250pm/V. In some embodiments, the SST layer can be at least 12 microns thick to provide adequate support.

In the above example, according to the simulation, the DSA suspension exhibited a stroke sensitivity of 26.1 nm/V. In contrast, a 45 μm thick bulk PZT (d 31=320 pm/V) with the same geometry would typically exhibit a stroke sensitivity of only 7.2 nm/V.

The thickness ratio of SST layer to PZT layer can be as high as 1:1, even 1.25, or even higher. When the thickness ratio of constraining layer to PZT reaches about 1.

Figure 8A is a side cross-sectional view of PZT micro-actuator 114 of figure 7 when a voltage is applied to the PZT to cause it to expand. The stroke of the PZT consists of two vectors, one being the pure extension stroke δ e and the other being the extension contribution δ 1 due to the constraining layer causing the right end of the PZT to bend upwards (rather than downwards as would be the case without the constraining layer). The total stroke length is δ e + δ 1. Thus, in the expanded mode, the PZT assumes a slightly concave shape when viewed from the top, i.e., the top surface of the PZT assumes a slightly concave shape with a direction of curvature opposite to that of the prior art PZT of figure 4. Thus, the bending according to the invention increases the length of the active stroke, instead of decreasing it.

Figure 8B is a side cross-sectional view of the PZT micro-actuator of figure 7 when a voltage is applied to PZT 114 to cause it to contract. The stroke of the PZT is made up of two vectors, one being the pure contraction stroke- | δ c |, and the other being the contraction contribution δ 2 due to the constraining layer causing the right end of the PZT to bend downward (rather than upward as would be the case without the constraining layer). The total run length is- [ δ c + δ 2]. Thus, in the contracted mode, the PZT assumes a slightly convex shape when viewed from the top, i.e., the top surface of the PZT assumes a slightly convex shape with a direction of curvature opposite that of the prior art PZT of figure 4. Thus, such bending according to the invention increases the length of the active stroke, rather than decreasing it.

The addition of constraining layer 130 to PZT microactuator 114 has no significant effect on the stroke length of PZT 114, which is otherwise unconstrained and unbonded. However, when PZT 114 is bonded to suspension 18 at its bottom end (as shown in FIG. 4), the constraining layer acts to actually increase the stroke length slightly. The Young's modulus of stainless steel is about 190-210GPa. Preferably, the material of the constraining layer has a Young's modulus greater than 50GPa (more preferably greater than 100GPa, more preferably greater than 150 GPa).

FIG. 9 is a graph of stroke length per unit input voltage in nm/V versus constraining layer thickness for PZT 114 having a thickness of 130 μm with a constraining layer 130 of stainless steel bonded thereto, according to simulations. Adding 20, 40, and 60 μm thick SST constraining layers to the PZT top surface, each resulting in an increase in the total stroke length. Thus, adding a constraining layer actually increases the total stroke length.

It is also possible to keep the total combined thickness of the PZT and the constraining layer constant and determine the optimal thickness of the constraining layer. Figure 10 is a side cross-sectional view of a combined PZT and constraining layer bonded thereto, according to the present invention, with the total thickness held constant at 130 μm. FIG. 11 is a graph of run length versus PZT thickness for the PZT of FIG. 10 based on a simulation in which the combined thickness of the PZT and constraining layer is held constant at 130 μm. Without the constraining layer, the stroke length of 130 μm thick PZT was about 14.5nm/V. In the case where the constraining layer 130 is 65 μm thick and the PZT is 65 μm thick, the stroke length of the PZT is about 20nm/V. Thus, the addition of the constraining layer actually increases the effective stroke length by about 35%.

Figure 12 is a graph of GDA stroke sensitivity versus constraining layer thickness according to simulations in which a GDA suspension having the microactuator of figure 7 with a PZT element of 45 μm thickness with a stainless steel constraining layer of varying thickness on top. As can be seen from the figure, a 30 μm thick confinement layer increases the stroke sensitivity of the GDA from 9nm/V to slightly more than 14.5nm/V (μm), which means that the stroke length increases by more than 50%.

FIGS. 13 (a) -13 (h) illustrate a fabrication process by which a PZT micro-actuator assembly with a constraining layer according to the present invention may be produced. This method is an example of an additive method in which the PZT material is deposited onto a substrate that will become the constraining layer. As shown in fig. 13 (a), the process starts with a first substrate 140. In fig. 13 (b), a first UV (ultraviolet light)/thermal carrier tape 142 is applied to the substrate. In fig. 13 (c), a preformed SST layer 130 is added to the carrier tape. In fig. 13 (d), an electrode layer 126 is deposited onto the SST, for example by sputtering or other well-known deposition process. In fig. 13 (e), a PZT layer 120 is formed on the electrode layer by a sol-gel method or other known methods. In fig. 13 (f), a second electrode 128 is deposited, for example by sputtering, to the exposed side of the PZT. In fig. 13 (g), the SST layer 130 is separated from the carrier tape and the product is flipped over onto a second carrier tape 143 and a second substrate 141. In fig. 13 (h), the product is cut, for example, by a mechanical saw or laser cut, to separate individual micro-actuators 114. This process results in a microactuator 114 in which PZT element 120, including its electrodes, is bonded directly to SST constraining layer 130 without any other material in between (e.g., an organic material such as polyimide that would cause the constraining effect of the constraining layer to be reduced). The material of the electrode layer may be gold, nickel, chromium and/or copper. The Young's modulus of gold is about 79GPA, that of copper is about 117GPa, that of nickel is about 200GPA, and that of chromium is about 278GPA. Preferably, there is no intermediate layer between SST constraining layer 130 and PZT element 120, and PZT element 120 has a young's modulus of less than 20GPa, or a young's modulus significantly less than that of the constraining layer, or less than half that of the constraining layer.

While other methods may be used to produce the product, such as bonding the constraining layer directly to the PZT surface by an adhesive (e.g., epoxy), it is presently contemplated that the method shown in FIGS. 13 (a) -13 (g) is the preferred method.

SST constraining layer 130 serves as a substrate for PZT layer 120 in both the additive manufacturing process and in the finished product. Therefore, the constraining layer 130 is sometimes referred to as a substrate.

Figures 14 (a) and 14 (b) are oblique views of a gimbaled, dual-stage actuated (GSA) suspension 150 equipped with a thin film PZT micro-actuator motor 114 according to the present invention. In a GSA suspension, the PZT is mounted on a trace gimbal, which includes a gimbal assembly, and acts directly on the gimbal region of the suspension that holds the read/write head (head) slider 164. Figure 14 (a) shows suspension 150 prior to attachment of PZT micro-actuator assembly 114. Each of the two micro-actuators 114 will be bonded to the tab 154 and the portion 156 of the trace gimbal and will span the gap 170 between the tab 154 and the portion 156, with the distal end of the micro-actuator 114 bonded to the tab 154 and the proximal end of the micro-actuator 114 bonded to the portion 156. Figure 14 (b) shows suspension 150 after PZT micro-actuator 114 is attached. When the microactuator assembly 114 is activated, it expands or contracts, thereby changing the length of the gap 170 between the tongue 154 and the trace gimbal portion 156, thereby affecting fine positioning movement of the head slider 164 carrying the read/write transducer.

