JP2004062954A - Evaluation element for thin film magnetic head , thin film magnetic head wafer, and thin film magnetic head bar - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation element for a thin film magnetic head, capable of changing a magnetic resistance by a small magnetic field change, and to provide a thin film magnetic head wafer and a thin film magnetic head bar. <P>SOLUTION: Two orthogonal axes perpendicular in the thickness direction (Z axis) of a magnetic shield L<SB>D</SB>are set as a longitudinal axis (X axis) and a lateral axis (Y axis). The ratio (X<SB>D</SB>/Y<SB>D</SB>) of the longitudinal length X<SB>D</SB>of the magnetic shield L<SB>D</SB>to a lateral length Y<SB>D</SB>is 6 or higher. By setting the aspect ratio of the magnetic sheild L<SB>D</SB>in such a manner, the magnetic resistance of a magneto-resistive effect element TMR<SB>D</SB>in the evaluation element D is easily changed with respect to the change of a measured magnetic field. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thin-film magnetic head evaluation element, a thin-film magnetic head wafer, and a thin-film magnetic head bar.
[0002]
[Prior art]
2. Description of the Related Art As the capacity and size of a magnetic disk device have been reduced and the recording density has been increased, the performance of a thin-film magnetic head has been required to be improved. Instead of a thin-film magnetic head that performs recording and reproduction with an inductive electromagnetic transducer, a composite thin-film magnet having a structure in which a recording head having an inductive electromagnetic transducer for writing and a reproducing head having a magnetoresistive element for reading are stacked Heads are widely used.
[0003]
The element resistance of a magnetoresistive element changes with respect to an external magnetic field. Since a magnetic field other than the magnetic field from the magnetization transition region to be measured in the magnetic recording medium is unnecessary at the time of detection, in a thin-film magnetic head, a magnetic shield that blocks such an unnecessary magnetic field sandwiches the magnetoresistive element. I have.
[0004]
Examples of the thin film magnetic head having such a structure include a GMR (Giant Magneto Resistive) element and a TMR (Tunnel Magneto Resistive) element. Note that thin-film magnetic heads are also classified according to the direction in which electrons pass, and a magnetic sensing element structure in which electrons flow along the thickness direction of the free magnetic layer is a CPP (Current Perpendicular to Plane) structure, which flows in a plane perpendicular to the CPP structure. The structure of the magnetic sensing element is CIP (Current
In Plane) structure.
[0005]
In each of the thin-film magnetic heads, a characteristic test is performed. Since the number of thin-film magnetic heads formed in a single substrate such as a wafer and a bar is relatively large, it is not reasonable to inspect all elements. Therefore, for some thin-film magnetic heads, it is conceivable to arrange the substrate on which the thin-film magnetic heads are formed in a magnetic field at a stage before completion, and to inspect the characteristics of the substrates.
[0006]
[Problems to be solved by the invention]
However, due to the presence of the magnetic shield, even when a magnetic field is applied to the thin-film magnetic head in a stage before completion, the resistance of the magnetoresistive element is hard to change. A strong magnetic field must be applied. However, in such a state where a strong magnetic field is applied, precise characteristic inspection is difficult.
[0007]
Further, since high-speed reading from the magnetization transition region of the magnetic recording medium corresponds to high-speed reading of an alternating magnetic field, it is expected that such a characteristic test is applied to a thin-film magnetic head. However, even if the thin-film magnetic head is placed in an alternating magnetic field that changes at a high speed, the hysteresis loop of the magnetic shield hardly causes a change in the resistance of the magnetoresistive element, so that a precise characteristic test cannot be performed.
[0008]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a thin-film magnetic head evaluation element, a thin-film magnetic head wafer, and a thin-film magnetic head bar whose magnetic resistance can be changed by a small magnetic field change. I do.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the evaluation element for a thin-film magnetic head according to the present invention is arranged such that a magnetoresistance effect element whose magnetoresistance changes according to a measured magnetic field and a magnetoresistance effect element are sandwiched in a thickness direction. In a thin-film magnetic head evaluation element including a pair of magnetic shields, when two axes perpendicular to the thickness direction of the magnetic shield are defined as a vertical axis and a horizontal axis, respectively, the vertical length with respect to the horizontal length Y of the magnetic shield The ratio of the length X is 6 or more.
