JP7402264B2 - Multilayer PZT microactuator with a PZT suppression layer that is polarized but inactive - Google Patents

Description

[Cross reference to related applications]
This application is a continuation-in-part of U.S. Patent Application No. 15/055,618, filed on February 28, 2016, and filed on March 28, 2015. U.S. Patent Application No. 14/672,122, filed March 14, 2014, is a continuation of U.S. Patent Application No. 14/672,122, now U.S. Patent No. 9,330,698. U.S. Patent Application No. 14/214,525, filed in March 2013, is a continuation-in-part of U.S. Patent Application No. 14/214,525, now U.S. Patent No. 9,117,468. It claims priority to U.S. Provisional Patent Application No. 61/802,972, filed on September 18, 2013, and U.S. Provisional Patent Application No. 61/877,957, filed on September 14, 2013. be. U.S. Patent Application No. 14/672,122 is also a continuation-in-part of U.S. Patent Application No. 14/566,666, which was filed on December 10, 2014 and is now U.S. Patent No. 9,330,694. U.S. Patent Application No. 14/566,666 claims priority to U.S. Provisional Patent Application No. 62/061,074, filed on October 17, 2014. U.S. Patent Application No. 14/672,122 also claims priority to U.S. Provisional Patent Application No. 62/085,471, filed on November 28, 2014. All of these applications are incorporated by reference herein as if set forth in their entirety.

[Technical field]
The present invention relates to the field of hard disk drive suspension. In particular, the present invention relates to the field of multilayer piezoelectric microactuators having one or more active piezoelectric suppression layers for use in two-stage actuator suspensions.

Other types of rotating media drives, such as magnetic hard disk drives and optical disk drives, are well known. FIG. 1 is a perspective view of an exemplary prior art hard disk drive and suspension to which the present invention may be applied. Prior art disk drive unit 100 includes a rotating magnetic disk 101 containing a pattern of magnetic ones and zeros that constitute disk drive stored data. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 on which a magnetic head slider (not shown) is mounted near the distal end of load beam 107 . The "proximal" end of a suspension or load beam is the end that is supported, ie, the end closest to the base plate 12 that is crimped or mounted to the actuator arm. The "distal" end of a suspension or load beam is the end opposite the proximal end, ie, the "distal" end is the end of the cantilever.

The suspension 105 is connected to an actuator arm 103 that is connected to a voice coil motor 112 that moves the suspension 105 in an arc to position the head slider over the appropriate data track of the data disk 101. The head slider is held by a gimbal that allows the slider to swing back and forth and side to side so that the slider follows the appropriate data track on the rotating disk and is sensitive to inertial events such as disk vibrations, bumping, and changes in the surface of the disk. Variations such as irregularities are allowed.

Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspensions are well known. In a one-stage actuator type suspension, only the voice coil motor 112 operates the suspension 105.

In DSA suspensions, in addition to the voice coil motor 112 that operates the entire suspension, at least one additional microactuator drives minute movements of the magnetic head slider, such as in U.S. Pat. is placed on the suspension to bring and properly align it on the data track of the rotating disk. Microactuators provide finer control of the servo control loop and higher bandwidth than a voice coil motor alone, which only provides relatively large movements of the suspension, or magnetic head slider. Although piezoelectric elements, sometimes referred to simply as PZT, are often used as microactuator motors, other types of macroactuator motors can also be used.

FIG. 2 is a top view of the prior art suspension 105 in FIG. The two PZT microactuators 14 are mounted on a suspension 105 on a microactuator mounting shelf 18 formed in the base plate 12 such that the PZT bridges each gap in the base plate 12. Microactuator 14 is attached to mounting shelf 18 by epoxy 16 at each end thereof. Positive and negative electrical connections can be made from the PZT to the flexible wire traces and/or plates of the suspension by various techniques. When actuated, the microactuator 14 expands or contracts to change the length of the gap between the mounting shelves and provide fine movement of the read/write head mounted at the distal end of the suspension 105.

3 is a side cross-sectional view of the prior art PZT microactuator and implementation of FIG. 2; FIG. Microactuator 14 includes the PZT element 20 itself and top and bottom metallization layers 26 and 28 on the PZT that define electrodes for actuating the PZT. The PZT 14 is mounted with epoxy or solder 16 across the gap on both its left and right sides as shown.

In DSA suspensions, it is generally desirable to obtain a long stroke distance from the PZT per unit of input voltage, or simply "stroke length."

Many past DSA suspension designs have implemented PZT on the mounting plate. In such designs, the linear motion of the PZT is increased by the length of the arm between the PZT's center of rotation and the read/write transducer head. Therefore, the small linear motion of the PZT results in a relatively long radial motion of the read/write head.

Other suspension designs implement PZT at or near the gimbal. An example of a gimbal-mounted PZT is the DSA suspension shown in commonly assigned US Pat. Obtaining long stroke lengths is especially important in gimbal-mounted DSA suspensions ("GSA" suspensions) because these designs are not as long as the arm length between the PZT and the read/write transducer head. It is. With shorter arm lengths, the resulting read/write head movement is correspondingly smaller. Thus, obtaining long stroke lengths is particularly important in GSA design.

US Patent No. 7,459,835 U.S. Patent No. 8,879,210

The inventors of the present application have identified the cause of the short PZT stroke length in suspensions with mounted PZT microactuators in the prior art, and have developed a PZT microactuator structure and its manufacturing method that eliminates the cause of the short stroke length. .

FIG. 4A is a side cross-sectional view of the PZT microactuator 14 mounted on the prior art suspension of FIG. 2 when the PZT is actuated by an applied drive voltage to expand the PZT. The bottom layer 22 of PZT does not expand as linearly as the top layer 24 because it is partially restrained by being bonded to the suspension 18 on which it is mounted. Because the top layer 24 expands more than the bottom layer 22, the PZT 14 curves downward and assumes a slightly convex shape when viewed from the top. The resulting loss in linear stroke length is shown in the figure as δ1.

FIG. 4B shows the PZT microactuator 14 of FIG. 4A when the PZT is actuated by an applied drive voltage to contract the PZT. The bottom layer 22 of PZT is partially restrained by being bonded to the suspension 18 on which it is mounted, so it does not shrink as linearly as the top layer 24. As the top layer 24 contracts more than the bottom layer 22, the PZT 14 curves upward and assumes a slightly concave shape when viewed from the top. The resulting loss in linear stroke length is shown in the figure as δ2.

Thus, while it is desired that the PZT simply expand and contract linearly during actuation, in conventional implementations the PZT undergoes upward or downward curvature resulting in a loss of stroke length.

FIG. 5 is a schematic diagram and related equations of the amount of effective linear stroke added or lost due to PZT curvature. As shown in FIG. 4B, when the beam curves and lifts, the bottom tip has a positive displacement δ in the x direction when the curve angle is small.

FIG. 6 is a plot of stroke loss due to bending versus bending angle for three different thicknesses of PZT. As shown in the figure, for PZT with a length of 1.50 mm and a thickness of 45 μm, the curvature results in a positive displacement δ in the x direction when the curvature angle is less than 5 degrees. It can be seen that for this amount of curvature, a thicker beam yields a larger displacement in the x direction than a thinner beam. Similarly, when the PZT expands under an applied voltage, the right half of the PZT curves downward and the bottom tip of the PZT bonded to the suspension undergoes a negative displacement in the x direction. In other words, in conventional PZT implementations of suspensions, the component of linear displacement due to curvature, δ, is in the opposite direction of the PZT actuation. It is therefore desirable to reduce or eliminate this δ, or even reverse the sign of this δ, with the end result being that the total linear expansion or contraction is actually increased.

The present invention provides a method for reducing, eliminating, changing the direction of, or controlling the curvature of the PZT when actuated on the side or face opposite to the side or face on which the PZT is mounted on the suspension. The present invention relates to a PZT element having at least one bonded hard constraining layer or element. A counterintuitive result is that although the PZT has an additional hard layer that, at least ostensibly, suppresses the expansion and contraction of the PZT, the resulting effective linear stroke distance actually increases. The PZT with constraining layer of the present invention can be used as a microactuator in hard disk drive suspensions, but can also be used in other applications.

In a preferred embodiment, the effect of the restraining layer is to actually change the direction of curvature. Thus, in PZT bonded to the suspension at the bottom surface, the effect of the presence of the constraining layer is that the piezoelectric element, when actuated by a voltage that expands the piezoelectric element, tends to cause the top surface to become ostensibly concave. When actuated by a voltage that causes the piezoelectric element to contract, it bends in a direction that causes the upper surface to have an ostensibly convex shape. Therefore, this effect actually increases the effective linear expansion in expansion mode and increases the effective linear contraction in contraction mode. Thus, the presence of the suppression layer actually increases the effective stroke length.

