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A “ubiquitous human health care system” will require a monolithic optical total analysis system (TAS) consisting of waveguides and microfluidic channels based on a transparent resin chip. Together with the rapid development of the fluorescent marking method, fluorescence analysis by TAS of mixed-microparticle specimen attached to different fluorescent substances will be necessary. Towards realization of this, we here propose a novel method for using a part of the fluorescence acquired by irradiating microparticles with AC-modulated laser power as light dedicated to the discrimination of fluorescent substances. Since the light power for discrimination was extremely weak, we extracted effective signal components using a lock-in detection method. Then, by comparison with the signal of the original fluorescence, we could determine whether the fluorescence signal was from the microparticles attached to the fluorescent substance to be discriminated. Using a mixed specimen composed of microparticle-attached fluorescent substances with emission peaks of 520 nm and 600 nm, we found that 10% of the acquired fluorescence could successfully determine the specified fluorescent substance as a discrimination signal. The peak value of the discrimination signal was approximately double the amplitude of the stationary noise in the discrimination signal.

In this paper, we attempt to drastically improve the S/N ratio of detected fluorescence signals from the resin-based optical TAS chip by applying AC-modulated laser power for irradiation on a fluorescent substance attached micro-particles at a frequency of approximately 1 MHz. We also try to precisely optimize both the drive frequency and voltage of the optical scanner (light switch) which utilizes optical fiber’s resonance characteristics, in order to completely suppress variation of apparent transmittance of radially arranged light waveguides for laser power irradiation. Through these countermeasures, we successfully obtained high-quality fluorescence signal waveforms corresponding to angular scanning irradiation on 5-μm diameter resin particles. The high-quality signal waveforms also ensured that “directivities” of fluorescence with high reproducibility were obtained under conditions of a wider range of particle running velocity in a TAS chip.

An optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a “ubiquitous human healthcare system” in the near future. We have already proposed the fundamental structure for a light waveguide capable of irradiating a living cell or particle running along a microfluidic channel, and of detecting fluorescence even from the extremely weak power of a minute particulate body. In order to foster advanced functions for obtaining information concerning the internal structure of living cells or particles conveniently, an angular scanning method that sequentially changes the direction in which the minute cell or particle is irradiated may be crucial. In this paper, we investigate fluorescence detection from resin particles attached to a fluorescent substance by switching irradiation direction of the exciting laser source power using a newly fabricated TAS chip with a unique intersection structure. To construct the experimental system cost effectively, we adopted a special light waveguide structure in which the intersection to a fluidic channel was arranged radially, with laser power inlet/outlet portions arranged in parallel. In addition, we incorporated a forced vibration mechanism on an optical fiber apex to construct a simple light-switching system. Preliminary experiments combining this unique TAS chip and the optical scanning mechanism revealed that the function of the radially arranged light waveguide switching worked adequately, and variation of transmittance of each light waveguide was accurately evaluated. Results were successfully applied to compensation of detected angular scanning signals. Finally, we performed an angular scanning experiment for a fluorescent substance attached to a microparticle under conditions of higher intersection-passing velocity of several 10s mm/s (single-shot scanning) and lower intersection-passing velocity of several mm/s (multiple-shot scanning). Based on the obtained scanning data, we successfully constructed directivities of emitting fluorescence from particles, and clarified that fluorescence emission indicated its peak at the forward and orthogonal directions of the incident light beam.

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a "ubiquitous human healthcare system" in the near future. We have already proposed the fundamental structure for a light waveguide capable of illuminating a living cell or particle running along a microfluidic channel, as well as of detecting fluorescence even from the extremely weak power of such a minute particle. In order to develop novel functions to detect the internal structure of living cells quickly, an angular scanning method that sequentially changes the direction of illumination of the minute cell or particle may be crucial. In this paper, we investigate fluorescence detection from moving particles by switching the laser power delivery path of plural light waveguides as a preliminary experiment toward this novel method. To construct an experimental system able to incorporate a switching light source mechanism cost effectively, we utilized a conventional TAS chip with plural waveguide pairs arranged in parallel, and a forced vibration mechanism on an optical fiber tip by a piezoelectric actuator. With this system, we performed an experiment to detect extremely weak fluorescence using micro particles with a fluorescent substance attached and an optical TAS chip that incorporated a microfluidic channel and three pairs of laser-power-delivering light waveguide cores. We successfully obtained clear, quasi-triangular-shaped pulses in fluorescent signals from resin particles running across the intersection under three different conditions: (1) a particle with approximately the same velocity as that of a forced-vibrated optical fiber tip of approximately 700 mm/s, (2) a particle with velocity 1 digit smaller than that of an optical fiber tip, and (3) a particle with velocity approximately 1/20 that of an optical fiber tip.