[0010]
As a result of the present inventors' eager examination of the aspect ratio of the magnetic shield of the evaluation element, if the aspect ratio of the magnetic shield is set as described above, the resistance of the magnetoresistive effect element in this evaluation element, It turned out to be easy to change. In this way, by inspecting the evaluation element using a small change in the magnetic field, it is possible to indirectly inspect the characteristics of the thin-film magnetic head formed at the same time.
[0011]
Further, if the aspect ratio of the magnetic shield of the evaluation element is too large, the yield per wafer of the thin film magnetic head is reduced. Therefore, it is desirable that the above ratio is set to 100 or less.
[0012]
That is, the thin-film magnetic head wafer according to the present invention is formed at the same time as the evaluation element for the thin-film magnetic head, and is formed with a plurality of thin-film magnetic heads having an aspect ratio of the magnetic shield different from that of the evaluation element for the thin-film magnetic head. .
[0013]
Since the actual thin-film magnetic head is not an evaluation element, the aspect ratio differs from that of the evaluation element. The aspect ratio of the thin film magnetic head is optimized not from the viewpoint of characteristic evaluation but according to the original function. For example, the aspect ratio of the thin-film magnetic head is 1.
[0014]
The thin-film magnetic head bar is formed by cutting and processing the thin-film magnetic head wafer so that the ratio of the vertical length X to the horizontal length Y of the magnetic shield of the evaluation element for the thin-film magnetic head is 3 or more and less than 10. It is characterized by the following.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a thin-film magnetic head evaluation element, a thin-film magnetic head wafer, and a thin-film magnetic head bar according to the embodiment will be described. Note that the same reference numerals are used for the same elements, and duplicate descriptions are omitted.
[0016]
FIG. 1 is a perspective view of a thin-film magnetic head assembly on which a thin-film magnetic head evaluation element D and a thin-film magnetic head R are formed. The thin-film magnetic head assembly is a wafer, and by cutting the wafer, a thin-film magnetic head bar is formed. Further, by cutting the thin-film magnetic head bar, individual thin-film magnetic heads R are finally separated. By combining with a magnetic recording medium, a magnetic recording device such as a hard disk device is completed.
[0017]
The normal direction of the magnetic recording medium is defined as the X axis. Two axes perpendicular to the X axis are defined as a Y axis and a Z axis. When the final magnetic storage device is completed, the surface facing the magnetic recording medium is defined as a medium facing surface (air bearing) ABS.
[0018]
In the thin-film magnetic head assembly in a wafer state, the thin-film magnetic head evaluation element D has a magnetoresistive element TMR _D whose magnetoresistance changes according to a measured magnetic field and a magnetoresistive element TMD _D sandwiched in the thickness direction. And a pair of magnetic shields U _D , L _D arranged at the same time. Toward the lower magnetic shield L _D is greater than the magnetic shield U _D at the top. Magnetic shield U _D, the shape of the L _D are the same is described herein with only one magnetic shield L _D, the following description conform to the other magnetic shield U _D.
[0019]
Each vertical axis perpendicular two orthogonal axes in the thickness direction (Z-axis) of the magnetic shield L _D (X-axis) and the horizontal axis is (Y-axis). The ratio of the longitudinal length _{X D} with respect to the lateral direction length _{Y D} of the magnetic shield _{L D (X D / Y D} ) is 6 or more.
[0020]
If set as the aspect ratio of the magnetic shield L _D above, the magnetic resistance of the magnetoresistive effect element TMR _D in the evaluation device D it is easily changed with respect to changes in the measured magnetic field. The magnetic resistance of the evaluation element D, each magnetic shield U _D, L while the current supplied to (sense current) is constant between _D, the magnetic shield U _D, the lead wire is electrically connected to the L _D U _D1 , L _D1 is measured according to Ohm's law. Alternatively, the current flowing between U _D and L _D may be detected with the voltage kept constant.
