Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1994-07-15
2001-09-25
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192200, C204S192300, C427S129000, C216S080000, C216S097000, C216S100000, C216S075000
Reexamination Certificate
active
06294058
ABSTRACT:
GENERAL BACKGROUND OF INVENTION
As thin film magnetic disc media has evolved, continuing problems have persisted with respect to the attainment of optimal disc operating conditions and magnetic properties.
One particular problem of concern has involved the maintenance of suitable, low friction characteristics on the exposed disc surface, this traditionally being attained by fluid lubricant materials applied to the disc surface to be read by a magnetic head.
While efforts to apply and maintain such lubricant coatings have engendered substantial research effort, particular attention has been devoted to the formation of roughened or textured media surfaces. These textured surfaces provide alternating arrays of recesses and peaks which are intended to prevent migration of lubricant and undesired, localized lubricant build-up or loss and reduce friction and sticking between the disk and landed head, ie., reduce stiction.
The disadvantage of providing such texturing (usually mechanical) is that it frequently caused undesired, extremely high modulation disparity due to the differences in elevation between portions of the thin film media being traversed by the magnetic head and also tended to cause head damage. (As used herein, the term elevation refers to the difference in displacement of features as measure generally parallel to the axis of disc rotation.)
The present invention is uniquely concerned with the presentation of new and enhanced micro-texturing techniques and apparatus, and the resulting thin film, magnetic media disc product, such being characterized by the attainment of tightly controlled, and localized modulation disparity, which is confined to normal head landing zones, while effectively controlling the distribution of lubricant during disc operation so as to avoid head sticking problems, commonly referred to as “stiction”, such problems being produced when heads inadvertently come to rest on disc areas having excessive lubricant accumulation. In addition, optimal head glide characteristics are preserved.
The unique texturing approach of this invention is characterized by composite, physically and chemically disparate, composite micro-texturing which produces synergistic benefits in providing extraordinarily improved modulaltion and virtual elimination of stiction in the head landing zone and across the remainder of the disc.
Invention Overview—Presently Preferred Embodiment
The first stage of the implementation of this invention preferably entails the use of removable masking and chemical etching to form recesses in the surface of a glass substrate.
In the second stage of this composite micro-texturing process, a eutectic seed layer and micro-texturing treatment is implemented over the top of the etched valleys and resulting peaks of the glass substrate so as to provide a solidified eutectic alloy, rounded globule-defined, peak-type texturing, superimposed on top of the etched valley/peak roughness. Preferably these solidified eutectic alloy globules comprise a eutectic Indium and Bismuth alloy.
It is significant to here note that both the physical and chemical characertistics of the two separate texturing stages are fundamentally distinct.
The first stage, involving masking and etching, will produce an eroded valley/peak configuration in the substrate which is much different from the rounded, solidified, eutectic alloy, globule peak structure resulting in the second stage from the micro-texturizing globule deposition treatment.
General Discussion of the Art
With respect to the use of multiple texturizing steps, a European Patent Application 579 399 A2 (Wilson et al), filed by Pilkington Brothers P. L. C., expressly recognizes the possibility of a supplemental texturizing step, designed to follow an initial masking/etching step. As is set forth on page 6 of the specification of this EPO application:
Although an acceptable texture can be obtained by the use of the etching step as a final texturing step of the glass substrate, it is, in accordance with the present invention, possible additionally to incorporate a further post etch treatment of the glass surface so as to further to modify the texture of the surface. For example, the etched surface may be treated by very light polishing or by other forms of additional whole surface etching, which may be either wet etching or dry etching. This further processing step may be employed either to roughen the surface or further to smooth the peaks of the texture, depending on the requirements of the particular product which is being manufactured. Thus the man skilled in the art will appreciate that the present invention provides a comprehensive scheme for manufacturing a glass disc substrate for a magnetic disc with the desired texture.
Moreover, a much earlier Fujitsu et al patent, i.e., Sakai et al U.S. Pat. No. 4,675,075, also discloses a multi-stage technique for providing texturing on a metallic substrate such as an aluminum substrate.
This technique employs masking/etching in both stages, with the first stage producing eroded valleys in the substrate (FIG.
9
(
4
)) and the second stage producing a peak-type, eroded layer, deposited on top of the valley-containing base.
With respect to the alloy globule features of the present invention, prior art United States patents such as Baseman et al U.S. Pat. No. 5,1334,038 (1992) and U.S. Pat. No. 5,053,250 (1991) do disclose a form of globule texturing. However, these IBM patents appear to be restricted to situations where there is an interaction between the magnetic media layer and globules while they are in a transient, liquid stage. No such phenomena is believed to be involved in connection with the eutectic alloy approach of this present invention.
General State of the Art Summary
By way of summarizing the general state of the art, the following compilation of United States patents, in addition to the Pilkington EPO application noted above, generally are indicative of the various approaches which have been pursued in connection with micro-texturing technology. In this compilation, at the end of each patent title, a code has been applied, generally indicating the principle nature of the disclosure, with the meaning of these codes being identified in the code table at the end of the patent listing.
U.S.
PAT. NO.
INVENTOR
ASSIGNEE
TITLE (SUBJECT)
3,019,125
Eggenberger et al
IBM
Thin Magnetic
Film (CG)
3,193,362
Hespenheide
Burroughs Corp.
Magnetic Materials
(M)
4,326,229
Yanagisawa
Nippon Electric Co.
Magnetic Record
Member And
Process for
Manufacturing The
Same (M)
4,499,122
Economy et al
IBM
Process For
Finishing Surfaces
Achieving Improved
Mangetic Disk
Performance (P)
4,616,237
Pettigrew et al
Pa Management
Data Storage
Consultants, Ltd.
Medium (CG)
4,675,075
Sakai et al
Fujitsu Limited
Magnetic Recording
Production
Processes (ME) (H)
4,698,251
Fukuda et al
Victor Company of
Magnetic Recording
Japan, Limited
Medium And
Method Of
Producing The
Same (CG)
4,724,444
Pettigrew et al
Plasmon Data
Data Storage
Systems, Inc.
Medium (CG)
4,734,810
Nakayama et al
TDK Corporation
Magnetic Recording
Medium Comprising
Protrusion On Its
Surface And A
Plasma Treated
Substrate And
Recording/
Reproducing
Method Therefor
(PE)
4,375,840
Hedgcoth
Cyberdisk, Inc.
Magnetic Recording
Disk And Sputtering
Process And
Apparatus For
Producing Same
(CG)
4,828,899
Arioka et al
TDK Corporation
Magnetic Recording
Medium And
Recording/
Reproducing
Method Thereof (P)
4,833,001
Kijima et al
Asahi Glass
Glass Substrate For
Company, Ltd.
A Magnetic Disc
And Process For Its
Production (CE)
4,894,133
Hedgcoth
Virgle L. Hedgcoth
Method And
Apparatus Making
Magnetic Recording
Disk (CG)
4,925,738
Tsuya et al
—
Substrate For A
Mangetic Disk And
Process For Its
Production
(PO) (CB)
4,393,614
Shirakura et al
Hitachi, Ltd.
Magnetic Disk
Medium With
Circumferentially
Textured Surfaces
And Varied Surface
Roughness And
Method Of
Producing Same
(CG)
4,973,496
Kruger et al
IBM
Method For
Texturing Magnetic
Disks (CG)
4,985,306
Morizane et al
—
Base Plate For
Recording Disk
And A Method For
Its Manufacture
(CE)
4,996,622
Clark Bryan K.
Eltoukhy Atef H.
Goh Wilfred M.
Teng Edward F.
Law+
McDonald Rodney G.
United Module Corporation
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