Multilayer PZT microactuator with active PZT constraint layer for DSA suspension

Abstract

We provide microactuator assemblies and suspensions for disk drives. [Solution] The microactuator assembly comprises at least one piezoelectric element, a first electrode located on a first side surface of the at least one piezoelectric element, having a first height extending along the entire length of the first side surface of the at least one piezoelectric element, and a second electrode located on a second side surface of the at least one piezoelectric element, having a second height smaller than the first height of the first electrode, extending shorter than the entire length of the second side surface of the at least one piezoelectric element, and configured to bend when a voltage is applied to resist the constraint exerted by the bonding adhesive.

Description

Technical Field

[0003]

[0001] The present invention relates to the technical field of suspensions for hard disk drives. More specifically, the present invention relates to the technical field of multilayer piezoelectric micro actuators having one or more active piezoelectric restraint layers used in two-stage actuated suspensions.

Background Art

[0002] Other types of rotating media drives, such as magnetic hard disk drives and optical disk drives, are well known. FIG. 1 is a perspective view of a conventional hard disk drive and suspension to which the present invention is applicable. The conventional disk drive unit 100 has a rotating magnetic disk 101 that magnetically stores the patterns of 1s and 0s that make up the data stored in the disk drive. The magnetic disk is driven by a drive motor (not shown). The disk drive unit 100 further has a disk drive suspension 105, and a magnetic head slider (not shown) is attached near the tip of the load beam 107 of the disk drive suspension 105. The "base end" of the suspension or load beam is the supported end, that is, the end closest to the base plate 12 attached to the actuator arm by caulking or the like. The "tip" of the suspension or load beam is the end on the opposite side of the base end, that is, the "tip" is a cantilever end.

[0003] The suspension 105 is connected to an actuator arm 103 connected to a voice coil motor 112. The voice coil motor 112 moves the suspension 105 in an arc to position the head slider on the correct data track on the data disk 101. The head slider is placed on a gimbal, allowing the pitch and roll of the slider so that it can follow the correct data track on the rotating disk. Thus, it can cope with vibrations of the disk, inertial events such as bumping, and variations such as irregularities on the disk surface.

[0004] Both single-stage disc drive suspensions and dual-stage (DSA) suspensions are well known. In a single-stage suspension, the suspension 105 is driven solely by the voice coil motor 112.

[0005] In DSA suspensions, as seen, for example, in Patent Document 1 granted to Mei et al. and many other examples, at least one microactuator is additionally positioned on the suspension in addition to the voice coil motor 112 that drives the entire suspension. This microactuator enables fine movements of the magnetic head slider, allowing it to be precisely aligned with the data track of the rotating disk. The presence of the microactuator allows for finer control of the servo control loop and a significantly higher bandwidth compared to a voice coil motor alone, which can only move the suspension and magnetic head slider relatively coarsely. Piezoelectric elements, sometimes simply referred to as PZTs, are often used as microactuator motors, but other types of microactuator motors may also be used.

[0006] Figure 2 is a top view of the conventional suspension 105 of Figure 1. Two PZT microactuators 14 are mounted to the suspension 105 by microactuator mounting shelf portions 18 formed on the base plate 12, positioned to straddle each gap in the base plate 12. Both ends of the microactuators 14 are attached to the mounting shelf portions 18 by epoxy 16. Positive and negative electrical connections from the PZT to the flexible wiring traces and / or plates of the suspension can be made by various methods. When actuated, the microactuators 14 extend or contract, thereby changing the length of the gap between the mounting shelf portions. This results in fine movement of the read / write head mounted on the tip of the suspension 105.

[0007] Figure 3 is a side cross-sectional view of the prior art PZT microactuator and assembly shown in Figure 2. The microactuator 14 comprises the PZT element 20 itself and an upper metallized layer 26 and a lower metallized layer 28 which are placed on the PZT and form electrodes that actuate the PZT. The PZT 14 is mounted by epoxy or solder 16 on both the left and right sides in the figure, spanning a gap.

[0008] In DSA suspensions, it is generally desirable to increase the stroke distance (or simply "stroke length") of the PZT per unit input voltage. In many previous DSA suspension designs, the PZT was mounted to a mounting plate. In such designs, the linear motion of the PZT is amplified by the length of the arm between the PZT's center of rotation and the read / write transducer head. Therefore, a small linear motion of the PZT causes the read / write head to move relatively large in the radial direction.

[0009] In other suspension designs, the PZT is mounted on or near a gimbal. Concurrent Patent Document 2, assigned to the assignee of the present invention, describes a DSA suspension, which is an example of a gimbal-mounted PZT. In a gimbal-mounted DSA suspension ("GSA" suspension), increasing the stroke length is particularly important because the arm length between the PZT and the read / write transducer head is not long. As the arm length decreases, the movement of the read / write head also decreases. Therefore, increasing the stroke length is particularly important in the design of a GSA. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 7459835 [Patent Document 2] U.S. Patent No. 8879210 [Overview of the project] [Problems that the invention aims to solve]

[0011] The inventors of this application have identified the cause of stroke length loss of a PZT in a conventional suspension to which a PZT microactuator is attached, and have developed a PZT microactuator structure and a method for manufacturing the structure that eliminate the cause of stroke length loss.

[0012] Figure 4A is a side cross-sectional view of a PZT microactuator 14 attached to the conventional suspension shown in Figure 2, showing the PZT in operation by a drive voltage applied to extend the PZT. The lower layer 22 of the PZT is partially constrained because it is bonded to the attached suspension 18. Therefore, the lower layer 22 does not extend as much in the linear direction as the upper layer 24. Since the upper layer 24 extends more than the lower layer 22, the PZT 14 bends downward and appears slightly convex when viewed from above. The resulting loss in linear stroke length is shown as δ1 in the figure.

[0013] Figure 4B shows the PZT microactuator 14 from Figure 4A in the state where the PZT is being operated by the drive voltage applied to contract the PZT. The lower layer 22 of the PZT is partially constrained because it is bonded to the attached suspension 18. Therefore, the lower layer 22 does not contract as linearly as the upper layer 24. Since the upper layer 24 contracts more than the lower layer 22, the PZT 14 bends upward and becomes slightly concave when viewed from above. The resulting loss in linear stroke length is shown as δ2 in the figure.

[0014] Thus, while it is desirable for the PZT to extend and contract only in a linear direction during operation, in conventional assembly, the PZT bends upward or downward, resulting in a loss of stroke length. Figure 5 shows the amount of effective linear stroke added or lost due to bending of the PZT, along with the associated equations. When the beam bends upward as shown in Figure 4A, a positive displacement δ occurs in the x-direction at the lower tip when the bending angle is small.

[0015] Figure 6 is a graph showing the stroke loss due to bending as a function of bending angle for three PZTs of different thicknesses. As shown in the figure, for a PZT with a length of 1.50 mm and a thickness of 45 μm, a positive x-displacement δ is generated by bending when the bending angle is less than 5 degrees. At this bending amount, a larger x-displacement is generated for the thicker beam than for the thinner beam. Similarly, when the PZT contracts due to the applied voltage, the right half of the PZT bends downward, and a negative x-displacement is generated at the lower end of the PZT bonded to the suspension. In other words, in conventional PZT mountings to suspensions, the linear displacement component δ due to bending is in the opposite direction to the movement of the PZT. Therefore, it is desirable to reduce or eliminate this delta, or reverse the sign of the delta, in order to actually increase the total amount of final linear extension or contraction. [Means for solving the problem]

[0016] The present invention relates to a PZT element having at least one high-rigidity suppression layer or suppression element bonded to at least one side or side opposite to the side or side to which the PZT is attached to the suspension, in order to reduce, eliminate, change the direction of, or otherwise control the bending of the actuated PZT. Although counterintuitive, the effective linear stroke distance achieved is actually increased by the addition of a high-rigidity layer that suppresses the stretching and contraction of the PZT, at least nominally. A PZT having a suppression layer according to the present invention can be used as a microactuator in a suspension for a hard disk drive, but can be used in other applications as well.

[0017] In a preferred embodiment, the action of the restraining layer actually changes the direction of bending. Therefore, in the case of a PZT whose lower surface is joined to a suspension, the presence of the restraining layer causes the piezoelectric element to bend in a direction such that its upper surface becomes substantially concave when the piezoelectric element is acted upon by a voltage that stretches it, and bends in a direction such that its upper surface becomes substantially convex when the piezoelectric element is acted upon by a voltage that contracts it. Thus, it acts to increase the effective linear stretch in the stretching mode and to increase the effective linear contraction in the contraction mode. In other words, the presence of the restraining layer increases the actual effective stroke length.

[0018] PZTs with a constraint layer can be manufactured by various methods. For example, the constraint layer may be laminated onto an existing PZT element, or one of the PZT element and the constraint layer may be formed on the other by an additive method. In such an additive method, a thin film PZT may be deposited on a substrate such as stainless steel (SST). The constraint layer can be formed from stainless steel, silicon, the same ceramic material as the ceramic material constituting the PZT element except that it is substantially unpoled (unexcited), or other relatively rigid material. If the constraint layer is non-conductive, the operating voltage or ground potential can be transmitted from the surface of the microactuator to the internal PZT element by passing multiple electrical vias made of columnar conductive material through the constraint layer.

[0019] The constraint layer may be larger than the PZT element (larger surface area), the same size as the PZT element, or smaller than the PZT element (smaller surface area). In a preferred embodiment, the constraint layer is smaller than the PZT element, so that the microactuator has a stepped surface structure, and the stepped shelf portion where electrical connections to the PZT element are made is not covered by the constraint layer. One advantage of such a structure having a shelf portion where electrical connections are made is that the height of the finished assembly with electrical connections can be lower than in a structure where the constraint layer covers the entire PZT. Lowering the height allows more hard drive platters and their suspensions to be stacked within a given platter stack height, thus providing the advantage of increasing the data storage capacity in a given volume of disk drive assembly.

[0020] Simulations showed that the microactuator configured according to the present invention exhibits improved stroke sensitivity and reduced oscillation mode gain and torsion mode gain. This allows for an increase in the bandwidth of the head positioning control loop, resulting in reduced data seek time and reduced susceptibility to vibration.

