Read/write head with reduced pole tip protrusion

A write element for use in a read/write head having an air bearing surface, so as to reduce pole tip protrusion. The write element includes a pole tip region; an insulation layer formed adjacent to the pole tip region; a coil embedded in the insulation layer which contributes to a protrusion force that generates a pole tip protrusion; and a layer of thermally expansive material formed over the insulation layer, and recessed from the air bearing surface, that expands in response to heat absorption, causing a rotational moment of force that counteracts the protrusion force thus reducing the pole tip protrusion.

FIELD OF THE INVENTION

The present invention generally relates to data storage devices such as disk drives, and it particularly relates to a read/write head for use in such data storage devices. More specifically, the present invention provides a method of incorporating a layer of expansive material in the read/write head to counteract the forces that cause undesirable pole tip protrusion of the read/write head during operation.

BACKGROUND OF THE INVENTION

An exemplary conventional read/write head comprises a thin film write element with a bottom pole P1and a top pole P2. The pole P1has a pole tip height dimension commonly referenced as “throat height”. In a finished write element, the throat height is measured between the ABS and a zero throat level where the pole tip of the write element transitions to a back region. The ABS is formed by lapping and polishing the pole tip. A pole tip region is defined as the region between the ABS and the zero throat level. Similarly, the pole P2has a pole tip height dimension commonly referred to as “nose length”. In a finished read/write head, the nose is defined as the region of the pole P2between the ABS and the “flare position” where the pole tip transitions to a back region.

Pole P1and pole P2each have a pole tip located in the pole tip region. The tip regions of pole P1and pole P2are separated by a recording gap that is a thin layer of non-magnetic material. During a write operation, the magnetic field generated by pole P1channels the magnetic flux from pole P1to pole P2through an intermediary magnetic disk, thereby causing the digital data to be recorded onto the magnetic disk.

During operation of the magnetic read/write head, the magnetic read/write head portion is typically subjected to various thermal sources that adversely cause ambient and localized heating effects of the read/write head. One such thermal source is attributed to a heat transfer process to the magnetic read/write head from the effect of the spinning magnetic disk.

During a typical operation, the magnetic disk spins at a rapid rate of rotation, typically on the order of several thousands of revolutions per minute (RPM). This rapid rotation generates a source of friction in the ambient air between the ABS and the spinning magnetic disk, thus causing an elevation in the air temperature.

Furthermore, the heating of the motor that drives the magnetic disk causes an additional elevation of the air temperature. In totality, the ambient air temperature may rise from a room temperature of about 25° C. to as high as 85° C. Typically, the read/write head is initially at a room temperature. Consequently, there exists a tendency for a heat transfer process to take place between the ambient air at a higher temperature and the read/write head at lower temperature. The heat transfer causes a rise in the temperature of the read/write head to promote a thermal equalization with the ambient air temperature.

Additionally, the read/write head is also subjected to various sources of power dissipation resulting from the current supplied to the write coils, eddy current in the core, and the current in the read sensor. The power dissipation manifests itself as a localized heating of the read/write head, resulting in a temperature rise similar to the foregoing ambient temperature effect.

The temperature increase of the read/write head further causes a variant temperature distribution as a result of the thermal conduction of diverse materials that compose the read/write head. Typically, most wafer-deposited materials such as those composing the poles P1and P2have greater coefficients of thermal expansion (CTE) than that of the substrate. Consequently, the temperature increase effects a general positive displacement of the read/write head as well as a local pole tip protrusion beyond the substrate.

In a static test environment without the effect of the spinning magnetic disk, the localized heating may cause a temperature elevation of as high as 70° C. However, in an operating environment of a magnetic disk drive, the temperature rise resulting from the localized heating may be limited to about 40° C., primarily due to the alleviating effect of a convective heat transfer process induced by the rotating air between the pole tip region and the spinning magnetic disk. The temperature increase associated with the localized heating further promotes an additional protrusion of the pole tip relative to the substrate.

A typical pole tip protrusion in a static environment may be approximately 30 to 35 nm. In an operating environment of a magnetic disk drive, the pole tip protrusion is reduced to a typical value of 7.5 nm to 12 nm. Since a typical flying height is approximately 12.5 nm, the pole tip protrusion associated with thermal heating of the read/write head can cause the read/write head to come into contact with the spinning magnetic disk. While a typical flying height may be about 12.5 nm, there are currently a significant number of low flying heads with flying heights less than 12.5 nm. A steady evolution to lower flying heights exacerbates the problem of physical interference between the pole tip protrusion and the spinning magnetic disk.

This physical interference with the spinning magnetic disk causes both accelerated wear and performance degradation. The wear effect is due to abrasive contact between the slider and the disk. Pulling the softly sprung slider slightly off track impacts the track following capability of the recording device.

