Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/739—Magnetic recording media substrates
  • G11B5/73911—Inorganic substrates
  • G11B5/73913—Composites or coated substrates
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
  • G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/7368—Non-polymeric layer under the lowermost magnetic recording layer
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/739—Magnetic recording media substrates
  • G11B5/73911—Inorganic substrates
  • G11B5/73917—Metallic substrates, i.e. elemental metal or metal alloy substrates
  • G11B5/73919—Aluminium or titanium elemental or alloy substrates
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/739—Magnetic recording media substrates
  • G11B5/73911—Inorganic substrates
  • G11B5/73921—Glass or ceramic substrates

Definitions

• the present invention relates to media for recording, storing and reading magnetic data, and more particularly to the use of radiant energy beams to control topographies of such magnetic media.
• Magnetic disks employ thin films of magnetizable material for storing data in magnetic form.
• magnetic disks are mounted to rotate, each of with magnetic data transducing heads positioned in close proximity to one of the magnetic disk recording surfaces.
• Each head is moved generally radially with respect to its associated disk as the disk is rotated.
• the disks are rotated at high speeds during reading and recording operations. The speed of rotation is sufficient to create an air cushion or bearing that supports each transducing head at a controlled distance from its associated recording surface, to maintain a consistent head "flying" height.
• the transducing heads contact their associated disks whenever the disks are stationary, accelerating from a stop, or decelerating just before coming to a complete stop.
• the transducing head is positionally controlled so that whenever the disk decelerates toward a stop, the head engages the disk at the landing zone rather than at the relatively smoother recording surface.
• This patent further discloses the use of laser energy to control the landing zone texture. More particularly, a neodymium:yttrium aluminum garnet (Nd:YAG) laser generates a pulsed laser beam focused upon the upper surface of an aluminum nickel-phosphorous substrate. The laser forms a series of laser marks or spots, each including a central depression surrounded by an annular, raised rim.
• an object of the present invention to provide a magnetic data recording medium in which the texture of a dedicated transducing head contact zone is more uniform and more precisely controlled. Another object is to provide a process for directing a coherent energy beam onto an exposed surface of a magnetic recording medium, controlling the beam to control the height and structural features of nodules and other discontinuities. A further object is to provide a process for selectively directing laser energy onto a data recording surface of a magnetic medium substrate after a surface of the substrate has been mechanically polished, to remove residual scratches without undesirably altering the character of the treated substrate.
• Yet another object is to provide a magnetic data recording medium with a data recording surface that is smooth, essentially free of residual scratches and other acicular features, and more resistant to corrosion.
• a process for polishing a non-magnetizable substrate in the course of fabricating a magnetic data reading and recording medium in which a magnetizable recording layer is applied over the non-magnetizable substrate includes: a. mechanically abrading a non-magnetizable substrate to form on the substrate a substantially planar substrate surface having a surface roughness, due to residual scratches formed by the mechanical abrasion, of at most about 25 nm; b.
• the application of radiant energy is achieved by directing a beam of coherent energy onto the substrate surface to define an irradiation area of beam impingement onto that surface, and translating the substrate and beam relative to one another to move the irradiation area along a path that substantially covers the selected surface portion.
• the beam profile and its angle of incidence to the substrate surface determine the shape of the irradiation area, e.g. circular, elliptical, etc.
• a beam with a circular profile, i.e. cross section is oriented perpendicular to the substrate surface, to form a circular irradiation area.
• the extent of surface heating, and thus the depth of the melt region, is controlled primarily by the level of energy at the irradiation area and the dwell time, i.e. the period during which a particular location on the substrate surface is irradiated.
• dwell time is controlled by the pulse duration and pulse frequency. Dwell time is influenced slightly by the velocity of the irradiation area relative to the substrate surface, although the pulse time is so short that this factor usually is insignificant.
• the energy level is controlled by the power at which the beam is generated, by any attenuation between the beam source and area of impingement, by the degree of beam focusing and the spatial characteristics of the beam.
