Abstract:
An effective heat sink is provided for a magnetic recording head. The heat sink conducts heat away from the recording head thus limiting the range of temperatures to which the recording head is subjected. A heat sink on a recording head significantly reduces heat induced protrusion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a magnetic recording head used in a disk drive, and more particularly to a magnetic recording head incorporating a heat sink. 
     2. Description of the Background Art 
     Disk drives using magnetic recording of digital information store most of the information in contemporary computer systems. A disk drive has at least one rotating disk with discrete concentric tracks of data. Each disk drive also has at least one recording head typically having a separate write element and read element for writing and reading the data on the tracks. The recording head is constructed on a slider and the slider is attached to a suspension. The combination of the recording head, slider, and suspension is called a head gimbal assembly. In addition, there is an actuator which positions the recording head over the specific track of interest. The actuator first rotates to seek the track of interest and after positioning the recording head over the track, maintains the recording head in close registration to that track. The disk in a disk drive has a substrate and a magnetic layer on the substrate for magnetic recording. The slider carrying the recording head has a disk facing surface upon which an air bearing is constructed. The air bearing allows the slider to float on a cushion of air and to be positioned close to the disk surface. Alternatively, the slider surface facing the disk can be adapted for partial or continuous contact with the disk. 
     The recording head is formed from various metals and is separated from the body of the slider by a thin insulating layer. The value of the coefficient of thermal expansion of the materials in the recording head is generally higher than the corresponding value for the insulating layer or the slider. Therefore as the temperature of the recording head and slider is increased, the physical expansion is greater for the recording head than for the insulating layer or the slider. The rise in temperature is most noticeable during writing when write current is passed through the write element of the recording head. During writing, heat is generated in the coils by Joule heating, and in the magnetic portion of the yoke by Eddy current heating. Upon heating, the recording head may protrude several nanometers out of the air bearing surface of the slider toward the disk because of the mismatch in thermal expansion coefficients and higher temperature in the region close to the coil compared with the slider body. 
     The flying height of the slider above the disk surface is generally lower for each new family of disk drive products to facilitate achieving ever higher densities of recorded information. The required flying heights are now comparable with the amount of recording head protrusion caused by temperature increases during writing. Contact between the recording head and the disk can cause damage to the recording head and can also lead to wear failure at the interface between the recording head and the disk. 
     The alternate contact recording apparatus allows contact between the slider and the disk. However, while a slider surface may be constructed to allow partial or continuous contact with the disk, a recording head which protrudes from the disk facing surface of a slider is subject to excessive wear damage. 
     Thus, the mismatch between the thermal expansion coefficients of the recording head and the slider leading to protrusion of the recording head is an increasingly serious problem. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the invention provides an effective heat sink for a recording head. The heat sink thus provided dissipates heat effectively and therefore limits the temperature excursions in the recording head. The present invention substantially improves the temperature induced protrusion of the recording head. 
     In one embodiment, a heat sink is embodied as a heat conducting layer disposed between the read element and the write element of the recording head. In an alternate embodiment, a heat sink is embodied as a heat conducting layer disposed over the write element. In another alternate embodiment, a heat sink is embodied as a heat conducting layer disposed between two layers of turns in the coil of the write element. The heat conducting layers in the embodiments are formed from a suitable material such as copper. A heat conducting layer may be in contact with or connected to the slider to increase the heat dissipation. In another embodiment, the heat sink is provided with a heat conducting portion and a smaller insulating portion. 