PZT with a restraining layer can be fabricated by a variety of techniques, including laminating the restraining layer onto an existing PZT element, or the PZT element and the restraining layer can be formed one on top of the other by additive methods. can. Such additive methods may include depositing a thin film of PZT on a substrate such as stainless steel (SST). The constraining layer may be a ceramic, such as stainless steel, silicon, a substantially unpolarized (inert) ceramic material, or the same ceramic material that makes up the PZT element, or other relatively hard material. If the suppression layer is electrically non-conductive, one or more electrical vias containing columns of conductive material are formed in the suppression layer to provide an activation voltage or ground potential from the surface of the microactuator to the interior of the PZT element. be able to.

The suppression layer may be larger than the PZT element (larger surface area), the same size as the PZT element, or smaller than the PZT element (smaller surface area). In a preferred embodiment, the constraining layer is smaller than the PZT element, giving the microactuator a stepped structure with a stepped shelf not covered by the constraining layer, and where the shelf makes the electrical connection to the PZT. One advantage of such a configuration that includes a shelf on which the electrical connections are made is that the entire assembly, including the electrical connections, has a lower profile than if the constraining layer covered the entire PZT. A lower profile is advantageous because additional hard disk platters or their suspensions can be stacked together within a given platter stacking height to increase data storage capacity within a given volume of the disk drive assembly. This is because it means that it is possible.

Simulations have shown that microactuators constructed in accordance with the present invention exhibit increased stroke sensitivity and reduced sway mode gain and torsion mode gain. These are advantageous in increasing head positioning control loop bandwidth, which translates into both reduced data seek time and reduced susceptibility to vibration.

A further advantage of adding a constraining layer or element to PZT in the present invention is that in current hard disk drives, suspensions and their components that include PZT are typically very thin. The microactuators used in current DSA suspension designs where PZT is mounted to the mounting plate are approximately 150 μm thick. In gimbal-mounted DSA suspension designs, PZT is even thinner, sometimes less than 100 μm thick. Therefore, the PZT material is very thin and brittle and can easily crack during manufacturing and assembly, including both the manufacturing process of the PZT microactuator motor itself and automated pick-and-place operations in the suspension assembly process. PZT in next generation hard drives is expected to be less than 75 μm thick, which exacerbates the problem. It is believed that such thin-walled PZT is not only susceptible to damage during manufacturing and assembly, but may also be susceptible to cracking or fracture when the disk drive is subjected to impact, or G-forces. The additional hard, elastic constraining layer in the present invention provides additional strength and resiliency to the PZT and helps prevent cracking or mechanical failure in the PZT during manufacturing and assembly and during impact events.

In another aspect of the invention, the microactuator assembly is a multilayer PZT structure with multiple active PZT layers, including one or more active PZT layers that act as suppression layers that tend to counteract the effects of the main active PZT layer. It is a device.

The idea that the overall final stroke length can be increased by adding one or more layers that counteract the movement of the main PZT layer is counterintuitive. Even more counterintuitive is the idea that the overall final stroke length can be further increased by adding one or more active layers that actively act in the opposite direction to the main PZT layer. However, this is a result demonstrated by the inventors.

In a further embodiment, the present invention relates to a multilayer PZT microactuator assembly in which the constraining layer includes a piezoelectric material that is polarized but inert. The inventors have demonstrated that since polarization of a piezoelectric material changes its dimensions, polarizing only one layer of a multilayer device introduces strains in the device that can make the device more susceptible to cracking and therefore failure. discovered. Thus, not only the primary or active PZT layer closest to the surface of the suspension assembly or other surrounding material to which the assembly is bonded, but also the inactive layer remote from the surrounding material to which the assembly is bonded, will polarize. , the reliability of the device increases.

Exemplary embodiments of the invention are further described below with reference to the drawings, in which like numerals relate to like parts. The features depicted are not to scale and certain parts are shown in generalized or schematic form and are identified by commercial designation for clarity and conciseness.

FIG. 1 is a top perspective view of a prior art magnetic hard disk drive. FIG. 2 is a top view of the disk drive suspension of FIG. 1. 3 is a side cross-sectional view of the prior art PZT microactuator and implementation of FIG. 2; FIG. 4, FIG. 4A is a side cross-sectional view of the PZT microactuator implemented in the prior art suspension of FIG. 2 when a voltage is applied to the PZT to expand the PZT, and FIG. 3 is a side cross-sectional view of the PZT microactuator implemented in the prior art suspension of FIG. 2 when a voltage is applied to the PZT to cause it to contract; FIG. FIG. 5 is a schematic diagram and related equations for the amount of linear stroke added or lost due to PZT curvature. FIG. 6 is a plot of stroke loss due to bending versus bending angle for three different thicknesses of PZT. FIG. 7 is a side cross-sectional view of PZT with a suppression layer bonded to the PZT in accordance with the present invention. 8, FIG. 8A is a side cross-sectional view of the PZT microactuator of FIG. 7 when a voltage is applied across the PZT to expand the PZT, and FIG. FIG. 8 is a side cross-sectional view of the PZT microactuator of FIG. 7 when . FIG. 9 is a graph showing stroke length per unit input voltage in nm/V versus suppression layer thickness for PZT that is 130 μm thick. FIG. 10 is a side elevational view of PZT with a constraining layer bonded to the PZT in accordance with the present invention. FIG. 11 is a graph of stroke length versus PZT thickness for the PZT of FIG. 10, where the combined thickness of the PZT and suppression layer is kept constant at 130 μm. FIG. 12 is a graph of GDA stroke sensitivity versus restraint layer thickness for suspensions with PZT with stainless steel restraint layers of various thicknesses. In FIG. 13, FIGS. 13A-13C illustrate one manufacturing process that can make PZT with a suppression layer of the present invention. In FIG. 13, FIGS. 13D-13H illustrate one manufacturing process that can make PZT with a suppression layer of the present invention. In FIG. 14, FIGS. 14A-14B are perspective views of a GSA suspension assembled with a thin film PZT microactuator motor in accordance with the present invention. FIG. 15 is a cross-sectional view of the microactuator region of FIG. 14B along section line B-B'. FIG. 16 shows a graph of stroke sensitivity versus SST substrate thickness of the microactuator of FIG. 15 in a simulation. In FIG. 17, FIGS. 17A-17F illustrate the process of manufacturing a thin film PZT structure with a stainless steel substrate in accordance with the present invention. FIG. 18 is a top view of a thin film PZT structure with a silicon substrate in accordance with the present invention. FIG. 19 is a side cross-sectional view of the thin film PZT structure of FIG. 18 taken along section line A-A'. FIG. 20 is a graph of stroke sensitivity versus silicon substrate thickness for the microactuator of FIG. 19 in a simulation. In FIG. 21, FIGS. 21A to 21E show steps for manufacturing the thin film PZT structure of FIG. 18. FIG. 22 is a top view of a thin film PZT with a substrate and side vias in an embodiment of the invention. FIG. 23 is a cross-sectional view of the microactuator of FIG. 22 along section line A-A'. FIG. 24 is a cross-sectional view of a PZT microactuator in a further embodiment of the invention. FIG. 25 is a perspective view of a GSA suspension with a pair of the PZT microactuators of FIG. 24. FIG. 26 is a cross-sectional view of the GSA suspension of FIG. 25 along section line A-A'. FIG. 27 is a graph of the PZT frequency response function of the suspension of FIG. 25 in a simulation. 28, FIGS. 28A-28E illustrate an exemplary process for manufacturing the PZT macro actuator assembly of FIG. 24. 28, FIGS. 28F-28J illustrate an exemplary process for manufacturing the PZT macro actuator assembly of FIG. 24. FIG. 29 is a side cross-sectional view of a multilayer PZT microactuator assembly in a further embodiment of the invention, where the PZT is multilayer PZT. FIG. 30 is a side cross-sectional view of a multilayer PZT microactuator assembly in a further embodiment of the invention, in which a particularly thick electrode acts as a restraining layer. FIG. 31 is a cross-sectional view of an embodiment in which the restraining layer of a microactuator assembly includes one or more active PZT layers that tend to act in the opposite direction of the main active PZT layer. FIG. 32 shows the polarization of the microactuator assembly of FIG. 31, including the resulting polarization directions of the various layers of active PZT material. FIG. 33 is an exploded view of the microactuator assembly of FIG. 31 conceptually illustrating the electrical connections. FIG. 34 is a graph showing the stroke sensitivity (nm/V) of a microactuator with one or more active suppression layers in simulations for various configurations. FIG. 35 is a cross-sectional view of another embodiment in which the microactuator assembly includes multiple active PZT layers, conceptually illustrating the polarization process and the resulting polarization direction. FIG. 36 is a side cross-sectional view of a multilayer PZT macroactuator assembly in a further embodiment where the PZT is a conventionally polarized multilayer PZT and the top layer is thicker than the bottom layer. FIG. 37 is a side cross-sectional view of the PZT microactuator assembly of FIG. 36 showing the assembly mounted within the suspension. FIG. 38 is a side cross-sectional view of a multilayer PZT macroactuator assembly in a further embodiment in which the PZT is a multilayer PZT with three individual poles and the PZT is counterpolarized. FIG. 39 is a side cross-sectional view of the PZT microactuator assembly of FIG. 38 showing the assembly mounted within the suspension. FIG. 40 is a graph showing the stroke sensitivity of the PZT microactuator assembly of FIGS. 37 and 39 in simulations as a function of the thickness of the top PZT layer as compared to the stroke sensitivity of standard single layer PZT. FIG. 41 is a side cross-sectional view of the PZT microactuator assembly of FIG. 36, showing the assembly mounted within a suspension by an alternative assembly method. FIG. 42 is a side cross-sectional view of a PZT microactuator in a further embodiment with a polarized but inactive suppression layer. FIG. 43 is a side cross-sectional view of the PZT microactuator assembly of FIG. 42 showing the assembly mounted within the suspension.