[0021] Another advantage of adding a restraint layer or restraint element to PZT according to the present invention is that in current hard disk drives, components including suspensions and PZT are generally very thin. The thickness of the microactuator used in the current DSA suspension design where PZT is attached to the mount plate is about 150 μm. In the DSA suspension design attached to the gimbal, PZT is even thinner and often has a thickness of less than 100 μm. Therefore, since the PZT material is very thin and brittle, it may easily crack during the manufacturing process of the PZT microactuator motor itself or in manufacturing / assembly including the automatic pick-and-place operation in the suspension assembly process. It is expected that the thickness of PZT in next-generation hard drives will be 75 μm or less, which may further exacerbate the problem. Such thin PZT is not only susceptible to damage during manufacturing / assembly, but there is also a concern that cracks and breakages may occur when the disk drive is subjected to shock (g-force). By adding the high-rigidity and elastic restraint layer according to the present invention, the strength and elasticity of PZT can be increased, and as a result, mechanical damage such as cracking of PZT can be suppressed during manufacturing / assembly and in shock events.

[0022] In another aspect of the present invention, the microactuator assembly is a multilayer PZT element and has a plurality of active PZT layers including one or more active PZT layers that function as a suppression layer having a tendency to counteract the action of the main active PZT layer.

[0023] The idea that adding one or more layers that resist the movement of the main PZT layer can increase the overall effective stroke length is counterintuitive. The idea that adding one or more active layers that act actively in the opposite direction to the main PZT layer can further increase the overall effective stroke length can be said to be even more counterintuitive. However, such results have been demonstrated by the present inventors.

[0024] Exemplary embodiments of the present invention will be described below with reference to the drawings. In the drawings, like parts are designated by like reference numerals. The drawings may not be to scale, and certain components may be shown in generalized or schematic form, and may be identified by commercial names for clarity and brevity.

Brief Description of the Drawings

[0025] [[ID=�]] [Figure 1] Top perspective view of a conventional magnetic hard disk drive. [Figure 2] Top view of the suspension of the disk drive of FIG. 1. [Figure 3] Side cross-sectional view showing a conventional PZT micro actuator and assembly of FIG. 2. [Figure 4A] Side cross-sectional view of a PZT micro actuator attached to the suspension according to the prior art of FIG. 2 in a state where a voltage for extending the PZT is applied. [Figure 4B] Side cross-sectional view of a PZT micro actuator attached to the suspension according to the prior art of FIG. 2 in a state where a voltage for contracting the PZT is applied. [Figure 5] Diagram and related formula of the amount of linear stroke added or lost by bending of PZT. [Figure 6] Graph showing stroke loss due to bending with respect to bending angle for three PZTs with different thicknesses. [Figure 7] Side cross-sectional view of PZT with a bonded constraint layer according to the present invention. [Figure 8A] Side cross-sectional view of the PZT micro actuator of FIG. 8 in a state where the PZT is extended by applying a voltage. [Figure 8B] ]>Side cross-sectional view of the PZT micro actuator of FIG. 8 in a state where the PZT is contracted by applying a voltage. [Figure 9] Graph showing the stroke length per unit input voltage (unit: nm / V) with respect to the thickness of the constraint layer for a PZT with a thickness of 130 μm. [Figure 10]A side view of a PZT with a restraining layer bonded to it, according to the present invention. [Figure 11] Figure 10 shows a graph illustrating the stroke length as a function of the PZT thickness, where the combined thickness of the PZT and the suppression layer is constant at 130 μm. [Figure 12] A graph showing the GDA stroke sensitivity as a function of the thickness of the restraint layer in a suspension equipped with PZT having stainless steel restraint layers of different thicknesses. [Figure 13A] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13B] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13C] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13D] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13E] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13F] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13G] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 13H] A diagram illustrating one manufacturing process capable of producing PZT having a restraining layer according to the present invention. [Figure 14A] A perspective view of a GSA suspension into which the thin-film PZT microactuator motor according to the present invention is incorporated. [Figure 14B] A perspective view of a GSA suspension into which the thin-film PZT microactuator motor according to the present invention is incorporated. [Figure 15] Figure 14B shows a cross-sectional view of the microactuator region along the line B-B'. [Figure 16] A graph showing the stroke sensitivity of the microactuator in Figure 15 against the SST substrate thickness, based on simulations. [Figure 17A] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 17B] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 17C] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 17D] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 17E] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 17F] A diagram illustrating the process for manufacturing a thin-film PZT structure having a stainless steel substrate according to the present invention. [Figure 18] A top view of a thin-film PZT structure having a silicon substrate according to the present invention. [Figure 19] Figure 18 shows a cross-sectional view of the thin-film PZT structure along the line A-A'. [Figure 20] A graph showing the stroke sensitivity of the microactuator in Figure 19 against the silicon substrate thickness, based on simulations. [Figure 21A] Figure 18 shows the process for manufacturing the thin-film PZT structure. [Figure 21B] Figure 18 shows the process for manufacturing the thin-film PZT structure. [Figure 21C] Figure 18 shows the process for manufacturing the thin-film PZT structure. [Figure 21D] Figure 18 shows the process for manufacturing the thin-film PZT structure. [Figure 21E] Figure 18 shows the process for manufacturing the thin-film PZT structure. [Figure 22] A top view of a thin-film PZT having a substrate and side vias according to one embodiment of the present invention. [Figure 23] Figure 22 shows a cross-sectional view of the microactuator along the line A-A'. [Figure 24] A cross-sectional view of a PZT microactuator according to an additional embodiment of the present invention. [Figure 25] Figure 24 shows a perspective view of a GSA suspension with a pair of PZT microactuators. [Figure 26] Figure 25 shows a cross-sectional view of the GAS suspension along line A-A'. [Figure 27] Graph of the PZT frequency response function of the suspension in Figure 25, based on simulation. [Figure 28A] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28B] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28C] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28D] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28E] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28F] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28G] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28H] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28I] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 28J] Figure 24 shows an exemplary process for manufacturing a PZT microactuator assembly. [Figure 29] Side cross-sectional view of a multilayer PZT microactuator assembly according to an additional embodiment of the present invention, wherein the PZT is a multilayer PZT. [Figure 30]Side cross-sectional view of a multilayer PZT microactuator assembly according to an additional embodiment of the present invention, in which an extra-thick electrode functions as a suppression layer. [Figure 31] A cross-sectional view of an embodiment in which the suppression layer of a microactuator assembly has one or more active PZT layers that tend to act in the opposite direction to the main active PZT layer. [Figure 32] Figure 31 shows the polling process of the microactuator assembly and the resulting polarization directions of various layers of the active PZT material. [Figure 33] Figure 31 is an exploded view of the microactuator assembly, conceptually illustrating the electrical connections. [Figure 34] A graph showing the stroke sensitivity (nm / V) of a microactuator having one or more active suppression layers, based on simulations of various structures. [Figure 35] A cross-sectional view showing another embodiment in which a microactuator assembly has multiple active PZT layers, conceptually illustrating the polling process and the resulting polarization direction. [Figure 36] An isometric view of one embodiment of a single-layer microactuator PZT assembly according to one embodiment of the present disclosure. [Figure 37] Figure 36 shows a cross-sectional view along the line C-C'. [Figure 38A] A plan view of a suspension gimbal having the single-layer microactuator PZT assembly shown in Figure 36, according to one embodiment of the present disclosure. [Figure 38B] A cross-sectional view taken along line D-D' in Figure 38A, according to one embodiment of the present disclosure. [Figure 39] Graph of the PZT frequency response function of the suspension in Figure 38, based on simulation. [Figure 40] A plan view of a gimbal-mounted two-stage suspension having the single-layer microactuator PZT assembly shown in Figure 36, according to an alternative embodiment of the present disclosure. [Figure 41] Graph of the PZT frequency response function of the suspension in Figure 40, based on simulation. [Figure 42] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 43] A cross-sectional view along the line E-E' in Figure 42, according to one embodiment of the present disclosure. [Figure 44A] Figure 37 shows a perspective view of the suspension gimbal with the single-layer microactuator PZT assembly rotated. [Figure 44B] A cross-sectional view along the line F-F' in Figure 44A, according to one embodiment of the present disclosure. [Figure 44C] A cross-sectional view along the line G-G' in Figure 44A, according to one embodiment of the present disclosure. [Figure 45A] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 45B] A cross-sectional view along the line H-H' in Figure 45A, according to one embodiment of the present disclosure. [Figure 45C] Graph of the PZT frequency response function of the suspension in Figure 45A, based on simulation. [Figure 46A] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 46B] A cross-sectional view along the line J-J' in Figure 46A, according to one embodiment of the present disclosure. [Figure 46C] Graph of the PZT frequency response function of the suspension in Figure 46A, based on simulation. [Figure 47A] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 47B] A cross-sectional view along the line K-K' in Figure 47A, according to one embodiment of the present disclosure. [Figure 47C] Graph of the PZT frequency response function of the suspension in Figure 47A, based on simulation. [Figure 48A]A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 48B] A cross-sectional view along the line L-L' in Figure 48A, according to one embodiment of the present disclosure. [Figure 48C] Graph of the PZT frequency response function of the suspension in Figure 48A, based on simulation. [Figure 49A] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 49B] A cross-sectional view along the line M-M' in Figure 49A, according to one embodiment of the present disclosure. [Figure 49C] Graph of the PZT frequency response function of the suspension in Figure 49A, based on simulation. [Figure 50A] A plan view of a suspension gimbal having a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure. [Figure 50B] A cross-sectional view along the line N-N' in Figure 50A, according to one embodiment of the present disclosure. [Figure 50C] Graph of the PZT frequency response function of the suspension in Figure 50A, based on simulation. [Figure 51] A cross-sectional view of one embodiment of a single-layer microactuator PZT assembly according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0026] Figure 7 is a side cross-sectional view of a PZT microactuator assembly 114 to which a restraining layer 130 is bonded, according to one embodiment of the present invention. Referring to the orientation shown in this figure, the side of the PZT that is bonded to the suspension is referred to as the lower surface 129 of the PZT 114, and the side of the PZT opposite to the side to which it is bonded to the suspension is referred to as the upper surface 127 of the PZT 114. According to the present invention, one or more restraining layers or restraining elements 130 are bonded to the upper surface 127 of the microactuator PZT element 120. The restraining layer 130 is preferably made of a highly rigid elastic material such as stainless steel, and is preferably directly bonded to the upper surface 127 of the PZT element 120 having an upper electrode 126, or the SST material itself may function as the upper electrode, thereby eliminating the need for a metal coating on the upper surface. The restraining layer 130 has rigidity that can significantly reduce, eliminate, or reverse the bending of the PZT during operation. The SST layer 130 preferably has a layer 131 of gold or other contact metal to ensure good electrical connection to the SST.

