Patent Publication Number: US-2015062759-A1

Title: Capping materials for magnetic read head sensor

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention generally relate to a magnetic read head for use in a hard disk drive. 
     2. Description of the Related Art 
     The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider towards the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of 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 signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
     As the areal storage density in hard disk drives (HDDs) increases, the demand for greater magnetoresistive (MR) ratio and reduction of shield to shield distance has increased. Since high enough MR using MgO barrier based magnetic tunnel junction (MTJ) has been obtained, the reduction of shield to shield distance, or read gap to increase the spatial resolution along the track and magnetic parameters such as free layer magnetostriction, anisotropy and damping constant are becoming important factors in order to meet the required high storage density. 
     Therefore, there is a need in the art for a magnetic head having a reduced read gap and improved magnetostriction and damping constant. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally relate to a magnetic head having a sensor structure comprising a pinned layer, a spacer layer, a free layer and a capping structure. The free layer has a topmost layer comprising CoB and the capping structure comprises an X layer adjacent to CoB layer, where X is an element such as Hf, Zr, Ti, V, Nb, or Ta etc. 
     In one embodiment, a magnetic head is disclosed. The magnetic head comprises a first shield layer and a sensor structure disposed over a first portion of the first shield layer. The sensor structure has sidewalls and the sensor structure comprises a pinned layer disposed over the first shield layer, a spacer layer disposed over the pinned layer, and a free layer disposed over the spacer layer. The free layer comprises at least two layers and the topmost layer comprises CoB. The sensor structure further comprises a capping structure disposed on the free layer. The capping structure comprises an X layer disposed over the CoB free layer. X comprises an element selected from the group consisting of Hf, Zr, Ti, V, Nb, and Ta etc. The magnetic head further comprises a bias layer disposed over a second portion of the first shied layer and over the sidewalls of the sensor structure, and a second shield layer disposed over the bias layer and the sensor structure. 
     In another embodiment, a magnetic head is disclosed. The magnetic head comprises a first shield layer and a sensor structure disposed over a first portion of the first shield layer. The sensor structure has sidewalls and the sensor structure comprises a pinned layer disposed over the first shield layer, a spacer layer disposed over the pinned layer, and a free layer disposed over the spacer layer. The free layer comprises at least two layers and the topmost layer comprises CoB. The sensor structure further comprises a capping structure disposed on the free layer. The capping structure comprises an X layer disposed over the CoB free layer. X comprises an element selected from the group consisting of Hf, Zr, Ti, V, Nb, and Ta. The magnetic head further comprises an insulation layer disposed over a second portion of the first shied layer and over the sidewalls of the sensor structure, a bias layer disposed over the insulation layer, a bias capping structure disposed over the bias layer, and a second shield layer disposed over the bias capping structure, the bias layer, the insulation layer and the sensor structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  illustrates an exemplary magnetic disk drive, according to an embodiment of the invention. 
         FIG. 2A  is a side view of a read/write head and magnetic disk of the disk drive of  FIG. 1 , according to one embodiment of the invention. 
         FIG. 2B  is a schematic cross-sectional view of portions of a magnetic head according to one embodiment of the invention. 
         FIG. 3A  is a schematic cross-sectional view of a capping structure according to one embodiment of the invention. 
         FIG. 3B  is a schematic cross-sectional view of a capping structure according to one embodiment of the invention. 
         FIG. 4A  is a schematic cross-sectional view of a portion of a sensor structure of the magnetic head of  FIG. 2B  according to one embodiment of the invention. 
         FIG. 4B  is a schematic cross-sectional view of a portion of a sensor structure of the magnetic head of  FIG. 2B  according to one embodiment of the invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     Embodiments of the present invention generally relate to a magnetic head having a sensor structure comprising a pinned layer, a spacer layer, a free layer and a capping structure. The free layer has a topmost layer comprising CoB and the capping structure comprises an X layer, where X is an element such as Hf, Zr, Ti, V, Nb, or Ta. 
