Multilayer PZT microactuator with active PZT constraining layer for DSA suspension

Abstract

A PZT microactuator, such as that used in a hard disk drive, has a constraining layer bonded to the side of the actuator opposite to the side on which the PZT is mounted. The constraining layer comprises a hard and resilient material, such as stainless steel. The constraining layer may cover most or all of the top of the PZT, making electrical connections to the PZT in areas not covered by the constraining layer. The constraining layer reduces the bending of the PZT when mounted, thereby increasing the effective stroke length, or reverses the sign of the bending, thereby further increasing the effective stroke length of the PZT. The constraining layer may be one or more layers of active PZT material that act in the opposite direction to the main PZT layer. The constraining layer may be thinner than the main PZT layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 16 / 857,133, filed on April 23, 2020, the entire contents of which are incorporated herein by reference.

[0003] Background of the Invention Technical Field

[0004] The present invention relates to the field of suspensions for hard disk drives. More specifically, the present invention relates to the field of multilayer piezoelectric microactuators having one or more active piezoelectric constraining layers for dual-stage actuation suspensions. Background Art

[0005] Magnetic hard disk drives and other types of rotating media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension to which the present invention is applicable. The prior art disk drive unit 100 includes a rotating magnetic disk 101 having a pattern of magnetic ones and zeros thereon, which constitutes data stored on the disk drive. The disk is driven by a drive motor (not shown). The disk drive unit 100 further includes a disk drive suspension 105, with a head slider (not shown) mounted near the distal end of a load beam 107. The "proximal end" of the suspension or load beam is the end that is supported, i.e., the end closest to the base plate 12, which is welded or otherwise mounted to the actuator arm. The "distal end" of the suspension or load beam is the end opposite the proximal end, i.e., the "distal end" is the cantilever end.

[0006] The suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 in an arc to position a head (head) slider over the correct data track on the data disk 101. The head slider is carried by a gimbal that allows the slider to pitch and roll to follow the correct data track on the rotating disk, allowing for variations in disk vibrations, inertial events (such as crashes), and irregularities in the disk surface.

[0007] Single-stage drive disk drive suspensions and dual-stage drive (DSA) suspensions are known. In a single-stage drive suspension, only the voice coil motor 112 can move the suspension 105.

[0008] In DSA suspensions, such as that shown in U.S. Pat. No. 7,459,835 to Mei et al. and many others, in addition to the voice coil motor 112 that moves the entire suspension, at least one additional microactuator is located on the suspension to achieve fine motion of the head slider and to properly align it with the data tracks on the spinning disk. The microactuator provides finer control and higher bandwidth of the servo control loop than a separate voice coil motor, which only produces relatively coarse motion of the suspension and head slider. Piezoelectric elements (sometimes referred to as PZTs) are often used as microactuator motors, although other types of microactuator motors are possible.

[0009] FIG2 is a top view of the prior art suspension 105 of FIG1. ​​Two PZT microactuators 14 are attached to microactuator mounting brackets 18 on the suspension 105, which are formed in the base plate 12 so that the PZTs span corresponding gaps in the base plate 12. The microactuators 14 are attached to the mounting brackets 18 at both ends of the microactuators by epoxy 16. Positive and negative electrical connections can be made from the PZT to the flexible traces of the suspension and / or to the board by various techniques. When the microactuator 14 is activated, it expands or contracts, thereby changing the gap length between the mounting brackets, thereby producing fine movement of the read / write head mounted at the far end of the suspension 105.

[0010] FIG3 is a side cross-sectional view of the prior art PZT microactuator and mounting of FIG2. The microactuator 14 includes the PZT element 20 itself and top and bottom metallization layers 26, 28 on the PZT that define electrodes for driving the PZT. As shown, the PZT 14 is mounted across the gap on its left and right sides with epoxy or solder 16.

[0011] In a DSA suspension, it is generally desirable to achieve a high travel distance per unit input voltage on the PZT, or simply "stroke length".

[0012] Many past DSA suspension designs mounted the PZT on a mounting plate. In such designs, the linear motion of the PZT is amplified by the arm length between the PZT's center of rotation and the read / write sensor head. Therefore, a small linear motion of the PZT results in a relatively large radial motion of the read / write head.

[0013] Other suspension designs mount the PZT on or near a gimbal. An example of a gimbal mounted PZT is the DSA suspension shown in co-owned U.S. Application 13 / 684,016, assigned to the assignee of the present invention. Achieving a high stroke length is particularly important in gimbal mounted DSA suspensions ("GSA" suspensions) because these designs do not have nearly as long an arm length between the PZT and the read / write sensor head. Since the arm length is shorter, the amount of movement of the read / write head is correspondingly less. Therefore, achieving a large stroke length is particularly important in GSA designs. Summary of the invention

[0014] The inventors of the present application have found that, in a suspension on which a PZT microactuator is mounted according to the prior art, there is a factor causing a loss of the PZT stroke length, and have developed a PZT microactuator structure and a production method to eliminate the factor causing the loss of the stroke length.

[0015] FIG4A is a side cross-sectional view of a PZT microactuator 14 mounted on a suspension according to prior art FIG2 when the PZT is driven by a driving voltage applied thereto to expand the PZT. Because the bottom layer 22 of the PZT is partially constrained by bonding to the suspension 18 on which it is mounted, the bottom layer 22 does not expand as much in the linear direction as the top layer 24. Since the top layer 24 expands more than the bottom layer 22, the PZT 14 bends downward and presents a slightly convex shape when viewed from the top. The resulting linear stroke length loss is shown as δ1 in the figure.

[0016] FIG4B shows the PZT microactuator 14 of FIG4A when the PZT is driven by a driving voltage applied thereto to contract the PZT. Since the bottom layer 22 of the PZT is partially constrained by bonding to the suspension 18 on which it is mounted, the bottom layer 22 does not contract as much in the linear direction as the top layer 24. Since the top layer 24 contracts more than the bottom layer 22, the PZT 14 bends upward and presents a slightly concave shape when viewed from the top. The resulting linear stroke length loss is shown as δ2 in the figure.

[0017] Therefore, while it is desirable for a PZT to exhibit purely linear expansion and contraction when actuated, in conventional mountings the PZT will experience upward or downward bending, resulting in a loss of stroke length.

[0018] Figure 5 is a graph and related equation for the amount of effective linear travel increased or lost due to PZT bending. When the beam bends upward as shown in FIG4A , the bottom end point will have a positive displacement δ in the x direction when the bending angle is small.

[0019] Figure 6is a graph of travel loss due to bending versus bending angle for three different thicknesses of PZT. As shown, for a PZT 1.50 mm long and 45 μm thick, bending causes a positive x-displacement δ when the bending angle is less than 5 degrees. For this amount of bending, it can also be seen that the thicker beam produces a larger x-displacement than the thinner beam. Similarly, when the PZT contracts under an applied voltage, the right half of the PZT bends downward, and the bottom end of the PZT bonded to the suspension will experience a negative x-displacement. In other words, in the traditional way of mounting the PZT on the suspension, the component of the linear displacement due to bending δ is opposite to the direction of the PZT's drive. Therefore, it is desirable to reduce or eliminate this δ, or even reverse the sign of this δ, so that the net result is that the total linear expansion or contraction is actually increased.

[0020] The present invention is a PZT element having one or more rigid constraining layers or constraining elements bonded to at least one side or face opposite (opposite) the side or face on which the PZT is mounted on a suspension to reduce, eliminate, change the direction of, or otherwise control the bending of the PZT when actuated. An unexpected result is that even though a rigid layer is added to the PZT that at least nominally inhibits the expansion and contraction of the PZT, the effective linear travel distance achieved is actually increased. In accordance with the present invention, the PZT with the constraining layer can be used as a microactuator in a hard disk drive suspension, although it can also be used in other applications.

[0021] In a preferred embodiment, the effect of the constraining layer is to actually change the direction of bending. Thus, for a PZT bonded to the suspension at its bottom surface, the presence of the constraining layer has the effect that when the piezoelectric element is driven by a voltage that causes the piezoelectric element to expand, the piezoelectric element bends in a direction that causes the top side to become a net concave shape; and when the piezoelectric element is driven by a voltage that causes the piezoelectric element to contract, the piezoelectric element bends in a direction that causes the top side to become a net convex shape. Thus, the effect is to actually increase the effective linear expansion in the expansion mode and increase the effective linear contraction in the contraction mode. Thus, the presence of the constraining layer actually increases the effective stroke length.

[0022] PZT with a constraining layer can be manufactured by various techniques, including laminating the constraining layer onto an existing PZT element, or one of the PZT element and the constraining layer can be formed on top of the other by an additive process. Such an additive process can include depositing a thin film of PZT onto a substrate such as stainless steel (SST). The constraining layer can be stainless steel, silicon, a ceramic, such as a substantially unpolarized (unactivated) ceramic material, or the same ceramic material as that forming the PZT element, or other relatively hard material. If the constraining layer is non-conductive, one or more electrical vias containing posts of conductive material can be formed through the constraining layer to conduct an activation voltage or ground potential from the surface of the microactuator to the PZT element inside.

[0023] The constraining layer can be larger (larger surface area), the same size as, or smaller (smaller surface area) than the PZT element. In a preferred embodiment, the constraining layer is smaller than the PZT element, thereby providing the microactuator with a stepped structure, wherein the ledge of the step is not covered by the constraining layer, and the ledge is where electrical connections are made to the PZT element. One benefit of such a structure including the ledge where electrical connections are made is that the complete assembly including the electrical connections has a smaller profile than if the constraining layer covered the entire PZT. A smaller profile is advantageous because it means that more hard drive platters and their suspensions can be stacked together within a given platter stack height, thereby increasing data storage capacity within a given volume of the disk drive assembly.

[0024] Simulations show that the microactuator constructed according to the present invention exhibits enhanced stroke sensitivity and reduced swing mode gain and torsion mode gain, which are beneficial in increasing the bandwidth of the head positioning control loop, which will reduce data seek time and reduce sensitivity to vibration.

[0025] Another advantage of adding a constraining layer or element to the PZT according to the present invention is that in current hard disk drives, the suspension and its components including the PZT are typically very thin. The thickness of the microactuator used in current DSA suspension designs (where the PZT is mounted on a mounting plate) is about 150 μm. In universal joint mounted DSA suspension designs, the PZT is even thinner, typically less than 100 μm thick. Therefore, the PZT material is very thin and brittle and is easily cracked during manufacturing / assembly, which includes the manufacturing process of the PZT microactuator motor itself and the automatic pick and place operation in the suspension assembly process. It is expected that the PZT in future generations of hard disk drives will be 75 μm thick or thinner, which will make the above problems more serious. It is expected that such a thin PZT will not only be easily damaged during manufacturing / assembly, but also easily cracked or broken when the disk drive encounters shocks (i.e. g-forces). In accordance with the present invention, the additional rigid, elastic constraining layer provides additional strength and resilience to the PZT, thereby helping to prevent the PZT from cracking or other mechanical failure during manufacturing / assembly and in shock events.