Fig. 15 is a sectional view of fig. 14 (B) taken along section line B-B'. GSA suspension 150 includes a trace gimbal 152, which trace gimbal 152 includes multiple layers of stainless steel, an insulator 157 (e.g., polyimide), and a layer of signal conducting traces 158 (e.g., copper) covered by a protective metal 159 (e.g., gold or a combination of nickel/gold). The distal end of the micro-actuator 114 is attached to a stainless steel tongue 154 extending from the gimbal region by a conductive adhesive 162 (e.g., an epoxy containing Ag particles to make it conductive) and the proximal end is attached to a stainless steel mounting region 156 by a non-conductive adhesive 161 (e.g., a non-conductive epoxy). The electrical connection of the drive voltage is made by a dot of conductive adhesive 160 that extends from a gold-plated copper contact pad 158 to the top surface of PZT micro-actuator 114 (and more specifically to SST layer 130 in this case, which constitutes the top electrode of the micro-actuator). The thickness of the SST substrate can vary to some extent without affecting the advantages of the disclosed thin film PZT structure. Fig. 16 is a graph of stroke sensitivity versus SST constraining layer thickness for the micro-actuator of fig. 15, obtained from simulations. According to simulations, thin film PZT with a 40 μm thick SST confinement layer shows a stroke sensitivity of 20nm/V, which is almost 3 times the stroke sensitivity of the 45 μm thick bulk PZT described above. However, a 45 μm thick SST constraining layer would provide better protection for the thin film PZT micro-actuator.

Figures 17 (a) -17 (f) illustrate an alternative process for fabricating a thin film PZT structure with an SST constraining layer in accordance with the present invention. In fig. 17 (a), the process starts with a silicon substrate 144, rather than the substrate 140 and carrier tape 142 as in fig. 18 (b). In fig. 17 (b), the SST layer (130) is bonded to silicon. The process is otherwise performed in substantially the same manner as the process of fig. 13 (c) -13 (h), including flipping the assembly and removing the silicon substrate in fig. 17 (e). Furthermore, these figures clearly show the addition of the final NiCr/Au layer 131, which is not explicitly shown in fig. 13 (e).

As described above, different types of constraining layers may be used in different embodiments. Other rigid materials (whether conductive or non-conductive) may also be used as the constraining layer or substrate. For example, silicon may be used as the confinement layer material. Figure 18 is a top view of a thin film PZT structure with a silicon constraining layer according to one embodiment of the present invention. FIG. 19 isbase:Sub>A cross-sectional view of the micro-actuator of FIG. 18, taken along section line A-A'. Because the silicon constraining layer 230 is non-conductive, vias 232 are provided to conduct the PZT actuation voltage from a conductive top layer 234 (e.g., au) on the silicon 230 to the metallized electrodes 126 on the PZT element 120. The vias may be formed and filled with a conductive metal as disclosed in U.S. patent 7,781,679 to Schreiber et al, owned by the assignee of the present invention, the teachings of which are incorporated herein by reference with respect to conductive vias and methods of forming conductive vias.

Fig. 20 is a graph of stroke sensitivity versus silicon substrate thickness for the micro-actuator of fig. 19, obtained from simulations. As shown in the figure, the thin film PZT having a thickness of 3 μm and the silicon substrate having a thickness of 20 μm may exhibit a stroke sensitivity of 31.5 nm/V. This is 4 times higher than the stroke sensitivity of the design using 45 μm thick bulk PZT. The silicon substrate also contributes to the improvement of the reliability of the thin film PZT.

FIGS. 21 (a) -21 (e) illustrate a process for fabricating the thin film PZT structure of FIG. 18. In fig. 21 (a) and 21 (b), the process begins with a silicon substrate having a hole or via 232, the hole or via 232 having been formed therein, for example, by laser drilling. In FIG. 21 (c), a NiCr/Au layer is added to the silicon substrate 230 to form the top electrode 126. The NiCr/Au also fills the hole so that it becomes an electrical via 232. More generally, the vias may be filled with other conductive materials. In FIG. 22 (d), the PZT thin film 120 is deposited, for example, by a sol-gel method, and another layer of NiCr/Au is added to form the bottom electrode 128. In fig. 22 (e), the material is flipped over and a final NiCr/Au layer 131 is added. The layers 131 and 126 are electrically connected by vias 232 so that a voltage (or ground potential) applied to the conductive gold layer 131 will be transferred to the PZT element 126. The fabrication process of such a thin film PZT micro-actuator having a silicon substrate may be less complicated than the fabrication process of thin film PZT having an SST substrate.

In an alternative embodiment, the intermediate via on the silicon substrate may be replaced by one or more vias at the ends of the silicon substrate. Thus, after the final cut, a semi-circle will be formed at each end of the silicon substrate. Figure 22 is a top view of a thin film PZT micro-actuator having a silicon or other non-conductive constraining layer 330, the constraining layer 330 having a conductive top layer 231 (e.g., a metallization layer) thereon, and having side vias 234, 236, the side vias 234, 236 electrically connecting the top layer 231 with the top electrode 126. FIG. 23 isbase:Sub>A cross-sectional view of the PZT of FIG. 22 taken along section line A-A'. The manufacturing process of this embodiment may be the same as that of fig. 21 (a) -21 (e).

The constraining layer may be larger (larger surface area) than the PZT element, the same size as the PZT element, or may be smaller (smaller surface area) than the PZT element. Figure 24 is a side cross-sectional view of a PZT micro-actuator assembly 414 where the constraining layer 430 is smaller than the PZT element 420, thus giving the micro-actuator a stepped structure with steps 434 and an exposed platform 422 not covered by the constraining layer 430 where the platform 422 is electrically connected to the PZT element 420. One advantage of this structure including steps to make the electrical connections is that the complete assembly including the electrical connections has a smaller profile than if the constraining layer 430 covered the entire PZT 420. A smaller profile is advantageous because it means that more hard drive platters and their suspensions can be stacked together within a given platter stack height, thereby increasing data storage capacity within a given volume of the disk drive assembly. It is contemplated that the constraining layer 430 will cover more than 50% but less than 95% of the top surface of the PZT element 420 to accommodate electrical connections on the stage 422.

Simulations indicate that a micro-actuator constructed in accordance with the present invention exhibits enhanced stroke sensitivity, and also exhibits reduced rocking mode gain and torsional mode gain. These are advantageous in increasing the head positioning control loop bandwidth, which reduces data search time and reduces sensitivity to vibration.

Fig. 25 is an oblique view of a GSA suspension having a pair of PZT micro-actuators 414 of fig. 24.

Fig. 26 isbase:Sub>A cross-sectional view of the GSA suspension of fig. 25 taken along section linebase:Sub>A-base:Sub>A'. In this embodiment, the conductive adhesive 460 (e.g., conductive epoxy) does not extend onto the constraining layer 430. Instead, the conductive epoxy 460 extends onto the stage 422 on top of the PZT element 420 and establishes electrical connection with the PZT 420 and the entire microactuator assembly 414 through that surface. As depicted, the uppermost portion of the electrical connection defined by conductive epoxy 460 is below the top surface of SST constraining layer 430. More generally, electrical connection 461 to micro-actuator assembly 414 may be no higher or even lower than the uppermost portion of micro-actuator 414, whether the electrical connection is made by a conductive adhesive or by a wire bonded, for example, by thermo-acoustic bonding, soldering, or other technique. This allows the electrical connections of the microactuator assembly 414 to be as thin as possible, which in turn allows for a denser stack of data storage disks in the disk stack of the disk drive assembly.

Also shown explicitly is a layer of gold 469 on the stainless steel portion 154 of the trace gimbal to which the micro-actuator 414 is mounted. Gold layer 469 provides SST with corrosion resistance and enhanced electrical conductivity.

In this embodiment, as in all other embodiments, the constraining layer, and more generally the top surface of the PZT micro-actuator assembly, typically has nothing bonded to it other than electrical connections.

Figure 27 is a frequency response graph of PZT frequency response functions for the suspension of figure 26 according to the simulation. The suspension exhibited reduced roll mode gain and torsional mode gain compared to the simulation without the constraining layer 430. These are advantageous in increasing the head positioning control loop bandwidth, which reduces data search time and reduces sensitivity to vibration.

