Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
1999-03-05
2001-10-02
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S247000, C324S252000, C324S261000
Reexamination Certificate
active
06297630
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining the distribution of magnetic fields in multi-dimensional space. In particular, the invention relates to the measurement of such fields in read/write heads for magnetic storage media. The invention also relates to a device for carrying out said method.
With the continuously increasing recording density and the continual improvement in quality in the development of magnetic heads in recent years it has become ever more important to be able to measure the multi-dimensional spatial distribution of a magnetic field as accurately as possible, since this distribution in the vicinity of the gap in a magnetic head represents a factor which has a profound influence on the recording and/or playback properties.
If a magnetic head is guided over a magnetic recording medium, for example, a magnetic disk, carrying a magnetic thin film layer, then a magnetization which lies in the micron or submicron region will be produced in the magnetic layer of the disk. As a result of the increasing write density on the disk the gap between neighboring tracks is becoming ever narrower. It is therefore important that the magnetization always remains sharply contoured and, for example, does not extend into neighboring tracks, since this could lead to write or read errors.
It is therefore important to be able to analyze or measure the distribution of the magnetic field as accurately as possible, in order to avoid such write or read errors. For this purpose it is particularly advantageous if such a characterization can already be effected beforehand, i.e. in the manufacture of a magnetic head, and not in a separate test only after manufacture.
J. H. J. Fluitman, “Recording Head Field Measurement with a Magnetoresistive Transducer”, Transactions on Magnetics, Vol. 4, No. 5, September 1978; pages 433-435, describes the measurement of field distributions of magnetic heads with a magneto resistive (MR) element in the form of a one-dimensional scan process of the MR element in the direction of its short axis and subsequent calculation of the MR signal output.
“So-called electron beam tomography, in which the field distribution is reconstructed three-dimensionally by the tomography method (tomography stands for the determination of a split image by means of an algebraic reconstruction starting from measured values, which represent the material or spatial properties along a measuring beam), where the starting point is the magnitude of the deviation of an electron beam because of the action of the Lorentz force of the magnetic field on the electron beam after passing through the magnetic field, has recently been proposed as one method for measuring the magnetic field distribution in the micron region. An application of a computer simulation then leads to a simple model of the magnetic field distribution (cf. “Evaluation of Three-Dimensional Micromagntic Stray Fields by Means of Electron-Beam Tomography”, IEEE Trans. Magn., MAG-21, 5, pages 1593,1594 (1985)).”
J. P. J. Groenland et al., “Measurement System for Two-Dimensional Magnetic Field Distributions, Applied to the Investigation of Recording Head Fields”, J. Phys. E: Sci. Instrum., Vol. 14, 1981, p.503 ff, describes the measurement of the magnetic field distribution of a magnetic head with the aid of a magneto resistive sensor. Here, however, no attempt was made to determine the field distribution directly from the measured values obtained, but simulations were calculated with the aid of which the measurements could then be interpreted.
In U.S. Pat. No. 5,075,623 a method is described for high precision measurement of the three-dimensional spatial distribution of magnetic fields, which connects the deflection of an electron beam in the magnetic field (Lorentz force) with the algebraic reconstruction method. The method is characterized by: (a) a reference axis, in which the magnetic field distribution is measured and several planes vertical to it selected, (b) an electron beam in any one of these planes to be measured is scanned at predetermined angles of incidence and the magnitude of the deviation of the electron beam subsequently measured on the basis of the Lorentz force, (c) an algebraic reconstruction of the magnetic field distribution in any of the planes carried out on the basis of the corresponding. measured deviation, (d) the flight path of the electron beam calculated to obtain a deviation value, which corresponds to any of the successively measured deviations, (e) the differences of the calculated deviations of the electron beam from the corresponding measured deviation calculated and (f) the reconstructed magnetic field corrected on the basis of this difference, until the difference falls below a pre-determined value.
SUMMARY OF THE INVENTION
A disadvantage of the state of the art methods is that, to some extent, they do not permit determination of the multi-dimensional distribution of the magnetic field and, in addition, they are very time-consuming and expensive. Thus the electron beam method requires the use of a vacuum chamber, leading to high equipment expenditure and greatly increased costs. In addition, the characterization of, for example, magnetic heads is very difficult, since it is not possible to obtain a high throughput with the apparatus mentioned because of the necessity to charge up the part to be measured in the vacuum chamber and to discharge it again. In addition, with this method the specimen to be measured is always between a transmitter and a receiver, where the gap is measured in cm, which is a disadvantage particularly where the specimen has a pronounced topography, since the electron beam frequently cannot be detected by the receiver because of shielding by the specimen itself.
It is therefore an object of the present invention to provide a method for the determination of multi-dimensional distribution of a magnetic field which will allow the distribution of a magnetic field to be determined in an economic manner without the need for expensive equipment.
It is a further object to provide a method of said type with which a satisfactory result can be obtained even in the case where the specimen to be measured has a pronounced topography.
This and other objects are achieved by a method for the determination of the multi-dimensional distribution of a magnetic field in accordance with claim
1
and the device in accordance with claim
10
.
Further advantageous embodiments of the method and device in accordance with the invention are set out in the sub-claims.
Although the present invention is generally applicable where magnetic fields extend over microscopic dimensions (i.e., in the millimeter down to nanometer range), for example, in the case of circuits with small track separations, it will hereinafter be described in more detail in relation to the determination of the distribution of magnetic fields in the case of read/write heads.
The method in accordance with the invention permits the multi-dimensional distribution of magnetic fields to be determined simply and economically, particularly in the case of magnetic heads. The determination can be carried out without expensive equipment and makes it possible to characterize the magnetic fields even during manufacture, so that a preliminary forecast of subsequent performance can be made. Because,of the simplicity of the arrangement a substantial throughput can be achieved and accurate results obtained even in the case of specimens which are difficult to characterize on account of a complex topography.
REFERENCES:
patent: 5075623 (1991-12-01), Matsuda et al.
J.H.J. Fluitman, “Recording Head Field Measurement with a Magnetoresistive Transducer,” IEEE Transactions on Magnetics, vol. MAG-14, No. 5, pp. 433-435, Sep. 1978.
Dietzel Andreas
Fleischmann Friedrich
Andersen Henry S.
August Casey P.
International Business Machines - Corporation
McGinn & Gibb PLLC
Williams Hezron
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