Read sensors of the CPP type having nitrogenated hard bias layers and method of making the same

A read sensor of the current-perpendicular-to-the-planes (CPP) type includes a sensor stack structure formed in a central region between first and second shield layers which serve as leads for the read sensor; insulator layers formed in side regions adjacent the central region; seed layer structures formed over the insulator layers in the side regions; and hard bias layers formed over the seed layer structures in the side regions. The hard bias layers are made of a nitrogenated cobalt-based alloy, such as nitrogenated cobalt-platinum (CoPt). Suitable if not exemplary coercivity and squareness properties are exhibited using the nitrogenated cobalt-based alloy. The hard bias layers may be formed by performing an ion beam deposition of cobalt-based materials using a sputtering gas (e.g. xenon) and nitrogen as a reactive gas.

BACKGROUND

1. Field of the Technology

This present disclosure relates generally to magnetic read heads having read sensors for reading information signals from a magnetic medium, and more particularly to read sensors of the current-perpendicular-to-the-planes (CPP) type having hard bias layers made of nitrogenated cobalt-based alloys for improved hard magnet properties and methods of making the same.

2. Description of the Related Art

Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.

In high capacity disk drives, magnetoresistive read (MR) sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer. A common type of MR sensor is the giant magnetoresistance (GMR) sensor which manifests the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron (NiFe), cobalt (Co), or nickel-iron-cobalt (NiFeCo)) separated by a layer of nonmagnetic material (e.g., copper (Cu)) are generally referred to as spin valve (SV) sensors manifesting the SV effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., nickel-oxide (NiO), iridium-manganese (IrMn) or platinum-manganese (PtMn)) layer.

The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (the signal field). In the SV sensors, SV resistance varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. In addition to the magnetoresistive material, the GMR sensor has conductive lead structures for connecting the GMR sensor to a sensing means and a sense current source. Typically, a constant current is sent through the GMR sensor through these leads and the voltage variations caused by the changing resistance are measured via these leads.

To illustrate,FIG. 1shows a prior art SV sensor100of the current-perpendicular-to-the-planes (CPP) type having side regions104and106which are separated by a central region102. A free layer110is separated from a pinned layer120by a non-magnetic, electrically-conducting or insulating spacer115. Spacer115may be made of electrically-conductive materials if sensor100is a GMR sensor, or alternatively, electrically-insulative materials if sensor100is a tunnel magnetoresistive (TMR) sensor. The magnetization of pinned layer120is fixed by an AFM pinning layer121, which is formed on a shield layer132which may reside on a substrate180(not shown inFIG. 1). Cap layer108, free layer110, spacer layer115, pinned layer120, and AFM pinning layer121are all formed in central region102. Read sensor layers of read sensor100are generally sandwiched between shield layers123and125, which together serve as a shield and as leads for the sensor.

Conventionally, hard bias layers130and135are formed in side regions104and106in order to stabilize free layer10. These hard bias layers130and135are typically formed of a cobalt-based alloy which is sufficiently magnetized and perhaps shielded so that the magnetic fields of the media and/or the write head do not effect the magnetism of the hard magnets. Seed layers150and155are also deposited in side regions104and106underneath hard bias layers130and135to set a texture for the successful deposition of the hard magnets by promoting a desired c-axis in plane orientation. To perform effectively, hard bias layers130and135should have a high coercivity, a high MrT (magnetic remanence×thickness), and a high in-plane squareness on the magnetization curve. A preferred cobalt-based alloy for hard bias layers130and135is cobalt-platinum (CoPt) or cobalt-platinum-chromium (CoPtCr), while seed layers150and155typically comprise chromium (Cr) or other suitable metallic element.

Thus, as illustrated inFIG. 1, seed layers150and155and hard bias layers130and135are formed in side regions104and106, respectively, and provide longitudinal bias for free layer110. Cap layers140and145are formed over these hard bias layers130and135, respectively, in the side regions104and106. Seed layers150and155are formed over insulator layers190and192, respectively, which are in turn formed directly over shield layer123. Shield layers123and125, which are “leads” of the sensor100, provide electrical connections for the flow of the sensing current Isfrom a current source160to the sensor100. In read sensors of the CPP type, sensing current ISis generally forced through the layers in central region102but not through side regions104and106. Sensing means170, which is connected to these leads, senses the change in the resistance due to changes induced in the free layer110by the external magnetic field (e.g. field generated by a data bit stored on a disk). One material for constructing these leads/shield layers140and145is a highly conductive material, such as a metal.

