JPH077492B2 - Inspection method of thin film magnetic head - Google Patents

Description

The present invention relates to a method of inspecting a thin film magnetic head.

[Conventional technology]

When newly recording data, the magnetic disk device writes directly on unnecessary old data on a magnetic disk which is a magnetic recording medium. As a result, old data is erased and new data is recorded. Therefore, the magnetic field generated from the magnetic head used for writing needs to have a strength enough to write data at least over the entire thickness of the recording medium. If the magnetic field generated from the magnetic head is weak and the data cannot be written over the entire thickness of the recording medium, the old data remains unerased and is overwritten with the newly written data.

Therefore, in the magnetic head used in the magnetic disk device, the strength of the generated magnetic field is evaluated by the overwriting characteristic.

The overwriting characteristic is represented by the ratio of the reproduction output by the new data and the reproduction output by the remaining unerased data when the data written as described above is reproduced.

In practice, the overwrite characteristics are evaluated at the inspection stage in the manufacturing process of the magnetic head. Therefore, as the old data, the one written at the lowest frequency among the modulation methods used in the magnetic disk device is used. The highest frequency of the same modulation method is used as the data.

However, the current value of the signal for exciting the magnetic head is the same.

Letting ΔE1f be the reproduction output value due to the remaining unerased data written at the lowest frequency, and E2f being the reproduction output value of the new data written at the highest frequency, the value of the overwriting characteristics is It is expressed in decibels and expressed as OW = -20logE2f / ΔE1f (dB). In the magnetic head used as a product, -25
About dB is required.

In recent years, thin film magnetic heads have become indispensable for increasing the recording density on recording media and achieving large storage capacities in magnetic disk devices.

In the case of this thin film magnetic head, the strength of the magnetic field generated is
It depends on the shape of the tip of the magnetic core, and particularly on the depth of the magnetic gear.

Conventionally, in order to manufacture a thin film magnetic head having a writing characteristic such that a required OW value can be obtained, many methods of forming a magnetic gap depth to a predetermined size have been devised and implemented.

For example, it is disclosed in JP-A-60-254404.

[Problems to be solved by the invention]

However, in order to achieve a higher magnetic recording density, the track width, the pole length (thickness of the magnetic layer formed by the magnetic gear part), and the magnetic gear length (thickness of the non-magnetic layer forming the magnetic gear part). ) Tends to be produced in thin film magnetic heads. In this case, the writing characteristic cannot be determined only by forming the magnetic gear depth to a predetermined dimension, and the writing characteristic is affected by the entire shape of the tip of the magnetic core.

Further, in the above-mentioned thin film magnetic head, the depth of the magnetic gear becomes small as well as the track width and the like.
To some extent, it becomes impossible to measure the tip of the magnetic core of the magnetic head by an optical method.

Therefore, in order to judge whether the writing characteristics of the manufactured thin film magnetic head are acceptable or unacceptable, it has been necessary to measure the OW value by incorporating it in a magnetic disk device and performing a recording / reproducing operation.

In view of the above problems, an object of the present invention is to provide an inspection method capable of easily determining pass / fail regarding the writing characteristics of a thin film magnetic head, and thereby enabling the magnetic head to be manufactured with high accuracy.

[Means for solving problems]

According to the present invention, a DC bias current is applied to a thin film magnetic head to be inspected, and an impedance drop due to saturation of a magnetic core of the magnetic head is measured to detect a write characteristic of the magnetic head to inspect the magnetic head. It is an inspection method.

[Action]

In the thin-film magnetic head, the tip of the magnetic core is most likely to be magnetically saturated, and the state of magnetic saturation depends on the shape of the tip of the magnetic core.

The writing characteristics of the thin film magnetic head depend on the shape of the tip of the magnetic core.

Therefore, there is a strong correlation between the value of the decrease in impedance and the writing characteristic.