       FIG. 1  illustrates a top view of an exemplary hard disk drive (HDD)  100 , according to an embodiment of the invention. As illustrated, HDD  100  may include one or more magnetic disks  110 , actuator  120 , actuator arms  130  associated with each of the magnetic disks  110 , and spindle motor  140  affixed in a chassis  150 . The one or more magnetic disks  110  may be arranged vertically as illustrated in  FIG. 1 . Moreover, the one or more magnetic disks may be coupled with the spindle motor  140 . 
     Magnetic disks  110  may include circular tracks of data on both the top and bottom surfaces of the disk. A magnetic head  180  mounted on a slider may be positioned on a track. As each disk spins, data may be written on and/or read from the data track. Magnetic head  180  may be coupled to an actuator arm  130  as illustrated in  FIG. 1 . Actuator arm  130  may be configured to swivel around actuator axis  131  to place magnetic head  180  on a particular data track. 
       FIG. 2A  is a fragmented, cross-sectional side view through the center of a read/write head  200  mounted on a slider  201  and facing magnetic disk  202 . The read/write head  200  and magnetic disk  202  may correspond to the magnetic head  180  and magnetic disk  110 , respectively in  FIG. 1 . In some embodiments, the magnetic disk  202  may be a “dual-layer” medium that includes a perpendicular magnetic data recording layer (RL)  204  on a “soft” or relatively low-coercivity magnetically permeable underlayer (PL)  206  formed on a disk substrate  208 . The read/write head  200  includes an ABS, a magnetic write head  210  and a magnetic read head  211 , and is mounted such that its ABS is facing the magnetic disk  202 . In  FIG. 2A , the disk  202  moves past the write head  210  in the direction indicated by the arrow  232 , so the portion of slider  201  that supports the read/write head  200  is often called the slider “trailing” end  203 . 
     In some embodiments, the magnetic read head  211  is a MR read head that includes an MR sensing element  230  located between MR shields  51  and S 2 . In other embodiments, the magnetic read head  211  is a MTJ read head that includes a MTJ sensing device  230  located between MR shields S 1  and S 2 . The RL  204  is illustrated with perpendicularly recorded or magnetized regions, with adjacent regions having magnetization directions, as represented by the arrows located in the RL  204 . The magnetic fields of the adjacent magnetized regions are detectable by the MR (or MTJ) sensing element  230  as the recorded bits. 
     The write head  210  includes a magnetic circuit made up of a main pole  212  and a yoke  216 . The write head  210  also includes a thin film coil  218  shown in the section embedded in non-magnetic material  219  and wrapped around yoke  216 . In an alternative embodiment, the yoke  216  may be omitted, and the coil  218  may wrap around the main pole  212 . A write pole  220  is magnetically connected to the main pole  212  and has an end  226  that defines part of the ABS of the magnetic write head  210  facing the outer surface of disk  202 . 
     Write pole  220  is a flared write pole and includes a flare point  222  and a pole tip  224  that includes an end  226  that defines part of the ABS. The flare may extend the entire height of write pole  220  (i.e., from the end  226  of the write pole  220  to the top of the write pole  220 ), or may only extend from the flare point  222 , as shown in  FIG. 2A . In one embodiment the distance between the flare point  222  and the ABS is between about 30 nm and about 150 nm. 
     The write pole  220  includes a tapered surface  271  which increases a width of the write pole  220  from a first width W 1  at the ABS to a second width W 2  away from the ABS. In one embodiment, the width W 1  may be between around 60 nm and 200 nm, and the width W 2  may be between around 120 nm and 350 nm. While the tapered region  271  is shown with a single straight surface in  FIG. 2A , in alternative embodiment, the tapered region  271  may include a plurality of tapered surface with different taper angles with respect to the ABS. 