[0021]
The magnetoresistive element (TMR film) TMR _D used in the TMR element, for example, a multilayer structure such as a foundation layer / pinned layer / lower ferromagnetic layer / insulating layer (tunnel barrier layer) / upper ferromagnetic layer It consists of a laminated film. Here, the pinning layer is for fixing the direction of magnetization of the lower ferromagnetic layer to the direction of the magnetic field from the magnetic recording medium. In this case, the lower ferromagnetic layer is called a pinned layer, and the upper ferromagnetic layer whose magnetization direction changes with an external magnetic field is called a free layer.
[0022]
The thickness of the insulating layer is set to be thin enough to allow electrons to tunnel between the ferromagnetic layers while maintaining their spin. The free layer and the pinned layer are opposed to each other with the insulating layer interposed therebetween, and the ratio of electrons passing from one layer to the other layer is determined by the relative angle between the magnetization directions.
[0023]
That is, when a current flows through the TMR film from the upper and lower magnetic shields U _D and L _D , the tunnel current flowing between the ferromagnetic layers sandwiching the insulating film changes depending on the relative angle. This phenomenon is called a ferromagnetic tunnel effect, and the resistance of the TMR film is minimum when the magnetization directions of both magnetic layers are parallel and maximum when the magnetization directions are antiparallel, like the spin valve film.
[0024]
When the evaluation element D is formed in the wafer integration step, the evaluation element D is formed through exactly the same integration step as the thin-film magnetic head R. That is, in the wafer W on which the heads having the CPP structure are integrated, the evaluation element D has the CPP structure like the thin film magnetic head R, and the film configuration from the base is basically the same. That is, the evaluation element D is a TMR element, and similarly, the thin-film magnetic head R is also a TMR element.
[0025]
In the evaluation element D, for example, when a lead is newly formed between the lower shield material and the magnetoresistive film for wiring, the measured electromagnetic characteristics do not simulate the characteristics of the thin film magnetic head R. And the characteristics of the magnetoresistive film formed between the lower shield and the lead. That is, the characteristics of the magnetoresistive element used in the CPP structure are changed by the influence of the base before growth.
[0026]
The magnetoresistance of the thin-film magnetic head R changes in the same manner as the magnetoresistance of the evaluation element D as a dummy. That is, the multilayer structure of the thin film magnetic head R is the same as the laminated structure of the evaluation element D, sandwiched in the thickness direction and the magnetoresistive element TMR _R magnetic resistance changes, the magnetoresistive element TMR _R in accordance with the measured magnetic field a pair of magnetic shields U _R disposed so as _to, and a L _R.
[0027]
Toward the lower magnetic shield _{L R} is greater than the magnetic shield _{U R} of the upper, lateral length _Y ratio of the longitudinal length _{X R} for _{R (X} R / _{Y R)} of the magnetic shield _{L R} in example 1 is there. The magnetic shield U _R of the thin film magnetic head _R, L _R to be the lead wire U _R1, L _R1 is electrically connected to the wiring between the voltage has become possible to measure this voltage element the actual Used for data reading when incorporated in a magnetic storage device.
[0028]
As described above, setting the aspect ratio of the magnetic shield L _D to 6 above, by arranging the evaluation element D in a magnetic field of small intensity change is performed by examining its characteristics, this to have been formed at the same time The characteristics of the thin-film magnetic head R can be inspected indirectly.
[0029]
FIG. 2 is a perspective view of a wafer W as the thin-film magnetic head assembly. From the wafer W, a plurality of thin-film magnetic head bars B are cut out by cutting. After the thin-film magnetic head bar B is cut off, the surface that becomes the medium facing surface ABS is subjected to a process such as mechanical polishing.
