Abstract:
A read/write head for use in a data storage device to control the low dynamic flying height in order to achieve high data recording storage capacity of magnetic hard drives. The read/write head is designed for use in a data storage device that includes a storage medium having a recording surface. The head comprises a pole tip region and an actuator. In turn, the actuator includes an excitation source for generating a magnetic field, and a magnetostrictive plate for expanding in response to the magnetic field, resulting in a protrusion in a section of the pole tip region along a direction towards the recording surface, so that the head flies above the recording surface at a flying height lower than a nominal flying height.

Description:
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 new type of actuators comprising a magnetostrictive plate and magnetic excitation coils into the read/write head for dynamic flying height control during a read/write operation. The expansion of the magnetostrictive plate during actuation results in a reduction of the magnetic spacing between the read/write head and the magnetic medium to achieve higher data recording capacity of magnetic disks. 
   BACKGROUND OF THE INVENTION 
   An exemplary conventional read/write head comprises a thin film write element with a bottom pole P 1  and a top pole P 2 . The pole P 1  has 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 P 2  has 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 P 2  between the ABS and the “flare position” where the pole tip transitions to a back region. 
   Pole P 1  and pole P 2  each have a pole tip located in the pole tip region. The tip regions of pole P 1  and pole P 2  are separated by a recording gap that is a thin layer of non-magnetic material. During a write operation, the magnetic field generated by pole P 1  channels the magnetic flux from pole P 1  to pole P 2  through an intermediary magnetic disk, thereby causing the digital data to be recorded onto the magnetic disk. 
   The magnetic read/write head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the read/write head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk. 
   The flying height is defined as the magnetic spacing between the surface of the spinning magnetic disk and the lowest point of the slider assembly. One objective of the design of magnetic read/write heads is to obtain a very small flying height between the read/write element and the disk surface. With the ever increasing areal density, by maintaining a flying height as close to the magnetic disk as practically feasible, it is possible to record short wavelength or high frequency signals, thereby achieving high density and high storage data recording capacity. 
   A significant design challenge in a conventional read/write head is to achieve an ultra low flying height without causing physical damage to either the slider or the disk that may result in reliability problems and head crashes. Such as damage could cause both accelerated wear and performance degradation. The wear effect is due to the abrasive contact between the slider and the disk, which tends to cause the slider off track, thereby causing errors in the track following capability of the read/write head. 
   Typically, during operation, the magnetic read/write head is subjected to various mechanical and thermal conditions that tend to compromise the ability to attain the ultra low flying height in a conventional read/write head. For example, ambient pressure variations in the hard disk operating condition may contribute to the flying height variations. Similarly, mechanical disturbances during operation, such as vibration, also pose as a source of difficulty in maintaining the ultra low flying height. 
   Furthermore, during a typical operation, the magnetic disk spins at a rapid rate of rotation, typically on the order of several thousands revolutions per minute (RPM). This rapid rotation is a source of friction in the ambient air between the ABS and the spinning magnetic disk, causing an elevation in the operation temperature of the read/write head. 
   Additionally, the read/write head is also subjected to various other thermal sources of power dissipation resulting from the motor heating, 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 further temperature rise of the read/write head. 
   The combined mechanical and thermal effect therefore generally render the pole tip of the read/write head in a very close proximity to the magnetic disk in an uncontrolled manner that may possibly cause a physical interference of the read/write head. 
   In an attempt to resolve the foregoing problem, a number of conventional designs of read/write heads incorporate the use of heater coils to control the dynamic flying height of the read/write head. 
   Although this technology may have proven to be useful in controlling the dynamic flying height of the read/write head, it is still not entirely satisfactory in practice. Due to the reliance on the thermal expansion effect as a means to control the dynamic flying height, the response time is relatively slow. Since the ultra low flying height is typically lower than 12.5 nm, a flying height that is lower than 10 nm could cause a reliability problem. 
   Therefore, there remains a need for a read/write head that is capable of controlling the ultra low dynamic flying height during a read/write operation without causing undesirable pole tip protrusion during idle flying time. 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 control the ultra low dynamic flying height in order to achieve high data recording storage capacity of magnetic hard drives. The read/write head is designed for use in a data storage device that includes a storage medium having a recording surface. 
