JPS5927008B2 - thin film magnetic head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film magnetic head for reproducing recorded information recorded on a magnetic recording medium, and for reading information even when the recording medium is stopped.

The purpose of the present invention is to realize a magnetic head that is stable and has a long service life. Conventionally, as shown in FIG. 1, a magnetoresistive element (hereinafter simply referred to as an MR element) 1 is formed on a substrate 2, an external extraction electrode 3 is provided, and information is recorded on a magnetic recording medium 4. It was used to reproduce signal information from track 5.

In this case, one MR element was usually arranged for one track storing one flow of information. Further, the MR element 1 is configured to be exposed to the magnetic recording medium 4 side, and has been used in such a manner that space loss is minimized even for the shortest recording wavelength component written on a track. The operating principle of the MR element is already clarified in various documents and patent information, so the explanation will be omitted, but since the electrical resistance of the MR element changes depending on the recorded information from the magnetic recording medium, M
A conductor layer is formed on both ends of the R element, and for example, direct current is
By flowing the R element, the voltage across the MR element corresponds to recorded information. In the case of an MR element, since it responds to the amount of magnetic flux in this way, signal detection is possible even if the relative speed between the MR element and the magnetic recording medium becomes extremely slow, and the voltage level is independent of the relative speed. This is a major difference from a wire-wound magnetic head, which depends on relative velocity. However, when the magnetic recording medium completely stops, normal signal processing cannot handle the problem because the S/N ratio cannot be obtained. A case where there is only one MR element as shown in FIG. 1 will be described. That is, the magnetization of the MR element is rotated by the recorded information from the magnetic recording medium, and the MR
Assume that the resistivity of the element changes by Δρ. MR element thickness 50
0λ, element width 10μm, element length 100μm, resistivity ρ in a non-magnetic field is 25μΩ・? The resistance value of the element Rp50
If the DC current j flowing through the Ω element is 5 mA, the voltage change Δ
It can be expressed as e-(Δρ/ρ)Rj. ΔρMax/ρ is 8
In the case of 3% Ni-17% Fe permalloy, if it is about 1.5%, an AC output of ΔEmax=3.75 mV is obtained, which is sufficient as a signal level. However, when the recording medium stops, it is necessary to sense a DC voltage level change of 3.75 mV against a DC voltage level of 250 mV.
Accurate detection cannot be achieved due to drift. Such DC level reproduction can usually be achieved by constructing a bridge, arranging an MR element on one side of the bridge circuit, and arranging a compensation element on the other side. Up to now, no configuration method has been thought of in which such compensation elements are provided on the same substrate to obtain recorded information when the magnetic recording medium is stopped.

The present invention provides a thin film magnetic head that embodies these objects.

Generally, the use of recorded information when a magnetic recording medium is stopped involves reproduction of a synchronization signal, and this synchronization signal is usually a rectangular wave signal with an extremely low repetition frequency.

For example, in the case of a magnetic recording/reproducing device (VTR), a 30 Hz rectangular wave is recorded corresponding to the vertical synchronization section of one field. When the magnetic tape speed is 3.3 crn/sec, the wavelength on the magnetic tape corresponding to the repetition frequency is 1.3 crn/sec. im, which is an extremely long wavelength. If it is possible to read such synchronization signals even when the magnetic tape is stopped, the magnetic tape position can be accurately detected when the magnetic tape is stopped, and in principle, still operation and slow motion and fast forward functions at variable speeds are possible. becomes. That is, if the position of the video head is controlled by accurately knowing the position of the magnetic tape, it is possible to follow the correct video signal track position immediately after the start of playback, making it possible to obtain a high-quality playback screen without fluctuations. The circuit processing and principles related to this are not directly related to the present invention and will therefore be omitted. FIG. 2 is a plan view of the first embodiment of the present invention, and FIG. 3 is its A.
-A sectional view.

A material having a magnetoresistive effect, such as Fe-Ni alloy or Ni
-CO alloy or the like is deposited by a technique such as vapor deposition, and the first and second MR elements 7 are formed on the substrate 6 by a photolithography technique.
, 8.

