Glass Disk Substrates Research Articles

Comparison of surface energy and adhesion energy of surface-treated particles

The mineral industry uses tremendous amounts of water every year in the processing of ores. Sustainable practices associated with the processing of ores are, therefore, of critical importance. The project described herein is the first step toward producing a dry, particle-separation process based upon control and exploitation of adhesive forces. In this research, the goal is to determine the surface energy of particles, and further, whether the solid surface energy can be used to understand the adhesion between these particles and surface-modified substrates. Glass spheres were chosen to represent silicate minerals, the most abundant type of minerals found in mineral deposits. The solid surface energy was found by using contact angle measurements and by applying the van Oss-Good-Chaudhury (VOGC) method. The VOGC method utilizes three-liquid triads to determine the Lifshitz-van der Waals, Lewis acid and Lewis base surface energy components. Surface energies from plasma-cleaned glass were between 40.2 and 60.2 mJ/m2; for the same glass with a hydrophobic chemical surface treatment, trichloro(octadecyl)silane (TCOD), the surface energy was between 20.8 and 20.9 mJ/m2; and for the glass with a hydrophilic chemical surface treatment (n1-(3-trimethoxysilylpropyl) diethylenetriamine (TMPA)) the surface energy was between 46.3 and 61.6 mJ/m2. The particle-substrate adhesion was also measured using a mechanical impact tester. Glass disks and beads were used, cleaned and surface treated with TCOD and TMPA. A custom horizontal impact tester was designed and used to measure the adhesion force between the glass spheres and a glass disk substrate. Impact of the disk/particle puck causes particle removal as tensile forces act on the particles. The tensile detachment force and adhesive force are equal at a critical particle size. Johnson-Kendall-Roberts (JKR) theory was used to determine the interfacial energy between the particles and the surface. The average interfacial energy of plasma cleaned glass, glass treated with TCOD and with TMPA were 44.8 mJ/m2, 21.6 mJ/m2, and 40.1 mJ/m2, respectively. These values are in good agreement with the literature values and with the interfacial energy determined using the VOGC method described above, demonstrating that two approaches compare favorably, despite the dramatically different methods (molecular vs mechanical) utilized.

Chemical Mechanical Polishing of Glass Disk Substrates: Preliminary Experimental Investigation

Glass disk substrates are used in a wide range of portable devices because of their relatively high resistance to heat and shocks compared with aluminum substrates. Chemical mechanical polishing (CMP) is an available method to eliminate residual surface defects induced by grinding/lapping to meet final product requirements. In this work, CMP experiments with a low-cost fabric cloth pad were performed to study the effects of four key process factors on the material removal rate (MRR), flatness, and surface finish of polished glass disk substrates, and to explore the feasibility to achieve high machining efficiency, sub-nanometric surface roughness, and micrometric flatness of polished glass disk substrates simultaneously under optimized CMP conditions. The experimental results and analyses reveal that the interaction of pad rotational speed and polish head rotational speed had significant effect on the roughness (Ra), down force, and the interaction of down force and pad rotational speed had significant effects on the flatness, and down force and pad rotational speed had significant effects on the MRR. After compromise and prioritization analyses are performed, a combination of the four variables, which is the combination of 50 g/cm2 for down force, 40 rpm for pad rotational speed, 20 rpm for polish head rotational speed, and 100 ml/min for slurry supply velocity, is obtained to achieve high machining efficiency, sub-nanometric surface roughness and micrometric flatness of polished glass disk substrates simultaneously.

Development of fixed abrasive chemical mechanical polishing process for glass disk substrates

Glass disk substrates are used in a wide range of portable devices because of their relatively high resistance to heat and shocks compared to aluminum substrates. Chemical mechanical polishing (CMP) with fixed abrasive pad is an alternative glass disk substrates finishing method to loose abrasive lapping and polishing with traditional pad. In this paper, we developed a chemical mechanical polishing process for 2.5-inch glass disk substrates using a fixed abrasive pad. A serial of CMP experiments were carried out under different polishing variables and conditioning modes (ex situ and in situ conditioning). The polishing performances were evaluated and analyzed in terms of surface roughness, surface topography, and material removal rate. The polishing characteristics were also discussed to reveal material removal mechanism and surface generation involved in fixed abrasive CMP for glass disk substrates.