FIG. 7 is a side cross-sectional view of a PZT microactuator assembly 114 with bonded constraining layer 130 in an embodiment of the invention. According to the arrangement shown in the figure, the side of the PZT that is joined to the suspension is referred to as the bottom side 129 of the PZT 114, and the side of the PZT that is away from the side where the PZT is joined to the suspension is referred to as the top side 127. be done. In the present invention, one or more suppression layers or suppression 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, including the top electrode 126, or the SST material itself. Functioning as a top electrode, it eliminates the need for separate metallization of the top surface. The constraining layer 130 is sufficiently rigid to significantly reduce, eliminate, or even reverse the bowing of the PZT when actuated. SST layer 130 preferably has a layer 131 of gold or other contact metal to achieve a good electrical connection to the SST.

Alternatively, the suppression layer 130 may be a ceramic instead of stainless steel, such as an inert (non-polarized or unpolarized) layer of the same ceramic material that forms the piezoelectric layer 120. and may be integrated into the assembly by bonding or film deposition. The ceramic material is unpolarized, meaning that it exhibits substantially less piezoelectric behavior, such as less than 10% of the same piezoelectric behavior as the polarized ceramic that makes up the piezoelectric layer 120. Such an assembly, consisting of a laminate of electrode, polarized PZT, electrode, unpolarized PZT from below, is easier to manufacture than a laminate of electrode, PZT, electrode, SST.

In the following description, for the sake of brevity, the upper and lower electrodes 126, 128 may be omitted from the drawings and description, but it is noted that PZT microactuators almost always have at least some type of upper and lower electrodes. is understood.

A copper or nickel layer is applied to the SST layer 130 before the gold layer 131 is added to increase the adhesion of the gold to the SST, as described in U.S. Pat. No. 8,395,866 by Schreiber et al. It is preferable that a film is formed. No. 5,030,502, owned by the assignee of the present application, is incorporated herein by reference for its teachings on electrodepositing other metals onto stainless steel. Similarly, electrodes 126, 128 may include a combination of nickel and/or chromium and gold (NiCr/Au).

124-167 (FIG. 5) In one exemplary embodiment, the thicknesses of the various layers are:
130 PZT 3μm
126, 128, 131 NiCr/Au 0.5μm
Met.

The thin PZT film had a length of 1.20 mm, the PZT junction had a width of 0.15 mm at both ends, and the piezoelectric coefficient d31 was 250 pm/V. In some embodiments, the SST layer may be at least 12 micrometers thick to provide adequate support.

In the above example, the DSA suspension exhibited a stroke sensitivity of 26.1 nm/V according to simulation. On the other hand, 45 μm thick bulk PZT of the same geometry (d31=320 pm/V) typically exhibits a stroke sensitivity of only 7.2 nm/V.

The thickness ratio of the SST layer to the PZT layer can be 1:1, or even 1.25:1, or even higher. When the thickness ratio of the suppression layer to PZT reaches about 1:25, the stroke sensitivity improvement by the suppression layer begins to become negative, suggesting a limit to the thickness of the PZT suppression layer.

FIG. 8A is a side cross-sectional view of the PZT microactuator 114 of FIG. 7 when a voltage is applied to the PZT to expand the PZT. The PZT stroke consists of two vectors, one is a pure elongation stroke δe, and the other is the elongation contribution by the inhibition layer that curves the right tip of the PZT upward instead of downward curvature as in the absence of the inhibition layer. δ1. The total stroke length is δe+δ1. In expansion mode, the PZT therefore assumes a slightly concave shape when viewed from the top, i.e., the PZT top surface assumes a slightly concave shape, which is opposite to the curvature of the prior art PZT in FIG. This is the direction of curvature. Therefore, this curvature of the present invention does not reduce the effective stroke length, but rather increases it.

8B is a side cross-sectional view of the PZT microactuator of FIG. 7 when a voltage is applied to the PZT to cause the PZT 114 to contract. The PZT stroke consists of two vectors, one is a pure contraction stroke - |δc|, and the other is a suppression layer that curves the right tip of the PZT downward instead of upward curvature as in the absence of the suppression layer. The contraction contribution δ2 is δ2. The total stroke length is -[δc+δ2]. In the contraction mode, therefore, the PZT takes a slightly convex shape when viewed from the top, i.e., the PZT top surface takes a slightly convex shape, which is different from the curvature of the prior art PZT in FIG. The direction of curvature is opposite. Therefore, this curvature of the present invention does not reduce the effective stroke length, but rather increases it.

Adding a constraining layer 130 to the PZT microactuator 114 has no discernible effect on stroke length for otherwise unconstrained and unbonded PZT 114. However, as shown in FIG. 4, when the PZT is joined to the suspension 18 at its bottom end, the effect of the constraining layer actually increases the stroke length slightly. Stainless steel has a Young's modulus of about 190-210 GPa. Preferably, the material for the constraining layer has a Young's modulus greater than 50 GPa, more preferably greater than 100 GPa, even more preferably greater than 150 GPa.

FIG. 9 is a graph showing stroke length per unit input voltage in nm/V versus constraint layer thickness for a PZT 114 that is 130 μm thick and has a bonded stainless steel constraint layer 130 in a simulation. Adding 20 μm, 40 μm, and 60 μm thick SST suppression layers to the PZT top surface increases the total stroke length, respectively. That is, the total stroke length was actually increased by adding the suppression layer.

It is also possible to keep the total thickness of PZT and suppression layer constant and determine the optimal thickness of the suppression layer. FIG. 10 is a side elevational view of a combination of PZT and a restraining layer bonded to the PZT in the present invention, where the total thickness is kept constant at 130 μm. FIG. 11 is a graph of stroke length versus PZT thickness for the PZT of FIG. 10, where the combined PZT and suppression layer thickness is kept constant at 130 μm in the simulation. Without the suppression layer, 130 μm PZT has a stroke length of approximately 14.5 nm/V. For a suppression layer 130 thickness of 65 μm and a PZT thickness of 65 μm, the PZT has a stroke length of about 20 nm/V. Therefore, adding the restraint layer actually increased the effective stroke length by about 35%.

FIG. 12 is a graph of GDA stroke sensitivity versus restraint layer thickness for the GDA suspension with the microactuator of FIG. 7 with a 45 μm thick PZT element and top stainless steel restraint layer of various thicknesses in simulations. As can be seen in the graph, a 30 μm thick suppression layer increases the GDA stroke sensitivity from 9 nm/V to just over 14.5 μm, which represents an increase in stroke length of over 50%.