[0027] Alternatively, instead of forming the constraint layer 130 from stainless steel, it may be a layer of the same ceramic material as the piezoelectric layer 120, but not excited (not poling or polarization treated), and may be incorporated into the assembly by bonding or deposition. The fact that the ceramic material is not polarization treated means that it exhibits a significantly lower piezoelectric effect than the poling treated ceramic forming the piezoelectric layer 120, for example, less than 10%. Such an assembly, with electrodes / poling treated PZT / electrodes / unpoling treated PZT stacked from bottom to top, is easier to manufacture than an electrode / PZT / electrode / SST stack.

[0028] In the following explanation, for the sake of simplicity, the illustration and description of the upper electrode 126 and lower electrode 128 may be omitted, but please note that almost all PZT microactuators have at least some kind of upper and lower electrode.

[0029] As described in U.S. Patent No. 8,395,866 granted to Schreiber et al., owned by the assignee of this application, a layer of copper or nickel may be deposited on the SST layer 130 before the gold layer 131 is applied to enhance the adhesion of gold to the SST. The aforementioned patent relates to the electrodeposition of other metals onto stainless steel and is incorporated herein by reference. Similarly, electrodes 126, 128 may also include a combination of nickel and / or chromium with gold (NiCr / Au).

[0030] 124–167 (Figure 5). In one exemplary embodiment based on simulation, the thickness of each layer was as follows: 130 PZT 3μm 126, 128, 131 NiCr / Au 0.5μm The length of the thin film PZT was 1.20 mm, the width of the PZT junctions at both ends was 0.15 mm, and the piezoelectric coefficient d31 was 250 pm / V. In some embodiments, the thickness of the SST layer was set to 12 micrometers or more to ensure adequate support.

[0031] According to the simulation, the stroke sensitivity of the DSA suspension in the above example was 26.1 nm / V. In contrast, the stroke sensitivity of bulk PZT (d31=320 pm / V) with the same shape but a thickness of 45 μm was generally only 7.2 nm / V.

[0032] The ratio of the PZT layer thickness to the SST layer thickness was large, at 1:1, or 1.25:1 or higher. When the ratio of the constraint layer thickness to the PZT thickness reached approximately 1:25, the improvement in stroke sensitivity due to the constraint layer began to decline, indicating that this ratio represents the limit of the PZT constraint layer thickness.

[0033] Figure 8A shows a side cross-sectional view of the PZT microactuator 114 of Figure 7 in a state where voltage is applied to the PZT and it is stretched. The PZT stroke consists of two vectors. One is the pure stretch stroke δE, and the other is the stretch contribution δ1 due to the constraint layer. Instead of bending downward as in a PZT without a constraint layer, the right tip of the PZT bends upward because a constraint layer is provided, generating the stretch contribution δ1. The total stroke length is δE + δ1. Therefore, in the stretch mode, the PZT becomes slightly concave when viewed from above, that is, the upper surface of the PZT becomes slightly concave, and the bending direction is opposite to that of the conventional bending shown in Figure 4. For this reason, bending in the present invention does not reduce the effective stroke length, but rather increases the effective stroke length.

[0034] Figure 8B is a side cross-sectional view of the PZT microactuator shown in Figure 7, in a state where voltage is applied to the PZT114 to cause it to contract. The PZT stroke consists of two vectors. One is the pure contraction stroke -|δC|, and the other is the contraction contribution δ2 due to the constraining layer. Unlike a PZT without a constraining layer that bends upward, the right tip of the PZT bends downward due to the presence of the constraining layer, generating the contraction contribution δ2. The total stroke length is -[δC+δ2]. Therefore, in contraction mode, the PZT becomes slightly convex when viewed from above, that is, the upper surface of the PZT becomes slightly convex, and the bending direction is opposite to that of the conventional bending shown in Figure 4. For this reason, the bending in the present invention does not reduce the effective stroke length, but rather increases it.

[0035] Adding the restraining layer 130 to the PZT microactuator 114 does not significantly affect the stroke length if the PZT 114 is not restrained or bonded to anything other than the restraining layer 130. However, if the lower end of the PZT 114 is bonded to the suspension 18 as shown in Figure 4, the restraining layer actually acts to slightly increase the stroke length. The Young's modulus of stainless steel is approximately 190-210 GPa. Preferably, the Young's modulus of the restraining layer material is greater than 50 GPa, more preferably greater than 100 GPa, and even more preferably greater than 150 GPa.

[0036] Figure 9 is a graph showing the stroke length per unit input voltage (in nm / V) as a function of the constraint layer thickness for a 130 μm thick PZT114 with a stainless steel constraint layer 130 bonded to it, based on simulations. The total stroke length increases by adding SST suppression layers of 20 μm, 40 μm, and 60 μm thicknesses to the top surface of the PZT. Thus, the total stroke length actually increased by adding the constraint layer.

[0037] Furthermore, the total thickness of the PZT and the constraint layer can be kept constant, and the optimal thickness of the constraint layer can be determined. Figure 10 is a side view showing a combination of a PZT and a constraint layer bonded to the PZT, according to the present invention, where the total thickness is kept constant at 130 μm. Figure 11 is a simulation-based graph showing the stroke length as a function of the PZT thickness in the case where the total thickness of the PZT and the constraint layer is constant at 130 μm, for the PZT in Figure 10. Without a constraint layer, the stroke length of a 130 μm thick PZT is approximately 14.5 nm / V. When the thickness of the constraint layer 130 is 65 μm and the thickness of the PZT is 65 μm, the stroke length of the PZT is approximately 20 nm / V. In other words, by adding a constraint layer, the effective stroke length actually increased by approximately 35%.

[0038] Figure 12 is a graph showing the GDA stroke sensitivity as a function of the constraint layer thickness in a GDA suspension with the microactuator shown in Figure 7, based on simulations. The thickness of the PZT element is 45 μm, and the thickness of the stainless steel constraint layer formed on top of it is different. As can be seen from this graph, a 30 μm thick constraint layer increased the GDA stroke sensitivity from 9 nm / V to slightly over 14.5 μm. In other words, the stroke length increased by more than 50%.

[0039] Figures 13A to 13H show one manufacturing process capable of producing a PZT microactuator assembly having a constraint layer according to the present invention. This method is an example of an additive method for depositing PZT material onto a substrate that will serve as the constraint layer. As shown in Figure 13A, the process begins with a first substrate 140. In Figure 13B, a first UV / thermal tape 142 is applied to the substrate. In Figure 13C, a pre-formed SST layer 130 is added to the tape. In Figure 13D, an electrode layer 126 is deposited on the SST by sputtering or other well-known deposition processes. In Figure 13E, a PZT layer 120 is formed on the electrode layer by the sol-gel method or other well-known method. In Figure 13F, a second electrode 128 is deposited on the exposed surface of the PZT by sputtering or the like. In Figure 13G, the SST layer 130 is separated from the tape, and the product is placed upside down on the second tape 143 and the second substrate 141. In Figure 13H, the product is die-cut by mechanical sawing or laser cutting to separate it into individual microactuators 114. This process forms a microactuator 114 in which a PZT element 120 equipped with electrodes is directly bonded to the SST suppression layer 130, without the interposition of other materials such as organic materials (e.g., polyimide) that reduce the suppression effect of the suppression layer. The electrode layer material is Au, Ni, Cr and / or Cu, etc. The Young's modulus of Au is approximately 79 GPa, the Young's modulus of Cu is approximately 117 GPa, the Young's modulus of Ni is approximately 200, and the Young's modulus of Cr is approximately 278. Preferably, there is no intermediate layer between the SST suppression layer 130 and the PZT element 120 having a Young's modulus of less than 20 GPa, a Young's modulus significantly smaller than the Young's modulus of the suppression layer, or a Young's modulus less than half the Young's modulus of the suppression layer.

[0040] While it is possible to manufacture the product by other methods, such as directly bonding the inhibitory layer to the PZT surface with an adhesive like epoxy, the method shown in Figures 13A to 13G is currently considered the preferred method.

[0041] The SST suppression layer 130 functions as a substrate for the PZT layer 120 both during the additive manufacturing process and in the finished product. For this reason, the suppression layer 130 is sometimes referred to as the substrate.

[0042] Figures 14A and 14B are perspective views of a gimbal-mounted two-stage actuation (GSA) suspension 150 to which a thin-film PZT microactuator motor 114 according to the present invention is assembled. In a GSA suspension, the PZT acts directly on the gimbal region of the suspension, which is mounted on a trace gimbal having a gimbal assembly and holds a read / write head slider 164. Figure 14A shows the suspension 150 before the PZT microactuator assembly 114 is mounted. The two microactuators 114 are bonded to a tongue-shaped portion 154 to which the tips of the microactuators 114 are joined, and to a portion of the trace gimbal 156 to which the base ends of the microactuators 114 are joined, straddling a gap 170 between them. Figure 14B shows the suspension 150 after the PZT microactuator 114 is mounted. The microactuator assembly 114 extends or contracts when actuated, thereby changing the length of the gap 170 between the tongue-shaped portion 154 and the portion of the trace gimbal 156. This allows for precise positioning and movement of the head slider 164, which holds the read / write transducer.

[0043] Figure 15 is a cross-sectional view taken along line B-B' in Figure 14B. The GSA suspension 150 has a trace gimbal 152 including a stainless steel layer, an insulator 157 such as polyimide, and a layer of signal transmission traces 158 made of Cu or similar material covered with a protective metal 159 such as Au or a Ni / Au combination. The tip of the microactuator 114 is attached by a conductive adhesive 162 to a stainless steel tongue-shaped portion 154 extending from the gimbal region. The adhesive 162 is an epoxy or similar material containing Ag particles to be conductive. The base end of the microactuator 114 is attached to a stainless steel mounting portion 156 by a non-conductive adhesive 161 such as a non-conductive epoxy. The electrical connection of the drive voltage is provided by the conductive adhesive 160. The conductive adhesive 160 extends from the gold-plated copper contact pad 158 to the top surface of the PZT microactuator 114, and in more detail in this example, to the SST layer 130 that constitutes the upper electrode of the microactuator. The thickness of the SST substrate may be varied to some extent without compromising the advantages of the disclosed thin-film PZT structure. Figure 16 is a graph showing the stroke sensitivity as a function of the SST constraint layer thickness in Figure 15, based on simulations. According to the simulations, the stroke sensitivity of the thin-film PZT with a 40 μm thick SST constraint layer was 20 nm / V, which was approximately three times that of the bulk PZT with a thickness of 45 μm. However, the 45 μm thick SST constraint layer provides better protection for the thin-film PZT microactuator.