Numerical Study on Heat Transfer and Lubricant Depletion in a Heat Assisted Magnetic Recording System with Multilayer Disk Structure

Heat transfer and lubricant depletion in a HAMR system with multilayer disk substrate are numerically simulated in this study. Cases under two types of multilayer disk substrates with different materials on the top layer as well as different laser powers are examined. The results show the significant effects of the material property and the laser power. Compared with pure glass disk substrate, larger thermal conductivity of top-layer material in the multilayer disk substrate causes faster heat conduction and thus substantial reductions in the temperature increase and lubricant depletion on the top surface. Hence it is necessary and important to incorporate the real multilayer structure in modeling heat transfer and lubricant depletion in practical HAMR systems.

Transient slider-disk contacts in the presence of spherical contamination particles

Transient thermal–mechanical contacts between a slider and a rotating disk in the presence of contamination particles are investigated using finite element analysis. The maximum temperature rise due to frictional heating, the maximum plastically deformed area, and the maximum residual penetration into the disk surface are determined as a function of particle properties for aluminum and glass disk substrate. It is found that contact with soft and deformable particles can cause a large temperature rise, sufficient for thermal erasure, even though physical damage of the media is not observed. Contact with hard and rigid particles can lead to severe plastic deformation as well as high temperature rise of the media, representing the worst case for tribological integrity of the slider-disk interface.

Electrochemical Fabrication and Characterization of CoPt Bit Patterned Media: Towards a Wetchemical, Large-Scale Fabrication

This paper describes the fabrication process of CoPt nandot arrays on a glass disk substrate with a CoZrNb underlayer as a soft magnetic underlayer (SUL) by using an electrochemical process, and also the analysis on the magnetic properties of these fabricated CoPt nanodot arrays. We formed nano-patterned substrates by UV-nanoimprint lithography (UV-NIL) on the glass disk substrate. CoPt was electrodeposited into the nano-patterned substrates optimizing the electrodeposition condition and bath composition as well as a Cu intermediate layer. The construction of the nanodot arrays were CoPt nanodot arrays (20 nm)/Cu (5 nm)/CoZrNb (100 nm)/Cr (5 nm)/Glass disk. Magnetic signals were clearly observed on the dc magnetized state and multi domain were observed in each nanodot on the ac magnetized state by magnetic force microscopy (MFM). The perpendicular coercivity of the CoPt nanodot arrays was 430 kA/m. These results showed electrochemical process can be used for the manufacture of magnetic recording media.

Fabrication of magnetic nanodot array using electrochemical deposition processes

We investigated fabrication processes of magnetic nanodot arrays for the ultra-high density magnetic recording media by using an electrodeposition. A CoZrNb underlayer was sputter-deposited on a glass disk substrate as a soft magnetic underlayer (SUL). Nano-patterns were formed on the substrate by UV-nanoimprint lithography (UV-NIL) and CoPt was electrodeposited into the nano-patterns. For obtaining uniform CoPt nanodot arrays with high perpendicular coercivities, we applied thin Cu intermediate layer on CoZrNb SUL and minimized its thickness. As a result, we obtained CoPt nanodot arrays with 150-nm diameter, 300-nm pitches, and 20-nm heights, which have uniform structures, on the substrates with the construction of Cu (1–2 nm)/CoZrNb (100 nm)/Cr (5 nm)/glass disk. The perpendicular coercivity of the CoPt nanodot arrays was as high as 5.4 kOe. From these results, we showed that the Cu intermediate layer with even 1–2 nm thick considerably improved the deposition condition on the substrates with CoZrNb SUL to successfully fabricate CoPt nanodot arrays with the diameter and pitches of 80 nm and 160 nm with sufficient uniformity.

