Reference disk for determining glide height

A reference disk, used to determine the glide height of a transducer head above the surface of a magnetic recording medium, is accurately formed by employing a laser light beam to produce protrusions on the reference disk. The protrusions can be formed in a variety of effective patterns to obtain a stable electrical signal. Embodiments include circumferential rows of uniformly or randomly spaced protrusions.

TECHNICAL FIELD 
The present invention relates to a reference disk for use in a glide tester 
apparatus to determine the glide height of a transducer head above the 
surface of a magnetic recording medium, and to a method for manufacturing 
a reference disk. The invention has particular applicability in accurately 
measuring the glide height of the transducer head above the surface of a 
magnetic recording medium required to have a minimal glide height. 
BACKGROUND ART 
Thin film magnetic recording disks and disk drives are conventionally 
employed for storing large amounts of data in magnetizable form. In 
operation, a typical contact start/stop (CSS) method involves floating a 
transducer head in air at a predetermined distance from the surface of the 
disk due to dynamic pressure effects caused by airflow generated between 
the sliding surfaces of the transducer head and the disk. During reading 
and recording operations, the transducer head is maintained at a 
controlled distance from the recording surface, supported on a bearing of 
air as the disk rotates, such that the transducer head can be freely moved 
in both the circumferential and radial directions allowing data to be 
recorded on and retrieved from the surface of the disk at a desired 
position. It is considered desirable during reading and recording 
operations to maintain each transducer head as close to its associated 
recording surface as possible, i.e., to minimize the flying height or 
glide of the transducer head. 
There are, however, inevitable topographical asperities, typically of only 
a few microns in diameter and few microinches in height, formed on the 
surface of a conventional magnetic recording media, which surface 
comprises a data zone and a landing zone. These asperities stem from a 
variety of sources, e.g., thermal treatment, magnetic orientation of the 
magnetic alloy layer, groove generation and polishing. Moreover, these 
asperities vary in height, diameter and frequency among magnetic recording 
media. 
Conventional disk drives are manufactured with precise specifications, 
including a precise maximum glide height for a transducer head flying 
above the data zone. In recognition of the inevitable topographical 
asperities formed on the data zones of magnetic recording media, 
conventional practices comprise testing each magnetic recording medium to 
determine if the particular magnetic recording medium satisfies the 
maximum glide height requirement for a particular magnetic disk drive. 
Such testing typically comprises the use of a device known as a glide 
tester commercially available from various sources, such as Cambrian or 
Phase-Matrix of California. 
Conventional glide testers accommodate the particular magnetic recording 
medium to be tested and a reference disk typically containing a single 
protrusion thereon formed by photolithographic techniques and having a 
defined height, i.e., glide height. The reference disk is rotated and a 
transducer head lowered until the transducer head contacts the protrusion 
at which point a first electrical signal is generated indicative of glide 
height as a function of the height of the reference disk protrusion. The 
magnetic recording medium is then rotated and the transducer head lowered 
onto the media surface until contact is made to generate a second 
electrical signal. The second electrical signal is compared to the first 
electrical signal to determine whether the tested magnetic recording 
medium satisfies the glide height requirement for a particular disk drive. 
The proper functioning of the glide tester, manifestly, requires the 
generation of a strong, stable and repeatable signal for effective 
comparison. Of particular significance is the necessity for the protrusion 
on the reference disk to accurately simulate topographical asperities 
inevitably present on the surface of a magnetic recording media. 
There are significant disadvantages attendant upon conventional practices 
for manufacturing and employing a reference disk comprising a single 
protrusion formed by photolithographic techniques. For example, the 
protrusion formed by photolithographic techniques is significantly greater 
in diameter than actual topographical asperities formed on the data zone 
of a magnetic recording medium and, hence, does not provide a basis for an 
accurate simulation. The protrusion typically produced by a 
photolithographic technique, such as made by StorMedia or Akashic of 
California, is about 100 .mu.m to about 200 .mu.m in diameter; whereas, 
topographical asperities are generally only a few microns in diameter. A 
single protrusion formed by a photolithographic technique does not 
accurately simulate the aerodynamic conditions generated by a plurality of 
protrusions characteristic of inevitable topographical asperities. 