     In an alternate embodiment, a disk drive is provided wherein the recording head is provided with a heat sink. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, which when taken in conjunction with the drawings, illustrate by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a top view of a disk drive having a recording head with a heat sink; 
         FIG. 2  illustrates a perspective view of a slider and a recording head with a heat sink; 
         FIG. 3  illustrates a cross sectional view of a recording head having a heat sink disposed between the write element and read element; 
         FIG. 4  illustrates a detailed cross sectional view of a recording head having a heat sink disposed between the write element and read element; 
         FIG. 5  illustrates a cross sectional view of a recording head wherein a heat sink is formed over the upper pole of the write element; and, 
         FIG. 6  illustrates a cross sectional view of a recording head having a heat sink disposed between the layers of the turns in a write element coil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is embodied in a heat sink which effectively dissipates heat from a recording head. The heat sink limits the temperature excursions of the recording head and therefore limits the amount of protrusion of the recording head from the disk facing surface of a slider. The risk of wear damage to the recording head and the risk of interface damage between the recording head and the disk is significantly reduced. 
     Referring to  FIG. 1 , a magnetic disk drive  100  has at least one rotatable magnetic disk  102  supported by a spindle  104  and rotated by a motor (not shown). There is at least one slider  106  with an attached recording head  108  and heat sink (described in detail below) positioned over the disk  102  surface while reading and writing. The slider  106  is attached to a suspension  110  and the suspension  110  is attached to an actuator  112 . The actuator  112  is pivotally attached  114  to the housing  116  of the disk drive  100  and is driven by a voice coil motor  118 . As the disk is rotating, the actuator  112  positions the slider  106  along with the suspension  110  radially or along an arcuate path  120  over the disk  102  surface to access the data track of interest. 
     Referring to  FIG. 1 , during operation of the disk drive  100 , the motion of the rotating disk  102  relative to the slider  106  generates an air bearing between the slider  106  and the disk  102  surface which exerts an upward force on the slider  106 . This upward force is balanced by a spring force from the suspension  110  urging the slider  106  toward the surface of the disk  102 . Alternatively, the slider  106  may be in either partial or continuous contact with the disk  102  surface during operation. 
       FIG. 1  also shows an optional load/unload tab  122  on the distal end of the suspension  110 . This load/unload tab  122  operates in conjunction with a load/unload fixture  124  to lift the slider  106  away from the disk  102  surface when the disk drive  100  is turned off or enters a power saving mode. When an unload operation is initiated, the actuator  112  rotates far enough in a clockwise direction  126  such that the load/unload tab  122  then slides up the load/unload fixture  124  gently lifting the slider  106  off of the disk  102  surface.  FIG. 1  also shows the electrical connection  128  as wires or a flex cable between the recording head  108  and the preamplifier  130 . 
       FIG. 2  shows a more detailed view of a slider  202 . The recording head and heat sink  204  are preferably constructed on the trailing surface  206  of the slider  202 .  FIG. 2  illustrates the upper pole  208  and the turns  210  of the coil  214  of the write element of the recording head. The read element is not illustrated in  FIG. 2 . The electrical connection pads  212  which allow connection with the write element and read element are illustrated. One embodiment of a heat sink  204  is illustrated in  FIG. 2 . This embodiment of the heat sink is a layer of heat conductive material physically close enough to the coil  214  and at least one of the poles  208  of the write element to be effective in conducting heat away from the write element. A ceramic composite of titanium carbide and alumina is commonly used to form sliders. This material is a better heat conductor than the substantially pure alumina commonly used to separate the recording head from the slider. Thus, the heat sink is somewhat more effective if a portion of the heat sink is in physical contact, or connected, with the slider.  FIG. 2  illustrates two areas  216  of the heat sink conductive layer  204  which are in contact with the trailing surface  206  of the slider  202  through openings (described in more detail below) in the underlying insulation layer (not shown). 
