Abstract:
A write head structure for use with thermally assisted recording is disclosed. Improved heat sinking is provided for removing thermal energy created by a ridge aperture near field light transducer. Metal films conduct heat away from the region near the ridge aperture to the high pressure air film at the ABS between the head and media. This heat is further dissipated by the media. The metal films have varying thickness to improve lateral conductivity and may be composed of Au combined with a harder metal such as Ru to improve wear characteristics at the ABS.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to structures of thin film magnetic write heads. More specifically, the invention relates to structures of a thin film write heads for thermally assisted magnetic recording, wherein an optical aperture serving as ridge waveguide near field optical source is integrated with heat sinking components situated at the air bearing surface. 
     2. Description of the Related Art 
     The ongoing quest for higher storage bit densities in magnetic media used in, for example, hard disk drives, have reduced the size (volume) of data cells to the point where the cell dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, there is concern that data stored within the cells is no longer thermally stable, as random thermal fluctuations at ambient temperatures are sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or lowering the temperature. Lowering the temperature is not a practical option when designing hard disk drives for commercial and consumer use. Raising the coercivity is a practical solution, but requires write heads employing higher magnetic moment materials, or techniques such as perpendicular recording (or both). 
     One additional solution has been proposed, which employs heat to lower the effective coercivity of a localized region on the magnetic media surface; writes data within this heated region with a broad magnetic field; and, “fixes” the data state by cooling the media to ambient temperatures. This technique is broadly referred to as “thermally assisted (magnetic) recording”, TAR or TAMR. Heat is applied to a magnetic substrate via a very small, but intense light source to reduce the anisotropy of fine grain magnetic media. A potential advantage is that lower field gradients produced by heads having broader field dimensions may be used, which relaxes the tight dimensional requirements of the magnetic source or write head. It can be applied to both longitudinal or perpendicular recording systems, although the highest density state of the art storage systems are more likely to be perpendicular recording systems. Heating of the media surface is accomplished by a number of techniques such as focused laser beams or near field optical sources. To be useful for high density recording, the light source utilized for heating must be on the order of 50 nm or less in diameter. This is far beyond the optical diffraction limit for conventional light sources such as solid state lasers, which leaves near field optical sources as the preferred heating method. 
     One method that commonly used to produce near-field light is the ridge aperture or “C” shaped aperture. The device consists of rectangular shaped aperture fashioned in an electrically conductive metal film. Extending into the center portion of the aperture is an electrically conductive ridge, generally an extension of the surrounding metal film. Incident radiation, polarized in the direction parallel to the ridge produces an intense pattern of near-field light which appears close to or at the end of the ridge, in the gap between the end of the ridge and the opposing boundary of the aperture. 
     While the near field light source is positioned to induce heating in the magnetic media, a certain percentage of heat will also be generated in the magnetic head, particularly in the vicinity of the ridge aperture. This heating can affect the shape of the head at the ABS, and therefore impact the fly height. Heating of the head can also impact the reliability and performance of the head because high temperatures can accelerate thermal migration of various films and structures, causing inter-diffusion and dimensional smearing. Therefore it may be necessary to dissipate excessive heat created by the near field light source and radiated to the magnetic head by providing appropriate heat sinking. 
     What is needed is an improved method for thermally assisted recording. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a thin film magnetic head for thermally assisted recording, having a near field light source, containing an upper pole tip layer; a pole lip, magnetically coupled to the upper pole tip layer; a metal layer, having an outer surface located approximately co-planar with the air bearing surface, the metal layer thermally coupled to the upper pole tip layer and the pole lip; and a ridge aperture, fashioned within the metal layer and bounded on one side by the pole lip, the metal layer having a first thickness at an inner boundary defining the ridge aperture, the metal layer having a second thickness at an outer boundary defining the metal layer, the second thickness being greater than the first thickness. 
