Tremendous progress has been made in magnetic data storage by applying theoretical considerations to technologies accumulated empirically through a great deal of research and development. In Japan, the recording demagnetization phenomenon was eagerly analyzed by many researchers because it was a serious problem in analogue signal recording such as video tape recording using a relatively thick magnetic recording medium. Consequently, perpendicular magnetic recording was proposed as a method for extremely high-bit-density recording. This paper describes the theoretical background which has resulted in the idea of perpendicular magnetic recording. Furthermore, the possibility of magnetic recording is discussed on the basis of the results obtained theoretically by magnetic recording simulators. Magnetic storage has the potential for extremely high-bit-density recording exceeding 1 Tb/cm². We propose the idea of 'spinic data storage' in which binary digital data could be stored into each ferromagnetic single-domain columnar particle when the perpendicular magnetizing method is used.

A vertical magnetoresistive (MR)/inductive head using the current bias technique has been developed for high-density magnetic recording. In this head, the sense current is orthogonal to the air-bearing surface (ABS). The area exposed at the ABS of the MR element is beneath the front lead, and the active area of the sensor is positioned behind that area. The MR element is composed of two permalloy films separated by a thin nonmagnetic material. The easy axis of the films is oriented parallel to the ABS and the films are magnetostatically coupled. The magnetic field created by the sense current is applied in the direction of the easy axis and the MR element is stabilized. In this head structure, no MR-element-stabilizing layer, such as an antiferromagnetic film or a hard magnetic film, is needed. Since the permalloy film beneath the front lead acts as a front flux guide, the signal flux propagates in the sensing area of the MR element behind the ABS. The new vertical MR head has the same electrical performance characteristics as the conventional horizontal MR head. The offtrack signal profile is symmetric against the track center because the magnetization of the two permalloy films rotates symmetrically in the signal-flux direction. The output signal level of this head is independent of the read trackwidth, which favors a narrow trackwidth. The exposed portion at the ABS is only connected to the common lead and is at ground potential. In this design, electrostatic breakdown does not occur and no corrosion is observed. Tests have shown that as the flying height is reduced, the error rate is reduced and noise does not increase. This head structure appears suitable for the near-contact recording of the near future.

Computer circumstance have changed drastically, and larger capacity removable media is indispensable. Magneto-optical disk is promising candidate to satisfy computer user's needs. In this report, future perspective of high density magneto-optical recording technology is investigated.

A three-dimensional micromagnetic simulation using the Landau-Lifshitz-Gilbert equation was performed for thin-film magnetic recording media and magnetoresistive (MR) heads with soft adjacent layers (SAL). For recording media the simulation results for magnetization curves and media noise were compared with the results of experiments. Although the media model needs to be improved, the qualitative agreement between simulation results and experimental results shows that this micromagnetic simulation can be a useful tool for analyzing and predicting magnetic properties and recording characteristics. This work also showed that media noise is influenced by magnetostatic interaction, and that the decrease of the magnetostatic interaction is favorable for obtaining a high signal-to-noise ratio. For an MR head the output obtained with a nonuniform sense current distribution is similar to the output obtained with uniform sense current distribution for both low and high anisotropy fields (H_k=2 Oe and 10 Oe) SAL. With the low H_k SAL, however, the asymmetry of the output obtained for nonuniform sense current differs from the asymmetry obtained for uniform sense current; the difference is due to a magnetization vortex in a biased state in the SAL. With the high H_k SAL, the difference between the asymmetry obtained for nonuniform sense current and the one obtained for uniform sense current is not large; no vortices are found in the SAL at the biased state.

Extremely narrow track width of deep submicron range is examined in perpendicular magnetic recording. Head field distribution of a single-pole head analyzed by 3-dimensional computer simulation results in a sharp gradient, but relatively large cross-sectional area is required to maintain head field strength. Based on this design concept, a lateral single-pole head is described and proved to attain track width of 0.4 µm. In addition, multilevel partial response appropriate to the new multitrack recording system is proposed.

A soft magnetic force microscope (MFM) tip was used to evaluate the magnetic recording characteristics of compositionally separated Co-Cr perpendicular media. Small magnetic bits were recorded on thick (350 nm). and thin (100 nm) films, focusing on the fineness of compositionally separated microstructures. MFM images showed bit marks 230 and 150 nm in diameter, measured at full-width at half maximum (FWHM) for the thick and thin films, respectively. These results verify that the recordable bit size can be decreased by using a thinner film with a finer compositionally separated microstructure. Simulation was used to clarify the relationship between the actual sizes of the recorded bits and the sizes of their MFM images. The recorded bit size was found to closely correspond to the FWHM of the MFM bit images.