[0030]
That is, the thin film magnetic head bar B is a thin-film magnetic head wafer W is cut and processed along the Y direction, and three or more and less than 10 the ratio of the vertical length X with respect to the lateral direction length Y of the magnetic shield L _D However, since this ratio is greater than 1 in the first place, the magnetoresistance can be detected more effectively than the thin-film magnetic head R even in the subsequent inspection.
[0031]
Each thin-film magnetic head bar B also has a plurality of thin-film magnetic heads R, forming a thin-film magnetic head assembly. FIG. 1 shows a thin-film magnetic head bar provided with one evaluation element D for seven thin-film magnetic heads R. Included in thin film magnetic head bar B. Although the evaluation element D is located substantially at the center of the thin-film magnetic head bar B, it can also be arranged at both ends of the thin-film magnetic head bar B or at equally divided positions.
[0032]
As described above, the thin-film magnetic head wafer W according to the present embodiment is formed simultaneously with the thin-film magnetic head evaluation element D, and a plurality of thin-film magnetic heads R having different aspect ratios from the thin-film magnetic head evaluation element are formed. It becomes. Since the actual thin-film magnetic head R is not an evaluation element, the aspect ratio differs from that of the evaluation element D. The aspect ratio of the thin-film magnetic head R is optimized not in terms of characteristic evaluation but in accordance with the original function. In this example, the aspect ratio is set to 1, for example.
[0033]
FIG. 3 is a graph showing the relationship between the measured magnetic field (Oe) and the MR (magnetic resistance) change rate (%) in the evaluation element D according to the example. The aspect ratio in this graph is 6. Even when the measurement magnetic field is slightly changed (within ± 100 (Oe)), the MR change rate changes by 25%.
[0034]
FIG. 4 is a graph showing the relationship between the measured magnetic field (Oe) and the MR (magnetic resistance) change rate (%) in the evaluation element D according to another embodiment. The aspect ratio in this graph is 10. Even when the measurement magnetic field is slightly changed (within ± 10 (Oe)), the MR change rate changes by 25%. In other words, the demagnetizing coefficient of the evaluation element D is substantially zero.
[0035]
FIG. 5 is a graph showing the relationship between the measured magnetic field (Oe) and the MR (magnetic resistance) change rate (%) in the evaluation element D according to the comparative example. The aspect ratio of the magnetic shield in this graph is 1. Unless the measured magnetic field is changed greatly (± 1200 (Oe) or more) by the hysteresis of the magnetic shield, the MR change rate does not change. Of course, even when an AC magnetic field is applied near the measurement magnetic field of 0 (Oe), the MR change rate hardly changes.
[0036]
As is clear from the above graph, in the evaluation element D (actual element) according to the comparative example, the lower magnetic shield and the upper magnetic shield generate a demagnetizing field with respect to the measured magnetic field, and the internal magnetoresistance effect element TMR _D There is a magnetic field region in which the magnetic field applied to is effectively canceled to zero (magnetic shield effect).
[0037]
Therefore, measuring the magnetic field does not enter the magnetic field in the internal of which does not exceed the saturation magnetic field of the magnetic shield, parallel and anti-parallel state of the magnetic field of the pinned layer and the free layer of the magnetoresistive element TMR _D becomes unstable. As a result, in the magnetic field region of about ± 1200 (Oe), the dependence of the MR change rate on the magnetic field is disturbed, and an accurate MR change rate cannot be obtained.
[0038]
In addition, the element of the comparative example has a problem that a response near zero magnetic field, which is particularly important as head characteristics, cannot be measured due to the magnetic shielding effect. In the embodiment, since the aspect ratio of the upper and lower magnetic shields of the evaluation element D is increased with respect to the direction of the measurement magnetic field, the influence of the demagnetizing field generated in the longitudinal direction of the upper and lower magnetic shields on the element is suppressed, and the magnetoresistance is reduced. The magnetic properties of the effect film can be precisely evaluated.
[0039]
As described above, according to the evaluation element D according to the embodiment, it is possible to change the magnetic resistance with a small change in the magnetic field. If the aspect ratio is too large, the yield per wafer of the thin-film magnetic head decreases, so that the aspect ratio is desirably set to 100 or less.