[0044] Figures 17A-17F show an alternative process for manufacturing a thin-film PZT structure having an SST-constrained layer according to the present invention. As shown in Figure 17A, the process begins with a silicon substrate 144, rather than a substrate 140 and tape 142 as in Figure 18B. In Figure 17B, the SST layer 130 is bonded to the silicon. Otherwise, this process is substantially the same as the process in Figures 13C-13H, except that the assembly is turned over and the silicon substrate is removed, as shown in Figure 17E. Furthermore, this figure clearly shows that a NiCr / Au layer 131, which was not explicitly shown in Figure 13E, is added at the end.

[0045] As mentioned above, different types of restraint layers can be used for different applications. Other highly rigid materials, whether conductive or nonconductive, can also be used as restraint layers or substrates. For example, the material of the restraint layer may be silicon. Figure 18 is a plan view of a thin-film PZT structure having a silicon restraint layer according to one embodiment of the present invention. Figure 19 is a cross-sectional view taken along line A-A' of the microactuator in Figure 18. Since the silicon restraint layer 230 is nonconductive, vias 232 are provided to transmit the PZT drive voltage from a conductive upper layer 234, such as Au, on the silicon 230 to a metallized electrode 126 on the PZT element 120. The formed vias may be filled with a conductive metal, as disclosed in U.S. Patent No. 7,781,679 granted to Schreiber et al. The above patent is owned by the assignee of the present invention and is incorporated herein by reference with respect to conductive vias and methods for forming conductive vias.

[0046] Figure 20 is a graph showing the stroke sensitivity of the microactuator in Figure 19 against silicon substrate thickness, based on simulations. As shown in the graph, the stroke sensitivity for a 3 μm thick thin-film PZT and a 20 μm thick silicon substrate is 31.5 nm / V. This is more than four times the stroke sensitivity of the design using a 45 μm thick bulk PZT. The silicon substrate also contributes to improving the reliability of the thin-film PZT.

[0047] Figures 21A to 21E show the process for manufacturing the thin-film PZT structure shown in Figure 18. This process begins with a silicon substrate having holes or vias 232 formed by laser drilling or the like, as shown in Figures 21A and 21B. In Figure 21C, a NiCr / Au layer is added to the silicon substrate 230 to form the upper electrode 126. NiCr / Au is also used to fill the holes, forming electrical vias 232. More generally, other conductive materials may be used to fill the vias. In Figure 22D, the PZT thin film 120 is deposited by a sol-gel method or the like, and another layer of NiCr / Au is added to form the lower electrode 128. In Figure 22E, the material is turned over, and the final NiCr / Au layer 131 is added. Layers 131 and 126 are electrically connected by vias 232 so that the voltage (or ground potential) applied to the conductive gold layer 131 is transmitted to the PZT element 126. The manufacturing process for thin-film PZT microactuators using silicon substrates is simpler than the manufacturing process for thin-film PZT using SST substrates.

[0048] In an alternative embodiment, instead of a central via in the silicon substrate, one or more vias are formed at the edges of the silicon. Thus, after the final dicing, semicircles are formed at both ends of the silicon. Figure 22 is a top view of a thin-film PZT microactuator comprising silicon or other non-conductive constraint layer 330 having a conductive upper layer 231 such as a metallization layer on the upper side, and side vias 234, 236 electrically connecting the upper layer 231 to an upper electrode 126. Figure 23 is a cross-sectional view of the PZT of Figure 22 along the line A-A'. The manufacturing process of this embodiment is the same as the manufacturing processes of Figures 21A to 21E, except as described above.

[0049] The constraint layer may be larger than the PZT element (larger surface area), the same size as the PZT element, or smaller than the PZT element (smaller surface area). Figure 24 is a side cross-sectional view showing a PZT microactuator assembly 414 having a stepped surface structure with a step 434 and an exposed shelf portion 422 not covered by the restraining layer 430, because the constraint layer 430 is smaller than the PZT element 420. Electrical connections to the PZT element 420 are made at the shelf portion 422. One advantage of the above structure with a step where electrical connections are made is that the height of the finished assembly with electrical connections can be lower than when the restraining layer 430 covers the entire PZT 420. Lowering the height allows more hard drive platters and their suspensions to be stacked within a given platter stack height, thus increasing the data storage capacity in a given volume of the disk drive assembly. The restraining layer 430 is assumed to cover an area of ​​more than 50% but less than 95% of the upper surface of the PZT element 420 in order to enable electrical connections on the shelf portion 422.

[0050] Simulations showed that the microactuator configured according to the present invention exhibits improved stroke sensitivity and reduced oscillation mode gain and torsion mode gain. This allows for an increase in the bandwidth of the head positioning control loop, resulting in reduced data seek time and reduced susceptibility to vibration.

[0051] Figure 25 is a perspective view of the GSA suspension having a pair of PZT microactuators 414 as shown in Figure 24. Figure 26 is a cross-sectional view of the GAS suspension in Figure 25 along the line A-A'. In this embodiment, the conductive adhesive 460, such as conductive epoxy, is not placed on top of the suppression layer 430. Instead, the conductive epoxy 460 is located on the upper shelf portion 422 of the PZT element 420, and its surface provides electrical connections to the PZT 420 and the entire microactuator assembly 414. As shown, the highest part of the electrical connection formed by the conductive epoxy 460 is lower than the top surface of the SST suppression layer 430. More generally, regardless of whether the electrical connection is made by conductive adhesive, wires joined by ultrasonic thermocompression bonding, soldering, or other methods, the electrical connection portion 461 of the microactuator assembly 414 is located no higher than, or lower than, the top of the microactuator 414. This allows the microactuator assembly 414 with electrical connections to be made as thin as possible, resulting in a higher density stacking of data storage disk platters within the platter stack of the disk drive assembly.

[0052] This figure also clearly shows the gold layer 469 on the stainless steel portion 154 of the trace gimbal to which the microactuator 414 is attached. The gold layer 469 provides corrosion resistance and enhances conductivity to the SST.

[0053] In this embodiment, as in all other embodiments, the constraint layer, more generally the upper surface of the PZT microactuator assembly, is typically not bonded to anything other than electrical connections.

[0054] Figure 27 is a graph showing the frequency response of the PZT frequency response function of the suspension in Figure 26, based on simulation. In this suspension, the oscillation mode gain and torsion mode gain were reduced compared to the simulation without the constraint layer 430. This allows for an increase in the bandwidth of the head positioning control loop, resulting in reduced data seek time and reduced susceptibility to vibration.

[0055] Figures 28A to 28J show the process for manufacturing the thin-film PZT assembly 114 shown in Figure 24. In Figure 28A, the bulk PZT wafer 420 is placed on the transfer tape 422. In Figure 28B, the upper electrode layer 426 is formed by sputtering and / or electrodeposition. In Figure 28C, the mask 436 is placed on a portion of the upper electrode 426. In Figure 28D, conductive epoxy 432 is applied. In Figure 28E, the stainless steel layer that will become the constraint layer 430 is applied on the epoxy and then cured. In Figure 27F, the mask 436 is removed. In Figure 27G, the assembly is turned over and placed on the second transfer tape 443. In Figure 27H, the lower electrode layer 428 is formed by sputtering and / or electrodeposition. Next, the PZT element 420 is subjected to polarization treatment. In Figure 27I, the assembly is turned over again and placed on the third transfer tape 444. In Figure 28J, the assembly is cut into individual pieces to form the completed PZT microactuator assembly 414.

[0056] Figure 29 is a side cross-sectional view of a multilayer PZT assembly 514 according to an additional embodiment of the present invention. This assembly includes a multilayer PZT element 520, a first electrode 526 surrounding the element, a second electrode 528, and a constraint layer 530 bonded to the PZT element 520 by conductive epoxy 532. A two-layer PZT element is shown. More generally, the element may be an n-layer PZT element.

[0057] Figure 30 is a side cross-sectional view of a multilayer PZT microactuator assembly 614 according to an additional embodiment of the present invention, in which an extra-thick electrode functions as a suppression layer. In this embodiment, the PZT element 620 has an upper electrode 626 and a lower electrode 628. The upper electrode 626 has a thinner first portion 622 that forms a shelf and a thicker second portion 630 that is responsible for most of the suppression function. A step 634 is located at the transition from the thinner first portion 622 to the thicker second portion 630. The second electrode 626 can be applied to the PZT element 620 by a deposition process that includes a masking step to form the step 634, or by a deposition process that selectively removes material to form the step. Alternatively, the second electrode 626 may be a component of a conductive material such as an SST that is formed separately and then bonded to the PZT element 620. Therefore, the material of the upper electrode 626 may be the same as or different from the material of the lower electrode 628. The thicker second portion 630 may be at least 50% thicker than the thinner portion 622 and / or the second electrode 628. Alternatively, the thicker second portion 630 may be at least twice as thick as the thinner portion 622 and / or the second electrode 628. Similar to the embodiments shown in Figures 24-26, the electrical connection can be provided on the shelf portion formed by the thinner portion 622 and can be formed so as not to exceed the height of the upper surface of the thicker portion 630 that forms the suppression layer.

[0058] The scope of the present invention is not strictly limited to the embodiments described herein. Those skilled in the art can make various modifications based on the teachings herein. For example, the restraint layer does not have to be stainless steel, but may be other relatively rigid elastic material. The restraint layer does not have to be a single layer of one material, but may consist of multiple layers of different materials. The restraint layer may cover the entire surface or substantially the entire top surface. However, the restraint layer may cover less than the entire surface, for example, more than 90%, 75%, 50%, or 25% of the top surface area. In embodiments with steps, it is assumed that the restraint layer covers less than 95% of the top surface of the microactuator. The restraint layer does not have to be a single, integral layer, but may have multiple parts, such as multiple restraint pieces arranged side by side on the top surface of the PZT. Such restraint pieces may extend in the direction of extension / contraction or in a direction perpendicular thereto. In one embodiment, the restraining layer includes two restraining pieces made of stainless steel or other material bonded to the upper surface of the PZT, the size, position and bonding of the two restraining pieces being substantially symmetrical with the mounting areas of two mounting shelf sections to which the lower surface of the PZT is bonded. When the overall stiffness added by the upper restraining layer of the element substantially matches the overall stiffness added to the lower part of the element by bonding to the suspension, and the bonded areas are substantially symmetrical with respect to each other, the resulting substantial bending is zero or near zero. For this reason, a PZT microactuator mounted and implemented on a suspension bends very little during operation.

