Abstract:
A magnetic write head having a spin torque oscillator with a magnetic field sensor for accurately determining magnetic field oscillation frequency. The spin torque oscillator has one or more tunnel junction (TMR) sensors formed at the side of the spin torque oscillator. The TMR sensor advantageously detects a magnetic field signal that is an additive signal of both fields from the spin polarization layer and the magnetic field generation layer, thereby providing efficient detection of magnetic field and associated oscillation frequency.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to magnetic data recording, and more particularly to a magnetic write head having a magnetic spin torque oscillator located between a magnetic write pole and a magnetic trailing shield and having a structure for detecting the magnetic oscillation frequency of the spin torque oscillator. 
       BACKGROUND 
       [0002]    At the heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected tracks on the rotating disk. The read and write heads are directly located on a slider that has an air beating surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
         [0003]    The write head includes at least one coil, a write pole and one or more return poles. When current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the coil, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic media, thereby recording a bit of data. The write field then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head. 
         [0004]    A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor, a Tunnel Junction Magnetoresistive (TMR) sensor or a scissor type magnetoresistive sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the magnetic media. 
       SUMMARY 
       [0005]    The present invention provides a magnetic write head for microwave assisted magnetic recording. The magnetic write head includes a spin torque oscillator having a leading edge, a trailing edge and a side extending from the leading edge to the trailing edge. The write head also includes a magnetic sensor formed at the side of the spin torque oscillator. 
         [0006]    The magnetic sensor formed at the side of the spin torque oscillator advantageously detects magnetic field from the spin torque oscillator in order to accurately determine the oscillation frequency of the oscillating magnetic field produced by the spin torque oscillator. 
         [0007]    The spin torque oscillator can be formed with a magnetic spin polarization layer, a magnetic field generation layer, and a non-magnetic interlayer located between the spin polarization layer and the magnetic field generation layer. The magnetic sensor formed at the side of the spin torque oscillator advantageously detects magnetic field from both the magnetic field generation layer and also the magnetic spin polarization layer and does so in an additive manner to produce a strong signal for accurately determining the magnetic oscillation frequency of the field generated by the spin torque oscillator. 
         [0008]    The magnetic sensor formed at the side of the spin torque oscillator can be in the form of a tunnel junction sensor, including a non-magnetic barrier layer such as Mg—O formed at the side of the spin torque oscillator, a magnetic layer such as Co—Fe—B formed on the non-magnetic barrier layer, and an electrically conductive lead layer formed on the magnetic layer. 
         [0009]    These and other features and advantages of the invention will be apparent upon reading of the following detailed description of the embodiments taken in conjunction with the figures in which like reference numeral indicate like elements throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale. 
           [0011]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
           [0012]      FIG. 2  is side, cross-sectional, schematic view of a magnetic read write head; 
           [0013]      FIG. 3  is an enlarged view of a spin torque oscillator structure for use with the write head of  FIG. 2 , as seen from the media facing surface; 
           [0014]      FIG. 4  is a side, cross sectional view of a spin torque oscillator for use with the magnetic read write head of  FIG. 2  according to an alternate embodiment; and 
           [0015]      FIGS. 5-7  are views of a spin torque oscillator in various intermediate stages of manufacture illustrating a method of manufacturing a spin torque oscillator according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein. 
         [0017]    Referring now to  FIG. 1 , there is shown a disk drive  100 . The disk drive  100  includes a housing  101 . At least one rotatable magnetic disk  112  is supported on a spindle  114  and rotated by a disk drive motor  118 . The magnetic recording on each disk may be in the form of annular patterns of concentric data tracks (not shown) on the magnetic disk  112 . 
         [0018]    At least one slider  113  is positioned near the magnetic disk  112 , each slider  113  supporting one or more magnetic head assemblies  121 . As the magnetic disk rotates, slider  113  moves in and out over the disk surface  122  so that the magnetic head assembly  121  can access different tracks of the magnetic disk where desired data are written. Each slider  113  is attached to an actuator arm  119  by way of a suspension  115 . The suspension  115  provides a slight spring force which biases the slider  113  against the disk surface  122 . Each actuator arm  119  is attached to an actuator means  127 . The actuator cans  127  as shown in  FIG. 1  may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by the controller  129 . 