By using this correlation, the write characteristic can be detected from the value of the decrease in impedance.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. An upper magnetic layer 1, a lower magnetic layer 2, a conductor winding 4, an electrical insulating layer, etc. are deposited in a predetermined order by a photolithography technique, and a tip portion of a magnetic core composed of the upper magnetic layer 1 and the lower magnetic layer 2 is deposited. In the magnetic head 5 in which the magnetic head 3 is formed, the overwrite characteristic of the magnetic head 5 is detected from the impedance of the magnetic head 5.

As shown in FIG. 1, the impedance measuring apparatus according to the present embodiment incorporates the magnetic head 5 in one side, and a coil having the same degree of inductance as the magnetic head 5 in the other side facing the magnetic head 5. 6, a bridge circuit 7 having a capacitor 12 for cutting a DC current, an AC oscillator 8 as a high frequency signal (several MHz to several tens of MHz) source for detecting the impedance of the magnetic head 5, the magnetic head 5, a pulse oscillator (several Hz to several tens Hz) 9 as a bias current source for exciting the magnetic core 5 to generate magnetic saturation of the magnetic core, a high frequency differential amplifier 10 for amplifying the output of the bridge circuit 7, It is composed of an AC-DC converter 11 and an arithmetic unit 14.

Next, the operation of the above embodiment will be described.

A high frequency signal from the AC oscillator 7 is input to the bridge circuit 7, and the output of the bridge circuit 7 is taken out through a capacitor 13. This is amplified by the differential amplifier 10 and then the amplitude is detected by the AC-DC converter 11. This amplitude is
It is proportional to the potential difference caused by the impedance imbalance of the bridge circuit 7 caused by the impedance of the magnetic head 5, and this is detected as a signal corresponding to the impedance of the magnetic head 4.

Here, the high-frequency signal applied to the bridge circuit 7 causes its vibration so that the excitation of the magnetic head 5 is reversible.
It shall be sufficiently small within the range that can be measured by the AC-DC converter 11.

A current generated from the pulse oscillator 9 is applied as a bias current to the conductor winding 4 of the magnetic head 5 to periodically magnetically saturate the magnetic head 5.

For example, as shown in (a) of FIG. 2, when the current value is 0, I1, I2
When a pulse current that is periodically repeated is generated from the pulse oscillator 9, the inductance value output from the AC-DC converter 11 is as shown in FIG.

Therefore, in the arithmetic unit 14, the impedance Z0 when the bias current is zero is used as a reference, and the impedance change amount | Z1-Z0 | and | Z2-Z0 | ratio when the bias currents I1 and I2 are | Z2-Z0 |
Calculate 1-Z0 | / | Z2-Z0 | and output.

This output value is a value characterizing the state of magnetic saturation of the magnetic head 5 due to the bias current. The correlation between this value and the overwriting characteristic of the magnetic head 5 is shown in FIG.

This data is measured by extracting a dozen magnetic heads made by the same design.

In addition, the frequencies of the write signals used when measuring the overwrite characteristics are 2.3 MHz and 9 MHz, respectively.

Bias currents I1 and I2 are 7.5 mA and 15 mA, respectively.

As shown in FIG. 3, a value that characterizes the state of magnetic saturation of the magnetic head 5 due to overwriting characteristics and bias current | Z1-
There is a strong correlation with Z0 | / | Z2-Z0 |.

Therefore, by creating a correlation diagram as shown in FIG. 3 and storing it in the arithmetic unit 14, the above | Z1-Z0 | / | Z2-
The pass / fail of overwriting characteristics can be measured from the value of Z0 |.

Also, the | Z1-Z0 | / | Z2-Z0 |
The bias currents I1 and I2 are detected, and from these current values,
A method of detecting the writing characteristic of the magnetic head 5 is also possible.

Next, the principle of the present invention based on the magnetic saturation of the magnetic core of the magnetic head 5 by the bias current will be described with reference to FIGS.

