Multiple heaters independently controlling clearance of two or more read transducers

A apparatus includes first and second read transducers arranged on a media-facing surface. The read transducers detect magnetic fields of a recording medium. First and second heaters are disposed proximate the respective first and second read transducers. The first and second heaters independently control respective first and second protrusions of the first and second read transducers from the media-facing surface.

BACKGROUND

Magnetic recording devices such as hard disk drives utilize magnetic read and write transducers that are held close to the surface of a spinning magnetic disk. The write transducer generates a varying magnetic field that causes a change in magnetic orientation of bits within tracks on the disk. The read transducer follows the tracks and generates a signal based on variations in magnetic field, and these signals are used to read the bits. For both read and write transducers, a clearance between the transducer and disk may be actively adjusted to ensure optimum performance of the transducers.

SUMMARY

The present disclosure is related to multiple heaters independently controlling clearance of two or more read transducers. In one embodiment, an apparatus includes first and second read transducers arranged on a media-facing surface. The read transducers detect magnetic fields of a recording medium. First and second heaters are disposed proximate the respective first and second read transducers. The first and second heaters independently control respective first and second protrusions of the first and second read transducers from the media-facing surface.

In another embodiment, a system includes a slider having first and second read transducers arranged on a media-facing surface of the slider. The read transducers detect magnetic fields of a recording medium. First and second heaters are disposed proximate the respective first and second read transducers. The system includes a control circuit coupled to the first and second heaters. The control circuit provides a current to the first and second heaters that independently control respective first and second clearances between the first and second read transducers and the recording medium.

In another embodiment, a method involves reading a signal from a magnetic recording medium via first and second read transducers arranged on a media-facing surface of a slider. A first clearance between the magnetic recording medium and the first read transducer is controlled via a first heater. Independently of the first clearance, a second clearance between the magnetic recording medium and the second read transducer is controlled via a second heater.

DETAILED DESCRIPTION

The present disclosure is related to systems, methods, and apparatuses utilizing magnetic readers with multiple read sensors for reading magnetic recording media, e.g., hard disks. Generally, current hard disk devices utilize a read/write head (also referred to as a slider) with a single read transducer for reading data. Multiple read/write heads may be used, e.g., separate read/write heads positioned at top and bottom surfaces of one or more magnetic disks. New architectures are being proposed that use more than one read transducer per read/write head. These new architectures use multiple read transducers to read recording media that recorded at an increased areal density compared to current recording architectures (e.g., perpendicular recording media). These architectures may also employ multiple writers.

The theoretical maximum areal density of current magnetic recording architectures is bounded by what is known as the superparamagnetic limit. The superparamagnetic limit relates to the tendency of magnetic grains to randomly flip magnetic orientation in response to thermal fluctuations, and defines a lower bound on the area in which an individual bit can be reliably stored. In order to address the superparamagnetic limit, technologies such as heat assisted magnetic recording (HAMR) and bit patterned media (BPM) are being developed to increase areal density beyond what is current possible with perpendicular architectures.

A HAMR recording device uses an energy source such as a laser to heat a spot on a high-coercivity medium to locally reduce coercivity during recording. After the spot has cooled, the data is less susceptible to data loss due to thermal fluctuations. A BPM device has a media that is patterned via nanolithography to form magnetic cells used to store bits of data. The use of nanolithography allows for greater areal density than if the cells were defined in a continuous medium by a write transducer.

Another technique to increase storage capacity, known as shingled recording, utilizes drive architectures different from the ones in use today, but may be implemented using existing perpendicular media and conventional (e.g., non-HAMR) read-write heads. Shingled recording involves writing tracks that overlap part of previously written tracks. The write head includes features such as high field strength and sharp corner-edge field that can result in narrower tracks. While this can be achieved using existing technologies, the architecture needs to take into account potential impact on random writes that are introduced by shingled writing.

Whether areal density is increased using HAMR, BPM, or shingled writing, existing read transducers may have difficulty reading back these narrower tracks. For example, shrinking the read transducers in a cross-track direction may decrease signal-to-noise ratio. As a result, two-dimensional magnetic recording (TDMR) is proposed to facilitate reading back data from narrower tracks using a read transducer that is wider than the tracks.

Conventional magnetic recording is sometimes categorized as a one-dimensional (1-D) architecture, even though a magnetic recording surface is, in principle, a two-dimensional (2-D) system. For example, grains on a conventional media surface are not formed based on specific direction assumptions, and performance of the magnetic grains does not depend which direction is along-track and which direction is cross-track. Conventional magnetic recording systems generally constrain an inherently 2-D system to 1-D system in attempt to reduce system cost and complexity.