     It is another object of the present invention to provide a thin film magnetic head for thermally assisted recording, having a near field light source, containing an upper pole tip layer; a pole lip, magnetically coupled to the upper pole tip layer; a first metal layer, having an outer surface located approximately co-planar with the air bearing surface, the metal layer in contact with the upper pole tip layer and the pole lip, the first metal layer having a first thickness at contact with the pole lip, transitioning to a second thickness greater than the first thickness; a second metal layer, having a outer surface located approximately co-planar with the air bearing surface, the second metal layer in contact with the first metal layer; and a ridge aperture, fashioned within the second metal layer and bounded on one side by the pole lip, the second metal layer having the first thickness at a boundary with the ridge aperture, transitioning to the second thickness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein: 
         FIG. 1   a  is partial, cross section view of a thin film perpendicular write head design incorporating a ridge aperture near field optical source and integrated heatsink, in accordance with an embodiment of the present invention; 
         FIG. 1   b  is a partial cross section expanded view of detail  101  in  FIG. 1   a , in accordance with an embodiment of the present invention; 
         FIG. 2   a  is a partial air bearing surface view of the perpendicular write head of  FIG. 1   a , in accordance with a first embodiment of the present invention; 
         FIG. 2   b  is a partial air bearing surface view of the perpendicular write head of  FIG. 1   a , in accordance with a second embodiment of the present invention; 
         FIG. 3   a  is a partial plan view through section B-B of  FIG. 2   a , in accordance with the first embodiment of the present invention; 
         FIG. 3   b  is a partial plan view through section C-C of  FIG. 2   b , in accordance with the second embodiment of the present invention; 
         FIG. 3   c  is a partial plan view illustrating structural dimensions of  FIGS. 3   a  and  3   b , in accordance with embodiments of the present invention; 
         FIG. 4   a  is a partial plan view through section D-D of  FIG. 2   a , in accordance with the first embodiment of the present invention; and 
         FIG. 4   b  is a partial plan view through section E-E of  FIG. 2   b , in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Near field light sources are effective for heating the media used in thermally assisted recording. However, the proximity of the intense near field light pattern to the head itself may cause other problems if head temperatures are not controlled. These problems may include unwanted thermal expansion which can affect the shape of the head near the ABS, which in turn impacts fly height due to aerodynamic effects. Higher head temperatures may also impact device interlayer thermal migration, which in turn impacts electrical performance and long term reliability. 
     One method that can be used to reduce the impact of thermal loading is to incorporate heat sinks thermally coupled to the metal film surrounding the ridge (or “C”) aperture. Preferably, the heat sinking provides a low heat conduction path away from the near field light source by using conductive metals and increasing the film thickness. The heat sink surface is preferably located at or near the air bearing surface (ABS) to take advantage of the high conduction (via diffusion) heat transfer provided by the high pressure air layer between the media and head. The high pressure is created by aerodynamic effects as the head “flies” above the media surface. Increasing the surface area and lateral conductivity (by increasing the film thickness) increases the heat transfer away from the regions near the ridge aperture. 
     Subsequently described embodiments of the present invention disclose near field light sources having a ridge aperture. It will be recognized by those skilled in the art however, that other geometries of near field light generating apertures may also be used, such as those having more than one ridge generating both single and/or multiple near field light patterns, such as those described in US Patent Application No. 2008/0149809 by Hamann et al. 
