CURRENT-PERPENDICULAR-TO-PLANE (CPP) READ SENSOR WITH MULTIPLE REFERENCE LAYERS
A current-to-perpendicular-to-plane (CPP) read sensor with multiple reference layers and associated fabrication methods are disclosed. According to one embodiment of the invention, the multiple reference layers of a CPP tunneling magnetoresistance (TMR) read sensor includes a first reference layer formed by a ferromagnetic polycrystalline Co—Fe film, a second reference layer formed by a ferromagnetic substitute-type amorphous Co—Fe—X film where X is Hf, Zr or Y, and a third reference layer formed by a ferromagnetic interstitial-type amorphous Co—Fe—B film. The first reference layer facilitates the CPP TMR read sensor to exhibit high exchange and antiparallel-coupling fields. The second reference layer provides a thermally stable flat surface, thus facilitating the CPP TMR read sensor to exhibit a low ferromagnetic-coupling field. The multiple reference layers may induce spin-dependent scattering, thus facilitating the CPP TMR sensor to exhibit a high TMR coefficient.
The patent application is a divisional of U.S. patent application having the Ser. No. 11/964,673, and filed on Dec. 26, 2007, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention is related to the field of magnetic storage systems, and in particular, to a disk drive including a current-perpendicular-to-plane (CPP) read sensor with multiple reference layers.
2. Statement of the Problem
In many magnetic storage systems, a hard disk drive is the most extensively used to store data. The hard disk drive typically includes a hard disk along with an assembly of write and read heads. The assembly of write and read heads is supported by a slider that is mounted on a suspension arm. When the hard disk rotates, an actuator swings the suspension arm to place the slider over selected circular data tracks on the surface of the rotating hard disk. An air flow generated by the rotation of the hard disk causes the slider with an air bearing surface (ABS) to fly on a cushion of air at a particular height over the rotating hard disk. The height depends on the shape of the ABS. As the slider flies on the air bearing, the actuator moves the suspension arm to position the write and read heads over selected data tracks on the surface of the hard disk. The write and read heads thus write data to and read data from, respectively, a recording medium on the rotating hard disk. Processing circuitry connected to the write and read heads then operates according to a computer program to implement writing and reading functions.
In a reading process, the read head passes over transitions of a data track in the magnetic medium, and magnetic fields emitting from the transitions modulate the resistance of a read sensor in the read head. Changes in the resistance of the read sensor are detected by a sense current passing through the read sensor, and are then converted into voltage changes that generate read signals. The resulting read signals are used to decode data encoded in the transitions of the data track.
In a typical read head, a current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) read sensor is electrically separated by side oxide layers from longitudinal bias layers in two side regions for preventing a sense current from shunting into the two side regions, but is electrically connected with lower and upper shields for the sense current to flow in a direction perpendicular to the sensor plane. A typical CPP GMR read sensor comprises an electrically conducting spacer layer sandwiched between lower and upper sensor stacks. The spacer layer is typically formed by a nonmagnetic Cu or oxygen-doped Cu (Cu—O) film having a thickness ranging from 1.6 to 4 nanometers. When the sense current flows across the Cu or Cu—O spacer layer, changes in the resistance of the CPP GMR read sensor is detected through a GMR effect. A typical CPP TMR read sensor comprises an electrically insulating barrier layer sandwiched between the lower and upper sensor stacks. The barrier layer is typically formed by a nonmagnetic oxygen-doped Mg (Mg—O) or Mg oxide (MgOX) film having a thickness ranging from 0.4 to 1 nanometers. When the sense current “quantum-jumps” across the Mg—O or MgOX barrier layer, changes in the resistance of the CPP GMR read sensor is detected through a TMR effect.