Additionally, a single photolithographically formed protrusion wears out 
in a short period of time as a result of repeated contacts with the 
transducer head of the glide tester and, hence, yields inconsistent 
results. Moreover, the reference disk comprising a single 
photolithographically formed protrusion must be replaced frequently. It is 
also extremely expensive to produce a reference disk having a protrusion 
formed by photolithographic techniques. 
Accordingly, there exists a need for a reference disk for use in a glide 
tester to accurately determine the glide height above the surface of a 
magnetic recording medium. There also exists a need for an efficient and 
cost effective method to produce a reference disk containing protrusions 
simulating actual topographical asperities on the surface of a magnetic 
recording media. 
DISCLOSURE OF THE INVENTION 
An object of the present invention is a reference disk for accurately 
determining the glide height above the surface of a magnetic recording 
medium. 
Another object of the present invention is a method of manufacturing a 
reference disk for use in a glide tester to accurately determine the glide 
height above the surface of a magnetic recording medium. 
Additional objects, advantages and other features of the invention will be 
set forth in part in the description which follows and in part will become 
apparent to those having ordinary skill in the art upon examination of the 
following or may be learned from the practice of the invention. The 
objects and advantages of the invention may be realized and obtained as 
particularly pointed out in the appended claims. 
According to the present invention, the foregoing and other objects are 
achieved in part by a reference disk for determining the glide height 
above the surface of a magnetic recording medium, which reference disk 
comprises a surface and at least one protrusion formed on the surface by a 
laser light beam. 
A further aspect of the present invention is a reference disk for 
determining the glide height above the surface of a magnetic recording 
medium, which reference disk comprises at least one circumferential row of 
protrusions, which circumferential row is spaced radially from the center 
of the disk. 
Another aspect of the present invention a method of manufacturing a 
reference disk for determining the glide height above the surface of a 
magnetic recording medium, which method comprises exposing a surface of a 
disk to a laser light beam to form at least one protrusion thereon. 
A further aspect of the present invention is a method of manufacturing a 
reference disk for determining the glide height above a surface of a 
magnetic recording medium, which method comprises exposing a surface of a 
disk to a laser light beam to form at least one circumferential row of 
protrusions, which circumferential row is spaced radially from the center 
of the disk. 
Additional objects and advantages of the present invention will become 
readily apparent to those skilled in this art from the following detailed 
description, wherein only the preferred embodiment of the invention is 
shown and described, simply by way of illustration of the best mode 
contemplated for carrying out the invention. As will be realized, the 
invention is capable of other and different embodiments, and its several 
details are capable of modifications in various obvious respects, all 
without departing from the invention. Accordingly, the drawings and 
description are to be regarded as illustrative in nature, and not as 
restrictive.

DESCRIPTION OF THE INVENTION 
In accordance with the present invention, a reference disk is produced 
comprising a pattern of protrusions which substantially accurately 
simulates the height, diameter and spacing of topographical asperities 
typically formed on the surface of magnetic recording media. Moreover, in 
accordance with the present invention, such a reference disk is fabricated 
in a cost effective, efficient manner. A reference disk in accordance with 
the present invention can be used in conventional glide testers to 
accurately determine the glide height of a transducer head above the 
surface of a magnetic recording medium. 
In an embodiment of the present invention, a pattern of protrusions is 
formed by exposing the surface of a disk to a laser light beam, preferably 
a pulsed, focused, laser light beam, to accurately form a plurality of 
protrusions extending above the surface of the disk to a controlled height 
and having a controlled diameter and a controlled spacing. The use of a 
laser light beam to form a protrusion is considerably less expensive than 
conventional photolithographic processing. Moreover, the use of a pulsed, 
focused laser light beam enables the formation of a plurality of 
protrusions which substantially accurately simulate topographical 
asperities formed on the surface of magnetic recording media. 
