JP3717628B2 - 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 effect type magnetic head evaluation method and evaluation apparatus using a magnetoresistive effect 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. (MagnetorHereinafter, the head is referred to as an MR head. ). The MR head uses the magnetoresistive effect of a ferromagnetic thin film such as permalloy, and a large reproduction output can be obtained regardless of the relative speed with respect to the magnetic disk. However, there is a problem of deviation in the bias state called fluctuation in reproduction output or peak asymmetry due to Barkhausen noise or the like. The peak asymmetry is the positive amplitude intensity V seen in the output waveform during playback operation.⁺And negative amplitude intensity V^-  Asymmetry (V⁺-V^-) / (V⁺+ V^-). Playback output is the amplitude of the positive and negative output waveforms (V⁺+ V^-When the recording / reproducing operation is repeated, the reproduction output fluctuates and adversely affects the error rate of the hard disk device. In a hard disk device using an MR head, a signal detection method called PRML is adopted, and an even higher recording density is realized. However, in PRML, since the shape of the reproduction waveform directly affects the error rate of the drive, it is important to reduce the reproduction output fluctuation of the MR head and the peak asymmetry. Therefore, it is necessary to detect and select reproduction characteristics such as fluctuations in reproduction output and peak asymmetry as inspection at the time of manufacturing the MR head, and various evaluation methods and evaluation apparatuses have been proposed.
[0003]
Conventionally, as a method for evaluating such reproduction characteristics, an assembly in which a suspension is attached to an MR head after gap depth processing (MRHeadGimbalAHereinafter referred to as MR HGA. ) Is actually floated on the magnetic disk, and a head with poor reproduction characteristics is removed from the output voltage waveform obtained as a result. However, in such an evaluation method, since measurement evaluation cannot be performed unless the MR HGA is assembled, it takes time and cost to assemble the MR HGA, it takes a long time for evaluation per head, and the MR becomes a defective product. HGA has problems such as being disposed of and impossible to regenerate, and is not an efficient evaluation method.
[0004]
Further, the technique described in Japanese Patent Application Laid-Open No. 6-150264 is based on the fact that an alternating external that changes sinusoidally in a direction perpendicular to the air bearing surface with respect to a plurality of MR heads after gap depth processing arranged on a head block. An electromagnetic conversion characteristic of the MR head with respect to the change of the alternating external magnetic field is obtained by applying a magnetic field. However, the content disclosed therein is merely a look at the state of resistance change with respect to an external magnetic field, and does not mention any specific method for quantifying Barkhausen noise. Further, it is very difficult to take a correspondence between this evaluation result and the actual result obtained by floating on the magnetic disk, and the instability of the reproduction characteristic due to the Barkhausen noise of the MR head cannot be accurately detected. Further, in the MR head, the upper and lower shield magnetic layers are arranged so as to cover the MR element in order to shield the MR element from unnecessary magnetic fields. Due to the influence of the shield magnetic layer, in the MR head before the gap depth processing, the change of the external magnetic field is not sufficiently applied to the MR element. Therefore, it is difficult to detect the reproduction characteristics of the MR head before the gap depth processing by this method. It was.
[0005]
In the technique described in Japanese Patent Application Laid-Open No. 60-105286, a test element having no shield magnetic layer on at least one side is arranged on a wafer and used as a means for judging the quality of a wafer bias state. Is disclosed. In this technique, since there is no shield magnetic layer on at least one side, a change in the external magnetic field is sufficiently applied to the MR layer, so that the bias state can be detected to some extent. However, since the bias state of the MR element changes depending on the presence or absence of the shield, the actual bias state of the MR head with the shield magnetic layer cannot be determined, and the reproduction output fluctuation due to Barkhausen noise or the like cannot be detected accurately. It has been difficult to determine whether the reproduction characteristics of the wafer are good or bad.
[0006]
The present invention was created in view of the problems of the conventional example, and even during the manufacturing process, the reproduction characteristics such as the bias state of the MR head and the reproduction output fluctuation can be inspected. Provided are a magnetoresistive effect element or magnetoresistive effect element wafer evaluation apparatus capable of discovering product defects even in the course of a process and performing appropriate process management, and remarkably improving manufacturing efficiency, and an evaluation method thereof. Is.