     The tapering improves magnetic performance. For example, reducing the width W 1  at the ABS may concentrate a magnetic field generated by the write pole  220  over desirable portions of the magnetic disk  202 . In other words, reducing the width W 1  of the write pole  220  at the ABS reduces the probability that tracks adjacent to a desirable track are erroneously altered during writing operations. 
     While a small width of the write pole  220  is desired at the ABS, it may be desirable to have a greater width of the write pole  220  in areas away from the ABS. A larger width W 2  of the write pole  220  away from the ABS may desirably increase the magnetic flux to the write pole  220 , by providing a greater thickness of the write pole  220  in a direction generally parallel to the ABS. In operation, write current passes through coil  218  and induces a magnetic field (shown by dashed line  228 ) from the write pole  220  that passes through the RL  204  (to magnetize the region of the RL  204  beneath the write pole  220 ), through the flux return path provided by the PL  206 , and back to an upper return pole  250 . In one embodiment, the greater the magnetic flux of the write pole  220 , the greater is the probability of accurately writing to desirable regions of the RL  204 . 
       FIG. 2A  further illustrates one embodiment of the upper return pole or magnetic shield  250  that is separated from write pole  220  by a nonmagnetic gap layer  256 . In some embodiments, the magnetic shield  250  may be a trailing shield wherein substantially all of the shield material is on the trailing end  203 . Alternatively, in some embodiments, the magnetic shield  250  may be a wrap-around shield wherein the shield covers the trailing end  203  and also wraps around the sides of the write pole  220 . As  FIG. 2A  is a cross section through the center of the read/write head  200 , it represents both trailing and wrap-around embodiments. 
     Near the ABS, the nonmagnetic gap layer  256  has a reduced thickness and forms a shield gap throat  258 . The throat gap width is generally defined as the distance between the write pole  220  and the magnetic shield  250  at the ABS. The shield  250  is formed of magnetically permeable material (such as Ni, Co and Fe alloys) and gap layer  256  is formed of nonmagnetic material (such as Ta, TaO, Ru, Rh, NiCr, SiC or Al 2 O 3 ). A taper  260  in the gap material provides a gradual transition from the throat gap width at the ABS to a maximum gap width above the taper  260 . This gradual transition in width forms a tapered bump in the non-magnetic gap layer that allows for greater magnetic flux density from the write pole  220 , while avoiding saturation of the shield  250 . 
     It should be understood that the taper  260  may extend either more or less than is shown in  FIG. 2A . The taper may extend upwards to an end of shield  250  opposite the ABS (not shown), such that the maximum gap width is at the end of the shield opposite the ABS. The gap layer thickness increases from a first thickness (the throat gap width) at the ABS to greater thicknesses at a first distance from the ABS, to a greatest thickness at a second distance (greater than the first distance) from the ABS. 
       FIG. 2B  is a schematic cross-sectional view of portions of magnetic head  211  according to one embodiment. The thickness of each layer, and the width of each layer, are for example only, and each layer may be thicker/thinner and/or wider/narrower. The magnetic head  211  includes a first shield layer  231 . The first shield layer  231  may comprise a ferromagnetic material. Suitable ferromagnetic materials that may be utilized include Ni, Fe, Co, NiFe, NiFeCo, NiCo, CoFe and combinations thereof 
     The magnetic head  211  also includes a sensor structure  250  comprising a pinned magnetic layer  233 , a spacer layer  234 , a free layer  236  and a sensor capping structure  238 . The pinned magnetic layer  233  may be one of several types of pinned layers, such as a simple pinned, antiparallel pinned, self pinned or antiferromagnetic pinned sensor. For purposes of simplicity, the sensor will be described herein as a self pinned sensor having a first pinned layer, a second pinned layer, and a non magnetic layer, such as Ru sandwiched therebetween. The first and second pinned layers can be constructed of several magnetic materials such as, for example NiFe, CoFe, CoFeB, or diluted magnetic alloys etc. The spacer layer  234  may comprise an insulating material such as MgO or alumina or a metal layer such as Cu, Ag or AgSn etc. The free layer  236  and the sensor capping structure  238  are described in detail below. 
