JPH0343686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of processing a gap portion of a thin film magnetic head, and particularly to a method of manufacturing a thin film magnetic head suitable for a high recording density magnetic disk recording device.

[Background of the invention]

In recent years, thin film magnetic heads have become widely used in magnetic disk recording devices and the like.

By the way, the writing characteristics of this thin film magnetic head largely depend on the depth direction dimension (gap depth) of the magnetic gap, and therefore, it is necessary that this dimension be polished to a necessary and minimum size.

For this purpose, it is necessary to accurately detect the end point of machining, and for this reason, for example, as described in Japanese Patent Laid-Open No. 54-5708, changes in the inductance of a magnetic head are used to detect the end of polishing. A method of detecting the end point has been proposed. In this process, first, the gap depth is ensured to be at least a predetermined value, and the upper and lower magnetic layers are brought into contact with each other at the tips of the gaps, thereby manufacturing a magnetic head with an intermediate shape in which the magnetic core forms a closed magnetic circuit. In this method, the end point of the machining is determined by detecting the change in the inductance of the magnetic head at this time when the magnetic core becomes an open magnetic circuit by polishing the tip of the gap portion.

However, in recent years, there has been a significant demand for higher density magnetic recording, and in line with this, thin film magnetic heads are also being shifted to ones with smaller track widths.

However, such a thin film magnetic head has a small inductance of about 250nH, for example.
Furthermore, the change in inductance when changing from a closed magnetic circuit to an open magnetic circuit as described above is minute, for example, about 10 nH, so the conventional method described above cannot accurately detect the end of machining. ,
Therefore, there was a drawback that the yield of the product was insufficient and the cost was likely to increase.

[Purpose of the invention]

An object of the present invention is to provide a thin film that eliminates the above-mentioned drawbacks of the prior art, makes it possible to detect the end point of magnetic gap polishing with high precision, and makes it possible to manufacture a thin film magnetic head for high-density recording with a good yield. An object of the present invention is to provide a method for manufacturing a magnetic head.

[Summary of the invention]

To achieve this objective, the present invention supplies a DC bias current varying in a rectangular waveform to the thin film magnetic head during polishing, so that the changing process of the impedance reduction of the magnetic head due to magnetic saturation of the core can be investigated. As a result, the end point of the polishing process can be detected with high sensitivity and accuracy.

At this time, not only changes in inductance but also changes in resistance are considered as changes in impedance, thereby sufficiently ensuring highly sensitive and highly accurate detection at the end point mentioned above. It is also characterized by

In one embodiment of the present invention, a Wheatstone bridge circuit network is used to detect the impedance of the thin-film magnetic head, and the magnetic head is connected to one side of this circuit network, thereby allowing the impedance of the magnetic head to be detected by the electric signal. It is characterized by the fact that it can be taken out in a single shape, thereby making it possible to automatically stop the polishing process.

Furthermore, in one embodiment of the present invention, the above-mentioned DC bias current is made into a low frequency rectangular wave pulse, and the impedance is sequentially detected in response to the change in the DC bias current caused by this, and the difference and ratio thereof are determined. It is characterized by being able to eliminate the effects of environmental changes, etc., and detecting the end of machining with high accuracy.

[Embodiments of the invention]

Hereinafter, a method for manufacturing a thin film magnetic head according to the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which H
2 shows a thin film magnetic head with an intermediate shape before the gap is processed, and the head is brought into contact with the tips of the upper magnetic layer 1 and the lower magnetic layer 2 so as to maintain a predetermined gap depth Gd. A contact portion 3 is provided, and a gap depth Gd is left by polishing.
Processing is performed to remove the.

Furthermore, the embodiment shown in FIG. 1 incorporates the coil 4 of the magnetic head H to be polished on one side.
A Wheatstone bridge circuit network 6 has an inductance 5 and a capacitor 15 for cutting DC current on the other side facing the coil 4, and a high frequency signal (several MHz to several + MHz) for detecting the impedance of the magnetic head H. ) The impedance of the magnetic head H is detected from the output of the AC oscillator 7 serving as a source, the DC current source 8 for generating magnetic saturation in the magnetic head H, and the bridge circuit 6, and the end point of the machining is determined from the change. High frequency differential amplifier 9, transformer 12 and AC-DC converter 1 for detecting
an arithmetic device 11 which takes in the output of the differential amplifier 9 through 0, determines impedance changes, and outputs a polishing device stop signal from the output device 16; and a switch 1 which turns the DC current source 8 on and off.
4.

