Physical limitation of the conventional longitudinal media has been actualized recent days according to the dramatic increase in storage area density with a growth ratio of more than 100%/year so that perpendicular recording is being watched with keen interest. Development in perpendicular recording media from the proposal to actual usage for HDD system are reviewed in terms of historical back ground, recent media design and preparation, new media proposal and recording performances, mainly basing on the author's results. In case of perpendicular media, physical limit of thermal stability could not be so serious but media noise reduction with sophisticated preparation method has been research topics as the breakthrough for the commercialization. Improvements on Co-Cr system alloy media were made by introducing proper additives and under layers so that a high storage density over 60 Gb/inch² has been achieved. Far higher density up to 1 Tera bits/ inch² is expected to be possible by using newly proposed Co/Pd multilayer or Fe-Pt metal compound films. It is prospected that breakthrough for the future progresses would be mechanical issues such as head medium spacing and tribology problems rather than magnetic properties of media.

Microstructures of CoCr-alloy thin film media were investigated by cross-sectional transmission electron microscopy focussing on the initial growth region of the magnetic layer grown on nonmagnetic underlayers. An introduction of nonmagnetic hcp-CoCrRu layer between an hcp-CoCrPt recording layer and an hcp- or a bcc-underlayer improved the crystallographic quality of the initial growth region. Sharp compositional distributions of alloying elements at the interfaces of a CoCrPt/CoCrRu/CrTi perpendicular medium and a CoCrPt/CoCrRu/CrTi longitudinal medium were respectively confirmed by electron energy loss spectroscopy employing a finely focussed electron beam. Coercivity and squareness of the thin film media increased by realizing good hetero-epitaxy between the nonmagnetic and the magnetic hcp-layers.

Magnetoplumbite type Ba ferrite (BaM) disks were prepared on Pt and Pt-Ta underlayers using facing targets sputtering apparatus. Pt underlayers are more effective than ZnO underlayers to promote c-axis orientation of BaM layers, especially for extremely thin BaM films. Pt-Ta underlayer was used to decrease the grain size of BaM layers. BaM/Pt-Ta disks revealed larger S/N ratio than BaM/Pt disks because of their larger signal output and lower media noise level. BaM disks with 50 nm thick BaM layers revealed lower noise level and larger S/N ratio than that with 100 nm thick BaM layers due to smaller grain size.

Employing reactive sputtering using an electron-cyclotron-resonance microwave plasma without oxidation process, high coercivity ferrite thin-films with perpendicular magnetic anisotropy were successfully prepared without NiO underlayer at low substrate temperature. The ferrite thin-film deposited on glass substrate had smooth surface and were composed of small grains. Perpendicular recording was performed on the ferrite thin-film hard disk. The ferrite thin-films with high coercivity could be prepared on flexible film substrates (Polyimide and PET).

Particulate media composed of very small particles were studied to determine high-density recording performance and thermal stability. Studied media included metal particulate media with mean particle length of 71, 102 and 148 nm, and Ba ferrite particulate media with mean diameter of 22, 28 and 50 nm. Using a loss-term simulation program, taking into account gap-loss, spacing-loss and particle length loss, the recording capability (D₂₀ of 265 kFRPI for MP and 290 kFRPI for Ba ferrite media) was estimated. Thermal stability was evaluated from magnetization time decay measurements. It was found that MP media with large K_u values and 71 nm particles were satisfactorily stable, and the particle volume is still large enough in respect of thermal stability. However, 22-nm Ba ferrite media were less stable, primarily because of small K_u values and particle volume. It was also clarified that positive inter-particle interaction accelerates magnetization time decay, in the presence of a large reverse field.

Single crystal MnZn Ferrites are used as core materials for the reader of inductive magnetic heads. Magnetic phase homogeneity of the material is one of the parameters, which affects the quality of the devise. We used static magnetic measurements above the apparent Curie temperature of the Ferrite materials to determine the presence of such phases. High performance samples are non-magnetic at high temperature. In low performance materials, a small but non-zero spontaneous magnetization at high temperature indicates the presence of the second phase.

Two isolated pulse models, the Lorentzian-like and the Mixture model, were used to investigate the effect of GMR heads-media with different geometric and magnetic parameters on the readback pulse shape. The matching of these two models with an actual pulse was compared in detail. The dependence of the readback pulse shape of GMR head on the head-media parameters and non-linear distortions was discussed in this paper. When applying these models to evaluate the performance of a recording system, it is necessary to take into account of the difference between the linear superposition of the isolated pulse and the actual readback data pattern. It was suggested to linearize the captured isolated pulse in order to use the model correctly as a useful tool for evaluating the system performance.