   The head comprises a pole tip region and an actuator. In turn, the actuator includes an excitation source for generating a magnetic field, and a magnetostrictive plate for expanding in response to the magnetic field, resulting in a protrusion in a section of the pole tip region along a direction towards the recording surface, so that the head flies above the recording surface at a flying height lower than a nominal flying height. 
   According to one embodiment, the actuator is placed within the read/write head at any one or more of a plurality of possible locations such as behind the first pole, the second pole, the third pole, the first shield, the second shield, or any other suitable location. Alternatively, the actuator may be placed in the middle of the overcoat layer. 
   According to another embodiment, a non-magnetic stop material is disposed at one end of the magnetostrictive plate, remotely from the ABS, in order to limit the pole tip expansion in the direction away from the ABS. 
   According to yet another embodiment, the magnetic coil provides a resistance heating for additional control of the dynamic flying height in addition to the magnetostriction effect. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary perspective view of a data storage device utilizing a read/write head of the present invention; 
       FIG. 2  is a perspective view of a head gimbal assembly comprised of a suspension, and a slider to which the read/write head of  FIG. 1  is secured, for use in a head stack assembly; 
       FIG. 3  is a cross-sectional view of an exemplary perpendicular recording read/write head of  FIGS. 1 and 2 , incorporating the actuator, according to one embodiment of the present invention; 
       FIG. 4  is a perspective view of the actuator of  FIG. 3 , comprising a magnetostrictive plate and an excitation source; 
       FIG. 5  is a perspective view of the magnetostrictive plate of  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of the read/write head of  FIGS. 1 and 2 , showing the actuator located behind a second coil layer, according to an alternative embodiment of the present invention; 
       FIG. 7  is a cross-sectional view of the read/write head of  FIGS. 1 and 2 , showing the actuator located in an overcoat layer, according to another alternative embodiment of the present invention; 
       FIG. 8  is cross-sectional view of the read/write head of  FIGS. 1 and 2 , showing a stop layer placed behind the actuator of  FIG. 4 ; 
       FIG. 9  is a diagram illustrating the working principle of the present invention; and 
       FIG. 10  is a cross-sectional view of an exemplary longitudinal recording read/write head, incorporating the actuator according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a hard disk drive  100  in which an embodiment of the present invention may be used. An enclosure of the hard disk drive  100  comprises a cover  102  and a base  104 . The enclosure is suitably sealed to provide a relatively contaminant-free interior for a head disk assembly (HDA) portion of the hard disk drive  100 . The hard disk drive  100  also comprises a printed circuit board assembly (not shown) that is attached to base  104  and further comprises the circuitry for processing signals and controlling operations of the hard disk drive  100 . 
   Within its interior, the hard disk drive  100  comprises a magnetic disk  126  having 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 drive  100  illustrated in  FIG. 1  comprises three magnetic disks  126 ,  128 , and  130  providing six recording surfaces, and further comprises six magnetic heads. 
   Disk spacers such as spacers  134  and  136  are positioned between magnetic disks  126 ,  128 ,  130 . A disk clamp  132  is used to clamp disks  126 ,  128 ,  130  on a spindle motor  124 . In alternative embodiments, the hard disk drive  100  may 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 drive  100  further comprises a magnetic latch  110  and a rotary actuator arrangement. The rotary actuator arrangement generally comprises a head stack assembly  112  and voice coil magnet (“VCM”) assemblies  106  and  108 . The spindle motor  124  causes each magnetic disk  126 ,  128 ,  130  positioned on the spindle motor  124  to 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 assemblies  106 ,  108 , and head stack assembly  112  coupled to base  104 . A pivot bearing cartridge is installed in a bore of the head stack assembly  112  and comprises a stationary shaft secured to the enclosure to define an axis of rotation for the rotary actuator arrangement. 