FIG. 2shows a prior art read sensor200of the CPP type, similar to prior art read sensor100(FIG. 1), having side regions204and206separated by a central region202. A free layer210is separated from a pinned layer220by a non-magnetic, electrically-conducting or insulating spacer215. The magnetization of pinned layer220is fixed by an AFM pinning layer221, which is formed on a shield layer223which may reside on a substrate (not shown inFIG. 2). Cap layer208, free layer210, spacer layer215and pinned layer220are all formed in central region202. Unlike prior art read sensor100ofFIG. 1, prior art read sensor200ofFIG. 2is a partial mill design with materials of AFM pinning layer221of sensor200extending into side regions204and206. By “partial mill design”, it is meant that the read sensor layers are not fully etched or milled in side regions204and206prior to the deposition of the seed, hard bias, and lead materials. A partial mill design may be desirable in order to better align free layer210with hard bias layers230and235.

As illustrated inFIG. 2, seed layers250and255and hard bias layers230and235are formed in side regions204and206, respectively. Hard bias layers230and235provide longitudinal biasing for free layer210. Cap layers240and245are formed over these hard bias layers230and235, respectively, in side regions204and206. Seed layers250and255are formed over insulator layers290and292, respectively, which are in turn formed directly over AFM pinning layer221.

Similarly, as described earlier inFIG. 1, shield layers223and225which serve as “leads” of the sensor200provide electrical connections for the flow of the sensing current Isfrom a current source260to the sensor200. Sensing current ISis generally forced through the layers in central region202but not through side regions204and206. Sensing means270, which is connected to these leads, senses the change in the resistance due to changes induced in the free layer210by the external magnetic field (e.g. field generated by a data bit stored on a disk).

Again, to perform effectively, hard bias layers of a CPP read sensor should have a high coercivity, a high MrT, and a high in-plane squareness on the magnetization curve. What are needed are methods and apparatus for improving hard magnet properties in read sensors of the CPP type.

SUMMARY

A read sensor of the current-perpendicular-to-the-planes (CPP) type includes a sensor stack structure formed in a central region between first and second shield layers which serve as leads for the read sensor, insulator layers formed in side regions adjacent the central region, seed layer structures formed over the insulator layers in the side regions, and hard bias layers formed over the seed layer structures in the side regions. The hard bias layers are made of a nitrogenated cobalt-based alloy, such as nitrogenated cobalt-platinum (CoPt) or nitrogenated cobalt-platinum-chromium (CoPtCr). Suitable if not exemplary coercivity and squareness properties are exhibited using the nitrogenated cobalt-based alloy. The hard bias layers may be formed by performing an ion beam deposition of cobalt-based materials using a sputtering gas (e.g. xenon) and nitrogen as a reactive gas. The magnetic head having the read sensor may incorporated into a data storage apparatus, such as a hard disk drive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is the best embodiment presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein.

A read sensor of the current-perpendicular-to-the-planes (CPP) type includes a sensor stack structure formed in a central region between first and second shield layers which serve as leads for the read sensor, insulator layers formed in side regions adjacent the central region, seed layer structures formed over the insulator layers in the side regions, and hard bias layers formed over the seed layer structures in the side regions. The hard bias layers are made of a nitrogenated cobalt-based alloy, such as nitrogenated cobalt-platinum (CoPt). Advantageously, suitable if not exemplary coercivity and squareness properties are exhibited with use of the nitrogenated cobalt-based alloy. The hard bias layers may be formed by performing an ion beam deposition of cobalt-based materials using a sputtering gas (e.g. xenon) and nitrogen as a reactive gas. The magnetic head having the read sensor may incorporated into a data storage apparatus, such as a hard disk drive. The read sensor of the CPP type may be, for example, a giant magnetoresistive (GMR) read sensor or a tunnel magnetoresistive (TMR) read sensor.

Referring now toFIG. 3, there is shown a disk drive300embodying the present invention. As shown inFIG. 3, at least one rotatable magnetic disk312is supported on a spindle314and rotated by a disk drive motor318. The magnetic recording media on each disk is in the form of an annular pattern of concentric data tracks (not shown) on disk312. At least one slider313is positioned on the disk312, each slider313supporting a magnetic read/write head321which incorporates the SV sensor of the present disclosure. As the disks rotate, slider313is moved radially in and out over disk surface322so that head321may access different portions of the disk where desired data is recorded. Each slider313is attached to an actuator arm319by means of a suspension315. The suspension315provides a slight spring force which biases slider313against the disk surface322. Each actuator arm319is attached to an actuator means327. The actuator means as shown inFIG. 3may 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 controller329.

