High speed sub-micron bit detection using tapered aperture mounted optical slider flying above a patterned metal medium

Rapid advances in the development of the digital network society have necessitated both large capacity and higher data transfer rate for every type of digital storage equipment. Proximity optical recording based on the near-field interaction principle promises to provide breakthroughs in overcoming rigid optical diffraction limits and wave length shortening limits. We have previously presented a compact optical head assembly consisting of a combination of a pyramidal hole processed silicon slider and light-wave guide combined suspension. Attaining higher recording density requires both a much smaller sized aperture and a highly efficient laser power delivery mechanism. To satisfy these requirements, we have introduced a planar lens and tapered aperture processed optical slider, delivering laser power through a single mode optical fiber, and we have demonstrated sub-micron size (150–200 nm-long) bit signals at more than a 10 MHz frequency band.The authors would like to thank Mr. Tamotsu Kusumi and Tadashi Sasagawa, Nikon Corp. for their processing of fine 350 nm line and space patterns on thin chromium films using short wavelength light lithography. The authors would like to thank Dr. Hisataka Takenaka and Dr. Hisashi Ito, NTT Advance Tecnology Corp., for forming a high quality carbon protective overcoat on the patterned media. The authors also would like to thank Dr. Takanori Doi, Toda Corp., for his helpful suggestions and careful treatment in forming the lubricant layer on the patterned metal media. The authors would also like to thank Mr. Masanori Sahara and Mr. Takashi Suzuki for their useful advice in applying the APD in our readout system.     

Readout characteristics of a non-circular aperture mounted on an optical head slider flying above a medium having sub-100-nm-long patterns

The near-field principle combined with thin-film gas-lubricated slider bearing technology is thought to be one of the most promising breakthroughs to overcome the difficult optical diffraction limit (or wavelength shortening limit), which governs traditional optical recording performance. In light of this, we have demonstrated high linear density (150 nm pattern length) and high speed 10 MHz readout signals using the combination of a tapered circular aperture and a planar lens mounted on a quartz slider, flying above a metal patterned medium. In order to further improve both the spatial resolution and signal-to-noise ratio of this device, it is essential to minimize the spacing and laser power throughput of an aperture. Also investigated was the effectiveness of a non-circular aperture, which has approximately triangular configuration in combination with polarized light in simultaneously improving spatial resolution and increasing signal output. In this paper, we confirmed the predicted effectiveness on more practical condition of both high speed and compactness of head construction using a sub-micrometer size non-circular aperture, which was mounted on a 1.5-mm-long miniaturized optical head slider, flying above a ROM medium having sub-100-nm-long chromium patterns. The influence of the electric-field direction of the incident light and aperture to medium spacing on the readout signal are carefully evaluated by flying the aperture at spacing down to less than 50 nm.     

100-nm-Wide track pattern readout using a protruded triangular aperture mounted optical head slider

In this study, we evaluated the read-out signal quality from narrow track patterns, utilizing linearly arranged slender track patterns, while changing the track width from 10 to 0.1 ??m and the pattern density from 200?nm line-and-space (L/S) to 120?nm L/S. To acquire narrow track readout signals, we adjusted the aperture??s in-plane position to cross a linear track at shallow angles of less than 1°, and we could successfully transform directly acquired signals into those of an aperture crossing tracks at a right angles. The results of an experiment utilizing a 10-??m-wide track (which is thought to represent an infinitely wide track) clarified that the stationary field was spread to an approximately 1.2?C1.6?times larger region than the typical aperture size of 330?nm. The results also clarified that the ??field spread?? depended on the pattern density, that is, the case in which polarization direction ?? equals 0 or 45°, and that the field spread increased monotonically as the line or space width became smaller. When the polarization direction equals 90°, the field spread had its local maximum when the line or space width was approximately 150?nm. An approximate prediction of the read-out signal amplitude was based on the rule that the signal amplitude was proportional to the net field spread that passed across the track pattern, and this prediction corresponded well to the experimental results, except when the interaction between the stationary field and the track side walls was not taken into account.     