[0007]
[Means for Solving the Problems]
As shown in FIG. 1, a first evaluation apparatus for a magnetoresistive effect element (hereinafter referred to as an MR element) according to the present invention provides a test element having a shield magnetic layer on at least one side arranged for wafer evaluation. Means for generating a static magnetic field (hereinafter referred to as an offset magnetic field) from the outside in a direction to cancel the longitudinal bias magnetic field of the test element, means for generating an alternating magnetic field in the lateral direction of the test element, and applying the offset magnetic field Measuring means for measuring a resistance change of the test element with respect to a change of an alternating magnetic field, and accurately evaluating a bias state after gap depth processing of an MR element with a shield magnetic layer formed on the same wafer. To do.
[0008]
According to a first evaluation method of the present invention, the test element against a change in a lateral alternating magnetic field of the test element while applying an offset magnetic field for correcting the influence of a shield magnetic film to the test element for wafer evaluation By measuring the resistance change, the bias state after the gap depth processing of the MR element with the shield magnetic layer formed on the same wafer is accurately evaluated.
[0009]
The second evaluation apparatus according to the present invention obtains a change in resistance of the MR element with respect to a change in an alternating magnetic field in the lateral direction while applying an offset magnetic field from the outside in a direction that cancels the longitudinal bias magnetic field of the MR element. According to the offset magnetic field dependency, there is provided determination means for determining whether the MR element is good or bad.
[0010]
The second evaluation method of the present invention measures the resistance change of the MR element with respect to the change of the alternating magnetic field in the transverse direction of the MR element while applying the offset magnetic field to the MR element, and the dependence of the resistance change on the offset magnetic field. To determine whether the MR element is good or bad.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
The configuration and principle of the present invention will be described below with reference to the drawings. As shown in FIG. 14, the reproducing portion of the permanent magnet bias type MR head includes a bias magnetic field (transverse bias magnetic field) by magnetostatic coupling to the MR layer 1 that exhibits the magnetoresistive effect, the spacer layer 2 that is a nonmagnetic layer, and the MR layer 1. SAL ()SofAdjacentLayer) 3 layers. Further, permanent magnets are arranged at both ends of the MR element and magnetized in the direction of the arrow in FIG. 14, thereby biasing the magnetization of the MR layer in the longitudinal direction. A read gap layer 7, an upper shield magnetic layer 5 and a lower shield magnetic layer 6 for shielding an external magnetic field are disposed above and below the MR element. The bias state of the MR head is determined by the balance between the lateral bias in the y-axis direction in FIG. 14 and the longitudinal bias in the x-axis direction from the permanent magnet due to SAL magnetostatic coupling. In the following description, the x-axis direction in FIG. 14 is referred to as the vertical direction, and the y-axis direction is referred to as the horizontal direction.
[0012]
The bias state of the MR head can be known by applying a lateral external magnetic field to the MR element and measuring the resistance change. At the wafer stage, the MR element is not subjected to gap depth processing and is covered with a shield magnetic layer. For this reason, the change in the external magnetic field is not sufficiently applied to the MR element, and the MR element shape is different before the gap depth processing, so that the reproduction characteristics of the MR head cannot be measured correctly. In order to solve this problem, the quality of the reproduction characteristics of a wafer is evaluated by evaluating the magnetic characteristics of a test element that does not have a shield magnetic layer on at least one side disposed on the wafer. FIG. 4 shows an embodiment in which test elements for characteristic evaluation are arranged on an MR element wafer. However, in the case of the test element, most of the longitudinal bias magnetic field from the permanent magnet is applied to the MR element (FIG. 5A), whereas in the MR element having the shield magnetic layer, the magnetic flux from the permanent magnet is shielded. Since it is absorbed by the magnetic layer, the effective longitudinal bias applied to the MR element is reduced (FIG. 5B). When the magnitude of the lateral bias applied to the MR layer is constant, when the longitudinal bias is increased, the magnetization of the MR layer becomes the under bias in the longitudinal direction, and when the longitudinal bias is reduced, the magnetization becomes the over bias in the lateral direction. . For this reason, the evaluation result of the test element does not necessarily match the bias state of the MR element with the shield magnetic layer formed on the same wafer.
