Thin-film Disk Research Articles

Three-Dimensional Contact Analysis of Elastic-Plastic Layered Media With Fractal Surface Topographies

Three-dimensional rough surfaces were generated using a modified two-variable Weierstrass-Mandelbrot function with fractal parameters determined from real surface images. The number and size of truncated asperities were assumed to follow power-law relations. A finite element model of a rigid sphere in normal contact with a semi-infinite elastic-plastic homogeneous medium was used to obtain a constitutive relation between the mean contact pressure, real contact area, and corresponding representative strain. The contact model was extended to layered media by modifying the constitutive equation of the homogeneous medium to include the effects of the mechanical properties of the layer and substrate materials and the layer thickness. Finite element simulations of an elastic-plastic layered medium indented by a rigid sphere validated the correctness of the modified contact model. Numerical results for the contact load and real contact area are presented for real surface topographies resembling those of magnetic recording heads and smooth rigid disks. The model yields insight into the evolution of elastic, elastic-plastic, and fully plastic deformation at the contact interface in terms of the maximum local surface interference. The dependence of the contact load and real contact area on the fractal parameters and the carbon overcoat thickness is interpreted in light of simulation results obtained for a tri-pad picoslider in contact with a smooth thin-film hard disk.

Magnetic response of the superconducting thin film

Based on the London theory, the supercurrent density and penetrating magnetic field in response to an applied perpendicular magnetic are calculated for a superconducting thin film (strip or disk). Using the method of the Hankel transform, the formulations for the supercurrent density and penetrating magnetic field are given in two limits: a⪢ Λ and a⪡ Λ ( a is the width of the superconducting thin film and Λ is the effective screening length). From these formulations it is shown that the supercurrent density and penetrating magnetic field decrease by a power law with the distance from the edge of a superconducting thin film, unlike the exponential decrease in bulk superconductors.

Evolution of the corrosion process on thin-film media

Thin-film hard disks were exposed to elevated temperature/humidity, and dilute acidic vapor environment. These tests are designed to simulate possible galvanic corrosion, which, for the thin-film media, is characterized by the formation of Co and Ni containing corrosion nodules. The evolution of the corrosion process was elucidated by inducing different degrees of corrosion on the media, and these distinct corrosion stages were characterized morphologically by Scanning electron microscopy and chemically by Auger electron spectroscopy compositional analysis. In addition, an x-ray photoelectron spectroscopy chemical state study on the reactivity of Co, Cr, and Ni to ambient and chlorinated environments was conducted. A probable galvanic corrosion mechanism is proposed to understand the chemistry observed during the evolution of the corrosion process. In particular, the effects of ionic contaminants as corrosion accelerators and the role of the Cr underlayer as a corrosion-preventing barrier layer are discussed.

Lubrication studies of head-disk interfaces in a controlled environment: Part 1: Effects of disk texture, lubricant thermal treatment and lubricant additive on the durability of the head-disk interface

Decomposition and tribological performance of Z-Dol and X-1P lubricants on the magnetic recording thin-film disks are studied during sliding in a high-vacuum environment. Gaseous products generated from the head-disk interfaces and frictional force are detected and monitored as functions of the sliding distance by using a quadrupole mass spectrometer and friction measurements. The thin-film disks with mechanical and laser texture were used and different thermal treatments were applied to the lubricant films. The effects of the disk texture, lubricant thermal treatment and lubricant additive on the degradation and durability of head-disk interface, are studied in detail. Experimental results show that, firstly, fluorocarbon fragments are generated from lubricants during a period of sliding with a low and stable coefficient of friction, followed by a sharp rise in the frictional force and generation of gaseous products of diamond-like carbon overcoat material. The disk texture has effects on the decomposition of the lubricant and durability of the head-disk interface; the laser-textured disk surface caused Z-Dol lubricant to decompose at lower sliding distances and with more gaseous species compared with the mechanically textured disk. Thermal treatment of the lubricant films and the application of X-1P as an additive to the Z-Dol lubricant improved the durability of the head-disk interfaces.

Investigation of advanced position error signal patterns in patterned media

A potential approach to extending current thin film media to 100 Gbits/in2 recording density is physical patterning of the media, perhaps via an etching technique. An advantage of patterning is the capability of creating advanced position error signal (PES) patterns that are difficult or impossible to generate with writing by a recording head. This study uses spin stand tester to investigate various PES patterns generated by a focused ion beam etching technique on conventional thin film disks. For all practical purposes, the patterned PES eliminates transition noise, track edge noise, and erase band, therefore, demonstrates a much better PES signal than conventionally written servo patterns.