     Following the formation of the sensor structure  250 , an insulating layer  240  may be deposited on the first shield layer  231  as well as the sidewalls of the sensor structure  250 . The insulating layer  240  may comprise an insulating material such as aluminum oxide or silicon nitride etc. The insulating layer  240  may be deposited by well known deposition methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), ion beam sputtering (IBD), etc. After the insulating layer  240  is deposited, a bias layer  242  is then deposited. The bias layer  242  may comprise a single or laminated magnetic materials such as CoPt, high moment CoFe or NiFe etc. 
     Once the bias layer  242  is deposited, a bias capping structure  244  may be formed over the bias layer  242 . In one embodiment, the bias capping structure  244  may comprise a multiple layered structure comprising one or combination of a tantalum layer, an iridium layer, a chromium layer, a titanium layer and a ruthenium layer. A second shield layer  246  is deposited over the bias capping structure  244 , the bias layer  242 , the insulating layer  240 , and the sensor capping structure  238 . The second shield layer  246  may comprise a ferromagnetic material. Suitable ferromagnetic materials that may be utilized include Ni, Fe, Co, NiFe, NiFeCo, NiCo, CoFe and combinations thereof. 
       FIG. 3A  is a schematic cross-sectional view of the sensor capping structure  238  according to one embodiment of the invention. The capping structure  238  comprises a hafnium layer  302 , a first ruthenium layer  304  disposed over the hafnium layer  302 , a tantalum layer  306  disposed over the first ruthenium layer  304 , and a second ruthenium layer  308  disposed over the tantalum layer  306 . The hafnium layer  302  and the first ruthenium layer  304  may have a combined thickness of about 15 Angstroms. The tantalum layer  306  may have a thickness of about 15 Angstroms and the second ruthenium layer  308  may have a thickness of about 50 Angstroms. 
       FIG. 3B  is a schematic cross-sectional view of the sensor capping structure  238  according to another embodiment of the invention. The capping structure  238  comprises a first capping layer  312  and a second capping layer  314 . The first capping layer  312  may be an element such as hafnium, zirconium, titanium, vanadium, niobium, or tantalum. The second capping layer  314  may be a single layer or a multi-layer structure. The second capping layer  314  functions as a milling buffer and is also used to prevent oxidation during post sensor processes. In one embodiment, the second capping layer  314  comprises a first ruthenium layer, a tantalum layer, and a second ruthenium layer, which is similar to the layers  304 ,  306  and  308  described in  FIG. 3A . 
     An intermixing layer  310  is formed as the first capping layer  312  is deposited on the topmost layer of the free layer  236  (described in detail below), and the intermixing layer  310  has a thickness ranging from about 4 Angstroms to about 6 Angstroms. In one embodiment, the first capping layer  312  comprises hafnium and the intermixing layer  310  comprises CoHf. 
       FIG. 4A  is a schematic cross-sectional view of a portion of the sensor structure  250  of the magnetic head  211  according to one embodiment. As shown in  FIG. 4A , a free layer  402 , which may be the free layer  236  described in  FIG. 2B , comprises a first magnetic layer  404  and a second magnetic layer  406 . The first magnetic layer  404  may comprise Co, Fe, or combinations thereof. In one embodiment, the first magnetic layer  404  comprises C ox F e100−x , where x is a positive integer less than 100. The first magnetic layer  404  may comprise multiple layers of CoFe, where each CoFe layer has a different iron atomic content ranging from zero to 100%. The second magnetic layer  406  may comprise Co, Fe, B, or combinations thereof. In one embodiment, the second magnetic layer  406  comprises C ox F e80−xB20 , where x is a positive integer less than  80 . The second magnetic layer  406  has a different composition as the first magnetic layer  404 . In one embodiment, the second magnetic layer  406  comprises CoB. The capping structure  238  as described in  FIGS. 3A  or  3 B is disposed over the free layer  402 . 