[0026] In another aspect of the invention, the microactuator assembly is a multilayer PZT device wherein a plurality of active PZT layers including one or more active PZT layers act as constraining layers tending to counteract the effects of the primary active PZT layer.

[0027] It was not foreseeable that the overall net stroke length could be increased by adding one or more layers that resisted the motion of the main PZT layer. Even more unforeseeable was the idea that the overall net stroke length could be further increased by adding one or more active layers that acted in the opposite direction to the main PZT layer. Yet, this is what the inventors have demonstrated.

[0028] Exemplary embodiments of the present invention will be further described below with reference to the accompanying drawings, in which similar reference numerals refer to similar parts. The accompanying drawings may not be drawn to scale, and certain components may be shown in generalized or schematic form and identified by commercial names to facilitate clarity and conciseness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a top perspective view of a prior art magnetic hard disk drive;

[0030] FIG2 is a top view of the suspension of the disk drive of FIG1 ;

[0031] FIG3 is a side cross-sectional view of the prior art PZT microactuator and installation of FIG2;

[0032] 4A is a side cross-sectional view of a PZT microactuator mounted on a suspension according to prior art FIG. 2 when a voltage is applied to the PZT to expand it;

[0033] 4B is a side cross-sectional view of a PZT microactuator mounted on the suspension according to the prior art FIG. 2 when a voltage is applied to the PZT to cause it to contract;

[0034] Figure 5 It is a schematic diagram and related equations of the amount of linear travel gained or lost due to PZT bending;

[0035] Figure 6 This is a graph showing the relationship between the travel loss and the bending angle caused by the bending of PZTs of three different thicknesses;

[0036] Figure 7 is a side cross-sectional view of a PZT having a constraining layer bonded thereto in accordance with the present invention;

[0037] Fig. 8A When voltage is applied to PZT to cause it to expand Figure 7 Side cross-sectional view of a PZT microactuator;

[0038] Figure 8B When voltage is applied to PZT to cause it to contract Figure 7 Side cross-sectional view of a PZT microactuator;

[0039] Fig. 9 is a graph showing the stroke length per unit input voltage in nm / V versus the thickness of the confinement layer, where the PZT is 130 μm thick;

[0040] Fig.10 is a side view of a PZT having a constraining layer bonded thereto according to the present invention;

[0041] Fig.11 yes Fig.10 Plot of the stroke length of the PZT versus the thickness of the PZT, where the combined thickness of the PZT and the constraining layer remains constant at 130 μm;

[0042] Fig.12 is a graph of the GDA travel sensitivity of the PZT suspension with different thicknesses of the stainless steel constraint layer versus the thickness of the constraint layer;

[0043] Figures 13A-13H A manufacturing process is described by which a PZT with a constraining layer according to the present invention can be produced;

[0044] Fig.14A and 14B is an oblique view of a GSA suspension assembled with a thin film PZT microactuator motor according to the present invention;

[0045] Fig.15 It is taken along the section line B-B' Fig. 14B A cross-sectional view of the microactuator region;

[0046] Fig.16 It is obtained based on simulation Fig.15 The stroke sensitivity of the microactuator and the thickness of the SST substrate;

[0047] Figures 17A-17F A process for fabricating a thin film PZT structure having a stainless steel substrate according to the present invention is described;

[0048] Fig.18 is a top view of a thin film PZT structure with a silicon substrate according to the present invention;

[0049] Fig.19 It is taken along the section line A-A' Fig.18 Side cross-sectional view of a thin film PZT structure;

[0050] Fig. 20 It is obtained based on simulation Fig.19 A graph showing the travel sensitivity of the microactuator versus the thickness of the silicon substrate;

[0051] Figures 21A-21E Explains the manufacturing Fig.18 The process of thin film PZT structure;

[0052] Fig. 22 is a top view of a thin film PZT having a substrate and side holes according to an embodiment of the present invention;

[0053] Fig.23 It is taken along the section line A-A' Fig. 22 A cross-sectional view of a microactuator;

[0054] Fig.24 is a cross-sectional view of a PZT microactuator according to another embodiment of the present invention;

[0055] Fig.25 Is a pair Fig.24 Oblique view of the GSA suspension of the PZT microactuator;

[0056] Fig.26 It is taken along the section line A-A' Fig.25 A cross-sectional view of the GSA suspension;

[0057] Fig. 27 It is obtained based on simulation Fig.25 A graph of the PZT frequency response function of the suspension;

[0058] Figures 28A-28J Explains the manufacturing Fig.24 An exemplary process for a PZT microactuator assembly;

[0059] Fig.29is a side cross-sectional view of a multilayer PZT microactuator assembly according to another embodiment of the present invention, wherein the PZT is a multilayer PZT;

[0060] Fig.30 is a side cross-sectional view of a multilayer PZT microactuator assembly according to another embodiment of the present invention, wherein an ultra-thick electrode acts as a constraining layer;

[0061] Fig.31 is a cross-sectional view of an embodiment wherein the constraining layer of the microactuator assembly includes one or more active PZT layers that tend to act in an opposite direction to the main active PZT layer;

[0062] Fig.32 Shows Fig.31 The polarization of the microactuator assembly, including the resulting polarization directions of the active PZT material layers;

[0063] Fig.33 yes Fig.31 An exploded view of a microactuator assembly of FIG. 1 , which conceptually shows the electrical connections;

[0064] Fig.34 is a graph showing the stroke sensitivity (in nm / V) of a microactuator having one or more active confinement layers obtained from simulations for various configurations;

[0065] Fig.35 is a cross-sectional view of another embodiment in which a microactuator assembly includes a plurality of active PZT layers and conceptually illustrates a poling process and resulting poling directions;

[0066] Fig.36 is an isometric view of one embodiment of a single-layer microactuator PZT assembly according to one embodiment of the present disclosure;

[0067] Fig.37 It is taken along the section line C-C' Fig.36 sectional view of;

[0068] Fig.38A According to one embodiment of the present disclosure, Fig.36 A plan view of the gimbal of the suspension of a single-layer microactuator PZT assembly;

[0069] Fig.38B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line D-D'. Fig.38A sectional view of;

[0070] Fig.39 It is obtained based on simulation Fig.38A A graph of the PZT frequency response function of the suspension;

[0071] Fig.40 According to an alternative embodiment of the present disclosure, Fig.36 Plan view of the gimbal-mounted dual-stage actuation (GSA) suspension of a single-layer microactuator PZT assembly;

[0072] Fig.41 It is obtained based on simulation Fig.40 A graph of the PZT frequency response function of the suspension;

[0073] Fig.42 is a plan view of a gimbal of a suspension including a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0074] Fig.43 According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line EE'. Fig.42 sectional view of;

[0075] Fig.44A is an oblique view of the universal joint of the suspension, where Fig.37 The single-layer microactuator PZT assembly is rotated at the universal joint;

[0076] Fig.44B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line F-F'. Fig.44A sectional view of;

[0077] Fig.44C According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line G-G'. Fig.44A sectional view of;

[0078] Fig.45A is a plan view of a universal joint of a suspension assembled with a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0079] Fig.45B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line H-H'. Fig.45A sectional view of;

[0080] Fig.45C It is obtained based on simulation Fig.45A A graph of the PZT frequency response function of the suspension;

[0081] Fig.46A is a plan view of a gimbal of a suspension including a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0082] Fig.46B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line J-J'. Fig.46A sectional view of;

[0083] Fig.46CIt is obtained based on simulation Fig.46A A graph of the PZT frequency response function of the suspension;

[0084] Fig.47A is a plan view of a universal joint of a suspension assembled with a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0085] Fig.47B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line K-K'. Fig.47A sectional view of;

[0086] Fig.47C It is obtained based on simulation Fig.47A A graph of the PZT frequency response function of the suspension;

[0087] Fig.48A is a plan view of a universal joint of a suspension assembled with a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0088] Fig.48B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line L-L'. Fig.48A sectional view of;

[0089] Fig.48C It is obtained based on simulation Fig.48A A graph of the PZT frequency response function of the suspension;

[0090] Fig.49A is a plan view of a universal joint of a suspension assembled with a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0091] Fig.49B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line M-M'. Fig.49A sectional view of;

[0092] Fig.49C It is obtained based on simulation Fig.49A A graph of the PZT frequency response function of the suspension;

[0093] Fig.50A is a plan view of a universal joint of a suspension assembled with a single-layer microactuator PZT assembly according to an alternative embodiment of the present disclosure;

[0094] Fig.50B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line N-N'. Fig.50A sectional view of;

[0095] Fig.50C It is obtained based on simulation Fig.50A A graph of the PZT frequency response function of the suspension;

[0096] Fig.51 is a cross-sectional view of one embodiment of a single-layer microactuator PZT assembly according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0097] Figure 7 1 is a side cross-sectional view of a PZT microactuator (microactuator) assembly 114 having a constraining layer 130 bonded thereto in accordance with one embodiment of the present invention. To be consistent with the orientation shown in the figure, the side of the PZT bonded to the suspension will be referred to as the bottom side 129 of the PZT 114, and the side of the PZT away from the side of the PZT bonded to the suspension will be referred to as the top side 127. In accordance with the present invention, one or more constraining layers or constraining elements 130 are bonded to the top side 127 of the microactuator PZT element 120. The constraining layer 130 preferably comprises a hard and resilient material such as stainless steel, and is preferably bonded directly to the top surface 127 of the PZT element 120, which includes its top electrode 126 on the top surface 127, or the SST material itself can serve as the top electrode, thereby eliminating the need for separate metallization of the top surface. The constraining layer 130 has sufficient hardness to greatly reduce, eliminate, or even reverse the bending of the PZT when actuated (activated). The SST layer 130 preferably has a layer of gold or other contact metal 131 to ensure good electrical connection to the SST.

[0098] Alternatively, the constraining layer 130 is not stainless steel but can be a ceramic, for example an inactive (non-polar or non-polarized) layer of the same ceramic material as the piezoelectric layer 120, and can be integrated into the assembly by bonding or deposition. The ceramic material is non-polarized, which means that the piezoelectric properties exhibited by the ceramic material are significantly lower than the piezoelectric properties of the polarized ceramic defining the piezoelectric layer 120, for example lower than 10%. Such an assembly defining a stack consisting of electrode / polar PZT / electrode / non-polar PZT from bottom to top is easier to manufacture than a stack of electrode / PZT / electrode / SST.