Interface reactions between quaternary cobalt alloys and carbon coating in thin film disk media

A study of interface reactions between the magnetic layer and the protective carbon coating, and the influence of these interactions on magnetic properties of rigid disk media for magnetic data storage is presented. Quaternary CoPtCrB and CoPtCrTa alloy films and protective hydrogenated or nitrogenated carbon coatings were deposited by dc magnetron sputtering onto metal hard disks (AlMg substrate/electroplated NiP layer/Cr underlayer). Core level x-ray photoelectron spectroscopy of nitrogenated carbon films on B-containing alloys showed the formation of boron nitride and small amounts of chromium nitride at the interface, and also indicated the likely presence of chromium carbide. The amount of boron nitride at the interface varied depending on substrate bias voltage and temperature during deposition of the carbon coating. From a quantitative analysis of the x-ray photoelectron spectra it was inferred that boron nitride formation was controlled by the diffusion of boron from deeper regions of the magnetic layer to the interface. Surprisingly, compared to disks using the same magnetic alloy but with a hydrogenated or pure carbon coating, no effects of these interface reactions on the magnetic properties of the disks could be detected. In contrast, for a Ta-containing alloy the same comparison revealed a drop in the coercivity of up to 200 Oe in disks with nitrogenated carbon overcoats. Strong evidence for the formation of tantalum nitride as well as small amounts of chromium nitride was found in the photoelectron spectra. Thus, while the formation of boron nitride at the interface of CoPtCrB media and protective carbon coating does not affect the magnetic properties of the disks in the range of boron and nitrogen concentrations investigated here, small changes in the chemical environment of Ta and/or Cr can lead to significant changes in the magnetic properties of the CoPtCrTa media.

Head–disk interface contact mechanics for ultrahigh density magnetic recording

Extremely smooth surfaces, high relative speeds, and remarkably low flying heights are required in ultrahigh density magnetic recording. As a consequence, higher contact stresses and shear strains can be encountered at the head–disk interface (HDI) due to the enhancement of asperity interactions. Detailed knowledge of the damage due to inelastic deformation at asperity microcontacts is therefore of paramount importance to the durability of high-performance disk drives. A comprehensive elastic–plastic contact analysis for the HDI that is based on a realistic surface topography description and a finite element model is presented in this publication. Magnetic head and smooth and textured rigid disk surfaces were scanned with an atomic force microscope (AFM) at various scales in order to determine the corresponding fractal parameters. Surface topographies equivalent to those of a slider in contact with smooth and textured disks were determined from a fractal analysis of the obtained AFM surface images. The equivalent surface corresponding to smooth disk surfaces was incorporated into a finite element model of the thin-film disk medium to provide a more realistic approximation of the actual surface topographies. Simulation results for the contact pressure at asperity microcontacts and subsurface von Mises equivalent stress, maximum tensile stress, and equivalent plastic strain are interpreted in terms of the carbon overcoat thickness and maximum surface interference distance. The evolution of plasticity and likelihood of cracking in the carbon and magnetic layers of smooth rigid disks are discussed. It is shown that AFM measurements, fractal surface characterization, and finite element modeling can be combined in contact analyses of layered media possessing realistic surface topographies and mechanical properties typical of engineering components.

Demonstration of 1 Gbit/sec magnetic recording using an integrated inductive write/GMR read head

1 Gbit/sec magnetic recording was demonstrated with integrated inductive write/GMR read heads on a thin film disk with a coercivity of 3200 Oe and an Mrt of 0.34 memu/cm/sup 2/ with a spinstand tester. The write heads were made with high moment materials on both P1 and P2 and a densely packed coil using conventional manufacturing processes, and the read heads were made of dual synthetic spin valve sensor used for the 36 Gbit/in/sup 2/ areal density demonstration. The interconnect between the head and pre-amplifier is a pair of twisted wires of about 2 inch length. The demonstration was done at the outer diameter of the disk rotating at 15000 RPM. With a modest 35 mA (0-P) write current, we achieved an overwrite of about 30 dB and an on track error rate of better than 10/sup -7/. BER test on a disk with a coercivity of 4000 Oe also showed very good results.

Study of Contact-Action of a Positive-Pressure Step-Slider at Low Flying-Height.

We studied the contact characteristics of a positive-pressure step-slider flying over a thin-film disk under two conditions : rotating at a low velocity at normal pressure (LV condition) and rotating at normal velocity at low pressure (LP condition). Drag test revealed head wear on the leading pads of the step-slider tested under the LP condition, while there was no change on the pads of the slider tested under the LV condition. To find the cause of this head wear, we measured acoustic emission (AE) signal, friction force, and head flying characteristics under both conditions. It was thus, (1) that the friction force between the slider and the disk is larger under the LP condition than under the LV condition, and, (2) that the contact angle between the slider and the disk is larger under the LV condition than that under the LP condition. And we think that the low contact angle under the LP condition makes the leading pads contact the disk and, thus, cause the head wear. It is therefore concluded that the slider must fly in a steep attitude to achieve a low flying height.