Sub-100-nm ROM pattern readout using a triangular protruded aperture mounted optical head slider

The continual advancement of the digital network society demands higher density and higher data transfer rates for all sorts of data storage. Optical memory based on the “near-field” principle is considered one of the most promising ones because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have previously demonstrated the superior readout performance of an optical head slider which is mounted on a non-circular aperture, specifically a triangular aperture having a bottom side size of 330 nm irradiated by polarized light, with this scheme indicating a clear signal response corresponding to a 70-nm-long single slit pattern. In order to fully realize the superior potential of the triangular aperture’s high spatial resolution and high signal output, it is essential to minimize aperture-to-medium spacing. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 20 nm from an air-bearing surface level based on nano-step lithography technology. Utilizing a triangular aperture of 140 nm per side, a readout experiment was carefully performed at an aperture-to-medium spacing down to approximately 30 nm, corresponding to a circumferential velocity of 2.18 m/s. The influence of the incident light’s polarization direction (in relation to the bottom side of the triangular aperture) on the readout signals was evaluated by flying the aperture above a chromium patterned medium having single-space or line-and-space patterns whose line lengths ranged from 300 to 50 nm.     

Contact force detection on a minute aperture mounted optical contact slider using an acoustic emission sensor

Advances in the digital network society require both higher density and higher transfer rates in all sorts of storage systems. Especially in optical recording, the trend toward higher density and larger capacity requires novel surface-recording technologies that can drastically diminish head-to-medium spacing, resulting in an improvement in spatial resolution and, finally, a higher recording density. To this end, we have already proposed a novel contact optical head slider that is able to almost cancel the suspension load by generating hydrodynamic pressure, thus realizing a lower net contact force. Evaluating the dynamic contact force is requisite in realizing its stable sliding operation and higher signal readout performance. In this study, a continuous acoustic emission (AE) signal was utilized to detect the dynamic contact force. AE signal modulation was compared with the applied out-of-plane acceleration on a medium generated by a spindle combined piezo-electric actuator. It was clarified that the detected AE modulation amplitude was approximately proportional to the applied acceleration, and that utilizing AE modulation will be a useful method for evaluating dynamic contact force.     

Mechanical characteristics of a contact optical head slider operating on a metal-layered medium

 Advances in a digital network society require both higher density and higher transfer rates in all sorts of storage systems. Even in optical recording, the trend toward higher density and larger capacity requires novel surface-recording technologies that can drastically diminish head-to-medium spacing, resulting in an improvement in spatial resolution and, finally, a higher recording density. In this paper, we propose a novel contact optical head slider that is able to almost cancel the suspension load by generating hydrodynamic pressure, thus realizing a lower net contact force. A trial-manufactured contact slider being processed four sliding pads on air-bearing surfaces has indicated a gentle variation of both the acoustic emission signal intensity and the friction force as the circumferential velocity changes. Furthermore, a time-domain simulation was performed to investigate the effects of the damping of a medium surface (lubricant) both on slider bouncing and on contact force. Received: 5 July 2001/Accepted: 1 November 2001     

Air-bearing design and flying characteristics of flexible optical head slider combined with visible laser light guide

 We propose a novel optical head slider for near-field recording. An air-bearing pad pattern is formed on the apex of a cantilever-like polymeric waveguide so that, by using the cantilever itself as the slider suspension, a single body structure incorporates the functions of the flying slider, suspension, and waveguide. This structure (a flexible optical head slider) can be fabricated using a method similar to a lithographical technique. This structure can be expected to provide several great advantages in miniaturizing head assemblies, in simplifying the assembly and optical trimming processes, and in producing a lighter head to thus allow a wider tracking bandwidth. In this paper, we first discuss the air-bearing design of the flexible optical head slider, and then propose two possible designs. We also report the results of an experimental evaluation of the static and dynamic floating characteristics of prototypes. Received: 5 July 2001/Accepted: 11 December 2001     

Readout signal evaluation of optical flying head slider with visible light-wave guide flexure

 The need for both higher recording density and faster transfer rates continues to propel the research and development of high-performance storage equipment. The optical first-surface recording method promises to overcome tough optical diffraction limits and/or wavelength-shortening limits. We have already proposed a novel compact optical head suspension assembly combining a flying optical slider with a resin-based flexible light-wave guide flexure, and we have confirmed this assembly's stable flying performance during head-arm out-of-plane disturbances. Following this technical progress, we here describe the successful detection of optical signals of sub-micron-size bits by flying this slider above a metal patterned medium through spacing of several tens of nanometers. Signal amplitude dependencies upon both bit pattern lengths and spacings are evaluated in detail, and it is predicted that sub-micron-long and -wide bit will be able to detect increasing the incident laser power up to its maximum value of several mW in our system. Received: 22 June 2001/Accepted: 1 November 2001     

Numerical analysis of microwaviness-excited vibrations of a flying head slider at touchdown

Microsystem Technologies - The dynamics and stability of a flying head slider at proximity to and touchdown on a magnetic recording disk are attracting considerable research attention, because it...     