         [0019]    During operation of the disk storage system, the rotation of the magnetic disk  112  generates an air bearing between the slider  113  and the disk surface  122 , which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of the suspension  115  and supports the slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
         [0020]    The various components of the disk storage system are controlled in operation by control signals generated by control unit  129 , such as access control signals and internal clock signals. Typically, the control unit  129  comprises logic control circuits, and a microprocessor. The control unit  129  generates control signals to control various system operations such as drive motor control signals on line  123  and head position and seek control signals on line  128 . The control signals on line  128  provide the desired current profiles to optimally move and position the slider  113  to the desired data track on the media  112 . Write and read signals are communicated to and from write and read heads  121  by way of recording channel  125 . 
         [0021]    With reference to  FIG. 2 , a magnetic read/write head  200  can include a read head  202  and a write head  204 . The read head  202  can include a read sensor  206  such as a giant magnetoresistive sensor or tunnel junction sensor, which can be sandwiched between first and second magnetic shields  208 ,  210 . The space between the read and write heads  202 ,  204  can be filled with a non-magnetic, electrically insulating material  212 , as can the space behind the sensor  206  between the shields  208 ,  210 . 
         [0022]    The write head  204  can include a magnetic write pole  214  and a magnetic return pole  216 , both of which can extend to a media facing surface MFS. The magnetic return pole  216  can be connected with the magnetic write pole  214  by a magnetic back gap layer  218  and a magnetic shaping layer  220 . The magnetic shaping layer  220  helps to channel magnetic flux to the tip of the magnetic write pole  214 . The write head  204  can also include a trailing magnetic shield  222  formed near the trailing edge of the write pole  214  at the media facing surface MFS. The trailing magnetic shield  222  can be connected with the back portion of the write head  204  by a trailing magnetic return pole  224 . 
         [0023]    The write head  204  also includes a non-magnetic, electrically conductive write coil  226  (shown in cross section in  FIG. 2 ) that can pass above and below the write pole  214 . The write coil  226  can be embedded in a non-magnetic, electrically insulating material such as alumina  228 . When an electrical current flows through the write coils  226 , a magnetic field is generated. This causes a magnetic flux to flow through the write pole  214 . The resulting write field travels from the tip of the write pole  214  to a magnetic media (not shown in  FIG. 2 ) and then travels back through the return pole  216 . Because the return pole  216  has a larger cross section at the media facing surface NHS than does the write pole  214  the return of the magnetic write field to the return pole  216  does not erase the previously recorded bit of data. 
         [0024]    As demands for increased data density require ever smaller magnetic bit sizes, the magnetic bits recorded to a recording media become inherently, magnetically unstable. In order to make the recorded magnetic bits more stable, the magnetic media can be designed to have an increased magnetic anisotropy, and or magnetic coercivity. This however makes the media harder to record to, especially with the smaller write pole required to record the smaller magnetic bit. 
         [0025]    One way to overcome this challenge is to generate an oscillating magnetic field just at or adjacent to the location of the write pole. This oscillating magnetic field temporarily reduces the magnetic anisotropy of the magnetic media, making it easier to record to. To this end, as shown in  FIG. 2  a magnetic oscillator such as a spin torque oscillator  230  can be employed. The spin torque oscillator  230  can be located between the write pole  214  and the trailing magnetic shield  222 . The spin torque oscillator  230  generates an oscillating magnetic field that moves in a precessional manner as indicated by arrow  308 . 
         [0026]    A current source  234  can be provided to supply an electrical current to flow through the spin torque oscillator  230 . The current source  234  can be connected with the magnetic write head  204  so that current flows between the write pole  214  and the trailing shield  222  through the spin torque oscillator  230 . This current causes the spin torque oscillator to generate the oscillating magnetic field  308 . An electrically insulating layer  235  can be provided at the back of the write head  204  to prevent this electrical current from being shunted through the back portion of the write head  204 . 
