Patent Publication Number: US-8982513-B1

Title: Disk drive head suspension with dual piezoelectric elements adhered to rotary-actuated and non-actuated portions of a structural layer of a tongue of a laminated flexure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional U.S. Patent Application Ser. No. 61/825,837, filed on May 21, 2013, which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read are referred to as “read heads” herein, regardless of other devices and functions the read head may also perform (e.g., writing, flying height control, touch down detection, lapping control, etc.). 
     In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a slider, and a read/write transducer deposited on a trailing end of the slider. The read/write transducer typically comprises a magneto-resistive read element (e.g., so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element), and an inductive write structure comprising a flat coil deposited by photolithography, and a yoke structure having pole tips that face a disk media. 
     The HGA typically also includes a suspension assembly that includes a mounting plate, a load beam, and a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA). The HSA typically includes a rotary actuator having a plurality of actuator arms, a plurality of HGAs (attached to the actuator arms), and a flexible printed circuit that includes a flex cable. The mounting plate of each suspension assembly is attached to an arm of the rotary actuator (e.g., by swaging), and each of the laminated flexures includes a flexure tail that is electrically connected to the HSA&#39;s flex cable (e.g., by solder reflow bonding or ultrasonic bonding). 
     Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that are electrically connected to a plurality of electrically conductive bonding pads on the head (e.g., by 90° solder jet bonding), and extend from adjacent the head to terminate at electrical connection points at the flexure tail. 
     The position of the HSA relative to the spinning disks in a disk drive, and therefore the position of the read heads relative to data tracks on the disks, is actively controlled by the rotary actuator which is typically driven by a voice coil motor (VCM). Specifically, electrical current passed through a coil of the VCM applies a torque to the rotary actuator, so that the read head can seek and follow desired data tracks on the spinning disk. 
     However, the industry trend towards increasing areal data density has necessitated substantial reduction in the spacing between data tracks on the disk. Also, disk drive performance requirements, especially requirements pertaining to the time required to access desired data, have not allowed the rotational speed of the disk to be reduced. In fact, for many disk drive applications, the rotational speed has been significantly increased. A consequence of these trends is that increased bandwidth is required for servo control of the read head position relative to data tracks on the spinning disk. 
     One solution that has been proposed in the art to increase disk drive servo bandwidth is dual-stage actuation. Under the dual-stage actuation concept, the rotary actuator that is driven by the VCM is employed as a coarse actuator (for large adjustments in the HSA position relative to the disk), while a so-called “microactuator” having higher bandwidth but lesser stroke is used as a fine actuator (for smaller adjustments in the read head position). Various microactuator designs have been proposed in the art for the purpose of dual-stage actuation in disk drive applications. Some of these designs utilize one or more piezoelectric microactuators that are affixed to a component of the suspension assembly. For example, the piezoelectric microactuator may be affixed to the mounting plate or an extension thereof, and/or the load beam or an extension thereof, or to the flexure tongue (a.k.a. the “gimbal tongue”) to which the read head is bonded. 
     However, generally, the further the microactuator is disposed from the read head on the suspension assembly, the less bandwidth it can provide. This is due to the dynamics introduced by the intermediate structure of the suspension assembly. On the other hand, the closer the microactuator is disposed to the read head on the suspension assembly, the lesser stroke it can typically provide. As track density increases, the need for additional bandwidth tends to exceed the need for additional stroke, tending to favor microactuator designs that are more distally located (e.g., at or near the read head). Hence there is a need in the information storage device arts for a distally located microactuator design that can provide both adequate stroke and adequate bandwidth for fine actuation. 
     Moreover, certain prior art design concepts in which the microactuator is disposed on the flexure tongue may have other performance disadvantages. For example, in certain designs, the motion imparted by the microacutator may be undesirably coupled with the yaw or “sway” mode of vibration of the head gimbal assembly. Also for example, the microactuator operation may require relative motion at the dimple contact location between the flexure tongue and the load beam, which can cause undesirable fretting, debris, and a stick-slip motion characteristic. Also for example, the flexure design for accommodating the microactuator may lack desired stiffness in certain directions (e.g., vertical stiffness or yaw stiffness), and/or may lack desired compliance in other directions (pitch compliance or roll compliance). Also for example, the microactuated HGA design may include additional parts and complexity that add cost and time to the manufacturing process, such as where the structure that supports the microactuator components is attached to (rather than built into and integral with) the flexure tongue. Also for example, the flexure design for accommodating a microactuator on the tongue may not provide for adequate bonding area to reliably bond the head to the tongue with consistently adequate strength in a practical high volume manufacturing process. 