The lower sensor stack comprises nonmagnetic seed layers, an antiferromagnetic pinning layer, a ferromagnetic keeper layer, a nonmagnetic antiparallel-coupling layer, and a ferromagnetic reference layer. The upper sensor stack comprises ferromagnetic sense (free) layers and a nonmagnetic cap layer. In the lower sensor stack, the keeper layer, the antiparallel-coupling layer, and the reference layer form a flux-closure structure where four fields are induced. First, a unidirectional anisotropy field (HUA) is induced by exchange coupling between the antiferromagnetic pinning layer and the keeper layer. Second, an antiparallel-coupling field (HAPC) is induced by antiparallel coupling between the keeper layer and the reference layer across the antiparallel-coupling layer. Third, a demagnetizing field (HD) is induced by the net magnetization of the keeper layer and the reference layer. Fourth, a ferromagnetic-coupling field (HF) is induced by ferromagnetic coupling between the reference layer and the sense layer across the spacer or barrier layer. To ensure proper sensor operation, HUA and HAPC should be high enough to rigidly pin magnetizations of the keeper layer and the reference layer in opposite transverse directions perpendicular to the ABS, while HD and HF should be small and balance with each other to orient the magnetization of the sense layers in a longitudinal direction parallel to the ABS.
In the flux-closure structure of the CPP TMR read sensor, the Co—Fe keeper layer is selected to ensure high exchange and antiparallel coupling. Its composition is optimized and its magnetic moment is small, so that high HUA and HAPC can be attained. The Co—Fe—B reference layer is selected to ensure a strong TMR effect and mild ferromagnetic coupling. Its B content is high enough for B atoms, which are much smaller than Co and Fe atoms, to occupy interstitial sites of a crystalline structure and thus interfere with the ability of the Co and Fe atoms to crystallize. As a result, an interstitial-type amorphous film with a flat surface is formed, which facilitates the Mg—O or MgOX barrier layer to grow with a preferred <001> crystalline texture on the flat surface, thus increasing a TMR coefficient (ΔRT/RJ) and decreasing HF. Its Co and Fe contents are optimized and its magnetic moment is small, so that a high HAPC can be attained.
The use of the Co—Fe—B reference layer in the prior art generally meets the requirements of high HAPC, low HF, and high ΔRT/RJ. However, it is still desirable to further improve the reference layer for the CPP TMR sensor to operate more robustly.
SUMMARYEmbodiments of the invention include a CPP read sensor with multiple reference layers. According to one embodiment, the multiple reference layers of a CPP TMR read sensor include a first reference layer formed by a ferromagnetic polycrystalline Co—Fe film, a second reference layer formed by a ferromagnetic substitute-type amorphous Co—Fe—X film where X is Zr, Hf or Y, and a third reference layer formed by a ferromagnetic interstitial-type amorphous Co—Fe—B film. The first reference layer facilitates the TMR sensor to exhibit high exchange and antiparallel-coupling fields. The second reference layer provides a thermally stable flat surface, thus facilitating the CPP TMR sensor to exhibit a low ferromagnetic-coupling field. The multiple reference layers induce spin-dependent scattering, thus facilitating the CPP TMR sensor to exhibit a high TMR coefficient.
The invention may include other exemplary embodiments as described below.
The same reference number represents the same element or same type of element on all drawings.
When the hard disk 104 rotates, an air flow generated by the rotation of the hard disk 104 causes the slider 114 with an air bearing surface (ABS) to fly on a cushion of air at a particular height over the rotating hard disk 104. The height depends on the shape of the ABS. As the slider 114 flies on the air, the actuator 108 moves the suspension arm 110 to position a write head (not shown) and a read head (not shown) over selected data tracks on the surface of the hard disk 104. The write and read heads write data to and read data from, respectively, a recording medium on the rotating hard disk 104. Processing circuitry connected to the write and read heads then operates according to a computer program to implement writing and reading functions.
Although
The TMR read sensor 810 includes an electrically insulating barrier layer 819 sandwiched between a lower sensor stack and an upper sensor stack. The barrier layer 819 may be formed by a nonmagnetic oxygen-doped Mg (Mg—O) film in-situ formed in only one module of a sputtering system, as described below. After heavily cleaning a Mg target for 60 seconds with a target power of 600 W, a 0.2 nanometer thick Mg film is DC sputtered in an argon gas of 3×10−4 torr with a target power of 40 W. A first oxygen treatment in an oxygen gas of 5×10−7 torr is then applied to the Mg film, resulting in oxygen doping into the Mg film. A 0.4 nanometer thick Mg—O film is then DC sputtered in a mixture of argon and oxygen gases of 3 and 0.4×10−4 torr, respectively, with a target power of 100 W. A second oxygen treatment in an oxygen gas of 5×10−7 ton is then applied to the Mg—O film. A 0.2 nanometer thick Mg—O film is then DC sputtered in a mixture of argon and oxygen gases of 3 and 0.1×10−4 ton, respectively, with a target power of 100 W. A third oxygen treatment in an oxygen gas of 5×10−5 ton is then applied to the Mg—O film.