After extensive experimentation and investigation, it was found that 
certain types of protrusion patterns are particularly effective in 
generating strong, stable and repeatable electric signals upon contact 
with the transducer head during glide height testing. Such patterns are, 
therefore, particularly effective for accurately determining the glide 
height above the data zone of a magnetic recording medium. Such 
particularly effective protrusion patterns in accordance with an 
embodiment of the present invention comprise at least one circumferential 
row of protrusions, which circumferential row is radially spaced from the 
center of the disk. Embodiments of the present invention include forming a 
plurality of radially spaced circumferential rows of protrusions. In 
aspects of these embodiments, the protrusions are spaced apart 
substantially uniformly in the radial direction and/or substantially 
uniformly in the circumferential direction. In other aspects of such 
embodiments, the protrusions are randomly spaced in a radial and/or 
circumferential direction. For example, embodiments of the present 
invention comprise a reference disk having three to eight radially spaced 
circumferential rows of protrusions, which circumferential rows are 
uniformly or randomly spaced in a radial direction and/or uniformly or 
randomly spaced in a circumferential direction. 
The mechanism underlying the effectiveness of a reference disk comprising a 
plurality of radially spaced circumferential rows of protrusions for 
accurately determining the glide height above the surface of a magnetic 
recording medium is not known. However, it is believed that a plurality of 
radially spaced circumferential rows of protrusions accurately simulate 
the topographical asperities typically formed on the surface of a magnetic 
recording medium. 
The substrate employed to produced the reference disk in accordance with 
the present invention can comprise any of various materials, such as a 
glass, ceramic or glass-ceramic material, and can further comprise a 
metallic coating thereon, such as a coating of nickel or a nickel alloy. 
Laser beam technology has been employed to texture the surface, i.e., 
landing zone, of a magnetic recording medium by forming a plurality of 
protrusions thereon. Such conventional laser beam technology can be 
employed to produce protrusions on a reference disk in accordance with the 
present invention. As such laser beam technology is conventional, it is 
not described herein in detail. Reference is made to European Patent 
Application 0652554A1; Ranjan et al., U.S. Pat. No. 5,062,021; and 
Baumgart et al. "A New Laser Texturing Technique for High Performance 
Magnetic Disk Drives," IEEE Transactions on Magnetics, Vol. 31, No. 6, pp. 
2946-2951, November 1995. The laser beam texturing techniques disclosed is 
copending Application Ser. No. 08/666,374 filed on Jun. 27, 1996 and in 
copending Application Ser. No. 08/647,407 filed on May 9, 1996 can also be 
employed in practicing the present invention. The entire disclosures of 
European Patent Application EP 0652554 A1, Ranjan et al., Baumgart et al., 
and copending Application Ser. Nos. 08/666,374 filed Jun. 27, 1996 and 
08/647,407 filed May 9, 1996 are incorporated herein by reference. 
In employing laser beam technology to form protrusions on glass or ceramic 
material surfaces, it has been found particularly suitable to employ a 
CO.sub.2 laser source. It has also been found suitable to rotate the 
substrate, particularly during laser beam formation of circumferential 
rows of protrusions. 
One having ordinary skill in the art could easily optimize the height, 
diameter and spacing of the laser beam formed protrusions consistent with 
the disclosed objective herein. For example, it has been found suitable to 
form protrusions having a height of about 100 .ANG. to about 300 .ANG., a 
diameter of about 3 .mu.m to about 9 .mu.m, such as about 5 .mu.m to about 
7 .mu.m, and a protrusion spacing of about 30 .mu.m to about 100 .mu.m, 
such as about 50 .mu.m to about 80 .mu.m. 
An embodiment of the present invention is depicted in FIG. 1 and comprises 
a reference disk 10 having a diameter from its center 10A to a 
circumferential point 10B of 4 or 5 inches consistent with conventional 
magnetic recording media. A circumferential alignment pattern of 
protrusions 11 can be formed to facilitate aligning reference disk 10 with 
the reference transducer head of a glide tester apparatus. In accordance 
with the embodiment depicted in FIG. 1, a laser beam protrusion pattern 12 
is formed comprising a linear row of radial protrusions, with four 
protrusions illustrated, although the number of protrusions can vary. The 
center of the radially extending strip of protrusion 12 is spaced at about 
1.2 inches from the center 10A of reference disk 10, indicated by 
reference numeral 13. 
Another embodiment of the present invention found particularly effective is 
depicted in FIG. 2 and comprises reference disk 20 having a center at 20A. 