In an attempt to resolve the foregoing problem, a number of conventional designs of read/write heads incorporate the use of a material with a coefficient of thermal expansion (CTE) that is lower than that of the substrate. Functionally, the low CTE material is generally used as an insulator between various metals in a conventional magnetic read/write head. An exemplary material used in a conventional magnetic read/write head is silicon oxide, SiO2, which typically has a CTE of 2 parts per million.

In the presence of a temperature rise resulting from a thermal heating of the read/write head, such a material tends to expand at a lower rate than the substrate. This lower expansion rate develops a thermally induced axial restraining force between the material and the substrate. This restraining force effectively reduces the expansion of the substrate, thus mitigating the natural protrusion of the pole tip.

Although this technology has proven to be useful, it would be desirable to present additional improvements. SiO2has poor thermal conductivity that generally impedes the heat extraction process from the surrounding material to the SiO2material. Consequently, in spite of the low CTE associated with SiO2, the low thermal conductivity of SiO2does not sufficiently reduce the temperature rise of the pole tip region and the pole tip protrusion is not adequately reduced with the use of SiO2.

Furthermore, SiO2lacks elasticity due to its ceramic characteristics. In the presence of the thermally induced axial restraining force, a shear stress is developed at the interface of SiO2and the surrounding material. This shear stress tends to promote a delamination of the SiO2material, posing a reliability problem for the read/write head of a conventional design.

In recognition of the issues associated with the use of SiO2in a conventional read/write head, some alternative materials have been proposed but have not been entirely successfully applied to a read/write head. As an example, while these materials such as Cr, W, possess higher thermal conductivities than SiO2, they are not readily available for deposition and patterning in a read/write head at a wafer-level process.

Thus, there is a need for a read/write head that provides a reduced pole tip protrusion resulting from a thermal heating of the magnetic read/write head during operation. The need for such a design has heretofore remained unsatisfied.

SUMMARY OF THE INVENTION

The present invention can be regarded as a read/write head for use in a data storage device to reduce pole tip protrusion. The read/write head includes an air bearing surface; a pole tip region; an insulation layer formed adjacent to the pole tip region; a coil embedded in the insulation layer contributing to a protrusion force that generates a pole tip protrusion; and a layer of thermally expansive material formed over the insulation layer, and recessed from the air bearing surface, that expands in response to heat absorption, causing a rotational moment of force that counteracts the protrusion force thus reducing the pole tip protrusion.

The present invention can also be regarded as a write element for use in a read/write head having an air bearing surface, so as to reduce pole tip protrusion. The write element includes a pole tip region; an insulation layer formed adjacent to the pole tip region; a coil embedded in the insulation layer which contributes to a protrusion force that generates a pole tip protrusion; and a layer of thermally expansive material formed over the insulation layer, and recessed from the air bearing surface, that expands in response to heat absorption, causing a rotational moment of force that counteracts the protrusion force thus reducing the pole tip protrusion.

The present invention can also be regarded as a disk drive that includes a base; a spindle motor attached to the base; a disk positioned on the spindle motor; and a head stack assembly that is coupled to the base. The head stack assembly includes an actuator body; an actuator arm cantilevered from the actuator body; and a read/write head that is coupled to the actuator arm. The read/write head includes an air bearing surface; a pole tip region; an insulation layer formed adjacent to the pole tip region; a coil embedded in the insulation layer which contributes to a protrusion force that generates a pole tip protrusion; and a layer of thermally expansive material formed over the insulation layer, and recessed from the air bearing surface, that expands in response to heat absorption, causing a rotational moment of force that counteracts the protrusion force thus reducing the pole tip protrusion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1illustrates a hard disk drive100in which an embodiment of the present invention may be used. An enclosure of the hard disk drive100comprises a cover102and a base104. The enclosure is suitably sealed to provide a relatively contaminant-free interior for a head disk assembly (HDA) portion of the hard disk drive100. The hard disk drive100also comprises a printed circuit board assembly (not shown) that is attached to base104and further comprises the circuitry for processing signals and controlling operations of the hard disk drive100.

Within its interior, the hard disk drive100comprises a magnetic disk126having a recording surface typically on each side of the disk, and comprises a magnetic head or slider that may suitably be a magneto-resistive (“MR”) head such as a GMR head. The GMR head has an MR element for reading stored data on a recording surface and an inductive element for writing data on the recording surface. The exemplary embodiment of the hard disk drive100illustrated inFIG. 1comprises three magnetic disks126,128, and130providing six recording surfaces, and further comprises six magnetic heads.