FIGS. 28 (a) -28 (j) illustrate a process for fabricating the thin film PZT assembly 114 of FIG. 24. In fig. 28 (a), a bulk PZT wafer 420 is placed on a transfer tape 422. In fig. 28 (b), a top electrode layer 426 is formed, for example, by sputtering and/or electrodeposition. In fig. 28 (c), a mask 436 is placed over a portion of the top electrode 426. In fig. 28 (d), a conductive epoxy 432 is applied. In fig. 28 (e), a stainless steel layer as a constraining layer 430 is applied to the epoxy resin, which is then cured. In fig. 27 (f), the mask 436 is removed. In fig. 27 (g), the component is turned upside down and laid down on the second transfer tape 443. In fig. 27 (h), the bottom electrode layer 428 is formed, for example, by sputtering and/or electrodeposition. The PZT element 420 is then polarized. In fig. 27 (i), the assembly is then flipped over again onto the third transfer tape 444. In FIG. 28 (j), the assembly is then separated by dicing to produce the finished PZT micro-actuator assembly 414.

Figure 29 is a side cross-sectional view of a multi-layer PZT assembly 514 according to another embodiment of the present invention. The assembly includes a multi-layer PZT element 520, a first electrode 526 encasing the device, a second electrode 528, and a constraining layer 530 bonded to the PZT element 520 by a conductive epoxy 532. A two-layer PZT arrangement is shown. More generally, the device may be an n-layer PZT device.

FIG. 30 is a side cross-sectional view of a multi-layer PZT micro-actuator assembly 614 in accordance with another embodiment of the present invention, with the extra thick electrode as a constraining layer. In this embodiment, the PZT element 620 has a top electrode 626 and a bottom electrode 628. The top electrode 626 includes a thinner first portion 622 defining a stage and a thicker second portion 630, the second portion 630 performing most of the constraining function. A step 634 is located at the transition from the thinner first portion 622 to the thicker second portion 630. Second electrode 626 can be applied to PZT element 620 by a deposition process that includes a mask to form step 634 or to PZT element 620 by a deposition process in which material is selectively removed to form a step. Alternatively, the second electrode 626 can be a piece of conductive material (e.g., SST) that is separately formed and then bonded to the PZT element 620. Thus, the material of the top electrode 626 may be the same as or different from the material of the bottom electrode 628. The thicker second portion 630 may be at least 50% thicker than the thinner portion 622 and/or the second electrode 628, or the thicker second portion 630 may be at least twice as thick as the thinner portion 622 and/or the second electrode 628. As with the embodiment of fig. 24-26, electrical connections may be provided on the lands defined by the thinner portions 622 that do not extend as high or above the top surface of the thicker portions 630 defining the constraining layer.

The scope of the invention is not limited to the exact embodiments shown. Various modifications will be apparent to those skilled in the art upon receiving the teachings herein. For example, the constraining layer need not be stainless steel, but could be some other relatively rigid and resilient material. The constraining layer need not be a single layer of one material, but may be composed of different materials in different layers. Although the constraining layer may cover the entire surface or substantially the entire top surface, the constraining layer may cover less than the entire surface, for example, covering more than 90% of the top surface area, covering more than 75% of the top surface area, covering more than 50% of the top surface area, or even covering more than 25% of the top surface area. In embodiments having a step feature, it is expected that the constraining layer will cover less than 95% of the top surface of the micro-actuator. The constraining layer need not be a single monolithic layer, but may comprise multiple pieces, such as multiple constraining strips arranged side-by-side on the top surface of the PZT, where the constraining strips extend in the expansion/contraction direction or in a direction perpendicular to the expansion/contraction direction. In one embodiment, the constraining layer may comprise two constraints of stainless steel or other material bonded to the top surface of the PZT, the size and location of the two constraints and their bonding substantially mirror the mounting areas of the two mounting platforms to which the PZT is bonded to the bottom surface thereof. When the overall stiffness added by the constraining layer on top of the device is substantially matched (coincident) with the overall stiffness added by the bonding of the bottom of the device to the suspension, and the bonded areas are substantially mirror images of each other, the net bending produced should be zero or near zero. The result would be a PZT micro-actuator that exhibits little bending when driven and deployed on a suspension.

In any and all of the embodiments discussed herein or suggested thereby, the constraining layer may be selected to reduce PZT bending that occurs during actuation, or may be selected to eliminate as much PZT bending as possible, or may be selected to reverse (reverse) the sign (sign, direction) of the PZT bending. In applications where PZT will be used as a hard disk drive micro-actuator, it is contemplated that in most cases it will be desirable to use a constraining layer to reverse the sign of the bend shown and described in the illustrative examples above, as this increases the effective stroke length. However, in other applications of PZT, reversing the sign may be undesirable. Thus, the present invention is generally applicable to controlling the direction and amount of bending of the PZT, regardless of how the PZT is mounted or otherwise affixed to other components in any particular application. Depending on the application and parameters chosen, the constraining layer may be used to reduce the bending of the PZT to less than 50% of its original, or to less than 25% of its original, or to reverse the sign of the bending. When the sign is reversed, a PZT bonded at or near its bottom surface with a constraining layer on top will bend when the PZT is in an expanded or extended mode, causing its top surface to assume a concave shape, rather than a convex shape as a similar PZT without the constraining layer. Likewise, when the PZT is in the collapsed mode, the PZT will exhibit a convex shape, rather than a concave shape as would a similar PZT without the constraining layer.

For various reasons, PZT elements are sometimes pre-stressed in application such that when they are not actuated by any voltage, the PZT has been bent in one direction or the other, i.e., it has been concave or convex. Of course, such pre-stressed PZT may be used as a micro-actuator in the present invention. In this case, the PZT may not bend into a net or absolute concave shape or a net or absolute convex shape. For example, if the PZT is pre-stressed such that it already has a concave shape, the device may bend into a more concave shape when activated with a positive activation voltage, and a less concave shape, which may be a nominally planar shape or a convex shape, when activated with a negative activation voltage. Thus, unless otherwise specified, the terms "concave" and "convex" are to be understood as relative terms, not as absolute terms.

Figure 31 is a cross-sectional view of one embodiment of a multi-layer micro-actuator PZT assembly 3100 having constraining layers comprising one or more active (active ) PZT layers 3130, 3140, the one or more active PZT layers 3130, 3140 tending to act in an opposite direction to a primary active PZT layer 3120, the primary active PZT layer 3120 being adjacent to a surface of a suspension to which the micro-actuator 3100 is bonded. Thus, PZT constraining layer 3130, 3140 constrains and actively opposes the action of primary PZT layer 3120, and thus may be referred to as a "constraining layer" or "resistive layer".

The PZT layers 3120, 3130, and 3140 are arranged in a stacked planar relationship with each other. The primary PZT layer 3120 includes an active PZT region 3121, the active PZT region 3121 being subjected to an electric field during polarization and thus being polarized and being subjected to an electric field during device activation and thus expanding or contracting, and inactive (passive ) PZT regions 3122 and 3123, neither of the inactive PZT regions 3122 and 3123 being subjected to a significant electric field during polarization or activation and thus having no significant piezoelectric activity. The device includes: a first or bottom electrode 3124; a second and top electrode 3126 for the active PZT region; a third electrode 3132, the third electrode 3132 comprising an end portion 3128, such that the electrode 3132 both extends between the first active constraining layer 3130 and the second active constraining layer 3140, and wraps around the end portions of the PZTs; and a fourth electrode 3142, the fourth electrode 3142 being positioned on top of the second active confinement layer 3140 and including a encapsulation portion 3143, the encapsulation portion 3143 encapsulating the sides and bottom of the device. The device may be bonded to the suspension using a conductive adhesive such as conductive epoxy 3160 and conductive epoxy 3162, the conductive epoxy 3160 mechanically and electrically bonding the electrode 3142 to the drive voltage electrical contact pad 158 providing the microactuator drive voltage, the conductive epoxy 3162 mechanically and electrically bonding the electrodes 3124 and 3128 of the device to the ground portion 154 of the suspension.