[0099] In the discussion that follows, the top and bottom electrodes 126, 128 are sometimes omitted from the figures and discussions to simplify the discussion, with the understanding that PZT microactuators almost always have at least some type of top and bottom electrodes.

[0100] Prior to applying the gold layer 131, a layer of copper or nickel may be deposited on the SST layer 130 to increase the adhesion of the gold to the SST, as discussed in U.S. Pat. No. 8,395,866 to Schreiber et al., owned by the assignee of the present application, which is hereby incorporated by reference for its teachings on electrodeposition of other metals onto stainless steel. Similarly, the electrodes 126, 128 may include a combination of nickel and / or chromium and gold (NiCr / Au).

[0101] 124-167( Figure 5 ). In one illustrative embodiment based on simulations, the thickness of each layer is:

[0102] 130PZT 3μm

[0103] 126, 128, 131NiCr / Au 0.5μm

[0104] The length of the thin film PZT is 1.20 mm, the width of the two ends of the PZT bonding is 0.15 mm, and the piezoelectric coefficient d31 is 250 pm / V. In some embodiments, the SST layer can be at least 12 microns thick to provide sufficient support.

[0105] In the above example, according to simulations, the DSA suspension exhibits a travel sensitivity of 26.1 nm / V. In comparison, a 45 μm thick bulk PZT (d31=320 pm / V) with the same geometry would typically exhibit a travel sensitivity of only 7.2 nm / V.

[0106] The thickness ratio of the SST layer to the PZT layer can be as high as 1:1, or even 1.25:1, or even higher. When the thickness ratio of the constraining layer to the PZT reaches about 1:25, the stroke sensitivity improvement due to the constraining layer may begin to be negative, indicating the thickness limit of the PZT constraining layer.

[0107] Fig. 8A yes Figure 7 A side cross-sectional view of a PZT microactuator 114 when a voltage is applied to the PZT so as to expand it. The stroke of the PZT consists of two vectors, one vector being the pure extension stroke δe, and the other vector being the extension contribution δ1 due to the fact that the right end of the PZT is bent upward (rather than downward as would be the case without the constraint layer) caused by the constraint layer. The total stroke length is δe+δ1. Therefore, in the expansion mode, when viewed from the top, the PZT presents a slightly concave shape, that is, the top surface of the PZT presents a slightly concave shape, and its bending direction is opposite to the bending of the prior art PZT of Figure 4A. Therefore, the bending according to the present invention increases the length of the effective stroke rather than reducing the length of the effective stroke.

[0108] Figure 8B yes Figure 74B . FIG. 4B is a side cross-sectional view of a PZT microactuator when a voltage is applied to the PZT 114 so as to cause it to contract. The stroke of the PZT consists of two vectors, one vector being the pure contraction stroke -|δc|, and the other vector being the contraction contribution δ2 due to the fact that the right end of the PZT is bent downward (rather than upward as in the absence of the constraining layer) caused by the constraining layer. The total stroke length is -[δc+δ2]. Therefore, in the contraction mode, when viewed from the top, the PZT presents a slightly convex shape, that is, the top surface of the PZT presents a slightly convex shape, and its bending direction is opposite to the bending of the prior art PZT of FIG. 4B . Therefore, this bending according to the present invention increases the length of the effective stroke rather than reducing the length of the effective stroke.

[0109] Adding the constraining layer 130 to the PZT microactuator 114 has no significant effect on the stroke length of the otherwise unconstrained and unbonded PZT 114. However, when the PZT 114 is bonded to the suspension 18 at its bottom end (as shown in FIG. 2 ), the effect of the constraining layer actually increases the stroke length slightly. The Young's modulus of stainless steel is approximately 190-210 GPa. Preferably, the material of the constraining layer has a Young's modulus greater than 50 GPa (more preferably greater than 100 GPa, more preferably greater than 150 GPa).

[0110] Fig. 9 Graph of stroke length per unit input voltage in nm / V versus constraining layer thickness based on simulations, where PZT 114 is 130 μm thick with a stainless steel constraining layer 130 bonded to it. Adding 20 μm, 40 μm, and 60 μm thick SST constraining layers to the top surface of the PZT each results in an increase in the total stroke length. Therefore, adding constraining layers actually increases the total stroke length.

[0111] It is also possible to keep the total combined thickness of the PZT and the constraining layer constant and determine the optimum thickness of the constraining layer. Fig.10 is a side cross-sectional view of a combined PZT and a constraining layer bonded thereto according to the present invention, wherein the total thickness is kept constant at 130 μm. Fig.11 It is obtained based on simulation Fig.10 Figure 2 shows a graph of the stroke length of a PZT versus the thickness of the PZT, where the combined thickness of the PZT and the constraining layer is held constant at 130 μm. Without the constraining layer, the stroke length of the 130 μm thick PZT is about 14.5 nm / V. With a constraining layer 130 thickness of 65 μm and a PZT thickness of 65 μm, the stroke length of the PZT is about 20 nm / V. Therefore, adding the constraining layer actually increases the effective stroke length by about 35%.

[0112] Fig.12The GDA travel sensitivity and constraint layer thickness curve obtained from the simulation, where the GDA suspension has Figure 7 The microactuator has a PZT element with a thickness of 45μm and a stainless steel constraint layer of different thicknesses on top. As can be seen from the figure, a constraint layer with a thickness of 30μm increases the stroke sensitivity of the GDA from 9nm / V to just over 14.5nm / V(μm), which means an increase in stroke length of more than 50%.

[0113] Figures 13A-13H A manufacturing process is described by which a PZT microactuator assembly with a constraining layer according to the present invention can be produced. The method is an example of an additive method, in which the PZT material is deposited onto a substrate that will become the constraining layer. Fig.13A As shown, the process starts with a first substrate 140. Fig. 13B In the process, a first UV (ultraviolet light) / heat carrier tape 142 is applied to the substrate. Fig. 13C In the embodiment, a preformed SST layer 130 is added to the carrier tape. Fig.13D In the embodiment, the electrode layer 126 is deposited onto the SST, for example by sputtering or other well-known deposition processes. Fig.13E In the embodiment, the PZT layer 120 is formed on the electrode layer by a sol-gel method or other known methods. Fig.13F In , the second electrode 128 is deposited onto the exposed side of the PZT, for example by sputtering. Figure 13G In the process, the SST layer 130 is separated from the carrier tape, and the product is turned over onto the second carrier tape 143 and the second substrate 141. Fig.13H In the process, the product is cut, for example, by mechanical sawing or laser cutting, so as to separate the individual microactuators 114. This process produces a microactuator 114 in which the PZT element 120 including its electrode is directly bonded to the SST confinement layer 130 without any other material in between (for example, an organic material such as polyimide that will reduce the confinement effect of the confinement layer). The material of the electrode layer can be gold, nickel, chromium and / or copper. The Young's modulus of gold is about 79 GPa, the Young's modulus of copper is about 117 GPa, the Young's modulus of nickel is about 200 GPA, and the Young's modulus of chromium is about 278 GPA. Preferably, there is no intermediate layer between the SST confinement layer 130 and the PZT element 120, and the Young's modulus of the PZT element 120 is less than 20 GPa, or its Young's modulus is significantly less than the Young's modulus of the confinement layer, or its Young's modulus is less than half of the Young's modulus of the confinement layer.

[0114] Although other methods can be used to produce this product, such as bonding the constraining layer directly to the PZT surface via an adhesive (such as epoxy), it is currently expected that Figures 13A-13H The method shown is the preferred method.

[0115] The SST constraining layer 130 serves as a substrate for the PZT layer 120 both during the additive manufacturing process and in the finished product. Therefore, the constraining layer 130 is sometimes referred to as a substrate.

[0116] 14(A) and 14(B) are oblique views of a gimbal-supported dual-stage actuation (GSA) suspension 150 equipped with a thin film PZT microactuator motor 114 according to the present invention. In a GSA suspension, the PZT is mounted on a trace gimbal that includes a gimbal assembly and directly acts on the gimbal area of ​​the suspension that holds a read / write head (head) slider 164. FIG. 14(A) shows the suspension 150 before the PZT microactuator assembly 114 is attached. Each of the two microactuators 114 will be bonded to a tongue 154 and a portion 156 of the trace gimbal and will span a gap 170 between the tongue 154 and the portion 156, wherein the distal end of the microactuator 114 is bonded to the tongue 154 and the proximal end of the microactuator 114 is bonded to the portion 156. FIG. 14(B) shows the suspension 150 after the PZT microactuator 114 is attached. When the microactuator assembly 114 is activated, it expands or contracts, thereby changing the length of the gap 170 between the tongue 154 and the portion 156 of the trace gimbal, thereby affecting the fine positioning movement of the head slider 164 carrying the read / write sensor.

[0117] Fig.15 14(B) is a cross-sectional view taken along the section line BB'. The GSA suspension 150 includes a trace gimbal 152, which includes multiple layers of stainless steel, an insulator 157 (such as polyimide) and a layer of signal conducting traces 158 (such as copper) covered by a protective metal 159 (such as gold or a nickel / gold combination). The distal end of the microactuator 114 is connected to the stainless steel tongue 154 extending from the gimbal area by a conductive adhesive 162 (such as an epoxy containing Ag particles to make it conductive) and its proximal end is connected to the stainless steel mounting area 156 by a non-conductive adhesive 161 (such as non-conductive epoxy). The electrical connection of the drive voltage is achieved by a dot-shaped conductive adhesive 160 extending from the gold-plated copper contact pad 158 to the top surface of the PZT microactuator 114 (more specifically, in this case, to the SST layer 130, which constitutes the top electrode of the microactuator). The thickness of the SST substrate may be varied to some extent without affecting the advantages of the disclosed thin film PZT structures. Fig.16 It is obtained based on simulation Fig.15Figure 2 shows the stroke sensitivity of the microactuator versus the thickness of the SST confinement layer. According to the simulation, the thin film PZT with a 40μm thick SST confinement layer exhibits a stroke sensitivity of 20nm / V, which is almost 3 times the stroke sensitivity of the 45μm thick bulk PZT mentioned above. However, the 45μm thick SST confinement layer will provide better protection for the thin film PZT microactuator.

[0118] Figures 17A-17F An alternative process for fabricating a thin film PZT structure with an SST confinement layer according to the present invention is described. Fig.17A In the process, the process starts with a silicon substrate 144, rather than Fig. 13B Starting from substrate 140 and carrier tape 142. Fig. 17B In the process, the SST layer (130) is bonded to the silicon. Figures 13C-13H The process is carried out in essentially the same manner, including Fig.17E In addition, these figures clearly show the addition of the final NiCr / Au layer 131, which is Fig.13E Not explicitly shown.