Next, the operation of this embodiment will be explained.

A high frequency signal from the AC oscillator 7 is input to the bridge network 6, and the output of the bridge network 6 is taken out through the capacitor 13. After this is amplified by the differential amplifier 9, it is detected as an amplitude signal by the AC-DC converter 10.

This amplitude is proportional to the potential difference due to the impedance imbalance of the bridge network 6 caused by the impedance of the magnetic head H, and is detected as a signal corresponding to the impedance of the magnetic head H.

Here, in order to prevent the excitation of the magnetic head H from going out of the reversible range, the high frequency signal applied to the bridge circuit network 6 should be sufficiently high within the range where the amplitude can be measured by the AC-DC converter 10. It shall be kept small.

Next, switch 14 is activated by a low frequency pulse (several Hz to
Turns ON and OFF depending on the number of seconds + mHz). As a result, a DC bias current is caused to flow from the DC current source 8 to the coil 4 of the magnetic head H, and excitation is repeated at regular intervals to periodically bring the magnetic head H into magnetic saturation.

When the tip of the thin film magnetic head H is polished while the detection is continued in this manner, the impedance of the magnetic head H changes as shown in FIG.

As is clear from FIG. 2, the AC-DC converter 1 represents the impedance of the magnetic head H.
The output of 0 changes greatly up and down depending on whether the DC bias current is turned on or off by the switch 14. At this time, the output value representing the impedance when ON is a, and the output value representing the impedance when OFF is b. Then, the difference between these output values (b
-a) shows a change of about 10 times before and after polishing.

Therefore, the arithmetic unit 11 sequentially detects the output values a and b, and tracks temporal changes in these output values a and b during polishing of the magnetic head H. Then, from this result, the points c, d, e, and f at which changes appear in these output values a and b are determined, thereby making it possible to know the progress of the machining and the end point.

Here, the output of the AC-DC converter 10 may include changes in device characteristics due to changes in the surrounding environment. However, in this embodiment, since the impedance of the magnetic head H is alternately detected in two types of states, ie, a state in which it is magnetically saturated and a state in which it is not magnetically saturated, fluctuations in the surrounding environment is longer than at least one cycle of the switch 14, the impedance in one state is used as a reference and the impedance in the other state is detected, thereby removing the influence of fluctuations in the surrounding environment and purely detecting the magnetic head H. It is possible to detect only changes in impedance.

Thus, in this example, the difference in output values (b-
a), or by the ratio (b/a), exactly
Furthermore, the high sensitivity makes it possible to detect the end of the polishing process without being affected by changes in the surrounding environment.

Incidentally, when mass producing the magnetic head H, it is conceivable that variations in impedance characteristics may occur. Therefore, in this case, the output values a and b of the magnetic head H before being polished are
ai, and bi, and the magnetic head H
The output values a and b when polishing are normalized by ai and bi, respectively, and a/ai,
By further providing a b/bi function, it becomes possible to stably detect the end point of the polishing process.

Note that here, a fluctuation of about several percent occurs in the output value b, but this is caused by a difference in the magnetic domain structure that settles down in the process of the magnetic head H being released from magnetic saturation and relaxing. For this, for example, the DC bias current is turned OFF.
Stabilization can be achieved by demagnetizing the magnetic head H at the same time as the magnetic head H becomes stable.

Another method is to use a DC bias current.
Instead of ON and OFF, 2 or 3 different types
Apply a DC bias current of a certain level in the form of a rectangular wave, or apply a small DC current constantly.
It may be superimposed on the bias current due to ON and OFF described above.

Furthermore, at this time, by changing the value of the DC bias current, the relative positions of points c, d, e, and f in Figure 2 can be changed, and according to this, the end point of the polishing process can be changed. It becomes possible to predict this point when it approaches, and even more precise polishing becomes possible.

Next, the magnetic head H is heated by a DC bias current.
The principle of the above embodiment, which is based on the excitation of , will be explained with reference to FIGS. 3 to 5. Here, FIG. 3 shows the magnetic field line distribution of the magnetic head H, and FIGS.
The figure shows the inductance and resistance values of the magnetic head H measured using a high frequency of 10 MHz.