[0059] In any embodiment described or suggested herein, the constraint layer may be selected to reduce the bending that would occur during operation if there were no constraint layer, to eliminate bending of the PZT as much as possible, or to reverse the sign of the PZT bending. In applications where the PZT is used as a microactuator in a hard disk drive, it is often desirable to reverse the sign of the bending by using a constraint layer, as illustrated and described in the above exemplary examples, because this configuration allows for a longer effective stroke length. However, there are also PZT applications where reversing the sign is undesirable. Therefore, generally speaking, the present invention can be used to control both the direction and amount of bending of the PZT, regardless of how the PZT is mounted or attached to other components in a particular application. By using a constraint layer, depending on the selected application and parameters, the bending may be reduced to less than 50% or less than 25% of the bending that would occur if there were no constraint layer, or the sign of the bending may be reversed. If the sign is reversed, a PZT that is joined at or near the end of its lower surface and has an inhibitory layer on the upper side will bend so that its upper surface becomes concave in the stretching or expansion mode. In other words, it will not become convex like a similar PZT without an inhibitory layer. Similarly, in the contraction mode, the PZT will become convex, rather than concave like a similar PZT without an inhibitory layer.

[0060] In certain applications, PZT elements may have pre-stressed for various reasons, causing them to bend in a predetermined direction even when not operated by voltage. That is, they may already be concave or convex. Naturally, such pre-stressed PZTs can also be used as microactuators in this invention. In this case, the PZT may not bend into a substantially or completely concave or substantially or completely convex shape. For example, if a PZT is pre-stressed and already concave, when operated by a positive operating voltage, the element will bend into a more concave shape. Conversely, when operated by a negative operating voltage, it will bend into a less concave shape, nominally becoming flat or convex. Unless otherwise defined, the terms "concave" and "convex" should be understood as relative terms, not absolute terms.

[0061] Figure 31 is a cross-sectional view of one embodiment of a multilayer microactuator PZT assembly 3100. The suppression layer of this microactuator assembly includes one or more active PZT layers 3130, 3140 which tend to act in the opposite direction to the main active PZT layer 3120. The main active PZT layer 3120 is located near the surface of the suspension to which the microactuator 3100 is bonded. The PZT suppression layers 3130, 3140 are sometimes referred to as “restraining layers” or “counter-layers” because they restrain and actively oppose the operation of the main PZT layer 3120.

[0062] The PZT layers 3120, 3130, and 3140 are arranged in a flat, stacked relationship with respect to each other. The main PZT layer 3120 has an active PZT region 3121 and inactive PZT regions 3122 and 3123. The active PZT region 3121 is polarized when an electric field is applied during polling, and therefore expands or contracts when an electric field is applied during device operation. The inactive PZT regions 3122 and 3123 do not act piezoelectrically significantly because no significant electric field is applied during polling and operation. The element comprises a first electrode or lower electrode 3124, a second electrode or upper electrode 3126 for the active PZT region, a third electrode 3132 having an end 3128 and extending between the first active restraint layer 3130 and the second active restraint layer 3140, and surrounding the end of the PZT, and a fourth electrode 3142 located above the second active restraint layer 3140 and having a surrounding portion 3143 that surrounds both the side and bottom surfaces of the element. The element is bonded to the suspension by a conductive adhesive such as conductive epoxy 3160. The conductive epoxy 3160 mechanically and electrically bonds the electrode 3142 to a drive voltage electrical contact pad 158 that supplies the microactuator drive voltage. The element is also bonded to the suspension by conductive epoxy 3162, which mechanically and electrically bonds the electrodes 3124 and 3128 to the ground portion 154 of the suspension.

[0063] To understand the operation of the element, it is necessary to understand how the element is polled. Figure 32 shows the polling process of the element in Figure 31. This figure shows the resulting polarization directions of multiple layers of the active PZT material. Three voltages are applied: a positive voltage (Vp+) is applied to electrode 3124, a negative voltage (Vp-) is applied to electrode 3128, and ground is applied to electrode 3142. The arrows in the figure indicate the resulting polarization directions of the active PZT layers 3120, 3130, and 3140.

[0064] Referring again to Figure 31, this figure shows how element 3100 is connected in this exemplary embodiment. Conductive epoxy 3162 electrically connects electrodes 3124 and 3132 by filling the gap between them, thereby changing the element from a 3-pole element during polling to a 2-pole element during operation. Electrode connection can also be achieved by means other than conductive epoxy 3162 using other known electrical connection methods, but by utilizing the conductive epoxy 3162 used for bonding the element to the suspension assembly, the connection function can be obtained without requiring a separate connection process.

[0065] When a voltage is applied to electrode 3142, and the main PZT layer 3120 is stretched in the x-direction (left-right direction) as shown in the figure due to the expansion of the active region 3121, the active PZT constraint layers 3130 and 3140 contract in the x-direction. In other words, the two constraint layers 3130 and 3140 tend to act in opposition to the main PZT layer 3120, i.e., in the opposite direction.

[0066] More specifically, when the element is polled as shown in Figure 32 and electrically connected as shown in Figure 31, the element operates as follows: With electrode 3124 grounded, the following reaction occurs due to the positive element operating voltage applied to the electrical contact pad 158 and electrode 3142: The polarity of the operating voltage applied to the main PZT layer 3120 is opposite to the polarity during the polling process. Therefore, the main PZT layer 3120 contracts in the z direction and, consequently, expands in the x direction. On the other hand, the polarity of this operating voltage is the same as the polarity applied to the two constraint layers 3130 and 3140 during the polling process. Therefore, these PZT layers expand in the z direction and, consequently, contract in the x direction. Thus, the two constraint layers 3130 and 3140 tend to contract, and the main PZT layer 3120 tends to expand in the corresponding direction.

[0067] The effect of the restraining layer acting in the opposite direction to the main PZT layer is similar to that of a passive restraining layer such as restraining layer 130 in Figure 10, and similar restraining layers 230, 330, 430, 530, and 630 in the other embodiments described above. The action of the active PZT restraining layer reduces the bending caused by the main PZT layer and its assembly (joining) to the suspension, and can even reverse the sign of the bending. In either case, the substantial displacement brought about by the attached microactuator increases.

[0068] Figure 33 is an exploded view of the microactuator assembly shown in Figure 31, conceptually illustrating the electrical connections. Optional features shown in Figure 33, though not shown in Figures 31 and 32, include the patterning 3133 of electrode 3132 and the voltage suppressor 3144 associated with electrode 3142, the functions of which will be discussed later.

[0069] The reasons for the desire to make the microactuator assembly thin are as follows: (1) The mass of the gimbal or its vicinity in the suspension, especially in DSA suspensions (sometimes called GSA suspensions) that use a gimbal, can be reduced, resulting in increased lift-off force, measured as g-force, i.e., resistance to shock. (2) Windage losses can be reduced. (3) The stacking density of the head stacking assembly can be increased, allowing more data to be stored in the same volume of disk drive stacking assembly space. For these reasons, it is desirable to make the PZT constraint layer very thin. However, the thinner the PZT constraint layer, the higher the electric field strength of the entire layer during operation, and excessively high electric field strength makes passivity more likely during operation. Therefore, nominally, the thickness of the main PZT layer and the constraint PZT layer should be the same.

[0070] One method for thinning a constrained PZT layer without causing negativity is to reduce the overall electric field strength of the constrained layers by one or more means without significantly reducing the electric field of the main PZT layer. A first means to achieve this objective is to pattern one or more electrodes that are operationally associated with one of the active PZT constrained layers but not operationally associated with the main PZT layer. Patterning can be done by adding holes 3133 to electrode 3132 or by adding other electrical voids. The patterning may be a mesh pattern such as a grid of parallel or intersecting conductors, which may have electrical voids in between. By reducing the proportion of the conductive area in the planar electrode 3132, the electric field strength of the constrained layers 3130 and 3140 can be effectively reduced without reducing the electric field strength of the main PZT layer 3120.

[0071] A second method is to increase the coercivity of the constraining layer to make it less susceptible to negative deformation. Coercivity (or simply "coercivity" when referring to piezoelectric materials) is a measure of the electric field strength required to negatively deform a piezoelectric material. By making the coercivity of the constraining layers 3130 and 3140 higher than that of the main PZT layer 3120, these constraining layers can be made thinner while avoiding the risk of negative deformation occurring when the same operating voltage as the main PZT layer is applied. The constraining layers 3130 and 3140 can also be formed to have higher coercivity at the expense of some loss of d31 stroke length or other desirable characteristics by using different or slightly different piezoelectric materials or by other treatments.

[0072] Another method involves using a voltage suppressor, such as a voltage divider resistor network, diodes, voltage regulators, or various functionally similar well-known devices, to reduce the effective voltage applied to the drive electrodes associated with the confinement layer. In the figure, a typical voltage suppressor 3144 reduces the voltage received by electrode 3142, thereby reducing the electric field strength experienced by the confinement layer 3140, but not the electric field strength experienced by the main PZT layer 3120. Voltage dividers can be integrally formed and placed between adjacent piezoelectric layers, for example, by forming electrode layers through a metallization process that forms a voltage divider resistor network on the surface of the PZT material. Simple resistor voltage dividers may require a ground, but the ground can be provided in the same layer. As will be apparent to designers of such devices, many configurations are possible.

[0073] Both the patterning 3133 and the voltage suppressor 3144 weaken the electric field strength of the constraining layer 3140, allowing the constraining layer 3140 to be made thinner without generating undesirable passivity during operation. Electrode patterning, voltage suppressors, and other means of reducing the electric field strength of the constraining layers 3130 and / or 3140 can be used. Since the patterning 3133 is formed integrally with the electrode 3132, it is integrally formed and incorporated into the microactuator assembly. The voltage suppressor for one of the electrodes may be integrally formed and incorporated into the assembly, or it may be provided externally if the corresponding electrode itself has an electrical lead and is not connected to the other electrodes.

[0074] Any of the three methods described above can be applied to piezoelectric microactuators with a single active constraint layer, two active constraint layers (Figures 31-33), or more generally, n active constraint layers (Figure 35).

[0075] Figure 34 is a graph showing the stroke sensitivity (nm / V) of a microactuator having one or more active suppression layers, based on simulations of various constraint layer (CLC) structures. This graph is for the following three different structures, where the main PZT layer thickness is 45 μm and there is no patterning 3133 or voltage suppressor 3144 to reduce the electric field strength. a) One inactive suppression layer ("passive CLC", diamond-shaped data points) b) One active suppression layer ("single layer", square data points) c) Two active inhibition layers ("two layers", triangular data points) From this data, it can be seen that, at least for the parameters considered, a PZT microactuator equipped with one active suppression layer acting in the opposite direction to the main PZT layer consistently exhibits higher stroke sensitivity than when the suppression layer is made of a non-active material. The highest stroke sensitivity is achieved by multiple active PZT thin layers acting as suppression layers (i.e., acting in the opposite direction to the main PZT layer). Specifically, the highest stroke sensitivity is achieved by providing two suppression layers, each with a thickness of 5 μm or approximately 11% of the thickness of the main PZT layer. Therefore, the thickness of the restraint layer is preferably less than 50% of the thickness of the main PZT layer, more preferably less than 20% of the thickness of the main PZT layer, and even more preferably 5-15% of the thickness of the main PZT layer.