       FIG. 3  illustrates a cross sectional view of a typical recording head  302  and one embodiment of a heat sink  304 . The recording head  302  typically has a read element  306  which is separated from the slider body  308  by a layer  310  of insulating material. The read element  306  has a thin film sensor  312  and two magnetic shield layers  314 . The read element  306  typically has an exposed end  316  for communicating with the disk (not shown). The write element  318  has a lower  320  and upper pole  322  and turns  324  forming a coil disposed between the poles  320 ,  322 . The poles  320 ,  322  of the write element  318  have exposed ends  326  for communicating with the disk (not shown). Both the read element  306  and write element  318  are usually surrounded by insulation material except for the exposed ends  316 ,  326 . There may be a very thin protective layer of carbon material formed over the exposed ends  316 ,  326  to retard corrosion of the write  318  and read  306  elements. A recording head with a thin carbon overcoat is considered to have exposed ends for purposes of magnetically communicating with the disk. The heat sink  304  in  FIG. 3  is embodied as a layer of heat conducting material disposed between the read element  306  and the write element  318 . One or more openings  329  in the insulation  310  allowing a portion  328  the heat conducting material of the heat sink  304  to be in contact with the slider  308  incrementally improves the heat conduction. 
       FIG. 4  illustrates an expanded view of a recording head  402  having an embodiment of a heat sink. The write element  418  of the recording head has an upper pole  422  and a lower pole  420 . The write element  418  also has coil turns  424  and an exposed end  426  for communicating with the disk (not shown). The read element  406  has two shields  414 , a read sensor  412 , and an exposed end  416  for communicating with the disk (not shown). The heat sink illustrated in  FIG. 4  is embodied as a layer  428  disposed between the write element  418  and read element  406 . In the particular embodiment illustrated in  FIG. 4 , the heat sink layer  428  has one portion  432  composed of a heat conducting material, preferably with a high thermal conductivity, and another smaller portion  430  composed of an insulating material. The insulating portion  430  is positioned near the exposed ends of the write element  426  and read element  416 . The insulating portion  430  of the heat sink, preferably formed of a stable insulator such as alumina, helps protect the heat conducting portion  426  from possible corrosion or wear. Alternatively, the smaller portion  430  may be formed from a stable capping material such as permalloy or other alloy of nickel and iron. 
       FIG. 5  illustrates an alternative embodiment of a heat sink. In this embodiment, the heat sink is comprised of a layer  528  formed over the upper pole  522  of the write element  518 . The heat sink layer  528  has a portion  532  formed from a heat conducting material and an optional portion  530  formed from an insulator. The lower pole  520  and the turns  524  of the write coil are illustrated. 
     The heat sink may be embodied as a heat conducting layer positioned adjacent to the turns in the write head coil. This configuration of the heat sink provides for an effective heat sink since a primary heat source is the heat generated in the coil during writing.  FIG. 6  illustrates a specific embodiment of a heat sink which comprises a heat conducting layer  632  disposed between the turns  624 ,  625  of a two layer coil in a write element  618 . The write element  618  has a lower pole  620  and an upper pole  622 . 
     In the embodiments of the heat sink discussed above, the heat conducting material may be formed from any suitable material. Copper is a preferred heat conducting material because the heat conductivity is high and a copper layer is easily constructed by known methods of electroplating or vacuum deposition. The coil of the write element is usually formed from copper. Magnetic materials are not as suitable for use as heat conductors because of the possible interference with the function of the write or read elements. The optional insulating portion of the heat sink may conveniently be formed from alumina which is widely used in recording head construction as an insulator. Other insulating materials such as silicon oxide are known to those skilled in the art. The methods of forming the heat sink are well known to those skilled in the art and include forming a mask, plating, sputtering or other suitable techniques. 
     In numerical experiments simulating an increase in temperature due to writing, recording heads having a heat sink indicated a temperature increase as low as 70% compared with the temperature increase for recording heads which did not have a heat sink. Correspondingly, the temperature induced protrusion was reduced by up to 30% for recording heads having a heat sink compared with recording heads without a heat sink. 
     From the foregoing it is apparent that the invention provides an effective heat sink for a recording head. The embodiments of the heat sink significantly limit the increase in temperature of the recording head and significantly reduce the temperature induced recording head protrusion. Although this invention has been described with respect to specific embodiments, the details thereof are not to be construed as limitations for it will be apparent that various embodiments, changes, and modifications may be resorted to without departing from the spirit and scope thereof, and it is understood that such equivalent embodiments are intended to be included within the scope of this invention.