As shown in FIG. 3, by providing the contact portion 3, the magnetic core of the magnetic head H, which has the closed magnetic circuit configuration shown in FIG. 3b, becomes open as shown in FIG. When forming a magnetic core in a magnetic circuit configuration, the magnetic path resistance of the magnetic core increases and the magnetic flux within the magnetic core decreases. Therefore, as shown in FIG. 4, the inductance of the magnetic head H decreases A. Note that the conventional example (Japanese Patent Laid-Open No. 54-5708) is a method using only A.

Further, the upper magnetic layer step portion 10 of the magnetic head H
In No. 1, the smaller the track width, the smaller the cross-sectional area of the magnetic layer, and the narrower the magnetic path. Therefore, when a direct current (for example, 5 mA) is applied to the magnetic head H to excite it, the magnetic flux density of the upper magnetic stepped portion 101 becomes high as shown in FIG. 3b, and magnetic saturation occurs. This causes a decrease B in inductance.

On the other hand, the magnetic head H is polished,
When the contact part 3 is removed as shown in figure c,
The magnetic resistance of the magnetic head H increases. Therefore, the magnetic flux within the magnetic core generated by the same DC current decreases, and the decrease in inductance C becomes smaller than the above B. Furthermore, Anderson (NC
Anderson) and REJones, Jr.
Ai Ei Ei, Transaction on Magnetake MAG-17, 2896,
(1981) (IEEE Trans. on Mag.,) shows the relationship between the track width of a magnetic head and the applied DC current.

On the other hand, as shown in FIG. 5, although the overall change in the resistance value of the magnetic head H is small, the fourth
A similar trend can be seen with the inductance shown in the figure. This is presumed to be due to the effect that the hysteresis loss and eddy current loss of the magnetic core of the magnetic head H are reduced by magnetic saturation of the magnetic core.

Therefore, in the present invention, based on the above principle, in order to detect the end point of the processing, a method is adopted in which impedance is detected, including not only the inductance of the magnetic head but also the resistance value. By simultaneously detecting the impedance at the time of the machining, it is possible to detect the end point of the machining process with high sensitivity and accuracy.

Next, the detection operation according to the embodiment shown in FIG. 1 will be explained in more detail with reference to FIGS. 6 and 7.

In the explanation so far, as shown in a of Fig. 6, the DC bias current is changed to two values of B and C (C=O in the case of Fig. 1).
For example, this embodiment uses a method called a binary bias method, which detects impedance changes as shown in FIG. b.

Therefore, in the following, another embodiment will be described in which more detailed detection including the progress status of the polishing process can be performed.

In this embodiment, a three-value DC bias current having three levels A, B, and C as shown in FIG. 7a is used.

Then, the impedance corresponding to each bias level A, B, and C changes as the processing progresses (that is, as time progresses), as shown by curves s, t, and u in FIG. 7b. In the first embodiment, as shown in FIG. 6b, the processing end point was determined from the relationship between the curves t and u. Here, the curve t rises as it approaches the processing end point. This is because when the tip of the head becomes thinner due to processing, the tip becomes saturated by the bias current B, and magnetically approaches the state of an open magnetic core. Therefore, when a larger bias current A is applied, the thickness at the tip of the head magnetic body is thicker than the embodiment shown in FIG. 6 (that is, the amount of machining is less), but the thickness is the same as that of the embodiment shown in FIG. This shows the impedance change. As described above, by applying the third bias level A and comparing the curves s, t, and u, it is possible to detect a state in which the machining amount is insufficient by a specific value. Therefore, according to this embodiment, the optimum machining It is possible to generate a warning signal before reaching the end point, and if the machining speed is reduced by the warning signal, the detection accuracy of the optimal end point can be improved with a slight increase in machining time.

Next, an example of a method and jig for polishing the magnetic head H will be explained.

As shown in FIG. 8, the magnetic head is formed on a head slider 17 until the contact portion 3 between the upper magnetic layer 1 and the lower magnetic layer 2 is removed, as shown in _FIG . The head slider 17 is polished together with the head slider 17 from the position indicated by the solid line _Y2 .

FIG. 10 is a schematic diagram of the lap polishing machine 18 used for the above-mentioned polishing process. For example, an induction motor 19 rotates a lap surface plate 21 in the direction of the arrow through a pulley 20, while a lap jig 22 rotates. The position of the lapping jig 22 is fixed by a central shaft 23 in a freely rotating state, and the lapping jig 22 rotates as shown by the arrow in response to the revolution of the lapping surface plate 21. Uniform polishing can be achieved by this rotational action.