Demonstration and characterization of 36 Gb/in/sup 2/ recording systems

We have successfully demonstrated recording at areal densities as high as 36 Gb/in/sup 2/ at data rates as high as 173 Mbits/s (21.6 MB/s) and at a Bit-Aspect-Ratio (BAR) of 7.3, using merged inductive-write/spin-valve-read heads on low noise thin film disks. Recording at a data rate of 590 Mbits/s (73.8 MB/s) has also been achieved at the corresponding linear density of 231 KBPI. Comparisons with previous areal density demonstrations have also been summarized.

磁性材料 磁気ディスク用Ｂａ及びＳｒフェライト薄膜の作製

Ba and Sr ferrite thin films with M-type magnetoplumbite hexagonal structure have the great advantage available to incorporate the magnetic disk recording layer without surface protective coating due to their highly chemical stability and wear durability. This paper reports the design criteria of thin film disk media, methods of film formation of Ba and Sr ferrite, heating techniques requiredfor crystallization, the investigation of grain size control.

Rapidly annealed hexagonal ferrite thin films for recording medium

Bi added Ba-ferrite thin films were prepared at room temperature with different Bi composition, and successively annealed in a vacuum to crystallize. The addition of Bi is effective in reducing the grain size. The M/sub s/, H/sub c/ and grain size for Bi-BaM films were about 150 emu/cm/sup 3/, 4 kOe and 40 nm, respectively, after annealing at 750 C for 30 seconds. A recording density D/sub 50/ of 130 kfrpi was obtained with Bi-BaM thin film disk with the film thickness of 100 nm.

Recording, noise, and servo characteristics of patterned thin film media

In this paper, we present a combined experimental and micromagnetic simulation study of the recording, noise and position error signal characteristics in patterned thin film media. The medium is patterned with a focused ion beam etching technique on typical present thin film disks. It is found the transition noise is completely absent in the patterned thin film media. Comparing with continuous thin film media, the medium noise is reduced to the level of noise at saturation remnant state and is no longer density-dependent. With the elimination of transition noise, the signal-to-medium-noise ratio will be sufficient at very narrow track widths without further reduction of grain size. A slight increase of intergranular exchange coupling will have little impact on medium noise, but enhance thermal magnetic stability of the medium. Down track orientation of the crystalline easy axes will further improve the recording performances. Position error signal patterns in patterned media can be more versatile and significantly more effective and efficient.

1111 正圧型ステップスライダの低浮上時における接触挙動の解析(その 2)

We studied contact characteristics of a positive pressure step-slider flying over a thin-film disk rotating at a low velocity at normal pressure (LV condition) and that rotating at normal velocity at a low pressure (LP condition). Drag tests showed that there was head wear on the leading pads of the step-slider tested in LP condition, while there was no change on the pads tested in LV condition. To find the reason of above difference, we examined acoustic emission (AE) signal, friction force, and head flying characteristics in those conditions. We found that friction force is larger in LP condition than in LV condition and that the contact angle between head and disk is larger in LV condition than in LP condition. We think that the low contact angle in LP condition made the leading pads contact with disk and caused head wear.

Microwave intermodulation of a superconducting disk resonator

We calculate the third order intermodulation products for the TM010 mode of a thin film disk resonator and discuss the particular case of a 1 GHz resonator in order to obtain a quantitative idea of the performance that can be obtained. The linear and nonlinear microwave responses of a TM010 disk resonator are then compared to that of an equivalent half wavelength microstrip resonator. This analysis allows one to independently quantify the contributions to the nonlinear device performance from the material properties, device size and field configuration.

Removal of Contamination Deposits from Defects on Thin Film Magnetic Disks by Oxidative Cleaning Inside the SEM

Scanning Electron Microscopy (SEM) of thin film magnetic disk defects is challenging due to lubricant on the disk surface. The lubricant aids disk durability but interacts with the electron beam to form a contaminantation layer over the area of interest. A new cleaning technology allows the removal of the surface contamination while the specimen is in the SEM.Plasma dry ashing of SEM samples to remove surface hydrocarbons is a well-known technique for specimen preparation. A number of commercial external plasma cleaning units are on the market for sample preparation outside the microscope. Zaluzec developed a technique for plasma cleaning the specimen and stage together prior to insertion into the analytical region of the electron microscope. But similar plasma cleaning within the SEM chamber must be avoided due to ion bombardment damage to the SEM and the deleterious effect of argon plasmas on ion pumps. XEI Scientific has developed a new device that creates neutral oxygen radicals from air. This technique oxidizes surface hydrocarbons into volatile gases that are easily carried away to the roughing and diffusion pumps.