Electrochemical Fabrication of CoPt Nanodot Arrays on Glass Disks by UV Nanoimprint Lithography

A fabrication process for CoPt nanodot arrays using an electrochemical approach was proposed. The nano-patterned substrates were formed using electron beam lithography (EBL) and UV nanoimprint lithography (UV-NIL). CoPt was electrodeposited into nano-patterned Si substrates. CoPt nandot arrays with 35 nm diameter and 50 nm pitch using EBL and 50 nm diameter and 100 nm pitch using UV-NIL were successfully fabricated. In addition, we attempted to apply 1 inch glass disk substrates with CoZrNb underlayer as soft magnetic underlayer (SUL). We focused on the surface condition of the underlayers to deposit CoPt with uniformity and high magnetic properties. As a result, CoPt nanodot arrays were successfully fabricated on a 1 inch glass disk substrate with SUL using thin Cu intermediate layers. From these results, it has been found that the combination of the UV-NIL and electrochemical processes is a candidate for the fabrication of ultra high-density magnetic recording media.

Ｆｅ／Ｐｔ極薄２層構造膜からの垂直磁気記録媒体用ＦｅＰｔ規則合金（００１）配向膜の作製

Pt(3nm)/Fe(3nm) bilayered films deposited directly on glass disk substrates at room temperature exhibited preferential (100) orientation in Pt as well as Fe layers because of a hetero epitaxial growth from the bottom Fe(100) to the top Pt(100) textures. Highly ordered fct-FePt(001) alloy texture was appeared in the bi-layered film after annealed at 600°C in hydrogen atmosphere. Increase of substrate temperature up to 600°C during the deposition of 3nm-thick Pt layer on the Fe layer brought about a direct fabrication of fct-FePt(001) ordered alloy thin film.

Laser induced nanobump array on magnetic glass disk for low flying height application

Laser processing has found an important application in the hard disk drive (HDD) industry to fabricate bumps for screen testing of the manufactured magnetic disk media prior to HDD assembly. The flying height of the head slider needs to be calibrated by a specifically designed bump array. With areal density of HDD already exceeds 100Gbits/in2, the head slider flies at 6 nm flying height and will become even lower. Sub-10nm bump height, as low as 3.5nm, is required to match future slider flying height. In this study, bump arrays with sub- 10nm bump height, good height uniformity and precise distribution was fabricated on glass disk substrate using an integrative control system consisting of a pulsed CO2 laser and a high precision stage. The bump disk requirements were demonstrated successfully and compared with industrial specifications.

Improvement of in-plane anisotropy field in FeCoB/NiFe/Si thin films by Kr sputtering

Deterioration of magnetic anisotropy field in the FeCoB/NiFe/Si trilayers deposited on glass substrates was investigated. It was found that the choice of Kr as sputtering gas instead of Ar was quite effective to improve the soft magnetic characteristics of FeCoB/NiFe/Si thin films deposited on glass substrates. Kr sputtering is effective to reduce compressive residual stress in the film. The rotatable magnetic anisotropy observed in the FeCoB/NiFe/Si films deposited by Ar sputtering disappeared in the film deposited by Kr sputtering, even though they are prepared on glass disk substrates.

Fabrication of highly [001] oriented L1/sub 0/ FePt thin film using NiTa seed layer

A highly [001] oriented L1/sub 0/ FePt thin film has been successfully fabricated on glass disk substrates by using Ni-Ta alloy seed layer with O/sub 2/ exposure process. The [001] orientation of Fe-Pt was improved by exposing Ni-Ta surface to O/sub 2/ ambient in the deposition process of Ni-Ta/Cr/Pt/Fe-Pt film. An excess O/sub 2/ exposure degrades the coercivity because of the suppression of the ordering of FePt. Under the optimum O/sub 2/ exposure condition, perpendicular coercivity of as large as 6.9 kOe was achieved with good squareness and little remanence in the in-plane magnetization curve for the film stack of Ni-Ta (5 nm)/Cr (5 nm)/Pt (10 nm)/Fe-Pt (10 nm)/C (7 nm) structure. The total thickness of the underlayers is as thin as 20 nm.