During operation of the disk storage system, the rotation of disk312generates an air bearing between slider313(the surface of slider313which includes head321and faces the surface of disk312is referred to as an air bearing surface (ABS)) and disk surface322which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension315and supports slider313off and slightly above the disk surface by a small, substantially constant spacing during normal operation.

The various components of the disk storage system are controlled in operation by control signals generated by control unit329, such as access control signals and internal clock signals. Typically, control unit329comprises logic control circuits, storage means and a microprocessor. The control unit329generates control signals to control various system operations such as drive motor control signals on line323and head position and seek control signals on line328. The control signals on line328provide the desired current profiles to optimally move and position slider313to the desired data track on disk312. Read and write signals are communicated to and from read/write head321by means of recording channel325.

FIG. 4shows an air bearing surface (ABS) view of a spin valve (SV) sensor400of the CPP type of the present disclosure. SV sensor400may be structurally viewed as having a central region402and side regions404and406which are adjacent central region402. A sensing layer (free ferromagnetic layer)410is separated from a pinned layer (pinned ferromagnetic layer)420by a non-magnetic, electrically-conducting or insulating spacer layer415. Spacer415may be made of electrically-conductive materials if sensor400is a GMR sensor, or alternatively, electrically-insulative materials if sensor400is a tunnel magnetoresistive (TMR) sensor. The magnetization of pinned layer420is fixed by an antiferromagnetic (AFM) layer421which lies directly below it. A cap layer408is positioned over the structure, and specifically over free layer410. Cap layer408, sensing layer410, spacer layer415and pinned layer420are all formed in central region402and form components of a sensor stack structure of SV sensor400. Although SV sensor400is shown as having a “top-type” configuration, it may have a “bottom-type” or other type of configuration in the alternative.

Exemplary materials for SV sensor400of the present embodiment are provided as follows. Sensing layer410is formed of nickel-iron (NiFe) and cobalt-iron (CoFe), pinned layer420is formed of cobalt-iron (CoFe), and spacer layer415is formed of copper (Cu). Pinned layer420comprises a multi-layer film structure such as a first ferromagnetic layer/spacer/second ferromagnetic layer (e.g., cobalt-iron (CoFe)/ruthenium (Ru)/cobalt-iron (CoFe)). AFM pining layer421may be formed of platinum-manganese (PtMn), iridium-manganese (IrMn), and nickel-oxide (NiO).

Shield layers423and498serve as leads and provide electrical connections for the flow of the sensing current Isfrom a current source460to the read sensor400. Sensing means470, which is connected to these leads, senses the change in the resistance due to changes induced in the free layer410by the external magnetic field (e.g. field generated by a data bit stored on a disk).

Hard bias layers430and435are formed in the side regions404and406, respectively, and are in alignment with and provide longitudinal bias for free layer410. Cap layers440and445are formed over these hard bias layers430and435, respectively. Multi-layered seed layer structures480and485, which in this embodiment are “bi-layered” seed layer structures, are also formed in side regions404and406, respectively. More particularly, multi-layered structures480and485are formed below hard bias layers430and435, respectively, adjacent the sensor stack structure and over insulator layers482and492, respectively, in side regions404and406. Insulator layers482and492are formed over and directly on first shield layer423. Insulator layers482and492are made of electrically insulative materials and, preferably, made of alumina or atomic layer deposited (ALD) alumina.

Multi-layered structure480in side region404has a first layer484corresponding to a bottom layer of multi-layered structure480and a second layer486corresponding to a top layer of multi-layered structure480. First layer484may be made of nickel-tantalum (NiTa) or nitrogenated nickel-tantalum (NiTa+N), and second layer486may be made of CrMo. Multi-layered structure485in side region406has the same material structure in first and second layers494and496as does multi-layered structure480. Preferably, each first layer484has a thickness of between 3-100 Angstroms and each second layer486has a thickness of between 20-200 Angstroms. The hard bias materials exhibit an increased coercivity and squareness with use of such a multi-layered structure.

Preferably, the hard bias materials utilized in hard bias layers430and435are a cobalt-based material or alloy such as cobalt-platinum (CoPt) or cobalt-platinum-chromium (CoPtCr). The cobalt-based materials have a relatively small grain size, for example, on the order of 100 Angstroms. In accordance with the present disclosure, the cobalt-based alloy is nitrogenated so as to form hard bias layers430and435as a nitrogenated cobalt-based alloy. Thus, a preferred material for use as hard bias layers430and435is nitrogenated cobalt-platinum (CoPt+N). As will be described in more detail below in relation to the method ofFIGS. 5-8, hard bias layers430and435are formed by sputter-depositing a cobalt-based alloy using a sputtering gas as well as nitrogen as a reactive gas. The use of nitrogen in the deposition process causes the grain size of the CoPtCr to be reduced (e.g. to about 85 Angstroms).

