Patent Application
20220343949
Embodiments of the invention may relate generally to hard disk drives, and particularly to approaches to improving the stroke of a secondary actuator.
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. 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 (or “transducer”) that is positioned over a specific location of a disk by an actuator. A read-write head makes use of magnetic fields to write data to and read data from the surface of a magnetic-recording disk. A write head works by using the current flowing through its coil to produce a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head produces a localized magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
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 HDDs 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 tracks. Milli-actuators may be 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. Micro-actuators (or “microactuators”) may be broadly classified as actuators that move (e.g., rotate) 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 microactuator may be used solely in conjunction with a first stage actuator (e.g., VCM), or in conjunction with a first stage actuator and a second stage actuator (e.g., milli-actuator) for more accurate head positioning. The terms “microactuator” and “secondary actuator” and “dual stage actuator” are used herein to refer generally to a relatively fine-positioning actuator (e.g., technically, either secondary or tertiary) used in conjunction with a primary relatively coarse-positioning actuator, such as a VCM actuator in the context of an HDD. Piezoelectric (PZT) based and capacitive micro-machined transducers are two types of microactuators that have been developed for use with HDD sliders.
During manufacturing, an HDD undergoes a battery of operational and other tests including test(s) to measure the stroke (e.g., the distance displaced or the amount of rotation driven) of a microactuator sub-system, if applicable. If the operation of a microactuator is in some way impeded, then the sub-system may fail such a stroke test.
Any approaches that may be described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
Generally, approaches to improving the stroke of a microactuator in a hard disk drive (HDD), 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 may be shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein.
References herein to “an embodiment”, “one embodiment”, and the like, are intended to mean that the particular feature, structure, or characteristic being described is included in at least one embodiment of the invention. However, instances of such phrases do not necessarily all refer to the same embodiment,
The term “substantially” will be understood to describe a feature that is largely or nearly structured, configured, dimensioned, etc., but with which manufacturing tolerances and the like may in practice result in a situation in which the structure, configuration, dimension, etc. is not always or necessarily precisely as stated. For example, describing a structure as “substantially vertical” would assign that term its plain meaning, such that the sidewall is vertical for all practical purposes but may not be precisely at 90 degrees throughout.
While terms such as “optimal”, “optimize”, “minimal”, “minimize”, “maximal”, “maximize”, and the like may not have certain values associated therewith, if such terms are used herein the intent is that one of ordinary skill in the art would understand such terms to include affecting a value, parameter, metric, and the like in a beneficial direction consistent with the totality of this disclosure. For example, describing a value of something as “minimal” does not require that the value actually be equal to some theoretical minimum (e.g., zero), but should be understood in a practical sense in that a corresponding goal would be to move the value in a beneficial direction toward a theoretical minimum.
Recall that during HDD manufacturing, an HDD microactuator may undergo testing to measure the stroke, and if the operation of the microactuator is in some way impeded then the microactuator sub-system may fail the stroke test or other related sub-systems could consequently fail their related tests. One point of failure that has been observed corresponds to the effect that an uneven dispensing of the adhesive used to attach the slider to the suspension may have on the gap between the slider and the suspension at the slider leading edge (LE) side. For example, a normal gap may be on the order of 10 μm, whereas with undesired adhesive issues a zero or near zero gap may occur.
With an expected normal gap the microactuator stroke relative to voltage (i.e., the gain) is not dependent on the z-height of the slider-suspension assembly and, therefore, the servo system is able to generate the expected control.
By contrast, in the zero-gap scenario the microactuator stroke relative to voltage becomes dependent on the z-height of the slider-suspension assembly (e.g., due to the varying relative position and operation of the constituent parts, including the suspension flexure, at various flying heights) and the servo voltage control does not generate the desired slider motion, especially at lower voltages, because the actual assembly behaves differently than expected.