To understand the operation of the device, it is necessary to understand how the device is polarized. FIG. 32 shows the polarization of the device of FIG. 31, and includes the resulting polarization directions of the various layers of active PZT material. Three voltages were applied: applying a positive voltage (Vp +) to the electrode 3124; applying a negative voltage (Vp-) to electrode 3128; ground is applied to electrode 3142. The arrows in the figure show the resulting polarization directions of the active PZT layers 3120, 3130 and 3140.

Turning to fig. 31, this figure shows how device 3100 is connected in this illustrative embodiment. The conductive epoxy 3162 bridges between the electrodes 3124 and 3132 to electrically connect them, thereby converting the 3-pole device during polarization to an operating (running) 2-pole device. The electrodes may be electrically connected by other well-known means other than conductive epoxy 3162, but the use of the same conductive epoxy 3162 to bond the device to the suspension assembly may accomplish the connecting function without the need for a separate connecting step.

When a voltage is applied to the electrode 3142, causing the primary PZT layer 3120 to expand in the x-direction (from left to right) due to the expansion of the active region 3121 (as viewed in the figure), the active PZT constraining layers 3130 and 3140 will contract in the x-direction. That is, the two constraining layers 3130, 3140 tend to counter balance the primary PZT layer 3120, or act in opposite directions.

Explained in more detail, when the device is polarized as shown in fig. 32 and the device is electrically connected as shown in fig. 31, the device operates as follows. Applying a positive device activation voltage across electrical contact pad 158 and electrode 3142 while grounding electrode 3124 causes the following reactions. The activation voltage applied to the main PZT layer 3120 is opposite in polarity to the voltage during polarization. Therefore, the main PZT layer 3120 contracts in the z-direction, and thus expands in the x-direction. At the same time, the polarity of the actuation voltage is the same as the polarity of the voltage applied to the two confinement layers 3130, 3140 during poling. Thus, the PZT layers expand in the z-direction and contract in the x-direction. Thus, the two constraining layers 3130, 3140 tend to contract, while the primary PZT layer 3120 tends to expand in the relevant direction.

The effect of the constraining layer acting in the opposite direction as the primary PZT layer is similar to that described above with respect to the passive (passive, inactive) constraining layers (e.g., constraining layer 130 in fig. 10 and similar constraining layers 230, 330, 430, 530, and 630 in other embodiments discussed above). The active PZT constraining layer acts to reduce bending due to the primary PZT layer and its mounting (bonding) to the suspension, and may even reverse the sign of the bending, in either case increasing the net displacement caused by the micro-actuator mounting.

FIG. 33 is an exploded view of the micro-actuator assembly of FIG. 31, conceptually illustrating electrical connections. Optional features not visible in fig. 31 and 32 but visible in fig. 33 include a pattern 3133 on electrode 3132 and a voltage reducer 3144 associated with electrode 3142, the function of which will be described below.

Reasons for the desirability of thinner microactuator assemblies include: (1) Less mass on the suspension, particularly at or near the gimbal in gimbal-based DSA suspensions, sometimes referred to as GSA suspensions, which means more lift, i.e. more shock resistance, measured in the direction of gravity; (2) wind resistance reduction; and (3) greater stack density within the head stack assembly, which means that more data can be stored in the same volume of disk drive stack assembly space. Therefore, it is desirable to make the PZT constraining layer relatively thin. However, the thinner the PZT constraining layers, the higher the electric field strength on these layers during operation, so the PZT constraining layers are easily depolarized during operation because the electric field strength is too high. Thus, nominally, the primary and constraining PZT layers should have the same thickness.

One solution to thinning the constraining PZT layer without subjecting it to depolarization is to reduce the electric field strength on the constraining layer using one or more possible measures, but not significantly reducing the electric field on the main PZT layer. A first means to achieve this goal is to pattern one or more electrodes that are operatively associated with one of the active PZT constraining layers but operatively associated with the primary PZT layer, such as adding holes 3133 or other electrical voids in the electrode 3132. The patterning may also take the form of a mesh pattern, such as a grid of parallel or intersecting conductors with electrical gaps between them. By reducing the percentage of area of the electrical conductors in the planar electrode 3132, the electric field strength on the constraining layers 3130 and 3140 is effectively reduced, while the electric field strength on the primary PZT layer 3120 is not reduced.

A second solution is to increase the coercive electric field strength of the confinement layer in order to make the confinement layer more resistant to depolarization. Coercive electric field strength (or simply "coercive force" when referring to a piezoelectric material) is a measure of how much electric field strength is needed to depolarize the piezoelectric material. Having the constraining layers 3130, 3140 with a higher coercivity than the primary PZT layer 3120 allows these constraining layers to be thinner without risk of depolarization when subjected to the same activation voltage as the primary PZT layer. The constraining layers 3130, 3140 may be made to have a higher coercivity by using different or slightly different piezoelectric materials, or by other processes, but possibly at the expense of some loss of d31 stroke length or other desirable characteristics.

Another solution is to reduce the effective voltage applied to the drive electrode associated with the constraining layer by using some sort of voltage reducer, such as a divider resistor network, a diode, a voltage regulator, or any of a variety of functionally similar devices as will occur to those of skill in the art. In the figure, the common voltage reducer 3144 reduces the voltage received by the electrode 3142, thereby reducing the electric field strength experienced by the constraining layer 3140, but not the main PZT layer 3120. The voltage divider may be integrally formed so as to be disposed between adjacent piezoelectric layers, for example by applying metallisation forming electrode layers so as to form a divider resistive network on the surface of the PZT material. A simple resistive divider requires a ground line, which can be implemented on the same layer. Many configurations are possible, as will be apparent to the designer of such devices.

Both the pattern 3133 and the voltage reducer 3144 reduce the electric field strength on the confinement layer 3140, allowing the confinement layer 3140 to be made thinner without causing unacceptable depolarization thereof during operation. Electrode patterns and/or voltage reducers, and/or some other means may be used to reduce the electric field strength on the constraining layers 3130 and/or 3140. The pattern 3133 is integrally formed with the electrode 3132, and thus with the micro-actuator assembly. The step-down transformer for one of the electrodes may be formed integrally with and integrated into the assembly, or may be provided externally of the assembly if the relevant electrode has its own electrical lead and is not connected to the other electrodes.

All of the solutions discussed above can be applied to piezoelectric microactuators having a single active confinement layer, two active confinement layers (as shown in fig. 31-33), or more generally n active confinement layers (as shown in fig. 35).

Fig. 34 is a graph showing the stroke sensitivity (in nm/V) of a micro-actuator having one or more active constraining layers, which was obtained from simulations for various constraining layer structures (CLC) in which the primary PZT layer is 45 μm thick, without any pattern 3133 or voltage reducer 3144 to reduce the electric field strength, and has three different structures:

a) One inactive constraining layer ("passive CLC", diamond data points);

b) One active confinement layer ("single layer", square data points); and

c) Two active constraining layers ("double layers", triangular data points).

The data show that, at least for the parameters studied, a PZT micro-actuator with an active constraining layer acting in the opposite direction to the main PZT layer always produces higher stroke sensitivity than a micro-actuator with the constraining layer being an inactive material. Using multiple active thin PZT layers as constraining layers (i.e., acting in the opposite direction to the main PZT layer), the highest stroke sensitivity can be achieved. In particular, the highest stroke sensitivity can be obtained using two constraining layers (each of which has a thickness of 5 μm, or about 11% of the thickness of the primary PZT layer). Thus, the constraining layer preferably has a thickness that is less than 50% of the thickness of the primary PZT layer, or more preferably less than 20% of the thickness of the primary PZT layer, or more preferably in the range of 5-15% of the thickness of the primary PZT layer.