The thickness, element width w, and length l of the MR elements 7 and 8 are design matters whose optimal values are selected depending on the application, but in general,
Thickness is 200-4000λ, w is 10-3
It is 0ttm. The shapes of the first and second MR elements are substantially the same. The length l indicates the actual length of the MR element, which is actually formed by etching because it needs to be connected at both ends to the conductor layer 9 for connection to an external circuit. is longer than l. In order to make the connection at the end more stable, the width at the end may be wider than W, and various shapes at the end are possible. However, the actual M
In the range of length 1 of the R element, the MR element has a width w and has an elongated rectangular shape. Typically, an MR element is produced so that it has an axis of easy magnetization in its longitudinal direction.

The conductor layer 9 is then similarly formed in a manner similar to that described above. The material of the conductor layer 9 is Al. Al/Au. C
r/Au etc. are used. The conductor layer 9 is the first and second MR.
It is connected to both ends of elements 7 and 8 to enable connection to an external circuit. In this specific example, the first and second MR elements 7, 8
One of the ends of the conductor layer 9 is common in the pattern.
′ is connected.

This is to connect to the external circuit within the pattern.
This is effective in reducing the number of external connection terminals. Then, to cover the thin film part except for the external connection part, as a protective layer,
A nonmagnetic insulating layer 10 made of SiOSiO2, Al2O3, etc. is formed, and a nonmagnetic holding plate 11 made of glass, Al2O3, etc. is bonded. 12 indicates an adhesive layer.

However, depending on the purpose, a magnetic material such as ferrite may be used for the substrate 6 and the holding plate 11. Finally, the magnetic recording medium sliding surface side 13 is ground and polished to a predetermined location and into a predetermined shape. FIG. 4 shows a plan view of the second specific example. The difference here is that the second MR element 8
This is different from the first MR element 7 in its shape. That is, while the first MR element 7 has an elongated rectangular shape, the second MR element 8 has a bent shape. For ease of manufacturing, the first and second MR elements 7 and 8 have the same composition and the same thickness, and electrically, the first and second MR elements 7 and 8 have the same composition and the same thickness.
, 8 are selected such that they exhibit the same resistance. According to this example, the area in which the second MR element 8 is arranged can be made extremely small, and the head can be further downsized, allowing for a large number of heads per substrate. Furthermore, in the case of multi-channel heads, higher density packaging is possible. More specifically, as shown in FIG. 2, the first MR element 7 is arranged on the side closer to the magnetic recording medium, and the second MR element 8 is arranged on the side farther from the magnetic recording medium.

In this case, it is desirable that the second MR element 8 detects as little information from the magnetic recording medium as possible, and a distance S is maintained between the second MR element 8 and the first MR element 7. Increasing S without limit is meaningless, and would actually lower the mass production rate. For example, the control signal of a VTR is recorded with a 30Hz rectangular wave saturation, and as mentioned above, the tape speed is 3.3.
At CTrL/sec, the repetitive recording wavelength λ is 1.1 mm. In this case, the relationship between the reproduction output and the distance from the magnetic recording medium is experimentally shown as the solid line in FIG. Since the reproduced waveform is pulse-like and contains high frequency components, the calculated space loss when using a sine wave reproduced waveform is -54.6d.
The attenuation is faster than BX (distance from recording medium/recording wavelength), that is, the characteristic indicated by the broken line in FIG. Therefore,
If the second MR element 8 is separated from the magnetic recording medium by approximately 0.3 times the maximum recording wavelength, the four-signal attenuation is 40 dB.
It turns out that you can get more than that. On the other hand, the first MR element 7 is positioned so that it does not come into contact with the magnetic recording medium in order to ensure stability of the element and avoid the influence of spike-like thermal noise due to sliding contact with the magnetic recording medium. This also has a significant effect on head life due to wear. When 20 μm away from the magnetic recording medium, the signal attenuation is approximately 9 d.
B, which is a sufficient signal level, and the pulse half-width is also slightly wider to 600 microseconds, compared to 250 microseconds when in contact with a magnetic recording medium. In this way, the first MR element 7 is placed at a distance of 20 pm from the magnetic recording medium.
If the second MR element 8 and the first MR element 7 are placed at a distant position, and the distance is approximately 0.3 times the maximum recording wavelength, the first MR element 7 and the second MR element 7 MR element 8
It can be seen that the signal ratio of approximately 30 dB or more can be obtained. This ratio is the output voltage from the first MR element 7 and the output voltage from the second MR element 8.
Considering a circuit in which the output voltage from the output voltage is processed by a differential amplifier, this corresponds to a signal level equivalently being reduced by 3% due to the common phase, which can be said to be a sufficient and appropriate value. V
In the case of TR control signal reproduction, there is usually no problem with crosstalk.