Disk spacers such as spacers134and136are positioned between magnetic disks126,128,130. A disk clamp132is used to clamp disks126,128,130on a spindle motor124. In alternative embodiments, the hard disk drive100may comprise a different number of disks, such as one disk, two disks, and four disks and a corresponding number of magnetic heads for each embodiment. The hard disk drive100further comprises a magnetic latch110and a rotary actuator arrangement. The rotary actuator arrangement generally comprises a head stack assembly112and voice coil magnet (“VCM”) assemblies106and108. The spindle motor124causes each magnetic disk126,128,130positioned on the spindle motor124to spin, preferably at a constant angular velocity.

A rotary actuator arrangement provides for positioning a magnetic head over a selected area of a recording surface of a disk. Such a rotary actuator arrangement comprises a permanent-magnet arrangement generally including VCM assemblies106,108, and head stack assembly112coupled to base104. A pivot bearing cartridge is installed in a bore of the head stack assembly112and comprises a stationary shaft secured to the enclosure to define an axis of rotation for the rotary actuator arrangement.

The head stack assembly112comprises a flex circuit assembly and a flex bracket122. The head stack assembly112further comprises an actuator body114, a plurality of actuator arms116cantilevered from the actuator body114, a plurality of head gimbal assemblies118each respectively attached to an actuator arm116, and a coil portion120. The number of actuator arms116and head gimbal assemblies118is generally a function of the number of magnetic disks in a given hard disk drive100.

Each of the head gimbal assemblies (HGA)118is secured to one of the actuator arms116. As illustrated inFIG. 2, HGA118is comprised of a suspension205and a read/write head210. The suspension205comprises a resilient load beam215and a flexure220to which the read/write head210is secured.

The read/write head210comprises a slider225secured to the free end of the resilient load beam215by means of flexure220and a read/write element230supported by slider225. In the example illustrated inFIG. 2, the read/write element230is secured to the trailing edge235of slider225. Slider225can be any conventional or available slider. In another embodiment, more than one read/write element230can be secured to the trailing edge235or other side(s) of slider225.

FIG. 3is a cross-sectional view of the read/write element230incorporating a thermally expansive layer305that is comprised of thermally expansive material, according to the present invention. The read/write element230integrates a write element310and a read element315. An undercoat320is formed over a substrate layer325. The read element315is formed of a first shield layer (shield1)330that is formed on the undercoat320. The undercoat320is preferably made of alumina (Al2O3).

The first shield layer330is made of a material that is both magnetically and electrically conductive. As an example, the first shield layer330can have a nickel iron (NiFe) composition, such as Permalloy, or a ferromagnetic composition with high permeability. The thickness of the first shield layer330can be in the range of approximately 0.5 micron to approximately 20 microns.

An insulation layer (not shown) is formed over substantially the entire surface of the first shield layer330to define a non-magnetic, transducing read gap. The insulation layer can be made of any suitable material, for example alumina (Al2O3), aluminum oxide, or silicon nitride.

The read element315further comprises a second shield layer (shield2)335that is made of an electrically and magnetically conductive material that may be similar or equivalent to that of the first shield layer330. The second shield layer335is formed over substantially the entire surface of the insulating layer (not shown) and has a thickness that can be substantially similar or equivalent to that of the first shield layer330. A piggyback gap (not shown) is formed on the second shield layer335.

The write element310is comprised of a first pole or pole layer (P1)340that extends, for example, integrally from the piggyback gap. P1340is made of a magnetically conductive material. A first coil layer345comprises conductive coil elements. The first coil layer345also forms part of the write element310, and is formed within an insulating layer (12)350. The first coil layer345may comprise a single layer of, for example, 1 to 30 turns, though a different number of turns can alternatively be selected depending on the application or design.

A second pole or pole layer (P2)355is made of a magnetically conductive material, and may be, for example, similar to that of the first shield layer330and P1340. The thickness of P2355can be substantially the same as, or similar to, that of the first shield layer330.

A third pole or pole layer (P3)360is made of a hard magnetic material with a high saturation magnetic moment Bs. In one embodiment, the saturation magnetic moment Bs is equal to or greater than approximately 2.0 teslas. P3360can be made, for example, of CoFeN, CoFeNi, and CoFe.

A pole tip region365comprises P3360, P2355, and the portion of P1340near the air bearing surface of the read/write element230. The writing element310further comprises a third shield layer (shield3)370.

A second coil layer375comprises conductive coil elements. The second coil layer375forms part of the write element310, and is formed within an insulating layer (I3)380. The second coil layer375may comprise a single layer of, for example, 1 to 30 turns, though a different number of turns can alternatively be selected depending on the application or design.

A fourth shield layer (shield4)385(also referred to as the upper shield385) covers a portion of I3380. A diffuser390covers a portion of the fourth shield layer385and a portion of I3380.

In one embodiment, the thermally expansive layer305covers a portion of diffuser390and I3380. An overcoat395covers the thermally expansive layer305and the remaining exposed portion of the read/write element230.

