JP3877386B2 - Method and apparatus for evaluating magnetoresistive head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic head used in a magnetic recording apparatus such as a hard disk device or a VTR, and more particularly to a magnetoresistive head evaluation method and evaluation apparatus using a magnetoresistive element in a signal detection unit of the magnetic head.
[0002]
[Prior art]
Increasing the size and capacity of magnetic recording devices such as hard disk drives and VTRs is rapidly increasing. In response to these trends, the performance of magnetic heads has been improved. Magnetoresistance effect type magnetic heads using the magnetoresistance effect phenomenon due to the thin film of ferromagnetic material can be used as an alternative to thin film magnetic heads using electromagnetic induction. (Magneto Resistive head, hereinafter referred to as MR head). The MR head uses the magnetoresistive effect of a ferromagnetic thin film such as permalloy, and can produce a large reproduction output regardless of the relative speed with the recording medium and is suitable for reproduction of high-density recording. A head having unstable reproduction characteristics due to Hausen noise or the like may be generated.
[0003]
Barkhausen noise is caused by the fact that the domain wall in the ferromagnetic body moves while being caught by defects in the thin film or residues of the thin film. However, in the head in which such Barkhausen noise is generated, reliability in reproducing operation cannot be expected. In order to suppress this Barkhausen noise, an element structure has been devised in which a magnetic domain control film for applying a longitudinal bias is arranged on both sides of the MR layer so that the MR layer is made into a single magnetic domain.
[0004]
FIG. 9 is an enlarged front view showing a permanent magnet bias type MR head from the side where the recording medium faces. In the MR head of the permanent magnet bias system, SAL (Soft Adjacent) that applies SAL bias (lateral bias magnetic field in the y direction) to the MR layer 1 that exhibits the magnetoresistive effect, the spacer layer 2 that is a nonmagnetic layer, and the MR layer 1. Layer) 3. This three-layer structure is provided between the upper insulating layer 4 and the lower insulating layer 5. A method of laminating the permanent magnet layer 7 for applying a longitudinal bias magnetic field in the x direction to the MR layer 1 is called an abutted junction. This is a structure in which a taper portion is formed in three layers of MR layer 1 / spacer layer 2 / SAL 3 and a permanent magnet layer 7 is formed thereon, which is an effective structure for improving reproduction stability. One. The permanent magnet layer 7 is magnetized in the x direction, and applies a magnetic anisotropic magnetic field from the permanent magnet layer 7 to the MR layer 1 to make the MR layer 1 a single magnetic domain in the x direction. During the reproducing operation of the MR head, a steady current is applied from the lead layer 8 and the permanent magnet layer 7 to the MR layer 1 in the x direction. A transverse bias magnetic field is applied to the MR layer 1 in the y direction by magnetostatic coupling energy provided by the SAL 3 when a current flows through the MR layer 1. When the MR layer 1 is single-domained in the x direction by the permanent magnet layer 7 and a lateral bias magnetic field is applied from the SAL 3, the resistance change with respect to the magnetic field change of the MR layer 1 is set in a linear state.
[0005]
[Problems to be solved by the invention]
Incidentally, the MR head performs a recording / reproducing operation while flying over a very low place of several tens of nanometers on the recording medium. FIG. 10 is a schematic diagram of the reproducing head when flying over the recording medium. The leakage magnetic field 31 from the recording bit 30 written on the recording medium 29 is very large in the vicinity of the recording medium. For this reason, there is a possibility that the magnetization state of the permanent magnet near the ABS (Air Bearing Surface) surface changes due to the leakage magnetic field 31 from the recording bit 30 and deteriorates the reproduction stability. In order to avoid this, it is necessary to improve the coercive force of the permanent magnet.
[0006]
Conventionally, the coercive force of a permanent magnet is measured by measuring a BH curve of a single layer film of a permanent magnet formed on a monitor dummy substrate (if there is a base, a two-layer film of the base and permanent magnet). The method has been adopted. However, it is the permanent magnet in the vicinity of MR layer 1 / spacer layer 2 / SAL3 in FIG. 9 that affects the longitudinal bias, and the characteristics of the permanent magnet in a very small region are important. Further, when the hard magnetic material is formed in contact with the soft magnetic material, there is a phenomenon that exchange coupling occurs at the bonding interface, and coercive force and squareness are reduced. For this reason, there is a possibility that the permanent magnets in contact with the MR layer 1 and the SAL 3 exhibit characteristics different from the BH curve.