• the preferred energy source is a solid state laser, more particularly a neodymium:yttrium lithium fluoride (Nd:YLF) laser. As compared to the Nd:YAG laser discussed in the aforementioned U.S. Patent No.
• the solid state Nd:YLF laser is operable at lower energy levels and is substantially more stable in terms of pulse level and pulse duration. This yields a considerable improvement in the surface altering capabilities of the laser, for producing more uniform and repeatable features such as the rimmed depressions disclosed in the *781 patent. Moreover, the solid state laser has been found to enable surface polishing, and the formation of unique surface irregularities. As one example of the improvement achieved, the Nd:YLF laser can be pulsed and focused to provide a localized but relatively wide irradiation area, with the pulse duration selected to melt the substrate surface, but only momentarily and to a depth of at most about 40 microinches (1 micron) , more preferably about 250 nm and most preferably 38 nm.
• This approach is particularly effective to remove residual scratches after a conventional substrate disk (aluminum plated with a 3-10 micron thick layer of a nickel-phosphorous alloy) has been mechanically polished.
• the depth of material melting is more than ample to encompass the residual scratches. Yet, because the melting depth is selected to be at most about 10 percent of the Ni-P layer thickness in any event, the melting depth is minute in relation to the thickness of the Ni-P layer.
• the rapid cooling and resoiidification of the melted region and its shallowness in comparison to the alloy layer thickness preserve the non-magnetic character of the alloy layer, which would be destroyed if the layer were subjected to sufficient heat to cause a more general crystallization. More particularly, the original structure of the Ni-P layer is preserved throughout most of its thickness.
• laser polishing does not necessarily reduce surface roughness.
• a surface mechanically abraded to a peak roughness of about 2 nm when subjected to a laser polishing as described herein, may exhibit an increased roughness, e.g. to about a 3 nm maximum peak height.
• the resulting roughness is caused by a lower frequency waviness or undulation, as compared to the higher frequency, acicular character of the peaks and valleys of residual scratches. Accordingly, media performance is improved, in terms of reduced noise and better corrosion resistance, while a satisfactorily low roughness is retained.
• laser polishing not only removes acicular features, but also reduces surface roughness.
• the laser can be employed to control the texture of a selected surface zone dedicated to transducing head contact, and therefore having a roughness greater than that of an adjacent or proximate data recording zone.
• the dedicated zone is selectively textured by forming laser marks or spots.
• the laser beam generated at power levels comparable to those used in laser polishing but focused to a substantially smaller irradiation area, has been found to form a nodule or dimple that projects outwardly from the substrate surface.
• the formation of nodules, rather than the aforementioned rimmed depressions results from reduced energy levels and concentrations at the irradiation area. Beyond this, the exact reason for nodule formation as opposed to depression formation is not fully understood.
• the Gaussian nature of the impinging laser beam concentrates heat near the beam center.
• bump formation is that the beam impingement, when momentarily melting material in the beam irradiation area, forms a wave originating at the center of the irradiation area and tending to propagate radially outward. The wave is preserved due to the rapid cooling and solidifying of the substrate material. For higher energy levels, the wave propagates outward before material solidifies, forming a ring or rim surrounding a depression. At lower energy levels, the melted substrate material solidifies so rapidly that the wave has not begun to migrate radially outward. Thus, a bump or nodule, rather than a depression, is formed.
• the level of energy at which rimmed depressions become nodules varies with the substrate material, as might be expected. Further, it has been found to vary among different sets or batches of aluminum nickel-phosphorous substrates, although within a given batch there is a high degree of consistency and a close relationship between the energy level and nodule size. Accordingly, some testing is needed to determine the appropriate energy levels in different situations. Formation of nodules, rather than rimmed depressions, is a surprising and advantageous result. Nodules produced on a given substrate under the same conditions (pulse level, degree of attenuation and pulse duration) exhibit a high degree of uniformity in height, e.g. often with a standard deviation of less than about 1 nm. More generally, bumps are the preferred discontinuity since, as compared to the depressions, they are less likely to entrap debris and enhances liquid lubricant replenishment.