An HDD includes at least one head gimbal assembly (HGA) that generally includes a slider that houses the read-write transducer (or “head”), and a suspension assembly. Each slider is attached to the free end of a suspension assembly that in turn is cantilevered from the rigid arm of an actuator. Several actuator arms may be combined to form a single movable unit, a head stack assembly (HSA), typically having a rotary pivotal bearing system. The suspension of a conventional HDD typically includes a relatively stiff load beam with a mount plate at its base end, which attaches to the actuator arm, and whose free end mounts a flexure that carries the slider and its read-write head. Positioned between the mount plate and the functional end of the load beam is a “hinge” that is compliant in the vertical bending direction (normal to the disk surface). The hinge enables the load beam to suspend and load the slider and the read-write head toward the spinning disk surface. It is then the function of the flexure to provide gimbaled support for the slider so that the slider can pitch and roll in order to adjust its orientation.
According to an embodiment, the head slider 306 is adhesively mounted to the flexure 304. As discussed, an uneven dispensing or other undesired application of the adhesive used to attach a conventional head slider to the suspension may produce a zero or near zero gap between the slider and the suspension at the slider leading edge (LE) side. A portion of or a component 304a (e.g., a polyimide material) of the flexure 304 has been identified as mechanically interfering with the conventional slider, or at least with the adhesive used to mount the slider, at the LE side of the slider. Such interference can limit the movement of the microactuator 308 (i.e., the PZT devices 308a, 308b) underneath. According to an embodiment, the head slider 306 is constructed with a material void at its lower leading edge, as depicted in the magnified view of
According to an embodiment, and as depicted in
Regarding possible effects the material void 306a could have on the flying characteristics or flying dynamics of the slider 306, any effect is considered manageable and relatively insignificant at least in part because the material removal 306a is positioned generally on the suspension 302 side of the head slider 306 rather than on the media, or air bearing surface (ABS), side of the slider 306. It is noted, however, that material void 306a does alter the mass distribution relative to a conventional head slider not having a material void 306a as described and illustrated herein. Some amount of mass removal is tolerable in the context of the flying dynamics of the head slider 306, therefore various material voids or removals may be implemented insofar as such removals do not exceed a change in slider 306 mass over a certain threshold. Limiting factors or constraints with respect to slider material removal are considered design-specific relative to a given head slider design. With respect to the head slider 306 of
High volume magnetic thin film head slider fabrication involves high precision subtractive machining performed in discrete material removal steps. Slider processing starts with a completed thin film head wafer consisting of 40,000 or more devices, and is completed when all the devices are individuated and meet numerous and stringent specifications. A wafer comprises a matrix of unfinished head sliders having unfinished read-write transducers deposited on a substrate, for which AlTiC is commonly used. The matrix of sliders is typically processed in batches, i.e., subsets of the wafer, historically referred to as “quads” and now at times referred to as “chunks” or “blocks”. A block of unfinished head sliders comprises multiple rows (or “row-bars”) of unfinished head sliders. Each row comprises multiple head sliders. The individual devices ultimately become head sliders, housing a respective read-write head, for flying over a spinning disk.
A typical head slider fabrication process flow may include the following: a wafer fabrication process, which includes deposition of the reader and writer elements, followed by block (or “quad”) slicing to remove a block of unfinished sliders from the wafer. An outer row of sliders from the block may then be rough lapped (e.g., wedge angle lapped) in order to fabricate close to the desired reader and writer dimensions (e.g., flare point and stripe height), and then the outer rough-lapped row sliced from the block. From there, the row may be further lapped, such as “back-lapped” to form the flexure-side surface opposing the air bearing surface (ABS), and “fine-lapped” (or “final lapped”) to further refine the ABS surface. This then may lead to overcoating, and rail etching, etc. of the ABS surface to form the final air bearing or flying surface, at which point each head slider may be diced or parted from the row to individuate each finished head slider, whereby it can then be coupled with a flexure, assembled into a head-gimbal assembly (HGA), and so on.
In the context of the overall slider fabrication process, according to an embodiment the material removal procedure to create the material void 306 (i.e., at block 604) is performed after lapping each side of the row-bar, at block 602, and before annealing the row-bar, at block 606. While the described order of steps is found suitable within a relevant particular slider fabrication process, the order of such steps and where in the process the material removal is performed, may vary from implementation to implementation. Furthermore, rather than removing material to create the material void 306, the creation of the material void 306 could be implemented by a wafer/slider fabrication process in which slider material that would otherwise be present in a conventional slider lacking such a material void, is masked off and not deposited in the first place.