     Hence, there is a need in the information storage device arts for improved fine actuator (“microactuator”) designs for HGAs. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view of a disk drive capable of including an embodiment of the present invention. 
         FIG. 2  is a perspective view of a head stack assembly (HSA) capable of including an embodiment of the present invention. 
         FIG. 3  is a perspective view of an HGA according to an embodiment of the present invention. 
         FIG. 4A  depicts the distal portion of the structural layer of a laminated flexure, according to an embodiment of the present invention, with other layers of the laminated flexure removed so that details of the structural layer are not obstructed. 
         FIG. 4B  depicts the distal portion of the structural layer of  FIG. 4A , except with the relative position of a read head and piezoelectric elements indicated. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is an exploded perspective view of an example disk drive that is capable of including an embodiment of the present invention. The example disk drive includes a head disk assembly (HDA)  10  and a printed circuit board assembly (PCBA)  14 . The HDA  10  includes a base  16  and cover  18  that together form a disk drive enclosure that houses at least one annular magnetic disk  20 . Each disk  20  contains a plurality of magnetic tracks for storing data. The tracks are disposed upon opposing first and second disk surfaces of the disk  20  that extend between an inner disk edge  22  (corresponding to the inner diameter) and an outer disk edge  24  (corresponding to the outer diameter) of the disk  20 . The head disk assembly  10  further includes a spindle motor  26  for rotating the disks  20  about a disk axis of rotation  28 . The spindle motor  26  includes a spindle motor hub that is rotatably attached to the base  16  of the HDA  10 . Disks  20  may be stacked and separated with one or more annular disk spacers  12  that are disposed about the hub, all held fixed to the hub by disk clamp  11 . 
     In certain embodiments, the HDA  10  further includes a head stack assembly (HSA)  30  rotatably attached to the base  16  of HDA  10 . The HSA  30  includes an actuator comprising an actuator body  32  and one or more actuator arms  36  extending from the actuator body  32 . The actuator body  32  includes a bore and a pivot bearing cartridge  44  engaged within the bore for facilitating the HSA  30  to rotate relative to HDA  10  about actuator pivot axis  46 . For example, the actuator body  32  may be pivotally attached to the base  16  of HDA  10 , by the pivot bearing cartridge  44 . One or two head gimbal assemblies (HGA)  42  are attached to a distal end of each actuator arm  36 . In certain embodiments, each HGA  42  includes a head (e.g., head  40 ) for reading and writing data from and to the disk  20 , and a load beam to compliantly preload the head against the disk  20 . 
     In the example of  FIG. 1 , the HSA  30  further includes a coil support that extends from one side of the HSA  30  that is opposite head  40 . The coil support is configured to support a coil  50  through which a controlled electrical current is passed. The coil  50  interacts with one or more magnets  54  that are attached to base  16  via a yoke structure  56 ,  58  to form a voice coil motor for controllably rotating the HSA  30 . HDA  10  includes a latch  52  rotatably mounted on base  16  to prevent undesired rotations of HSA  30 . 
     In certain embodiments, the PCBA  14  includes a servo control system for generating servo control signals to control the current through the coil  50  and thereby position the HSA  30  relative to tracks disposed upon surfaces of disk  20 . In certain embodiments, the HSA  30  is electrically connected to PCBA  14  via a flexible printed circuit (FPC)  62 , which includes a flex cable and a flex cable support bracket  64 . The FPC  62  supplies current to the coil  50  and carries signals between the HSA  30  and the PCBA  14 . Before periods of non-operation, the HSA  30  is positioned so that the HGAs  42  are moved beyond the outer disk edge  24 , so that a distal tip (i.e. a load tab) of the load beam of each HGA  42  rides up on a head loading/unloading ramp  48 . With the HGAs  42  “parked” on the head loading/unloading ramp  48 , mechanical shock events are prevented from causing impacts between the heads  40  and the surfaces of the disks  20 . 
     In the magnetic hard disk drive of  FIG. 1 , each head  40  includes a body called a “slider” that carries a magnetic transducer on its trailing end (not visible given the scale of  FIG. 1 ). The magnetic transducer may include an inductive write element and a magnetoresistive read element. During operation the transducer is separated from the magnetic disk by a very thin hydrodynamic air bearing. As the motor  26  rotates the magnetic disk  20 , the hydrodynamic air bearing is formed between an air bearing surface of the slider of head  40 , and a surface of the magnetic disk  20 . The thickness of the air bearing at the location of the transducer is commonly referred to as “flying height.” 