• another aspect of the present invention is a process for selectively texturizing magnetic recording media, including: a. forming a specular substrate surface on a non-magnetizable substrate body, the substrate surface being substantially planar and having a nominal roughness; b. concentrating radiant energy selectively upon a plurality of locations over a treatment area of the substrate surface to controUably alter the topography of the selected surface at each of the locations to form a rounded nodule having a height, above a nominal surface plane of the selected one of the surfaces, in the range of about 2.5-25 nm and greater than said nominal roughness; and c. depositing a magnetizable film over the substrate surface as a layer substantially uniform in thickness to provide a recording surface.
• the treatment area is an annular band that provides a dedicated transducing head contact area adjacent a smoother data recording area.
• the band is relatively narrow and is disposed at a radially inward edge of the data recording area.
• the degree of control over nodule size affords a further improvement, namely a transition zone between the transducing head contact zone and the data recording zone.
• nodule sizes can be controUably varied to diminish in the radial direction, e.g. receding from a height of about 20 nm.
• the gradient across the transition zone reduces disturbances as the transducing head is translated radially between the contact and data zones, reducing the chance for head crash.
• a further aspect of the invention is a process for texturing a substrate surface of a glass substrate, in preparation for subsequent application of a magnetizable thin film.
• the process includes: a. depositing a metal onto a glass substrate as a metallic layer of uniform thickness of at least 5 nm; b. concentrating coherent radiant energy selectively upon a plurality of locations over a treatment area of the metallic layer to controUably alter the substrate topography at each of the locations to form at each location a surface irregularity said surface irregularities having heights, above a nominal surface plane of the substrate surface, in the range of 3-200 nm.
• radiant energy is selectively applied to magnetic recording media to control surface topography across data zones, contact zones and transition zones.
• Data zone smoothness, corrosion resistance and signal reproduction characteristics are enhanced by radiant energy polishing to remove the residual scratches and other acicularities produced by mechanical texturing and polishing.
• Formation of nodules by radiant energy texturing results in a highly uniform roughness throughout the contact zone, and a controlled roughness gradient radially across a transition zone if desired.
• Lower transducing head flying heights are realized, enabling storage of data at increased density.
• Figure 1 is a plan view of a rigid magnetic disk and a transducing head supported for generally radial movement relative to the disk;
• Figure 2 is an enlarged partial sectional view of the magnetic disk in Figure 1;
• Figure 3 is an elevational view of an apparatus for polishing and texturing magnetic disk substrates
• Figure 4 is an enlarged perspective view of a nodule in the surface of a magnetic disk substrate, formed by the apparatus of Figure 3
• Figure 5 illustrates the profile of the nodule in Figure 4;
• Figures 6-8 schematically illustrate laser polishing of a mechanically polished substrate
• Figure 9 depicts an atomic force microscopy surface profile of a mechanically textured substrate
• Figure 10 depicts the surface profile of Figure 9, following laser polishing of the substrate
• Figure 11 depicts an atomic force microscopy surface profile of a mechanically polished substrate
• Figure 12 illustrates the surface profile of Figure 11, following laser polishing of the substrate
• Figure 13 illustrates the surface profile of a substrate with a laser textured dedicated head contact zone
• Figure 14 illustrates the surface profile of a substrate with laser textured contact and transition zones, and a laser polished data zone
• Figure 15 illustrates the surface profile of a substrate with a mechanically textured contact zone and a mechanically polished data zone, both zones subsequently laser treated;
• Figure 16 is a sectional view of a glass substrate treated to enhance energy absorption near its upper surface
• Figure 17 is a plan view of the substrate upper surface, illustrating surface fracture discontinuities
• Figure 18 illustrates the profile of one of the discontinuities in Figure 17;
• Figure 19 is an elevational view of an alternative texturing and polishing apparatus;
• Figure 20 is an elevational view of a further alternative texturing and polishing apparatus.