   The head stack assembly  112  comprises a flex circuit assembly and a flex bracket  122 . The head stack assembly  112  further comprises an actuator body  114 , a plurality of actuator arms  116  cantilevered from the actuator body  114 , a plurality of head gimbal assemblies  118  each respectively attached to an actuator arm  116 , and a coil portion  120 . The number of actuator arms  116  and head gimbal assemblies  118  is generally a function of the number of magnetic disks in a given hard disk drive  100 . 
   Each of the head gimbal assemblies (HGA)  118  is secured to one of the actuator arms  116 . As illustrated in  FIG. 2 , a HGA  70  is comprised of a suspension  75  and a read/write head  80 . The suspension  75  comprises a resilient load beam  205  and a flexure  210  to which the read/write head  80  is secured. 
   The read/write head  80  comprises a slider  215  secured to the free end of the resilient load beam  205  by means of flexure  210  and a read/write element  220  supported by slider  215 . In the example illustrated in  FIG. 2 , the read/write element  220  is secured to the trailing edge  225  of slider  215 . Slider  215  can be any conventional or available slider. In another embodiment, more than one read/write element  220  can be secured to the trailing edge  225  or other side(s) of slider  215 . 
     FIG. 3  is a cross-sectional view of a read/write element  230 , shown incorporating an actuator  505  according to the present invention. The read/write element  230  integrates a write element  310  and a read element  315 . 
   The read element  315  is formed of a first shield (S 1 ) layer  330  preferably made of a material that is both magnetically and electrically conductive. For example, the S 1  layer  290  can have a nickel-iron (NiFe) composition, such as Permalloy, or a ferromagnetic composition with high permeability. The S 1  layer  330  has a thickness of approximately about 2 μm and one of its distal ends terminating at the ABS  255 . 
   A first insulating (I 1 ) layer  295  is formed over substantially the entire surface of the S 1  layer  330  to define a non-magnetic, transducing read gap  300 . The I 1  layer  295  can be made of any suitable material, for example alumina (Al2O3), aluminum oxide, or silicon nitride. 
   The read element  315  also includes a read sensor  244  that is formed within the I 1  layer  295 . The read sensor  244  can be any suitable sensor that utilizes a change in resistance caused by a change in magnetic field to sense that field, which may be measured as a change in current or voltage across the sensor, including anisotropic magnetoresistive (AMR) sensors, spin-valve (SV) sensors, spin-tunneling (ST) sensors, a giant magnetoresistive (GMR) sensors, and colossal magnetoresistive (CMR) sensors. Other electromagnetic sensors, such as optical sensors, can alternatively be employed to sense magnetic fields from the medium. 
   The read element  315  further comprises a second shield layer (S 2 )  335  that is made of an electrically and magnetically conductive material that may be similar or equivalent to that of the S 1  layer  330 . The S 2  layer  335  is 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 S 1  layer  330 . A piggyback gap is formed on the S 2  layer  335 . 
   The write element  310  is comprised of a first pole layer (P 1 )  340  that extends, for example, integrally from the piggyback gap. The P 1  layer  340  is made of a magnetically conductive material. A first coil layer  345  comprises conductive coil elements. The first coil layer  345  also forms part of the write element  310 , and is formed within an insulating layer (I 2 )  380 . The first coil layer  345  may 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 layer (P 2 )  355  is made of a magnetically conductive material, and may be, for example, similar to that of the S 1  layer  330  and the P 1  layer  340 . The thickness of the P 2  layer  355  can be substantially the same as, or similar to, that of the S 1  layer  330 . 
   A third pole layer (P 3 )  360  is made of a hard magnetic material with a high saturation magnetic moment Bs. In one embodiment, the P 3  layer  360  can be made, for example, of CoFeN, CoFeNi, and CoFe. 
   A pole tip region  365  comprises the P 3  layer  360 , the P 2  layer  355 , and the portion of the P 1  layer  340  near the air bearing surface (ABS) of the read/write element  230 . The writing element  310  further comprises a third shield layer (shield  3 )  370 . 
   An insulating layer (I 4 )  380  is formed between the P 3  layer  360  and the S 3  layer  370  to define a write gap  375 . The insulating layer I 4  can be made of any suitable material, for example alumina (Al 2 O 3 ), aluminum oxide, or silicon nitride. 