[0119] As described above, different types of constraining layers can be used in different embodiments. Other rigid materials (whether conductive or non-conductive) can also be used as constraining layers or substrates. For example, silicon can be used as a constraining layer material. Fig.18 is a top view of a thin film PZT structure with a silicon confinement layer according to an embodiment of the present invention. Fig.19 It is taken along the section line A-A' Fig.18 2. A cross-sectional view of a microactuator of FIG. 2. Because the silicon confinement layer 230 is non-conductive, a via 232 is provided to conduct the PZT drive voltage from a conductive top layer 234 (e.g., Au) on the silicon 230 to the metallized electrode 126 on the PZT element 120. The via can be formed and filled with a conductive metal as disclosed in U.S. Pat. No. 7,781,679 to Schreiber et al., which is owned by the assignee of the present invention and is incorporated herein by reference for its teachings on conductive vias and methods of forming conductive vias.

[0120] Fig. 20 It is obtained based on simulation Fig.19 Figure 2 shows a graph of the stroke sensitivity of a microactuator versus the thickness of the silicon substrate. As shown, a 3μm thick thin film PZT and a 20μm thick silicon substrate can exhibit a stroke sensitivity of 31.5nm / V. This is four times higher than the stroke sensitivity of a design using 45μm thick bulk PZT. The silicon substrate also helps improve the reliability of the thin film PZT.

[0121] Figures 21A-21E Explains the manufacturing Fig.18 The process of thin film PZT structure. Fig.21A and 21B In , the process starts with a silicon substrate having a hole or via 232 that has been formed therein, for example by laser drilling. Fig. 21C In FIG. 1 , a NiCr / Au layer is added to a silicon substrate 230 to form the top electrode 126. The NiCr / Au also fills the hole to make it an electrical via 232. More generally, the via can be filled with other conductive materials. Fig.21D In , a PZT thin film 120 is deposited, for example, by a sol-gel method, and another layer of NiCr / Au is added to form a bottom electrode 128. Fig.21E In the embodiment of the present invention, the material is turned over and the final NiCr / Au layer 131 is added. Layers 131 and 126 are electrically connected through vias 232 so that a voltage (or ground potential) applied to the conductive gold layer 131 will be transferred to the PZT element 126. The manufacturing process of this thin film PZT microactuator with a silicon substrate may not be as complicated as the manufacturing process of thin film PZT with an SST substrate.

[0122] In an alternative embodiment, the middle through hole on the silicon substrate can be replaced by one or more through holes at the ends of the silicon substrate.Therefore, after the final cutting, a semicircle will be formed at each end of the silicon substrate. Fig. 22 is a top view of a thin film PZT microactuator having a silicon or other non-conductive confinement layer 330 having a conductive top layer 231 (eg, a metallization layer) thereon and having side vias 234 , 236 electrically connecting the top layer 231 to a top electrode 126 . Fig.23 It is taken along the section line A-A' Fig. 22 The manufacturing process of this embodiment can be similar to Figures 21A-21E The manufacturing process is the same.

[0123] The constraining layer can be larger (larger surface area) than the PZT elements, the same size as the PZT elements, or can be smaller (smaller surface area) than the PZT elements. Fig.24is a side cross-sectional view of a PZT microactuator assembly 414 in which a constraining layer 430 is smaller than a PZT element 420, thereby giving the microactuator a stepped structure having a step 434 and an exposed ledge 422 not covered by the constraining layer 430, where electrical connections are made to the PZT element 420. One advantage of this structure including a step where electrical connections are made is that the complete assembly including electrical connections has a smaller profile than if the constraining layer 430 covered the entire PZT 420. A smaller profile is advantageous because it means that more hard drive platters and their suspensions can be stacked together within a given platter stack height, thereby increasing data storage capacity within a given volume of a disk drive assembly. It is expected that the constraining layer 430 will cover more than 50% but less than 95% of the top surface of the PZT element 420 to accommodate the electrical connections on the ledge 422.

[0124] Simulations show that the microactuator constructed according to the present invention exhibits enhanced stroke sensitivity and reduced rocking mode gain and torsional mode gain, which are beneficial in increasing the bandwidth of the head positioning control loop, which will reduce data seek time and reduce sensitivity to vibration.

[0125] Fig.25 Is a pair Fig.24 An oblique view of the GSA suspension of the PZT microactuator 414.

[0126] Fig.26 It is taken along the section line A-A' Fig.25 4. A cross-sectional view of a GSA suspension of FIG. 4. In this embodiment, the conductive adhesive 460 (e.g., conductive epoxy) does not extend onto the constraining layer 430. Instead, the conductive epoxy 460 extends onto the ledge 422 on top of the PZT element 420 and establishes electrical connections to the PZT 420 and the entire microactuator assembly 414 through that surface. As depicted, the uppermost portion of the electrical connections defined by the conductive epoxy 460 is below the top surface of the SST constraining layer 430. More generally, whether the electrical connections are made by a conductive adhesive or by wires bonded, for example, by thermosonic bonding, welding, or other techniques, the electrical connections 461 to the microactuator assembly 414 can be no higher than or even lower than the uppermost portion of the microactuator 414. This allows the electrical connections to the microactuator assembly 414 to be as thin as possible, which in turn allows for a more dense stack of data storage platters in the platters stack of the disk drive assembly.

[0127] Also clearly shown is a gold layer 469 on the stainless steel portion 154 of the trace gimbal that mounts the microactuator 414. The gold layer 469 provides corrosion resistance and enhanced conductivity to the SST.

[0128] In this embodiment, as in all other embodiments, the constraining layer, and more generally the top surface of the PZT microactuator assembly, typically has nothing bonded to it other than the electrical connections.

[0129] Fig. 27 Based on simulation Fig.26 A frequency response graph of the PZT frequency response function of the suspension. The suspension exhibits reduced rocking mode gain and torsional mode gain compared to the simulation without the constraining layer 430. These are beneficial in increasing the bandwidth of the head positioning control loop, which reduces data seek time and reduces sensitivity to vibration.

[0130] Figures 28A-28J Explains the manufacturing Fig.24 The process of thin film PZT component 114. Fig.28A In the embodiment, a bulk PZT wafer 420 is placed on a transfer carrier 422. Fig.28B In the embodiment, a top electrode layer 426 is formed, for example, by sputtering and / or electrodeposition. Fig.28C In , mask 436 is placed over a portion of top electrode 426. Fig.28D In the embodiment of the present invention, a conductive epoxy 432 is applied. Fig.28E In the embodiment of the present invention, a stainless steel layer as a constraining layer 430 is applied to the epoxy resin, which is then cured. Fig.28F , remove mask 436. Figure 28G In the process, the assembly is turned over and laid down on the second transfer carrier 443. Fig.28H In the process, a bottom electrode layer 428 is formed, for example, by sputtering and / or electrodeposition. Then, the PZT element 420 is polarized. Fig.28I The assembly is then flipped over again onto the third transfer carrier 444. Fig.28J The components are then separated by cutting to produce finished PZT microactuator assemblies 414.

[0131] Fig.29 5 is a side cross-sectional view of a multilayer PZT assembly 514 according to another embodiment of the present invention. The assembly includes a multilayer PZT element 520, a first electrode 526 encapsulating the device, a second electrode 528, and a constraining layer 530 bonded to the PZT element 520 by a conductive epoxy 532. A two-layer PZT device is shown. More generally, the device can be an n-layer PZT device.

[0132] Fig.306 is a side cross-sectional view of a multilayer PZT microactuator assembly 614 according to another embodiment of the present invention, wherein the extra thick electrode serves as a constraining layer. In this embodiment, the PZT element 620 has a top electrode 626 and a bottom electrode 628. The top electrode 626 includes a thinner first portion 622 and a thicker second portion 630, the first portion 622 defining a stage, and the second portion 630 performing most of the constraining function. The 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 including a mask to form the step 634, or by a deposition process in which material is selectively removed to form the step. Alternatively, the second electrode 626 can be a piece of conductive material (such as SST) formed separately and then bonded to the PZT element 620. Therefore, the material of the top electrode 626 can be the same or different from the material of the bottom electrode 628. The thicker second portion 630 may be at least 50% thicker than the thinner portion 622 and / or the second electrode 628, or the thicker second portion 630 may be at least twice as thick as the thinner portion 622 and / or the second electrode 628. Figure 24-26 As in the embodiment of FIG. 5 , electrical connectors may be disposed on a ledge defined by thinner portion 622 without extending as high as or above a top surface of thicker portion 630 defining a constraining layer.

[0133] The scope of the present invention is not limited to the exact embodiments shown. Various changes will be apparent to those skilled in the art after receiving the teachings herein. For example, the constraint layer need not be stainless steel, but can be some other relatively hard and resilient material. The constraint layer need not be a single layer of one material, but can be composed of different layers of different materials. Although the constraint layer can cover the entire surface or substantially cover the entire top surface, the constraint layer can cover less than the entire surface, for example, covering more than 90% of the top surface area, covering more than 75% of the top surface area, more than 50% of the top surface area, or even more than 25% of the top surface area. In embodiments with step features, it is expected that the constraint layer will cover less than 95% of the top surface of the microactuator. The constraint layer does not have to be a single integral layer, but can include multiple pieces, such as a plurality of constraint strips arranged side by side on the top surface of the PZT, wherein the constraint strips extend along the expansion / contraction direction or extend along a direction perpendicular to the expansion / contraction direction. In one embodiment, the constraining layer may include two stainless steel or other material constraints bonded to the top surface of the PZT, the size and location of the two constraints and their bonding generally mirroring the mounting areas of the two mounting scaffolds to which the PZT is bonded on its bottom surface. When the overall stiffness added by the constraining layer on the top of the device is generally matched (consistent) with the overall stiffness added by bonding the bottom of the device to the suspension, and the bonding areas are generally mirror images of each other, the net bending produced should be zero or close to zero. The result will be a PZT microactuator that exhibits little bending when actuated when mounted and deployed on the suspension.

[0134] In any and all embodiments discussed herein or suggested thereby, the constraining layer may be selected to reduce the PZT bending that occurs during actuation, or the constraining layer may be selected to eliminate as much of the PZT bending as possible, or the constraining layer may be selected to reverse (invert) the sign (positive or negative, direction) of the PZT bending. In applications where the PZT is to be used as a hard disk drive microactuator, it is contemplated that in most cases it will be desirable to use a constraining layer to reverse the sign of the bending shown and described in the above illustrative examples, as this increases the effective stroke length. However, in other applications of the PZT, reversing the sign may be undesirable. Thus, the present invention may be generally useful for controlling the direction and amount of bending of a PZT, regardless of how the PZT is mounted or otherwise attached to other components in any particular application. Depending on the application and parameters selected, the constraining layer may be used to reduce the bending of the PZT to less than 50% of its original value, or less than 25% of its original value, or to reverse the sign of the bending. When the sign is reversed, a PZT bonded at or near both ends of its bottom surface and having a constraining layer on top will bend when the PZT is in an expansion or stretching mode so that its top surface exhibits a concave shape, rather than a convex shape like a similar PZT without the constraining layer. Likewise, when the PZT is in a contraction mode, the PZT will exhibit a convex shape, rather than a concave shape like a similar PZT without the constraining layer.