• FIG. 1 and 2 a medium for recording and reading magnetic data, in particular a magnetic disk 16 rotatable about a vertical axis and having a substantially planar and horizontal upper surface 18.
• a rotary actuator (not shown) supports a transducing head support arm 20 in cantilevered fashion.
• a magnetic data transducing head 22 is mounted to the free end of support arm 20, through a suspension 24 which allows gimballing action of the head, i.e. limited vertical travel and rotation about pitch and roll axes.
• the rotary actuator and the support arm pivot to move head 22 in an arcuate path, generally radially with respect to disk 16.
• an opening 26 At the center of disk 16 is an opening 26 to accommodate a disk drive spindle (not shown) used to rotate the disk. Between opening 26 and an outer circumferential edge 28 of the disk, upper surface 18 is divided into four annular sectors; a radially inward sector 30 for clamping disk 16 to the spindle; a dedicated transducing head contact zone 32; a transition zone 34; and a data zone 36 that serves as the area for recording and reading the magnetic data.
• head 22 contacts upper surface 18. However, when the disk rotates within the normal operating range an air bearing or cushion, formed by air flowing between head 22 and upper surface 18 in the direction of disk rotation, supports the head in parallel, spaced apart relation to the recording surface.
• the distance between a planar bottom surface 38 of head 22 and upper surface 18, known as the head “flying height”, is about ten microinches (254 nm) or less.
• the flying height should be as low as practicable for maximizing the density of data stored on disk 16.
• disk rotation and rotary arm pivoting are controlled in concert to selectively position transducing head 22 near desired locations within data zone 36.
• support arm 20 is moved radially inward to position head 22 directly over contact zone 32.
• the head is positioned for engagement only with the contact zone.
• disk 16 is accelerated from stop, initially with head 22 engaged with a disk within contact zone 32.
• the rotary arm is not pivoted until head 22 is supported by an air bearing, free of the contact zone.
• Magnetic disk 16 is formed by polishing, grinding or otherwise mechanically finishing an aluminum substrate disk to provide a substantially flat upper surface 40.
• a nickel-phosphorous alloy is plated onto the upper surface of the substrate disk, to provide a non- magnetizable layer 42 with a uniform thickness within the range of about 2-10 microns.
• the upper surface of the Ni-P alloy layer i.e. a substrate surface 44
• a saturated cloth, paper or pad coated or flooded with cerium oxide, silicon carbide or another suitable grit is used for this purpose.
• a liquid slurry containing grit also may be used.
• Laser treatment preferably follows the mechanical polishing of substrate surface 44.
• apparatus 46 includes a spindle 48 for rotatably supporting the substrate disk, indicated at 50.
• a laser module 52 is supported on a carriage 54 for reciprocal movement radially of the substrate disk.
• the laser module includes a neodymium:yttrium lithium fluoride (Nd:YLF) diode laser 56, collimating optics 58 for collimating the diode laser output to produce a beam 60 having a diameter of about one mm, an attenuator 62, and converging optics 64 for focusing beam 60 at or approximately at substrate surface 44.
• Nd:YLF neodymium:yttrium lithium fluoride
• Attenuator 62 is a neutral density filter, for example a glass plate 66 bearing a film 68, applied by sputtering unevenly to provide a transmissivity gradient across the plate. Movement of plate 66, transversely of the longitudinal beam direction, controUably varies the proportion of beam energy transmitted to converging optics 58 and thus varies the energy intensity at the substrate surface.
• Diode laser 56 is an Nd:YLF diode pumped laser, e.g. as available from Spectra Physics.
• diode laser 56 is pulsed for texturing and polishing operations, although a continuous mode (less preferred) can be used in polishing.
• Apparatus 46 can be controlled in texturing and polishing operations to determine a variety of substrate surface topographies and characteristics. In essence, texturing and polishing involve rotating substrate disk 50 at a controlled speed while carriage 54 moves laser module 52 at a controlled radial speed.
• the diode laser is controlled to provide a pulsed beam at a predetermined frequency, and at a predetermined pulse duration.