The stroke sensitivity decreases sharply with increasing thickness of the confinement layer for both active confinement layers, and is highest for both active confinement layers, each about 5 μm thick. Thus, the microactuator preferably has two or more constraining layers having a combined thickness that is less than the thickness of the primary PZT layer, more preferably having a combined thickness that is less than 50% of the thickness of the primary PZT layer, more preferably having a thickness of each constraining layer that is less than half the thickness of the primary PZT layer, more preferably having a thickness of each constraining layer that is less than 20% of the thickness of the primary PZT layer, more preferably having a thickness of each constraining layer that is in the range of 5-15% of the thickness of the primary PZT layer.

For a microactuator assembly having a single active confinement layer, the loss of stroke sensitivity with increasing confinement layer thickness is not as severe as in the case of two active confinement layers. For a single active confinement layer, the local maximum (maximum of the stroke sensitivity) occurs over a thickness of about 10 μm. Thus, for a microactuator assembly having a single active constraining layer, the thickness of this layer is preferably in the range of 10-40% of the thickness of the primary PZT layer, and more preferably in the range of about 10-20% of the thickness of the primary PZT layer.

FIG. 35 is a cross-sectional view of another embodiment in which the microactuator assembly includes multiple active PZT layers and conceptually illustrates the poling process and the resulting poling direction. When the device of fig. 35 is electrically and mechanically bonded to a suspension as shown in fig. 31 (where electrodes 3524 and 3528 are connected by a conductive epoxy), the result is one primary active PZT layer and three active PZT layers that act as constraining layers because the three active PZT layers tend to act in the opposite direction to the primary active PZT layer. That is, the bottom PZT layer expands while the top three PZT layers contract, or vice versa.

The structure of the microactuator assembly can be readily extended from an apparatus having one active primary PZT layer and two active PZT confining layers as shown in fig. 31-33 and one active primary PZT layer and three active PZT confining layers as shown in fig. 35 to having any number of active primary and active confining layers. The electric field strength on the one or more constraining layers may be reduced by various means including electrode patterns and/or voltage reducers. Experiments will reveal the optimum number of constraining layers and the optimum thickness for different applications.

The PZT micro-actuators disclosed herein can be used as actuators in areas other than disk drive suspensions. Thus, such micro-actuators and their structural details constitute inventive devices, no matter under what environment they are used, no matter in a disk drive suspension environment or any other environment.

Figure 36 is an isometric view of one embodiment of a single layer micro-actuator PZT assembly 4000. Figure 37 is a cross-sectional view of a single layer micro-actuator PZT assembly 4000 taken through section line C-C' along the width of the PZT. Single layer micro-actuator PZT assembly 4000 further includes a top electrode 4042, PZT elements 4040, and bottom electrode 4032. A top electrode 4042 is mounted on the top surface 4048 of the PZT element 4040. The bottom electrode 4032 is mounted on the bottom surface 4034 of the PZT element 4040.

The top electrode 4042 has a width W1 that is narrower than a width W2 of the bottom electrode 4032. Top electrode 4042 includes a step 4044, and top electrode 4042 terminates at step 4044. The PZT element 4040 includes an exposed portion 4046 of the top surface 4048 that is not covered by the top electrode 4042. In some embodiments, the top electrode 4042 is positioned on the PZT element 4040 opposite the PZT bonding surface.

The top electrode 4042 may be applied to the PZT element 4040 by a deposition process that includes a mask to form step 4044, or by a deposition process in which material is selectively removed to form step 4044. Alternatively, the top electrode 4042 may be a piece of conductive material, such as SST or other material described herein, that is separately formed and then bonded to the PZT element 4040. Thus, the material of the top electrode 4042 may be the same as or different from the material of the bottom electrode 4032.

Figure 38A is a plan view of a gimbal for a suspension 4050 including a single layer micro-actuator PZT assembly 4000 according to one embodiment of the present disclosure. The exposed portion 4046 (i.e., the electrode dead zone) is located on the inside of the PZT, with the remainder of the PZT top surface being the top electrode 4042. The PZT is mounted on a gimbal that includes a gimbal assembly and acts directly on a gimbal region of the suspension that holds the read/write head slider. Each of the two micro-actuator PZT assemblies 4000 will be bonded between tab 4054 and trace gimbal portion 4056 and span the gap between tab 4054 and portion 4056, with the proximal end of micro-actuator 4000 being bonded to tab 4054 and the distal end of micro-actuator 4000 being bonded to portion 4056.

Figure 38B is a cross-sectional view of the suspension 4050 of figure 38A, taken along section line D-D', according to one embodiment of the present disclosure. The PZT bottom electrode 4032 is bonded proximally and distally by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. Conductive adhesive 504 is also applied to the proximal end of the top electrode 4042 to form a PZT electrical connection. When the micro-actuator assembly 4000 is activated, it expands or contracts, changing the gap length between the tongue 4054 and the portion 4056 of the trace gimbal (FIG. 38A), thereby enabling fine positioning motion of the head slider carrying the read/write sensor.

The narrower width dimension of the top electrode 4042 creates an artificial constraint that counteracts the constraint imposed on the bottom electrode 4032 by the adhesive bonded at the proximal non-conductive adhesive 502 and the distal conductive adhesive 504. By properly selecting the width of the top electrode 4042, the suspension PZT excitation Frequency Response Function (FRF) can have lower gain in several major modes throughout the frequency band.

Figure 39 is a graph of PZT frequency response function for the suspension of figure 38, obtained from simulations. The top electrode 4042 was 0.05mm narrower in width than the bottom electrode 4032. As a result, the first gimbal torsional mode (GT 1), the circuit torsional mode, and the load Liang Yaobai mode are gain improved. In particular, the gain of the load Liang Yaobai mode is reduced by 3dB, which helps to increase the head positioning servo control bandwidth, thereby reducing data search time and reducing sensitivity to vibration.

Figure 40 is a plan view of a gimbal of a suspension 4150 including a single layer micro-actuator PZT assembly 4000 according to an alternative embodiment of the present disclosure. In fig. 40, the exposed portion 4047 (electrode dead zone) is positioned outside of the PZT top surface 4048, while the remainder of the PZT top surface 4048 is the top electrode 4042.

Figure 41 is a graph of PZT frequency response function for the suspension of figure 40, obtained from simulations. The suspension exhibits a first gimbal torsional mode, a circuit torsional mode, and a gain variation of the load Liang Yaobai mode. This embodiment of the single layer micro-actuator PZT assembly described herein can be used to adjust the PZT FRF of one suspension with opposite gain peaks to optimize the PZT FRF in these modes.

Figure 42 is a plan view of a gimbal of a suspension 4250 comprising a single layer micro-actuator PZT assembly 4100 according to an alternative embodiment of the present disclosure. In fig. 42, the exposed portions 4146 (electrode dead zones) are located inside and outside the PZT top surface 4148, with the remainder of the PZT top surface 4148 being the top electrode 4142. Figure 43 is a cross-sectional view of a single layer micro-actuator PZT assembly 4100 with cross-sectional line E-E' in the width direction taken through the PZT. The single layer microactuator PZT assembly 4100 includes a top electrode 4142, a PTZ element 4140, and a bottom electrode 4132. The top electrode 4142 is mounted on the top surface 4148 of the PZT element 4140. The bottom electrode 4132 is mounted on the bottom surface 4134 of the PZT element 4140. The width W3 of the top electrode 4142 is narrower than the width W4 of the bottom electrode 4132. The top electrode 4142 includes a step 4144, and the top electrode 4142 terminates at the step 4144. The PZT element 4140 includes two exposed portions 4146 of the top surface 4148 that are not covered by the top electrode 4142. In some embodiments, the top electrode 4142 is positioned on the PZT element 4140 opposite the PZT bonding surface.