Recording mechanism of perpendicular recording was examined using analytical expression of shielded AMR/GMR head response. Pulse shape, roll-off performance, and noise spectra were reasonably explained by the calculated head transfer functions. Comparison with the calculation based on the formulae showed several fundamental characteristics of perpendicular recording: no large media noise at low frequencies in magnetic sense, but simply due to a reflection of a head transfer function: no severe resolution degradation: negligible noise power directly arisen from soft magnetic underlayer. This method will provide a convenient design tool for perpendicular magnetic recording.

Skew angle effects on the transition noise are analyzed in the longitudinal disk media by micromagnetic simulations at area densities from 14.3 Gb/in² to 31.5 Gb/in². The transition noise, including the peak, width and jitter noise, is the dominant noise in ultra-high density disk recording systems. An isotropic medium and an oriented medium, with a fixed grain size of 135 and a coercivity of 2900 Oe, are chosen for the noise analysis. The peak noise is studied by the distribution of the peak magnetization amplitude M_p in each bit. The transition a-parameter is no longer the value as given in the William-Comstock approximation. It is found that the transition noise is highly dependent on both the linear den sity and the skew angle, where the bit length and the grain size are on the same order. In both media, the medium noise increases severely when the skew angle is above 10 degrees.

Dual FDTS/DF detector is an advanced version of FDTS/DF detector that gives significant performance improvement over FDTS/DF scheme on linear channels, and moreover, in contrast to other dual-detector schemes, it is suitable for various d-constraint coded channels. As recording density increases, channel nonlinearities such as non-linear transition shift (NLTS) and partial erasure (PE) degrade the performance of detectors. In this paper, we use nonlinear channel models to study the BER performance of dual FDTS/DF detector and compare the performances with those of other detectors through bit-by-bit simulations. Simulation results show that the dual FDTS/DF detector is superior in performance compared to FDTS/DF and MDFE detectors even on nonlinear channels, and it gives comparable BER performance with M2DFE (adv.) on nonlinear channels. Results also indicate that the detectors on the d=1 coded channels are more robust to channel nonlinearities compared to those of other detectors (such as PRML family detectors) on the d=0 coded channels.

The effect of Unbalanced-Magnetic-Pull (UMP) on vibration and run-outs has become stringent in the design for high performance HDD spindle motors. In this paper, reducing the UMP and also minimizing its variability for an 8-pole 9-slot spindle motor to achieve robustness in the performance is described and illustrated using novel robust design methods. A screening experiment identifies the key design parameters. Using Design of experiment (DOE) and Analysis of Variance (ANOVA), the parameter design reduces the amplitude of UMP and minimizes its variability by product parameter optimization. The tolerance design improves the quality by tightening tolerances on product or process parameters to reduce the performance variation. The optimal design process includes considerations of manufacturing and process noises, such as manufacturing tolerances for the slot opening and variation of the rotor magnet magnetization distribution due to the magnetization fixture and process. The optimal design procedure is briefly introduced and the results are presented.

The present paper describes the finite difference time domain (FDTD) analysis of the light-beam diffraction from two- and three-dimensional (2-D and 3-D) magneto-optical (MO) disk structures. First, we show that the proposed new FDTD formulation is valid for MO disk medium and can avoid the divergence of fields encountered during the conventional FDTD calculations. Second, as the application of the present method to more complicated models, the main- and cross-polarized diffracted fields are numerically calculated for 2-D and 3-D four-layered MO disk models. The phase differences between two kinds of polarized components are shown. The results obtained here indicate that the proposed FDTD formulation can be applied to more complicated MO disk structures.

Current-voltage characteristics of Cr-doped hydrogenated amorphous silicon-V (Cr/p⁺a-Si:H/V) analogue memory switching devices have been measured over a wide range of device resistance from several kilo-ohms to several hundred kilo-ohms, and over a temperature range from 13 K to 300 K. Both the bias and temperature dependence of the conductance show similar characteristics to that of metal-insulator heterogeneous materials (i.e. discontinuous or granular metallic films), which are analysed in terms of activated tunnelling mechanism. A modified filamentary structure for the Cr/p⁺a-Si:H/V switching devices is proposed. The influence of embedded metallic particles on memory switching is analysed and discussed.

