Abstract:
A thin film magnetic head having one or more magneto-resistive (MR) elements. A thermally conductive stud is incorporated in an underlayer of the head, below the bottom shield of the MR element. This stud acts as a heat sink, and enhances the heat flow from the bottom shield to the substrate to thereby reduce thermal contact noise in the device, as well as allowing use of higher bias currents when reading signals from the media.

Description:
FIELD OF THE INVENTION 
   The present invention relates to magnetic storage devices, and more particularly, to magnetic storage devices which employ thin-film magnetic heads having one or more magneto-resistive (MR) transducer elements. 
   BACKGROUND OF THE INVENTION 
   Various types of magnetic storage devices employ thin-film heads, such as disk drives and tape drives. The thin-film head is typically composed of one or more read elements and one or more write elements used to read/write information on the tape media, such as that described in U.S. Pat. No. 5,963,401 entitled “Magnetic tape head assembly including modules having a plurality of magneto-resistive head elements” by Richard Dee et al., which is hereby incorporated by reference as background material. Writing is performed by delivering a write signal to one of the write elements. The write signal creates a variable magnetic field at a gap portion of the write element. This magnetic field induces magnetic polarity transitions into the desired media track to effectuate writing of data on the media. 
   Reading of data from the media is performed by sensing the magnetic polarity transitions on the media as the media is moved across a thin-film head in a longitudinal direction. The magnetic polarity transitions on the media present a varying magnetic field to a read transducer in the head. The read transducer converts the varying magnetic field into an analog read signal that is delivered to a read channel for appropriate processing. The read channel converts this analog signal into digital signal(s) that are then processed by a computer system. 
   In thin-film heads having a plurality of transducer elements, magneto-resistive (MR) elements are typically used to read information from the media, due to their increased sensitivity during a read operation. The resistance of an MR element varies almost linearly with an applied magnetic field. During a read operation, the MR element is held very near (in the case of disk) or in contact with (in the case of tape) the media, to sense the varying magnetic transitions on a particular track. A constant DC current is passed though the MR element resulting in a variable voltage across the MR element due to its varying resistance. By Ohm&#39;s law (e.g. V=IR), the variable voltage is proportional to the varying resistance of the MR element, and hence is representative of the data stored on a particular track of the media. This variable voltage signal, which is the read analog signal, is then processed and converted to digital form for subsequent processing. 
   A simple MR head consists of a thin film of magneto-resistive material, such as Permalloy, between two insulating layers or shields. When the MR layer is formed, a magnetic field is typically applied in a direction parallel to the plane of the thin layer. Thus, the MR layer exhibits a uniaxial anisotropy with an easy-axis of magnetization parallel to the direction of the applied field. If an external magnetic field, such as from a magnetic tape, is applied normal to the easy-axis, the magnetization direction of the MR layer will rotate away from the easy-axis and towards the direction of the applied magnetic field. This magnetization rotation causes a change in resistance in the MR layer. When no external field is applied, the resistance is greatest. The resistance decreases with increasing applied field. For practical geometries of the MR layer, resistance as a function of applied field traces a bell-shaped curve. The MR element is often biased with an applied current such that a zero magnitude applied field results in a resistance near an inflection point on the resistance curve. Thus, small changes about a zero magnitude applied external field result in nearly linear changes in resistance. 
   There are many variables that can adversely affect the performance of a media drive such as a disk drive or tape drive. Temperature variations of the MR element are one such variable with adverse consequences. Because MR elements have positive temperature coefficients, increases in the temperature of an MR element can cause in increase in the resistance of the MR element. Similarly, decreases in the temperature of an MR element can cause a decrease in the resistance of the MR element. Since the read voltage signal is proportional to variations in resistance of the MR element multiplied by the constant bias current, whenever the temperature of the MR element is increased or decreased, a thermal signal is generated which adversely adds or subtracts to the value of the desired analog signal being read. 
   In thin film tape heads, there is a kind of noise that is sometimes referred to as contact noise. Contact noise occurs when a bump on the tape hits the MR element (or shield adjacent thereto) and momentarily cools the device. This cooling causes a momentary decrease in resistance of the MR element, and thereby produces a voltage spike in the output of the element. This spike, if it is large enough, can cause errors in reading the data by the data channel. The magnitude of this temperature fluctuation is proportional to the temperature rise of the shields and MR element. Therefore, one factor that produces excessive contact noise is excessive MR element/shield temperature. 
   Because both magnetic data signals and thermal signals cause variations in the resistance of the MR element, there is a need to develop a method and apparatus that mitigates these undesired thermal signals and their resulting effects. The present invention is designed to overcome the aforementioned problems. There is yet another reason for improving transducer thermal characteristics. As track widths are narrowed and read sensors thinned, current density becomes an issue. It is desirable to drive as much current as possible through the sensor to get the greatest amplitude—thus providing an improved signal-to-noise ratio signal read from the media. If the read sensor could cool better, more current can be applied. The present invention is also designed to enhance the signal being read from the media. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved data storage device. 
   It is a further object of the present invention to provide an improved transducer for accessing information on a storage media. 
   It is another object of the present invention to provide an improved environment for an MR element that is used for reading data from a storage media. 
   It is yet another object of the present invention to provide an MR element having improved thermal characteristics. 
   It is a further object of the present invention to provide a data transducer with an integrated heat sink. 
   In accordance with the invention, a thin film head is provided having one or more MR elements. A thermally conductive stud is incorporated in an underlayer of the head, below the bottom shield of the MR element. This stud acts as a heat sink, and enhances the heat flow from the bottom shield to the substrate to thereby reduce thermal contact noise in the device, as well as allowing use of higher bias currents when reading signals from the media. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  depicts a side view of a partial thin-film magnetic head showing a thermally conductive stud. 