[0013]
Therefore, in consideration of the influence of the shield magnetic layer, an offset magnetic field in the reverse direction (negative x-axis direction in FIG. 5) that cancels a part of the longitudinal bias from the permanent magnet is applied from the outside, and is simulated in actuality. There is a need for a method for evaluating the magnetic characteristics close to the operating state of the MR element. FIG. 6 shows the result of numerical calculation of how the magnetic flux from the permanent magnet is shunted to the MR layer and the shield magnetic layer as a function of the thickness of the read gap. Since the test element is considered to have an infinite lead gap film thickness, when the read gap film thickness is 100 nm, the longitudinal bias magnetic field applied to the MR layer is reduced to about half by the shield magnetic layer. Therefore, if half the longitudinal bias magnetic field strength is applied as an offset magnetic field and measured opposite to the magnetization direction, the operation state of the MR element with the shield magnetic layer formed on the same wafer can be reproduced. In the case where there is a shield magnetic layer on one side, the operation state of the MR head with the shield magnetic layer formed on the same wafer can be reproduced by measuring by applying an offset magnetic field budgeted by the same calculation.
[0014]
FIG. 7 shows the correlation between the peak asymmetry of the MR element with the shield magnetic layer after gap depth processing and the peak asymmetry of the test element when correction is not performed by the offset magnetic field. The y-axis intercept of the primary correlation curve is about plus 20%, and the correlation is weak. Next, FIG. 8 shows the correlation of peak asymmetry when correction is performed using an offset magnetic field. The y-axis intercept of the primary correlation curve is close to zero, and the correlation is strong. Therefore, it is possible to accurately measure the magnetic properties of the wafer by measuring the resistance change against the external magnetic field while applying an offset magnetic field that corrects the influence of the shield to the test element provided for wafer evaluation. It is possible to estimate the characteristics of the MR element with the shield magnetic layer.
[0015]
As described above, the resistance change of the external magnetic field is measured by applying the offset magnetic field for correcting the influence of the shield to the test element provided for wafer evaluation according to the first embodiment of the present invention. It has been shown that an MR element wafer evaluation method capable of accurately measuring magnetic characteristics can be provided.
[0016]
(Example 2)
FIG. 1 shows a configuration diagram of an MR element wafer evaluation apparatus according to a second embodiment of the present invention. In FIG. 1, two pairs of coils, an alternating magnetic field generating coil 8 in the horizontal direction and an offset magnetic field generating coil 9 in the vertical direction, are arranged so as to be orthogonal to each other in the plane of the MR element 10. These coils are controlled by an alternating magnetic field coil power source 11 and an offset magnetic field coil power source 12 so that a longitudinal offset magnetic field and a lateral alternating magnetic field can be applied to the MR element 10. The sense current is set by the constant current source 13. The resistance value of the MR element is calculated from the potential difference measured by the sense current and the voltmeter 14. The MR element resistance change with respect to the measured magnetic field change is displayed on the display unit 15, and measurement data such as peak asymmetry calculated from the resistance change is stored in the data storage unit 16. Finally, the pass / fail judgment unit 17 judges pass / fail of the MR element. The control unit 18 has a function of managing all these measurement procedures.
[0017]
FIG. 2 is a flowchart showing the measurement procedure of the evaluation apparatus according to the second embodiment of the present invention. First, in step S1, the MR head is aligned so that an external magnetic field is effectively applied, and the probe electrode is connected to the current terminal and output terminal of the MR head. Next, in step S2, the set sense current is passed through the MR element, and in step S3, an offset magnetic field for correcting the influence of the shield magnetic layer is applied. In step S4, a lateral alternating magnetic field is applied, and the resistance change of the MR element is measured. The amplitude of the alternating magnetic field at this time is preferably a value corresponding to the magnetic field applied from the disk to the MR element when actually operated on the disk, but in this embodiment, ± 50 Oe was adopted. In step S5, the offset magnetic field, the alternating magnetic field, and the sense current are turned off, and the resistance change of the MR element measured in step 6 is displayed. Next, in step S7, reproduction characteristics such as a bias state, reproduction output, and Barkhausen noise are quantified from the measured resistance change, and the quality of the characteristics is determined by comparing with a quality determination criterion. Finally, in step S8, the measurement data and the pass / fail judgment result are saved, and the measurement ends.
[0018]
In this way, by measuring the resistance change with respect to the alternating magnetic field in the lateral direction while applying the offset magnetic field for correcting the influence of the shield to the test element for wafer evaluation according to the second embodiment of the present invention, It was shown that an MR element wafer evaluation apparatus that accurately measures the bias state of the MR element after gap depth processing in advance in the process can be provided.