[0007]
Furthermore, the formation process of Abatteddo junction MR layer 1 / spacer layer 2 / SAL3 and the permanent magnet layer 7 is performed by a lift-off method, such as shown in FIG. 4, for example. 11 (a), the after coating the photosensitive resist 9 on the first SAL3 / spacer layer 2 / MR layer 1 is deposited by like Suppata the Si0 ₂ 10. Then after removal of the excess portion of the SiO ₂ 10 by etching, selectively etching the resist or the like RIE (Reactive Ion Eching), to form a kind of shape in FIG. 11 (b). After then forming the tapered portion by ion milling, the base film 6 and the permanent magnet film 7 was formed in such sequential sputtering electrode film 8 (FIG. 11 (c)), finally the organic solvent of the resist 9 and SiO ₂ 10 removed, etc., Abattedo junction is formed (FIG. 11 (d)). Become this time problem, when the ion milling process shown in FIG. 11 (c) there are remaining insufficient SAL3, there is a possibility that the coercive force and squareness is degraded, as described above.
[0008]
In addition, the characteristics of the permanent magnet change sensitively depending on the cleanliness of the underlying surface and the crystal structure. Therefore, even when SiO ₂ 10 or resist 9 is reattached to the surface on which the permanent magnet film is formed by milling, the characteristics of the permanent magnet may be similarly deteriorated. For this reason, the characteristics of a permanent magnet having an actual element shape may not be measured by the BH curve of the single layer film. The present invention was created in view of the problems of the conventional example, and an evaluation apparatus and an evaluation method for measuring characteristics such as coercive force and squareness of a permanent magnet that affect reproduction stability in an actual element shape. Is to provide.
[0009]
[Means for Solving the Problems]
A first evaluation apparatus for an MR head according to the present invention comprises a magnetizing field generating coil for changing the magnetization state of a permanent magnet by applying a magnetic field in the longitudinal direction of the MR head, and the longitudinal direction of the MR head. Means for applying an alternating magnetic field and measuring means for measuring a resistance change of the MR head with respect to the change of the alternating magnetic field.
[0010]
A second evaluation apparatus for an MR head according to the present invention comprises a magnetizing magnetic field generating coil for changing a magnetization state of a permanent magnet by applying a magnetic field in the longitudinal direction of the MR head, and a lateral direction of the MR head. A coil for generating a demagnetizing magnetic field for demagnetizing the permanent magnet by applying a magnetic field to the magnetic head, means for applying an alternating magnetic field in the longitudinal direction of the MR head, and measuring a resistance change of the MR head with respect to the change of the alternating magnetic field And a measuring means.
[0011]
In the MR head evaluation method of the present invention, in the MR head, a magnetizing magnetic field is applied from the outside to the permanent magnet, which is a means for applying a longitudinal bias, in the longitudinal bias direction to change the magnetization state of the permanent magnet. And measuring a change in resistance of the MR head with respect to a change in the longitudinal alternating magnetic field of the MR head, and measuring the magnetization field dependence of a longitudinal bias magnetic field calculated from the change in resistance. To do.