• the disk rotational speed may be gradually reduced as the laser module is moved radially outward, to maintain a substantially constant linear velocity.
• Beam 60 is perpendicular to substrate surface 44 and defines a substantially circular area 70 of beam impingement onto the surface. It is to be appreciated that the impingement area can be made elliptical if desired, either by changing the beam to a non- perpendicular orientation, or by changing the converging optics, e.g. to a cylindrical lens. In either event, the manner in which the surface is altered depends on the energy distribution at the impingement area and the dwell time, i.e. the duration over which impingement area 70 coincides with a particular portion of the substrate surface.
• the effect of simultaneous disk rotation and laser module translation is to move impingement area 70 in a spiral path over the substrate surface.
• laser module 52 can be stepped at each disk rotation so that the path consists of concentric circles.
• Energy distribution at the impingement area depends on several factors, including the power at which diode laser 56 is fired, the degree of attenuation, and the extent of laser beam focus. Energy distribution also depends upon the mode in which diode laser 56 is operated. For example, the TEM 00 mode yields a Gaussian energy distribution that concentrates the energy near the center of the impingement area. Sharper focusing also tends to concentrate energy near the impingement area center.
• dwell time is primarily a function of pulse duration. Dwell time also is slightly influenced by the disk rotational speed and the radial speed of laser module 52. Further, when the diode laser is pulsed, surface topography is a function of the pulse frequency, i.e. the number of pulses per unit time.
• diode laser 56 is fired at levels of 1-50 ⁇ j, and more preferably within a range of 1-6 ⁇ J. Given the low energy level, beam 60 is sharply focused to a focal diameter, i.e. impingement area diameter, and more preferably in the range of 5-15 microns. Diode laser 56 is operated in the TEMo o mode, which produces a Gaussian distribution of energy in beam 60 and therefore across impingement area 70. The resultant concentration of energy near the center of the impingement area promotes nodule formation. Diode laser 56 preferably is pulsed as noted above, and the preferred pulse duration is in the range of 5-200 ns -15-
• duration encompassing the time during which the pulse level is at or above 10 percent of peak amplitude.
• a typical nodule formed by diode laser 56 is represented in perspective in Figure 4 and in profile in Figure 5.
• the nodule extends above the specular surface plane of the substrate surface, i.e. a nominal plane 72, by a height "h" of 0.3 microinches (7.6 nm) .
• Nodule 74 has a diameter "d" of about 5 microns. At its base, the nodule is surrounded by a minute annular depression.
• nodules which can be formed with heights as low as about 0.1 microinch (2.54 nm) .
• a closely related advantage is the enhanced uniformity of nodule formation, primarily due to better stability of the Nd:YLF diode laser, especially at lower power levels. While the rimmed depressions exhibit excellent uniformity when compared to the acicular features of a mechanically abraded surface of similar roughness, nodules 74 afford a further, substantial improvement in uniformity.
• Nodule texturizing enhances surface toughness, in terms of resistance to damage from episodes of contact -16-
• nodules 74 are more stable than rimmed depressions of comparable size, because of their rounded, slightly convex structure, i.e. the degree to which diameter "d" exceeds height "h".
• a nodule texturized surface exhibits improved friction characteristics due to better lubricant replenishment, and is less apt to collect or entrap debris.
• apparatus 46 is controlled to provide a desired pattern or distribution of nodules throughout a texturized region of the substrate surface.
• substrate disk 50 is rotated at a speed, variable depending upon the diode laser's radial rotation, to provide a linear (arcuate) velocity of about one meter per second.
• Pulses of ten nanosecond duration are provided at a frequency of 50,000 pulses per second, i.e. one pulse every twenty microseconds. This would yield a twenty micron distance between adjacent nodules, center to center.
• laser module 52 is translated radially at a velocity that varies with the disk rotational velocity, e.g. for translation of twenty microns with each revolution. The result is a spiral pattern of nodules, with spacing between adjacent nodules and spacing between adjacent circular tracks of nodules both equaling twenty microns.