For example, a 1-D system utilizes individually accessed tracks, which allows for a single read head, single write head, and simplified controller functionality. As a result of this, a 1-D system attempts to minimize inter-track interference, which can increase decoding errors. In contrast, a 2-D system may be designed to assume that multiple tracks may be read at once. A 2-D system may require more sophisticated decoding, but allows relaxing some constraints on erase bands, transducer width, etc.

Even in a confirmation where read transducers are not larger than the written tracks, a multiple-read-transducer arrangement may have benefits. The use of two read transducers can increase the data rate of read operations. The signals read by adjacent tracks can also be jointly decoded to reduce the effects of cross-track interference, skew, etc. For purposes of the following discussion, multiple-read-transducer data storage devices described herein may use read transducers that are smaller than, larger than, or the same as the written data tracks. Further, the number of read transducers may be larger than two.

In reference now toFIG. 1, a block diagram illustrates an example of reading 2-D tracks according to an example embodiment. Bits101-103are shown written in respective tracks104-106on a magnetic media surface100. Although the bits101-103are shown aligned to each other from track-to-track, this is not required. The arrows within the bits101-103represent magnetic orientations that will be sensed as ones or zeros by a reader, e.g., by read transducers108and/or110. The read transducers108,110may include magnetoresistive transducers, such as giant magnetoresistance (GMR) sensor, tunneling magnetoresistance (TMR) sensor, etc. Generally, these types of transducers include layers of magnetic and non-magnetic materials that change resistance in response to local magnetic fields. A current is passed through the sensor while the media moves underneath. The resulting signal is used to read bits on the tracks104,105.

The tracks104-106may be written by successive passes of a writer (not shown), e.g., forming shingled tracks by overlapping subsequent tracks during writing. In such a case, there may be limited erase bands between subsequent tracks104-106. It will be understood that the embodiments described herein need not be limited to shingled tracks/media, and the concepts may be equally applicable to other track writing technologies, such as perpendicular, HAMR, and BPM.

In some embodiments, a width of the read transducers108,110may be significantly wider than the tracks, such that the read transducers108will read signals from at least two adjacent tracks. For example, both read transducers108and110will read at least partially from both tracks104and105. The signals from the read transducers108,110may be processed using a two-dimensional decoding algorithm, where the individual track signals are determined from a combination of the signals from both transducers108,110.

A TDMR device may use other read transducer arrangements than what is shown for transducers108,110. For example, read transducer110may be shifted down so as to cover track105fully and track106partially. More than two read transducers may be used, as indicated by transducer array112. All of the transducers in array112are centered over the respective tracks104-106, and therefore overlap two adjacent tracks. In other embodiments, the read transducers may have a width that is the same as or less than a single recorded track. In some embodiments, not all of the read transducers are used to read back user data. For example, one read transducer on an outside edge could be used for thermal asperity detection. In another example, a read transducer could be dedicated to track locating, e.g., determining when the read/write head approaches the servo marks that define the tracks.

Generally, the present disclosure relates to the maintaining of a desired clearance between multiple read transducers and the recording media. In order to read data from the media, the transducers are held at a predetermined distance from the media surface without contact (or at least an attempt is made to minimize contact). Current read/write heads may roughly hold clearances through the use of air bearing features on the media-facing surface. The air bearing features cause the read/write head to be separated from the moving media via a thin layer of air. For fine adjustments, a heater or piezoelectric element can controllably deform a small portion of the read/write head near the read transducer to affect the clearance between the transducers and media.

The control of clearances can become more complicated when there are two read transducers on a single read/write head. The read transducers may be separated far apart enough that it is difficult to optimize the clearance for both heads at the same time. This may be due to, among other things, manufacturing tolerances of the read/write head, differences in surface conditions between adjacent tracks, etc. As a result, embodiments described below include more than one heater, as well as other features that facilitate independent adjustment of read transducer clearance.

The read transducers and media shown inFIG. 1may be included together in a hard disk data storage device. Details of such a device according to an example embodiment are shown inFIG. 2. Generally, first and second read transducers202,203are housed at a trailing edge of a slider206, also sometimes referred to as a read/write head. The slider206is coupled to arm208by way of a suspension210that allows some relative motion between the slider206and arm208. In addition to the read transducers202,203, the slider206may include one or more write transducers (not shown), such as a write pole and coil. When the slider206is located over surface212of a magnetic disk214, a flying height is maintained between the slider206and surface212by a downward force of arm208. This downward force is counterbalanced by an air cushion that exists between the surface212and a media-facing surface216of the slider206when the disk214is rotating.