[0135] For various reasons, PZT elements are sometimes prestressed in applications so that when the PZT is not actuated by any voltage, the PZT is already bent in one direction or the other, i.e., the PZT is already concave or convex. Of course, such a prestressed PZT can be used as a microactuator in the present invention. In this case, the PZT may not bend into a net or absolute concave shape or a net or absolute convex shape. For example, if the PZT is prestressed so that it already has a concave shape, when activated with a positive activation voltage, the device may bend into a more concave shape, and when activated with a negative activation voltage, the device may bend into a less concave shape, which may be a nominally planar shape or a convex shape. Therefore, unless otherwise specified, the terms "concave" and "convex" should be understood as relative terms, not absolute terms.

[0136] Fig.31is a cross-sectional view of an embodiment of a multilayer microactuator PZT assembly 3100, wherein the constraining layer of the microactuator assembly includes one or more active PZT layers 3130, 3140 that tend to act in an opposite direction to a main active PZT layer 3120 that is adjacent to the surface of the suspension to which the microactuator 3100 is bonded. Therefore, the PZT constraining layers 3130, 3140 constrain and actively resist the action of the main PZT layer 3120, and thus may be referred to as "constraining layers" or "resisting layers."

[0137] The PZT layers 3120, 3130 and 3140 are arranged in a stacked planar relationship with each other. The main PZT layer 3120 includes an active PZT region 3121, which is subjected to an electric field during polarization and is thus polarized, and is subjected to an electric field during device activation and thus expands or contracts, and the main PZT layer 3120 also includes inactive (passive) PZT regions 3122 and 3123, which are not subjected to significant electric fields during polarization or activation and therefore have no significant piezoelectric activity. The device includes: a first or bottom electrode 3124; a second and top electrode 3126 for the active PZT region; a third electrode 3132 including an end 3128 such that the electrode 3132 extends between the first active confinement layer 3130 and the second active confinement layer 3140 and wraps around the end of the PZT; and a fourth electrode 3142 located on top of the second active confinement layer 3140 and including a wrapping portion 3143 that wraps around the sides and bottom of the device. The device can be bonded to the suspension using a conductive adhesive such as conductive epoxy 3160 and conductive epoxy 3162, the conductive epoxy 3160 mechanically and electrically bonding the electrode 3142 to the drive voltage electrical contact pad 158 that provides the microactuator drive voltage, and the conductive epoxy 3162 mechanically and electrically bonding the electrodes 3124 and 3128 of the device to the ground portion 154 of the suspension.

[0138] To understand the operation of the device, it is necessary to understand how the device is polarized. Fig.32 Shows Fig.31 The polarization of the device is shown in Figure 31, and includes the resulting polarization direction of each layer of 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 show the resulting polarization direction of the active PZT layers 3120, 3130, and 3140.

[0139] Back to Fig.31 , which shows how the device 3100 is connected in this illustrative embodiment. Conductive epoxy 3162 bridges between electrodes 3124 and 3132, thereby electrically connecting them, thereby converting a 3-pole device during poling to a 2-pole device in operation (running). The connection of the electrodes can be made electrically connected by other well-known means other than conductive epoxy 3162, but using the same conductive epoxy 3162 to bond the device to the suspension assembly can complete the connection function without the need for a separate connection step.

[0140] When a voltage is applied to the electrode 3142 so that the main PZT layer 3120 expands in the x-direction (from left to right) as seen in the figure due to the expansion of the active area 3121, the active PZT constraining layers 3130 and 3140 will contract in the x-direction. In other words, the two constraining layers 3130, 3140 tend to counteract the main PZT layer 3120, or act in the opposite direction.

[0141] To explain in more detail, when the device is Fig.32 is polarized as shown and the device is Fig.31 When electrically connected as shown, the device operates as follows. Applying a positive device activation voltage across the electrical contact pad 158 and the electrode 3142 while grounding the electrode 3124 causes the following reaction. The activation voltage applied to the main PZT layer 3120 is opposite in polarity to the voltage applied during poling. Therefore, the main PZT layer 3120 contracts in the z-direction and therefore expands in the x-direction. At the same time, the polarity of the activation voltage is the same as the polarity of the voltage applied to the two constraining layers 3130, 3140 during poling. Therefore, these PZT layers expand in the z-direction and therefore contract in the x-direction. Therefore, the two constraining layers 3130, 3140 tend to contract, while the main PZT layer 3120 tends to expand in the relevant direction.

[0142] The effect of the constraining layer acting in the opposite direction to the main PZT layer is similar to that described above for passive (inactive) constraining layers (e.g. Fig.10 The effect of the active PZT constraining layer is to reduce the bending caused by the main PZT layer and the mounting (bonding) of the main PZT layer to the suspension, and can even reverse the sign of the bending, in either case increasing the net displacement caused by the microactuator when mounted.

[0143] Fig.33 yes Fig.31 An exploded view of the microactuator assembly showing the electrical connections conceptually. Fig.31 and Fig.32 Not visible in but in Fig.33 Optional features visible in FIG. 31 include pattern 3133 on electrode 3132 and voltage reducer 3144 associated with electrode 3142, the functions of which will be described below.

[0144] Reasons for wanting a thinner microactuator assembly include: (1) less mass on the suspension, particularly at or near the gimbal in a gimbal-based DSA suspension, sometimes referred to as a GSA suspension, which means greater lift measured in the direction of gravity, i.e., greater shock resistance; (2) reduced windage; and (3) greater stacking density within the head stack assembly, which means that more data can be stored in the same volume of disk drive stack assembly space. Therefore, it is desirable to make the PZT constraining layers relatively thin. However, the thinner the PZT constraining layers, the higher the electric field strength across these layers during operation, and thus the PZT constraining layers are susceptible to depolarization during operation due to the high electric field strength. Therefore, nominally, the main PZT layer and the constraining PZT layer should have the same thickness.

[0145] One solution to thinning the constrained PZT layer without subjecting it to depolarization is to use one or more possible measures to reduce the electric field strength on the constrained layer without significantly reducing the electric field on the main PZT layer. A first measure to achieve this goal is to pattern one or more electrodes that are operationally associated with one of the active PZT constrained layers but operationally unrelated to the main PZT layer, such as adding holes 3133 or other electrical voids in the electrode 3132. The patterning can also take the form of a mesh pattern, such as a grid of parallel or intersecting conductors with electrical voids between each other. By reducing the area percentage of the electrical conductor within the planar electrode 3132, the electric field strength on the constrained layers 3130 and 3140 is effectively reduced without reducing the electric field strength on the main PZT layer 3120.

[0146] A second solution is to increase the coercive field strength of the constraining layer in order to make the constraining layer more resistant to depolarization. Coercive field strength (or simply "coercivity" when referring to piezoelectric materials) is a measure of how much electric field strength is required to depolarize a piezoelectric material. Making the constraining layers 3130, 3140 have a higher coercivity than the main PZT layer 3120 allows these constraining layers to be thinner without the risk of depolarization when subjected to the same activation voltage as the main PZT layer. By using different or slightly different piezoelectric materials, or by other processes, the constraining layers 3130, 3140 can be made to have a higher coercivity, but may come at the expense of some d31 stroke length or other desirable characteristics.

[0147] Another solution is to reduce the effective voltage applied to the drive electrode associated with the constrained layer by using some kind of voltage reducer (e.g., a voltage divider resistor network, a diode, a voltage regulator, or any of a variety of functionally similar devices that would occur to a person skilled in the art). In the figure, a general voltage reducer 3144 reduces the voltage received by the electrode 3142, thereby reducing the electric field strength to which the constrained layer 3140 is subjected, but does not reduce the electric field strength to which the main PZT layer 3120 is subjected. The voltage divider can be formed as a whole so as to be arranged between adjacent piezoelectric layers, for example by applying metallization forming the electrode layers so as to form a voltage divider resistor network on the surface of the PZT material. A simple resistor voltage divider requires a ground line, which can be implemented on the same layer. Many structures are possible, which will be apparent to the designer of such a device.

[0148] Both pattern 3133 and voltage reducer 3144 reduce the electric field strength on constrained layer 3140, thereby allowing constrained layer 3140 to be made thinner without causing unacceptable depolarization during operation. Electrode patterns and / or voltage reducers, and / or some other measures can be used to reduce the electric field strength on constrained layers 3130 and / or 3140. Pattern 3133 is formed integrally with electrode 3132 and is therefore formed integrally with and integrated into the microactuator assembly. The voltage reducer for one of the electrodes can be formed integrally with and integrated into the assembly, or it can be provided external to the assembly if the relevant electrode has its own electrical leads and is not connected to the other electrodes.

[0149] All of these solutions discussed above can be applied to systems with a single active confinement layer, two active confinement layers (e.g. Figure 31-33 ) or more generally n active confinement layers (such as Fig.35 Piezoelectric microactuator shown in FIG.

[0150] Fig.34 is a graph showing the stroke sensitivity (in nm / V) of a microactuator having one or more active confinement layers, the graph being based on simulations of various confinement layer structures (CLC), wherein the main PZT layer is 45 μm thick, without any pattern 3133 or voltage reducer 3144 to reduce the electric field strength, and having three different structures:

[0151] a) an inactive confinement layer ("passive CLC", diamond-shaped data points);

[0152] b) an active constraint layer ("single layer", square data points); and

[0153] c) Two active constraint layers ("double layer", triangular data points).

[0154] The data show that, at least for the parameters studied, PZT microactuators with an active constraining layer that acts in the opposite direction to the main PZT layer always produce higher stroke sensitivity than microactuators with the constraining layer being an inactive material. The highest stroke sensitivity is achieved using multiple active thin PZT layers as constraining layers (i.e., acting in the opposite direction to the main PZT layer). Specifically, the highest stroke sensitivity is achieved using two constraining layers, each of which is 5 μm thick, or approximately 11% of the thickness of the main PZT layer. Therefore, the thickness of the constraining layer is preferably less than 50% of the thickness of the main PZT layer, or more preferably less than 20% of the thickness of the main PZT layer, or more preferably in the range of 5-15% of the thickness of the main PZT layer.