Dynamic characteristics of flying head slider with ultra thin spacing (CIP method and linearized method)

The cubic interpolated propagation (CIP) method, which is an effective numerical scheme for differential equations that include advection and nonadvection terms, is employed for the dynamic analyses of ultra thin gas film lubrication using the molecular gas-film lubrication equation. First, pressure generation caused by the running wavy disk under the fixed slider was analyzed by the CIP method and is found to agree well with the analytical solution for the running wavy disk with a small amplitude. 2-DOF slider dynamics with the spacing of several tens of nanometers caused by a running disk with projections were investigated by the CIP method and the linearized solutions, which show that both results agree well with each other and the CIP method is promising scheme for slider dynamics even in the near-contact region.     

Design theory and vibration characteristics of a contact head slider

In this study, the design theory of a previously proposed contact head slider was extended by considering a thermally protruding head slider and the intermolecular adhesive force between the head and disk surfaces. The waviness-excited vibration characteristics of the thermally protruding contact head slider were analyzed using a single-degree-of-freedom slider model, whose contact stiffness was calculated in accordance with the Johnson–Kendall–Roberts adhesive contact theory. It was found that, because of the adhesive force, the resonance frequency f _r of the contact slider changed from zero to a value higher than the original second-pitch-mode resonance frequency with an increase in the head-penetration depth. Because the waviness-excited vibration of the contact slider is amplified at f _r , the first- and second-pitch-mode vibrations of the thermally protruding slider can be excited when f _r approaches those resonance frequencies. Because the friction force varies with the vibration of the contact slider, vibration modes of the slider-suspension system often observed at the beginning of contact can be explained. It is suggested that the region of the head-penetration depth for perfect contact sliding can be widened by increasing the effective contact damping and decreasing the disk waviness.     

Readout characteristics of flexible monolithic optical head slider combined with visible laser light guide

Optical near-field recording is a candidate technology for overcoming the diffraction limit of conventional optical recording. In our previous work, we proposed a novel optical head slider for near-field recording that we call a flexible optical head slider. An air-bearing pad pattern is formed on the apex of a cantilever-like polymeric waveguide so that, by using the cantilever itself as the slider suspension, a single body structure incorporates the functions of the flying slider, suspension, and waveguide. This structure can be expected to provide several important advantages by miniaturizing head assemblies; simplifying the assembly and optical trimming processes; and producing a lighter head, thus allowing a wider tracking bandwidth. In this paper, we report the read-out signal evaluation of the flexible optical head slider. Using a slider with a sub-micron sized aperture, read-out of a test metal-patterned ROM (Read Only Memory) disk was successfully demonstrated down to a 0.2 μm linewidth line and space pattern.     

Examination of flying height of magnetic head slider in simulations and measurements at nanometer-order spacing

This paper describes a comparison with the experimental flying heights and the simulated flying heights, which were calculated by using the linearized Boltzmann equation and the conventional modified Reynolds equations. The experiments were measured under the ambient pressure from atmospheric pressure to 6.7 × 10^?3 MPa. The calculated results of the linearized Boltzmann equation were almost the same as the experimental results from the high spacing range to the low spacing range of 10 nm. At the slider spacing of 10 nm, it was confirmed that the difference between the experimentally measured results and the calculated results of the linearized Boltzmann equation was less than 5%, and the differences in the conventional slip flow approximation equations were over 30%.     

Development of an optical flying head for a next-generation magneto-optical recording system

We have developed an optical flying head (OFH) comprising a thin-film coil and a high numerical aperture lens for magneto-optical (MO) disk drives. Experiments have shown successful writing and reading of MO media. The following describes the design and testing of the OFH.     