13A-13H illustrate one manufacturing process by which a PZT microactuator assembly with a restraining layer of the present invention can be made. This method is an example of an additive method in which a PZT material is deposited on a substrate to serve as a suppression layer. The process begins with a first substrate 140 as shown in FIG. 13A. In FIG. 13B, a first UV/thermal tape 142 is applied to the substrate. In Figure 13C, a preformed SST layer 130 is added to the tape. In FIG. 13D, an electrode layer 126 is deposited on the SST, such as by sputtering or other well-known deposition processes. In FIG. 13E, a PZT layer 120 is formed on the electrode layer by sol-gel or other known methods. In FIG. 13F, a second electrode 128 is deposited on the exposed side of the PZT, such as by sputtering. In FIG. 13G, the SST layer 130 is separated from the tape and the fabrication is flipped onto a second tape 143 and a second substrate 141. Then, in FIG. 13H, the creation is cut into cubes, such as by mechanical sawing or laser cutting, to individualize the individual microactuators 114. In this step, the PZT element 120 containing the electrodes is bonded directly to the SST suppression layer 130 and does not have any other materials between them, such as organic materials such as polyimide, which would reduce the suppression effect of the suppression layer. , a microactuator 114 is manufactured. The electrode layer may be made of materials such as Au, Ni, Cr, and/or Cu. Au has a Young's modulus of about 79 GPa, Cu has a Young's modulus of about 117 GPa, Ni has a Young's modulus of about 200, and Cr has a Young's modulus of about 278. Preferably, the SST suppression layer 130 and a PZT element having a Young's modulus that is less than 20 GPa, or substantially less than the Young's modulus of the suppression layer, or less than half the Young's modulus of the suppression layer. There is no intermediate layer between 120 and 120.

Although other methods may be used to fabricate the fabrication, such as by bonding the constraining layer directly to the PZT surface with an adhesive such as an epoxy, the method shown in FIGS. 13A-13H is the current method. However, this is considered to be a preferable method.

SST suppression layer 130 acts as a substrate for PZT layer 120 both during the additive manufacturing process and in the final fabrication. Constraining layer 130 is therefore sometimes referred to as a substrate.

14A and 14B are perspective views of a gimbaled two-stage actuator (GSA) suspension 150 assembled with a thin film PZT microactuator motor 114 in accordance with the present invention. In the GSA suspension, the PZT is implemented in the trace gimbal that includes the gimbal assembly and acts directly on the gimbal area of the suspension that holds the read/write head slider 164. FIG. 14A shows suspension 150 before PZT microactuator assembly 114 is attached. Each of the two microactuators 114 is joined to a tongue 154 to which the distal end of the microactuator 114 is joined, and to a portion 156 of the trace gimbal to which the proximal end of the microactuator 114 is joined, and their The gap 170 in between is connected. FIG. 14B shows suspension 150 after PZT microactuator 114 is attached. When the microactuator assembly 114 is activated, it expands or contracts, changing the length of the gap 170 between the tongue 154 and the trace gimbal portion 156, causing the head slider 164 holding the read/write transducer to expand or contract. Brings about fine placement movements.

FIG. 15 is a cross-sectional view of FIG. 14B along section line B-B'. GSA suspension 150 includes a trace gimbal 152 that includes a layer 158 of signal conducting traces such as Cu coated with a layer of stainless steel, an insulator 157 such as polyimide, and a protective metal 159 such as Au or a combination of Ni and Au. . The microactuator 114 is attached at its distal end to a stainless steel tongue 154 extending from the gimbal region by a conductive adhesive 162, such as an epoxy containing Ag particles, to make it electrically conductive, and at its proximal end. It is attached to the stainless steel mounting area 156 by a non-conductive adhesive 161, such as a non-conductive epoxy. The drive voltage electrical connection is made by a spot of conductive adhesive 160 extending from the gold-plated copper contact pad 158 to the top surface of the PZT microactuator 114, and specifically to the SST layer 130, which in this case constitutes the top electrode of the microactuator.

The SST substrate thickness may vary to some extent without detracting from the advantages of the disclosed thin film PZT structure. FIG. 16 is a graph of stroke sensitivity versus SST suppression layer thickness for the microactuator of FIG. 15 in a simulation. Thin film PZT with a 40 μm thick SST suppression layer exhibits a stroke sensitivity of 20 nm/V in simulations, which is nearly three times the stroke sensitivity of the previously described 45 μm thick bulk PZT. However, a 45 μm thick SST suppression layer protects the thin film PZT microactuator better.

17A-17F illustrate an alternative process for fabricating a thin film PZT structure with an SST suppression layer in accordance with the present invention. In FIG. 17A, the process begins with a silicon substrate 144 instead of a substrate 140 or tape 142 as shown in FIG. 13B. In Figure 17B, an SST layer (130) is bonded to the silicon. The process then proceeds substantially the same as the process of FIGS. 13C-13H, including flipping the assembly and removing the silicon substrate in FIG. 17E. Additionally, these figures clearly show the addition of a final NiCr/Au layer 131, which is not clearly shown in FIG. 13E.

As mentioned above, different types of suppression layers may be used for various applications. Other rigid materials, conductive or non-conductive, may also be used as the restraining layer or substrate. For example, silicon can be used as the constraining layer material. FIG. 18 is a top view of a thin film PZT structure with a silicon suppression layer in an embodiment of the invention. FIG. 19 is a cross-sectional view of the microactuator of FIG. 18 along section line AA'. Since the silicon suppression layer 230 is non-conductive, vias 232 are provided to conduct the PZT drive voltage from the conductive top layer 234, such as Au on the silicon 230, to the metallized electrode 126 on the PZT element 120. . The vias may be formed and filled with a conductive metal as disclosed in Schreiber et al., U.S. Pat. The teachings of methods for forming conductive vias are incorporated herein by reference.

FIG. 20 is a graph of stroke sensitivity versus silicon substrate thickness for the microactuator of FIG. 19 in a simulation. As shown in the graph, the 3 μm thick thin film PZT and the 20 μm thick silicon substrate exhibit a stroke sensitivity of 31.5 nm/V. This is more than four times the stroke sensitivity of the 45 μm thick bulk PZT design. Silicon substrates are also utilized to improve the reliability of thin film PZT.

21A-21E illustrate the steps for manufacturing the thin film PZT structure of FIG. 18. In FIGS. 21A and 21B, the process begins with a silicon substrate that has holes or vias 232 formed therein, such as by laser drilling. In FIG. 21C, a NiCr/Au layer is added to the silicon substrate 230 to form the top electrode 126. Electrical vias 232 are also created by filling the holes with NiCr/Au. More generally, other conductive materials may be used to fill the vias. In FIG. 21D, a PZT thin film 120 is deposited, such as by a sol-gel method, and another layer of NiCr/Au is added to form a bottom electrode 128. In Figure 21E, the material is turned over and a final NiCr/Au layer 131 is applied. Since layer 131 and layer 126 are electrically connected by via 232 , the voltage (or ground potential) applied to conductive gold layer 131 is transmitted to PZT element 126 . This manufacturing process for thin film PZT microactuators with silicon substrates is not as complex as that for thin film PZT with SST substrates.

In alternative embodiments, the intermediate vias in the silicon substrate may be replaced by one or more vias at the edges of the silicon. Thus, after cutting into final cubes, a semicircle is formed at each end of the silicon. FIG. 22 has a silicon or other non-conductive constraining layer 330 with a conductive top layer 231, such as a metallized layer, with side vias 234, 236 electrically connecting the top layer 231 to the top electrode 126. , a top view of a thin film PZT microactuator. FIG. 23 is a cross-sectional view of the PZT of FIG. 22 along section line A-A'. The manufacturing process for this embodiment may otherwise be identical to that of FIGS. 21A-21E.

The suppression layer may be larger than the PZT element (larger surface area), the same size as the PZT element, or smaller than the PZT element (smaller surface area). FIG. 24 is a side cross-sectional view of a PZT microactuator assembly 414 in which the constraining layer 430 is smaller than the PZT element 420 and has a stepped portion 434 and an exposed shelf 422 not covered by the constraining layer 430. A shelf 422 is where electrical connections are made to the PZT element 420, providing a similar structure to the microactuator. One advantage of such a configuration that includes steps where the electrical connections are made is that the entire assembly, including the electrical connections, has a lower profile than if the constraining layer 430 covered the entire PZT 420. A lower profile is advantageous because additional hard disk platters and their suspensions can be stacked together within a given platter stacking height to increase data storage capacity within a given volume of the disk drive assembly. This is to mean that. To obtain electrical connections on the shelf 422, the constraining layer 430 is believed to cover more than 50%, but less than 95%, of the top surface of the PZT element 420.

Simulations have shown that microactuators constructed in accordance with the present invention exhibit increased stroke sensitivity and reduced sway mode gain and torsion mode gain. These are advantageous in increasing head positioning control loop bandwidth, which translates into both reduced data seek time and reduced susceptibility to vibration.