In order to facilitate understanding of the thrust of the present 
invention, alignment patterns and reference points have been omitted. 
Reference disk 10 is subjected to a pulsed, focused laser light beam to 
form a circumferential ring 21 radially spaced from the center 20A by a 
distance 22 and comprising a plurality of protrusions having a 
substantially uniform height, diameter and spacing. It has been found 
suitable to form circumferential row 21 at a radial distance 22 of about 
30 mm from center 20A of reference disk 20, which is 95 mm in diameter. 
FIG. 3 represents a mechanical stylus surface profile of the embodiment 
depicted in FIG. 1 comprising a radially extending substantially linear 
strip of 12 of protrusions. The uniformity of the laser light beam formed 
protrusions is apparent. 
It has been found particularly effective in obtaining a strong, stable and 
repeatable signal to form a laser light beam protrusion pattern comprising 
a plurality of radially spaced circumferential rows of protrusions. FIG. 
4A illustrates a laser light beam formed pattern comprising six radially 
spaced circumferential rows of protrusions, wherein a protrusion in each 
radially extending circumferential row is identified by reference numerals 
40 through 45. The radially spaced apart circumferential rows of 
protrusions can be advantageously formed so that the protrusions exhibit a 
substantially uniform height, diameter and spacing. The protrusions can 
also be formed so that they are substantially uniformly aligned in a 
radial direction and/or substantially radially aligned in a 
circumferential direction. The protrusions can also be randomly formed in 
a radial direction and/or randomly formed in a circumferential direction. 
In the embodiment depicted in FIG. 4A, the protrusions are substantially 
uniformly aligned in a radial direction and in a circumferential 
direction. 
Another embodiment of the present invention is illustrated in FIG. 4B and 
comprises a plurality of four radially spaced circumferential rows of 
protrusions, wherein a protrusion in each circumferential row is 
identified by reference numerals 50 through 53, which are substantially 
uniformly aligned in a radial direction and in a circumferential 
direction. The protrusions in this embodiment also exhibit a substantially 
uniform height, diameter and spacing. 
The embodiment depicted in FIG. 4C comprises five radially extending 
circumferential rows of protrusions which are substantially uniform in 
height, diameter and spacing. However, in the embodiment depicted in FIG. 
4C, the protrusions are randomly formed in a radial direction, as 
indicated by the protrusions 60 through 64, each of which is in a 
different circumferential row. 
In accordance with the present invention, a reference disk for determining 
the glide height above the data zone of a magnetic recording medium is 
fabricated by employing laser light beam technology to form a plurality of 
protrusions extending above the surface of reference disk. The laser light 
beam can be advantageously pulsed and focused to obtain a uniform array of 
protrusions substantially accurately simulating actual topographical 
asperities formed on the surface of a magnetic recording media. The 
substrates employed to produce the reference disk in accordance with the 
present invention can comprise any of various materials, such as a glass, 
ceramic or glass-ceramic material having a metallic coating thereon, such 
as nickel or a nickel alloy. The present invention enables the formation 
of a reference disk for glide testing to accurately determine whether the 
glide height of a transducer head above the surface of a magnetic 
recording medium satisfies the requirements for a particular disk drive. 
The use of a laser light beam formed pattern in accordance with the present 
invention enables the production of a reference disk at a significantly 
reduced cause vis-a-vis conventional photolithographic procedures. In 
addition, the reference disks produced in accordance with the present 
invention are superior to conventional reference disks in that they enjoy 
greater durability and provide consistently accurate results. The present 
invention encompasses the formation of various protrusion patterns, such 
as a plurality of radially spaced circumferential rows of protrusions 
randomly or uniformly aligned in a radial direction and/or circumferential 
direction, to provide a strong, stable repeatable signal during glide 
testing. The present invention enjoys utility in various conventional 
glide testers to determine the glide height of a transducer head above a 
surface of any of various types of magnetic recording media. 
Only the preferred embodiment of the invention and but a few examples of 
its versatility are shown and described in the present disclosure. It is 
to be understood that the invention is capable of use in various other 
combinations and environments and is capable of changes or modifications 
within the scope of the inventive concept as expressed herein.