Embodiments may be used in the context of a digital data storage device (DSD) such as a hard disk drive (HDD). Thus, in accordance with an embodiment, a plan view illustrating a conventional HDD 100 is shown in
The HDD 100 further includes an arm 132 attached to the HGA 110, a carriage 134, a voice-coil motor (VCM) that includes an armature 136 including a voice coil 140 attached to the carriage 134 and a stator 144 including a voice-coil magnet (not visible). The armature 136 of the VCM is attached to the carriage 134 and is configured to move the arm 132 and the HGA 110 to access portions of the medium 120, all collectively mounted on a pivot shaft 148 with an interposed pivot bearing assembly 152. In the case of an HDD having multiple disks, the carriage 134 may be referred to as 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.
An assembly comprising a head gimbal assembly (e.g., HGA 110) including a flexure to which the head slider is coupled, an actuator arm (e.g., arm 132) and/or load beam to which the flexure is coupled, and an actuator (e.g., the VCM) to which the actuator arm is coupled, may be collectively referred to as a head-stack assembly (HSA). An HSA may, however, include more or fewer components than those described. For example, an HSA may refer to an assembly that further includes electrical interconnection components. Generally, an HSA is the assembly configured to move the head slider to access portions of the medium 120 for read and write operations.
With further reference to
Other electronic components, including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil 140 of the VCM and the head 110a of the HGA 110. The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle 124 which is in turn transmitted to the medium 120 that is affixed to the spindle 124. As a result, the medium 120 spins in a direction 172. The spinning medium 120 creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider 110b rides so that the slider 110b flies above the surface of the medium 120 without making contact with a thin magnetic-recording layer in which information is recorded. Similarly in an HDD in which a lighter-than-air gas is utilized, such as helium for a non-limiting example, the spinning medium 120 creates a cushion of gas that acts as a gas or fluid bearing on which the slider 110b rides.
The electrical signal provided to the voice coil 140 of the VCM enables the head 110a of the HGA 110 to access a track 176 on which information is recorded. Thus, the armature 136 of the VCM swings through an arc 180, which enables the head 110a of the HGA 110 to access various tracks on the medium 120. Information is stored on the medium 120 in a plurality of radially nested tracks arranged in sectors on the medium 120, such as sector 184. Correspondingly, each track is composed of a plurality of sectored track portions (or “track sector”) such as sectored track portion 188. Each sectored track portion 188 may include recorded information, and a header containing error correction code information and a servo-burst-signal pattern, such as an ABCD-servo-burst-signal pattern, which is information that identifies the track 176. In accessing the track 176, the read element of the head 110a of the HGA 110 reads 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 coil 140 of the VCM, thereby enabling the head 110a to follow the track 176. Upon finding the track 176 and identifying a particular sectored track portion 188, the head 110a either reads information from the track 176 or writes information to the track 176 depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system.
An HDD's electronic architecture comprises numerous electronic components for performing their respective functions for operation of an HDD, such as a hard disk controller (“HDC”), an interface controller, an arm electronics module, a data channel, a motor driver, a servo processor, buffer memory, etc. Two or more of such components may be combined on a single integrated circuit board referred to as a “system on a chip” (“SOC”). Several, if not all, of such electronic components are typically arranged on a printed circuit board that is coupled to the bottom side of an HDD, such as to HDD housing 168.
References herein to a hard disk drive, such as HDD 100 illustrated and described in reference to
In the foregoing description, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Therefore, various modifications and changes may be made thereto without departing from the broader spirit and scope of the embodiments. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
In addition, in this description certain process steps may be set forth in a particular order, and alphabetic and alphanumeric labels may be used to identify certain steps. Unless specifically stated in the description, embodiments are not necessarily limited to any particular order of carrying out such steps. In particular, the labels are used merely for convenient identification of steps, and are not intended to specify or require a particular order of carrying out such steps.
