Single sheet differential-poled piezoelectric microactuator for a hard disk drive

A piezoelectric (PZT) microactuator directly attached to a head slider, for mounting on a suspension for use as a third stage actuator in a hard disk drive, is fabricated from and comprises a single sheet of a piezoelectric material with the top and bottom covered with an electrically conductive material to form the electrodes. The piezoelectric material is differential-poled so that one lateral portion is poled in one direction and another lateral portion is poled in the opposite direction. When a drive voltage is applied between the top and bottom electrodes, one portion of the piezoelectric material expands while the other portion contracts, thereby providing a rotational movement. The direction of motion of each respective portion is determined by the direction of the applied voltage and the respective direction of poling.

FIELD OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention relate generally to hard disk drives and more particularly to a piezoelectric (PZT) microactuator.

BACKGROUND

A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.

A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head, which is housed in a slider, and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies in part on a suspension's force on the slider and on the aerodynamic characteristics of the slider air bearing surface (ABS) to provide the proper distance between the read/write head and the surface of the magnetic-recording disk (the “flying height”) while the magnetic-recording disk rotates.

Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) has led to the necessary development and implementation of secondary and even tertiary actuators for improved head positioning through relatively fine positioning, in addition to a primary voice coil motor (VCM) actuator which provides relatively coarse positioning. Some hard disk drives employ micro- or milli-actuator designs to provide second and/or third stage actuation of the recording head to enable more accurate positioning of the head relative to the recording track. Milli-actuators are broadly classified as actuators that move the entire front end of the suspension: spring, load beam, flexure and slider, and are typically used as second stage actuators. Microactuators are typically used as third stage actuators and are broadly classified as actuators that move only the slider, moving it relative to the suspension and load beam, or move only the read-write element relative to the slider body. A third stage actuator is used in conjunction with a first stage actuator (e.g., VCM) and a second stage actuator (e.g., milli-actuator) for more accurate head positioning.

Piezoelectric (PZT) based and capacitive micro-machined transducers are two types of microactuators that have been proposed for use with HDD sliders. Typical PZT transducers are designed as two cantilevers joined with a rigid body at the free ends, a structure which leads to a modestly high bandwidth of 20 kHz but which is very complicated to manufacture because the two cantilevers are fabricated using sand blasting techniques. In the case of capacitive micro-machined microactuators, the net displacement that can be achieved is relatively high but is offset in part by a low servo bandwidth due to a relatively low resonant frequency, often in the range of 5 kHz.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention are directed towards a piezoelectric (PZT) microactuator which may be implemented, for example, for use as a third stage actuator in a hard disk drive. The described microactuator is fabricated from and comprises a single sheet, or block, of a piezoelectric material, with the top and bottom covered with an electrically conductive material to form the electrodes. The piezoelectric material is differential-poled so that one lateral portion is poled in one direction and another lateral portion is poled in the opposite direction. The piezoelectric material is poled by applying a large initial electrical field to the material so that all the individual dipole moments of the material align in the same direction within each respective portion.

Thus, when a drive voltage is applied between the top and bottom electrodes, one portion of the piezoelectric material expands while the other portion contracts, thereby providing a rotational movement. The direction (expansion or contraction) of each respective portion is determined by the direction of the applied voltage and the direction of poling.

A single sheet, differential-poled PZT microactuator configuration as described achieves a relatively high resonant frequency and thus high servo bandwidth, provides precise control of slider motion, and can be batch processed and poled which, therefore, provides a readily manufacturable component.

Embodiments discussed in the Summary of Embodiments of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section.

DETAILED DESCRIPTION

Approaches to the configuration and the manufacturing process for a single sheet differential-poled piezoelectric microactuator are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein.

Physical Description of Illustrative Embodiments of the Invention

Embodiments of the invention may be used in the context of the manufacturing and use of a magnetic writer for a hard-disk drive (HDD). In accordance with an embodiment of the invention, a plan view of a HDD100is shown inFIG. 1.FIG. 1illustrates the functional arrangement of components of the HDD including a slider110bthat includes a magnetic-reading/recording head110a. Collectively, slider110band head110amay be referred to as a head slider. The HDD100includes at least one head gimbal assembly (HGA)110including the head slider, a lead suspension110cattached to the head slider, and a load beam110dattached to the lead suspension110c. The HDD100also includes at least one magnetic-recording disk120rotatably mounted on a spindle124and a drive motor (not shown) attached to the spindle124for rotating the disk120. The head110aincludes a write element and a read element for respectively writing and reading information stored on the disk120of the HDD100. The disk120or a plurality (not shown) of disks may be affixed to the spindle124with a disk clamp128.

The HDD100further includes an arm132attached to the HGA110, a carriage134, a voice-coil motor (VCM) that includes an armature136including a voice coil140attached to the carriage134; and a stator144including a voice-coil magnet (not shown). The armature136of the VCM is attached to the carriage134and is configured to move the arm132and the HGA110to access portions of the disk120being mounted on a pivot-shaft148with an interposed pivot-bearing assembly152. In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage134is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb.