[0012]
Alternatively, in the MR head evaluation method of the present invention, in the MR head, a demagnetizing magnetic field in a direction substantially perpendicular to the longitudinal bias is externally applied to a permanent magnet that is a means for applying a longitudinal bias, and the magnetization of the permanent magnet is performed. After changing the state, measuring a change in resistance of the MR head with respect to a change in the longitudinal alternating magnetic field of the MR head, and measuring the dependence of the longitudinal bias magnetic field calculated from the change in resistance on the demagnetizing field. It is characterized by.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1) The configuration and principle of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic diagram of a reproducing portion of the permanent magnet bias type MR head. There are permanent magnet layers 7 on both sides of the MR layer 1, which are magnetized in the direction of the arrow, and a longitudinal bias magnetic field is applied to the MR layer 1 in the track width direction (hereinafter referred to as the longitudinal direction). When a bias current is applied to the MR head, a transverse bias magnetic field is generated in the MR height direction (hereinafter referred to as the transverse direction) by magnetostatic coupling energy provided by SAL3. When the magnetization direction θ _MR of the MR layer 1 is defined as shown in FIG. 2 , the resistance of the MR head has the relationship as shown in FIG. 3 with respect to θ _MR , and therefore the resistance change linearity is good θ _MR = 45 degrees The longitudinal bias magnetic field and the lateral bias magnetic field are set so as to satisfy the following conditions. In FIG. 2 , when an external magnetic field is applied in the direction opposite to the direction of magnetization of the permanent magnet, θ _MR rotates to the plus side, and rotation stops at θ _MR = 180 degrees. The resistance at this time changes as shown by the arrow in FIG. 3 as the external magnetic field increases, and shows a minimum value when θ _MR = 90 degrees.
[0014]
FIG. 4 shows the measurement results of the resistance change of the MR head with respect to the external magnetic field in the vertical direction. The state where the resistance shows the minimum value is θ _MR of 90 degrees, and the bias from the permanent magnet is cancelled. Therefore, the magnitude of the external magnetic field at this time is the longitudinal bias magnetic field. Since the longitudinal bias magnetic field is proportional to the total amount of magnetic flux supplied from the permanent magnet layer 7 to the MR layer 1, it is estimated that the longitudinal bias magnetic field is proportional to the residual magnetization film thickness product of the permanent magnet layer. FIG. 5 shows the change in the longitudinal bias magnetic field due to the change in the residual magnetization film thickness product of the permanent magnet. The residual magnetization film thickness product was calculated from the residual magnetization value calculated from the BH curve of the dummy substrate for monitoring, and the longitudinal bias magnetic field was calculated from the resistance change curve with respect to the longitudinal external magnetic field of the MR head. As shown in FIG. 5 , since the longitudinal bias magnetic field is proportional to the residual magnetization film thickness product of the permanent magnet, it was confirmed that the residual magnetization of the permanent magnet can be grasped by measuring the longitudinal bias magnetic field. From this, a test element having the same shape as that after MR height processing is placed on the MR head wafer, and the longitudinal bias magnetic field is measured in the course of wafer manufacture, so that the residual magnetization of the permanent magnet can be measured at the wafer stage. Obviously it can be monitored.
[0015]
As described above, according to the first embodiment of the present invention, it was shown that the residual magnetization of the permanent magnet can be grasped at the wafer stage by measuring the longitudinal bias magnetic field.
[0016]
(Embodiment 2) FIG. 6 is a BH curve of a dummy substrate for monitoring the characteristics of a permanent magnet. The coercive force is 1.5 kOe, and the coercive force squareness ratio SR ^* is 0.91. Thus, sufficient characteristics are obtained. Since the longitudinal bias magnetic field is considered to be proportional to the residual magnetization of the permanent magnet, the longitudinal direction magnetic field (hereinafter referred to as a magnetizing magnetic field) is applied to the permanent magnet from the outside to change the magnetization state, and then the MR head. The longitudinal bias magnetic field of was measured. At this time, it is considered that the coercive force and the coercive force squareness ratio of the permanent magnet can be measured by measuring the dependence of the longitudinal bias magnetic field on the magnetization field. 7 (a) is a magnetizing field dependence of the measurement result of the longitudinal bias field. The measurement procedure is shown below. First, after applying a magnetic field of +2.5 kOe in the longitudinal direction as an initial state, the longitudinal bias magnetic field is measured, and then the magnetizing magnetic field is gradually reduced by 0.1 kOe step between -0.1 and -2.5 kOe. The longitudinal bias magnetic field is measured at each step. Subsequently, the magnetization field is gradually increased between +0.1 and +2.5 kOe in 0.1 kOe steps, and the longitudinal bias magnetic field is measured in the same manner. Thus measured results is FIG. 7 (a), the magnetizing magnetic field of magnitude when the longitudinal bias field is zero coercivity Hc, the coercivity squareness ratio SR ^* as shown in the figure, the coercive SR ^* = A / Hc, where A is the distance between the tangent at the magnetic force Hc and the point of intersection with the longitudinal bias magnetic field in the initial state and the initial state. As a result, the coercive force was calculated to be 1.5 kOe, and the coercive force squareness ratio was calculated to be 0.87, and almost the same result as that of the dummy substrate for characteristic monitoring shown in FIG. 6 was obtained.