• the same pattern can be formed with constant velocities of disk rotation and laser module radial translation, if the pulse frequency is controUably varied from a mean value of 50,000 pulses per second, depending on the beam's radial position. In either event, at the meter per second linear velocity, beam impingement area 70 travels only ten nm during each pulse. Because this distance is slight in relation to the impingement area diameter, the impingement area can be considered essentially stationary during the formation of each nodule.
• a spiral pattern of nodules is preferred, since it involves a single, continuous path that requires only several seconds for a full texturing, i.e. complete nodule formation throughout contact zone 32.
• Apparatus 46 is not limited to texturing surfaces, but also can be used to polish data zone 36, or any other chosen region of the substrate surface.
• Laser polishing is illustrated schematically in Figures 6-8. As seen in Figure 6, laser beam 60 is focused upon substrate surface 44, i.e. the upper surface of nickel-phosphorous layer 42. Beam 60 is not as sharply focused as in the case of nodule formation.
• the preferred diameter of the focal spot or beam impingement area is within the range of 50-100 microns.
• Diode laser 56 is fired at a power level within the range of 1-50 ⁇ J and more preferably 1-6 ⁇ J.
• the use of spatial filtering allows the more uniform (i.e. non-Gaussian) distribution of power over the surface.
• the energy distribution within beam 60 and upon impingement area 70 is considerably more uniform, i.e. non-Gaussian. Consequently the tendency to form nodules is considerably reduced. However, there is a sufficient distribution of energy to melt the nickel- phosphorous material within and proximate the impingement area, with the area of melted material having a diameter of at least about thirty microns.
• the pulse duration is the same as that in nodule formation, i.e. 5-200 ns and more preferably about 20-40 ns.
• the extent of nickel-phosphorous melting is limited. Most preferably the melt region is extremely thin, e.g. on the order of 38 nm (1.5 microinches) . However, good results are obtained with thicknesses up to about 250 nm (10 microinches) , with less preferred but satisfactory results up to a thickness of about 1000 nm, provided that non-magnetizable layer 42 is sufficient in its thickness. More particularly, the depth of melt region 76 should not exceed about 10 percent of the nickel-phosphorous layer thickness. The minimal depth of melt region 76 is determined by heat loss to the surrounding disk material, virtually instantaneously upon completion of the pulse.
• polishing may be accomplished by continuous operation of diode laser 56, a pulsed laser is preferred. Given the nanosecond pulse duration and a frequency of 50,000 pulses per second, substrate disk 50 is rotated at a substantially reduced speed, so that successive pulses are directed onto overlapping impingement areas. Thus, despite the relatively larger impingement area, laser polishing requires more time than texturing, for example 10-30 seconds.
• Figures 9-12 depict surface roughness traces measured by atomic force microscopy and illustrate two applications of laser polishing.
• the first, in Figures 9 and 10 is the laser treatment of a mechanically textured surface 77, either a dedicated head contact zone or a data zone that does not involve an extremely low transducing head flying height.
• Figure 9 illustrates the acicular features 78 present after mechanical texturing. Surface roughness, in terms of maximum peak heights above a nominal surface plane 80, is about 25 nm.
• the roughness trace in Figure 10 illustrates a substantial reduction in surface roughness, to about 10 nm. Further, substrate material melted by the laser energy has flowed, removing substantially all of the acicular features and leaving smoother, rounded features 82 that provide a lower frequency waviness. The removal of the sharp peaks is particularly advantageous, since the peaks tend to fracture upon head contact. Thus, the surface after laser treatment is better able to withstand intentional or incidental head contact, generating less debris.
• Figure 11 shows a surface roughness trace 84 of an extremely finely abraded or "superpolished" substrate disk. Surface roughness based on peak heights is less than 2 nm, but residual scratches form acicular features 86.
• Figure 13 illustrates part of a substrate disk 90 having a substrate surface 92 selectively treated to provide a laser textured contact zone 94 and a mechanically abraded, superpolished data zone 96.