With further reference toFIG. 1, in accordance with an embodiment of the present invention, electrical signals, for example, current to the voice coil140of the VCM, write signal to and read signal from the head110a, are provided by a flexible interconnect cable156(“flex cable”). Interconnection between the flex cable156and the head110amay be provided by an arm-electronics (AE) module160, which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE160may be attached to the carriage134as shown. The flex cable156is coupled to an electrical-connector block164, which provides electrical communication through electrical feedthroughs (not shown) provided by an HDD housing168. The HDD housing168, also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover (not shown) provides a sealed, protective enclosure for the information storage components of the HDD100.

With further reference toFIG. 1, in accordance with an embodiment of the present invention, other electronic components (not shown), including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil140of the VCM and the head110aof the HGA110. The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle124which is in turn transmitted to the disk120that is affixed to the spindle124by the disk clamp128; as a result, the disk120spins in a direction172. The spinning disk120creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider110brides so that the slider110bflies above the surface of the disk120without making contact with a thin magnetic-recording medium of the disk120in which information is recorded.

The electrical signal provided to the voice coil140of the VCM enables the head110aof the HGA110to access a track176on which information is recorded. Thus, the armature136of the VCM swings through an arc180which enables the HGA110attached to the armature136by the arm132to access various tracks on the disk120. Information is stored on the disk120in a plurality of stacked tracks (not shown) arranged in sectors on the disk120, for example, sector184. Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion188. Each sectored track portion188is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track176, and error correction code information. In accessing the track176, the read element of the head110aof the HGA110reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil140of the VCM, enabling the head110ato follow the track176. Upon finding the track176and identifying a particular sectored track portion188, the head110aeither reads data from the track176or writes data to the track176depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system.

Embodiments of the invention relate to a single sheet, differential-poled piezoelectric (PZT) microactuator (also referred to as “third stage actuator”) for high servo bandwidth and precise control of slider motion.FIG. 2Ais a plan view of a piezoelectric microactuator andFIG. 2Bis a side view of the piezoelectric microactuator ofFIG. 2A, according to an embodiment of the invention.

Piezoelectric microactuator (PZT MA)200comprises a first lateral portion202and a second lateral portion204, substantially centered about a longitudinal centerline axis. “Lateral portions”202and204are referred to as such because they are configured laterally with respect to a longitudinal centerline of PZT MA200, as well as laterally with respect to a longitudinal axis of slider302(FIG. 3A) and a longitudinal axis of suspension304(FIG. 3B) along the length of each. Further, the opposing terms “top” and “bottom, “over” and “under”, “above” and “below”, “upper” and “lower”, and the like, if used herein are used relatively but arbitrarily and not in an absolute sense because PZT MA200does not necessarily have a true top or bottom.

Lateral portion202is poled in a certain direction: “up”, or out of the page, as depicted as poling203ofFIG. 2A. By contrast, lateral portion204is poled in the opposite direction as lateral portion202: “down”, or into the page, as depicted as poling205ofFIG. 2A. The poling203and205directions depicted inFIG. 2Aare arbitrary and could be reversed, just so long as the poling directions are opposite. Poling203and poling205are formed by applying a large electric field to the PZT material so that all the individual dipole moments of the material align in the same direction for each of the respective polings203and205and, likewise, for each of the corresponding lateral portions202and204.

Referring toFIG. 2B, the side view of PZT MA200shows that PZT material212has atop surface215and a bottom surface217. The top surface215of PZT material212is covered (e.g., coated or deposited) with a top, or first, conductive electrode layer214. Similarly, the bottom surface217of PZT material212is covered (e.g., coated or deposited) with a bottom, or second, conductive electrode layer216. Each of the electrode layer214and electrode lay16is electrically coupled to the PZT material212to drive the actuation of the PZT MA200.

FIG. 3Ais a plan view of a piezoelectric microactuator and slider assembly, andFIG. 3Bis a side view of the piezoelectric microactuator and slider assembly ofFIG. 3A, according to an embodiment of the invention.FIGS. 3A and 3Billustrate the assembly300of the PZT MA200and slider302, as well as the operation of the assembly300.

The PZT MA200is fixed to the suspension304via affixing means305. For example, PZT MA200may be fixed to the suspension304by soldering or using an adhesive. Slider302is coupled to PZT MA200, for example, using an adhesive303such as a soft epoxy. The location at which PZT MA200is fixed to the suspension304, and thus the location of affixing means305, may vary from implementation to implementation. Similarly, the location at which slider302is coupled to PZT MA200, and thus the location of adhesive303, may vary from implementation to implementation. For example, the location of affixing means305and adhesive303as illustrated inFIGS. 3A and 3Bare shown as an example, and may be reversed such that PZT MA200is fixed to the suspension at the leading edge side (left-hand side ofFIGS. 3A and 3B) and the slider302is fixed to the PZT MA200at the trailing edge side (right-hand side ofFIGS. 3A and 3B).