[0076] In the configuration of two active suppression layers, stroke sensitivity decreased significantly as the thickness of the suppression layers increased, with the highest stroke sensitivity observed in a configuration of two active restraint layers with a thickness of approximately 5 μm. Therefore, it is preferable for the microactuator to have two or more suppression layers whose total thickness is thinner than the thickness of the main PZT layer, and more preferably the total thickness is less than 50% of the thickness of the main PZT layer. More preferably, the thickness of each restraint layer is less than half the thickness of the main PZT layer. Even more preferably, the thickness of each restraint layer is less than 20% of the thickness of the main PZT layer, and even more preferably 5-15% of the thickness of the main PZT layer.

[0077] In the case of a microactuator assembly with a single active suppression layer, the decrease in stroke sensitivity with increasing suppression layer thickness was not as pronounced as in the case of two active suppression layers. The local maximum value for a single active suppression layer occurred at a thickness of approximately 10 μm. Therefore, in the case of a microactuator assembly with a single active suppression layer, the layer thickness is preferably 10-40% of the thickness of the main PZT layer, and more preferably approximately 10-20% of the thickness of the main PZT layer.

[0078] Figure 35 is a cross-sectional view showing another embodiment in which a microactuator assembly has multiple active PZT layers, conceptually illustrating the polling process and the resulting polarization direction. When the element of Figure 35 is electrically and mechanically joined to a suspension as shown in Figure 31, with electrodes 3524 and 3528 connected by conductive epoxy, one main active PZT layer and three active PZT layers are formed. The three active PZT layers act as inhibitory layers because they tend to act in the opposite direction to the main active PZT layer. That is, the lower PZT layer stretches and the three upper PZT layers contract, or vice versa.

[0079] The configuration of the microactuator assembly can be extended from elements with one main active PZT layer and two active PZT suppression layers as shown in Figures 31-33, or elements with one main active PZT layer and three active PZT suppression layers as shown in Figure 35, to elements with any number of main active layers and active suppression layers. The electric field strength of one or more constraint layers can be reduced by various means, including electrode patterning and / or voltage suppressors. The optimal number and thickness of constraint layers for the application can be determined by experimentation.

[0080] The PZT microactuators disclosed herein can also be used as actuators in art fields other than disk drive suspension. Therefore, details of such microactuators and their structures are included in the elements according to the present invention, regardless of the environment in which they are used, the disk drive suspension environment, or any other environment.

[0081] Figure 36 is an isometric view of one embodiment of a single-layer microactuator PZT assembly 4000. Figure 37 is a cross-sectional view of the single-layer microactuator PZT assembly 4000 along the C-C' cutting line in the width direction of the PZT. This single-layer microactuator PZT assembly 4000 also has an upper electrode 4042, a PZT element 4040, and a lower electrode 4032. The upper electrode 4042 is attached to the upper surface 4048 of the PZT element 4040. The lower electrode 4032 is attached to the lower surface 4034 of the PZT element 4040.

[0082] The width W1 of the upper electrode 4042 is narrower than the width W2 of the lower electrode 4032. The upper electrode 4042 has a step 4044 which is the end of the upper electrode 4042. The PZT element 4040 has an exposed portion 4046 on its upper surface 4048 that is not covered by the upper electrode 4042. In some embodiments, the upper electrode 4042 is positioned on the PZT element 4040 on the opposite side of the PZT junction surface.

[0083] The upper electrode 4042 can be applied to the PZT element 4040 by a deposition process that includes a masking step to form a step 4044, or by a deposition process that selectively removes material to form a step 4044. Alternatively, the upper electrode 4042 may be a component of an SST or other conductive material described herein that is formed separately and then bonded to the PZT element 4040. Thus, the material of the upper electrode 4042 may be the same as or different from the material of the lower electrode 4032.

[0084] Figure 38A is a plan view of a suspension gimbal 4050 having a single-layer microactuator PZT assembly 4000 according to one embodiment of the present disclosure. The exposed portion 4046 (i.e., electrode dead zone) is located inside the PZT, and the remaining portion of the upper surface of the PZT is the upper electrode 4042. The PZT is mounted on a gimbal having a gimbal assembly and acts directly on the gimbal region of the suspension holding a read / write head slider. Two microactuator PZT assemblies 4000 are bonded to a tongue-shaped portion 4054 to which the proximal ends of the microactuators 4000 are joined, and to a portion of the trace gimbal 4056 to which the proximal ends of the microactuators 4000 are joined, extending through the gap between them.

[0085] Figure 38B is a cross-sectional view taken along line D-D' of the suspension 4050 of Figure 38A according to one embodiment of the present disclosure. The proximal and tip ends of the PZT lower electrode 4032 are joined by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. The proximal end of the upper electrode 4042 is also coated with conductive adhesive 504 to form a PZT electrical connection. The microactuator assembly 4000 extends or contracts when actuated, thereby changing the length of the gap between the tongue-shaped portion 4054 and the trace gimbal portion 4056 (Figure 38A). This allows for fine positional movement of the head slider holding the read / write transducer.

[0086] The narrow width of the upper electrode 4042 creates an artificial suppression that counteracts the suppression applied to the lower electrode 4032 by the adhesive bonding between the non-conductive adhesive 502 at the base and the conductive adhesive 504 at the tip. By appropriately selecting the width of the upper electrode 4042, the gain of the suspension PZT excitation frequency response function (FRF) can be reduced across the entire frequency band in several major modes.

[0087] Figure 39 shows a graph of the PZT frequency response function of the suspension in Figure 38, based on simulation. The width of the upper electrode 4042 is 0.05 mm narrower than that of the lower electrode 4032. As a result, the gains of the first gimbal torsion mode (GT1), circuit torsion mode, and load beam oscillation mode are improved. In particular, the gain of the load beam oscillation mode is reduced by 3 dB, improving the bandwidth of the head positioning servo control, which in turn reduces data seek time and makes the system less susceptible to vibration.

[0088] Figure 40 is a plan view of a suspension gimbal 4150 having a single-layer microactuator PZT assembly 4000 according to an alternative embodiment of the present disclosure. In Figure 40, the exposed portion 4047 (electrode dead zone) is located outside the PZT upper surface 4048, and the remaining portion of the PZT upper surface is the upper electrode 4042.

[0089] Figure 41 shows a graph of the PZT frequency response function of the suspension in Figure 40, based on simulation. In this suspension, the first gimbal torsion mode, circuit torsion mode, and load beam swing gain were varied. This embodiment of the single-layer microactuator PZT assembly described herein can be used to optimize the FRF of the PZT in the above modes by tuning the FRF of the PZT of one suspension having opposite gain peaks.

[0090] Figure 42 is a plan view of a suspension gimbal 4250 having a single-layer microactuator PZT assembly 4100 according to one embodiment of the present disclosure. In Figure 42, the exposed portion 4146 (electrode dead zone) is located both inside and outside the PZT top surface 4148, and the remainder of the PZT top surface 4148 is the upper electrode 4142. Figure 43 is a cross-sectional view of the single-layer microactuator PZT assembly 4100 along the E-E' cutting line in the width direction of the PZT. The single-layer microactuator PZT assembly 4100 has an upper electrode 4142, a PTZ element 4140, and a lower electrode 4132. The upper electrode 4142 is attached to the top surface 4148 of the PZT element 4140. The lower electrode 4132 is attached to the bottom surface 4134 of the PZT element 4140. The width W3 of the upper electrode 4142 is narrower than the width W4 of the lower electrode 4132. The upper electrode 4142 has a step 4144 which is the end of the upper electrode 4142. The PZT element 4140 has an exposed portion 4146 on its upper surface 4148 that is not covered by the upper electrode 4142. In some embodiments, the upper electrode 4142 is positioned on the PZT element 4140 on the opposite side of the PZT junction surface.

[0091] The upper and lower electrodes can be formed on the PZT element 4140 by a film deposition process that includes a masking step to form a step 4144, or by a film deposition process that selectively removes material to form the upper surface. Alternatively, the upper electrode may be a separate part made of a conductive material such as SST that is formed separately and then bonded to the PZT element 4140. Therefore, the material of the upper electrode may be the same as or different from the material of the lower electrode 4132.

[0092] The narrow dimensions of the upper electrode 4142 create an artificial suppression that counteracts the suppression exerted on the lower electrode 4132 by the PZT junctions at the proximal and tip ends of the lower electrode. By appropriately selecting the width of the upper electrode, the gain of the suspension PZT-excited FRF can be further reduced across the entire frequency band in several key modes.

[0093] Figure 44A is a perspective view of the gimbal of the suspension 4250 with the single-layer microactuator PZT assembly 4000 rotated. Because the single-layer microactuator PZT assembly 4000 is rotating, the upper electrode 4042 becomes the first side electrode 5042, and the exposed portion 4046 is also located on the side. The lower electrode 4032 becomes the second side electrode 5032. In this configuration, the first side electrode 5042 and the second side electrode 5032 are electrically connected to copper bonding pads on two sides.

[0094] Figure 44B is a cross-sectional view taken along the line F-F' of Figure 44A according to one embodiment of the present disclosure. The first side electrode 5042 of the PZT is bonded to the tip copper pad 606 by conductive adhesive 604. The first side electrode 5042 is also coated with non-conductive adhesive 602. Figure 44C is a cross-sectional view taken along the line G-G' of Figure 44A according to one embodiment of the present disclosure. The second side electrode 5032 of the PZT is bonded to the base copper pad 608 by conductive adhesive 604. The microactuator assembly 4000 extends or contracts when actuated, allowing for fine positional movement of the head slider holding the read / write transducer.

[0095] The narrow width of the first side electrode 5042 creates an artificial suppression that counteracts the suppression applied to the second side electrode 5032 by adhesive bonding with the non-conductive adhesive 602 at the tip and the conductive adhesive 604 at the base. By appropriately selecting the width of the first side electrode 5042, the gain of the suspension PZT excitation frequency response function (FRF) can be further reduced in several major modes across the entire frequency band.