       FIG. 2  is a perspective view of a head stack assembly (HSA)  200  capable of including an example embodiment of the present invention. The HSA  200  includes an actuator body  232  and a plurality of actuator arms  236  extending from the actuator body  232 . The actuator body  232  may comprise aluminum, for example. The actuator body  232  may include a pivot bearing cartridge  244  disposed in a bore in the actuator, and a coil  250  that extends from the actuator body  232  in a direction that is generally opposite the actuator arms  236 . 
     In the example of  FIG. 2 , the HSA  200  also includes a plurality of head gimbal assemblies (HGA)  242  attached to the actuator arms  236 . For example, such attachment may be made by swaging. Note that the inner actuator arm includes two HGAs, while each of the outer actuator arms includes only one HGA. This is because in a fully populated disk drive the inner arms are positioned between disk surfaces while the outer actuator arms are positioned over (or under) a single disk surface. In a depopulated disk drive, however, any of the actuator arms may have one or zero HGAs, optionally replaced by a dummy mass. 
     In certain embodiments, each HGA  242  includes a head  292  for reading and/or writing to an adjacent disk surface. Each head  292  is attached to a tongue portion of a laminated flexure  282 . The laminated flexure  282  is part of the HGA  242 , and is attached to a load beam subcomponent of the HGA  242 . The laminated flexure  282  may include a structural layer (e.g., stainless steel), a dielectric layer (e.g., polyimide), and a conductive layer into which traces are patterned (e.g., copper). 
     In the example of  FIG. 2 , the HSA  200  also includes a laminar flexible printed circuit (FPC)  262  adjacent the actuator body  232 . The FPC  262  may comprise a laminate that includes two or more conventional dielectric and conductive layer materials (e.g., one or more polymeric materials, copper, etc.). A preamplifier chip  266  may also be mounted on the FPC  262 . Each of the laminated flexures  282  includes a flexure tail that is electrically connected to bond pads of the FPC  262 . 
       FIG. 3  is a perspective view of a HGA  300  according to an embodiment of the present invention. The HGA  300  includes a load beam  302  that defines a load beam longitudinal axis  396 , and a read head  310  for reading and writing data from and to a magnetic disk. A purpose of the load beam  302  is to provide limited vertical compliance for the read head  310  to follow vertical undulations of the surface of a disk as it rotates, and to preload an air bearing surface of the read head  310  against the disk surface by a preload force that is commonly referred to as the “gram load.” In certain embodiments, the load beam may preferably comprise stainless steel sheet metal having a thickness in the range of 20 to 103 microns. 
     In the embodiment of  FIG. 3 , the HGA  300  also includes a laminated flexure  303 . In the embodiment of  FIG. 3 , a distal portion  308  of the laminated flexure  303  includes a tongue  306  to which the read head  310  is adhered. Only a portion of the tongue  306  is visible in the view of  FIG. 3  because the read head  310  (and other components of the HGA  300  that will be subsequently described) partially obscures it. The distal portion  308  of the laminated flexure  303  is connected to a non-distal portion  304  of the laminated flexure  303  by outrigger beams  334 ,  336 . 
     A first purpose of the laminated flexure  303  may be to provide compliance for the head  310  to follow pitch and roll angular undulations of the surface of the disk as it rotates, while restricting relative motion between the read head  310  and the load beam  302  in the lateral direction and about a yaw axis. A second purpose of the laminated flexure  303  may be to provide a plurality of electrical paths to facilitate signal transmission to/from the read head  310 . For that second purpose, the laminated flexure  303  may include a plurality of electrically conductive traces that are defined in an electrically conductive (e.g., copper) sub-layer of the laminated flexure  303 . The electrically conductive traces may be insulated from a support layer (e.g., stainless steel) by a dielectric layer (e.g., polyimide). The electrically conductive traces may extend away from the read head  310  along a flexure tail  305  of the laminated flexure  303 , to reach a portion of the flex cable (not shown) that includes a preamplifier chip near the body of the actuator. 
     In the embodiment of  FIG. 3 , a proximal region of the load beam  302  is attached to a mounting plate  320 , for example by a plurality of spot welds. The load beam  302 , the mounting plate  320 , and the laminated flexure  303 , may together be referred to as a “suspension assembly.” Accordingly, the mounting plate  320  may also be referred to as a suspension assembly mounting plate  320 . In certain preferred embodiments, the suspension assembly mounting plate  320  includes an annular swage boss  326  to facilitate attachment of the suspension assembly to an actuator arm by the well-known conventional attachment process known as swaging. In that case, the suspension assembly mounting plate  320  may also be referred to as a “swage mounting plate.” 