A resin-based optical total analysis system (O-TAS) which consists both of microfluidic channels and light waveguides [1] is thought to be one of the most promising components in developing a “ubiquitous human healthcare system” in the near future. Along with this technology trend, we have already developed a transparent epoxy-resin-based optical TAS chip which has a specially prepared light waveguide structure of radially arranged configuration at an intersection portion with a microfluidic channel, in order to detect directivity of fluorescence from fluorescent substance attached micro particles [2],[3]. Schematic diagram of the optical TAS is shown in Figure 1. In the latest research, utilizing an AC modulated laser source and time-series averaging function on detected signal waveforms, we could have successfully obtained directivities of fluorescence from 5-μm-diameter particles with higher signal to noise (S/N) ratio [3].

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the essential functional components needed to realize a "ubiquitous human healthcare system". In accordance with this, we have proposed the fundamental structure for a light waveguide capable of illuminating a cell or particle running along a microfluidic channel and detecting fluorescence even from the extremely weak power of such a minute particle. We successfully trial-manufactured an optical TAS chip with a microfluidic channel containing a 15 × 20-μm cross-section, and a higher aspect ratio (6-μm wide, 10-μm high) core of a light waveguide. To obtain extremely weak forward- and side-direction emitted fluorescence within the chip, we utilized the L- or T-shaped microfluidic channels used in previous studies. As we could predict the fluorescent substances would have very low efficiency, we created a high-power light source using a semiconductor laser (488-nm-wavelength), and a high-performance fluorescence detecting optical system, consisting mainly of a dichroic mirror and interference filters. With this system, we were able to obtain fluorescent responses emitted from substances attached to a particle, adjusting gains in value of the maximum photoelectron multiplier tube modules. Response signal waveforms indicated higher signal-to-noise ratio in forward-direction emitted fluorescence and side-direction emitted. These two detected fluorescences and the side-scattered source light were fully synchronized. Furthermore, a series of experiments revealed that the forward-direction and side-direction emitted fluorescence components had approximately the same order of magnitude. Typical pulse magnitude detected in both directions ranged from 1 pW to several hundreds of pW.

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the most functional components that will be needed to realize a “ubiquitous human healthcare system”. A transparent resin-based TAS chip incorporated with a light waveguide [1] is quite preferable in such a cost-effective and disposal use. In line with the technical demand, we have already proposed a specially fabricated structure for an epoxy resin-based monolithic light waveguide capable of illuminating a cell or particle running along a microfluidic channel [2], as well as of obtaining directivity of fluorescence with a radially arranged waveguide structure (as shown in Figure 1) and a sequential light scanning mechanism based on a forced vibrated optical fiber [3]. Utilizing this TAS system, we have successfully detected preliminary results of fluorescence directivity of a 5-μm-diameter polystyrene particle with scanning angle range of 180 degrees, at illuminating light scanning frequency of approximately 1.7 kHz [4]. However, the transmittance of the trial-manufactured light waveguides was slightly lower owing mainly to its smaller cross section size, and, as a result, signal-to-noise ratio of detected fluorescence signal waveform was not as good as we have expected. To improve the S/N ratio, it is necessary to increase illuminating power of a laser source, and, at the same time, to increase multiplication factor of a photo-electron multiplier sensor to beyond its performance limit. Unfortunately, with the capability of the current equipment, it is difficult to drastically improve the S/N ratio. In this paper, we attempted to apply AC detection method to measure extremely weak fluorescence with a high frequency modulated laser source of its wavelength of 488 nm, and with a high speed lock-in-amplifier having both higher reference frequency up to 3MHz and smaller time constant.