[0155] For two active confinement layers, the stroke sensitivity decreases sharply with increasing confinement layer thickness, and is highest for two active confinement layers each about 5 μm thick. Therefore, the microactuator preferably has two or more confinement layers whose combined thickness is less than the thickness of the main PZT layer, more preferably their combined thickness is less than 50% of the thickness of the main PZT layer, more preferably the thickness of each confinement layer is less than half the thickness of the main PZT layer, more preferably the thickness of each confinement layer is less than 20% of the thickness of the main PZT layer, and more preferably the thickness of each confinement layer is in the range of 5-15% of the thickness of the main PZT layer.

[0156] For a microactuator assembly with a single active confinement layer, the loss of stroke sensitivity with increasing confinement layer thickness is not as dramatic as in the case of two active confinement layers. For a single active confinement layer, the local maximum (maximum of stroke sensitivity) occurs at a thickness of about 10 μm. Therefore, for a microactuator assembly with a single active confinement layer, the thickness of this layer is preferably in the range of 10-40% of the thickness of the main PZT layer, more preferably in the range of about 10-20% of the thickness of the main PZT layer.

[0157] Fig.35 is a cross-sectional view of another embodiment in which a microactuator assembly includes multiple active PZT layers and conceptually illustrates the poling process and resulting poling directions. Fig.35 The device is electrically and mechanically bonded to Fig.31 When the suspension is shown (where electrodes 3524 and 3528 are connected by conductive epoxy), the result is one main active PZT layer and three active PZT layers that act as constraining layers because the three active PZT layers tend to act in opposite directions to the main active PZT layer. That is, the bottom PZT layer expands while the top three PZT layers contract, or vice versa.

[0158] The structure of the microactuator assembly can be easily derived from Figure 31-33The device shown has an active main PZT layer and two active PZT confinement layers and Fig.35 The one active main PZT layer and three active PZT confinement layers shown extend to having any number of active main layers and active confinement layers. The electric field strength on one or more confinement layers can be reduced by various measures, including electrode patterns and / or voltage reducers. Experimentation will reveal the optimal number of confinement layers and the optimal thickness for different applications.

[0159] The PZT microactuators disclosed herein can be used as actuators in fields other than disk drive suspensions. Thus, such microactuators and their structural details constitute inventive devices regardless of the environment in which they are used, whether a disk drive suspension environment or any other environment.

[0160] Fig.36 is an isometric view of one embodiment of a single-layer microactuator PZT assembly 4000 . Fig.37 4 is a cross-sectional view of the single-layer microactuator PZT component 4000 taken along the cross-sectional line CC' in the PZT width direction. The single-layer microactuator PZT component 4000 further includes a top electrode 4042, a PZT element 4040, and a bottom electrode 4032. The top electrode 4042 is mounted on the top surface 4048 of the PZT element 4040. The bottom electrode 4032 is mounted on the bottom surface 4034 of the PZT element 4040.

[0161] The width W1 of the top electrode 4042 is narrower than the width W2 of the bottom electrode 4032. The top electrode 4042 includes a step 4044 at which the top electrode 4042 terminates. The PZT element 4040 includes an exposed portion 4046 of a top surface 4048 not covered by the top electrode 4042. In some embodiments, the top electrode 4042 is positioned on the PZT element 4040 opposite the PZT bonding surface.

[0162] The top electrode 4042 can be applied to the PZT element 4040 by a deposition process that includes a mask to form the step 4044, or by a deposition process in which material is selectively removed to form the step 4044. Alternatively, the top electrode 4042 can be a piece of conductive material, such as SST or other materials described herein, that is formed separately and then bonded to the PZT element 4040. Thus, the material of the top electrode 4042 can be the same as or different from the material of the bottom electrode 4032.

[0163] Fig.38A4050 according to an embodiment of the present disclosure including a single-layer microactuator PZT assembly 4000 of the gimbal. The exposed portion 4046 (i.e., the electrode dead zone) is located on the inner side of the PZT, and the remaining portion of the top surface of the PZT is the top electrode 4042. The PZT is mounted on a gimbal that includes a gimbal assembly and directly acts on the gimbal area of ​​the suspension that holds the read / write head slider. Each of the two microactuator PZT assemblies 4000 will be bonded between the tongue 4054 and the portion 4056 of the trace gimbal and span the gap between the tongue 4054 and the portion 4056, wherein the proximal end of the microactuator 4000 is bonded to the tongue 4054 and the distal end of the microactuator 4000 is bonded to the portion 4056.

[0164] Fig.38B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line D-D'. Fig.38A 4050. The PZT bottom electrode 4032 is bonded at the proximal end by a non-conductive adhesive 502 and a conductive adhesive 504 at the distal end. Conductive adhesive 504 is also applied to the proximal end of the top electrode 4042 to form the PZT electrical connection. When the microactuator assembly 4000 is activated, it expands or contracts, thereby changing the tongue 4054 and the portion 4056 of the trace gimbal ( Fig.38A ), thereby achieving fine positioning movement of the head slider carrying the read / write sensor.

[0165] The narrow width dimension of the top electrode 4042 creates an artificial constraint to offset the constraints imposed on the bottom electrode 4032 by the adhesive bonded at the proximal non-conductive adhesive 502 and the distal conductive adhesive 504. By appropriately selecting the width of the top electrode 4042, the suspension PZT excitation frequency response function (FRF) can have lower gain in several major modes across the entire frequency band.

[0166] Fig.39 It is obtained based on simulation Fig.38A FIG. 4 is a graph of the PZT frequency response function of the suspension. The width of the top electrode 4042 is 0.05 mm narrower than the bottom electrode 4032. As a result, the first gimbal torsion mode (GT1), the circuit torsion mode, and the load beam rocking mode are improved in gain. In particular, the gain of the load beam rocking mode is reduced by 3 dB, which helps to improve the head positioning servo control bandwidth, thereby reducing data seek time and reducing sensitivity to vibration.

[0167] Fig.40 is a plan view of a universal joint of a suspension 4150 including a single-layer microactuator PZT assembly 4000 according to an alternative embodiment of the present disclosure. Fig.40In the example, the exposed portion 4047 (electrode dead area) is positioned outside the PZT top surface 4048, while the rest of the PZT top surface 4048 is the top electrode 4042.

[0168] Fig.41 It is obtained based on simulation Fig.40 Graph of the PZT frequency response function of a suspension of FIG. The suspension exhibits gain variations in the first gimbal torsion mode, the circuit torsion mode, and the load beam rocking mode. This embodiment of the single-layer microactuator PZT assembly described herein can be used to adjust the PZT FRF of a suspension with opposite gain peaks to optimize the PZT FRF in these modes.

[0169] Fig.42 is a plan view of a gimbal of a suspension 4250 including a single-layer microactuator PZT assembly 4100 according to an alternative embodiment of the present disclosure. Fig.42 In the figure, the exposed portion 4146 (electrode dead area) is located on the inner and outer sides of the PZT top surface 4148, and the rest of the PZT top surface 4148 is the top electrode 4142. Fig.43 4 is a cross-sectional view of a single-layer microactuator PZT component 4100 taken along a cross-sectional line EE' in the width direction through the PZT. The single-layer microactuator PZT component 4100 includes a top electrode 4142, a PTZ element 4140, and a bottom electrode 4132. The top electrode 4142 is mounted on a top surface 4148 of the PZT element 4140. The bottom electrode 4132 is mounted on a bottom surface 4134 of the PZT element 4140. A width W3 of the top electrode 4142 is narrower than a width W4 of the bottom electrode 4132. The top electrode 4142 includes a step 4144, at which the top electrode 4142 terminates. The PZT element 4140 includes two exposed portions 4146 of a top surface 4148 that are not covered by the top electrode 4142. In some embodiments, the top electrode 4142 is positioned on the PZT element 4140 opposite to the PZT bonding surface.

[0170] The top electrode and the bottom electrode may be applied to the PZT element 4140 by a deposition process that includes a mask to form the step 4144, or by a deposition process in which material is selectively removed to form the top electrode. Alternatively, the top electrode may be a plurality of separate pieces of conductive material, such as SST, that are formed separately and then bonded to the PZT element 4140. Thus, the material of the top electrode may be the same as or different from the material of the bottom electrode 4132.

[0171] The narrower dimensions of the top electrode 4142 create an artificial constraint to counteract the constraints imposed on the bottom electrode 4132 by the PZT bonding to the proximal and distal ends of the bottom electrode. By properly selecting the width of the top electrode, the suspended PZT excited FRF can have lower gain in several major modes across the frequency band.

[0172] Fig.44A 4 is an oblique view of the universal joint of the suspension 4250 of the rotating single-layer microactuator PZT assembly 4000. The single-layer microactuator PZT assembly 4000 is rotated so that the top electrode 4042 is now the first side electrode 5042, and the exposed portion 4046 is also on the side surface. The bottom electrode 4032 is now the second side electrode 5032. In this configuration, the first side electrode 5042 and the second side electrode 5032 are electrically connected to the copper pad from both side surfaces thereof.

[0173] Fig.44B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line F-F'. Fig.44A The PZT first side electrode 5042 is bonded to the distal copper pad 606 by a conductive adhesive 604. A non-conductive adhesive 602 is also applied to the first side electrode 5042. Fig.44C According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line G-G'. Fig.44A The PZT second side electrode 5032 is bonded to the proximal copper pad 608 by a conductive adhesive 604. When the microactuator assembly 4000 is activated, it expands or contracts, thereby achieving fine positioning movement of the head slider carrying the read / write sensor.

[0174] The narrow width dimension of the first side electrode 5042 creates an artificial constraint to offset the constraint imposed on the second side electrode 5032 by the adhesive bonded at the proximal non-conductive adhesive 602 and the distal conductive adhesive 604. By appropriately selecting the width of the first side electrode 5042, the suspension PZT excitation frequency response function (FRF) can have lower gain in several major modes across the entire frequency band.

[0175] Fig.45A 4 is a plan view of a universal joint of a suspension 4350 assembled with a single-layer microactuator PZT assembly 4200 according to an alternative embodiment of the present disclosure. Fig.45A 4200, the exposed portion 4246 (electrode dead zone) is located on the inner and outer sides of the PZT top surface 4248, and the remaining portion of the PZT top surface 4248 is the top electrode 4242. The exposed portion 4246 (electrode dead zone) is configured to bend inwardly, thereby reducing the surface area of ​​the top electrode 4242 at or near the center of the PZT top surface 4246. The cross-sectional area of ​​the top electrode 4242 increases toward the distal and proximal ends of the single-layer microactuator PZT assembly 4200.