FIG. 25 is a perspective view of a GSA suspension with a pair of the PZT microactuators of FIG. 24.

FIG. 26 is a cross-sectional view of the GSA suspension of FIG. 25 along section line A-A'. In this embodiment, a conductive adhesive 460, such as a conductive epoxy, does not extend over the constraining layer 430; rather, the conductive epoxy 460 extends over the top shelf 422 of the PZT element 420 and connects the PZT 420 and the macroscopic layer through the surface. Electrical connections are made to the entire actuator assembly 414. As shown, the electrical connection defined by conductive epoxy 460 has a top that is lower than the top surface of SST suppression layer 430. More generally, electrical connections to the microactuator assembly 414, whether the electrical connections are made with conductive adhesives, wires bonded such as by ultrasonic thermal bonding, solder, or other techniques. 461 can be made to be less than or lower than the top of microactuator 414. This allows the microactuator assembly 414, including the electrical connections, to be as thin as possible. This allows for higher density stacking of data storage disk platters within the platter stack of the disk drive assembly.

The figure also clearly shows the gold layer 469 on the stainless steel portion 154 of the trace gimbal on which the microactuator 414 is mounted. Gold layer 469 provides corrosion resistance and improves conductivity to the SST.

In this embodiment, as in all other embodiments, the constraining layer and more generally the top surface of the PZT microactuator assembly typically have no bonding other than electrical connections.

FIG. 27 is a graph of the frequency response of the PZT frequency response function of the suspension of FIG. 26 in a simulation. The suspension showed a reduction in sway mode gain and torsion mode gain compared to simulations without the suppression layer 430. These are advantageous in increasing head positioning control loop bandwidth, which translates into both reduced data seek time and reduced susceptibility to vibration.

28A-28J illustrate a process for manufacturing the thin film PZT assembly 114 of FIG. 24. In FIG. 28A, bulk PZT wafer 420 is placed on transition tape 422. In FIG. 28B, a top electrode layer 426 is formed, such as by sputtering and/or electrodeposition. In FIG. 28C, a mask 436 is placed over a portion of the top electrode 426. In Figure 28D, conductive epoxy 432 is applied. In Figure 28E, a stainless steel layer, which becomes the restraining layer 430, is added to the epoxy and the epoxy is cured. In Figure 28F, mask 436 is removed. In FIG. 28G, the assembly is flipped and placed onto the second transition tape 443. In FIG. 28H, a bottom electrode layer 428 is formed, such as by sputtering and/or electrodeposition. The PZT element 420 is then polarized. In FIG. 28I, the assembly is flipped once more onto the third transition tape 444. In FIG. 28J, the assembly is singulated by cutting to produce the final PZT microactuator assembly 414.

FIG. 29 is a side cross-sectional view of a multilayer PZT assembly 514 in a further embodiment of the invention. The assembly includes a multilayer PZT element 520, a first electrode 526 surrounding the device, a second electrode 528, and a constraining layer 530 bonded to the PZT element 520 by epoxy 532. The figure shows a two-layer PZT device. More generally, the device may be an n-layer PZT device.

FIG. 30 is a side cross-sectional view of a multilayer PZT microactuator assembly 614 in a further embodiment of the invention, in which particularly thick electrodes act as restraining layers. In this embodiment, PZT element 620 has a top electrode 626 and a bottom electrode 628. Top electrode 626 includes a thinner first portion 622 that defines a shelf and a thicker second portion 630 that performs most of the suppression function. A step 634 is at the transition from the thinner first portion 622 to the thicker second portion 630. The second electrode 626 may be added to the PZT element 620 by a deposition process that includes masking to create the steps 634 or by a deposition process that selectively removes material to create the steps. . Alternatively, the second electrode 626 may be a piece of conductive material, such as SST, that is separately formed and bonded to the PZT element 620. Therefore, the top electrode 626 may be of the same material as the bottom electrode 628, or may be of a different material. 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 50% thicker than the thinner portion 622 and/or the second electrode 628. Preferably it is twice as thick. As in the embodiment of FIGS. 24-26, electrical connections are provided on the shelf defined by the thinner section 622, and the electrical connections are as high as the top surface of the thicker section 630 that defines the constraining layer. It is preferable that it does not extend to a length of 100 cm or less than that.

The scope of the invention is not limited to the precise embodiments presented. Modifications will be apparent to those skilled in the art after having the teachings herein. By way of example, the constraining layer need not be stainless steel, but may be other relatively hard and resilient materials. The suppression layer need not be a single layer of one material, but may consist of different layers of different materials. The restraining layer may cover the entire surface or substantially the entire top surface, but for example, over 90% of the top surface area, over 75% of the top surface area, over 50% of the top surface area, or even over the top surface area. More than 25% of less than the entire surface may be covered. In embodiments having a stepped configuration, the suppression layer will cover less than 95% of the top surface of the microactuator. The constraining layer need not be a single monolithic layer, but may include multiple pieces, such as multiple constraining strips placed side by side on the top surface of the PZT, where the strips may extend in the expansion/contraction direction or in the vertical direction. It's fine. In one embodiment, the restraining layer may include two restraining pieces of stainless steel or other material bonded to the top surface of the PZT, and the size and placement of the two restraining pieces, as well as their bonding, is typically controlled by the PZT. It is similar to the mounting area of two mounting shelves joined at the bottom. This is obtained when the overall stiffness imparted by the constraining layer on the top of the device typically matches the overall stiffness imparted to the bottom of the device by being bonded to the suspension, and the bonded areas are in a generally symmetrical relationship. The final curvature is zero or near zero. As a result, the PZT microactuator, when mounted and placed in a suspension, exhibits substantially no curvature upon actuation.

In any or all of the embodiments described or presented herein, the constraining layer is selected to reduce PZT curvature that may otherwise occur upon actuation. or may be selected to eliminate as much as possible any PZT curvature, or to reverse the sign of the PZT curvature. In applications where PZT is used as a hard disk drive microactuator, it is often found desirable to use a constraining layer to reverse the sign of curvature, as presented and described in the exemplary embodiments above, and this is to increase the effective stroke length. However, in other PZT applications, reversing the sign may be undesirable. Thus, the present invention can generally be used to control both the direction and amount of PZT curvature, no matter how the PZT is implemented or attached to other components in any particular application. Depending on the application and parameters chosen, the suppression layer can be used to reduce PZT curvature to less than 50% of its potential, or to less than 25% of its potential, or to reverse the sign of the curvature. can be used. When the sign is reversed, the PZT bonded at or near the edge of the bottom surface and having a restraining layer on top will have a concave shape on its top surface and having a restraining layer when in the expansion or elongation mode. It is curved so that it does not take on the convex shape that similar PZT does. Similarly, PZT assumes a convex shape when in contraction mode and does not assume a concave shape as similar PZT without a constraining layer would.

For various reasons, PZT elements are preloaded in applications such that when the PZT is not actuated at any voltage it is already curved in either direction, i.e. it is already concave or convex. Sometimes. Such preloaded PZT can naturally be used as a microactuator of the present invention. In such cases, the PZT may not curve into a net or appreciably concave shape or a net or appreciably convex shape. As an example, if the PZT is preloaded and already has a concave shape, upon activation with a positive activation voltage, the device will curve to a shape that is more concave; Upon activation, the device may be ostensibly flat in shape, curved into a less concave shape, or become convex. And unless otherwise defined, the terms "concave" and "convex" should be understood in a relative rather than an absolute sense.

FIG. 31 is a cross-sectional view of an embodiment of a multilayer microactuator PZT assembly 3100 in which the constraining layer is in the opposite direction of the main active PZT layer 3120 near the suspension surface to which the microactuator 3100 is bonded. It includes one or more active PZT layers 3130, 3140 that tend to act. The PZT suppression layers 3130, 3140 may be referred to as "suppression layers" or "counterlayers" because they suppress and actively counteract the operation of the main PZT layer 3120.

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 that is polarized when an electric field is applied during poling and expands or contracts when an electric field is applied during device actuation, such that no significant electric field is applied during either poling or actuation. It also includes inactive PZT regions 3122 and 3123, which therefore are not significantly piezoelectrically active. The device includes a first or bottom electrode 3124, a second or top electrode 3126 for the active PZT region, a third electrode 3132 extending between the first active suppression layer 3130 and the second active suppression layer 3140, and the ends of the PZT. and a fourth electrode 3142 on top of the second active suppression layer 3140, including a surrounding portion 3143 surrounding both the sides and bottom of the device. The electrodes 3124 and 3124 of the device are connected using a conductive adhesive, such as conductive epoxy 3160, to mechanically and electrically bond the electrode 3142 to the drive voltage electrical contact pads 158 that provide the microactuator drive voltage, and to the ground portion 154 of the suspension. The device may be joined to the suspension using a conductive epoxy 3162 that mechanically and electrically joins 3128.