[0017]
Next, a case where the correspondence between the characteristics of the permanent magnet film on the dummy substrate for characteristic monitoring and the characteristics of the permanent magnet film of the actual MR head cannot be obtained will be described. In the step of forming the taper portion shown in FIG. 7 (b) 11 at the time Abatteto Bu bonding (c), the wafer SAL3 was deposited a permanent magnet in a state that is not completely removed by ion milling is insufficient It is a measurement result. The characteristics of the dummy for monitoring the characteristics at this time are almost the same as those in FIG. Figure 7 than coercivity (b) has decreased to 1.0KOe, changes in the vicinity coercivity is in two stages. This is considered to be caused by the exchange coupling between the SAL 3 and the permanent magnet layer 7.
[0018]
In this way, according to the second embodiment of the present invention, after applying the magnetizing magnetic field to the MR head, the longitudinal bias magnetic field of the MR head is measured, and the dependence of the longitudinal bias magnetic field on the magnetizing magnetic field is measured. By doing so, it was shown that the coercive force, coercive force squareness ratio, etc. of the permanent magnet of the actual element shape can be measured. Further, this measurement method can be applied to the test element on the MR head wafer, and is an evaluation method capable of measuring the characteristics of the permanent magnet film more accurately than the BH measurement of the permanent magnet film on the dummy substrate. Became clear.
[0019]
(Embodiment 3) As shown in FIG. 10 , the leakage magnetic field from the recording bit on the recording medium is applied in the lateral direction with respect to the MR head. There is. For this reason, the coercive force of the permanent magnet with respect to a lateral magnetic field (hereinafter referred to as a demagnetizing magnetic field) is also important. FIG. 8 shows measurement results of the demagnetizing field dependence of the longitudinal bias magnetic field for the two MR heads measured in Example 2. The measurement procedure is as follows. In the initial state, a magnetizing magnetic field of +2.5 kOe is applied in the vertical direction, magnetized in the normal direction, the longitudinal bias magnetic field is measured, and then the demagnetizing magnetic field in the horizontal direction is set to 0.1 to 2.. The longitudinal bias magnetic field was measured at each step with a gradual increase in 0.1 kOe steps between 5 kOe. After that, after applying a magnetizing magnetic field of +2.5 kOe again and magnetizing the permanent magnet in the normal direction, this time, the demagnetizing magnetic field in the lateral direction is set between -0.1 and -2.5 kOe by 0.1 kOe step. The same measurement as in Example 2 was performed. When the demagnetizing field when the longitudinal bias magnetic field with respect to the longitudinal bias field in the initial state is demagnetized to 90% and the coercive force in this case, the head characteristics of the permanent magnets is good in FIG. 8 (a) 1.0kOe FIG. 8B shows a coercive force of 0.6 kOe in a head having poor permanent magnet characteristics. The difference in these results is due to the same reason as in Example 2. Compared with the measurement of Example 2, this measurement method is considered to evaluate the stability of the permanent magnet with respect to the external magnetic field in a more realistic manner. Note that the longitudinal bias magnetic field in FIG. 8 is normalized by the value of the longitudinal bias magnetic field in the initial state.
[0020]
As described above, according to the third embodiment of the present invention, after applying a demagnetizing magnetic field to the MR head, the longitudinal bias magnetic field of the MR head is measured, and the dependence of the longitudinal bias magnetic field on the demagnetizing magnetic field is measured. By doing so, it was shown that the stability of an actual element-shaped permanent magnet against an external magnetic field can be evaluated in a manner close to the actual operating conditions of an MR head.