The top and bottom electrodes may be applied to the PZT element 4140 by a deposition process that includes a mask to form the steps 4144 or by a deposition process in which material is selectively removed to form the top electrode on the PZT element 4140. Alternatively, the top electrode may be multiple pieces of separate conductive material, such as SST, that are separately formed and then bonded to the PZT element 4140. Thus, the material of the top electrode may be the same as or different from the material of the bottom electrode 4132.

The narrower dimension of the top electrode 4142 creates an artificial constraint to counteract the constraint imposed on the bottom electrode 4132 by the PZT bonding to the proximal and distal ends of the bottom electrode. By properly selecting the width of the top electrode, the suspension PZT excitation FRF can have lower gain in several major modes throughout the band.

Figure 44A is an oblique view of the gimbal of suspension 4250 rotating a single layer microactuator PZT assembly 4000. The single layer micro-actuator PZT assembly 4000 is rotated so that the top electrode 4042 is now the first side electrode 5042 and the exposed portion 4046 is also on the side surface. The bottom electrode 4032 is now the second side electrode 5032. In this configuration, the first side electrode 5042 and the second side electrode 5032 are electrically connected with the copper pads from both side surfaces thereof.

FIG. 44B is a cross-sectional view of FIG. 44A taken along section line F-F' according to one embodiment of the present disclosure. The PZT first side electrode 5042 is bonded at the distal copper pad 606 by a conductive adhesive 604. A non-conductive adhesive 602 is also applied on the first side electrode 5042. FIG. 44C is a cross-sectional view of FIG. 44A taken along section line G-G' according to one embodiment of the present disclosure. The PZT second side electrode 5032 is bonded to the proximal copper pad 608 by a conductive adhesive 604. When the microactuator assembly 4000 is activated, it expands or contracts, thereby effecting fine positioning movement of the head slider carrying the read/write transducer.

The narrower width dimension of the first side electrode 5042 creates an artificial constraint to counteract the constraint imposed on the second side electrode 5032 by the adhesive bonded at the proximal nonconductive adhesive 602 and the distal conductive adhesive 604. By properly selecting the width of the first side electrode 5042, the suspension PZT excitation Frequency Response Function (FRF) can have lower gain in several primary modes throughout the band.

Figure 45A is a plan view of a gimbal of suspension 4350 assembled with a single layer micro-actuator PZT assembly 4200 according to an alternative embodiment of the present disclosure. In fig. 45A, the exposed portions 4246 (electrode dead zones) are located inside and outside the PZT top surface 4248, while the rest of the PZT top surface 4248 is the top electrode 4242. The exposed portions 4246 (electrode dead zones) are configured to bend inward, thereby reducing the surface area of the top electrode 4242 at or near the center of the PZT top surface 4246. The cross-sectional area of top electrode 4242 increases toward the distal and proximal ends of single layer microactuator PZT assembly 4200.

Figure 45B is a cross-sectional view of single layer micro-actuator PZT assembly 4200, taken along section line H-H' across the width of the central PZT of single layer micro-actuator PZT assembly 4200. The top electrode 4242 is mounted on the top surface 4248 of the PZT element 4240. The bottom electrode 4232 is mounted on the bottom surface 4234 of the PZT element 4240. The top electrode 4242 has a variable width W5 that increases proximally and distally. The variable width W5 of the top electrode 4242 is narrower than the width W6 of the bottom electrode 4232. The top electrode 4242 comprises a step 4244, at which the top electrode 4242 terminates. The PZT element 4240 includes two exposed portions 4246 of the top surface 4248 that are not covered by the top electrode 4242. In some embodiments, the top electrode 4242 is positioned on the PZT element 4240 opposite the PZT bonding surface.

The top and bottom electrodes may be applied to PZT element 4240 by a deposition process that includes masking to form steps 4244, or by a deposition process in which material is selectively removed to form the top electrode on PZT element 4240. Alternatively, the top electrode 4242 may be multiple pieces of separate electrically conductive material, such as SST or other materials described herein, that are separately formed and then bonded to the PZT element 4240. Thus, the material of the top electrode 4242 may be the same as or different from the material of the bottom electrode 4232.

The variable cross-section of the top electrode 4242 creates artificial constraints to counteract the constraints imposed on the bottom electrode 4232 by the PZT bonding on the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4242, the suspension PZT excitation FRF can have lower gain in several major modes throughout the band.

Figure 45C is a graph of PZT frequency response function for the suspension of figure 45A, obtained from simulations. The curved exposed portions on either side of the electrode (electrode dead zone) can be used to optimise the gain of the second gimbal torsion mode (GT 2).

Figure 46A is a plan view of a gimbal including a suspension 4450 of a single layer micro-actuator PZT assembly 4300 according to an alternative embodiment of the present disclosure. In fig. 46A, the exposed portion 4346 (electrode dead zone) is positioned inside the PZT top surface 4348, while the remaining portion of the PZT top surface 4348 is the top electrode 4342. The exposed portion 4346 (electrode dead zone) is configured to bend inward, thereby reducing the surface area of the top electrode 4342 at or near the center of the PZT top surface 4348. The cross-sectional area of the top electrode 4342 increases towards the distal and proximal ends of the single layer micro-actuator PZT assembly 4300.

Figure 46B is a cross-sectional view of single layer micro-actuator PZT assembly 4300 taken across the center PZT width of single layer micro-actuator PZT assembly 4300 along section line J-J'. The top electrode 4342 is mounted on the top surface 4348 of the PZT element 4340. The bottom electrode 4332 is mounted on the bottom surface 4334 of the PZT element 4340. The top electrode 4342 has a variable width W7 that increases proximally and distally. The variable width W7 of the top electrode 4242 is narrower than the width W8 of the bottom electrode 4332. The top electrode 4342 includes a step 4344, at which the top electrode 4342 terminates. The PZT element 4340 includes an exposed portion 4346 of the top surface 4348 that is not covered by the top electrode 4342. In some embodiments, the top electrode 4342 is positioned on the PZT element 4340 opposite the PZT bonding surface.

The top and bottom electrodes can be applied to PZT element 4340 by a deposition process that includes masking to form step 4344, or by a deposition process in which material is selectively removed to form the top electrode 4340. Alternatively, the top electrode 4342 may be multiple pieces of a separate conductive material, such as SST or other materials described herein, that are separately formed and then bonded to the PZT element 4340. Thus, the material of the top electrode 4342 may be the same as or different from the material of the bottom electrode 4332.

The variable cross-section of the top electrode 4342 creates artificial constraints to counteract the constraints imposed on the bottom electrode 4332 by the PZT being bonded to the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4342, the suspension PZT excitation FRF can have lower gain in several major modes throughout the band.

Figure 46C is a graph of PZT frequency response function for the suspension of figure 46A, obtained from simulations. The curved exposed portion inside the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT 1) gain (increasing GT1 phase lag) and the rocking gain (increasing rocking mode phase lead).

Figure 47A is a plan view of a gimbal of a suspension 4550 including a single layer micro-actuator PZT assembly 4400 in accordance with an alternative embodiment of the present disclosure. In fig. 47A, exposed portions 4446 (electrode dead zones) are positioned outside the PZT top surface 4448, while the rest of the PZT top surface 4448 is the top electrode 4442. The exposed portions 4446 (electrode dead zones) are configured to bend inward, thereby reducing the surface area of the top electrode 4442 at or near the center of the PZT top surface 4448. The cross-sectional area of the top electrode 4442 increases toward the distal and proximal ends of the single layer micro-actuator PZT assembly 4400.