   A second coil layer  374  comprises conductive coil elements. The second coil layer  374  forms part of the write element  310 , and is formed within an insulating layer (I 4 )  380 . The second coil layer  374  may 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 (S 4 )  385  (also referred to as the upper shield  385 ) covers a portion of the I 3  layer  380 . The S 4  layer  385  is made of a material that is both magnetically and electrically conductive, and may be, for example, similar to that of the S 1  layer  330  and the P 1  layer  340 . An insulation overcoat  444  overlays shield layer S 4 . 
   Referring now to  FIG. 4 , the actuator  505  is comprised of a magnetostrictive plate  510  and an excitation source  515 . The magnetostrictive plate  510  is formed by a plating or sputtering process using a material that exhibits a magnetic property known as magnetostriction. Physically, the magnetostrictive plate  510  changes its shape and dimension upon being saturated by a magnetic field. According to the present invention, the magnetostrictive plate  510  may be composed of any suitable material with a magnetostriction of approximately 5×10 −5  or greater, including but not limited to the combination of: cobalt; nickel; iron; rare earth material; their oxides; and additives of oxygen, nitrogen, fluoride, or boron. 
   The excitation source  515  is comprised of a plurality of magnetic coils  530  that are spaced tightly together in close proximity to the magnetostrictive plate  510 . For example only, the magnetostrictive plate  510  may be separated from the magnetic coils  530  by a distance of less than 1 μm. The magnetic coils  530  are generally formed by a plating process and can be of any suitable shape such as a rectangular shape as illustrated in  FIG. 4 . A pair of electrical leads  532 ,  533  connect the various coils  530  of the excitation source  515 , and conduct a current therethrough, to generate the excitation saturation magnetic field. 
   The magnetostrictive plate  510  may assume various shapes, such as a rectangular shape ( FIG. 4 ), a trapezoidal shape ( FIG. 5 ), a square, an elliptical, or any other suitable shape. 
   With further reference to  FIG. 5 , the magnetostrictive plate  510  is generally shaped as a trapezoid having a thickness T, a length L, a forward facing edge  520  of a width W, and a shorter edge  525  of a width S that is oppositely disposed relative the forward facing edge  520 . For example only, the thickness T may be about 1 μm and the length L may be about 100 μm. The widths W and S may range from approximately 1 to 100 μm. 
   The length of the magnetic coils  530  ( FIG. 4 ) is generally greater than the width of the forward facing edge  520  of the magnetostrictive plate  510 , to ensure that the magnetic coils  530  produce a uniform magnetic field relative to the magnetostrictive plate  510 . The magnetic coils  530  are so arranged that they span or extend beyond the length of the magnetostrictive plate  510 , to ensure magnetization saturation of the magnetostrictive plate  510 . 
   The actuator  505  may be disposed behind any one of the pole layers (P 1 )  340 , (P 2 )  355 , or (P 3 )  360 ; behind any one of the shield layers (S 1 )  330 , (S 2 )  335 , (S 3 )  370 , or (S 4 )  385 ; behind the read gap  300 ; or behind the write gap  375 . For example purpose only,  FIG. 3  illustrates the actuator  505  disposed immediately behind the P 1  layer  340 , with the understanding that it can alternatively be placed in any other aforementioned location within the read/write element  230 . 
   With further reference to  FIG. 3 , the magnetostrictive plate  510  of the actuator  505  is disposed with its length aligned along an axis that is substantially perpendicular to the ABS surface of the head. Furthermore, the magnetostrictive plate  510  is oriented with its forward facing edge  520  disposed in the forward direction toward the ABS. This orientation is designed to ensure that the actuator  505  undergoes a greater dimensional change in the forward direction to result in a protrusion of the pole tip region  365  toward the magnetic disk  126 . 
     FIG. 6  illustrates an alternative embodiment of the present invention wherein the actuator  505  may be disposed behind the second coil layer  374 . According to yet another alternative embodiment as illustrated in  FIG. 7 , the actuator  505  may also be placed above the upper shield S 4  layer  385  and then is covered by an overcoat layer  444 . 
