JPH06187619A - Checking method for thin film magnetic head - Google Patents

Abstract

PURPOSE:To accurately check the noise characteristic of a thin film magnetic head by exciting the head by a built-in recording head coil. CONSTITUTION:An AC exciting current Ir is supplied to a built-in recording head coil 10 by a transmitter 12 and a constant current amplifier 13. Thus, a thin film magnetic head 20 is excited. This exciting current value is converted into voltage by a resistance 14 and supplied to an X axis of an oscilloscope 21. Then, a sense current Is is supplied from a constant current source 16 of a magneto-resistance effect element 1. The head output is amplified by an amplifier 17 and supplied to a Y axis of the oscilloscope 21. Then, a specific curve of the head output is observed in an X-Y display mode. Furthermore, a DC bias current Ib is supplied to a bias conductor 3 contained in the head 20 so than an MR characteristic curve is made as an optimum action point. Meanwhile, the output of the amplifier 17 is transmitted through a differentiation circuit and a circuit 18 which eliminates the basic wave of the AC exiting current Ir, and a signal Y' from which the noise is extracted is supplied to the Y axis of the oscilloscope 21. Thus, the noises can be measured with higher sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a signal magnetic field to a magnetic core made of a ferromagnetic thin film, ferrite, etc. and a ferromagnetic thin film having uniaxial anisotropy, and uses it as an electric resistance change in the easy magnetization axis direction. The present invention relates to a method for inspecting a thin film magnetic head (hereinafter referred to as MR head) which includes a magnetoresistive effect element (hereinafter referred to as MR element) for detecting and which detects a signal recorded on a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, an MR head receives a signal magnetic field written on a magnetic recording medium such as a magnetic tape to generate an M
The magnetization direction inside the R element changes, and the resistance change of the MR element according to the change in the magnetization direction is extracted as an external output.

As described above, the MR head is a magnetic flux response type head and can reproduce the signal magnetic field without depending on the speed of the magnetic recording medium.

Further, the MR head can be easily highly integrated and have a large number of elements by applying a semiconductor fine processing technique. Therefore, a magnetic head for reproducing a fixed head type digital audio for high density recording. It is used as such. Further, in recent years, such a magnetoresistive thin film magnetic head has been used for reproducing an analog tape.

In such a magnetoresistive effect thin-film magnetic head, the MR head is better than the MR head composed of a single MR element.
A yoke type MR head (Y) in which a magnetic flux introduction path (yoke) for guiding the magnetic flux generated from the magnetic recording medium from the head tip to the MR element part is arranged by separating the element from the head tip.
It is known that a thin film magnetic head called an MR head is advantageous for improving signal resolution and MR element durability.

Also in the recording head, the magnetic core,
An induction type thin film magnetic head including a magnetic thin film, a conductive thin film, and an insulating film is used by applying a semiconductor fine processing technique to a coil winding or the like.

Further, in order to make the head compact and to improve the alignment of the recording / reproducing head track position with high accuracy, a composite type thin film magnetic head in which a magnetoresistive thin film magnetic head and an inductive thin film magnetic head are integrally formed is developed. Has been done. FIG. 2 shows a perspective view of the composite type thin film magnetic head.
Further, FIG. 3 shows a sectional view thereof. 2 and 3,
Reference numeral 7 is a substrate of Mn-Zn, Ni-Zn ferrite or the like, in which a groove is formed and a glass 8 is filled in a part thereof. Further, the recording head coil conductor 10 is arranged. A lower yoke 5, which is a magnetic core of the recording head and also a reproducing head magnetic core, is formed on the upper portion of the recording layer via an insulating layer serving as a recording gap 6. A reproducing head is formed on the upper part of the reproducing gap 9, the bias conductor 3, the MR element 1, the MR element lead wire 2, and the upper yoke 4.

When reproducing with the composite type thin film magnetic head, the magnetic field generated from the magnetic recording medium is generated by the upper yoke 4.
The magnetic field is guided to the MR element 1 via the magnetic field and is branched to the lower yoke 5 and the magnetic substrate 7 to return to the magnetic recording medium. Then, in the magnetization process of each part of the magnetic head in the reproducing process, noise due to magnetization switching due to magnetization rotation and Barkhausen noise due to domain wall movement may occur, and noise may occur in the head output.

Conventionally, the characteristics of the YMR head with respect to noise are evaluated by a uniform external magnetic field in the direction normal to the tape sliding surface or by an internal current generated by energizing a bias conductor (3 in FIG. 2) arranged in the YMR head. This was done by examining the head output for noise in response to a bias magnetic field.

[0010]

In the conventional head noise evaluation method, when the internal bias magnetic field generated by the bias conductor is used, the exciting magnetic field generated by passing a current through the bias conductor strongly magnetizes the MR element part and the upper yoke part. . Therefore, in order to sufficiently magnetize the lower yoke part, an excessively large bias current must be used, and the MR element part and the upper yoke part are excessively magnetized as compared with the actual reproducing operation. However, the accurate noise characteristics of the magnetic head cannot be evaluated. Even in the method using a uniform external magnetic field, the lower yoke portion (near the recording coil) cannot be sufficiently magnetized, and it is difficult to accurately evaluate the noise characteristic of this portion.

The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to provide a method for inspecting a thin film magnetic head capable of detecting with high sensitivity the presence or absence of noise generated from a lower yoke portion.

[0012]

In order to solve the above-mentioned problems, a method of inspecting a thin film magnetic head according to the present invention is designed so that an alternating current is passed through a built-in recording head coil (10 in FIG. 2) to output a head output. It is characterized by measuring the presence or absence of noise in the.

