This invention relates to a multichannel type magnetic head utilizing the Hall effect and adapted for use as a magnetic-electric conversion means.
There are known two types of magnetic heads for reading information from magnetic recording media. One includes a magnetic flux circuit comprised of a high-permeability core and a winding wound about the core. The other is composed of a similar magnetic flux circuit and a semiconductor Hall element inserted in a front or back gap provided in the magnetic flux circuit. Hereinafter the first-mentioned-type will be called a "winding-type magnetic head" and the other type a "Hall-element type magnetic head".
The output of the winding-type magnetic head is proportional to the time-based changing rate d.phi./dt of magnetic flux .phi. detected. The output is therefore reduced as the frequency of the magnetic flux is lowered. Accordingly it is impossible to detect magnetic flux which has undergone no time-based change. The output voltage of the magnetic head is remarkably reduced as the tape running speed becomes lower when flux .phi., if any, varies with time, especially when the recording track of the tape is narrow. The track intervals between channels of the winding-type magnetic head can be narrowed but to a limited extent. This is because the winding-type magnetic head needs to have a winding space.
The output of the Hall-type magnetic head is proportional to the magnitude of magnetic flux detected. Thus, the output level will hardly depend on frequency if the magnitude of the magnetic flux passing through the magnetic flux circuit undergoes a negligibly small frequency-based change. This means that the Hall-type magnetic head can have a frequency characteristic which is flat over a considerably wide frequency range, from the DC region to the high-frequency region. What is more, the Hall element occupies but so small space that the track intervals between channels may be narrowed enough. Thus, the magnetized surface of the tape may be utilized efficiently, and the track density of the tape may be increased.
A multichannel magnetic head utilizing the features of the Hall element is disclosed in Japanese Pat. No. 44814/75. The magnetic head uses Hall elements for respective channels in order to eliminate crosstalk between the channels. For each of the Hall elements there are provided current supply lines and signal output lines. Consequently, the magnetic head needs to have so many external terminals that it fails to make a sufficiently compact multichannel magnetic head with many channels. Furthermore, it becomes difficult for the magnetic head to have both a high S/N (signal-to-noise) ratio and a good resolution (or an excellent high frequency response) when the Hall elements are made of indium-antimonide (InSb) as stated in Japanese Pat. No. 44814/75.
When a Hall element is disposed in a front gap provided in the magnetic flux circuit, it should better be as thin as possible. The thinner is the Hall element, the narrower becomes the front gap and the better becomes the resolution of the multichannel magnetic head. Here arises a problem with a commonly used Hall element, i.e. a semiconductor polycrystalline thin film, a typical example of which is an indium-anitmonide film. That is, the thinner is the element, the more it is affected by the boundary regions of polycrystals and the greater becomes the current noise. The magnetic head having a thin semiconductor Hall element may indeed obtain a high resolution but cannot have a high S/N ratio.
This problem arises also in case the semiconductor Hall element is disposed in a back gap provided in the magnetic flux circuit. In this case, the thickness of the Hall element does not directly affect the resolution. But it affects the reproduction efficiency and eventually the resolution. That is, the narrower the front gap is, the lower bocomes the reluctance of the front gap. If the reluctance of the front gap is low, the reproduction efficiency will be deteriorated. This is because if the reluctance of the front gap is low, most of the detected magnetic flux is shunted at the front gap section, thus reducing the magnitude of the magnetic flux transmitted to the Hall element disposed in the back gap.
It is therefore essential to use an efficient magnetic flux circuit in case the front gap is narrow to improve the frequency characteristic (i.e. resolution) of the magnetic head. In other words, a magnetic flux circuit having a back gap with a Hall element inserted in the gap needs to have a sufficiently low reluctance.
The most effective method to lower the reluctance of a magnetic flux circuit is to narrow the back gap of the circuit. A semiconductor Hall element has a permeability much lower than that of the high-permeability ferromagnetic substance forming a magnetic flux circuit. Thus, the reluctance of the magnetic flux circuit can be much lowered by reducing the back gap to in the order of microns. This follows that the Hall element must be very thin. Then, just as in the case where the Hall element is disposed in the front gap, the Hall element must be made thinner and the current noise then inevitably increases if the front gap is narrowed to provide a higher resolution and if the back gap is narrowed to compensate for the resultant deterioration of reproduction efficiency.
This invention aims to overcome the above-mentioned problems of prior art. An object of this invention is to provide a multichannel magnetic head which has less external terminals than has the prior art head and which has improved resolution, S/N ratio, channel separation and track density. Another object of this invention is to provide a method for manufacturing such a multichannel magnetic head.
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