• substrate surface 92 is polished to a peak roughness of less than about 3 nm, comparable to the results of mechanical polishing illustrated in Figure 11.
• the substrate surface also preferably is polished to this extent. Then, the substrate surface is exposed to beam 60 throughout the contact zone, to form nodules 98 having heights of 0.3- 1.0 microinches
• the primary advantage, along with the surface improvement over the contact zone, is that no step is required between data zone 96 and contact zone 94. Thus, there is no need to choose between a gradual transition and step that takes up space that otherwise could be used for storing data and a narrow, steeper step that increases the risk of transducing head disturbances.
• a substrate surface 100 of a substrate disk 102 has been treated with apparatus 46 to provide a contact zone 104, a data zone 106 and a transition zone 108 between the contact and data zones.
• beam 60 is applied to form spaced apart nodules 110 having nodule heights in the range of 0.8-1.0 microinches (20.3-25.4 nm) , and more preferably about 0.8 microinches (about 20 nm) .
• nodules 112 Radially across transition zone 108, the heights of nodules 112 are ramped, i.e. gradually decreased from about 0.8-1.0 microinches (20.3-25.4 nm) to about 0.1-0.3 microinches (2.5-7.6 nm) .
• Nodules 112 are formed in a continuous spiral path by pulsing diode laser 56 as previously explained, but with the additional feature that energy at impingement area 70 is gradually reduced as beam 60 is moved radially outward. This is accomplished by maintaining a constant level of power at which the diode laser is fired, while gradually translating neutral density filter 62 in the transverse direction (arrow. Figure 3) , which gradually attenuates the beam beyond plate 66.
• the incline of transition zone 108 is a function of its radial width as well as the maximum and minimum nodule heights.
• Data zone 106 is treated first by laser polishing after a fine mechanical abrasion, as explained in connection with Figures 6-8, to achieve a surface profile similar to that depicted in Figure 12. Following laser polishing, data zone 106 further is exposed to beam 60 to form nodules 114 having heights in the range of 0.1-0.3 microinches (2.5-7.6 nm) , i.e. less than the minimum height of nodules 112. This imparts a controlled surface roughness satisfactory for most transducing head flying heights and provides a controlled texture that better withstands incidental transducing head contact.
• Figure 15 shows a substrate disk 116 having a substrate surface 118 treated to form a contact zone 120 and a data zone 122. Over contact zone 120, the substrate surface is mechanically textured to provide a surface peak roughness on the order of 25 nm. Data zone 122 is subjected to finer mechanical abrasion, yielding a surface peak roughness of at most about 3 nm.
• FIG. 16 shows a glass substrate 124, treated to provide an energy-absorbing layer 126.
• the energy-absorbing layer is a metallic layer, e.g. chromium sputtered, vapor deposited or plated onto glass substrate 124 to a thickness of at least 5 nm.
• Other metals can be employed, such as tungsten or titanium.
• Metallic layer 126 is exposed to a pulsed laser beam to texture a contact zone 128. This is accomplished in substantially the same manner as the formation of nodules discussed above in connection with Figures 4 and 5, with the same operating ranges for laser power (1-50 ⁇ J, more preferably 1-6 ⁇ J) , focal area diameter (5-15 microns) , and pulse duration (5-200 ns, more preferably 20-40 ns) . Surface topographies can be influenced by varying these parameters in the manner discussed above.
• surface topographies are influenced by the thickness of the chromium layer.
• the chromium acts virtually exclusively as an agent for localized energy absorption, thereby causing localized deformations (surface melting and local microfracturing) in the glass.
• Figure 17 illustrates the irregular, somewhat star-like profiles of the fractures 130
• Figure 18 is an atomic force microscopy profile trace showing the more acicular character of these fractures, as compared to the nodules discussed above.
• the fractures have heights varying over a wide range as compared to nodules, i.e. 0.1-8 microinches (2.54-200 nm) .
