Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2000-05-25
2003-07-08
Resan, Steven A. (Department: 1773)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S555000, C427S129000, C427S596000, C428S690000
Reexamination Certificate
active
06589609
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having textured surfaces for contact with cooperating magnetic transducer heads. The invention has particular applicability to high areal density magnetic recording media designed for drive programs having a reduced flying height and improve shock resistance for mobile computer data storage applications.
BACKGROUND ART
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (CSS) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surface of the 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 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. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against a landing zone of the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the stop and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk landing zone and stopping.
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 of the head. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in close proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces eventually leading to what is referred to as a “head crash.” Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as “texturing.” Conventional texturing techniques involve polishing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers.
The escalating requirements for high areal recording density impose increasingly greater requirements on thin film magnetic media in terms of coercivity, stiction squareness, low medium noise and narrow track recording performance. In addition, increasingly high density and large-capacity magnetic disks require increasingly smaller flying heights, i.e., the distance by which the head floats above the surface of the disk in the CSS drive. The requirement to further reduce the flying height of the head renders it particularly difficult to satisfy the requirements for controlled texturing to avoid head crash.
Conventional laser texturing techniques have previously been applied to metal-containing substrates or substrates having a metal-containing surface, such as Ni—P plated Al or Al-base alloys. Such substrates, however, exhibit a tendency toward corrosion and are relatively fragile, thereby limiting their utility so that they are not particularly desirable for use in mobile computer data storage applications, such as laptop computers. Glasses and glass-ceramics, i.e., two-phase materials comprising an amorphous glass phase and a crystalline ceramic phase, exhibit superior “hardness”, resistance to shock, heat resistance and chemical stability (acid and alkali resistance) than Ni—P plated Al or Al-alloy substrates. Accordingly, glass and glass-ceramic substrates are capable of being polished to a greater smoothness than Ni—P plated Al or Al-alloy substrates for high areal density ultra-low flying height application and provide better shock resistance for use in mobile computer data storage application. However, it is extremely difficult to provide an adequate texture on a glass or a glass-ceramic substrate, particularly in view of the escalating requirements for high areal recording density.
Conventional practices for texturing a glass or glass-ceramic substrate comprise heat treatment during which the crystallization temperature is maintained for about 1 to about 5 hours to generate secondary crystal grains forming the surface texture characterized by irregular protrusions with surrounding valleys extending into substrate.
The use of heat treatment to form a textured surface on alternate substrates, such as glass or glass-ceramic substrates, is undesirably slow and inefficient in terms of energy consumption. Significantly, it is extremely difficult to exercise control over the size and shape of the secondary crystal grains due to inherent limitations in controlling temperature uniformity. Accordingly it is virtually impossible to provide a glass or glass-ceramic substrate with a controlled textured landing zone for optimizing flying height and maximizing data zone recording density. Moreover, the resulting texture comprises irregularly shaped protrusions with surrounding valleys extending into the substrate, thereby creating undesirable stress profiles during subsequent deposition of layers by sputtering at elevated temperatures. Such undesirable stress, profiles render it extremely difficult to accurately replicate the texture in subsequently deposited layers. It is also difficult to optimize both the bulk and surface properties at the same time because the entire substrate is heated. In addition, it is not possible to provide a glass-ceramic substrate with a controlled textured landing zone together with a super-smooth data zone to maximize recording density.
Pulsed laser light beams have also been employed to laser texture substrates, such as glass-ceramic substrates. Kuo et al. in U.S. Pat. No. 5,853,820 disclose a method of manufacturing a magnetic recording medium comprising texturing a surface of a glass-ceramic substrate with a pulsed, focused laser light beam to form a plurality of protrusions, wherein the crystalline phase of the glass-ceramic substrate is less than about 70% by volume. Kuo in U.S. Pat. No. 5,714,207 discloses a method of manufacturing a magnetic recording medium comprising texturing a surface of a glass or glass-ceramic substrate with a pulsed, focused laser light beam to form a plurality of protrusions and controlling the height of the protrusions by controlling the quench rate during resolidification of the laser formed protrusions. Xuan in U.S. Pat. No. 5,955,154 discloses a method of manufacturing a magnetic recording medium by comprising laser texturing an upper surface of a glass-ceramic substrate wit
Pan Zhengda
Shih Chung Y.
Xuan Jialuo Jack
Resan Steven A.
Seagate Technology LLC
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