Figure 47B is a cross-sectional view of the single layer micro-actuator PZT assembly 4400 taken along section line K-K' across the width of the central PZT of the single layer micro-actuator PZT assembly 4400. The top electrode 4442 is mounted on the top surface 4448 of the PZT element 4440. The bottom electrode 4432 is mounted on the bottom surface 4334 of the PZT element 4440. The top electrode 4442 has a variable width W9 that increases proximally and distally. The variable width W9 of the top electrode 4442 is narrower than the width W10 of the bottom electrode 4432. The top electrode 4442 includes a step 4444, where the top electrode 4442 terminates at the step 4444. The PZT element 4440 includes an exposed portion 4446 of the top surface 4448 that is not covered by the top electrode 4442. In some embodiments, the top electrode 4442 is positioned on the PZT element 4440 opposite the PZT bonding surface.

The top and bottom electrodes may be applied to PZT element 4440 by a deposition process that includes a mask to form step 4444, or by a deposition process in which material is selectively removed to form the top electrode on PZT element 4440. Alternatively, the top electrode 4442 may be multiple pieces of separate conductive material, such as SST or other materials described herein, that are separately formed and then bonded to the PZT element 4440. Thus, the material of the top electrode 4442 may be the same as or different from the material of the bottom electrode 4432.

The variable cross-section of the top electrode 4442 creates artificial constraints to counteract the constraints imposed on the bottom electrode 4432 by the PZT bonding to the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4442, the suspension PZT excitation FRF can have lower gain in several primary modes throughout the band.

Figure 47C is a graph of PZT frequency response function for the suspension of figure 47A, obtained from simulations. The curved exposed portion outside the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT 1) gain (increasing GT1 phase lag) and the rocking gain (increasing rocking mode phase lead).

Figure 48A is a plan view of a gimbal of a suspension 4650 including a single layer micro-actuator PZT assembly 4500 according to one embodiment of the present disclosure. Exposed portion 4546 (i.e., the electrode dead zone) is located at the distal end of the PZT and is curved such that the exposed portion on the outside is larger than the exposed portion on the inside. The remainder of the PZT top surface is the top electrode 4542. Each of the two micro-actuator PZT assemblies 4500 will be bonded to tongue 4554 and trace gimbal portion 4556 and will span the gap between tongue 4554 and trace gimbal portion 4556, wherein the proximal end of micro-actuator 4500 will be bonded to tongue 4554 and the distal end of micro-actuator 4500 will be bonded to trace gimbal portion 4556.

Figure 48B is a cross-sectional view of the suspension 4650 of figure 48A taken along section line L-L' according to one embodiment of the present disclosure. The PZT bottom electrode 4532 is bonded proximally and distally by the non-conductive adhesive 502 and the conductive adhesive 504, respectively. Conductive adhesive 504 is also applied on the proximal end of the top electrode 4542 to form the PZT electrical connection. When the micro-actuator assembly 4500 is activated, it expands or contracts, changing the gap length between the tongue 4554 and the portion 4556 of the trace gimbal (FIG. 48A), thereby enabling fine positioning movement of the head slider carrying the read/write transducer.

Figure 48C is a graph of PZT frequency response function for the suspension of figure 48A, obtained from simulations. The curved exposed portion of the electrode distal end (electrode dead zone) may be used to optimize the gain of the first torsional mode (T1) and the first gimbal torsional mode (GT 1).

Figure 49A is a plan view of a gimbal of a suspension 4750 including a single layer micro-actuator PZT assembly 4600 according to an alternative embodiment of the present disclosure. In fig. 49A, the exposed portion 4646 (electrode dead zone) is positioned on a portion of the exterior side of the PZT top surface 4648, while the remaining portion of the PZT top surface 4446 is the top electrode 4642. Specifically, the top electrode 4642 may include a distal portion, a proximal portion, and a coupling portion connecting the distal and proximal portions. As shown, the proximal portion may have a larger surface area than the distal portion of the top electrode 4642. Alternatively, the distal portion may have a larger surface area than the proximal portion of the top electrode 4642. In other embodiments, the proximal and distal portions may have the same or substantially the same surface area. The exposed portion 4646 (electrode dead zone) is defined by the distal portion, proximal portion, and coupling portion of the top electrode 4642. The distal and proximal portions have a larger cross-sectional area than the coupled portion of the top electrode 4642.

Figure 49B is a cross-sectional view of the single layer micro-actuator PZT assembly 4400 taken along section line M-M' across the width of the central PZT of the single layer micro-actuator PZT assembly 4600. The top electrode 4642 is mounted on the top surface 4648 of the PZT element 4640. The bottom electrode 4632 is mounted on the bottom surface 4634 of the PZT element 4640. The coupling portion of the top electrode 4642 has a width W11 that is narrower than the proximal and distal portions (not shown). The width W11 of the top electrode 4642 is narrower than the width W12 of the bottom electrode 4632. The top electrode 4642 includes a step 4644, where the top electrode 4642 terminates at the step 4644. The PZT element 4640 includes one exposed portion 4646 of the top surface 4648 that is not covered by the top electrode 4642. In some embodiments, the top electrode 4642 is positioned on the PZT element 4640 opposite the PZT bonding surface.

The top and bottom electrodes may be applied to the PZT element 4640 by a deposition process that includes a mask to form the steps 4644, or by a deposition process in which material is selectively removed to form the top electrode on the PZT element 4640. Alternatively, the top electrode 4642 may be a plurality of separate pieces of electrically conductive material, such as SST or other materials described herein, that are separately formed and then bonded to the PZT element 4640. Thus, the material of the top electrode 4642 may be the same as or different from the material of the bottom electrode 4632.

The multiple cross-sections of the top electrode 4642 create artificial constraints to counteract the constraints imposed on the bottom electrode 4632 by the PZT being bonded to the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4642, the suspension PZT excitation FRF can have lower gain in several primary modes throughout the band.

Figure 49C is a graph of the PZT frequency response function for the suspension of figure 49A, obtained from simulations. The curved exposed portion outside the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT 1) gain (increasing GT1 phase lag) and the rocking gain (increasing rocking mode phase lead).

Figure 50A is a plan view of a gimbal including a suspension 4850 of a single layer micro-actuator PZT assembly 4700 according to one embodiment of the present disclosure. The micro-actuator PZT assembly 4700 includes a plurality of exposed portions 4746 (i.e., electrode dead zones), each exposed portion 4746 being located on a portion of the exterior side of the PZT top surface 4748, with the remainder of the PZT top surface 4748 being the top electrode 4742. In particular, the top electrode 4742 may include a distal portion, a proximal portion, one or more intermediate portions between the distal and proximal portions, and a coupling portion connecting the portions along the inside of the PZT top surface 4748. In alternative embodiments, the patterned dead zone may be located along the inside of the PZT top surface 4748. In other embodiments, the patterned dead zones may be positioned to alternate between the interior sides of the PZT top surface 4748 and the exterior sides of the PZT top surface 4748.

The portions of the top electrode 4742 may have the same or substantially the same surface area. An exposed portion 4746 (electrode dead zone) is defined by the distal portion, proximal portion, intermediate portion, and coupling portion of the top electrode 4742. The distal, proximal and intermediate portions have a larger cross-sectional area than the coupling portion of the top electrode 4742.

Fig. 50B is a cross-sectional view of suspension 4750 of fig. 50A taken along section line N-N' according to one embodiment of the present disclosure. The PZT bottom electrode 4732 is bonded proximally and distally by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. The top electrode 4742 includes, along the inside of the PZT top surface 4748, a distal portion 4742C, a proximal portion 4742A, and one or more intermediate portions 4742B between the distal and proximal portions. Conductive adhesive 504 is also applied on the proximal portion 4742A to form a PZT electrical connection. When the micro-actuator assembly 4700 is activated, it expands or contracts, changing the gap length between the tongue 4754 and the portion 4756 of the trace gimbal (FIG. 50A), thereby enabling fine positioning motion of the head slider carrying the read/write sensor.