• topography is a combination of the above-discussed microfractures and rounded nodules formed of chromium in the manner discussed in connection with the aluminum nickel-phosphorous substrate. Finally, for aterial thicknesses greater than 100 nm, topography is determined virtually exclusively by nodule formation.
• Figure 19 illustrates a laser texturizing and polishing apparatus 132 similar to apparatus 46, in that a laser beam 134 is focused onto a substrate surface 136 of a substrate disk 138.
• the disk is rotated on a spindle 140, while a carriage 142 radially translates a laser module 144.
• the laser module includes a diode laser 146 providing energy to beam collimating optics 148.
• the columnar beam is transmitted through an attenuator 150 to focusing optics 152, then to the substrate surface.
• Attenuator 150 is a polarizing device that includes an upstream polarizing disk 154, a downstream polarizing disk 156 aligned with disk 154, and a mechanism 158 for rotating disk 156.
• disk 156 is positionable to align the respective polarization axes of disks 154 and 156 (indicated by the arrows) , for maximum transmission of the laser energy.
• transmissivity of the polarizing device gradually decreases.
• rotation of disk 156 achieves the same result as linear translation of neutral density filter 62 in Figure 3.
• fabrication of magnetic disk 16 involves application of several layers after the substrate disk has been selectively textured and polished.
• a layer of chrome is sputter deposited onto substrate surface 44, preferably to a thickness of about 10-100 nm.
• This provides an underlayer 160 particularly well suited for subsequent deposition of a magnetic thin film, in that the crystalline structure of underlayer 160 can advantageously control the epitaxy and crystalline structure of the magnetic film.
• a recording layer 162 of a magnetizable material e.g. a cobalt/tantalum/chromium or a cobalt/platinum/chromium alloy, is sputter deposited to a thickness of about 10-50 nm.
• a protective layer 164 e.g. carbon, is sputter deposited onto the recording layer to a thickness of about 5-30 nm.
• the removal of acicular features through laser polishing of the substrate surface enables depositing of carbon layer 164 at a more uniform thickness, increasing resistance to corrosion.
• Figure 20 illustrates another alternative laser texturing and polishing apparatus 166 for focusing a laser beam 168 onto a substrate surface 170 of a substrate disk 172.
• a diode laser 174 generates the laser beam, which is collimated at collimating optics 176, and then provided to a scanning assembly 178.
• An attenuator 180 e.g. a neutral density filter, is movable horizontally as indicated by the arrows, to selectively attenuate the beam.
• optics within scanning assembly 178 are manipulated to translate the beam relative to substrate disk 172, over a spiral path that replicates the path achieved by radial movement of the laser diode in concert with disk rotation as in apparatus 46 and apparatus 132. Accordingly, while the optics are more complex in apparatus 166, the substrate disks undergoing treatment can remain stationary.
• magnetic recording media can be selectively textured to provide transducing head contact zones, data zones and intermediate transition zones that are tightly controlled as to surface roughness, either for enhanced uniformity in a contact zone or landing zone, or for a controlled ramping or roughness gradient radially across a transition zone.
• Controlled roughness is achieved by forming rounded nodules, and it is through control of the individual nodule heights that the desired surface roughness is achieved.
• the nodules exhibit better uniformity, improved resistance to head contact at lower surface roughnesses, better lubricant replenishment and reduced debris entrapment.
• Laser polishing enhances performance, even as compared to extremely smooth mechanically polished surfaces, in eliminating residual scratches for improved corrosion resistance and signal integrity.

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• Inorganic Chemistry (AREA)
• Metallurgy (AREA)
• Ceramic Engineering (AREA)
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• Manufacturing Of Magnetic Record Carriers (AREA)

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• 1995
  • 1995-08-22 EP EP02077006A patent/EP1271484A3/de not_active Withdrawn
  • 1995-08-22 WO PCT/US1995/010697 patent/WO1997007931A1/en not_active Application Discontinuation
  • 1995-08-22 JP JP53283996A patent/JP3199266B2/ja not_active Expired - Fee Related
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