       FIG. 4A  depicts the distal portion  400  of the structural layer of a laminated flexure, according to an embodiment of the present invention. Note that in  FIG. 4A , only the structural layer of the flexure is shown; the conventional dielectric layer, and the conventional traces of the conductive layer of the laminated flexure are not shown, so that certain novel features of the structural layer of the flexure tongue can be seen more clearly.  FIG. 4B  depicts the distal portion  400  of the structural layer of  FIG. 4A , except with the relative position of a read head  410  and piezoelectric elements  492 ,  494  being indicated. 
     In the embodiment of  FIG. 4B , the read head  410  includes a slider substrate having an air bearing surface (the label  410  points to this surface) and an opposing top surface (not visible in the view of  FIG. 4B ). The slider substrate preferably comprises AlTiC, although another ceramic or silicon might also be used. The slider substrate of the read head  410  also includes a trailing end  412  that includes a read/write transducer, and a leading end  414 . Note: During disk drive operation, the read head  410  will be disposed adjacent a disk surface, with the disk surface moving from the leading end  414  towards the trailing end  412 . In certain embodiments, the read/write transducer is preferably an inductive magnetic write transducer merged with a magneto-resistive read transducer (e.g., a tunneling magneto-resistive read transducer). 
     In the embodiment of  FIGS. 4A and 4B , the distal portion  400  of the structural layer of a laminated flexure includes a tongue  406  disposed between two outrigger beams  436 ,  434 . The first piezoelectric element  492  and the second piezoelectric element  494  are adhered to portions of the tongue  406 . The read head  410  is also adhered to a portion of the tongue  406  as described further herein. 
     In the embodiment of  FIGS. 4A and 4B , the tongue  406  includes an actuated portion  440  that is rotated about a center of rotation (preferably coincident with dimple contact location  435 ) by expansion of the first piezoelectric element  492  relative to the second piezoelectric element  494 . The tongue  406  also includes a non-actuated portion  430  that is not rotated by expansion of the first piezoelectric element  492  relative to the second piezoelectric element  494 . In the embodiment of  FIG. 4A , the actuated portion  440  and the non-actuated portion  430  of the tongue  406 , and the outrigger beams  434 ,  436  are optionally a single component having material continuity rather than being an assembly of sub-components. For example, these components may be distinct regions of a single stainless steel sublayer of the laminated flexure, each distinct region being at least partially bounded and defined by etched openings through the single stainless steel sublayer. 
     In the embodiment of  FIGS. 4A and 4B , the non-actuated portion  430  of the tongue  406  adjoins and forms a bridge between the two outrigger beams  434 ,  436 , and so the non-actuated portion  430  may also be referred to herein as the “bridge”  430 . The bridge  430  includes a dimple contact location  435  that is in contact with a dimple of the HGA load beam. For example, the load beam (e.g., load beam  302  of  FIG. 3 ) may include a conventional dimple (e.g., a hemispherical dimple) that protrudes towards the read head  410 , and contacts the non-actuated portion  430  of the tongue  406  coincident with the dimple contact location  435 . 
     In the embodiment of  FIGS. 4A and 4B , the actuated portion  440  of the tongue  406  includes at least one head mounting plate  441  that is adhered to the read head  410  closer to the leading end  414  than to the trailing end  412 . Each of the first and second piezoelectric elements  492 , 494  has an anchored end (e.g.,  486 ) that is adhered to the bridge  430  closer to the trailing end  412  than to the leading end  414  of the read head  410 . Each of the first and second piezoelectric elements  492 , 494  has an opposing actuated end (e.g.,  488 ) that is adhered to the actuated portion  440  of the tongue  406  closer to the leading end  414  than to the trailing end  412  of the read head  410 . 
     Note that in the present context, a “read head” is any head that can read, even if it can also perform other functions or includes other structures, such as a writer, heater, etc. Note also that each of the first and second piezoelectric elements  492 , 494  may optionally be a multilayer piezoelectric element, comprising a plurality of piezoelectric material layers sandwiched between conductive (e.g., gold) electrode layers. The first and second piezoelectric elements  492 , 494  may optionally have a total piezoelectric element thickness in the range of 35 microns to 150 microns. In certain embodiments, the piezoelectric element thickness may be greater than the thickness of the laminated flexure. For example, in certain embodiments the piezoelectric element thickness may be in the range 35 microns to 150 microns, while the thickness of the laminated flexure may be in the range 18 microns to 80 microns. 