The thermally expansive layer305is preferably comprised of a material having a coefficient of thermal expansion that ranges between approximately 5 ppm/K and 100 ppm/K. For example, the thermally expansive layer305can be made of photoresist material.

The thermally expansive layer can be, for example, approximately 10 microns thick, 70 microns long, and 340 microns wide as illustrated by the top view of the read/write element230, shown inFIG. 4relative to pads401,402,403,404, and405.

FIG. 5illustrates the forces generated by the expansion of the thermally expansive layer305. During operation, the temperature of the read/write element230increases, resulting from ambient heating and current heating.

Current heating comprises resistive heating in the first coil layer345and in the second coil layer375, and eddy currents in the magnetic materials of P1340, P2355, and P3360. Ambient heating comprises friction heating of the air between the read/write head and the spinning magnetic disk, and heating from the drive motor of the data storage device.

The thermally expansive layer305absorbs a portion of the thermal energy in the read/write element230, and consequently expands. The expansion of the thermally expansive layer305exerts forces that are illustrated by forces F1505, F2510, and F3515.

Force F2510applies pressure to the overcoat395, causing a clock-wise rotational moment of force420around a central region of rotation421, near the pole tip region365. The rotational moment of force420counteracts a protrusion force in the pole tip region365, reducing the pole tip protrusion. The size, shape, and placement of the thermally expansive layer305are designed to optimally place the rotational moment of force420so as to reduce pole tip protrusion. In addition, force F3515applies pressure to a portion of I3380, limiting the expansion of I3380.

For comparison purposes, a conventional read/write element600is illustrated by the diagram ofFIG. 6. The conventional read/write element600is constructed generally similarly to the read/write element230, but without the thermally expansive layer305.

The force diagram ofFIG. 7illustrates the expansion forces induced in the conventional read/write element600. The material used in I3380and I2350is typically thermally expansive. During operation, the temperature of I3380and I2350increases as a result of thermal transfer from the heat sources in the read/write element230: the current heating and the ambient heating.

The resultant force created by the expansion of I3380and I2350can be characterized as forces F4710, F5715, F6720, F7725, F8730, F9735, and F10740. Protrusion forces F6720, F7725, F8730, F9735, and F10740cause pole tip protrusion into the ABS.

The force diagram ofFIG. 8illustrates the effect of adding the thermally expansive layer305to the read/write element230. The resultant forces created by the expansion of the thermally expansive layer305, I3380, and I2350can be characterized as forces F11805, F12810, F13815, F14820, and F15825. The forces F1505, F2510, and F3515(ofFIG. 5) exerted by the thermally expansive layer305counteract and redirect the forces exerted by I3380and I2350.

The rotational moment of force420created by the forces F1505, F2510, and F3515, which are exerted by the thermally expansive layer305, redirect the protrusion forces, as illustrated by reduced protrusion forces F11805, F12,810, and F13,815. Rather than pushing the pole tip region365into the ABS, the direction of the forces F11805and F13815is generally along (or parallel to) the ABS, reducing the protrusion forces F11805, F12,810, and F13,815. The rotational moment of force420also changes the direction of force F5715to that of force F14820. Force F4710is counteracted by force F15825that is created by the thermally expansive layer305, thus reducing the expansion of I3380.

The effect of the thermally expansive layer305on pole tip protrusion is further illustrated by the graphs of pole tip protrusion shown inFIGS. 9 and 10. The x-axis corresponds to the ABS surface. The zero point on the x-axis corresponds to a write gap of the read/write element230or the conventional read/write element600. The write gap is located between P1and P2. The heat source for the graph ofFIG. 9is ambient heating. The heat source for the graph ofFIG. 10is current heating.

As shown inFIG. 9, the pole tip protrusion of the conventional read/write element600at the write gap is approximately 8.5 nm due to ambient heating. In contrast, the pole tip protrusion of the read/write element230of the present design, incorporating the thermally expansive layer305, is less than approximately 6 nm, that is a reduction in pole tip protrusion of approximately 45%.

As further illustrated inFIG. 10, the pole tip protrusion of the conventional read/write element600at the write gap is approximately 10 nm due to current heating. In contrast, the pole tip protrusion of the read/write element230having a thermally expansive layer305is less than approximately 8 nm, that is a reduction in pole tip protrusion of approximately 20%.

In a further embodiment illustrated by the diagram ofFIG. 11, the thermally expansive layer305may be used in a read/write element1105that does not comprise a diffuser. In this embodiment, the thermally expansive layer305is placed in the range of approximately 0 um to approximately 1.0 um above poles P1340, P2355, and P3360, primarily over layer I3355. An overcoat395covers the thermally expansive layer305and the remaining exposed portion of the read/write element1105.