       FIG. 2   a  depicts the partial thin-film magnetic head of  FIG. 2 , with inclusion of a second magnetic shield layer disposed above the MR element. 
       FIG. 2   b  depicts standard insulating layers disposed between an MR element and the magnetic shield layers of a thin-film magnetic head. 
       FIGS. 3   a – 3   g  depict a thin-film magnetic head during various manufacturing steps. 
       FIGS. 4   a – 4   b  are a flowchart describing various thin-film magnetic head manufacturing steps. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , a side view of a partial MR head is generally shown at  10 . The MR element is not shown in this particular view, for better clarity in showing the details of the underlying conductive stud. Starting at the bottom and working up, thin-film head  10  comprises layer  100  that includes substrate  12 , which is preferably composed of an AlTiC composite material. Above layer  100  is layer  110 , which is preferably composed of an underlayer alumina portion  14 , a thermally conductive stud  16 , and an insulator alumina portion  18 . Above layer  110  is layer  120 , which comprises bottom shield  20 , composed of a magnetically soft material such as CZT, FeN, NiFe, etc. Insulator alumina portion  18  insulates the thermally conductive stud  16  from bottom shield  20 . However, other materials exhibiting similar insulating properties could also be used, such as SiC and aluminum nitride. 
   Referring now to  FIG. 2 , a top view of a partial thin-film head  10  is depicted. The underlying alumina layer  14  and insulator alumina layer  18  are shown together, since the same material (alumina) is used for both the underlying layer and the insulating layer immediately above such underlying layer. The thermally conductive stud  16  is shown, with the dotted line showing its footprint when viewed from the top. This thermally conductive stud is part of the layer  110  ( FIG. 1 ) that also includes the underlying alumina layer. The thermally conductive stud  16  is beneath insulating alumina layer  18 , which is relatively thin to ensure excellent thermal conductivity. The bottom CZT shield extends across the entire surface of the underlying stud  16 , and further extends toward the bottom of this top view to provide an area for locating the MR element  22  such that the MR element is laterally displaced from the underlying stud region  16 . Finally, conductor legs  26  are shown, which provide an outside electrical connection to the MR element  22 . A top shield over the MR element  22  is not shown, for ease of clarity in seeing the relationship between the MR element  22  and underlying stud  16 .  FIGS. 2   a  and  2   b  show this top shield at  25 .  FIG. 2   b  also depicts standard electrical insulating layers disposed between the MR element  22  and the shields. 
   In manufacturing the thin-film head  10 , and referring now to  FIGS. 3   a – 3   g  and the flow chart shown in  FIGS. 4   a – 4   b , the starting point is an AlTiC wafer or substrate material  12  as shown in  FIG. 3   a . A layer of conductor stud material  16  is deposited on the substrate at step  204  and shown in  FIG. 3   b , and then patterned as shown in  FIG. 3   c . These studs  16  are plated up following standard processing techniques (i.e. seedlayer deposit, photo definition, electroplating, resist strip). The resulting studs should be slightly taller than the final underlayer thickness, to accommodate a subsequent polishing step. The studs should be formed using materials having good thermal conductivity, such as copper or aluminum. An alumina underlayer  14  is then deposited over the stud material  16  and substrate  12  at step  206  and shown in  FIG. 3   d . The deposition thickness is greater than the final desired thickness to ensure stud encapsulation. The alumina underlayer is then polished at step  208  using a standard CMP process to remove the excessive underlayer material and obtain the desired underlayer thickness, and to expose the top  28  of conductor stud  16 . A thin (i.e. 100–2,000 angstrom) insulating layer of alumina  18  is then deposited over the entire wafer at step  210  and shown in  FIG. 3   f . Again, any material having suitable insulating properties may be used in lieu of alumina. A layer of magnetically soft material such as CZT, FeN or NiFe is then deposited above the thin alumina layer  18 , and patterned using traditional techniques at step  212 , to form bottom shield  20  as shown in  FIG. 3   g . The outer footprint of the resulting bottom shield  20  should extend outward from the stud sidewalls  24  at least 20 microns, as shown at  32  in  FIG. 3   g , to ensure that the stud is protected from later processing steps. 
   The thin alumina layer  18  thus prevents electrical shorting of the bottom shield  20  to the substrate  12 , since there is now an electrically conductive layer  16  between the bottom shield  20  and the substrate  12 . Prior thin-film heads had no need for this thin insulating layer, as the only material between the bottom shield and the substrate was an insulating material such as alumina—i.e. there previously was no thermally conductive stud which is also electrically conductive, and hence no need for further electrical isolation between the bottom shield and substrate. 
   From this point on, standard reader processing is used to complete manufacture of the MR transducer, and is not described in detail as such processing is well known to those of skill in the art. It should be noted, however, that the MR element is laterally displaced from the underlying stud  16  to ensure that the topology from the boundary between the stud  16  and the underlying alumina  14  does not propagate to the MR element where it could influence the magnetics of the sensor. This lateral displacement can more clearly be seen when viewing the top view of the thin-film head shown in  FIG. 2 , where the MR element  22  is shown to be outside the dotted stud region  16 . 
   It is also possible to create the conductive stud  16  beneath the shield  20  in many other ways. The conductive stud material could be deposited by sputtering, evaporation, ion beam deposit, etc. Alternatively, the underlayer  14  could initially be deposited on the substrate  12  and patterned to create voids. The conductive stud material  16  is then deposited to fill the voids, and polished, followed by deposition of the thin insulating layer  18  and formation of the bottom shield  20 . 
   It has thus been shown how a thin-film head can be built that has improved characteristics by mitigating undesired thermal events that would otherwise cause improper data detection when reading information stored in a magnetic media. 
   The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.