We have previously argued that an optical sensor combined total analysis system (TAS) is one of the indispensable functional components needed to realize a "ubiquitous human healthcare" system. To achieve this goal, we have proposed a fundamental structure for illuminating a minute cell or particle running along a microfluidic channel using a flat waveguide construction. It is desirable that the TAS light source should be arranged as close to the specimen flow as possible in order to acquire the necessary optical properties; hence, artificial defects formed on the surface of a flat light waveguide are considered to be a promising candidate for realizing the arbitrary-shaped light source for a highly functional optical TAS structure. Based on this idea, we fabricated a structure, constructing a flat and square light source consisting of rectangular solids, sub-micrometer in size, with a 1-μm thick and a 12-μm wide light waveguide core. We successfully trial-manufactured an optical TAS chip with a fluidic channel containing a 14 × 10-μm cross section, and an extremely flat light waveguide core. We repeatedly confirmed that the defect array could function as an approximately square light source when a 650-nm wavelength laser power was carefully introduced. Furthermore, we developed a hybrid numerical calculation method base on the finite-difference, time-domain method together with the beam propagation method. Utilizing this hybrid method, we evaluated the optical response when a particle runs across the light source while changing the aperture length of a shading mask to obtain signals with both higher intensity and shorter full width at half maximum. The numerical results were compared with experimental results obtained using an image acquisition system, and demonstrated good qualitative accord.

An optical sensor combined total analysis system (TAS) is thought to be one of the most powerful functional elements needed to realize a “ubiquitous human healthcare” system. In accordance with this concept, we have proposed a fundamental structure of detecting side scattered light from a minute cell or particle running along a microfluidic channel, partially utilizing the channel filled with water or saline solution as a light waveguide. Based on this concept, we have fabricated a trial-manufactured optical TAS chip and carefully evaluated its side scattered light measuring performance in in-plane direction, supplying and detecting visible laser power by using multiple optical fibers and their precise positioning mechanisms. We have successfully obtained experimental results of both transmitted light power change and that of side scattered light, and we confirmed that there was a strong relationship between their signal waveforms. Furthermore, we have developed a hybrid numerical calculation method on the basis of the finite-difference time-domain method, in addition to the beam propagation method. Based on this hybrid method, we tried to compare results between the experimental inverse pulse of transmitted light and a pulse of side scattered light, and those based on numerical calculations. Excellent qualitative accordance was obtained between the inverse pulse of numerical and experimental results. In contrast, the experimental pulse of side scattered light indicated a considerably spread base in comparison to the numerical results.

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a “ubiquitous human healthcare system” in the near future. We have already proposed the fundamental structure for a light waveguide capable of illuminating a living cell or particle running along a microfluidic channel, as well as of detecting fluorescence even from the extremely weak power of such a minute particle. In order to develop novel functions to detect the internal structure of living cells conveniently, an angular scanning method that sequentially changes the direction of illumination of the minute cell or particle may be crucial. In this research paper, we investigated fluorescence detection from moving resin particles by switching direction of laser power illumination by radially arranged outlet portions of several light waveguides, as a step-by-step examination toward this novel scanning method. To cost effectively construct an experimental system able to incorporate a mechanism of switching illumination direction, we utilized a monolithic resin-based TAS chip[1] with plural waveguide pairs whose outlet portions were arranged radially and inlet portions were arranged in parallel, and a forced vibration mechanism on an optical fiber tip by a piezoelectric actuator. With this chip and system, we constructed an experimental system to detect extremely weak fluorescence using micro particles with a fluorescent substance attached and an optical TAS chip that incorporated a microfluidic channel and five pairs of laser-power-delivering light waveguide.

An optical sensor combined total analysis system (TAS) is thought to be one of the most effective functional elements in realizing a ubiquitous human healthcare system. In accordance with this concept, we have proposed a fundamental structure of a light-wave-guide incorporated TAS and have developed a micro fluidic channel fabricated chip, where two light waveguides having approximately 10-μm cores were facing each other across a fluidic channel with a width of 12 μm. By passing 5-μm-diameter polystyrene particles across the portion where a light-wave-guide and the fluidic channel intersect at a right angles, we confirmed that changes to transmitted light and scattered light were detectable even with an extremely low laser source power of 5 μW, and they increased proportionally as the introduced laser power became higher. Increasing the introduced laser power clearly increased the correlation between the transmitted and scattered light change. Here we discuss in detail the two different correlation tendencies that appeared in the correlation maps.

