Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data verification
Reexamination Certificate
2000-10-25
2003-07-01
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data verification
C360S046000
Reexamination Certificate
active
06587295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method, an apparatus, a system, a computer process, and a recording medium on which a program is stored for improving a property of a thin-film magnetic head incorporating at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Consequently, in place of thin-film magnetic heads that perform reading and writing by an induction-type electromagnetic transducer, composite thin-film magnetic heads have been widely used. A composite head is made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading.
With regard to a thin-film magnetic head having an induction-type electromagnetic transducer, it is known that so-called popcorn noise may occur in a read signal when reading is performed after writing is performed. The popcorn noise is pulse-shaped noise having a peak value much higher than that of normal white noise. The popcorn noise causes problems such as a reduction in accuracy of alignment of the thin-film magnetic head. While the definite cause of popcorn noise is not clear, it is assumed to be caused by a delay in change when the magnetic domain of a magnetic layer of the induction-type electromagnetic transducer shifts from the state of writing operation to the stationary state.
To reduce the popcorn noise, measures have been taken in prior art with regard to the design of the thin-film magnetic head and the manufacturing process, such as optimization of the geometry and the composition of the magnetic layers of the induction-type electromagnetic transducer.
However, such measures are not enough to eliminate the popcorn noise completely, due to problems such as a shift in composition and variations in composition in a wafer.
Another problem of the prior-art measures is that a complete product with high added values, such as a thin-film magnetic head attached to a suspension, an extension line and terminals being connected to the head, may be found faulty due to popcorn noise. Such faulty products must be discarded, and a great loss thereby results.
In Published Unexamined Japanese Patent Application Hei 11-328603 (1999), a technique is disclosed for removing Barkhausen noise resulting from the domain wall shift of the MR film of the reproducing head by feeding a current to the recording head. However, the above-mentioned popcorn noise is not considered in this technique.
Although the above-mentioned publication does not disclose the magnitude of the current fed to the recording head to remove Barkhausen noise, the magnitude of the current is assumed to be the same as the current fed during a normal writing operation, since the current is fed to the recording head through driving the read/write circuitry. However, as will be disclosed in the detailed description of the preferred embodiment of the invention, it is almost impossible to reduce the popcorn noise only by feeding a current to the recording head, the current being nearly as large as the current fed during a normal writing operation.
The above publication states that it is preferred to remove Barkhausen noise by feeding a current to the recording head after an occurrence of reading error. In an embodiment described in this publication Barkhausen noise is removed after an occurrence of reading error. However, such processing is not capable of improving the property of the thin-film magnetic head fundamentally.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a method, an apparatus, a system, a computer process, and a recording medium on which a program is stored, each of which is provided for reducing noise made in a read signal of a thin-film magnetic head after a writing operation is completed, and for reducing nonconforming products.
A first method of the invention is provided for improving a property of a thin-film magnetic head by reducing noise made in a read signal after a writing operation is completed, the head incorporating at least an induction-type electromagnetic transducer and performing reading and writing. A current is fed to the transducer, the current having a value greater than a value of a current fed when a normal writing operation is performed.
According to the first method of the invention, a current is fed to the electromagnetic transducer, the current having a value greater than the value of the current fed when a normal writing operation is performed. As a result, the temperature of the transducer increases, and the noise made in the read signal after the writing operation is completed is thereby reduced.
According to the first method of the invention, the current may be fed while the head is not facing toward a recording medium.
A second method of the invention is provided for improving a property of a thin-film magnetic head by reducing noise made in a read signal after a writing operation is completed, the head incorporating at least an induction-type electromagnetic transducer and performing reading and writing. The method includes: a first step of measuring the noise in the read signal of the head and determining whether the noise falls within a permissible range; and a second step of feeding a current to the transducer, the current having a value greater than a value of a current fed when a normal writing operation is performed. While the value of the current fed to the transducer is gradually increased in the second step, the first and second steps are alternately repeated until it is determined that the noise falls within the permissible range in the first step, or the current value reaches a specific upper limit.
According to the second method of the invention, a current is fed to the electromagnetic transducer of the thin-film magnetic head producing noise beyond the permissible range, the current having a value greater than the value of the current fed when the normal writing operation is performed, until it is determined that the noise falls within the permissible range, or the current value reaches a specific upper limit. As a result, noise of many of thin-film magnetic heads manufactured falls within the permissible range.
According to the second method of the invention, the second step may be performed while the head is not facing toward a recording medium.
According to the second method, the first and second steps may be performed when the head is in any of states of a wafer in which a plurality of rows of thin-film magnetic heads are aligned; a row of a plurality of thin-film magnetic heads; the single thin-film magnetic head; the head mounted on a suspension; a plurality of thin-film magnetic heads each of which is mounted on a carriage through a suspension; and the head incorporated in a magnetic disk device.
A first apparatus of the invention is provided for improving a property of a thin-film magnetic head by reducing noise made in a read signal after a writing operation is completed, the head incorporating at least an induction-type electromagnetic transducer and performing reading and writing. The apparatus comprises: a determination means for measuring the noise in the read signal of the head and determining whether the noise falls within a permissible range; an energizing means for feeding a current to the transducer, the current having a value greater than a value of a current fed when a normal writing operation is performed; and a control means for controlling the determination means and the energizing means such that, while the value of the current fed to the transducer is gradually increased, the determination and the energizing are alternately repeated until the determination means determines that the noise falls within the permissible range, or the current value reaches a specific upper limit.
A second apparatus of the invention is provided for improvin
Kiyono Hiroshi
Nishio Nobutaka
Davidson Dan
Hudspeth David
Oliff & Berridg,e PLC
TDK Corporation
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