[0096] Figure 45A is a plan view of a gimbal of a suspension 4350 having a single-layer microactuator PZT assembly 4200 according to an alternative embodiment of the present disclosure. In Figure 45A, the exposed portion 4246 (electrode dead zone) is located both inside and outside the PZT top surface 4248, with the remainder of the PZT top surface 4248 being the upper electrode 4242. The exposed portion 4246 (electrode dead zone) is configured to curve inward, with the surface area of ​​the upper electrode 4242 being smaller at or near the center of the PZT top surface 4246. The cross-sectional area of ​​the upper electrode 4242 is larger as it approaches the tip and base of the single-layer microactuator PZT assembly 4200.

[0097] Figure 45B is a cross-sectional view of the single-layer microactuator PZT assembly 4200 along a cutting line H-H' that traverses the center of the single-layer microactuator PZT assembly 4200 in the PZT width direction. The upper electrode 4242 is attached to the upper surface 4248 of the PZT element 4240. The lower electrode 4232 is attached to the lower surface 4234 of the PZT element 4240. The upper electrode 4242 has an indeterminate width W5 that increases toward the base and tip. The indeterminate width W5 of the upper electrode 4242 is narrower than the width W6 of the lower electrode 4232. The upper electrode 4242 has a step 4244 which is the end of the upper electrode 4242. The PZT element 4240 has an exposed portion 4246 on its upper surface 4248 that is not covered by the upper electrode 4242. In some embodiments, the upper electrode 4242 is positioned on the PZT element 4240 opposite the PZT junction surface.

[0098] The upper and lower electrodes can be applied to the PZT element 4240 by a film deposition process that includes a masking step to form a step 4244, or by a film deposition process that selectively removes material to form the upper electrode. Alternatively, the upper electrode 4242 may be a separate component made of a conductive material such as SST or other materials described herein, which is formed separately and then bonded to the PZT element 4240. Therefore, the material of the upper electrode 4242 may be the same as or different from the material of the lower electrode 4232.

[0099] The non-constant cross-section of the upper electrode 4242 creates an artificial suppression that counteracts the suppression exerted on the lower electrode 4232 by the PZT junctions at the proximal and tip ends of the lower electrode. By varying the width of the upper electrode 4242, the gain of the suspension PZT-excited FRF can be further reduced across the entire frequency band in several key modes.

[0100] Figure 45C is a graph of the PZT frequency response function of the suspension in Figure 45A, based on simulation. The curved exposed areas on both sides of the electrode (electrode dead zones) can be used to optimize the second gimbal torsion mode (GT2) gain.

[0101] Figure 46A is a plan view of a gimbal of a suspension 4450 having a single-layer microactuator PZT assembly 4300 according to an alternative embodiment of the present disclosure. In Figure 46A, the exposed portion 4346 (electrode dead zone) is located inside the PZT upper surface 4348, with the remainder of the PZT upper surface 4348 being the upper electrode 4342. The exposed portion 4346 (electrode dead zone) is configured to curve inward, with the surface area of ​​the upper electrode 4342 being smaller at or near the center of the PZT upper surface 4348. The cross-sectional area of ​​the upper electrode 4342 is larger as it approaches the tip and base of the single-layer microactuator PZT assembly 4300.

[0102] Figure 46B is a cross-sectional view of the single-layer microactuator PZT assembly 4300 along a cutting line J-J' that traverses the center of the single-layer microactuator PZT assembly 4300 in the PZT width direction. The upper electrode 4342 is attached to the upper surface 4348 of the PZT element 4340. The lower electrode 4332 is attached to the lower surface 4334 of the PZT element 4340. The upper electrode 4342 has an indeterminate width W7 that increases toward the proximal and tip ends. The indeterminate width W7 of the upper electrode 4342 is narrower than the width W8 of the lower electrode 4332. The upper electrode 4342 has a step 4344 which is the end of the upper electrode 4342. The PZT element 4340 has an exposed portion 4346 on its upper surface 4348 that is not covered by the upper electrode 4342. In some embodiments, the upper electrode 4342 is positioned on the PZT element 4340 opposite the PZT junction surface.

[0103] The upper and lower electrodes can be applied to the PZT element 4340 by a film deposition process that includes a masking step to form a step 4344, or by a film deposition process that selectively removes material to form the upper electrode. Alternatively, the upper electrode 4342 may be a separate component made of a conductive material such as an SST or other material described herein that is formed separately and then bonded to the PZT element 4340. Therefore, the material of the upper electrode 4342 may be the same as or different from the material of the lower electrode 4332.

[0104] The non-constant cross-section of the upper electrode 4342 creates an artificial suppression that counteracts the suppression exerted on the lower electrode 4332 by the PZT junctions at the proximal and tip ends of the lower electrode. By varying the width of the upper electrode 4342, the gain of the suspension PZT-excited FRF can be further reduced across the entire frequency band for several major modes.

[0105] Figure 46C is a graph of the PZT frequency response function of the suspension in Figure 46A, based on simulation. The curved exposed portion inside the electrode (the electrode dead zone) can be used to optimize the gain of the first gimbal torsion mode (GT1) (increase in GT1 phase lag) and the sway gain (increase in sway mode phase lead).

[0106] Figure 47A is a plan view of a gimbal of a suspension 4550 having a single-layer microactuator PZT assembly 4400 according to an alternative embodiment of the present disclosure. In Figure 47A, the exposed portion 4446 (electrode dead zone) is located outside the PZT top surface 4448, with the remainder of the PZT top surface 4448 being the upper electrode 4442. The exposed portion 4446 (electrode dead zone) is configured to curve inward, with the surface area of ​​the upper electrode 4442 being smaller at or near the center of the PZT top surface 4448. The cross-sectional area of ​​the upper electrode 4442 is larger as it approaches the tip and base of the single-layer microactuator PZT assembly 4400.

[0107] Figure 47B is a cross-sectional view of the single-layer microactuator PZT assembly 4400 along a cutting line K-K' that traverses the center of the single-layer microactuator PZT assembly 4400 in the PZT width direction. The upper electrode 4442 is attached to the upper surface 4448 of the PZT element 4440. The lower electrode 4432 is attached to the lower surface 4334 of the PZT element 4440. The upper electrode 4442 has an indeterminate width W9 that increases toward the proximal and tip ends. The indeterminate width W9 of the upper electrode 4442 is narrower than the width W10 of the lower electrode 4432. The upper electrode 4442 has a step 4444 which is the end of the upper electrode 4442. The PZT element 4440 has an exposed portion 4446 on its upper surface 4448 that is not covered by the upper electrode 4442. In some embodiments, the upper electrode 4442 is positioned on the PZT element 4440 opposite the PZT junction surface.

[0108] The upper and lower electrodes can be applied to the PZT element 4440 by a film deposition process that includes a masking step to form the step 4444, or by a film deposition process that selectively removes material to form the upper electrode. Alternatively, the upper electrode 4442 may be a separate component made of a conductive material such as an SST or other material described herein that is formed separately and then bonded to the PZT element 4440. Therefore, the material of the upper electrode 4442 may be the same as or different from the material of the lower electrode 4432.

[0109] The non-constant cross-section of the upper electrode 4442 creates an artificial suppression that counteracts the suppression exerted on the lower electrode 4432 by the PZT junctions at the proximal and tip ends of the lower electrode. By varying the width of the upper electrode 4442, the gain of the suspension PZT-excited FRF can be further reduced across the entire frequency band for several key modes.

[0110] Figure 47C is a graph of the PZT frequency response function of the suspension in Figure 47A, based on simulation. The curved exposed portion outside the electrodes (the electrode dead zone) can be used to optimize the gain of the first gimbal torsion mode (GT1) (increase in GT1 phase lag) and the sway gain (increase in sway mode phase lead).

[0111] Figure 48A is a plan view of a suspension gimbal 4650 having a single-layer microactuator PZT assembly 4500 according to one embodiment of the present disclosure. The exposed portion 4546 (i.e., electrode dead zone) is located at the tip of the PZT and is curved such that the outer portion of the exposed portion is larger than the inner portion. The remaining portion of the upper surface of the PZT is the upper electrode 4542. Two microactuator PZT assemblies 4500 are bonded to a tongue-shaped portion 4554 to which the proximal ends of the microactuators 4500 are joined, and to a portion of the trace gimbal 4556 to which the proximal ends of the microactuators 4500 are joined, extending through the gap between them.

[0112] Figure 48B is a cross-sectional view taken along the line L-L' of the suspension 4650 of Figure 48A according to one embodiment of the present disclosure. The proximal and tip ends of the PZT lower electrode 4532 are joined by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. The proximal end of the upper electrode 4542 is also coated with conductive adhesive 504 to form a PZT electrical connection. The microactuator assembly 4500 extends or contracts when actuated, thereby changing the length of the gap between the tongue-shaped portion 4554 and the trace gimbal portion 4556 (Figure 48A). This allows for fine positional movement of the head slider holding the read / write transducer.

[0113] Figure 48C is a graph of the PZT frequency response function of the suspension in Figure 48A, based on simulation. The curved exposed portion of the electrode tip (electrode dead zone) can be used to optimize the first torsional mode (T1) gain and the first gimbal torsional mode (GT1).

[0114] Figure 49A is a plan view of a gimbal of a suspension 4750 having a single-layer microactuator PZT assembly 4600 according to an alternative embodiment of the present disclosure. In Figure 49A, the exposed portion 4646 (electrode dead zone) is located outside the PZT upper surface 4648, and the remaining portion of the PZT upper surface 4446 is the upper electrode 4642. Specifically, the upper electrode 4642 has a tip, a base, and a connector connecting the tip and the base. As shown, the surface area of ​​the base of the upper electrode 4642 is larger than the surface area of ​​the tip. Alternatively, the surface area of ​​the tip of the upper electrode 4642 may be larger than the surface area of ​​the base. In other embodiments, the surface areas of the base and tip are the same or substantially the same. The exposed portion 4646 (electrode dead zone) is defined by the tip, base, and connector of the upper electrode 4642. The cross-sectional areas of the tip and base are larger than the cross-sectional area of ​​the connector of the upper electrode 4642.

[0115] Figure 49B is a cross-sectional view of a single-layer microactuator PZT assembly 4600 along a cutting line M-M' that crosses the center of a single-layer microactuator PZT assembly 4400 in the PZT width direction. The upper electrode 4642 is attached to the upper surface 4648 of the PZT element 4640. The lower electrode 4632 is attached to the lower surface 4634 of the PZT element 4640. The width W11 of the connection portion of the upper electrode 4642 is smaller than the width of the base and tip portions (not shown). Also, the width W11 of the upper electrode 4642 is narrower than the width W12 of the lower electrode 4632. The upper electrode 4642 has a step 4644 which is the end of the upper electrode 4642. The PZT element 4640 has an exposed portion 4646 on its upper surface 4648 that is not covered by the upper electrode 4642. In some embodiments, the upper electrode 4642 is positioned on the PZT element 4640 on the opposite side of the PZT junction surface.