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 μm 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-μm-wide track (which is thought to represent an infinitely wide track) clarified that the stationary field was spread to an approximately 1.2–1.6 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 θ 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.

In near-field optical recording, the combination of a triangular aperture and a polarized illuminating light is thought to be one of the most promising breakthroughs for improving both spatial resolution and signal-to-noise ratio. In light of this, we have already fabricated a triangular-aperture mounted optical head slider and demonstrated its superior performance while clarifying the influence of the polarization direction on the spatial resolution in the circumferential direction. When the polarization direction was perpendicular to the bottom side (which is parallel to the slider trailing edge) of the aperture, the highest spatial resolution and signal contrast were obtained, in spite of the usage of a fairly large aperture, indicating the presence of clear readout signal waveforms corresponding down to 100 nm line-and-space (L/S) patterns. In this study, we tried to experimentally clarify the influence of the polarization direction of the illuminating light on an aperture's field spread in the radial direction. In order to concretely evaluate the field spread, we prepared 1-mm-long linearly arranged (in the circumferential direction) L/S patterns on a metal-layered medium, and a piezo-electric actuator combined positioner. Intersecting the aperture at two portions of the tracks, directly acquired signal waveforms could be successfully transformed into the waveforms that would be obtained if the aperture had crossed the track at right angles. The field spreads in the radial direction were estimated to be approximately 250 nm when the polarization direction was perpendicular to the bottom side. In contrast, when the polarization direction was 45 degrees, the stationary field spread in the radial direction was estimated to be approximately 350 - 370 nm. It could be confirmed experimentally that both the highest spatial resolution in the circumferential direction and the smallest field spread in the radial direction were realized with the combination of the triangular aperture and the illuminating polarized light whose direction was perpendicular to the bottom side. Based on these results, the signal-to-noise ratio will be evaluated and discussed in the future with respect to the above-mentioned optimum aperture structure and conditions.

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.

Optical memory based on the “near-field” principle is considered one of the most promising technological breakthroughs 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 demonstrated the superior readout performance of an optical head slider mounted on a triangular aperture with a typical side size of 140 nm irradiated by polarized light. With this scheme, we have indicated a clear signal response corresponding to a 150-nm line-and-space (L/S) pattern. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 25 nm from an air-bearing surface. Utilizing a triangular aperture irradiating polarized violet laser light, we performed a readout experiment at an aperture-to-medium spacing down to approximately 29 nm. A clear readout signal was obtained corresponding to the pattern down to 100-nm line width, in spite of the usage of a fairly large side size of 330 nm. We also evaluated the influence of the incident light’s polarization direction on the readout signals while changing the line width of the L/S patterns from 300 to 100 nm. A polarization direction perpendicular to the bottom side of the aperture provided both higher spatial resolution and better signal contrast. We also observed a “spike phenomenon” when the aperture passed through the boundaries between the metal portion and the space (or line-and-space) portion. We believe this phenomenon is the cause of the enhancement or suppression of specific L/S pattern or period signals.

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.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (NA) limit of the optics utilized. Storage based on the “near-field” principle is thought to be one of the most promising breakthroughs for overcoming various limitations governing traditional optical recording. We have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated the accuracy of the tracking characteristics of an aperture-mounted head slider by using linearly arranged 1-mm-long line-and-space patterns. Based on the step or inverse step responses that occur when an aperture flies obliquely across the linearly arranged pattern region boundary, we present a simple method of predicting accurate tracking characteristics in detail, and also by using a 350-nm line-and-space pattern signal, we were able to predict both tracking characteristics and tracking sensitivities of arbitrary wide tracks to a track width of 100 nm.

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.

We have developed a small near-field optical head for high-recording-density data storage applications, to overcome the disadvantage of conventional near-field optical heads, such as large light introduction, low optical throughput, and difficulty in controlling the aperture-medium distance. The optical head structure has miniaturized light introduction using an optical fiber placed horizontally. To decrease the optical loss, an integrated microlens focuses on the aperture tip that has a shortened cut-off region. The fabricated optical head (3.2×3.6×0.9 mm3) with a 200 nm aperture of the same height as the sliders shows a clear readout signal of a 200-nm-wide line and space pattern at a speed of 5.2 MHz. We show that the optical head has the ability to read 4 times the recording density by simulations of the finite difference time domain (FDTD).