Suitable if not exemplary coercivity and squareness properties are exhibited using the nitrogenated cobalt-based alloy. In the present embodiment, the squareness of hard bias layers430and435is between about 0.78-0.82 (e.g. about 0.81) with use of the nitrogenated cobalt-based alloy. Coercivity of the read sensor is maintained at sufficient and acceptable levels, between about 1500-2500 Oersteds.

Thus, the magnetic head has a sensor stack structure of a read sensor formed in central region402between shield layers423and498, insulator layers482and492formed in side regions404and406adjacent central region402(e.g. formed over or directly on shield layer423), seed layer structures480and485formed over insulator layers482and492in side regions404and406, and hard bias layers430and435formed over seed layer structures480and485, where hard bias layers430and435are made of a nitrogenated cobalt-based alloy. More particular, hard bias layers430and435are preferable made of nitrogenated cobalt-platinum (CoPt) or cobalt-platinum-chromium (CoPtCr). Hard bias layers430and435are formed in side regions404and406adjacent and in (planar) alignment with free layer410in central region402.

FIG. 5is a flowchart describing a method of making a read sensor of the present disclosure having improved hard magnet properties.FIG. 5will be described in combination withFIGS. 6-8, which are cross-sectional views of partially-fabricated read sensor structures made in accordance with the method ofFIG. 5.

Beginning at a start block502ofFIG. 5, a sensor stack structure600is formed in central region402as shown inFIG. 6(step503ofFIG. 5). To reach this stage of processing, SV sensor structure600is generally formed using full-film deposition, lithography, and etching techniques. In particular, a mask structure652is applied and patterned in central region402over a plurality of read sensor layers which are deposited in full film over shield layer423. Mask structure652is formed with a suitable width so as to define an appropriate trackwidth (TW) for the SV sensor to be fabricated.

Mask structure652may be or include, for example, a resist such as a photoresist. However, non-resist materials in mask structure652may be utilized. Mask structure652is preferably formed so as to not have any undercuts, but rather straight sidewalls from top to bottom; that is, the mask structure sidewalls are substantially normal to a plane defined by the previously deposited read sensor layers. Although mask structure652may be a monolayer mask structure (e.g. a monolayer resist or photoresist), it may alternatively be a multi-layered mask structure (e.g. bilayer or trilayer structure) which is formed without undercuts. Alternatively, mask structure652may be structured so as to have undercuts (e.g. a bilayer resist having undercuts).

An etching (e.g. an ion beam milling process) is then performed with mask structure652kept in place. During the ion beam milling process, mask structure652masks what will become an active region of the SV sensor. The layers formed under mask structure652are protected during the ion milling process and remain intact. However, the portions of pinned layer420, spacer layer415, sensing layer410, and capping layer408that are not protected by the mask during the ion milling process are removed in side regions404and406by the ion mill. The ion milling process may be stopped at shield layer423, but alternatively may be stopped at any suitable one of the sensor layers (e.g. in a “partial-mill” design).

InFIG. 7, insulator materials (e.g. alumina or ALD alumina) are deposited over the structure so as to form insulator layers482and492in side regions404and406, respectively, and over the top of mask structure652(step504ofFIG. 5). Next, seed layer structures480and485are deposited over insulator layers482and492, respectively, and over the top of mask structure652(step505ofFIG. 5). In this embodiment, seed layer structures480and485are bi-layer seed layer structures having a first (bottom) layer484of nickel-tantalum (NiTa) (or nitrogenated NiTa) and a second (top) layer (486) made of chromium-molybdenum (CrMo). To form first layer484, NiTa may be deposited in a nitrogen (N2) atmosphere over first layer482. Preferably, first layer484of the NiTa is deposited to a thickness between about 3 to 100 Å, and preferably has a specific thickness of about 15 Å. In one embodiment, the NiTa is deposited in the nitrogen atmosphere with a nitrogen partial pressure of about 2.5×10−5Torr. The NiTa may be then exposed to oxygen for a time period of about 30 seconds, for example. The partial pressure of the oxygen may be between about 5×10−6Torr and 5×10−5Torr, or preferably to about 2.5×10−5Torr. Second layer486made of CrMo is then deposited over second layer484made of the nickel-tantalum. Preferably, second layer486is deposited to a thickness between 20 to 200 Å, and preferably has a specific thickness of about 50 Å.