[0176] Fig.45B 4 is a cross-sectional view of a single-layer microactuator PZT assembly 4200, the cross-sectional view being taken along the cross-sectional line H-H' through the central PZT width direction of the single-layer microactuator PZT assembly 4200. A top electrode 4242 is mounted on a top surface 4248 of the PZT element 4240. A bottom electrode 4232 is mounted on a bottom surface 4234 of the PZT element 4240. The top electrode 4242 has a variable width W5 that increases toward the proximal end and the distal end. The variable width W5 of the top electrode 4242 is narrower than the width W6 of the bottom electrode 4232. The top electrode 4242 includes a step 4244 at which the top electrode 4242 terminates. The PZT element 4240 includes two exposed portions 4246 of the top surface 4248 that are not covered by the top electrode 4242. In some embodiments, the top electrode 4242 is positioned on the PZT element 4240 opposite to the PZT bonding surface.

[0177] The top and bottom electrodes may be applied to the PZT element 4240 by a deposition process that includes a mask to form the step 4244, or by a deposition process in which material is selectively removed to form the top electrode. Alternatively, the top electrode 4242 may be a plurality of separate pieces of conductive material, such as SST or other materials described herein, that are formed separately and then bonded to the PZT element 4240. Thus, the material of the top electrode 4242 may be the same or different from the material of the bottom electrode 4232.

[0178] The variable cross-section of the top electrode 4242 creates an artificial constraint to counteract the constraint imposed on the bottom electrode 4232 due to the PZT bonding on the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4242, the suspended PZT excitation FRF can have lower gain in several major modes across the frequency band.

[0179] Fig.45C It is obtained based on simulation Fig.45A A graph of the PZT frequency response function of the suspension. The curved exposed portions on both sides of the electrode (electrode dead zone) can be used to optimize the gain of the second gimbal torsional mode (GT2).

[0180] Fig.46A 4 is a plan view of a gimbal of a suspension 4450 including a single-layer microactuator PZT assembly 4300 according to an alternative embodiment of the present disclosure. Fig.46A43, the exposed portion 4346 (electrode dead zone) is positioned on the inner side of the PZT top surface 4348, and the rest of the PZT top surface 4348 is the top electrode 4342. The exposed portion 4346 (electrode dead zone) is configured to bend inwardly, thereby reducing the surface area of ​​the top electrode 4342 at or near the center of the PZT top surface 4348. The cross-sectional area of ​​the top electrode 4342 increases toward the distal and proximal ends of the single-layer microactuator PZT assembly 4300.

[0181] Fig.46B 4 is a cross-sectional view of a single-layer microactuator PZT assembly 4300, the cross-sectional view being taken along the cross-sectional line J-J' through the central PZT width direction of the single-layer microactuator PZT assembly 4300. A top electrode 4342 is mounted on a top surface 4348 of the PZT element 4340. A bottom electrode 4332 is mounted on a bottom surface 4334 of the PZT element 4340. The top electrode 4342 has a variable width W7 that increases toward the proximal end and the distal end. The variable width W7 of the top electrode 4342 is narrower than the width W8 of the bottom electrode 4332. The top electrode 4342 includes a step 4344 at which the top electrode 4342 terminates. The PZT element 4340 includes an exposed portion 4346 of the top surface 4348 that is not covered by the top electrode 4342. In some embodiments, the top electrode 4342 is positioned on the PZT element 4340 opposite to the PZT bonding surface.

[0182] The top and bottom electrodes may be applied to PZT element 4340 by a deposition process that includes a mask to form step 4344, or by a deposition process in which material is selectively removed to form the top electrode. Alternatively, top electrode 4342 may be multiple separate pieces of conductive material, such as SST or other materials described herein, that are formed separately and then bonded to PZT element 4340. Thus, the material of top electrode 4342 may be the same or different from the material of bottom electrode 4332.

[0183] The variable cross-section of the top electrode 4342 creates an artificial constraint to offset the constraint imposed on the bottom electrode 4332 by the PZT being bonded to the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4342, the suspended PZT excited FRF can have lower gain in several major modes across the frequency band.

[0184] Fig.46C It is obtained based on simulation Fig.46A A graph of the PZT frequency response function of the suspension. The curved exposed portion of the inner side of the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT1) gain (increase GT1 phase lag) and the rocking gain (increase rocking mode phase lead).

[0185] Fig.47A is a plan view of a gimbal of a suspension 4550 including a single-layer microactuator PZT assembly 4400 according to an alternative embodiment of the present disclosure. Fig.47A 4448, the exposed portion 4446 (electrode dead zone) is positioned outside the PZT top surface 4448, and the remaining portion of the PZT top surface 4448 is the top electrode 4442. The exposed portion 4446 (electrode dead zone) is configured to bend inwardly, thereby reducing the surface area of ​​the top electrode 4442 at or near the center of the PZT top surface 4448. The cross-sectional area of ​​the top electrode 4442 increases toward the distal and proximal ends of the single-layer microactuator PZT assembly 4400.

[0186] Fig.47B 4 is a cross-sectional view of a single-layer microactuator PZT assembly 4400, the cross-sectional view being taken along the cross-sectional line K-K' through the central PZT width direction of the single-layer microactuator PZT assembly 4400. A top electrode 4442 is mounted on a top surface 4448 of a PZT element 4440. A bottom electrode 4432 is mounted on a bottom surface 4334 of the PZT element 4440. The top electrode 4442 has a variable width W9 that increases toward the proximal end and the distal end. The variable width W9 of the top electrode 4442 is narrower than the width W10 of the bottom electrode 4432. The top electrode 4442 includes a step 4444 at which the top electrode 4442 terminates. The PZT element 4440 includes an exposed portion 4446 of the top surface 4448 that is not covered by the top electrode 4442. In some embodiments, the top electrode 4442 is positioned on the PZT element 4440 opposite to the PZT bonding surface.

[0187] The top and bottom electrodes may be applied to PZT element 4440 by a deposition process that includes a mask to form step 4444, or by a deposition process in which material is selectively removed to form the top electrode. Alternatively, top electrode 4442 may be multiple separate pieces of conductive material, such as SST or other materials described herein, that are formed separately and then bonded to PZT element 4440. Thus, the material of top electrode 4442 may be the same or different from the material of bottom electrode 4432.

[0188] The variable cross-section of the top electrode 4442 creates an artificial constraint to counteract the constraint imposed on the bottom electrode 4432 by the PZT bonding to the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4442, the suspended PZT excitation FRF can have lower gain in several major modes across the frequency band.

[0189] Fig.47C It is obtained based on simulation Fig.47AA graph of the PZT frequency response function of the suspension. The curved exposed portion of the outer side of the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT1) gain (increase GT1 phase lag) and the rocking gain (increase rocking mode phase lead).

[0190] Fig.48A 45 is a plan view of a gimbal of a suspension 4650 including a single-layer microactuator PZT assembly 4500 according to an embodiment of the present disclosure. The exposed portion 4546 (i.e., the electrode dead zone) is located at the distal end of the PZT and is curved so that the exposed portion on the outside is larger than the exposed portion on the inside. The remainder of the top surface of the PZT is the top electrode 4542. Each of the two microactuator PZT assemblies 4500 will be bonded to the tongue 4554 and the portion 4556 of the trace gimbal, and will span the gap between the tongue 4554 and the portion 4556 of the trace gimbal, wherein the proximal end of the microactuator 4500 will be bonded to the tongue 4554 and the distal end of the microactuator 4500 will be bonded to the portion 4556 of the trace gimbal.

[0191] Fig.48B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line L-L'. Fig.48A 4650. The PZT bottom electrode 4532 is bonded at the proximal and distal ends by non-conductive adhesive 502 and conductive adhesive 504, respectively. Conductive adhesive 504 is also applied to the proximal end of the top electrode 4542 to form the PZT electrical connection. When the microactuator assembly 4500 is activated, it expands or contracts, thereby changing the tongue 4554 and the portion 4556 of the trace gimbal ( Fig.48A ), thereby achieving fine positioning movement of the head slider carrying the read / write sensor.

[0192] Fig.48C It is obtained based on simulation Fig.48A A graph of the PZT frequency response function of the suspension. The curved exposed portion of the distal end of the electrode (electrode dead zone) can be used to optimize the gain of the first torsion mode (T1) and the first gimbal torsion mode (GT1).

[0193] Fig.49A 4 is a plan view of a gimbal of a suspension 4750 including a single-layer microactuator PZT assembly 4600 according to an alternative embodiment of the present disclosure. Fig.49A, the exposed portion 4646 (electrode dead zone) is positioned on a portion of the outer side of the PZT top surface 4648, and the rest of the PZT top surface 4446 is the top electrode 4642. Specifically, the top electrode 4642 may include a distal portion, a proximal portion, and a coupling portion connecting the distal portion and the proximal portion. As shown, the proximal portion may have a larger surface area than the distal portion of the top electrode 4642. Alternatively, the distal portion may have a larger surface area than the proximal portion of the top electrode 4642. In other embodiments, the proximal portion and the distal portion may have the same or substantially the same surface area. The exposed portion 4646 (electrode dead zone) is defined by the distal portion, the proximal portion, and the coupling portion of the top electrode 4642. The cross-sectional area of ​​the distal portion and the proximal portion is larger than the coupling portion of the top electrode 4642.

[0194] Fig.49B 4 is a cross-sectional view of a single-layer microactuator PZT assembly 4400, the cross-sectional view being taken along the cross-sectional line M-M' through the central PZT width direction of the single-layer microactuator PZT assembly 4600. A top electrode 4642 is mounted on a top surface 4648 of a PZT element 4640. A bottom electrode 4632 is mounted on a bottom surface 4634 of the PZT element 4640. A coupling portion of the top electrode 4642 has a width W11 that is narrower than a proximal portion and a distal portion (not shown). The width W11 of the top electrode 4642 is narrower than a width W12 of the bottom electrode 4632. The top electrode 4642 includes a step 4644 at which the top electrode 4642 terminates. The PZT element 4640 includes an exposed portion 4646 of a top surface 4648 that is not covered by the top electrode 4642. In some embodiments, the top electrode 4642 is positioned on the PZT element 4640 opposite the PZT bonding surface.

[0195] The top and bottom electrodes may be applied to PZT element 4640 by a deposition process that includes a mask to form step 4644, or by a deposition process in which material is selectively removed to form the top electrode. Alternatively, top electrode 4642 may be multiple separate pieces of conductive material, such as SST or other materials described herein, that are formed separately and then bonded to PZT element 4640. Thus, the material of top electrode 4642 may be the same or different from the material of bottom electrode 4632.

[0196] The multiple cross sections of the top electrode 4642 create artificial constraints to offset the constraints imposed on the bottom electrode 4632 due to the PZT bonding on the proximal and distal ends of the bottom electrode. By varying the width of the top electrode 4642, the suspended PZT excitation FRF can have lower gain in several major modes across the frequency band.