That is, the tracks adjacent to the control track are video signal tracks, and since their frequency bands are quite different, they can be easily distinguished by passing them through an appropriate filter circuit. In another application, when adjacent tracks have similar signal components, it is necessary to consider crosstalk.
When the signal becomes off-track, the signal is attenuated by 40 dB compared to when it is on-track (rectangular wave saturation recording). Therefore, when determining the spacing S between the second MR element 8 and the first MR element 7, instead of considering the spacing between adjacent tracks, it is determined based on the maximum recording wavelength on the magnetic recording medium. What is important is how much. Furthermore, in the present invention, one of the respective ends of the first MR element 7 and the second MR element 8 is connected by a common conductor layer 9'', and the conductor layer 9' is MR element 7, second MR element 8
are arranged at opposing intervals, and the width of the conductor layer 9'' is the first
, is longer than the length l of the second MR elements 7 and 8.

That is, it is advantageous in terms of thermal drift, etc., that the temperature environmental conditions of the first and second MR elements 7 and 8 be as equal as possible, and the conductor layer 91 with good thermal conductivity can improve the thermal conductivity. The structure is as follows. In order to further promote this, the first and second MR elements 7 and 8 have the same non-magnetic insulating layer 10 and non-magnetic holding plate 11 on their upper parts, so that the surrounding conditions are similar. Attention is being paid. Although there is no conventional example of such a specific configuration, basically, compensation for thermal drift, etc.
This is known as pointed out in the specification of No. 33508. However, compensation for the thermal spike noise mentioned above is not the main purpose of the present invention, and in the case of the main application of the present invention, extremely long wavelengths are handled, so how much signal components are compensated for by the first and second MR. The key point is whether the elements can be used for discrimination. In other words, since the magnetic recording medium travels at an extremely slow speed of about 3.3 (1/sec) or less, thermal noise due to sliding contact with the magnetic recording medium is hardly a problem, and the first MR element itself is also magnetic. Since there is no direct sliding contact with the recording medium, thermal spike noise is significantly reduced.Experimentally, this thermal spike noise is related to the material, surface condition, and environment of the recording medium, but at a running speed of 10 cTrL/
It was confirmed that it is extremely small in seconds or less. M.R.
In order to increase the sensitivity of the element, a bias magnetic field is applied to the MR element, but a description of this method will be omitted since it is not directly related to the present invention.

According to the configuration of the present invention as described above, the first and second MR
By arranging the elements in a positional relationship that takes into account the recording wavelength, it is possible to reproduce information favorably even when the magnetic recording medium is stopped.

Furthermore, since the first MR element does not come into direct sliding contact with the magnetic recording medium, the stability and life characteristics of the head can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional device using a thin film magnetic head, FIG. 2 is a plan view of a thin film magnetic head according to an embodiment of the present invention, and FIG. 3 is a sectional view taken along line A-A in FIG. FIG. 4 is a plan view of a thin film magnetic head according to another embodiment of the present invention, and FIG. 5 is a characteristic diagram for explaining the thin film magnetic head of the present invention. 7, 8...MR element, 6...substrate, 9
, 9''... Conductor layer, 10... Nonmagnetic insulating layer, 11... Holding plate, 12... Adhesive layer.

Claims (1)

[Claims] 1. A magnetic head that produces a predetermined reproduction function by arranging a plurality of elements having a magnetoresistive effect on the same substrate and combining two of these elements;
Among the elements, the first element is arranged at a position closer to the recording medium, and the second element is arranged at a position farther from the recording medium than the first element by 0.3 or more of the maximum recording wavelength recorded on the recording medium. and the information recorded in the rectangular wave on the recording medium that is stopped or running at a speed of 10 cm/sec or less is reproduced as the difference between the output from the first element and the output from the second element. Thin film magnetic head.