     The first magnetic layer  404  has high spin polarization, high moment and positive magnetostriction. The second magnetic layer  406  has a negative magnetostriction, so the overall magnetostriction is near zero. The hafnium layer  302  or the first capping layer  312  in the capping structure  238  is deposited at the interface between the free layer  402  and the capping structure  238 . Consequently, magnetostriction is reduced due to boron diffusion out of the second magnetic layer  406  and the formation of the intermixing layer  310  at the interface. With the second magnetic layer  406  and the capping structure  238 , the free layer  402  has equivalent magnetic and electrical performances while having a reduced thickness that results in reader gap reduction which is desired for bit error rate improvement. The free layer  402  may have a thickness of about 50 Angstroms, which is about 15 to 20 Angstroms less than the thickness of conventional multilayer free layer having a conventional capping structure disposed thereon while with equivalent magnetic and electrical performance. In the embodiment where the second magnetic layer  406  is CoB, the boron in the CoB layer  406  diffuses from the free layer  402  to the hafnium layer  302  or the first capping layer  312 . Such diffusion leaves the CoB layer  406  more Co dominant, which leads to the free layer  402  having negative magnetostriction. 
     In addition, hafnium has low Young&#39;s modulus (i.e., less stiff), compared to ruthenium or tantalum in a conventional capping layer. A stiff capping layer having high Young&#39;s modulus may prevent the second magnetic layer of a two-layered free layer from expanding, causing the first magnetic layer having positive magnetostriction to become dominant for total magnetostriction. Thus, to maximize negative magnetostriction from the second magnetic layer, a material having low Young&#39;s modulus may be used. The hafnium layer  302  in the capping structure  238  has a Young&#39;s modulus of about 78 N/m 2 , while ruthenium and tantalum have a Young&#39;s modulus of about 414 N/m 2  and 186 N/m 2 , respectively. 
     The hafnium layer  302  in the capping structure  238  also reduces the spin pumping effect, resulting in a low free layer damping constant, which may lead to better device performance due to potential noise reduction and a gain in signal to noise ratio (SNR). 
       FIG. 4B  is a schematic cross-sectional view of a portion of the sensor structure  250  of the magnetic head  211  according to one embodiment. As shown in  FIG. 4B , a free layer  408 , which may be the free layer  236  described in  FIG. 2B , comprises a first magnetic layer  410 , a second magnetic layer  412 , a blocking layer  414 , and a third magnetic layer  416 . The first magnetic layer  410  may comprise Co, Fe, or combinations thereof. In one embodiment, the first magnetic layer  410  comprises Co x Fe 100−x , where x is a positive integer less than  100 . The second magnetic layer  412  may comprise Co, Fe, B, or combinations thereof. In one embodiment, the second magnetic layer  412  comprises Co x Fe 80−xB20 , where x is a positive integer less than 80. The blocking layer  414  may comprise an amorphous diluted magnetic or non-magnetic material such as Hf, Zr or Ta doped alloy. The third magnetic layer  416  may comprise Ni, Fe, or combinations thereof. In one embodiment, the third magnetic layer  416  comprises Ni x Fe 100−x , where x is a positive integer less than 100. The capping structure  238  as described in  FIG. 3  is disposed over the free layer  408 . 
     With the four layered free layer  408 , the first and second magnetic layers  410 ,  412  have positive magnetostriction and the third magnetic layer  416  has negative magnetostriction. As described above, the hafnium layer  302  in the capping structure  238  may help in reducing magnetostriction and damping constant. 
     In summary, a sensor structure in a magnetic head is disclosed. The sensor structure has a free layer with a topmost layer comprised of CoB. A capping structure is disposed on the free layer and an intermixing layer is formed at the interface between the CoB layer and the capping structure. The bottom layer of the capping structure disposed over the free layer comprises an element such as Hf, Zr, Ti, V, Nb, or Ta. The CoB free layer, intermixing layer and the bottom layer of the capping structure causes the free layer to have a negative magnetostriction. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.