[0197] Fig.49C It is obtained based on simulation Fig.49A A graph of the PZT frequency response function of the suspension. The curved exposed portion of the outer side of the electrode (electrode dead zone) can be used to optimize the first gimbal torsion mode (GT1) gain (increase GT1 phase lag) and the rocking gain (increase rocking mode phase lead).

[0198] Fig.50A 47 is a plan view of a gimbal of a suspension 4850 including 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 of which is located on a portion of the outer side of a PZT top surface 4748, while the remainder of the PZT top surface 4748 is a top electrode 4742. Specifically, the top electrode 4742 may include a distal portion, a proximal portion, one or more intermediate portions between the distal portion and the proximal portion, and a coupling portion connecting the portions along the inner side of the PZT top surface 4748. In alternative embodiments, the patterned dead zones may be located along the inner side of the PZT top surface 4748. In other embodiments, the patterned dead zones may be located to alternate between the inner side of the PZT top surface 4748 and the outer side of the PZT top surface 4748.

[0199] The above-mentioned parts of the top electrode 4742 can have the same or substantially the same surface area. The exposed portion 4746 (electrode dead zone) is defined by the distal portion, the proximal portion, the middle portion and the coupling portion of the top electrode 4742. The cross-sectional area of ​​the distal portion, the proximal portion and the middle portion is larger than that of the coupling portion of the top electrode 4742.

[0200] Fig.50B According to an embodiment of the present disclosure, the cross-sectional view is taken along the cross-sectional line N-N'. Fig.50A 47. A cross-sectional view of a suspension 4750 of FIG. The PZT bottom electrode 4732 is bonded at the proximal and distal ends by a non-conductive adhesive 502 and a conductive adhesive 504, respectively. The top electrode 4742 includes a distal portion 4742C, a proximal portion 4742A, and one or more intermediate portions 4742B located between the distal portion and the proximal portion along the inner side of the PZT top surface 4748. A conductive adhesive 504 is also applied to the proximal portion 4742A to form an electrical connection to the PZT. When the microactuator assembly 4700 is activated, it expands or contracts, thereby changing the tongue 4754 and the portion 4756 of the trace gimbal ( Fig.50A ), thereby achieving fine positioning movement of the head slider carrying the read / write sensor.

[0201] Fig.50C It is obtained based on simulation Fig.50A Graph of the PZT frequency response function of the suspension. The patterned dead zone in the PZT top electrode 4742 can be used for resonance (response) optimization of the first torsion mode (T1) (increase T1 phase lag), the first gimbal torsion mode (GT1) (increase GT1 phase lead) and rocking (increase rocking phase lag). As demonstrated herein, the effect on the travel 3.7nm / V vs. 3.4nm / V is minimal.

[0202] Fig.51 5000 is a cross-sectional view of an embodiment of a single-layer microactuator PZT assembly according to an embodiment of the present disclosure. The single-layer microactuator PZT assembly 5000 also includes a top electrode 5042, a PZT element 5040, and a bottom electrode 5032. The top electrode 5042 is mounted on a top surface 5048 of the PZT element 5040. The bottom electrode 5032 is mounted on a bottom surface 5034 of the PZT element 5040.

[0203] The top electrode 5042 has a narrower width W1 than the PZT element 5040. The top electrode 5042 includes a step 5044 at which the top electrode 5042 terminates. The PZT element 5040 includes an exposed portion 5046 of a top surface 5048 that is not covered by the top electrode 5042. In some embodiments, the top electrode 5042 is positioned on the PZT element 4040 opposite the PZT bonding surface. The top electrodes of some embodiments have variable widths or are configured to expose portions of the PZT element according to the techniques described herein.

[0204] The width W2 of the bottom electrode 5032 is narrower than that of the PZT element 5040. The bottom electrode 5032 includes a step at which the bottom electrode 5032 terminates. The PZT element 5040 includes an exposed portion of the bottom surface that is not covered by the bottom electrode 5032. The bottom electrode of some embodiments has a variable width or is configured to expose portions of the PZT element according to the technology described herein. Some embodiments include a top electrode and a bottom electrode that are configured to have similar exposed surfaces on the top and bottom surfaces of the PZT element. Other embodiments include a top electrode and a bottom electrode so that the top and bottom surfaces of the PZT element have different exposed surfaces. Therefore, the top electrode may not cover the entire surface of the PZT element and may have a second electrode of the same shape and size or a different shape and size but located within the outer dimensions of the PZT element.

[0205] The top electrode 5042 and the bottom electrode 5032 can be applied to the PZT element 5040 by a deposition process that includes a mask to form the steps, or by a deposition process in which material is selectively removed to form the steps. Alternatively, the top electrode 5042 and / or the bottom electrode 5032 can be a piece of conductive material, such as SST or other materials described herein, that is formed separately and then bonded to the PZT element 5040. Thus, the material of the top electrode 5042 can be the same as or different from the material of the bottom electrode 5032.

[0206] Although a single PZT layer is described herein, the disclosed embodiments are applicable to multilayer PZT microactuator assemblies having multiple PZT elements using similar techniques described herein. The PZT FRF of a microactuator suspension assembled using a set of multilayer PZTs can be effectively tuned by appropriately selecting the width of the top electrode.

[0207] It is understood that the terms "generally," "approximately," "substantially," and "coplanar" used in the specification and claims allow for some variance from any precise size, measurement, and arrangement, and that these terms are to be interpreted in the context of the description and operation of the invention disclosed herein.

[0208] It will be further understood that terms such as "top", "bottom", "above" and "below" used in this specification and claims are terms of convenience that refer to the spatial relationship of components relative to each other rather than any particular spatial orientation or gravitational direction. Therefore, these terms are intended to include assembly of components regardless of whether the assembly is in the particular orientation shown in the figures and described in the specification, inverted from that orientation or with any other rotational variation.

[0209] All features disclosed in this specification, including claims, abstracts and drawings, and all steps of any method or process disclosed, can be combined in any way, except that at least some of such features and / or steps are mutually exclusive combinations. Each feature disclosed in the specification, including claims, abstracts and drawings, can be replaced by an alternative feature serving the same, equivalent or similar purpose, unless otherwise expressly stated. Therefore, unless otherwise expressly stated, each feature disclosed is only an example of a general series of equivalent or similar features.

[0210] It will be understood that the term "present invention" as used herein should not be construed as proposing only a single invention having a single essential element or group of elements. Likewise, it will also be understood that the term "present invention" includes a number of separate innovations, each of which may be considered a separate invention. Although the present invention has been described in detail with respect to its preferred embodiments and accompanying drawings, it will be apparent to those skilled in the art that various adjustments and modifications of the present invention may be accomplished without departing from the spirit and scope of the present invention. Therefore, it should be understood that the above detailed description and accompanying drawings are not intended to limit the breadth of the present invention, which should only be inferred from the following claims and their properly construed legal equivalents.

Claims

1. A micro-actuator assembly, the micro-actuator assembly comprising: at least one PZT element, the at least one PZT element comprising a first longitudinal side and an opposing second longitudinal side; a first electrode on a first surface of the microactuator assembly, the first surface of the microactuator assembly extending from the first longitudinal side to the second longitudinal side of the microactuator assembly, the first electrode having a first width extending over the entire length of the first longitudinal side of the at least one PZT element; as well as a second electrode located on a second surface of the microactuator assembly, the second surface of the microactuator assembly being opposite to the first surface of the microactuator assembly and extending from the first longitudinal side to the second longitudinal side of the at least one PZT element, the second electrode having a second width extending from the first longitudinal side and being less than a width of the first electrode, the second electrode being configured to offset the first electrode constraint applied by the piezoelectric adhesive.

2. The microactuator assembly according to claim 1, wherein: The first electrode and the second electrode are electrically connected by a conductive adhesive that bonds the microactuator assembly to a surface of a device.

3. The microactuator assembly according to claim 1, wherein: The at least one PZT element is a plurality of PZT elements disposed between the first electrode and the second electrode.

4. The microactuator assembly according to claim 1, wherein: The width of the second electrode may be variable along a longitudinal axis of the second electrode.

5. The microactuator assembly according to claim 4, wherein: The second electrode is configured to expose at least two portions of the at least one PZT element.

6. The microactuator assembly according to claim 4, wherein: The second electrode is configured to expose a portion of the at least one PZT element.

7. The microactuator assembly according to claim 1, wherein: The width of the second electrode may be variable along a latitudinal axis of the second electrode.

8. The microactuator assembly according to claim 7, wherein: The second electrode is configured to expose at least two portions of the at least one PZT element.

9. The microactuator assembly according to claim 7, wherein: The second electrode is configured to expose a portion of the at least one PZT element.

10. The microactuator assembly according to claim 1, wherein: The second electrode includes at least one exposed portion.

11. The microactuator assembly according to claim 10, wherein: The second electrode is configured to have a distal portion, a proximal portion, and a coupling portion connecting the distal portion and the proximal portion.

12. The microactuator assembly according to claim 10, wherein: The at least one exposed portion is a plurality of exposed portions.

13. A suspension for a disk drive, the suspension comprising: A micro-actuator assembly, the micro-actuator assembly comprising: at least one PZT element, the at least one PZT element comprising a first longitudinal side and an opposing second longitudinal side, a first electrode on a first surface of the microactuator assembly, the first surface of the microactuator assembly extending from the first longitudinal side to the second longitudinal side of the microactuator assembly, the first electrode having a first width extending the entire length of the first longitudinal side of the at least one PZT element; and a second electrode located on a second surface of the microactuator assembly, the second surface of the microactuator assembly being opposite to the first surface of the microactuator assembly and extending from the first longitudinal side to the second longitudinal side of the at least one PZT element, the second electrode having a second width extending from the first longitudinal side and being less than a width of the first electrode, the second electrode being configured to offset the first electrode constraint applied by the piezoelectric adhesive.

14. The suspension according to claim 13, wherein: The at least one PZT element is a plurality of PZT elements disposed between the first electrode and the second electrode.

15. The suspension according to claim 13, wherein: The width of the second electrode may be variable along a longitudinal axis of the second electrode.

16. The suspension according to claim 15, wherein: The second electrode is configured to expose at least two portions of the at least one PZT element.

17. The suspension according to claim 15, wherein: The second electrode is configured to expose a portion of the at least one PZT element.

18. The suspension according to claim 13, wherein: The width of the second electrode may be variable along a latitudinal axis of the second electrode.

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

20. The suspension according to claim 18, wherein: The second electrode is configured to expose a portion of the at least one PZT element.

21. The suspension according to claim 13, wherein: The second electrode includes at least one exposed portion.

22. The suspension according to claim 21, wherein: The second electrode is configured to have a distal portion, a proximal portion, and a coupling portion connecting the distal portion and the proximal portion.

23. The suspension according to claim 21, wherein: The at least one exposed portion is a plurality of exposed portions.

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