Tribology of proximity magnetoresistive head–disk interface for 5 Gb/in.2 recording

Low fly-height magnetoresistive (MR) sliders and low glide-height laser-texture thin film disks were introduced to meet the tribological challenges of proximity MR recording, with which an areal density of 5 Gb/in.2 has been achieved when using the sliders with dual-stripe MR heads and the disks with low-noise media. The 30% pico sliders employed two air-bearing designs with a fly height around 12.5 nm. The thin film disks used superfinish substrates with a glide-avalanche-height falling well below 10.0 nm. In the contact start/stop (CSS) zones, small crater-shape laser texture bumps were generated to meet both low stiction and low glide-height requirements. An 80 Å thin amorphous nitrogenated carbon was added over the magnetic layers as a protective overcoat. A layer of perfluoropolyether with an additive of phosphazene compounds was applied on the disk surface to improve the reliability of head–disk interfaces. The near contact head–disk interface survived for 20 k-cycle hot/wet and hot/dry CSS tests without wear and high stiction. Twenty-four-hour hot/wet park-stiction values after 20 k CSS cycles were within the acceptable range. Remarkably, thermal-asperity tests showed no hits by using the proximity heads on the ultralow glide-height thin film disks.

Chemical depth profiling on submicron regions: a combined focused ion beam/scanning electron microscope approach

The combination of focused ion beam (FIB) milling and field emission scanning electron microscopy (SEM) with x-ray energy-dispersive spectroscopy (EDS) makes possible high-spatial-resolution (< 1 μm) element-specific depth profiling. The depth profile resolution is controlled via the FIB to < 5 nm sputter depths. Depth profiles through thin-film hard disk media on NiP substrates and through similar film structures deposited on a carbon-coated substrate are presented. The high spatial resolution of the FIB/SEM depth profile is not necessary for blanket films, and depth profiles through them are used to benchmark the spatial and depth resolution of the technique using a field emission SEM. Energy depth profiles that use increasing primary electron beam voltages in the spectrometer are shown on the same samples in comparison to FIB depth profiles. A brief overview of this technique in relation to XPS, AES and SIMS illustrates applications where FIB depth profiling analysis offers some advantages.

In situ quantitative analysis of nano-scale lubricant migration at the slider–disk interface

A thin layer of lubricant is a critical element of the head/disk interface needed to improve its tribological durability and to prevent media corrosion. Local thinning of lubricant with its subsequent breakdown often leads to the immediate failure of the interface. This paper is devoted to the in situ quantitative analysis of nano-scale lubricant migration on the surface of a thin-film disk using the Optical Surface Analyzer (OSA). The calibration procedure, which enables quantitative measurements, is discussed and the technique's capabilities are demonstrated using specially prepared samples. Two cases of slider/disk interaction are analyzed: low-speed, when the slider is dragged over the disk surface, and high-speed, when the slider is flown over the same track for several days. Lubricant migration phenomena, such as depletion and pooling, are investigated quantitatively to analyze the origination of carbon wear and the mechanisms of interfacial failure. A model of high-speed slider/disk interaction involving the dynamic formation of a liquid bridge at the interface is proposed.

Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous CNx overcoats for next generation hard disks

Further insight into processing-structure-property relationships have been carried out for existing and candidate carbon-based protective overcoats used in the magnetic recording industry. Specifically, 5 nm thick amorphous diamond-like carbon (a:C) and nitrogenated diamond-like carbon (a:CNx) overcoats were deposited by low deposition rate sputtering onto a thin film disk consisting of either CoCrPt/CrV/NiP/AlMg or CoCrPt/CrV/glass. The wear durability and frictional behavior of these hard disks were ascertained using a recently developed depth sensing reciprocating nanoscratch test. It was determined that the CN0.14/CoCrPt/CrV/glass disk exhibited the most wear resistance, least amount of plastic deformation, and lowest kinetic friction coefficient after the last wear event. Core level x-ray photoelectron spectroscopy (XPS) results of sputter cleaned overcoats indicated that nitrogen up to 14 at. % incorporated into the amorphous network resulted in these improvements near the overcoat/magnetic layer interface, since there was an increase in the number of N-sp3 C bonded sites in a predominantly N-sp2 C bonded matrix. However, nonsputter cleaned overcoats exhibited a more graphitic pyridine-like (nondoping configuration) structure near the surface as evidenced by the increase in C=N versus C–N bonds and the valence band XPS determined appearance of the 2p-π band near the Fermi level (EF). Therefore, XPS sputter cleaning revealed a gradient in the chemical nature of the overcoats through the thickness. In addition, micro-Raman spectroscopy established that a further increase of nitrogen (⩾18 at. %) weakened the overcoat structure due to the formation of terminated sites in the amorphous carbon network, since nitrogen failed to connect the sp2 domains within the network. This, in conjunction with an increase in the intensity of the 2p-π band from the valence band XPS spectra and the increase in the G-band position and ID/IG ratio from the Raman spectra, confirmed the increase in the size and number of sp2 bonds in the CN0.18 overcoat.