       FIG. 1   a  is partial, cross section view  100  of a thin film perpendicular write head design incorporating a ridge (or “C”) aperture near field optical source and integrated heatsink, in accordance with an embodiment of the present invention. In order to simplify and clarify the structures presented, spacing layers, insulating layers, and write coil layers have been omitted. The write head comprises lower return pole layer  102 , back-gap layer(s)  104 , upper return pole layer  106 , upper pole tip layer  108 . Lower return pole layer  102  may also have a lower pole tip (not shown) at the ABS. Layer  110  is an optical waveguide. Cladding layers, if present, are excluded from the figure for clarity. Layer  110  extends through at least a portion of back-gap layers  104 . Detail  101  is shown in an expanded view in  FIG. 1   b . Coil layers (not shown) and various associated insulating and spacer layers (not shown) would reside within layers  112 , bounded by the ABS, back-gap  104 , lower return pole  102 , and upper bounding layers  106 , and  108  as would be recognized by those of skill in the art. Layers  102 ,  104 ,  106 , and  108  are comprised of a suitable magnetic alloy or material, containing Co, Ni, and Fe. Layer  110  is comprised of a suitable light transmitting material, preferably tantalum pentoxide and/or titanium dioxide. 
       FIG. 1   b  is a partial cross section expanded view of detail  101  in  FIG. 1   a , in accordance with an embodiment of the present invention. Pole lip  116  is magnetically coupled to upper pole tip layer  108 , and to optional magnetic step layer  114 . Optically transparent layer  118  (contained within the boundaries of the ridge aperture), ridge metal layer  122 , surrounding metal layer  120 , and pole lip  116  comprise the near field aperture optical source, which is supplied light energy via optical waveguide  110 . Pole lip  116  and optional magnetic step layer  114  are comprised of a suitable magnetic alloy, containing Co, Fe, and Ni. Metal layer  120  and ridge layer  122  are made of Au or Au alloys. Pole lip  116  has a nominal depth (as measured from the ABS) approximately equal to that of layer  120 , with a value between 50 and 150 nm, preferably between 75 and 125 nm. 
       FIG. 2   a  is a partial air bearing surface view  200  of the perpendicular write head of  FIG. 1   a , in accordance with a first embodiment of the present invention.  FIG. 1   a  is a view through section A-A of  FIG. 2   a . The ridge aperture  202  is formed by surrounding metal layer  120  and pole lip  116 . Ridge layer  122  extends into the aperture from metal layer  120 . Metal layers  204  are thermally coupled to pole tip layer  108 , pole lip  116  and metal layer  120 . Heat sinking is provided by heat transfer from layers  120 ,  204 , pole lip  116 , and pole tip layer  108  to the media via the high pressure air film at the ABS while the head is in operation. Optically transparent layer  118  is contained within the boundaries of surrounding metal layers  120 ,  122 , and  116  which define the ridge aperture  202 . Generally, layer  118  is comprised of a dielectric material having suitable optical transparency. Metal layers  204  typically are made from Cr, Ir, Pt, Pd, Ru and Rh, as these metals are good heat conductors as well as being harder than Au. They also exhibit good corrosion resistance. The hardness and corrosion resistance are important for surfaces used at the ABS, to provide the required longevity and reliability of the head. Preferably, metal layer  204  is comprised of Ru. 
       FIG. 3   a  is a partial plan view  300  through section B-B of  FIG. 2   a , in accordance with the first embodiment of the present invention. Metal layer  120  thickness (as measured from the ABS inward) progressively increases as the structure extends from the boundaries of the ridge aperture. The increased thickness can range from 100 nm to 1000 nm, but is preferably between 250 to 500 nm. This shape facilitates improved conductive heat transfer within layer  120  to metal layers  204  and upper pole tip layer  108  (not shown, refer to  FIG. 2   a ). Furthermore, extension of layer  120  along the ABS increases the heat transfer area through which heat can be dissipated through the high pressure air film at the ABS to the media. Heat transfer also occurs from pole lip layer  116 , metal layers  204 , and upper pole tip layer  108  to the media in a similar manner. Conductive heat transfer may also occur from layers  120 ,  204 ,  116  to other structures within the body of the head via upper pole tip layer  108 , but this is expected to be of minor importance when compared to the conduction/diffusion heat transfer to the recording media. 
       FIG. 4   a  is a partial plan view  400  through section D-D of  FIG. 2   a , in accordance with the first embodiment of the present invention. Metal layer  204  thickness (as measured from the ABS) parallels that of metal layer  120  below it. This increase in thickness not only improves the conduction of heat away from the ridge aperture, but also improves conduction to upper pole tip layer  108 . 