Highly (0 0 1) oriented FePt ordered alloy thin films fabricated from Pt(1 0 0)/Fe(1 0 0) structure on glass disks without seed layers

Sputter-deposited Fe thin films exhibited (100) preferential orientation when they were deposited at a lower deposition rate below 0.6Å/s. The (100)-oriented Fe layer attained at a lower deposition rate condition induced (100) orientation of Pt layers deposited on it. Fe(100)/Pt(100) thin bilayered films deposited directly on glass disk substrates, without any seed layers, exhibited FePt highly ordered FCT alloy phase with (001) preferential orientation after annealing at 600°C in hydrogen atmosphere. Fe[3nm]/Pt[3nm] thin bilayered films exhibited squareness ratio and coercivity in perpendicular direction of 1.0 and 4.8kOe, respectively, after the annealing process.

Crystal Orientation of Mn–Ir Antiferromagnetic Films for Exchange-Biased Soft-Magnetic Underlayer in Perpendicular Recording Media

Three kinds of crystal orientations for Mn-Ir antiferromagnetic films were successfully obtained on the glass disk substrates. Mn-Ir(111) film was prepared on an underlayer of Nb-Permalloy/Ta/glass-disk. Mn-Ir(001) film was obtained on MgO/glass-disk. On the other hand, Nb-Permalloy was found to exhibit [110] orientation at sputtering temperatures between 200/spl deg/C and 400/spl deg/C on the MgO layer, thus Mn-Ir(110) was first realized on the underlayer of Nb-Permalloy/MgO/glass-disk. The exchange-bias fields, H/sub ex/, and possibility of increasing the H/sub ex/ were investigated.

High density magnetic recording on protein-derived nanoparticles

Self-organized Co/Pt nanoparticulate arrays offer a novel approach to fabricating magnetic recording media with the potential for supporting Terabit/in.2 recording densities. Protein-derived Co/Pt nanoparticles are prepared within apoferritin from aqueous reactants, with synthesis conditions controlling grain size, structure, and composition. Smooth films on glass disk substrates are produced by either spin coating or dip coating from aqueous dispersions of the precursor material. Films are typically annealed at 590 °C for 60 min with a 19 kPa (190 mBar) partial pressure of H2 to form the L10 phase. By varying the annealing conditions we are able to produce coercivities in the range of 500–8000 Oe. Electrical testing of Co/Pt nanoparticulate media using a contact test recorder shows that these nanoparticle films are capable of sustaining recording densities of more than 12.6 Gbits/in.2 (143.6 kfci, kilo flux changes per inch). In this article we will present results from finished films with regard to film structure, magnetic properties, and recording capabilities.

弾性定盤を用いたガラス磁気ディスク基板のポリシング特性

Glass disk substrates of 2.5 inch diameter were polished using two types of epoxy resin plate, which were of intermediate hardness between that of the metal lapping plate and polisher. The polishing characteristics were measured for various experimental conditions, such as the grooving condition, polishing pressure, and loose and/or fixed abrasives. From the experimental results, polishing using a combination of epoxy resin plates and CeO2 abrasives of average diameter 0.7 μm shows a higher removal rate (MRR > 1.0 μm /min) with good surface roughness (Ra < 1.0 nm), flatness (within 0.3 μm in a diameter), and edge accuracy around the substrate. The higher removal rate was achieved due to an increase in the real micro-contact area between the resin plate and substrate. This can be explained well by the comparatively large elastic deformation of the resin plates, which was simulated with the aid of finite element analysis.