         [0027]      FIG. 3  shows an enlarged view of the spin torque oscillator  230  according to one embodiment. The spin torque oscillator  230  includes two magnetic layers  302 ,  304  separated by a non-magnetic interlayer  306  located between the magnetic layers  302 ,  304 . The first magnetic layer  302  is a spin polarization layer, and the second magnetic layer  304  is a magnetic field generation layer. When a current flows through the spin torque oscillator as indicated by arrow i, in a direction perpendicular to the layers  302 ,  304 ,  306 , the electrons flowing through the spin polarization layer  302  become spin polarized due to the magnetization of the spin polarization layer  302 . When these spin polarized electrons flow from the spin polarization layer  302 , through the interlayer  306  to the field generation layer  304 , they impart a spin torque on the field generation layer  304 . This spin torque causes the magnetization of the field generation layer  304  to oscillate as indicated by arrow  308 . The magnetic oscillation  308  of the field generation layer  304  can impart an oscillation  314  in the spin polarization layer  302  as a result of magnetostatic coupling between the magnetic layers  302 ,  304 . In addition to the layers  302 ,  304 ,  306 , the spin torque oscillator  230  may also include a seed layer  310  to promote a desired grain structure in the above formed layers  302 ,  304 ,  306  and may also include a capping layer  312  at the end opposite the seed layer  310 . 
         [0028]    An important design parameter for magnetic recording systems that employ spin torque oscillators is the frequency of the magnetic oscillation of the spin torque oscillation. A magnetic media has an optimal magnetic frequency oscillation range for promoting the writing of magnetic data to the magnetic media. Therefore, in order to maximize writing efficiency, the magnetic oscillation frequency of the spin torque oscillator is preferably matched to the magnetic media of the magnetic recording system. 
         [0029]    However, previously there has not been an effective way to measure the oscillation frequency of the spin torque oscillator. Measuring the voltage across the spin torque oscillator in a direction perpendicular to the layers  302 ,  304 ,  306  does not provide an effective measure of the magnetic field oscillation frequency. This voltage change is a factor of the relative angles of the oscillations  308 ,  314  and they combine in a subtractive, rather than additive manner, resulting in a weak signal. Furthermore, use of a conventional field sensor, such as a sensor wire located adjacent to the spin torque oscillator  230  also fails to provide an effective measure of oscillation frequency. This is because spin torque oscillators operate at very high frequencies at which conventional magnetic field sensors saturate. 
         [0030]    Therefore, in order to accommodate this long felt, but unmet need, the write head is provided with tunnel junction magnetic sensors  316  formed at the sides of (or behind the spin torque oscillator  230 . The tunnel junction magnetic sensor  316  can be at one side, or can be at both sides of the sensor as shown. As shown in  FIG. 3 , the magnetic tunnel junction sensor  316  includes a non-magnetic barrier layer  318 , a magnetic layer  320  and a non-magnetic, electrically conductive side lead  322 . The side lead  322  is electrically insulated from the shield  222  by an electrically insulating layer  325 , which may be a material such as alumina. 
         [0031]    The non-magnetic barrier layer  318  can be a material such as Mg—O, and as shown in  FIG. 3 , the non-magnetic barrier layer  318  can be thicker over the write pole  214  and thinner along the side of the spin torque oscillator  230 . The thicker barrier layer  214  over the write pole  214  will prevent current shunting to the write pole  214 , and the barrier layer  318  should be thin enough along the side of the spin torque oscillator  230  to allow quantum tunneling of charge carriers there-through in a manner similar to a standard tunnel junction magnetic sensor as might be used to read a magnetic signal from a magnetic media. The magnetic layer  320  can be constructed of Co—Fe—B, and the side leads  322  can be constructed of an electrically conductive material such as Cu or Au. 
         [0032]    As a result of spin tunneling of electrons through the barrier layer  318 , the electrical resistance between the spin torque oscillator  230  and the lead  322  will vary depending upon the relative directions of magnetizations of the magnetic layers  302 ,  304  and the magnetic layer  320  of the tunnel junction sensor. Therefore, because the magnetization  308 ,  314  of the magnetic layers  302 ,  304  are oscillating as described above, the resistance across the harrier layer will  318  will vary with the magnetic oscillations  308 ,  314 . What&#39;s more, this variation in electrical resistance will be additive for both the magnetic oscillations  314 ,  308 . By measuring the electrical resistance between the spin torque oscillator  230  and the lead  322 , the frequency of the oscillations  308 ,  314  can be efficiently and reliably measured. The lead  322  effectively forms a third electrical terminal, in addition to those provided by the write pole  214  and trailing shield  222 . The lead  322  and either or both of the write pole  214  and/or trailing shield  222  can be connected with circuitry  324  that can apply a voltage between the spin torque oscillator  230  and the lead  322 . The circuitry  324  can measure the change in resistance across the layers  318 ,  320  and can also determine the frequency of the electrical resistance change. Therefore, the frequency of magnetic oscillation produced by the spin torque oscillator  230  can be accurately measured. 