In order to understand the operation of the device, it is necessary to understand how the device is polarized. FIG. 32 shows the polarization of the device of FIG. 31, including the resulting polarization directions of the various layers of active PZT material. The following three voltages are applied. A positive voltage (Vp+) is applied to electrode 3124, a negative voltage (Vp-) is applied to electrode 3128, and ground is applied to electrode 3142. The arrows in the figure indicate the resulting polarization directions of the active PZT layers 3120, 3130, and 3140.

Returning to FIG. 31, the figure shows how devices 3100 are connected in this example embodiment. Conductive epoxy 3162 bridges and electrically groups electrodes 3124 and 3132, essentially turning a three-polar device upon polarization into a two-polar device upon actuation. Grouping of the electrodes may be accomplished by other well-known means of making electrical connections other than conductive epoxy 3162; however, by using the same conductive epoxy 3162 used to bond the device to the suspension assembly, individual Get group functionality without the need for another grouping step.

When a voltage is applied to the electrode 3142 to cause the main PZT layer 3120 to expand in the x direction (from left to right) as seen in the figure due to the expansion of the active region 3121, the active PZT suppression layers 3130 and 3140 shrink in the direction. That is, the two suppression layers 3130 and 3140 tend to react or act in the opposite direction from the main PZT layer 3120.

More specifically, when the device is polarized as shown in FIG. 32 and electrically connected as shown in FIG. 31, the device operates as follows. A positive device activation voltage applied to electrical contact pad 158 and electrode 3142, with electrode 3124 being grounded, results in the following reactions. The activation voltage applied to the main PZT layer 3120 is of opposite polarity during polarization. Therefore, the main PZT layer 3120 contracts in the z direction and expands in the x direction. At the same time, the activation voltage is of the same polarity as that applied to the two suppression layers 3130 and 3140 during polarization. That is, these PZT layers expand in the z direction and contract in the x direction. Therefore, when the two constraining layers 3130 and 3140 tend to contract, the main PZT layer 3120 tends to expand in a related direction.

The effect of a restraining layer acting in the opposite direction to the main PZT layer is similar to that of a passive restraining layer, such as restraining layer 130 of FIG. and 630 as described above. The action of the active PZT suppression layer is to reduce the curvature caused by the main PZT layer and its implementation (bonding) to the suspension, and it is also possible to reverse the sign of the curvature, in both cases brought about by the implemented microactuators. increase the final displacement.

FIG. 33 is an exploded view of the microactuator assembly of FIG. 31 conceptually illustrating the electrical connections. Optional features not shown in FIGS. 31 and 32 but shown in FIG. 33 include patterning 3133 on electrode 3132, voltage suppressor 3144 coupled to electrode 3142, the function of which will be described below.

Thinner microactuator assemblies result in: (1) less mass on the suspension (that is, measured in G-forces), especially at or near the gimbals of gimbaled DSA suspensions, sometimes referred to as DSA suspensions; (2) reduced windage, and (3) higher stack density within the head stack assembly (with the same volume disk drive stack assembly). It is desirable for many reasons, including the ability to store more data in the space. Therefore, it is desirable to make the PZT suppression layer thinner to some extent. However, thinner PZT suppression layers result in higher electric field strengths across these layers during actuation, and because the electric field strengths are significantly higher, they are more susceptible to depolarization during actuation. Therefore, for convenience, the main PZT layer and the suppressing PZT layer should be of the same thickness.

One solution to making the suppressing PZT layer thinner without depolarizing it is to reduce the electric field strength across the suppressing layer using various means that can be used, one or more, without significantly reducing the electric field across the main PZT layer. The goal is to reduce the A first means of achieving this goal is to operatively connect one of the active PZT suppression layers, such as by adding holes 3133 or other electrical gaps to the electrode 3132, but with the main PZT A layer is a pattern of one or more electrodes that are not operatively connected. The patterning may take the form of a mesh pattern, such as a grid of parallel or crossed conductors with electrical gaps therebetween. By reducing the percentage of electrically conductive area within planar electrode 3132, the electric field strength across suppression layers 3130 and 3140 is effectively reduced without reducing the electric field strength across main PZT layer 3120.

A second solution is to increase the coercive field strength of the suppression layer so that it becomes more resistant to depolarization. Coercive field strength, or simply "coercivity" when referring to piezoelectric materials, is a measure of how high field strength is required to depolarize the piezoelectric material. Having the suppression layers 3130, 3140 have a higher coercive force than the main PZT layer 3120 allows these suppression layers to be thinner without the risk of depolarization when the same activation voltage as the main PZT layer is applied. Is possible. The suppression layers 3130, 3140 can be made higher by using different or slightly different piezoelectric materials or by other treatments, possibly at the expense of some loss of d31 stroke length or other desired properties. It can be made to have coercive force.

Another solution is to use some kind of voltage suppressor, such as a resistor divider network, a diode, a voltage regulator, or any one of various functionally similar devices that occur to those skilled in the art. The purpose is to reduce the effective voltage applied to the driving electrode connected to the suppression layer. In the figure, the voltage suppressor 3144 schematically reduces the voltage experienced by the electrode 3142 to reduce the electric field strength experienced by the suppression layer 3140 rather than the main PZT layer 3120. It is also possible for the voltage divider to be integrally formed and placed between adjacent piezoelectric layers, such as by metallizing the PZT material surface to form an electrode layer to form a voltage divider resistor network. be. A simple resistive voltage divider may require grounding, which may be done on the same layer. Many configurations are possible, as will be apparent to the designer of such a device.

Patterning 3133 and voltage suppressor 3144 together reduce the electric field strength across suppression layer 3140, allowing suppression layer 3140 to be made thinner without unacceptably depolarizing during operation. Electrode patterning and/or voltage suppressors and/or some other means of reducing the electric field strength across the suppression layers 3130 and/or 3140 may be used. Since the patterning 3133 is integrally formed with the electrode 3132, it is integrally formed with and is integrally incorporated within the microactuator assembly. The voltage suppressor for one of the electrodes may be integrally formed with the assembly and integrated within the assembly, or the coupled electrode may have its own electrical leads and the other may be provided externally to the assembly, provided that it is not grouped with the electrodes.

All of these three solutions mentioned above can be implemented using a single active suppression layer, two active suppression layers as shown in Figures 31-33, or more generally n active suppression layers as shown in Figure 35. It can be applied to piezoelectric microactuators with a restraining layer.

FIG. 34 shows various constraining layer configurations with a 45 μm thick main PZT layer and without any patterning 3133 or voltage suppressor 3144 to reduce the field strength.
2 is a graph showing the stroke sensitivity (nm/V) of a microactuator with one or more active suppression layers in simulations for three different configurations:
a) One inert suppression layer (“passive CLC”, diamond data point)
b) one active suppression layer (“single layer”, square data points), and c) two active suppression layers (“two layers”, triangular data points)
is shown about.

In our data, at least for the parameters verified, PZT microactuators with one active inhibition layer acting in the opposite direction to the main PZT layer consistently yield higher stroke sensitivity than those in which the inhibition layer is an inert material. This shows that. The highest stroke sensitivity is obtained with multiple active PZT thin layers acting as suppression layers (ie, acting in the opposite direction to the main PZT layer). In particular, the highest stroke sensitivity was obtained with two suppression layers that were each 5μ thick, or about 11% of the main PZT layer thickness. Thus, the constraining layer preferably comprises less than 50% of the main PZT layer thickness, or more preferably less than 20% of the main PZT layer thickness, or even more preferably within the range of 5 to 15% of the main PZT layer thickness. be.

For two activity suppression layers, the stroke sensitivity decreases significantly with increasing suppression layer thickness, with the highest stroke sensitivity being obtained for two activity suppression layers, each approximately 5 μm thick. Thus, the microactuator preferably has two or more restraining layers with a combined thickness less than the main PZT layer thickness, more preferably a combined thickness less than 50% of the main PZT layer thickness; Even more preferably each suppression layer is less than half the thickness of the main PZT layer, even more preferably each suppression layer is less than 20% of the thickness of the main PZT layer, even more preferably each suppression layer is less than half the thickness of the main PZT layer. It is within the range of 5 to 15% of the layer thickness.