The lower sensor stack comprises a first seed layer 811 formed by a 3 nanometer thick nonmagnetic Ta film, a second seed layer 812 formed by a 3 nanometer thick nonmagnetic Ru film, a pinning layer 813 formed by a 6 nanometer thick antiferromagnetic 21.7Ir-78.3Mn film (composition in atomic percent), a keeper layer 814 formed by a 2.1 nanometer thick ferromagnetic 77.5Co-22.5 Fe film, and an antiparallel coupling layer 815 formed by a 0.8 nanometer thick nonmagnetic Ru film. The lower sensor stack further comprises a first reference layer 816 formed by a 0.4 nanometer thick ferromagnetic 77.5Co-22.5 Fe film, a second reference layer 817 formed by a 0.6 nanometer thick ferromagnetic 64.6Co-19.7 Fe-15.7Zr film, and a third reference layer 818 formed by a 1 nanometer thick ferromagnetic 51.9Co-34.6Fe-13.5B film.
The upper sensor stack comprises a first sense layer 820 formed by a 0.4 nanometer thick ferromagnetic 87.1Co-12.9Fe film, a second sense layer 821 formed by a 2.6 nanometer thick ferromagnetic 71.5Co-7.4Fe-21.1B film, and a cap layer 822 formed by a 6 nanometer thick nonmagnetic Ru film.
The first reference layer 816 facilitates the flux-closure structure to exhibit a high antiparallel-coupling field (HAPC), which is defined as a critical field aligning 95% of the saturation magnetization of the flux-closure structure in its direction.
The second reference layer 817 provides a thermally stable flat surface, thus facilitating the TMR read sensor 800 to exhibit a low ferromagnetic-coupling field (HF).
The multiple reference layers might induce spin-dependent scattering, thus facilitating the TMR read sensor 800 to exhibit a high TMR coefficient (ΔRT/RJ).
Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.
Claims
1. A method of fabricating a flux-closure structure for a current-perpendicular-to-plane (CPP) read sensor, the method comprising:
- depositing a keeper layer;
- depositing an antiparallel coupling layer on the keeper layer;
- depositing a first reference layer of a ferromagnetic polycrystalline film on the antiparallel coupling layer;
- depositing a second reference layer of a ferromagnetic substitute-type amorphous film on the first reference layer; and
- depositing a third reference layer of a ferromagnetic interstitial-type amorphous film on the second reference layer.
2. The method of claim 1 wherein the first reference layer is formed by a Co—Fe film including Co with a content ranging from 50 to 90 at % and Fe with a content ranging from 10 to 50 at %, and having a thickness ranging from 0.2 to 1 nanometers.
3. The method of claim 1 wherein the second reference layer is formed by a Co—Fe—X film including Co with a content ranging from 60 to 80 at %, Fe with a content ranging from 0 to 40 at %, and X with a content ranging from 6 to 30 at %, where X is Hf, Zr or Y, and having a thickness ranging from 0.6 to 2 nanometers.
4. The method of claim 1 wherein the third reference layer is formed by a Co—Fe—B film including Co with a content ranging from 60 to 80 at %, Fe with a content ranging from 0 to 40 at %, and B with a content ranging from 6 to 30 at %, and having a thickness ranging from 1 to 2 nanometers.
Type: Application
Filed: Oct 19, 2011
Publication Date: Feb 16, 2012
Inventor: Tsann Lin (Saratoga, CA)
Application Number: 13/276,527
International Classification: B05D 5/00 (20060101); B05D 1/36 (20060101);