[0013]

According to the present invention, since it is excited by the built-in recording head coil, it is possible to appropriately magnetize the lower yoke portion, especially the magnetic core near the recording coil, as compared with the MR element portion and the upper yoke portion. It is possible to inspect with high sensitivity whether or not the lower yoke portion and the substrate portion are good against noise.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method of inspecting a thin film magnetic head according to the present invention will be described below with reference to FIGS.

First, a method for measuring the output characteristic and noise characteristic of the head will be described with reference to the block diagram of the measuring system (FIG. 1). (The head is shown without the magnetic yoke.) The built-in recording head coil 10 has an oscillator 12,
An alternating excitation current Ir is passed by the constant current amplifier 13 to excite the thin film magnetic head 20. This exciting current value is the resistance 14
Is converted into a voltage by and input to the X axis of the oscilloscope 21. A constant current source 16 supplies a sense current Is to a magnetoresistive effect element 1 (hereinafter referred to as an MR element) in the head. The head output is amplified by the amplifier 17, and the Y of the oscilloscope 21 is output.
Enter on the axis. The oscilloscope is set to the XY display mode and the characteristic curve of head output (hereinafter referred to as MR characteristic curve) is observed. Further, a direct current bias current Ib is made to flow from the variable constant current source 19 to the bias conductor 3 in the head so that the MR characteristic curve becomes the optimum operating point. Further, the amplifier output is passed through a differentiating circuit and a fundamental wave removing circuit 18 for the AC exciting current Ir to input a signal Y ', which is noise extracted, to the Y axis of an oscilloscope 21 to measure the presence or absence of noise with higher sensitivity. it can.

Next, Table 1 shows the results of calculation of the ratio of the magnetic flux density of each head portion due to the current of the built-in recording head coil to the magnetic flux density of the MR element portion by the two-dimensional finite element method or the like.

[0017]

[Table 1]

The table also shows the results of calculations for the internal bias magnetic field and the uniform external magnetic field. The lower yoke part and the substrate part have remarkably higher magnetic flux density than other parts. Further, it can be seen that the magnetic flux densities of the lower yoke portion (particularly the portions (H), (I), (J)) and the substrate portion are higher than those in the case of the uniform external magnetic field and the internal bias magnetic field. That is, it is understood that these magnetic fields are selectively and strongly magnetized by this exciting magnetic field.

An example of the result measured by the above method is shown below.

FIGS. 5A, 5B, and 5C show MR characteristic curves when excited by an internal bias magnetic field, a uniform external magnetic field, and a built-in recording head coil magnetic field, respectively. Further, (d), (e), and (f) in FIG. 5 are characteristics of the head output after noise extraction processing when excited by the internal bias magnetic field, the uniform external magnetic field, and the built-in recording head coil magnetic field, respectively.

In the measurement results of the internal bias magnetic field excitation shown in (a) and (d) of FIG. 5, noise cannot be detected.
In addition, in the measurement results by the uniform external magnetic field excitation shown in FIGS. 5B and 5E, noise is not recognized in the MR characteristic curve (FIG. 5B), and noise is small in the noise extraction output (FIG. 5E). Noise is observed in. On the other hand, in the measurement results of the built-in recording head coil magnetic field excitation shown in FIGS. 5C and 5F, significant noise can be detected.

As is clear from the measurement results, when excited by the current of the built-in recording head coil, noise which cannot be detected by the excitation by the uniform external magnetic field and the internal bias magnetic field can be easily investigated, and the head can be easily detected. The quality of can be accurately inspected.

Further, the head to which the present invention can be applied may be any head as long as the recording head and the yoke type MR head share the core and the yoke part, and the head structure shown in FIGS. I can't.

[0024]

According to the present invention described above, since it is excited by the built-in recording head coil, the lower yoke portion, particularly the magnetic core near the recording coil, is more appropriately compared with the MR element portion and the upper yoke portion. It is possible to measure the noise generated in the lower yoke part and the substrate part by magnetizing with high sensitivity, and it is possible to inspect the noise characteristics of the thin film magnetic head with accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of an MR characteristic curve and noise measurement in an embodiment based on the present invention.

FIG. 2 is an overall perspective view showing a structure of a thin film magnetic head having a built-in recording head used in an embodiment.

3 is a cross-sectional view showing the structure of the thin film magnetic head shown in FIG.

FIG. 4 is a cross-sectional view showing points in the thin-film magnetic head where the ratio of magnetic flux densities was calculated in the example.

FIG. 5 is a photograph showing an MR characteristic curve and noise measurement results in an example based on the present invention.

[Explanation of symbols]

 1 MR element 2 MR element lead 3 bias conductor 4 upper yoke 5 lower yoke 6 recording head gap 7 substrate 8 glass 9 reproducing head gap 10 recording head coil 12 oscillator 13 constant current amplifier 14 resistance 16 constant current source 17 low noise amplifier 18 Differentiation, filter circuit 19 Variable constant current source 20 Magnetic head 21 Oscilloscope

Claims (1)

[Claims] 1. A thin film magnetic head having a magnetoresistive effect element for detecting a signal recorded on a magnetic recording medium, wherein a composite thin film magnetic head having an inductive thin film magnetic head built therein is used. An inspection method for a thin film magnetic head, characterized in that an AC current is applied to the head coil conductor to excite the composite type thin film magnetic head, and whether or not noise is generated in the output characteristics of the magnetoresistive effect element is measured.