[0019]
(Example 3)
FIG. 9 shows the resistance change of the MR element with respect to the change of the alternating magnetic field of ± 250 Oe while applying the offset magnetic field to the test element for wafer evaluation. As the offset magnetic field increases, the amount of change in resistance near the zero magnetic field increases, and it can be confirmed that the magnetic field sensitivity is increased. FIG. 10 shows the peak asymmetry measured with an alternating magnetic field of ± 50 Oe and the dependence of the reproduction output on the offset magnetic field. As the offset magnetic field increases, the peak asymmetry increases, and it can be seen that the longitudinal bias magnetic field is actually canceled. It is also clear from the dependence of the reproduction output on the offset magnetic field that the magnetic field sensitivity of the MR element is increased by decreasing the longitudinal bias magnetic field. When the offset magnetic field is further increased, the peak asymmetry and the output rapidly decrease in the vicinity of about 90 Oe. This is considered to be a result of the offset magnetic field becoming larger than the bias magnetic field from the permanent magnet and the magnetization of the MR layer rotating to the opposite side. The magnitude of the offset magnetic field corresponding to the peak asymmetry and the inflection point of the reproduction output is an index relating to the magnitude of the longitudinal bias magnetic field or the strength of the magnetic domain control. FIG. 11 shows the results of measuring the peak asymmetry of the test element on the wafer and the offset magnetic field dependence of the reproduction output for a wafer including an MR head with unstable reproduction characteristics. An inflection point occurs when the offset magnetic field is 50 Oe, which indicates that the magnetization of the MR layer is reversed with respect to a small offset magnetic field as compared with FIG. From this result, it can be determined that the longitudinal bias magnetic field by the permanent magnet is insufficient in the MR head having unstable reproduction characteristics.
[0020]
As described above, according to the third embodiment of the present invention, the strength of the magnetic domain control of the MR element can be evaluated by measuring the offset magnetic field dependency of the resistance change of the MR element, and the reproduction characteristic of the wafer manufacturing process can be evaluated. It has been shown that an MR element wafer evaluation method for measuring instability can be provided.
[0021]
Example 4
FIG. 3 is a flowchart showing the measurement procedure of the evaluation apparatus of the MR head evaluation apparatus according to the fourth embodiment of the present invention. First, in step S1, the MR head is aligned so that an external magnetic field is effectively applied, and the probe electrode is connected to the current terminal and output terminal of the MR head. Next, in step S2, the set sense current is passed through the MR element, and in step S3, the offset magnetic field is set to zero. In step S4, a lateral alternating magnetic field is applied, and the resistance change of the MR element is measured. The amplitude of the alternating magnetic field at this time is preferably a value corresponding to the magnetic field applied from the disk to the MR element when actually operated on the disk, but ± 50 Oe is adopted in this embodiment. In step S5, the offset magnetic field is increased. Steps S4 to S5 are repeated until the designated offset magnetic field is reached (determined in step S6), and the offset magnetic field dependency of the magnetic characteristics is measured. Thereafter, in step S7, the offset magnetic field, the alternating magnetic field, and the sense current are turned off, and the resistance change of the MR element measured in step S8 is displayed. Next, in step S9, reproduction characteristics such as a bias state, reproduction output, and Barkhausen noise are quantified from the measured resistance change, and the quality of the characteristics is determined by comparison with a quality determination criterion. Finally, in step S10, the measurement data and the pass / fail judgment result are saved, and the measurement ends.
[0022]
As described above, according to the fourth embodiment of the present invention, it is possible to evaluate the strength of the magnetic domain control of the MR element by measuring the offset magnetic field dependency of the resistance change of the MR element. It has been shown that an MR element wafer evaluation method for measuring qualitative properties can be provided.
[0023]
(Example 5)
The method and apparatus for evaluating the strength of magnetic domain control of MR elements using permanent magnets shown in Examples 3 and 4 are not limited to test elements for wafer evaluation, and are actual elements after gap depth processing. Is the same. FIG. 12 shows the peak asymmetry of the MR head having a stable reproducing characteristic and the unstable MR head and the dependence of the reproducing output on the offset magnetic field. In a head with stable reproduction characteristics, the peak asymmetry and the offset magnetic field at which the reproduction output changes rapidly is 60 Oe, whereas in a stable head, it is 120 Oe. FIG. 13 shows changes in resistance after applying an offset magnetic field to several heads with poor reproduction characteristics. It can be confirmed that the resistance that seems to be Barkhausen noise as shown in FIG. 13C changes abruptly or that the resistance change as shown in FIG. 13D has hysteresis. Since the offset magnetic field is considered to have an effect of increasing the frequency of occurrence of such Barkhausen noise and hysteresis, the Barkhausen noise and hysteresis observed in the resistance change of the MR element are quantified, and the criticality of the offset magnetic field that increases this By using a value as an index, for example, a head showing a critical value below a certain level is determined to be defective, so that a head with poor reproduction characteristics can be selected.