Measurements and modeling of soft underlayer materials for perpendicular magnetic recording

Measurements and modeling of soft magnetic underlayer (SUL) materials for perpendicular magnetic recording application are carried out. The process dependent magnetic properties of FeCoB, CoZrNb, and FeAlN SUL materials on glass and aluminum disk substrates are studied and correlated with spin-stand noise performance. The SUL-induced dc noise amplitude approaches the electronic noise floor for certain material combinations, e.g., FeCoB or CoZrNb on glass, when care is taken to relieve stress-induced perpendicular anisotropy by thermal annealing. Landau-Lifshitz-Gilbert micromagnetics, finite-element method calculations, and a micromagnetic recording model show that write field amplitude, write field gradient, and readback waveform are only slightly impacted by SUL moment in the 1-2 T range. Much more important are the head-to-SUL distance and the write head saturation moment. These results suggest that extremely high SUL moment may not be necessary, which can be leveraged to meet other key practical requirements such as corrosion resistance and manufacturability.

Magnetic Recording at High Densities on Protein-Derived CoPt Nanoparticles

ABSTRACTThis paper reports on the progress in developing self organized nanoparticulate arrays for magnetic recording at densities beyond 30 Gbit/cm2 (200 Gbit/in2), and in particular describes the beneficial use of biological templates in developing such arrays. Chemically synthesized, high magnetocrystalline anisotropy magnetic nanoparticles have demonstrated extremely narrow size distributions that are critical in reducing media noise. Due to their monodispersity, they also exhibit emergent self-patterning that could potentially support bit-per-particle densities up to 2–8 Tbit/cm2 (10–50 Tbit/in2).High anisotropy L10 CoPt precursor grains are prepared within apoferritin from aqueous reactants, with synthesis conditions controlling grain size, structure and composition. Smooth films on glass disk substrates are produced by either spin- or dip-coating from aqueous dispersions of the precursor material. Films are typically annealed at 590 °C for 60 minutes with a 19 kPa (190 mBar) partial pressure of H2 to form the L10 phase.We report on recently produced films that have demonstrated moderate-density recording using a contact drag tester with commercial, 0.35 μm-wide magnetoresistive (MR) heads. The highest areal density currently achieved for these nanoparticulate films is 0.93 Gbit/cm2 (6.0 Gbit/in2).

Flying height measurement considering the effects of the slider-disk interaction

As technology moves to a mechanical head-disk spacing of 4-8 nm for the recording density beyond 100 Gb/in/sup 2/, new testing methodology becomes necessary to achieve both high sensitivity in flying height measurement and accurate characterization of slider-lube-disk interaction. This paper reports a polarization intensity interferometer which retains high sensitivity in fly-height measurement even when the slider-disk spacing is down to nanometer level. The setup can also study the effect of slider-lube-disk interaction on the flying performance of the slider. This is achieved by covering the commercial glass disk substrate with a layer of carbon overcoat and a layer of lubricant which are same as those used in the actual disk media. Both simulation and experimental investigations were conducted and the results agree well with each other. Results also indicate that it is important to take the slider-disk interaction into account in the flying height measurement of the nanometer spaced head-disk interface.

Proposal of Ultrahigh Density Optical Disk System Using a Vertical Cavity Surface Emitting Laser Array

An ultrahigh density optical disk system of Tera bit/inch2 is described. This system utilizes a vertical cavity surface emitting laser (VCSEL) diode array as a parallel optical beam source which can make the disk system more useful at a high data transfer rate and bit density using evanescent waves from each laser cavity. In order to avoid the diffraction limited restriction to the optical beam the near-field optics is adopted to the parallel beam optical head. 1 bit size on the surface of the disk is 10–20 nm in diameter. A polished glass disk substrate is deposited by either phase change medium or photon mode optical medium. The medium thickness of the disk is approximately 10–20 nm. The optical gap size between the surface of the medium and laser output windows of a VCSEL array head is controlled within 20 nm using contact head technology.