Slider302may be coupled to PZT MA200in such a manner that the mass moment of the assembly300is balanced about the axis of rotation of the assembly300relative to the suspension304.

When drive voltage is applied between the top electrode (e.g., electrode layer214ofFIG. 2B) and the bottom electrode (e.g., electrode layer216ofFIG. 2B), one lateral portion of the PZT MA200expands and the other lateral portion of the PZT MA200contracts. The direction of movement of each respective lateral portion202and204(FIG. 2A), i.e., expansion or contraction, is determined by the applied voltage relative to the direction of poling of each respective lateral portion202and204. That is, if the applied voltage direction and poling voltage direction are the same, then that lateral portion of the PZT MA200contracts in the longitudinal direction. Similarly, if the applied voltage direction and poling voltage direction are opposite, then that lateral portion of the PZT MA200expands in the longitudinal direction. Thus, because each electrode layer214and216is in electrical coupling with both lateral portions202and204, a single applied voltage causes one lateral portion to contract and the other lateral portion to expand simultaneously, thereby generating a bending motion of the PZT MA200about the centerline, depicted as moment306inFIG. 3A. This bending motion causes rotational movement of the slider302. Further, the magnitude of the expansion/contraction is roughly proportional to the drive voltage, so that the motion of the slider302can be precisely controlled by applying accurate drive voltage.

Manufacturing a Single Sheet Differential-Poled Piezoelectric Microactuator

FIG. 4is a flow diagram illustrating a process for manufacturing a single sheet differential-poled piezoelectric microactuator, according to an embodiment of the on.FIGS. 5A,5C,5E and5G are plan views of stages of the manufacturing of a single sheet differential-poled piezoelectric microactuator, andFIGS. 5B,5D,5D(1),5F and5H are cross-sectional views of the stages of the manufacturing of the single sheet differential-poled piezoelectric microactuator, according to an embodiment of the invention. Having introduced the concept of a single sheet differential-poled piezoelectric microactuator, in reference to piezoelectric microactuator200ofFIGS. 2A and 2B, a method for manufacturing such a component is now described with reference toFIG. 4and all theFIGS. 5A-5H.

At block402, a first surface of a piezoelectric material is coated with a first electrode. Referring toFIG. 5AandFIG. 5B, for example, a very thin sheet of piezoelectric material512is coated with conductive material516(such as Cr, Au or Al) on one side (e.g., the bottom). According to an embodiment, the thin sheet of piezoelectric material from which the microactuator is manufactured is approximately 100 μm thick, so that the head slider assembly can be safely loaded on and unloaded from a toad/unload ramp.

At block404, a second surface of the piezoelectric material is coated with a conductive poling material. Referring toFIG. 5B, for example, piezoelectric material512is coated with conductive material514on the other side (e.g., the top).

At block406, the poling material is patterned to form a first poling electrode on a first portion of the second surface and a second poling electrode on a second portion of the second surface. Referring toFIG. 5CandFIG. 5D, for example, the poling material514is patterned to form a plurality of poling electrodes520and a plurality of poling electrodes522.

At block408, an electrical field is applied to the first poling electrode to pole a first portion of the sheet of piezoelectric material in a first direction normal to the sheet, and at block410, an electrical field is applied to the second poling electrode to pole a second portion of the sheet of piezoelectric material in a second direction normal to the sheet and opposing the first direction. Referring to FIG.5D(1), for example, a high voltage electrical field524is applied to poling electrodes520to pole the adjacent piezoelectric material512in one direction (block408), and an opposite direction high voltage electrical field526is applied to poling electrodes522to pole the adjacent piezoelectric material512in the other direction (block410). Because alternate rows of poling electrodes are electrically connected, batch poling of an entire wafer is facilitated by the application of only two respective high voltage electrical fields in opposing directions to the top528and bottom516electrodes.

At block412, a second electrode is deposited over the second surface. Referring toFIG. 5EandFIG. 5F, for example, the actuation electrode528is deposited over piezoelectric material512, which in an embodiment, includes depositing electrode528over the poling electrodes520and522. Alternatively, the poling electrodes520and522may be removed (e.g., by etching) prior to depositing the actuation electrode528.

Finally, the wafer assembly is diced to obtain the separate piezoelectric microactuators of the desired dimensions, such as microactuators530a,530b,530cshown nFIG. 5GandFIG. 5H. Each of microactuators530a,530b,530ccomprises differential-poled piezoelectric material512coupled to actuation electrodes528and516, to which drive voltage can be applied to drive the fine rotational movement of the microactuator and slider.

The piezoelectric microactuator as configured herein provides a third stage actuator enabling fine precision movement of an attached head slider and having a relatively high resonant frequency (e.g., greater than 100 kHz). This assists in achieving a relatively high servo bandwidth microactuator, which enables greater operation in the linear region of its transfer function and, therefore, more predictable and stable operation over a wider operational regime. Further, such a microactuator can be readily batch processed and poled at the wafer level, and does not require complicated fabrication steps such as sand blasting, thereby reducing manufacturing time in comparison with prior microactuator designs.