A near-field optical head with a triangular aperture has been precisely analyzed on the basis of a three-dimensional finite-difference time-domain method in order to obtain both higher spatial resolution and signal output performance for a near-field optical data storage system. The numerical analysis revealed that in contrast to a conventional aperture, this triangular-shaped aperture can successfully enhance energy distribution intensity at only the side perpendicular to the incident polarization direction, generating an extremely small optical spot not limited by its entire aperture size. The read-out performance was also simulated for the aperture passing over a space-patterned metal medium, resulting in both superior spatial resolution and signal output.

A precise light waveguide combined total analysis system (TAS)[1] is thought to be one of the most powerful functional elements needed to realize a “ubiquitous healthcare” system. In accordance with this concept, we have proposed a fundamental structure of detecting forward and side scattered light from small particles illuminating laser power through light waveguide formed in a thin resin layer. Based on this concept, we demonstrated its effectiveness of detecting both forward and side scattered light in in-plane direction[2] (Fig.1) by using a trial-manufactured TAS chip. Acquiring further various physiological properties, it is necessary to illuminate them with smaller cross section size of cores of light waveguide, and furthermore, to construct fluorescence detecting systems.Copyright © 2014 by ASME

A minute optical sensor combined total analysis system (TAS) is thought to be one of the most powerful functional elements needed to realize a “ubiquitous human healthcare” system. In accordance with this concept, we have proposed a fundamental structure of detecting forward and side scattered light from a small cell or particle illuminating laser power through light waveguide formed in a thin resin layer. Based on this concept, we have demonstrated its effectiveness by using a trial-manufactured optical TAS chip, supplying and detecting visible laser power by using multiple optical fibers. Acquiring further various physiological properties created by an internal structure of a particles or cells, it is necessary to illuminate them with a small and arbitrarily-shaped light source placed close vicinity to them.Copyright © 2013 by ASME

走査型プローブ顕微鏡のファミリの一つで,磁性サンプルの漏洩磁界を大気中において,非接触・非破壊で測定可能な磁気力顕微鏡について,その原理を概説した。また検出感度,空間分解能,応答速度などの基本性能の向上に寄与したいくつかの技術をピックアップし,これらにも焦点をあてて述べた。加えて,力顕微鏡の測定例を磁気記録の場合を例に示すとともに,磁界測定のみならず高密度記録を目的として積極的にサンプルの磁化操作を行った例もあわせて述べた。

Using magnetic force microscopy (MFM), we investigated the effect of compositional separation (CS) on the magnetic domain configurations in Co78Cr22 films. Scanning electron microscopy of chemicallyetched microstructures and nuclear magnetic resonance studies showed that a film deposited at room temperature (RT) was compositionally homogeneous, while a film deposited at 200°C was in a compositionally separated state. The MFM image of the RT film showed a typical maze-type domain structure. In contrast, the image of the 200°C film suggested the existence of a finer, discontinuous domain structure. Point magnetic recording, using a Permalloy tip, produced magnetic dots down to between 0.15 and 0.30 μm in diameter in the 200°C film. No such magnetic dots, however, were observable for the RT film. These MFM results are consistent with CS promoting a change from a continuous to a particulate type magnetic microstructure suitable for high density magnetic recording.

Near-field optical performance is greatly improved using our proposed near-field structure, in which a metal scatterer formed in an aperture enhances localized surface plasmon (LSP) excitation and functions as an alternative near-field light source. Based on the design through a finite-difference time-domain method, the scatterer-formed aperture is fabricated with an electron beam technique, and its near-field optical distribution is observed using a scanning near-field optical microscope. The scatterer-formed aperture enhances the near-field optical energy due to LSP excitation, thereby realizing a significant and simultaneous improvement in throughput and spatial resolution.