     In the embodiment of  FIGS. 4A and 4B , the first piezoelectric element  492  is shown to be embedded in a receiving well  460  of the laminated flexure, for example such that a mid-plane of the first piezoelectric element  492  may be preferably coincident with a mid-plane of the structural layer of the laminated flexure adjacent the receiving well  460 . Likewise, the second piezoelectric element  494  may be embedded in a receiving well  465  of the laminated flexure, such that a mid-plane of the second piezoelectric element  494  may be coincident with a mid-plane of the structural layer of the laminated flexure adjacent the receiving well  465 . In some embodiments, such embedding of the first and second piezoelectric elements  492 , 494  may advantageously reduce unwanted out-of-plane actuation. However, the piezoelectric elements  492 , 494  may alternatively be simply adhered on to top or bottom surfaces of the tongue  406 , rather than being embedded. 
     The receiving wells  460 ,  465  may each comprise an opening that optionally passes through the structural layer and the dielectric layer of the laminated flexure. The opening is optionally larger through the structural layer to allow the corresponding piezoelectric element to be received within the opening in the structural layer. However, the opening may be optionally smaller through the dielectric layer to prevent the corresponding piezoelectric element from passing through the dielectric layer. 
     Note that in the embodiment of  FIGS. 4A and 4B , each of the first and second piezoelectric elements  492 , 494  is elongated in the longitudinal direction  496 , and the read head  410  is disposed between the first and second piezoelectric elements  492 , 494 . In this context, being elongated in a direction means being longer than wide with respect to that direction. Also, in this context, “between” is as viewed from a viewing direction normal to the air bearing surface of the read head  410 . In certain embodiments, this may provide a design freedom advantage, in that it may then be possible to optionally mount the piezoelectric elements on the same side of the structural layer as is the read head  410 . 
     In the embodiment of  FIGS. 4A and 4B , the at least one head mounting plate  441  is connected to the non-actuated portion  430  of the tongue  406  by an elongated compliant member  455  that is oriented radially (and in this case also longitudinally) with respect to the dimple contact location  435 . In this context, being oriented radially does not require being oriented perfectly radially, but rather practically within ±20° of being oriented perfectly radially. 
     In certain embodiments, such radial orientation may help provide pure rotary motion about the dimple contact location  435 , which may reduce undesired coupling between microactuator operation and the HGA yaw or sway mode of vibration. Although it is preferred that the rotary motion of the microactuator be about an axis (i.e. center of rotation) that is coincident with the dimple contact location  435 , in this context being “coincident with” does not require that the axis of rotation perfectly passes through the dimple contact location  435 , but rather is approximately coincident with the dimple contact location  435 , considering part-to-part variations and tolerances in a real rather than ideal manufacturing environment. 
     In the embodiment of  FIGS. 4A and 4B , the two outrigger beams  434 ,  436  connect the non-actuated portion  430  of the tongue  406  to a proximal region  470  of the laminated flexure. In turn, the proximal region  470  of the laminated flexure overlaps and is attached to a proximal region of the load beam, which is itself attached to an actuator arm (e.g., via a swage mounting plate). 
     Each of the first and second piezoelectric elements  492 ,  494  may optionally comprise one or more of the many known piezoelectric materials, for example lead zirconate titanate, lead scandium tantalite, lanthanum gallium silicate, lithium tantalite, barium titanate, gallium phosphate and/or potassium sodium tartrate. 
     In certain embodiments, the adhesive used to bond the first and second piezoelectric elements  492 ,  494  within the receiving wells  460 ,  465  may be an electrically non-conductive cyanoacrylate, epoxy, polyimide, and/or acrylic. The non-conductivity of such adhesive may be advantageous in certain embodiments where electrode layers of a piezoelectric element might otherwise be shorted, though a conductive adhesive might provide an advantageous electrical connection (e.g., to ground) in certain embodiments where a coating on the piezoelectric element would otherwise prevent shorting. For example, in certain embodiments, a side of each piezoelectric element  492 ,  494  may be grounded via electrical conduction through the stainless steel parts of the suspension assembly (used as the ground conductor rather than or in addition to a ground trace of the laminated flexure). In certain embodiments, a conductive adhesive, solder, ribbon leads, and/or gold wire stitching may be used to make conventional electrical connections to the piezoelectric elements  492 ,  494 . However, if solder is used, then it may be desirable for the solder to have a low temperature melting point, since it may be undesirable for it to get so hot that the piezoelectric material becomes depolarized. 
     In the foregoing specification, the invention is described with reference to specific exemplary embodiments, but those skilled in the art will recognize that the invention is not limited to those. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. For example, the word “preferably,” and the phrase “preferably but not necessarily,” are used synonymously herein to consistently include the meaning of “not necessarily” or optionally. “Comprising,” “including,” and “having,” are intended to be open-ended terms.