[0024]
As described above, according to the fifth embodiment of the present invention, by measuring the resistance change of the MR element with respect to the alternating magnetic field while applying the offset magnetic field to the MR element after gap depth processing, the reproduction characteristics are poor. It was shown that an MR element evaluation method capable of selecting the head can be provided.
[0025]
(Example 6)
In this embodiment, the MR element evaluation apparatus and evaluation method for MR elements according to the first to fifth embodiments of the present invention will be described. An MR element having the RH characteristic as shown in FIG. 13 is judged as defective. FIG. 13A is an example in which the resistance change of the MR element with respect to the alternating magnetic field is not a straight line but is bent in the middle and the linearity is poor. For example, in order to quantify the linearity of FIG. 13A, the difference between the resistance change amount when the magnetic field is changed from zero to plus and the resistance change amount when the magnetic field is changed from zero to minus is calculated. The quality of the MR element can be determined by dividing by the total resistance change amount. The formula at that time is
| (Maximum resistance-resistance at zero magnetic field)-(resistance at zero magnetic field-minimum resistance) | / (maximum resistance-minimum resistance)
It becomes. The closer this value is to zero, the better the device performance. Calculate this value from the change in resistance when applying an offset magnetic field to correct the influence of the shield magnetic layer in the test element for wafer evaluation or the change in resistance when no offset magnetic field is applied to the MR element after gap depth processing. If the reference value is exceeded, it will be considered as defective.
[0026]
As shown in FIG. 13B, the linearity of the MR element is good, but the error rate of the hard disk drive is also deteriorated when the overall resistance change amount is small (reproduction output is small). Therefore, a reproduction output (maximum) is obtained from a resistance change when an offset magnetic field for correcting the influence of the shield magnetic layer is applied to the test element for wafer evaluation or a resistance change when no offset magnetic field is applied to the MR element after gap depth processing. (Resistance value−minimum resistance value) is calculated.
[0027]
A head showing a discontinuous change in resistance caused by Barkhausen noise as shown in FIG. 13C is also judged to be defective because it causes fluctuations in reproduction output. For example, in order to quantify such Barkhausen noise, it is only necessary to quantify the discontinuous change in resistance. The resistance value is differentiated from the external magnetic field, and the slope of the overall resistance change (dR / dH)_avgBy using the maximum value in the measurement data of the deviation of the differential value (dR / dH) with respect to as an index, the quality of the MR element can be determined. The formula at that time is
max [(dR / dH)-(dR / dH)_avg|]²
It becomes. The closer this value is to zero, the better the device performance. For this reason, this value is calculated from the resistance change when an offset magnetic field is applied to correct the influence of the shield magnetic layer in the test element for wafer evaluation or the resistance change when no offset magnetic field is applied to the MR element after gap depth processing. If the calculated value exceeds the reference value, it will be considered as defective.
[0028]
Since the head having hysteresis in the resistance change as shown in FIG. 13D also causes the reproduction output fluctuation, it is determined to be defective. For example, in order to quantify such hysteresis, it is only necessary to quantify the difference in resistance between the path when the magnetic field is increased and the path when the magnetic field is decreased. Whether the MR element is good or bad can be determined by using, as an index, a value obtained by integrating the difference in resistance value in the measurement data. The formula at that time is
Σ | R (H)⁺  -R (H)^-｜
It becomes. The closer this value is to zero, the better the device performance. For this reason, this value is calculated from the resistance change when an offset magnetic field is applied to correct the influence of the shield magnetic layer in the test element for wafer evaluation or the resistance change when no offset magnetic field is applied to the MR element after gap depth processing. If the calculated value exceeds the reference value, it will be considered as defective.
[0029]
As described above, according to the sixth embodiment of the present invention, it is possible to quantitatively determine the quality of an MR head with poor reproduction characteristics as shown in FIG. 13, and combine it with the evaluation apparatus and the evaluation method of the first to fifth embodiments. Thus, it has been shown that an MR element evaluation apparatus capable of inspecting the reproduction characteristics of the MR head can be provided even during the manufacturing process.