[0040]
The pattern of the evaluation element D described above can be arranged on the wafer W at a certain period (for example, one shot unit of a stepper), and the resistance value of this pattern is set in a zero magnetic field or a DC or AC magnetic field. By performing the measurement, the characteristic distribution of the thin-film magnetic head R in the plane of the wafer W can be evaluated without evaluating all the elements on the wafer W. Further, by grasping such electromagnetic characteristics at the time of manufacturing the wafer W, the quality of the thin-film magnetic head R can be determined and product management can be performed.
[0041]
Various TMR elements having a CPP structure are conceivable, but an example used in the above embodiment will be described.
[0042]
The TMR element of this example is formed by sequentially laminating an underlayer / pinning layer / lower ferromagnetic layer / insulating layer (tunnel barrier layer) / upper ferromagnetic layer / protective layer on an AlTiC substrate.
[0043]
That is, the underlayer: “Ta (5 nm) / NiFe (2 nm)”, the pinning layer: “PtMn (15 nm)”, the lower ferromagnetic layer (pinned layer): “CoFe (2 nm), Ru (0.8 nm), CoFe (3 nm) ", insulating layer (tunnel barrier layer):" Al ₂ O ₃ (0.75 nm) ", upper ferromagnetic layer (free layer):" CoFe (1.5 nm) / NiFe (2.5 nm) " , Protective layer: “Ta (10 nm)”.
[0044]
The above-described thin-film magnetic head R and evaluation element D can be applied to a GMR element having a CCP structure as long as they have a magnetic shield.
[0045]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the evaluation element for thin film magnetic heads, the thin film magnetic head wafer, and the thin film magnetic head bar of the present invention, the magnetic resistance can be changed by a small magnetic field change.
[Brief description of the drawings]
FIG. 1 is a perspective view of a thin-film magnetic head assembly on which a thin-film magnetic head evaluation element D and a thin-film magnetic head R are formed.
FIG. 2 is a perspective view of a wafer W as a thin-film magnetic head assembly.
FIG. 3 is a graph showing a relationship between a measurement magnetic field (Oe) and an MR (magnetoresistive) change rate (%) in an evaluation element D according to an example.
FIG. 4 is a graph showing a relationship between a measurement magnetic field (Oe) and an MR (magnetic resistance) change rate (%) in an evaluation element D according to another example.
FIG. 5 is a graph showing a relationship between a measurement magnetic field (Oe) and an MR (magnetic resistance) change rate (%) in an evaluation element D according to a comparative example.
[Explanation of symbols]
B ... thin film magnetic head bar, D ... thin-film magnetic head evaluation element, R ... thin-film magnetic head (actual element), _TMR D, _TMR R _... magnetoresistive _{element, U D, L D, U} R, L R ... Magnetic Shield, U _D1 , L _D1 , U _R1 , L _R1 ... lead wiring, W ... wafer.

Claims (4)

An evaluation element for a thin-film magnetic head, comprising: a magnetoresistive element whose magnetoresistance changes according to a measured magnetic field; and a pair of magnetic shields arranged so as to sandwich the magnetoresistive element in a thickness direction. Wherein the ratio of the vertical length X to the horizontal length Y of the magnetic shield is 6 or more, where the two orthogonal axes perpendicular to the thickness direction are the vertical axis and the horizontal axis, respectively. Evaluation element for head. The evaluation element according to claim 1, wherein the ratio is 100 or less. 2. A thin-film magnetic head wafer formed with a plurality of thin-film magnetic heads formed simultaneously with the thin-film magnetic head evaluation element according to claim 1 and having a magnetic shield having an aspect ratio different from that of the magnetic shield of the thin-film magnetic head evaluation element. . 4. The thin-film magnetic head wafer according to claim 3, wherein the ratio of the vertical length X to the horizontal length Y of the magnetic shield of the evaluation element for the thin-film magnetic head is 3 or more and less than 10. A thin film magnetic head bar characterized by the following.

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