For microactuator assemblies with a single active suppression layer, the loss in stroke sensitivity as the suppression layer thickness increased was not as great as with two active suppression layers. For a single active suppression layer, the local maximum is around 10 μm thick. Thus, for microactuator assemblies with a single active suppression layer, the layer thickness is preferably in the range of 10-40% of the primary PZT layer thickness, more preferably in the range of about 10-20% of the primary PZT layer thickness. It is.

FIG. 35 is a cross-sectional view of another embodiment in which the microactuator assembly includes multiple active PZT layers, conceptually illustrating the polarization process and the resulting polarization direction. When the device of FIG. 35 is electrically and mechanically bonded to the suspension as shown in FIG. 31 with electrodes 3524 and 3528 grouped by conductive epoxy, the result is one primary active PZT layer; Three active PZT layers are obtained which tend to act in the opposite direction of the main active PZT layer and therefore act as suppressor layers. That is, the bottom PZT layer expands while the top three PZT layers contract and vice versa.

The configuration of the microactuator assembly can be one active primary PZT layer and two active PZT suppressed layers as shown in FIGS. 31-33 or one active primary PZT layer and three active PZT suppressed layers as shown in FIG. 35. It is easily expandable from a device with layers to any number of active primary layers and active suppression layers. The electric field strength across one or more suppression layers can be reduced by various means including electrode patterning and/or voltage suppressors. Experiments show the optimal number of suppression layers and optimal thickness for different applications.

The effect of a restraining layer in PZT to improve stroke length is also due to the fact that the top PZT layer behaves differently than the bottom layer depending on the activation voltage, as in the embodiments of FIGS. It can also be obtained using a multilayer PZT device, which acts as a

FIG. 36 is a side cross-sectional view of a multilayer PZT macroactuator assembly 714 in a further embodiment, where the assembly 714 is a multilayer PZT device with multiple piezoelectric layers. The devices are generally polarized, meaning that a voltage applied to the devices either expands both devices or contracts both. A top piezoelectric layer 730 is mounted in a stacked manner onto a bottom piezoelectric layer 720, which is the layer closest to the suspension surface to which the assembly is bonded. Top piezoelectric layer 730 is thicker than bottom piezoelectric layer 720. The figure shows the configuration of the device and the voltage applied during polarization. The polarization method uses one positive voltage (Vp+) applied to the first electrode 726, a ground (GND) applied to the electrode 728, the polarization fields are oriented in opposite directions, and the two electrodes are connected to the top and bottom. In each of the electrodes, they are electrically separated from each other by gaps of non-conducting areas, such as strips or gaps of metallization. This is currently the most common method used for multilayer PZT polarization. This multilayer PZT 714 is said to be "generally polarized."

FIG. 37 is a side cross-sectional view of the PZT microactuator assembly 714 of FIG. 36, illustrating an example of how the assembly may be electrically and mechanically bonded to the suspension. In the figure, the suspension containing the electrical circuitry is the same as that of FIG. 26, but only conductive epoxy 460 and 162 and no non-conductive epoxy are used for bonding in this embodiment. In operation, when an actuation voltage is applied to electrodes 726, 728, piezoelectric layers 720, 730 expand longitudinally together or contract together longitudinally, depending on the polarity of the applied actuation voltage.

Because the top PZT layer 730 is thicker than the bottom PZT layer 720, when the same actuation voltage is applied to both layers, the top layer will not expand (or contract) as much as the bottom layer, creating a smaller electric field in the top layer. Therefore, due to the expansion difference between the two piezoelectric layers, the top piezoelectric layer acts as a restraining layer. The net effect may be that the effective stroke length of the device is increased compared to when the top piezoelectric layer is not present.

FIG. 41 is a side cross-sectional view of the PZT microactuator of FIG. 36, here showing the assembly mounted within the suspension using the same bonding technique shown in FIG. 26.

FIG. 38 is a side cross-sectional view of a multilayer PZT macroactuator assembly 814 in yet a further embodiment, where PZT is multilayer PZT and a top PZT layer 830 is a bottom PZT layer 820 referred to as a main PZT layer 820. The active layer tends to expand in the opposite direction. Assembly 814 has three individual electrodes 826, 827, 828 and corresponding poles when polarized. The device is said to be counterpolarized. The figure shows the structure of the device and the voltage applied during polarization. The polarization method consists of three separate electrodes 826, 827, 828, Vp+ applied to the bottom electrode 827, Vp- applied to the top electrode 826, and GND applied to the middle or common electrode 828. using different voltages.

During actuation, if the same voltage is applied to the top and bottom electrodes, but GND is applied to the common center electrode, the top PZT layer 830 or restraint layer expands lengthwise (or expands depending on the polarity of the applied actuation voltage). (or shrinks lengthwise), while the bottom main PZT layer 820 shrinks lengthwise (or expands lengthwise), and vice versa. That is, PZT layers 820 and 830 act or tend to act in opposite directions, with the action of the top piezoelectric layer at least partially counteracting the action of the bottom piezoelectric layer. This PZT is therefore said to be "reversely polarized."

FIG. 39 is a side cross-sectional view of the PZT microactuator assembly 814 of FIG. 38, illustrating an example of how the assembly may be electrically and mechanically bonded to the suspension. A conductive adhesive 162 on the right is added to bridge the non-conductive strip or gap 829 and ground the top electrode 826 and bottom electrode 827. In operation, when an actuation voltage is applied across the top and bottom electrodes, the top PZT layer 830 expands and the bottom layer 820 contracts (and vice versa). In this way, the top PZT layer acts in the opposite direction as the bottom PZT layer. The top PZT layer acts not only as a passive suppression layer, but also as an active layer that actively pushes or pulls in the opposite direction to the bottom layer.

FIG. 40 is a graph showing the stroke sensitivity of the PZT microactuator assembly of FIGS. 37 and 39 as a function of the thickness of the top PZT layer compared to the stroke sensitivity of the reference device; The layer is 45 μm thick. The reference device (shown in dashed lines) is a standard single layer PZT 45 μm thick. This reference device exhibits a stroke sensitivity of 9.0 nm/V. Data are from modeling simulations.

As can be seen from the graph, for the three-pole configuration of FIG. 39 with opposite polarization, the data represented by the triangular data points, the presence of the top PZT layer 830, which is opposite polarization, increases the stroke sensitivity compared to the reference device. increased significantly. As an example, if the top PZT layer is 15 μm thick, the suspension stroke sensitivity is 24.5 nm/V, which represents a 172% increase over the 9.0 nm/V reference. For this device, a reverse polarization configuration with a thin top suppression layer of about 10-15 μm thick, or about 22-33% of the thickness of the bottom PZT layer, provides the highest stroke sensitivity. Stroke sensitivity generally decreases as the thickness of the top PZT layer increases. Therefore, the three-pole configuration of FIG. 39 with a thin reverse polarization suppressing layer is generally the most effective and desirable configuration. The top PZT layer is preferably 5-50% of the thickness of the bottom PZT layer, more preferably about 10-40% of the thickness of the bottom PZT layer, even more preferably about 20-35% of the thickness of the bottom PZT layer. it is conceivable that.

As can further be seen from the graph, the configuration in which the top layer is an inert PZT material yields the second best stroke sensitivity, data represented by square data points. The top layer can be made inactive by not polarizing and/or by arranging the electrodes so that they do not create an electric field in the top layer when the entire microactuator device is activated. Any one of these can be done by cutting electrode 726 so that it does not surround the top of device 714 and therefore CLC portion 730 is not activated. The stroke sensitivity of this configuration is higher than the general polarization configuration of FIGS. 36-37 (represented by the diamond data points) where the actuation voltage is applied to the top PZT layer 730, but the reverse of FIGS. 38-39. less than the polarization configuration. The stroke sensitivity starts higher than that of the reference device, but increases with increasing thickness to about 25 μm or about 55% of the main PZT layer thickness, and increases with increasing thickness to about 55 μm or about 122% of the main PZT layer thickness. %, after which it decreases slightly as the thickness of the suppression layer increases further. Thus, the inert suppression layer has a thickness greater than zero, but preferably has a thickness in the range of 25-55 μm, or about 55-125% of the thickness of the active PZT layer.