Changes in local magnetic field caused by the moving disk214induce a change in resistance of the read transducers202,203. The read transducers are coupled to a preamplifier220by way of signal lines218. Generally, the preamplifier220amplifies and conditions the analog signals (which may include a two-dimensional signal) received via signal lines218. The preamplifier220may also provide bias voltages and to the read transducers to achieve a desired electrical operating point. The amplified signals received via the preamplifier220are used for other processing modules such as decoder222. The decoder222determines a digital output from the analog signals, the digital output being used by a host via host interface224, as well as other system components (not shown). The processing of the signals and data is generally managed by a controller226, which may include a microprocessor and/or other logic circuits.

The slider206includes first and second heaters204,205disposed proximate the respective first and second read transducers202,203. The first and second heaters204,205control respective first and second protrusions of the first and second read transducers202,203from the media-facing surface216. The first and second heaters204,205may be resistive and/or inductive heaters, and may operate in cooperation with other elements (not shown) that generate heat near the media facing surface216, such as a writer heater, write pole and/or HAMR laser.

A clearance control module228is coupled to the first and second heaters204,205to the controller226via control lines219. The clearance control module228may include analog conditioning and control circuitry to drive and monitor the first and second heaters204,205. The clearance control module228generally receives inputs from the controller226to increase or decrease electrical power applied to the first and second heaters204,205. The controller226may detect current clearance via a sensor (not shown) located near the read transducers202,203. Such a sensor may include a thermal sensor that detects thermal trends indicative of a current clearance between the read transducers202,203and the media surface212.

The clearance control module228facilitates independently controlling the first and second heaters204,205, which in turn facilitates independently controlling clearance of the first and second read transducers202,203. The first and second heaters204,205may be wired to the clearance control module228in parallel, in which case separate ones of the signal lines219may be dedicated to supplying a different current to respective first and second heaters204,205.

The first and second heaters204,205may be wired to the clearance control module228in series, in which case independent control may be achieved through variation of an alternating current signal, which is discussed in greater detail below. For example, series connected heaters may be coupled to frequency sensitive components. In such a case, applied AC frequencies may affect each heater differently, thereby facilitating independent control by varying the applied frequency.

As shown inFIG. 1, the first and second read transducers202,203may be offset from one another in a down-track direction, and may also be offset in a cross-track direction. There may be one or more writer as well. If there is one writer, it may be aligned with one of the read transducers202,203. In such a case, both the writer and the aligned reader may be controlled by one of the heaters204,205, e.g., a heater element that is elongated in the down-track direction. In other cases, the writer may not be aligned with the readers, e.g., aligned with down-track extending centerline of the slider206, with the read transducers202,203offset from this centerline. In such a case, the writer may have a separate clearance-control heater, and this writer heater may work independently from the heaters204,205, or operate together with one of the read heaters204,205to assist in independent clearance control of one of the read transducers202,203.

Generally, providing two heaters204,205at a minimum allows controlling individual close points near to the respective read transducers202,203. This not only allows for independent clearance control of each read transducer202,203, but can improve response speed, reduce maximum temperatures, and or reduce total heater power consumption. This is because individual heaters204,205can work using smaller heated volumes compared to a heater that controls clearance for both read transducers202,203together. The individual heated volumes can be made with high coefficient of thermal expansion (CTE) materials (e.g., push blocks) to assist in shaping the close point locations at lower heater power. The push blocks, together with individual heaters and other low thermal conductivity materials, can limit the amount of heat that could reach the read transducers202,203. Excessive heat can cause electrical instability of the read transducers202,203.

InFIG. 3, a block diagram shows a cross section of a read/write head300according to an example embodiment. InFIG. 4, a block diagram shows the read/write head300as viewed from the media facing surface302. A write transducer301includes a write pole304, upper return pole306, lower return pole307, and coil turns308. Below the write transducer301are two read transducers310,311. Each read transducer310,311may include a magnetoresistive stack, and are surrounded by respective top and bottom shields312-315. Electrical contacts316-319provide electrical connections between the shields312-316and an external device, e.g., for coupling the read transducers310,311to a preamplifier.