The magnetic properties and the structure of electroless-deposited NiFeB films were investigated in comparison with those of electrodeposited NiFe films. The electroless-deposited NiFeB film with 27at% Fe content had the lowest coercivity, H, as low as 0.5 Oe with a saturation magnetic flux density, B_s, of 1.0 T. The saturation magnetostriction, λ, and the uniaxial magnetic anisotropy, H_k, were 5.010^-6 and 10 Oe, respectively, which were larger than those of the conventional, electrodeposited permalloy film. The permeability of as-deposited Ni₇₀Fe₂₇B₃ film was 1000 at 1 MHz. In order to improve the permeability, the film was heated at 200 in a magnetic field applied in the hard-axis direction to decrease the H_k value, and the permeability became 2000 at 1 MHz. The crystal structure and grain size of NiFeB and NiFe films were investigated by XRD, THEED and TEM. Both films with low H_c had an fcc structure; the grain size of the NiFeB film was smaller than 10 nm, while that of the NiFe film was larger, approximately 20 nm. The results suggested that the electroless-deposited NiFeB film had a larger magnetic anisotropy than the electrodeposited NiFe film. Moreover, the films with H_c less than 10 Oe ded not show clear difference between their TEM bright images and THEED patterns.

A particulate recording medium with an ultrathin magnetic layer is presented in this paper. This medium consists of a magnetic layer and a nonmagnetic underlayer composed of very fine titanium dioxide powder. When metal powder was employed, we observed the anticipated advantages of decreasing the thickness of the magnetic layer in tapes and diskettes. By reducing the layer thickness to below 0.3 µm we were able to increase the reproduced output at short wavelengths, and improve both the overwrite erasability and the D50. There was also a decrease in the half peak width of an isolated pulse and a peak shift. Tribological advantages were also observed with this medium. When barium ferrite was employed as the magnetic powder, we observed that the modulation noise of thin-layer barium ferrite medium was less than that of a thinlayer MP medium while it generated an output as high as that of the MP medium. The advantages of the barium ferrite medium lie in its two-layer construction. Particulate media will continue to develop as magnetic powder is improved mainly in terms of its size, saturation magnetization, and coercivity.

The authors have studied the demagnetization phenomenon which is observed in a conventional CoCrTa/CoZrNb double-layered (DL) perpendicular recording medium. The authors have also investigated the effects of an in-plane hard magnetic layer in a triple-layered (TL) perpendicular recording medium. The in-plane hard magnetic underlayer is made of CoSm or CoCrTa/Cr and is laid under the CoZrNb soft magnetic layer. In the DL medium, a demagnetization phenomenon i.e. decrease of the readback signal, is observed when the CoCrTa layer has a strong perpendicular orientation and the CoZrNb underlayer has a low coercivity. The amount of the signal decrease depends strongly on the accumulated disk revolutions. This demagnetization is considered to be caused by fact that the recorded magnetization in the CoCrTa layer is reduced by the magnetic field generated from the domain walls in the CoZrNb layer, since the CoZrNb layer is very sensitive to a magnetic environment such as geo-magnetism and domain walls move as the disk rotates. On the other hand in the TL medium, the hard magnetic layer has an effect of pinning the magnetic domain in the CoZrNb layer, by which the demagnetization problem is successfully prevented. The hard magnetic layer remarkably reduces the domain walls in the CoZrNb layer and contributes to medium noise reduction. Thus the TL medium presents a higher SN ratio than DL medium.

The ultraclean sputtering process (UC-process) was newly introduced in the fabrication of Co_62.5Ni₃₀Cr_7.5 and Co_85.5Cr_10.5Ta₄ thin film media to establish a new concept in controlling microstructure. UC-process enables the realization of high coercive force H_c up to 2.7-3 kOe in both CoNiCr and CoCrTa media (15/50 nm magnetic/Cr thicknesses) without the decrement of saturation magnetization. The purification of the atmosphere during sputtering and the removal of the adsorbed oxygen impurity on the substrate surface play important roles in obtaining high H_c by applying the UC-process. This high H_c is mainly due to the realization of large magnetocrystalline anisotropy field of grains H_k^grain and low intergranular exchange coupling. UC-process realizes the adequate separation of grains by segregated grain boundaries even in media with thin Cr thickness of 2.5 nm, and enables grain size reduction without the remarkable increment in intergranular exchange coupling. In these media, the reduction of the grain size is most effective for the improvement of readback signal to media noise ratio S/Nm. In the media with grains sufficiently separated by segregated grain boundaries fabricated by the UC-process, control of grain size reduction and further increase in H_c/H_k^grain value through the decrement in intergranular magnetostatic coupling are required to obtain higher S/Nm value.