A scanning probe microscope (SPM) which can depict physical properties by scanning a sharp tip onto the surface of a material of interest has recently been developed. Further intensive work is being carried out for imaging finer patterns in an attempt to apply its technique to high magnetic recording density. This paper considers a magnetic case and very fine bits are written in a Co-Cr/Permalloy perpendicular medium by using a very sharp tip of a magnetic material and then detected by the same tip. As one attempt to increase recording density, a bidirectional field recording scheme has been examined where an overwriting was performed. The recording density in connection with a detection signal (magnetic field gradient) is discussed. Based on a systematic experiment using various radii of the tips, the recording density in the bidirectional case was found to be twice that for a unidirectional field recording. The linear density of 4000 - 5000 fr/mm and the bit-line width of about 500 nm were confirmed.

走査型トンネル顕微鏡を基礎として,さまざまな物理量を画像化できる走査型プローブ顕微鏡(SPM)技術が進展している。本稿では,SPM ファミリのひとつとしてサンプルの磁化状態を大気中で非接触,非破壊のまま測定できる磁気力顕微鏡(MFM)について,その測定原理を中心に概説するとともに,これを用いた測定例を紹介する。さらに MFM を評価・分析装置としてのみならず,積極的にサンプルに働きかける磁気的なマニピュレータとの考えから,これを高密度記録に応用するための基礎検討の経過と最近の結果についても言及する。

Signal output from a piezoelectric transducer bonded to a flying head slider for magnetic disk storage is analyzed. Slider-core natural vibrations induced by contacts between the slider and the recording medium are identified with frequency peaks of the signal output. The analyses are applied to highly sensitive contact detection and evaluation of dynamic characteristics of a slider on an actual recording medium. The influence of the medium surface roughness on the dynamic behavior of the slider is presented for both the full flying state and the contact start/stop operation.

Signal output from a small piezoelectric transducer bonded to a flying head slider is analyzed. Slider-core natural vibrations and slider rigid body oscillations are identified with the frequency peaks of the signal output. These analyses are applied to a highly sensitive contact detection and an evaluation of dynamic characteristics of a slider on a real medium.

This paper presents numerical analyses of the dynamic characteristics of gas-lubricated slider bearings under high Knudsen number conditions using a generalized lubrication equation based on the the Boltzmann equation. These analyses are compared with those of the slip flow approximation equations and the differences are clarified. The present analysis is applied to the dynamic response of flying head sliders for magnetic disk storage devices. For a small slider with ultra-thin spacing, the deviations of the slip flow approximation equations are remarkable in regard to steady flying characteristics, but insignificant in regard to dynamic characteristics.

Near-field optics is one of super-resolution techniques for future data storage system. We have already proposed a near-field optical flying head with a circular aperture. Realizing higher performance aperture, we also have developed a triangular one which has been experimentally evaluated with scanning near-field optical microscope probe. In this paper, we demonstrate readout performance of this novel aperture mounted near-field head introducing polarization control. In order to scan over a media surface at small spacing condition, we fabricate a "contact" type head having contact pads and a polarization maintaining fiber, because this type of an aperture can only effectively function on condition both of extremely small spacing and applying polarized light. The contact pads and the tip are formed by photolithography with hydrofluoric acid (HF) solution. An aluminum film is formed on the tip. The aperture is formed by squeezing the shading film. Measurement of surface configuration by an interferometer shows that the aperture and the contact pads are almost on the same plane within 5 nm deviation. The media consists of a glass substrate, a titanium layer, a carbon protective layer, and a lubricant layer in sequence. Line-and-space (L&S) patterns whose width are 40~200nm are formed on the titanium layer. The contact head approaches the media surface, and then the media is scanned by a piezo stage. The near-field light generate from the triangular aperture is scattered by the L&S pattern and detected by a photomultiplier tube. Signal readout from the 40-nm-wide L&S pattern is demonstrated.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (N.A.) limit of the optics utilized. Storage based on the "near-field" principle is thought to be one of the most promising breakthroughs for overcoming various tough limitations governing traditional optical recording. From this perspective, we have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated a tribological (glide height) property and flying stability of a miniaturized 1.5-mm-long optical head slider by using acoustic emission sensor signal and readout signal from the medium. We have also evaluated detecting performance separately using traditional 3.2-mm-long slider and a chromium patterned medium whose bit patterns are accurately scored with bit lengths less than 100 nm using electron beam lithography including reactive ion etching. We have confirmed stable flying performance of 1.5-mm-long slider assembly and furthermore, ability of detecting sub-100-nm long bit patterns.