         [0033]      FIG. 4  illustrates an alternate embodiment and shows a cross sectional view along a plane that is perpendicular to the media facing surface MFS.  FIG. 4  shows a tunnel junction sensor  316  located at the back edge (stripe height) of the spin torque oscillator  230 . The structure of the tunnel junction sensor  316  can be similar to that described above, having a non-magnetic electrically insulating barrier layer  318 , magnetic layer  320  and an electrically conductive lead  322 . Again, the layer  322  is electrically insulated from the lead  222  by an electrically insulating layer  325 . It should also be pointed out that, the tunnel junction sensor  316  formed at the back edge of the spin torque oscillator  230  can be in lieu of those formed at the sides as described above with reference to  FIG. 3 . Or, alternatively, the back edge tunnel junction sensor  316  can be in addition to those formed at the sides so as to form a tunnel junction sensor  316  that wraps around the sides and back edge of the spin torque oscillator. 
         [0034]    The above described side formed tunnel junction sensors  316  provide a way of producing a strong signal for determining the frequency of the magnetic oscillation of the magnetizations  308 ,  314  produced by the spin torque oscillator  230 . If a signal were measured across the spin torque oscillator  230  in a direction perpendicular to the planes of the layers  302 ,  304 ,  306  (essentially using the spin torque oscillator  230  as a giant magnetoresistive (GMR) sensor) the signal would be subtractive, with the signal resulting from oscillation  314  being subtracted from the signal resulting from oscillation  308 . The resulting signal would, therefore, be very week and ineffective. On the other hand, using the side tunnel junction sensors  316 , the signals from the magnetizations  308 ,  314  are additive rather than subtractive, resulting in a very strong effective signal. 
         [0035]    The side tunnel junction sensors  316  can be used to determine the actual oscillation frequency of the spin torque oscillator  230  early in the manufacture process. In this way, if the frequency is not within a desired range, the head can be scrapped without unnecessary further manufacturing. In addition, the use of the side tunnel junction sensors  316  can be used to determine the oscillation frequency during manufacture, and the various manufactured heads can be grouped by oscillation frequency to be later matched up with magnetic media most suitable for use in that frequency range. This can further reduce waste by allowing the head use to be optimized while avoiding the need to scrap heads or entire magnetic recording systems. 
         [0036]      FIGS. 5-7  illustrate a magnetic spin torque oscillator in various intermediate stages of manufacture in order to illustrate a method of manufacturing a magnetic write head such as those described above. With reference to  FIG. 5 , the magnetic layers of the spin torque oscillator are deposited over the magnetic write pole  214 . These layers can include: a seed layer  310 ; a first magnetic layer  302  deposited over the seed layer  310 ; a non-magnetic intermediate layer  306  deposited over the first magnetic layer  302 ; a second magnetic layer  304  deposited over the non-magnetic intermediate layer; and a capping layer  312  deposited over the second magnetic layer  304 . A mask  502  is formed over these layers, the mask being configured to define a width and/or stripe height of the spin torque oscillator. 
         [0037]    With reference to  FIG. 6 , a material removal process such as ion milling is performed to remove portions of the layers  310 ,  302 ,  306 ,  304 ,  312  that are not protected by the mask  502 . A non-magnetic, electrically insulating barrier layer such as Mg—O  318  is then deposited. The barrier layer  318  is deposited in such a manner as to have a thickness at the sides of the layers  302 ,  306 ,  304  that allows it to function as a barrier layer and to be thicker over the write pole  214  so as to prevent current shunting through the write pole  214 . Then, a magnetic layer  320  such as CoFeB is deposited over the barrier layer  318 , and an electrically conductive lead  322  such as Cu or Au is deposited over the magnetic layer  320 . An electrically insulating layer  325  is deposited over the lead material  322 , and can be a material such as alumina. Then, with reference to  FIG. 7 , a mask lift-off process and/or chemical mechanical polishing is performed to remove the mask  502  ( FIG. 6 ) and planarize the surface. The insulating layer  325  is deposited at a level and thickness such that it will remain after the mask removal and/or chemical mechanical polishing. 
         [0038]    While various embodiments have been described above, it should be understood that they have been presented by way of example only and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the inventions should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following Maims and their equivalents.