   With reference to  FIG. 8 , according to a further embodiment of the present invention that can be applied to all the embodiments described earlier, (e.g., shown in  FIGS. 3 ,  6 , and  7 ), a stop layer  535  made of a non-magnetic material is disposed behind the actuator  505  and adjacent to the shorter edge  525  of the magnetostrictive plate  510  to substantially constrain the magnetostrictive plate  510  and to allow it to expand in the forward direction during actuation of the actuator  505 . It should also be understood that the magnetic coils  530  may be positioned either above or below the magnetostrictive plate  510  without substantively affecting the functionality of the actuator  505 . 
   Referring now to  FIG. 9 , it illustrates the working principle of the actuator  505  to enable the read/write head  80  to fly above the magnetic disk  126  at an ultra low flying height. During a read or write operation, an excitation voltage source supplies a current  540  to the actuator  505 . The current  540  flows in a lengthwise direction through the magnetic coils  530 . By induction, a magnetic field comprising of magnetic flux lines  545  is generated within the magnetostrictive plate  510 . Using the well accepted right hand rule, the magnetic flux lines  545  must be perpendicular to the current  540 , and thus are parallel to the axis  400  pointing toward the ABS. 
   Upon being magnetically saturated, the magnetostrictive plate  510  expands dimensionally according to the physics of magnetostriction. This dimensional expansion causes the length L as well as the other dimensions of the magnetostrictive plate  510  to elongate by an amount of ΔL. As a result, the read/write element  230  including the pole tip region  365  increases in length accordingly. A resulting protrusion of the pole tip region  365  is thereby created to displace the read/write element  230  in a closer proximity to the magnetic disk  126 . By varying the amount of magnetic saturation impressed upon the magnetostrictive plate  510 , it is possible to control the dynamic flying height of the read/write head  80  in a manner as to attain an ultra low flying height. 
   In operation, the actuator  505  is energized during a read or write operation. When the read/write head  310  is in an idle state, the excitation voltage is turned off to de-energize the actuator  505 , whereupon the magnetostrictive plate  510  contracts to its original length L, thus causing the pole tip region to retract away from the magnetic disk  126 . The flying height is therefore increased to maintain a nominal value. 
   In one embodiment, the excitation source  515  is continuously energized during the operation of the head, to compensate for manufacturing intolerances, such as when the flying height of the head is not within an acceptable tolerance range when operating at idle speed. 
   According to another embodiment, the excitation source  515  is selectively energized only during a read operation. According to yet another embodiment, the excitation source  515  is selectively energized only during a write operation. 
   In the present invention, the principal physical effect produced by the actuator  505  is an elongation of the magnetostrictive plate  510  to cause a protrusion of the pole tip region  365  for controlling the dynamic flying height of the read/write head  80 . While this elongation is achieved by the effect of magnetostriction, it is also possible a combined effect of magnetostriction and thermal expansion could be employed in an alternative embodiment of the present invention. 
   According to another embodiment of the present invention, the coils  530  or additional coils, provide a heating effect to further control the dynamic flying height of the read/write head  80 . The coils  530  may be made of high resistance elements that can carry the current to induce a magnetic field to saturate the magnetostrictive plate  510  and at the same time generate heat to transfer to the magnetostrictive plate  510  by means natural convection conduction. By selectively varying the resistance or the magnetic field strength in a combination, the magnetostrictive plate  510  is subjected to both sources of thermal and magnetostrictive expansion. The actuator  505  therefore has one additional control authority for achieving an ultra low dynamic flying height of the read/write head  80 . 
     FIG. 10  shows an exemplary longitudinal recording read/write head  1000  that incorporates the actuator  505 , to illustrate the fact that the present invention is applicable to both longitudinal and perpendicular recording heads. While the actuator  505  is shown in  FIG. 10  as being disposed behind the first pole, P 1 , it should be clear that the actuator  505  may be positioned at any suitable location in the head  1000 , as described earlier in connection with the perpendicular recording head  230  of  FIG. 3 .