Dynamic flying characteristics of an air bearing slider over a disk with grooves and distribution of material properties

Bit-patterned media (BPM) consisting of land parts for read/writing and grooves, which are almost filled with non-magnetic materials to prevent magnetic interference between recording bits, are considered to be promising media for achieving ultrahigh density recording. A flying head slider flying over a BPM disk suffers from variations in both the spacing and van der Waals (vdW) attractive forces, which induce slider vibrations and spacing fluctuations. In the present study, we considered that BPM disks not only have a groove depth distribution, but that they also have a distribution of material properties (e.g., refractive index), which gives rise to a distribution in the vdW force. In the dynamic responses of sliders with small groove depths and a small variation in the refractive index, spacing fluctuations are found to be a superposition of fluctuations due to slider behaviors (1) over a disk with transverse grooves in a uniform material with a uniform refractive index (Case 1) and (2) over a flat disk with a refractive index distribution (Case 2). When the effects of Cases 1 and 2 cancel each other, the spacing fluctuations for the two cases cancel each other, reducing the total spacing fluctuation.     

Static and dynamic flying characteristics of a slider on bit-patterned media (dynamic responses based on frequency domain analysis)

Recording media with grooves, such as discrete track media (DTM) and bit-patterned media (BPM), are considered to be promising media for achieving ultrahigh recording densities. It is thus important to analyze the static and dynamic characteristics of flying head sliders on DTM and BPM using the molecular gas film lubrication equation and the van der Waals (vdW) equation. In this study, we consider BPM with rectangular bits. We express the disk recess as a Fourier series and determine the quasi-static and time-dependent components. We also develop a perturbation method for small groove depths for calculating static slider attitudes and dynamic responses in the frequency domain. The numerical results predict that the grooves will significantly reduce the quasi-static flying height h ₀. They also predict that for a small groove depth h _groove, flying height decrease Δh ₀ almost agree with the value of uniform disk recess obtained by a Fourier series expansion, which also agrees with empirical results. Dynamic slider characteristics obtained by the frequency domain analysis is useful for sliders suffering from excitations of several tens of kHz such as sliders flying at transition between data zone and servo zone, although the dynamic spacing fluctuation by realistic BPM media is negligible.     

Effects of disk surface roughness on static flying characteristics of air bearing slider by using a combined method of Reynolds equation and rough disk surface

Reynolds equation was modified with adding the surface roughness parameters to analyze the effects of disk surface roughness on the static flying characteristic of an air bearing slider. However, the modification demands the complicated mathematical expressions and related knowledge of physics and mathematics. In this paper, a combined method of Reynolds equation without introducing the roughness parameters and rough disk surface is proposed to investigate the effects of disk surface roughness on the static flying characteristics of an air bearing slider, it is different from those models of modified Reynolds equation introducing the disk surface roughness used by many researchers. More importantly, this method avoids the complicated numerical calculation resulted from the mathematical expressions including the Peklenik parameter \(\gamma\) and roughness R_a. By using an Ω air bearing slider, we investigated the effects of disk surface roughness on the static flying characteristics of this slider, the results show that the Peklenik parameter \(\gamma\) and roughness R_a have a significant influence on the pressure distribution, the load carrying capacity and the location of the pressure centre.     

Effect of vibration on eye,head and helmet movements while wearing a helmet‐mounted display

Previous research has demonstrated a loss of helmet‐mounted display (HMD) legibility for users exposed to whole body vibration. A pair of human factors studies was conducted to evaluate the effect of whole body vibration on eye, head, and helmet movements for seated users of a HMD while conducting simple fixation and smooth pursuit tracking tasks. These experiments confirmed that vertical eye motion can be demonstrated, that is consistent with the human visual systems' response to the vestibular–ocular reflex (VOR). Helmet slippage was also shown to occur, which could exacerbate loss of display legibility. The largest amplitudes in eye movements were observed during exposure to sinusoidal vibration in the 4–6 Hz range, which is consistent with the frequencies that past research has associated with whole‐body resonance and the largest decrease in display legibility. Further, the measured eye movements appeared to be correlated with both the angular acceleration of the user's head and the angular slippage of the user's helmet. This research demonstrates that the loss of legibility while wearing HMDs likely results from a combination of VOR‐triggered eye movements and movement of the display. Future compensation algorithms should consider adjusting the display in response to both VOR‐triggered eye and HMD motion.