Advances in a digital network society require both higher densities and higher transfer rates in all sorts of storage devices. In optical recording, the trend toward higher recording density and larger storage capacity requires novel surface recording technologies that would drastically improve recording density. To satisfy these severe requirements, we have already proposed a compact integrated optical head slider assembly for proximity optical recording based on the "near field principle". Using the optical head slider, we have successfully demonstrated readout signals from 200 to 150-nm-long bit patterns at frequency bands up to approximately 10 MHz. However, from the practical point of view, it is quite necessary to evaluate readout signals from patterns of smaller (sub-micron to sub-sub-micron) track width in order to prove high-density recording potential. In this paper, we have investigated tracking accuracy characteristics utilizing sub-micron sized alternate patterns of 1-mm length formed in a straight line in the circumferential direction of the medium. Arranging precisely the head's relative position to these recorded patterns, we have successfully obtained readout signals just crossing the sub-micron line-and-space pattern's boundaries. Assuming that an aperture runs along an accurate trajectory of the arc of a circle, readout signal amplitude variations when crossing the pattern edge at a right angle have precisely predicted. Also, the influences of track width on maximum readout signal intensity and tracking sensitivity are discussed in detail.

Near-field optics, a super-resolution technique, is expected for optical data storage with high recording density (E. Betzig et al., Appl. Phys. Lett. vol. 61, p. 142, 1992; S. Hosaka et al, Nanotechnology vol. 8, p. A58, 1997). Recently, near- field optical heads using sliders, which can keep the distance between an aperture and a medium surface in proximity, were proposed, and reading from 110-250 nm pattern at the speed of 1.5-7.5 MHz was demonstrated (H. Yoshikawa et al., Opt. Lett. vol. 25, p. 67, 2000; F. Issiki et al., Appl. Phys. Lett. vol. 76, p. 804, 2000; K.T. Yatsui et al., Opt. Lett. vol. 25, p. 1279, 2000). These optical heads use an objective lens above sliders separately, to introduce the focused light to the aperture. However, this large light introduction using the objective lens leads optical heads with actuators to be large. From this perspective, we had proposed a small near-field optical head module with miniaturized light introduction (K. Kato et al., Tech. Dig. ISOM2000, p. 188, 2000). In this paper, we fabricated the proposed optical head module with air-bearing surface, and high speed reading from 200 nm chromium pattern formed on an SiO/sub 2/ disk medium was demonstrated.

Recorded domains on perpendicular recording double-layer media were imaged by magnetooptical Kerr effect microscopy. The reversal domains were observed at the edge of tracks by a head whose leading pole is wider than its trailing pole. It was found that the perpendicular magnetic field of a trailing pole overwrites the domains written by that of a leading pole. >

We have developed an integrated micro-probe with improved detection efficiency for apertureless near-field scanning optical microscopy (NSOM) by using micromachining techniques; we call this probe a `photocantilever'. A photocantilever is an integrated micro-cantilever with a pn- junction at its end; it is fabricated using micromachining techniques. It has achieve higher collection efficiency than conventional NSOM probes because the detector is placed close to the scatterer. Two new types of NSOM can be performed using this photocantilever: totally-internal- reflection-illumination-based NSOM and differential NSOM. Both provide NSOMs with high spatial resolution. The photocantilever enables apertureless NSOM with high collection efficiency and high resolution.

One of the most important parameters related to the near-field readout principle is aperture-to-media spacing (effective spacing). We proposed a near-field optical head with a protruding aperture that can reduce the effective spacing beyond the mechanical limit of the flying height and localize the near-field on the medium. Using nanostep lithography, we fabricated the protruding aperture, whose extension is 20 nm with 5 nm accuracy, so that the effective spacing is successfully reduced to 50 nm on a 3.2×3.6 mm flying head. We demonstrated signal readout with a 150 nm-long line-and-space pattern in chromium with the head. The flying height was estimated to be 75 nm, so that the effective spacing was 54 nm. The circumferential speed was 2.7 m/s and the signal frequency was 9.1 MHz. We also propose a promising structure for an optical head of higher density.