As seen inFIG. 4, the read transducers310,311are offset from each other in a both a cross-track direction (left-to-right inFIG. 4) and a down-track direction (top-to-bottom inFIGS. 3 and 4). The cross-track offset facilitates reading two tracks at the same time, or overlapping parts thereof. The read transducers310,311are shown here with no cross-track overlap, although other embodiments may include such an overlap (see, e.g.,FIG. 1). Generally, the down-track offset facilitates, among other things, electrical isolation between the read transducers310,311.

The illustrated read/write head300further includes heaters320-322, as seen inFIG. 3. The heaters320-322are thin-film components that produce heat in response to an applied current, e.g., due to a resistance of the heaters320-322. Heater320may be used to control protrusion of write pole304. Heaters321and322are used to independently control the protrusions of the read transducers310,311. The writer heater320may be tied to (e.g., work dependently with) one of the reader heaters321,322, or may be operable to control protrusion of the write pole304independently of the reader heaters321,322.

The read/write head300may include features that assist in providing the desired protrusion profile for any of the read transducers310,311and the write pole304. An example of such a feature is shown as push block322located behind the lower return pole307. Generally, the push block322includes a layer of material with a coefficient of thermal expansion that is higher than that of the surrounding material (e.g., dielectric material) of the read/write head300. By regulating the size, location, and material of the push block322, a desired protrusion response may be obtained at the media-facing surface for any of the read transducers310,311or write transducer301.

Additional push blocks323,324may be included for each of the read transducers310,311. The push blocks323,324may be located with a cross-track offset from each other to correspond with the different cross-track locations of the read transducers310,311. The reader heaters321,322may be similarly offset in a cross-track direction. As such, each of the read transducers310,311and write pole304may have separately controllable protrusion regions325-327as generally indicated inFIG. 4.

InFIG. 5, a schematic diagram shows an arrangement of protrusion heaters500,501according to an example embodiment. The protrusion heaters500,501control protrusion regions512,513of respective read transducers502,503. The heaters500,501are coupled to a controller (not shown) via at least two control lines504,505, and optionally by a third, common control line506. Generally, if control line506is eliminated, the heaters500,501are configured in series, such that the same current will flow through each heater500,501. If control line506is used, the heaters500,501may be run in parallel, such that a different current flows through each heater500,501.

Generally, it is desired to independently control protrusion regions512,513during device operation to optimize performance of the read transducers502,503. As shown in the graph ofFIG. 6, the example protrusions curves602,603associated with the read transducers502,503are offset from one another in a cross-track direction. By using separately controllable protrusion regions602,603, the control response can be maximized by centering the peak protrusion of each region602,603over each read transducer502,503. This is opposed to a centrally located heater, which may produce a response such as shown by protrusion region604. It should be noted that if a separate writer heater is used for a single write transducer, the writer heater may be centrally located and may produce a protrusion similar to region604. In another case, two or more reader heaters could be used simultaneously to produce the protrusion region604.

In reference again toFIG. 5, independent control of protrusion regions512,513during device operation can be accomplished in one example by utilizing a parallel connection for heaters500,501. For example, common control line506can be tied to ground (or some other fixed potential) and current though heaters500,501can be independently varied by changing voltages applied at control lines504,505. While parallel current paths may be relatively simple to implement at a controller, the addition of a third control line506may be less easy to implement at the slider. The number of control lines coupled to the slider may be limited for reasons such as limited room for bonding pads, difficulty of manufacture, signal interference, reliability, etc.

Connecting heaters500,501in series minimizes the connections needed at the slider, although the series connection may cause the same current to flow through both heaters500,501. Even so, it may still be possible to independently control the protrusion regions using only two control lines504,505for the two heaters500,501. For example a separately controlled write heater may be included in the slider, and the write heater may be closer to one of the heaters500,501than to the other. In such a case, the write heater may also be used to adjust clearance for one of the read heaters. An example of this use of a write heater may be demonstrated by referring back toFIG. 4.

InFIG. 4, if the protrusion region325of the writer heater overlaps the protrusion region326of the proximate reader310but does not overlap the other reader protrusion region327, then the writer heater320(seeFIG. 3) could be activated during reads for purposes of controlling protrusion region326. In such a case, the protrusion326of the read transducer310would be due to the current flowing through its associated heater321(seeFIG. 3) plus protrusion325induced by write heater320. The protrusion327of read transducer311would also be due to the current flowing through its associated heater322(which is the same current flowing through heater321), but it would not be significantly affected by write-heater-induced protrusion325.