As shown in FIGS. 4A and 4B, the width of the magnetic core of the magnetic head 5 is narrowed at the tip portion 3 of the magnetic core. This is because the magnetic flux generated by the current flowing through the conductor winding 4 flows inside the magnetic core, and the tip 3 of the magnetic core is
This is because the magnetic flux is concentrated and the magnetic field generated from the magnetic head 5 is strengthened.

Such a magnetic flux flow can be considered as a magnetic circuit, and its equivalent circuit is shown in FIG. 4 (c).

The current flowing through the conductor winding 4 of the magnetic head 5 becomes the magnetomotive force of the magnetic circuit. The magnetic resistances of the upper magnetic layer 1 and the lower magnetic layer 2 are divided into the tip portion 3 of the magnetic core and the other portions, respectively, to be Rg1, R1, Rg2, R2. Further, the magnetic resistance to the magnetic flux leaking between the upper magnetic layer 1 and the lower magnetic layer 2 is divided into the tip portion 3 of the magnetic core and the other portion,
Let Rg and Rl. Further, the magnetic resistance to the magnetic field generated from the magnetic head 5 is R.

Therefore, only the magnetic flux passing through each magnetic resistance and finally passing through the magnetic resistance R with respect to the super magnetic force generated by the current flowing through the conductor winding 4 becomes the magnetic field generated by the magnetic head 5.

In general, Rg1 and Rg2 have a narrow magnetic path and therefore have a larger magnetic resistance than R1 and R2. In addition, since Rg has a short magnetic path, it has a smaller magnetic resistance than Rl. Therefore, it can be said that the magnetic resistances Rg1, Rg2, Rg included in the tip 3 of the magnetic core determine the amount of magnetic flux flowing through R.

Rg depends on the shape of the magnetic gap formed by the tips 3 of the magnetic cores of the upper magnetic layer 1 and the lower magnetic layer 2.
The larger the magnetic head depth is, the smaller the magnetic head becomes, and the smaller Rg becomes. Therefore, the amount of magnetic flux passing through the magnetic head increases and the amount of magnetic flux flowing through R decreases.

Also, since the track width and pole length are small and the magnetic head depth is large, Rg1 and Rg2 are larger,
The amount of magnetic flux flowing through R decreases.

From this, the strength of the magnetic field generated by the magnetic head 5 depends on the shape of the tip 3 of the magnetic core.

The tip portion 3 of the magnetic core has a structure in which magnetic flux is concentrated, as described above. For this reason, when the magnetic flux flowing in the magnetic core is increased, the magnetic saturation occurs first at the tip 3 of the magnetic core. In the case of magnetic cores made of the same magnetism, the portion with a large magnetic resistance is magnetically saturated first. When magnetically saturated, the magnetic resistance of that portion becomes even larger. Therefore, magnetic saturation has an effect of emphasizing a portion having a large magnetic resistance.

This increase in magnetic resistance increases the magnetic resistance of the entire magnetic core and can be detected as a decrease in the inductance of the magnetic head 5.

FIGS. 5 to 7 show how the inductance decreases due to magnetic saturation when the gear depth is different and when the pole length is different.

In each case, the longer the magnetic gear depth is and the shorter the pole length is, that is, the larger the magnetic resistance is, the weaker the bias current is, the more the magnetic saturation occurs.

Therefore, as the magnetic saturation at weak bias current increases, Rg
1 and Rg2 are large, a sufficient magnetic flux does not flow in R, and the generated magnetic field is a weak magnetic head.

In order to know that Rg1 and Rg2 are proper magnetic resistance,
It suffices to know how the inductance decreases.

In order to create a variable that characterizes the state of the decrease in inductance, it is necessary to measure the amount of change in inductance at least at two points with different bias currents and create the ratio.

However, the inductance of the thin film magnetic head is 200nH ~ 3
At about 00nH, the amount of decrease due to magnetic saturation is 20 to 30nH.

Therefore, an ordinary impedance meter cannot obtain sufficient accuracy, and it is necessary to measure with an apparatus as shown in FIG.