[0021]
(Embodiment 4) FIG. 1 is a block diagram schematically showing an evaluation apparatus of the present invention. In FIG. 1, reference numerals 13 and 14 denote Helmholtz coils for applying an external magnetic field to the MR head in the vertical direction and the horizontal direction, respectively. In this embodiment, the vertical direction is the horizontal direction and the horizontal direction is the vertical direction. Is set. The external magnetic fields in the vertical and horizontal directions are driven by Helmholtz coil power supplies 19 and 20 and can be set from the control computer 27. An XYZ-θ stage 17 is provided in the Helmholtz coil, and the MR head wafer 11 can be fixed thereon. The probe 12 is provided at the central portion of the Helmholtz coil, and can be brought into electrical contact with each electrode terminal of the MR head on the wafer. The probe 12 and each electrode terminal are aligned by an XYZ-θ stage 17 and an XYZ-θ controller 23 that controls the XYZ-θ stage 17. If this part is imaged by the CCD camera 24 via the optical system 18 and the position of the obtained information can be recognized using image processing or the like, the positioning can be automated.
[0022]
After aligning the probe 12, a bias current is applied from the constant current source 25 to the current terminal of the MR head. Subsequently, the Helmholtz coils 13 and 14 change the longitudinal or transverse magnetic field in the MR head, and the output voltage at that time is read by the voltmeter 26 via the probe 12 to measure the dependence of the resistance on the external magnetic field. . The measured data is taken into the control computer 27 and values such as longitudinal bias magnetic field, reproduction output, and symmetry of the reproduction waveform are calculated and displayed on the result display unit 28.
[0023]
The magnetizing magnetic field coil 15 and the demagnetizing magnetic field coil 16 are installed at locations away from the center of the Helmholtz coil so as not to disturb the magnetic field distribution at the center of the Helmholtz coil. It is driven by the magnetic field coil power supply 21. In addition, the coil gap tip is placed slightly higher than the tip of the probe 12 so that the tip of the coil gap does not physically contact the MR head on the wafer. Information about the distances in the X and Y directions from the probe position to the magnetizing magnetic field coil 15 and the demagnetizing magnetic field coil 16 is stored in the memory of the control computer 27 in advance. When a magnetizing magnetic field and a demagnetizing magnetic field are actually applied to the MR head on the wafer, the target MR head is first aligned with the probe 12, and then based on information stored in the memory of the control computer. By instructing the XYZ-θ controller 23 to move by the distance in the X direction and the Y direction, the magnetizing coil power supply 22 and the demagnetizing coil power supply 21 generate a magnetic field of arbitrary strength. realizable. The magnetizing magnetic field and the demagnetizing magnetic field at the head position on the wafer are calibrated in advance.
[0024]
The MR head evaluation apparatus in this embodiment is intended to measure the dependence of the longitudinal bias magnetic field of the MR head on the magnetization field and the demagnetization field. Therefore, while changing the magnetized state of the permanent magnet of the head magnetizing coil and demagnetization coils as described above, by measuring the resistance change with respect to the longitudinal direction of the external magnetic field, 10, 11 The dependence of the longitudinal bias magnetic field on the magnetizing field and the demagnetizing field can be measured, and characteristics such as the coercive force and coercive force squareness ratio of the permanent magnet can be measured in the actual element shape.
[0025]
As described above, according to the fourth embodiment of the present invention, the resistance change with respect to the external magnetic field is measured while changing the magnetization state of the permanent magnet of the MR head, and the longitudinal bias magnetic field obtained from this resistance change depends on the magnetization field. It was shown that an MR head wafer evaluation apparatus capable of measuring characteristics such as coercive force and coercive force squareness ratio of a permanent magnet in an actual element shape can be provided.