Another example of how series connected heaters can be independently controlled according to an embodiment is shown in the schematic diagram ofFIG. 7. Heaters700,701are series connected to each other and coupled to a control circuit via control lines704,705. Shunts710,711are placed in series with respective heaters700,701. The shunts710,711may be frequency and/or polarity dependent, and may include active components (e.g., diodes) and/or passive components (e.g., capacitors, inductors), Either one or both shunts710,711may be used, and one of ordinary skill in the art can readily adapt the embodiments described below for use with a single shunt device.

In one example, the shunts710,711may be frequency dependent such that the amount of alternating current (AC) that passes through the shunts710,711varies depending on frequency of an applied AC signal. Each shunt710,711can be configured with a different frequency response, such that current flowing through each of the heaters700,701is frequency dependent. As such, relative power output by heaters700,701can be varied by varying the frequency of an AC signal applied to control lines704,705. This is further illustrated in the graph ofFIG. 8, which shows relative power of heaters700,701based on frequency of an applied AC signal.

Curve800represent power output by heater700and curve801represents the power output by heater701. Generally, these curves800,801represent thermal power (I2R) dissipated by resistive elements, and the current I flowing through the heaters700,701is frequency dependent due to the shunts710,711. At frequency F1, heater700outputs more power than heater701, and vice versa at frequency F3. At frequency F2, both heaters700,701output the same power. As such, the shunts710,711facilitate independently controlling protrusion of transducer regions for series connected heaters by varying an AC signal applied to control lines704,705.

In another example, the shunts710,711may be polarity dependent (e.g., acting as diodes), such that they pass current in one direction of current flow but not the opposite direction. If the shunts710,711are arranged such that they block current in opposite directions, one of the shunts710,711will act as an open circuit during a positive part of an applied AC signal and the other will act as a short circuit. The heater700,701that is parallel with the open circuit will pass nearly all the current, and the other heater will pass little or no current. The current paths will be reversed in the negative part of the AC signal. In such a case, the relative power dissipated by the heaters700,701can be controlled by varying an asymmetry of the AC signal around some reference point, e.g., 0 V. An example of the use of an asymmetric signal according to an example embodiment is shown in the graph ofFIG. 9.

InFIG. 9, signal902represents a current waveform applied to series heaters, e.g., current driven through control lines704,705shown inFIG. 7. Signal902is offset in a negative direction relative to 0 V, e.g., using a negative direct current (DC) offset. In this example, signal900represents current passing through heater700inFIG. 7, where the shunt710is an open circuit during positive current flow of signal902, and shunt711is a closed circuit during positive current flow of signal902. Signal901represents current passing through heater701under the same conditions. As should be apparent from curves900,901, the net amount of current passing through heater700is less than that through heater701. This difference can be reduced or reversed by shifting the asymmetry of signal902in a positive direction.

It will be understood that the shunts710,711shown inFIG. 7can be used for static tuning of the current flow through heaters700,701. For example, the shunts710,711may be configured as resistors that are not frequency or polarity dependent. At least part of the shunts may be located on a region that is easily accessible after manufacture of the slider, e.g., a side surface. During initial testing of the slider (e.g., before attachment to a gimbal assembly) the heater response may be tested, and one or more of the shunts710,711adjusted (e.g., via laser trimming, abrasion) to equalize a response of the heaters700,701. Such adjustment may also be performed for shunts710,711that are frequency and/or polarity dependent as described above.

In reference now toFIG. 10, a flowchart illustrates a method according to an example embodiment. The method involves reading1000a signal from a recording medium via first and second read transducers arranged on a media-facing surface of a slider. The read transducers may be offset from each other in a down-track and/or cross-track direction. A first clearance between the magnetic recording medium and the first transducer is controlled1002via a first heater. Independently of the first clearance, a second clearance is controlled1004between the magnetic recording medium and the second transducer via a second heater.

It will be understood that the concepts described hereinabove may be applied to any number of read transducers, e.g., more than two. The concepts may be similarly applicable to recording systems using multiple writers. For example a slider may include two or more write poles separated from one another in a cross-track and/or down-track direction, and multiple writer heaters may be used to independently adjust clearances of the multiple writer poles.

The various embodiments described above may be implemented using circuitry and/or software modules that interact to provide particular results. One of skill in the computing arts can readily implement such described functionality, either at a modular level or as a whole, using knowledge generally known in the art. For example, the flowcharts illustrated herein may be used to create computer-readable instructions/code for execution by a processor. Such instructions may be stored on a non-transitory computer-readable medium and transferred to the processor for execution as is known in the art.