Co-Zr and Co-Zr-Ta amorphous films were prepared by the Kr sputtering method for use as the backlayers of Co-Cr perpendicular magnetic recording tape media. The effect of the addition of Ta to Co-Zr thin films was also investigated. Lower substrate temperature was required to prepare amorphous Co-Zr films with excellent soft magnetic properties. The relationships among Ta content X, magnetostriction constant λ and magnetic characteristics such as coercivity H_c and relative permeability µ_r were clarified. A method of evaluating λ of soft magnetic thin films deposited on polymer sheet substrate has been presented. Films with composition of (Co_95.7Zr_4.3) _100-X Ta_X at X of 10 at.% possessed sufficiency soft magnetic properties such as low H_c below 80 A/m and high µ_r above 600. Addition of Ta was effective in changing change the sign of λ from positive to negative. It was found that the negative magnetoelastic energy and the smaller λ caused the soft magnetism.

Ba ferrite films were deposited epitaxially on ZnO underlayer from targets with composition of BaO-6.5Fe₂O₃ at substrate temperature of 600 using the facing targets sputtering apparatus. The gas mixture of Ar and Xe of 0.18 Pa and O₂ of 0.02 Pa was used as the sputtering gas and the dependences of crystallographic and magnetic characteristics on the partial Xe pressure P_Xe(0.0-0.18 Pa) were investigated. Films deposited at various P_Xe were composed of BaM ferrite and spinel crystallites, and the minimum centerline average roughness R_a of 8.3 nm was obtained at P_Xe of 0.10 Pa. Since saturation 4πM_s of 5.1 kG and perpendicular anisotropy constant K_u1 of 4.2310⁵ J・m^-3 were larger than those of bulk BaM ferrite of 4.8 kG and 3.3010⁵ J・m^-3, respectively, these films appeared promising for use as perpendicular recording media.

Simplification of the Viterbi algorithm and the error rate performance are presented for a partial response maximum-likelihood (PRML) system employing the PR(1, 1) system as a PR system for (1, 7) run-length limited (RLL) code. The minimum run-length of 1's or O's in the output sequence of the precoder for (1, 7) RLL code is limited to 2. Two kinds of simplified Viterbi algorithms using this run-length constraint are proposed. One algorithm requires the path memory length of only two in the Viterbi detector. The Viterbi detector based on the other algorithm is equivalent to the simple PR(1, 1) system followed by a threshold detector. The bit-error rates of PRML systems with Viterbi detectors based on these algorithms are obtained by computer simulation and their performance is compared with that of conventional PRML systems for (1, 7) RLL code. It is shown that the proposed PRML system exhibits better performance than conventional PRML systems at high recording density.

The performance of decision-feedback equalization combined with maximum-likelihood detection (DFE/ML) using the fixed-delay-tree-search/decision feedback (FDTS/DF) algorithm was estimated analytically in terms of the length of the feedback-filter and the depth of the ML-detector. Performance degradation due to error propagation in the feedback-loop and in the ML-detector was taken into account by using a Markov process analysis. It was quantitatively shown that signal-to-noise-ratio (SNR) performance in high-density magnetic recording channels can be improved by combining an ML-detector with a feedback-filter and that the error propagation in the DFE channel can be reduced by using an ML-detector. Finally, it was found that near-optimum performance with regard to channel SNR and error propagation can be achieved, over the channel density range from 2 to 3, by increasing the sum of the feedback-filter length and the ML-detector depth to six bits.

A two-dimensional recording method that achieves double recording density by reducing the track pitch is described. This method uses a flat disk and the data are recorded with circular marks on lattice points. Two-dimensional interference consisting of crosstalk and inter-symbol interference is reduced by two-dimensional equalization. To minimize the two-dimensional interference, the optimum equalization coefficients are calculated dynamically with the reproduced signal of the training marks. Reproduction was simulated and this showed that the signal-to-noise ratio of the processed signal was 24.3 dB under ideal conditions and 19.8 dB under worst-case conditions with the usual magneto-optical media using double recording density. These simulation results were checked by a recording/reproduction experiment. The experimental result for the signal-to-noise ratio of the processed signal was 23.6 dB with an areal density of 2.3 Gbit/in².

Tilt margins for disk and lens for a magneto-optical (MO) head were studied for designing a disk system for use with objective lenses having numerical apertures (NA) of 0.55, 0.60, and 0.65. The tilt margins were examined to determine the aberration characteristics of objective lenses and bit error rate (BER) by recording and reproducing signal. In preparing the optical head for testing disk and lens tilt margins, the aberrations were measured by image processing from the CCD area sensor for the spot image of the focused beam, and BER dependencies on the tilting of lens and disk were obtained at the velocity of the outer diameter of the MO disk at the bit rate of 80-Mbps (1, 7 code modulation) recording. According to the aberration and BER characteristics, the limitation for effective wavefront aberration would be 0.05λ rms, the tilt margins corresponded to BER limitation at the level of 3^*10^-5. The disk margins for NA=0.55, 0.6, and 0.65 were 0.4, 0.2, and 0.1 degrees. The lens tilt margins for NA=0.55, 0.6, and 0.65 were 0.2, 0.1, and 0.05 degrees.