And the general polarization configuration of FIG. 37, where the top PZT layer is thicker than the bottom PZT layer, the data represented by the diamond data points, was the lowest performing design overall. For this configuration, stroke sensitivity improved over that of the reference single layer PZT only when the top PZT layer was about 37 μm thick, or greater than about 82% of the thickness of the main PZT layer. The effective stroke length increased with increasing top layer thickness. When the top PZT thickness is 65 μm, the suspension stroke sensitivity is 29% higher than the standard of 9.0 nm/V. This 29% increase in stroke sensitivity relative to the reference represents the best results obtained with this configuration. In the case of general polarization, the thickness is preferably at least 80% of the thickness of the main PZT layer, more preferably greater than the thickness of the main PZT layer, and even more preferably about 125% of the thickness of the main PZT layer. larger than

A design approach using a multilayer PZT microactuator as shown in FIGS. 36-39 with the top PZT layer used as a restraining layer consists of two, three, four or more layers, each acting as a restraining layer. It can be extended more generally to PZT with 3, 4, 5 or more layers with an active layer.

U.S. Pat. No. 9,070,394 to Hahn et al., owned by the present applicant and incorporated herein by reference, discloses that in FIGS. We are publishing multilayer piezoelectric devices including. Since polarization of a piezoelectric material results in permanent changes in its dimensions, we believe that polarizing less than all the layers of a multilayer piezoelectric device leads to non-uniform dimensional changes and therefore loads the device. I discovered that. Such loads are believed to cause cracking and hence premature failure of the device.

Such loads in multilayer piezoelectric devices where the constraining layer is a layer of inert PZT material can be reduced by polarizing the constraining layer. As such, the active PZT layer and the inactive layer undergo similar permanent dimensional changes upon polarization, so that the mechanical properties produced by polarizing only one layer, or usually not all layers, are target weight is removed.

FIG. 42 is a side cross-sectional view of a PZT microactuator 914 in such an embodiment with a polarized but inert suppression layer 930, illustrating the polarization of the device. In an embodiment, the PZT microactuator 914 comprises two PZT layers 920 and 930 attached together, such as by being arranged in a stacked relationship and integrally formed together, as described with respect to previous embodiments. including. The bottom piezoelectric material layer 920 will be the primary or active PZT layer and the top piezoelectric material layer 930 will be the polarized but inactive suppression layer.

A first method of polarizing the device is to apply a voltage difference across the top electrode 926 and bottom electrode 927, respectively, leaving the middle electrode 928 floating. For example, +Vp is applied to top electrode 926, -Vp is applied to bottom electrode 927, and middle electrode 928 is floated. This grounding method provides a uniform electric field that is applied to both piezoelectric layers 920 and 930, so that both piezoelectric layers are polarized simultaneously and to the same extent.

A second method is to apply +Vp and -Vp across these electrodes and ground intermediate electrode 928, as shown.

More generally, the device may be polarized by applying three or more different voltages to three or more terminals.

In many, but not all cases, equal polarization, ie, simultaneous polarization using equal field strengths, is preferred. In the case of two PZT layers of unequal thickness and three polarization voltage potentials, it is necessary to apply unequal voltage differences to the different PZT layers and therefore the same electric field strength, i.e. the same degree of polarization, across these different PZT layers. arise. As an example, if the two PZT layers are of unequal thickness, polarization voltages of +15V, Gnd, and -10V would be the voltages needed to produce equal field strength, and therefore equal polarization, of the two layers.

FIG. 43 is a side cross-sectional view of the PZT microactuator assembly of FIG. 42 showing the assembly mounted within the suspension. In operation, an actuation voltage is applied to middle electrode 928 and bottom electrode 927 is grounded through conductive epoxy 162, gold bond pad 469, and stainless steel 154 of the suspension flexure. Top electrode 926 is not electrically connected to anything and is therefore floating. This creates an actuation electric field across the main PZT layer 920 that expands or contracts, while the top PZT layer 930 is inactive and thus acts as a restraining layer. The presence of the polarized but inert suppression layer 930 acts to increase the effective stroke length of the device compared to the absence of the suppression layer 930, as described above with respect to other embodiments. .

In the illustrated embodiment, device 914 has a total of three electrodes, but only the first and second electrodes are accessible from the bottom of the assembly. Since the third electrode is a floating electrode that is neither connected to the drive voltage nor to ground, there is no need to make it electrically accessible from the bottom or other parts of the device.

Like the other embodiments, the embodiment of FIGS. 42 and 43 is not limited to two layers. Rather, more generally, such a multilayer piezoelectric actuator may include a plurality of PZT layers that are polarized and active, and a plurality of PZT layers that are polarized but inactive.

Although equal polarization is desired in many cases, the suppression layer need not be polarized exactly the same as the active piezoelectric layer. It is generally considered sufficient that the two layers are substantially equally polarized. The two layers may be polarized within 10% of each other or within 25% of each other. Similarly, it is not strictly necessary that the suppression layer be completely inert. Rather, the suppression layer has a voltage difference applied during actuation that is less than 10% of the activation voltage or field applied to the first or active PZT layer, or 25% of the activation voltage or field applied to the first or active PZT layer. % or even less than 50% of the activation voltage or electric field. Additionally, although the inventors currently believe that it is generally desirable for the PZT layers to have equal thicknesses, it is generally desirable that the PZT layers be within 10% of each other's thickness or within 25% of each other's thickness. It is considered that it is sufficient to have the same thickness.

The third electrode 926 may be floating during actuation as shown in FIG. 43, but ensures that there is no or substantially no electric field in the polarized but inert suppression layer 930. An alternative way to do this is to electrically group the third electrode 926 to the second electrode 928, thus ensuring that there is no voltage difference across the suppression layer 930.

The PZT microactuators disclosed herein can be used as actuators in fields other than disk drive suspensions. Such a microactuator and its construction details represent an advanced device regardless of what environment it is used in, whether it be a disk drive suspension environment or any other environment.

As used in this specification and the claims herein, the terms "generally," "approximately," "about," "substantially," and "coplanar" may be used in any precise manner. It is understood that certain degrees of variation from dimensions, measurements, and arrangements are tolerated and should be understood within the context of the description and practice of the invention as such terms are disclosed herein. This is understood.

As used in the specification and claims, terms such as "top," "bottom," "above," and "below" refer to each other rather than in any particular spatial or weight direction. It is further understood that it is a convenient term to describe the spatial relationship of parts. Thus, the term refers to an assembly of parts, whether the assembly is oriented in the particular direction shown in the figures and described in the specification, the opposite of that direction, or in any other degree of rotation. is intended to include.

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

It is recognized that the term "invention" as used herein is not to be understood to mean that only a single invention having a single essential element or group of elements is presented. . Similarly, it is understood that the term "invention" includes a number of separate inventions, each of which may be considered a separate invention. Although the invention has been described in detail with respect to preferred embodiments and drawings thereof, those skilled in the art will appreciate that various adaptations and modifications of the invention can be made without departing from the spirit and scope of the invention. is obvious. Therefore, the detailed description set forth above and the accompanying drawings are not intended to limit the scope of the invention, which can be determined solely from the following claims and their properly understood legal equivalents. is recognized.

Claims (6)

A multilayer piezoelectric microactuator assembly, comprising:
a first electrode;
a first polarized piezoelectric layer on the first electrode;
a second electrode on the first polarized piezoelectric layer;
a second polarized piezoelectric layer on the second electrode;
a third electrode on the second polarized piezoelectric layer remote from the first electrode and the second electrode;
The second electrode partitions the first polarization piezoelectric layer and the second polarization piezoelectric layer,
the first electrode and the second electrode are electrically accessible from the bottom of the assembly;
A multilayer piezoelectric microactuator assembly, wherein the third electrode is not electrically accessible from the bottom of the assembly. The microprocessor of claim 1, wherein each of the first electrode and the second electrode is connected to one of a drive voltage and ground, and the third electrode is not connected to either the drive voltage or ground . Actuator assembly. The microactuator assembly of claim 1 , wherein there is no electric field between the second electrode and the third electrode. 2. A method of using the microactuator assembly of claim 1 , comprising: inducing an electric field across the first polarized piezoelectric layer to make the first polarized piezoelectric layer a polarized active piezoelectric layer; The second polarized piezoelectric layer is a polarized but inert piezoelectric layer that tends to resist expansion or contraction of the first polarized piezoelectric layer without inducing an electric field across the second polarized piezoelectric layer. , a method including. 2. The microactuator assembly of claim 1, wherein the first polarized piezoelectric layer and the second polarized piezoelectric layer have equal thickness and are polarized to the same extent. 2. The microactuator assembly of claim 1 , wherein the first polarized piezoelectric layer and the second polarized piezoelectric layer have substantially equal thicknesses and are substantially equally polarized.