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US4861398A
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Method for making a thin film magnetic head
Assignee: Hitachi Ltd
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Filing: 1987-11-20
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Granted: 1989-08-29
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Expires: 2007-11-20
Abstract
Abstract DC bias currents are applied to a conducting wire of a thin film magnetic head to be inspected. When the DC bias currents (I 0 , I 1 , I 2 ) are supplied to the conducting wire, the impedances (Z 0 , Z 1 , Z 2 ) corresponding to the DC bias currents are measured. When a ratio (|Z 1 -Z 0 |/|Z 2 -Z 0 |) corresponding to an overwrite characteristic (OW) reaches to a predetermined value by lapping tip portions of an upper magnetic layer and a lower magnetic layer of the magnetic head, the lapping process of the magnetic head is finished.
Inventors
- 👤 Hirotsugu Fukuoka
- 👤 Kanji Kawakami
- 👤 Makoto Aihara
- 👤 Mitsuo Suda
- 👤 Kouji Takeshita
- 👤 Yukihiro Isono
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 08:12
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/127; G11B5/31; G11B5/3163; G11B5/3166; G11B5/455; Y; Y10; Y10T; Y10T29/00; Y10T29/49; Y10T29/49002; Y10T29/4902; Y10T29/49021; Y10T29/49032; Y10T29/49036; Y10T29/49043; Y10T29/49044; Y10T29/49046
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
195 words
A method for making a thin film magnetic head comprising the steps of: laminating magnetic layers, an electric insulating layer, and a conducting wire in the thickness directions thereof in a predetermined order; effecting lapping processing of tip portions of the layers so as to form the magnetic head with a throat height; detecting an overwrite characteristic of the magnetic head in such a manner that a ratio |Z 1 -Z 0 |/Z 2 -Z 0 of each variation Z 1 -Z 0 , Z 2 -Z 0 of an impedance Z 0 is lower than a predetermined value when the conducting wire has a DC bias current I 0 having a magnitude containing a zero value applied thereto so that the impedance value thereof is Z 0 , and when the conducting wire has at least two DC bias currents of I 1 and I 2 applied thereto so that the impedance values are Z 1 and Z 2 , respectively; and determining that the overwrite characteristic OW of the magnetic head reaches a desired value when the ratio |Z 1 -Z 0 |/|Z 2 -Z 0 | becomes lower than the predetermined value.
Claim 2
Independent Claim
195 words
A method for making a thin film magnetic head comprising the steps of: laminating magnetic layers, an electric insulating layer, and a conducting wire in the thickness directions thereof in a predetermined order; effecting lapping processing of tip portions of the layers so as to form the magnetic head with a throat height; detecting an overwrite characteristic of the magnetic head in such a manner that a ratio |Z 1 -Z 0 |/Z 2 -Z 0 of each variation Z 1 -Z 0 , Z 2 -Z 0 of an impedance Z 0 is lower than a predetermined value when the conducting wire has a DC bias current I 0 having a magnitude containing a zero value applied thereto so that the impedance value thereof is Z 0 , and when the conducting wire has at least two DC bias currents of I 1 and I 2 applied thereto so that the impedance values are Z 1 and Z 2 , respectively; and determining that the overwrite characteristic OW of the magnetic head reaches a desired value when the ratio |Z 1 -Z 0 |/|Z 2 -Z 0 | becomes lower than the predetermined value.
Claim 3
Dependent Claim
57 words
The method according to claim 1, wherein the lapping processing is completed by measuring the overwrite characteristic of the magnetic head based upon the ratio, and detecting that the magnetic head reaches the desired value, when the throat height formed by the lapping processing of the tip portions has a throat height greater than a predetermined value.
Claim 4
Dependent Claim
22 words
The method according to claim 2, wherein the tip portions of the magnetic layers are formed to have a predetermined throat length.
Claim 5
Dependent Claim
20 words
The method according to claim 2, wherein the tip portions of the magnetic layers are spaced apart from each other.
Claim 6
Dependent Claim
20 words
The method according to claim 2, wherein the tip portions of the magnetic layers are arranged to contact each other.
Claim 7
Dependent Claim
70 words
The method according to claim 1, wherein DC pulses O, I 1 , I 2 are repeatedly applied to the conductor wire from a pulse oscillator and the ratio |Z 1 -Z 0 |/|Z 2 -Z 0 | is calculated by a calculator on the basis of the impedances Z 0 , Z 1 , Z 2 in accordance with the DC pulses O, I 1 , I 2 .
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-08-28 | 1993-02-27 | 1993-08-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-08-28 | 1997-02-27 | 1997-08-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-08-28 | 2001-02-27 | 2001-08-29 | $7700.00 | Window Closed / Lapsed |