[0116] The upper and lower electrodes can be applied to the PZT element 4640 by a film deposition process that includes a masking step to form a step 4644, or by a film deposition process that selectively removes material to form the upper electrode. Alternatively, the upper electrode 4642 may be a separate component made of a conductive material such as an SST or other material described herein that is formed separately and then bonded to the PZT element 4640. Therefore, the material of the upper electrode 4642 may be the same as or different from the material of the lower electrode 4632.

[0117] The presence of multiple cross-sectional areas in the upper electrode 4642 creates an artificial suppression that counteracts the suppression applied to the lower electrode 4632 by the PZT junctions at the proximal and tip ends of the lower electrode. By varying the width of the upper electrode 4642, the gain of the suspension PZT-excited FRF can be further reduced across several key modes in the entire frequency band.

[0118] Figure 49C is a graph of the PZT frequency response function of the suspension in Figure 49A, based on simulation. The curved exposed portion outside the electrodes (the electrode dead zone) can be used to optimize the gain of the first gimbal torsion mode (GT1) (increase in GT1 phase lag) and the sway gain (increase in sway mode phase lead).

[0119] Figure 50A is a plan view of a suspension gimbal 4850 having a single-layer microactuator PZT assembly 4700 according to one embodiment of the present disclosure. The microactuator PZT assembly 4700 includes a plurality of exposed portions 4746 (i.e., electrode dead zones), each located on a portion of the outer side of the PZT upper surface 4748. The remaining portion of the PZT upper surface 4748 is the upper electrode 4742. Specifically, the upper electrode 4742 has a tip portion, a base portion, one or more intermediate portions between the tip portion and the base portion, and a connecting portion that connects the above portions along the inside of the PZT upper surface 4748. In another embodiment, the patterned dead zones are located on the inside of the PZT upper surface 4748. In yet another embodiment, the patterned dead zones are located alternately on the inside and outside of the PZT upper surface 4748.

[0120] The surface areas of each of the above-mentioned parts of the upper electrode 4742 may be the same or substantially the same. The exposed portion 4746 (electrode dead zone) is defined by the tip, base, middle, and connecting portion of the upper electrode 4742. The cross-sectional areas of the tip, base, and middle portions are larger than the cross-sectional area of ​​the connecting portion of the upper electrode 4742.

[0121] Figure 50B is a cross-sectional view of the suspension 4750 of Figure 50A according to one embodiment of the present disclosure, taken along the line N-N'. The proximal and tip ends of the PZT lower electrode 4732 are joined by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. The upper electrode 4742 has a tip portion 4742C, a proximal portion 4742A, and one or more intermediate portions 4742B positioned between the tip and proximal portions along the inside of the PZT upper surface 4748. The proximal portion 4742A is also coated with conductive adhesive 504 to form the PZT electrical connection. The microactuator assembly 4700 extends or contracts when actuated, thereby changing the length of the gap between the tongue portion 4754 and the trace gimbal portion 4756 (Figure 50A). This allows for fine positional movement of the head slider holding the read / write transducer.

[0122] Figure 50C is a graph of the PZT frequency response function of the suspension in Figure 50A, based on simulation. The dead zone of the patterned PZT upper electrode 4742 can be used for resonance optimization of the first torsional mode z(T1) (increasing T1 phase lag), the first gimbal torsional mode (GT1) (increasing GT1 phase lead), and oscillation (increasing oscillation phase lag). As can be seen from the graph, the effect on stroke is small, at 3.7 nm / V compared to 3.4 nm / V.

[0123] Figure 51 is a cross-sectional view of one embodiment of a single-layer microactuator PZT assembly according to one embodiment of the present disclosure. This single-layer microactuator PZT assembly 5000 also has an upper electrode 5042, a PZT element 5040, and a lower electrode 5032. The upper electrode 5042 is attached to the upper surface 5048 of the PZT element 5040. The lower electrode 5032 is attached to the lower surface 5034 of the PZT element 5040.

[0124] The width W1 of the upper electrode 5042 is narrower than the width of the PZT element 5040. The upper electrode 5042 has a step 5044 which is the end of the upper electrode 5042. The PZT element 5040 has an exposed portion 5046 on its upper surface 5048 that is not covered by the upper electrode 5042. In some embodiments, the upper electrode 5042 is positioned on the PZT element 4040 on the opposite side of the PZT junction surface. In some embodiments, the upper electrode has an indeterminate width or is configured to expose a portion of the PZT element according to the art described herein.

[0125] The width W2 of the lower electrode 5032 is narrower than the width of the PZT element 5040. The lower electrode 5032 has a step that is the end of the lower electrode 5032. The PZT element 5040 has an exposed portion on its lower surface that is not covered by the lower electrode 5032. In some embodiments, the lower electrode has an indeterminate width or is configured to expose a portion of the PZT element according to the art described herein. Some embodiments have upper and lower electrodes configured to have similar exposed surfaces on the upper and lower surfaces of the PZT element. Other embodiments have upper and lower electrodes such that the upper and lower surfaces of the PZT element have different exposed surfaces. Thus, the upper electrode does not have to cover the entire surface of the PZT element, and its shape and size may be the same as or different from that of the second electrode, but within the outer dimensions of the PZT element.

[0126] The upper electrode 5042 and the lower electrode 5032 can be applied to the PZT element 5040 by a deposition process that includes a masking step to form a step, or by a deposition process that selectively removes material to form a step. Alternatively, the upper electrode 5042 and / or the lower electrode 5032 may be separate conductive components made of SST or other materials described herein that are formed separately and then bonded to the PZT element 5040. Thus, the material of the upper electrode 5042 may be the same as or different from the material of the lower electrode 5032.

[0127] Although a single PZT layer is shown herein, the disclosed embodiments can be applied to multilayer PZT microactuator assemblies having multiple PZT elements using techniques similar to those described herein. By appropriately selecting the width of the upper electrode, the FRF of the PZTs in an arrayed microactuator suspension using a set of multilayer PZTs can be effectively tuned.

[0128] As used herein and in the claims, the terms “approximately,” “about,” “approximately,” “substantially,” and “coplanar” are understood to allow for a certain amount of variation from any exact dimensions or measurements. These terms should be understood within the context of the description and operation of the invention disclosed herein.

[0129] As used in the specification and claims herein, terms such as “upper,” “lower,” “up,” and “down” are convenient terms describing the spatial relationships of each part to one another, rather than any specific spatial or gravitational direction. Therefore, these terms are intended to encompass the assembly of components, regardless of whether they are oriented in a particular direction, the opposite direction, or any other rotational direction as depicted in the illustrations and specification of the assembly.

[0130] All features disclosed in the specification, including the claims, abstract, and drawings, and all steps of the disclosed methods or processes, may be combined in any combination, except for any combination in which at least some of the features and / or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, may be replaced by an alternative feature that serves the same, equivalent, or similar purpose, unless otherwise expressly stated. Thus, unless expressly stated, each disclosed feature is merely an example of a set of equivalent or similar general features.

[0131] The term “invention” as used herein should not be construed to mean that only a single invention having a single essential element or set of elements is presented. Similarly, the term “invention” is understood to encompass multiple distinct technological innovations, each of which may be considered a distinct invention. Although the invention has been described in detail with reference to preferred embodiments and drawings, it will be apparent to those skilled in the art that various modifications and variations of the invention can be carried out without departing from the spirit and scope of the invention. Accordingly, it should be understood that the above detailed description and accompanying drawings are not intended to limit the scope of the invention and should be inferred solely from the following claims and their legal equivalents as appropriately interpreted.

Claims

1. At least one piezoelectric element, A first electrode located on a first side surface of the at least one piezoelectric element, the first electrode having a first height extending along the entire length of the first side surface of the at least one piezoelectric element, A second electrode located on the second side surface of the at least one piezoelectric element, having a second height smaller than the first height of the first electrode, extending shorter than the total length of the second side surface of the at least one piezoelectric element, and configured to bend when a voltage is applied in order to resist the constraint exerted by the bonding adhesive, A microactuator assembly comprising:

2. The first electrode is electrically connected to a first conductive adhesive that bonds the microactuator assembly to its surface. The microactuator assembly according to claim 1.

3. The second electrode is electrically connected to a second conductive adhesive that bonds the microactuator assembly to its surface. The microactuator assembly according to claim 1.

4. The at least one piezoelectric element includes a plurality of piezoelectric elements disposed between the first electrode and the second electrode. The microactuator assembly according to claim 1.

5. The second height of the second electrode changes along the short-axis direction of the second electrode. The microactuator assembly according to claim 1.

6. The second electrode is configured to expose at least two portions of the at least one piezoelectric element. The microactuator assembly according to claim 5.

7. The second electrode is configured to expose one portion of the second side surface of the at least one piezoelectric element. The microactuator assembly according to claim 5.

8. The second electrode has at least one exposed portion. The microactuator assembly according to claim 1.

9. The second electrode is configured to have a tip portion, a base portion, and a connecting portion that connects the tip portion and the base portion. The microactuator assembly according to claim 8.

10. A suspension for a disk drive, comprising a microactuator assembly, wherein the microactuator assembly is At least one piezoelectric element, A first electrode located on a first side surface of the at least one piezoelectric element, the first electrode having a first height extending along the entire length of the first side surface of the at least one piezoelectric element, A suspension comprising: a second electrode located on the second side surface of the at least one piezoelectric element, having a second height smaller than the first height of the first electrode, extending shorter than the total length of the second side surface of the at least one piezoelectric element, and configured to bend when a voltage is applied in order to resist the constraint exerted by the bonding adhesive.

11. The suspension according to claim 10, wherein the first electrode is electrically connected to a first conductive adhesive that bonds the microactuator assembly to its surface.

12. The second electrode is electrically connected to a second conductive adhesive that bonds the microactuator assembly to its surface. The suspension according to claim 10.

13. The at least one piezoelectric element includes a plurality of piezoelectric elements disposed between the first electrode and the second electrode. The suspension according to claim 10.

14. The second height of the second electrode changes along the short-axis direction of the second electrode. The suspension according to claim 10.

15. The second electrode is configured to expose at least two portions of the at least one piezoelectric element. The suspension according to claim 14.

16. The second electrode is configured to expose one portion of the second side surface of the at least one piezoelectric element. The suspension according to claim 14.

17. The second electrode has at least one exposed portion. The suspension according to claim 10.

18. The second electrode is configured to have a tip portion, a base portion, and a connecting portion that connects the tip portion and the base portion. The suspension according to claim 17.

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