[0030]
【The invention's effect】
According to the evaluation method and the evaluation apparatus of the present invention, at the stage where the wafer on which the head element of the MR element and the test element for wafer evaluation are formed is manufactured, the test element is evaluated, thereby providing an actual shielded device. It is possible to quantitatively detect the reproduction instability due to the bias state of the MR element or Barkhausen noise. Depending on the quality of the test element, appropriate management of the manufacturing process can be performed and the quality can be improved. In addition, by performing the same evaluation on the MR element after gap depth processing, it is possible to quantitatively detect reproduction instability caused by Barkhausen noise and perform selection, so that the HGA assembly man-hours associated with defective reproduction characteristics are applied. And cost can be reduced.
[0031]
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an MR element evaluation apparatus according to second and fourth embodiments of the present invention.
FIG. 2 is a control flowchart of an MR element evaluation apparatus according to a second embodiment of the present invention.
FIG. 3 is a control flowchart of an MR element evaluation apparatus according to a fourth embodiment of the present invention;
FIG. 4 shows an example of element arrangement of an MR element wafer.
FIG. 5 is a schematic diagram showing a difference in the state of longitudinal bias depending on the presence or absence of a shield magnetic layer.
FIG. 6 shows the dependency of longitudinal bias on the read gap thickness.
FIG. 7 shows the correlation of the peak asymmetry between the MR element with a shield magnetic layer and the test element when the influence of the shield magnetic layer is not corrected.
FIG. 8 shows the correlation between the peak asymmetry of the MR element with a shield magnetic layer and the test element when the influence of the shield magnetic layer is corrected.
FIG. 9 shows the offset magnetic field dependence of the resistance change of the MR element with respect to the change of the alternating magnetic field.
FIG. 10 shows the peak asymmetry of the MR head having a stable reproduction characteristic and the offset magnetic field dependence of the reproduction output.
FIG. 11 shows the peak asymmetry of an MR head with unstable reproduction characteristics and the dependence of the reproduction output on the offset magnetic field.
FIG. 12 shows the peak asymmetry of the MR head with a shield magnetic layer after gap depth processing with stable and unstable reproduction characteristics, and the offset magnetic field dependence of the reproduction output.
FIG. 13 is a typical example of a resistance change with respect to a change in an external magnetic field of an MR element having poor reproduction characteristics.
FIG. 14 shows a reproducing portion of a permanent magnet bias type MR head.
[Explanation of symbols]
1 MR layer, 2 spacer layer, 3 SAL, 4 permanent magnet, 5 upper shield magnetic layer, 6 lower shield magnetic layer, 7 lead gap layer, 8 coil for applying alternating magnetic field, 9 coil for applying offset magnetic field, 10 MR element, 11 power supply for alternating magnetic field coil, 12 power supply for offset magnetic field coil, 13 constant current source, 14 voltmeter, 15 display unit, 16 data storage unit, 17 pass / fail judgment unit, 18 control unit, 19 test element for characteristic evaluation, 20 products MR element forming region, 21 non-magnetic substrate

Claims (4)

A longitudinal and lateral bias magnetic field is applied to a magnetoresistive element (hereinafter abbreviated as MR element) which is a magnetosensitive part and is sandwiched between shield magnetic layers (hereinafter abbreviated as MR head). And an offset magnetic field generating means for canceling the longitudinal bias magnetic field, an alternating magnetic field generating means in the same direction as the lateral bias magnetic field, and a test head with or without the shield layer formed on the wafer. And an MR head evaluation apparatus comprising means for measuring the electrical resistance of the MR element of the test head. 2. The MR head evaluation apparatus according to claim 1, further comprising determination means for determining a quality of the MR head by calculating a change amount from a measured value of electric resistance of the test MR element. An MR head evaluation method in which longitudinal and lateral bias magnetic fields are applied to an MR element serving as a magnetosensitive portion and sandwiched between shield magnetic layers, and a test head from which at least one of the shield layers is removed is applied to a wafer The characteristics of the MR head are determined by measuring the change in the electrical resistance of the MR element of the test head with respect to an alternating magnetic field in the same direction as the lateral bias magnetic field while applying an offset magnetic field that cancels the longitudinal bias magnetic field. MR head evaluation method characterized by the above 4. The MR head evaluation method according to claim 3, wherein the quality of the MR head is determined from the relationship between the measurement result of the change in electrical resistance of the MR element of the test head and the offset magnetic field.

Images