Subsequently, hard bias materials are deposited over the structure so as to form hard bias layers430and435in side regions404and406, respectively, and over the top of mask structure652(step506ofFIG. 5). Hard bias layers430and435are located in side regions404and406so as to be in alignment with free layer410in central region402. In general, hard bias layers430and435are provided for longitudinally biasing free layer410in central region402.

As described above in relation toFIG. 4, hard bias layers430and435are made of or include a nitrogenated cobalt-based alloy (e.g. CoPt+N, or CoPtCr+N). To form hard bias layers430and435, an ion beam sputtering system may be used. In this case, cobalt-based materials are deposited by ion beam deposition with use of a sputtering gas in nitrogen (N2) atmosphere. The sputtering gas may be, for example, an xenon (Xe) gas. The nitrogen is not used as part of the sputtering ions, but is rather supplied as a reactive gas in a deposition chamber of the system during the deposition. The cobalt-based materials have a reduced and relatively small grain size (e.g. on the order of approximately 85 Angstroms) due at least in part to use of the nitrogen in the deposition process. Furthermore, suitable if not exemplary coercivity and squareness properties are exhibited using the nitrogenated cobalt-based alloy. In the present embodiment, the squareness of hard bias layers430and435is between about 0.78-0.82 (e.g. about 0.81) with use of the nitrogenated cobalt-based alloy. Coercivity of the read sensor is maintained at sufficient and acceptable levels, between about 1500-2500 Oersteds (at least greater than 1000 Oersteds).

Next inFIG. 7, cap layers440and445are deposited over the structure in side regions404and406, respectively, as well as over mask structure652(step508ofFIG. 5). A chemical-mechanical polishing (CMP) is then performed over the structure to remove mask structure652and to form a top planar surface for the read sensor. In general, the mechanical interaction of a CMP pad during the CMP process removes the mask structure652from the remaining layers underneath it. The CMP pad makes physical contact with the mask structure materials (i.e. mask structure having the hard bias and lead layers formed thereover) and compresses them until the CMP pad reaches a top surface of the sensor structure. Alternatively, if mask structure652is formed with undercuts (e.g. a bilayer mask with undercuts), the mask structure may be removed by utilizing a suitable conventional solvent. Shield layer498is then formed over the structure. The resulting structure is shown inFIG. 8.

The resulting SV sensor400ofFIG. 8has an active SV structure formed in central region402in between shield layers423and498, and cap layers440and445and hard bias layers450and455formed in side regions404and406, respectively. Hard bias layers450and455are formed over seed layer structures480and485, respectively, which are formed over insulator layers482and492, respectively. Insulator layers482and492may be formed directly on shield layer423or other suitable material of the sensor. Hard bias layers450and455are suitably positioned so as to longitudinally bias free layer410. Shield layers423and498provide electrical connections for the flow of a sensing current Isfrom a current source to the sensor. A sensing means connected to shield layers423and498sense the change in the resistance due to changes induced in free layer410by an external magnetic field (e.g. field generated by a data bit stored on a disk). Additional conventional processing steps may be performed to complete the fabrication of read sensor600and the magnetic head (step510ofFIG. 5).

Final Comments. A read sensor of the current-perpendicular-to-the-planes (CPP) type includes a sensor stack structure formed in a central region between first and second shield layers which serve as leads for the read sensor, insulator layers formed in side regions adjacent the central region, seed layer structures formed over the insulator layers in the side regions, and hard bias layers formed over the seed layer structures in the side regions. The hard bias layers are made of a nitrogenated cobalt-based alloy, such as nitrogenated cobalt-platinum (CoPt). Suitable if not exemplary coercivity and squareness properties are exhibited using the nitrogenated cobalt-based alloy. The hard bias layers may be formed by performing an ion beam deposition of cobalt-based materials using a sputtering gas (e.g. xenon) and nitrogen as a reactive gas. The read sensor of the CPP type may be, for example, a GMR or TMR read sensor. The magnetic head having the read sensor may incorporated into a data storage apparatus, such as a hard disk drive.

It is to be understood that the above is merely a description of preferred embodiments of the invention and that various changes, alterations, and variations may be made without departing from the true spirit and scope of the invention as set for in the appended claims. The read sensor of the present disclosure may be any suitable type of read sensor, such as a current-in-plane (CIP) type GMR read sensor, a current-perpendicular-to-plane (CPP) type GMR read sensor, or a tunnel valve or magnetic tunnel junction (MTJ) type read sensor. Few if any of the terms or phrases in the specification and claims have been given any special particular meaning different from the plain language meaning to those skilled in the art, and therefore the specification is not to be used to define terms in an unduly narrow sense.