FIG. 11 shows an embodiment of the wrapping jig 22, in which the magnetic head H is fixed to the bottom surface of the wrapping jig 22.
is polished by the dummy head 24 at a constant inclination by the rotation of the lap jig 22.

In this embodiment, a circuit board 25 is assembled to the wrap jig 22, and the circuit board 25 includes the Wheatstone bridge circuit network 6, AC oscillator 7, DC current source 8, differential amplifier 9, and the like shown in FIG. It is equipped with a switch 14, etc., so that signals can be detected with a good S/N ratio. At this time, the power supply lines necessary for these devices are connected to the outside via the slip ring 26, while the output of the differential amplifier 9 is connected to the outside as described above.
Since it is a high frequency signal of 10 MHz, it is taken out to the outside using a well-known rotary transformer 12. For this reason, the rotating side 12b of the rotary transformer 12 is attached to the wrap jig 22, and the fixed side 12b is attached to the wrap jig 22.
a are respectively attached to the support member 28, and the center shaft 23 of the wrap jig 22 is held by the support member 28 by a ball bearing 27.

〔Effect of the invention〕

As explained above, according to the present invention, since a method is used to detect impedance including the resistance value of the magnetic head, in the conventional method of measuring the absolute value of inductance, the width of change in inductance is about 4%. In contrast, in the method of the present application,
The rate of change increases by 5 to 10 times, increasing the accuracy of detecting the end point of polishing.

Furthermore, it is possible to simplify the device by employing a bridge circuit, and an expensive impedance measuring device is not required.

Furthermore, the conventional method requires processing time (10 minutes to
While the accuracy and stability of the detection means is required within several hours, in this application, the accuracy and stability of the detection means is required between the presence and absence of bias (period
A stability of about 0.01 to 10 Hz is sufficient.
Therefore, the dependence of the entire detection means on the surrounding environment can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG.
The figure is a characteristic diagram to explain the operation, Figure 3 is an explanatory diagram of the magnetic field line distribution of the thin film magnetic head, Figure 4 is an explanatory diagram of inductance change, Figure 5 is an explanatory diagram of resistance change, and Figure 6 is an explanatory diagram of the detection principle. A characteristic diagram showing one method, FIG. 7 is a characteristic diagram showing another method of detection principle, FIG. 8 is an assembly diagram of the thin film magnetic head, FIG. 9 is a partially enlarged view of FIG. 8, and FIG. 10 11 is an explanatory diagram of a polishing machine, and FIG. 11 is an explanatory diagram of a lap jig in one embodiment of the present invention. H... Thin film magnetic head, 1... Upper magnetic layer, 2
...lower magnetic layer, 3...contact part, 4...coil,
5... Inductor, 6... Wheatstone bridge network, 7... AC oscillator, 8... DC current source, 9... Differential amplifier, 10... AC-DC converter, 11... Arithmetic unit, 14 ...electronic switch, 16...output device.

Claims (1)

[Claims] 1. A thin film magnetic head having an intermediate shape having a magnetic short-circuit portion at the tip is formed by depositing at least a magnetic thin film, an electrically insulating film, and an electrically conductive film in a predetermined order in the thickness direction. In a method for manufacturing a thin film magnetic head in which the tip of the thin film magnetic head is polished to a predetermined magnetic gap depth dimension, a direct current bias current is applied to the electrically conductive film wound around the thin film head during the polishing process. measuring the impedance exhibited by the electrical conductor film while supplying the electrical conductor, detecting that the range of change in the impedance when the DC bias current is varied in a rectangular waveform has decreased to a predetermined ratio, and generating a control signal; A method for manufacturing a thin film magnetic head, characterized in that the control signal controls the end of the polishing process. 2. In claim 1, the change in the DC bias current having a rectangular wave ranges from a first predetermined current value including zero to a minimum value, and a second predetermined current value larger than the first predetermined current value. 1. A method for manufacturing a magnetic film magnetic head, characterized by a step-like change with a maximum value of . 3. In claim 1, the change in the DC bias current having a rectangular wave ranges from a first predetermined current value including zero to a minimum value, and a second predetermined current value larger than the first predetermined current value. A method for manufacturing a magnetic film head, characterized in that the change is step-like over three stages, with the current value being an intermediate value and the third predetermined current value larger than the second predetermined current value being the maximum value.