Further, when the resistance of the conductor winding 4 of the magnetic head 5 is measured with a signal of several MHz to several tens of MHz, the same tendency as the above-mentioned decrease in inductance is shown. This is considered to be the effect of the phase delay of the hysteresis loss and eddy current loss of the magnetic core.

Thus, the detection sensitivity can be increased by detecting the inductance and the decrease in the resistance as impedances.

When the resistance value of the conductor winding 4 is large in the magnetic head 5 due to miniaturization or the like, the decrease of the impedance is reduced due to the influence of heat generation of the conductor winding 4 by the bias current. This is because the increase in the resistance value due to the temperature rise of the conductor winding 4 is included.

In this case, remove the resistance value from the amount of change in impedance,
It is better to carry out the present invention only with the inductance. The inductance is measured by comparing the output of the differential amplifier 10 of FIG. 1 with the signal of the AC oscillator 7 and adding a device for detecting the phase difference between them, and measuring the inductance from the impedance and the phase.

Furthermore, in a manufacturing method in which the depth of the magnetic gear of the thin film magnetic head is formed to a predetermined dimension or more, and the tip portion 3 of the magnetic core is ground to form the magnetic gear portion, the method of the present invention is used during the grinding. Impedance measurement can be used together.

In this case, in the present embodiment, it is detected that the overwrite characteristic has reached a predetermined value, the pass / fail of the magnetic head is determined, and if the polishing process is terminated, a thin film magnetic head with good write characteristics is obtained. It can be manufactured.

According to the above embodiment, since the phenomenon of magnetic saturation depending on the entire shape of the magnetic core tip of the magnetic head is used,
A direct correlation with the write characteristic of the magnetic head is obtained, and the write characteristic can be detected without actually measuring the write characteristic.

Further, the write characteristic can be easily detected by simply connecting a suitable device for measuring impedance and the magnetic head with a lead wire or a probe.

〔The invention's effect〕

According to the present invention, the pass / fail of the write characteristics of the magnetic head can be easily inspected, which has the effect of enabling the magnetic head to be manufactured with high accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the present invention, FIGS. 2 and 3 are operation explanatory views of an embodiment of the present invention, FIG. 4 is a principle explanatory view, FIG. 5 and FIG. FIG. 7 is a characteristic explanatory view of a head having different gear depths, and FIGS. 7 and 8 are characteristic explanatory diagrams when the pole length is different. 1 ... upper magnetic layer, 2 ... lower magnetic layer, 3 ... magnetic core tip, 4 ... conductor winding, 5 ... magnetic head, 6 ...
Coil, 7 ... Bridge circuit, 8 ... AC oscillator, 9 ...
… Pulse oscillator, 10… Differential amplifier, 11… AC-DC converter, 12… Capacitor, 13… Capacitor, 14… Arithmetic unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Suda 4026 Kujimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. Inside the factory (72) Inventor Chihiro Isono 2880 Kozu, Odawara City, Kanagawa Stock Company Hitachi Odawara Factory

Claims (2)

[Claims] 1. A method of inspecting a thin film magnetic head in which at least a magnetic thin film, an electric insulating film and a conductor film are laminated in a predetermined order, and a predetermined amount of DC bias including a zero value is applied to a conductor winding of the thin film magnetic head. Ratio of the amount of change in impedance in at least two states among the changes in impedance when a multi-valued DC bias current of two or more DC bias currents of other values is added to the impedance when a current is applied And a writing characteristic of the thin film magnetic head is inspected based on a correlation between the writing characteristics of the thin film magnetic head. 2. The overwriting characteristic of the thin film magnetic head with respect to a magnetic recording medium according to claim 1, wherein the correlation with the ratio of the amount of change in the impedance of the thin film magnetic head is checked. After being stored in a device for performing the above, the overwriting characteristic of the thin film magnetic head is predicted by measuring the ratio of the amount of change in the impedance of the thin film magnetic head by the inspection device, and the thin film magnetic head A method for inspecting a thin film magnetic head, characterized by determining whether the product is a pass product or a reject product.