A real-time read/write motion picture has been demonstrated by hole-burning holography using cryogenic Eu³⁺: Y₂SiO₅ crystal. In a holographic configuration the laser frequency was continuously scanned within the ⁷F₀-⁵D₀ absorption line while the object was in motion. This movie has no picture frames, and therefore is temporally continuous. This feature allows realization of high-speed and high-time-resolution motion recording.

Theoretical and experimental results are presented for angle-multiplexed and wavelength-multiplexed holographic recording. The recording medium is a cerium doped Sr_1-XBa_XNb₂O₆ (SBN) single crystal, and the light sources are a laser diode excited second harmonic generation (SHG) laser and a tunable laser diode. The SBN single crystal has high recording sensitivity, high diffraction efficiency and high temperature stability. The laser diodes miniaturize the holographic recording system. Crosstalk between hologram pages is theoretically calculated by using modified coupled-wave equations, and is also experimentally measured. The experimental results agree well with the theoretical results. Two-dimensional alphabetical character images are recorded using angle- and wavelength-multiplexed holographic methods, and are successfully reconstructed. The theoretical results indicate that several hundred multiplexed holograms can be recorded with little crosstalk using the proposed system. This multiplexed holographic recording technique will enable high-density recording and high data-transfer rates.

An automatic transistor-level performance fault tracing method is proposed which is applicable to the case where only CAD layout data is available in the CAD-linked electron beam test system. The technique uses an integrated algorithm that combines a previously proposed transistor-level fault tracing algorithm and a successive circuit extraction from CAD layout data. An expansion of the algorithm to the fault tracing in a combined focused ion beam and electron beam test system which enables us to measure signals on the interconnections in the lower layers is also described. An application of the technique to a CMOS model layout with about 100 transistors shows its validity.

This paper proposes a distributed built-in self-test (BIST) technique and its test design platform for VLSIs. This BIST has lower hardware overhead pattern generators, compressors and controller. The platform cuts down on the number of complicated operations needed for the BIST insertion and evaluation, so the BIST implementation turn-around-time (TAT) is dramatically reduced. Experimental results for the 110 k-gate arithmetic execution blocks of an image-processing LSI show that using this BIST structure and platform enables the entire BIST implementation within five days. The implemented BIST has a 1% hardware overhead and 96% fault coverage. This platform will significantly reduce testing costs for time-to-market and mass-produced LSIs.

The interstitial hyperthermia is an invasive heating method applied by inserting the applicator into the human body. We have been studying on coaxial-slot antennas for interstitial microwave hyperthermia. The characteristics of the square antenna array were theoretically examined. Firstly, the basic structure of the antenna, and a simplified analysis model taking account of the effect of the boundary surface were explained. Then analysis was performed by using the moment method. Finally, the calculated results were discussed. The catheter thickness has much effect on the characteristics and must be considered both in designing and in using the antenna. When the array spacing was increased, the effective heating area became larger and more uniform. As the insertion depth was increased, the effective heating area was also enlarged.

I have examined factors for implementing a high-speed, low-power-consumption thermal head. In conventional thermal heads, a heat insulation layer is provided between the heating resistor and the radiator. I found it desirable to implement fast operation and low power consumption to lower the thermal conductivity of the heat insulation layer and to thin the heat insulation layer. I also found there is an optimum heat characteristic to the thickness of one heat insulation layer. I assumed polyimide as a material for the heat insulation layer which could materialize the hypothesis, and studied necessary items based on the thermal calculation. I manufactured a trial thermal head on the basis of this result and confirmed that our assumptions were correct. In addition, to confirm that the assumption is also ultimately correct, I fabricated a trial thermal head only consisting of a heating resistor and without a protective coat and a heat insulation layer. I confirmed that the structure with only the heating resistor exhibited excellent heat response and consumed less power necessary for heating.

To evaluate the radial eigenmode field distributions and the resonance wavelengths of axially symmetric pillbox resonator, a numerical method is described which is based on the FE-BPM expression in cylindrical coordinates. Under the weakly guiding approximation, we solve Fresnel equation and can get a fairly accurate result. By using effective index method, 3-D pillbox guiding structure is reduced to 2-D one which is then used for the analysis. One advantage of this method is that it is applicable for the axially symmetric optical waveguides with arbitrary index distribution. The validity of this method is checked by comparing the results of this method with those of the analytical ones. This method is applied for the evaluation of the coupling properties of a coupled structure consisting of a pillbox resonator and a curved waveguide placed outside the pillbox. This coupled structure has a good prospect to be used as optical wavelength filter. By varying the separation distance between the pillbox and the outer curved waveguide, the power transfer due to coupling is determined near the resonance wavelength 0.9 µm.