[0026]
【The invention's effect】
According to the evaluation method and the evaluation apparatus of the present invention, by measuring the longitudinal bias magnetic field while changing the magnetization state of the permanent magnet for the MR head using the permanent magnet as means for applying the longitudinal bias, the permanent magnet Characteristics such as coercive force and squareness can be measured with the actual element shape. In addition, by measuring a test element having the same shape as that after MR height processing arranged on the MR head wafer with this evaluation method and evaluation apparatus, the characteristics of the permanent magnet can be measured at the wafer stage. Therefore, the instability of the MR head due to the permanent magnet characteristic failure can be grasped at an early stage of the MR head wafer manufacturing process, and wafers with poor characteristics can be selected before the MR head is completed as a single unit. The manufacturing cost of the post process associated with the non-defective product can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of a configuration of an MR head evaluation apparatus according to the present invention. FIG. 2 is a schematic diagram of a reproducing portion of a permanent magnet bias MR head. FIG. 3 is a relation between magnetization direction of MR layer and element resistance. [Fig. 4 ] Change in element resistance against external magnetic field in the vertical direction [Fig. 5 ] Relationship between the remanent magnetization film thickness product of the permanent magnet and the longitudinal bias magnetic field [Fig. 6 ] BH curve of the dummy substrate for monitoring the characteristics of the permanent magnet [ 7] the present invention demagnetizing field dependence of the permanent magnets in the actual element shape by magnetizing field dependence [8] the present invention of the permanent magnets in the actual element shape according to FIG. 9 MR head reproducing portion of the recording medium Enlarged view seen from the opposite surface [Fig. 10 ] Schematic diagram of MR head during playback operation [Fig. 11 ] Abutted junction formation process [Explanation of symbols]
1 MR layer, 2 spacer layer, 3 SAL, 4 upper insulating layer, 5 lower insulating layer, 6 underlayer, 7 permanent magnet layer, 8 electrode layer, 9 resist layer, 10 SiO ₂ layer, 11 MR head wafer, 12 Probe, 13 Helmholtz coil for longitudinal magnetic field, 14 Helmholtz coil for transverse magnetic field, 15 Coil for magnetic field, 16 Coil for demagnetizing magnetic field, 17 XYZ-θ stage, 18 Optical system, 19 Longitudinal magnetic field Helmholtz coil power supply, 20 transverse magnetic field Helmholtz coil power supply, 21 magnetizing magnetic field coil power supply, 22 demagnetizing magnetic field coil power supply, 23X-Y-Z-θ controller, 24 CCD camera, 25 constant current source, 26 voltage 27, computer for control, 28 result display section, 29 recording medium, 30 recording bits, 31 leakage magnetic field

Claims (4)

A magnetoresistive head evaluation apparatus having means for applying a longitudinal bias to a magnetoresistive element using a permanent magnet,
Magnetizing magnetic field generating coil for changing the magnetization state of the permanent magnet in the same direction as the longitudinal bias, means for applying an alternating magnetic field in the longitudinal bias direction, and the magnetoresistive head for changes in the alternating magnetic field A magnetoresistive head evaluation apparatus comprising: a measuring unit that measures a resistance change of the magnetoresistive element.   2. The magnetoresistive head evaluation apparatus according to claim 1, further comprising a demagnetizing field generating coil that demagnetizes the permanent magnet by applying a magnetic field substantially perpendicularly to the longitudinal bias.   A method for evaluating a magnetoresistive head using a permanent magnet as means for applying a longitudinal bias, wherein a magnetizing magnetic field is applied to the permanent magnet from the outside in the longitudinal bias direction to change the magnetization state of the permanent magnet. After the change, while applying an alternating magnetic field in the longitudinal bias direction, the resistance change of the magnetoresistive effect element with respect to the change is measured, and the dependence of the magnetization field on the longitudinal bias calculated from the resistance change value is calculated. A method for evaluating a magnetoresistive head. A method for evaluating a magnetoresistive head using a permanent magnet as means for applying a longitudinal bias, wherein a demagnetizing magnetic field in a direction substantially perpendicular to the longitudinal bias is applied to the permanent magnet from outside. after changing the magnetized state, the longitudinal bias direction while applying an alternating magnetic field by measuring the resistance change of the magnetoresistive element for the change, before Symbol demagnetization against the vertical bias calculated from the resistance change value A method for evaluating a magnetoresistive head characterized by calculating a magnetic field dependency.

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