       FIG. 2   b  is a partial air bearing surface view  201  of the perpendicular write head of  FIG. 1   a , in accordance with a second embodiment of the present invention. Ridge aperture  202 , optically transparent layer  118 , and ridge layer  122  are as described in  FIG. 2   a . However, the lateral dimension of softer metal layer  120  is reduced compared to layer  120  in  FIG. 2   a , and substituted with portions of a harder material in metal layer  206 . Metal layer  206  is composed of the same materials cited for metal layer  204  above. This embodiment provides improved wear characteristics at the ABS compared to the embodiment of  FIG. 2   a , due to the increased surface area of the harder metals comprising layer  206 . Heat sinking is provided by heat transfer from layers  120 ,  206 , and pole lip  116  to the media via the high pressure air film at the ABS, coupled with conduction to upper pole tip layer  108  which also transfers heat to the media via its exposed surface area at the ABS. 
       FIG. 3   b  is a partial plan view  301  through section C-C of  FIG. 2   b , in accordance with the second embodiment of the present invention. Metal layer  120  thickness (as measured from the ABS inward) progressively increases as the structure extends from the boundaries of the ridge aperture. The increased thickness can range from 100 nm to 1000 nm, but is preferably between 250 to 500 nm. Metal layer  120  transitions into metal layer  206  on both sides of the ridge aperture. Metal layers  120  and  206  are in intimate thermal contact, facilitating heat transfer from the ridge aperture. Heat transfer occurs from layer  120 , pole lip layer  116 , metal layers  206 , and upper pole tip layer  108  to the media via the high pressure air film at the ABS. 
       FIG. 4   b  is a partial plan view  401  through section E-E of  FIG. 2   b , in accordance with the second embodiment of the present invention. Metal layer  206  thickness (as measured from the ABS) parallels that of metal layers  120  and  206  below it. 
     EXAMPLES 
     The following serve to provide representative embodiments of the present invention, but in no manner are meant to limit the scope, range, and function of the invention. In these examples, please refer to  FIG. 3   c .  FIG. 3   c  is a partial plan view  303  illustrating structural dimensions of  FIGS. 3   a  and  3   b , in accordance with embodiments of the present invention. 
     Example 1 
     Refer to  FIGS. 2   a ,  3   a ,  3   c , and  4   a  in accordance with the first embodiment of the present invention. 
     Dimension  314 =approx. 400 nm 
     Dimension  318 =approx. 600 nm 
     Dimension  316 =approx. 1000 nm 
     Dimension  310 =approx. 575 nm 
     Dimension  320 =approx. 100 nm 
     Dimension  312 =approx. 310 nm 
     Dimension  306 =approx. 150 nm 
     Angle  304 =approx. 45 degrees 
     Angle  308 =approx. 20 degrees 
     Metal layer  120  is composed of Au, metal layer  204  is composed of Ru. 
     Example 2 
     Refer to  FIGS. 2   b ,  3   b ,  3   c , and  4   b  in accordance with the first embodiment of the present invention. 
     Dimension  314 =approx. 400 nm 
     Dimension  318 =approx. 600 nm 
     Dimension  316 =approx. 1000 nm 
     Dimension  310 =approx. 575 nm 
     Dimension  320 =approx. 100 nm 
     Dimension  312 =approx. 310 nm 
     Dimension  306 =approx. 150 nm 
     Angle  304 =approx. 45 degrees 
     Angle  308 =approx. 20 degrees 
     Metal layer  120  is composed of Au, metal layer  206  is composed of Ru. 
     Although the foregoing embodiments disclose thin film perpendicular write heads, it will be recognized by those of ordinary skill in the art, that such designs are equally applicable to thin film longitudinal write heads as well with minor modification. 
     The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.