Figure 50C is a graph of PZT frequency response function for the suspension of figure 50A, according to simulations. The patterned dead zone in the PZT top electrode 4742 can be used for resonance (response) optimization for the first torsional mode (T1) (increasing T1 phase lag), the first gimbal torsional mode (GT 1) (increasing GT1 phase lead), and the swing (increasing swing phase lag). As explained herein, the effect on the run lengths of 3.7nm/V and 3.4nm/V is small.

Figure 51 is a cross-sectional view of one embodiment of a single layer micro-actuator PZT assembly according to one embodiment of the present disclosure. Single layer micro-actuator PZT assembly 5000 also includes top electrode 5042, PZT element 5040, and bottom electrode 5032. A top electrode 5042 is mounted on the top surface 5048 of the PZT element 5040. The bottom electrode 5032 is mounted on the bottom surface 5034 of the PZT element 5040.

The top electrode 5042 has a width W1 that is narrower than the PZT element 5040. The top electrode 5042 includes a step 5044, and the top electrode 5042 terminates at the step 5044. The PZT element 5040 includes an exposed portion 5046 of the top surface 5048 that is not covered by the top electrode 5042. In some embodiments, the top electrode 5042 is positioned on the PZT element 4040 opposite the PZT bonding surface. The top electrode of some embodiments has a variable width or is configured to expose portions of the PZT element according to the techniques described herein.

The width W2 of the bottom electrode 5032 is narrower than the PZT element 5040. The bottom electrode 5032 comprises a step at which the bottom electrode 5032 terminates. The PZT element 5040 includes an exposed portion of the bottom surface not covered by the bottom electrode 5032. The bottom electrode of some embodiments has a variable width or is configured to expose portions of the PZT element according to the techniques described herein. Some embodiments include top and bottom electrodes configured to have similar exposed surfaces on the top and bottom surfaces of the PZT element. Other embodiments include top and bottom electrodes such that the top and bottom surfaces of the PZT element have different exposed surfaces. Thus, the top electrode may not cover the entire surface of the PZT element, and may have a second electrode of the same shape and size or of a different shape and size but within the outer dimensions of the PZT element.

The top electrode 5042 and the bottom electrode 5032 can be applied to the PZT element 5040 by a deposition process that includes masking to form a step, or by a deposition process in which material is selectively removed to form a step on the PZT element 5040. Alternatively, the top electrode 5042 and/or the bottom electrode 5032 can be a piece of conductive material, such as SST or other materials described herein, that is separately formed and then bonded to the PZT element 5040. Thus, the material of the top electrode 5042 can be the same as or different from the material of the bottom electrode 5032.

Although a single PZT layer is illustrated herein, the disclosed embodiments are applicable to multi-layer PZT micro-actuator assemblies having multiple PZT elements using similar techniques as described herein. By properly selecting the width of the top electrode, the PZT FRF of a tiled microactuator suspension using a set of multi-layer PZT's can be effectively tuned.

It is to be understood that the terms "generally," "about," "generally," and "coplanar" used in the specification and claims are allowed to differ from any precise dimensions, measurements, and arrangements, and that these terms are to be understood in the context of the description and operation of the invention disclosed herein.

It will be further understood that terms such as "top," "bottom," "above," and "below," as used in the specification and claims, are convenient terms for referring to the spatial relationship of components relative to one another and not to any particular spatial or gravitational direction. Accordingly, these terms are intended to encompass an assembly of parts, whether in the particular orientation illustrated in the figures and described in the specification, reversed from that orientation, or any other rotational variation.

All of the features disclosed in this specification, including the claims, abstract, and drawings, and all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

It is to be understood that the term "invention" as used herein is not to be construed as presenting only a single invention having a single essential element or group of elements. Likewise, it will also be understood that the term "invention" includes several separate innovations, each of which may be considered a separate invention. Although the present invention has been described in detail with respect to the preferred embodiments and the accompanying drawings, it is apparent to those skilled in the art that various adjustments and modifications of the present invention can be made without departing from the spirit and scope of the invention. It is, therefore, to be understood that the foregoing detailed description and accompanying drawings are not intended to limit the breadth of the invention, which should be inferred only from the following claims and their legal equivalents as properly interpreted.

Claims (25)

1. A micro-actuator assembly, the micro-actuator assembly comprising:

at least one PZT element;

a first electrode on a first side of the microactuator assembly, the first electrode having a first width extending the entire length of the first side of the at least one PZT element; and

a second electrode on a second side of the at least one PZT element, the second electrode having a second width less than a width of the first electrode.

2. The micro-actuator assembly of claim 1, wherein the second electrode is configured to counteract first electrode binding applied by a piezoelectric adhesive.

3. The micro actuator assembly of claim 1, wherein the first and second electrodes are electrically connected by a conductive adhesive that adheres the micro actuator assembly to a surface.

4. The microactuator assembly of claim 1 wherein said at least one PZT element is a plurality of PZT elements disposed between said first and second electrodes.

5. The micro-actuator assembly of claim 1, wherein a width of the second electrode is variable along a longitudinal axis of the second electrode.

6. The micro-actuator assembly of claim 5, wherein the second electrode is configured to expose at least two portions of the at least one PZT element.

7. The microactuator assembly of claim 5 wherein said second electrode is configured to expose a portion of said at least one PZT element.

8. The microactuator assembly of claim 1 wherein the width of said second electrode is variable along a latitudinal axis of said second electrode.

9. The micro-actuator assembly of claim 8, wherein the second electrode is configured to expose at least two portions of the at least one PZT element.

10. The microactuator assembly of claim 8 wherein said second electrode is configured to expose a portion of said at least one PZT element.

11. The microactuator assembly of claim 1 wherein said second electrode comprises at least one exposed portion.

12. The micro-actuator assembly of claim 11, wherein the second electrode is configured with a distal portion, a proximal portion, and a coupling portion connecting the distal portion and the proximal portion.

13. The micro-actuator assembly of claim 11, wherein the at least one exposed portion is a plurality of exposed portions.

14. A suspension for a disk drive, the suspension comprising:

a micro-actuator assembly, the micro-actuator assembly comprising:

at least one of the PZT elements is provided,

a first electrode on a first side of the microactuator assembly, the first electrode having a first width extending the entire length of the first side of the at least one PZT element; and

a second electrode on a second side of the at least one PZT element, the second electrode having a second width less than a width of the first electrode.

15. The suspension of claim 14, wherein the second electrode is configured to counteract first electrode binding applied by the piezoelectric adhesive.

16. The suspension of claim 14, wherein the at least one PZT element is a plurality of PZT elements disposed between the first and second electrodes.

17. The suspension according to claim 14, wherein the width of the second electrode is variable along the longitudinal axis of the second electrode.

18. The suspension of claim 17, wherein the second electrode is configured to expose at least two portions of the at least one PZT element.

19. The suspension of claim 17, wherein the second electrode is configured to expose a portion of the at least one PZT element.

20. The suspension according to claim 14, wherein the width of the second electrode is variable along a latitudinal axis of the second electrode.

21. The suspension of claim 20, wherein the second electrode is configured to expose at least two portions of the at least one PZT element.

22. The suspension of claim 20, wherein the second electrode is configured to expose a portion of the at least one PZT element.

23. The suspension according to claim 14, wherein the second electrode includes at least one exposed portion.

24. The suspension according to claim 23, wherein the second electrode is configured with a distal portion, a proximal portion, and a coupling portion connecting the distal portion and the proximal portion.

25. The suspension according to claim 23, wherein the at least one exposed portion is a plurality of exposed portions.

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