Magnetic tunnel junctions (MTJ), i.e., structures consisting of two ferromagnetic layers (FM₁ and FM₂), separated by a very thin insulator barrier (I), have recently attracted attention for their large tunneling magnetoresistance (TMR) which appears when the magnetization of the ferromagnets of FM₁ and FM₂ changes their relative orientation from parallel to antiparallel in an applied magnetic field. Using an ultrahigh vacuum magnetron sputtering system, a variety of MTJ structures have been explored. Double H_c magnetic tunnel junction, NiFe/Al₂O₃/Co and FeCo/Al₂O₃/Co, were fabricated directly using placement of successive contact mask. The tunnel barrier was prepared by in situ plasma oxidation of thin Al layers sputter deposited. For NiFe/Al₂O₃/Co junctions, the maximum TMR value reaches 5.0% at room temperature, the switching field can be less than 10 Oe and the relative step width is about 30 Oe. The junction resistance changes from hundreds of ohms to hundreds of kilo-ohms and TMR values decrease monotonously with the increase of applied junction voltage bias. For FeCo/Al₂O₃/Co junctions, TMR values exceeding 7% were obtained at room temperature. It is surprising that an inverse TMR of 4% was observed in FeCo/Al₂O₃/Co. The physics governing the spin polarization of tunneling electrons remains unclear. Structures, NiFe/FeMn/NiFe/Al₂O₃/NiFe, in which one of the FM layers is exchange biased with an antiferromagnetic FeMn layer, were also prepared by patterning using optical lithography techniques. Thus, the junctions exhibit two well-defined magnetic states in which the FM layers are either parallel or antiparallel to one another. TMR values of 16% at room temperature were obtained. The switching field is less than 10 Oe and step width is larger than 30 Oe.

This paper shows a comparison between several procedures to represent the Physical Optics (PO) current density into a hybrid Moment-Method-Physical-Optics (MM-PO) code. Some numerical results demonstrate that a set of basis functions suitable for the Method of Moments (MM) may be inappropriate to model the PO currents. A new evaluation of the PO operator is proposed. The radiation can be analytically determined and, since it includes a linear interpolation of the phase, it can be applied over large triangular domains. This allows a drastic reduction of the computational cost, maintaining or even improving the level of accuracy.

A nonlinear Volterra-series analysis of multiple ion-implanted GaAs FETs is given that relates carrier profile parameters of ion-implantation to nonlinear rf characteristics of a FET. Expressions for nonlinear coefficients of transconductance are derived from drain current-voltage characteristics of a multiple ion-implanted FET. Nonlinear transfer functions (NLTFs) are then obtained using Volterra series approach. Using these NLTFs third-order intermodulation distortion and power gain are explicitly given. A good agreement has been found between the calculation and the measurement for a medium power GaAs FET with a total gate width of 800 µm operated at 10-dB back off, verifying the usefulness of the present analysis.

This paper introduces a switched-voltage delay cell with differential inputs. It can be used as a building block for a range of analogue functions such as voltage-to-frenquency converter, A/D converter, etc. Applications incorporating the delay cell are presented. The performances are verified by simulations on PSpice.

We propose an effective model that can reproduce the reverse short channel effect (RSCE) of the threshold voltage (V_th) of MOSFETs using a conventional process simulator that solves one equation for each impurity. The proposed model is developed for local modeling which is effective within the limited process conditions. The proposed model involves the physics in which RSCE is due to the pile up of channel dopant at the Si/SiO₂ interface. We also report the application to actual device design using our model. The calculation cost is much lower than for a pair diffusion model, and device design in an acceptable turn around time is possible.

In this paper, a high-speed PLA based on dynamic array logic circuits with latch sense amplifiers is presented. The present circuit consists of logic cell arrays, dual-rail bit-lines, latch sense amplifiers, and control blocks. By using a charge sharing scheme and latch sense amplifiers, voltage swings of the bit-lines are reduced compared to the conventional circuits, thus a high-speed and low-power operation is achieved. The present array logic configuration can realize any logic function expressed in the sum-of-products form by using PLA structure. As an application of the proposed PLA, a 32-bit binary comparator is designed and implemented in a 0.6-µm double-poly triple-metal CMOS process. Results of HSPICE simulation show a better performance compared to the conventional circuits. Functional testing using electron beam probing shows that the present circuit operates correctly.

Feasibility of a color shutter using ferroelectric liquid crystal polymer panel and a field sequential ultra high-resolution CRT with the color shutter as a color field-switching device was studied. The color shutter consists of ferroelectric liquid crystal polymer panels and color polarizers. First, evaluation indices of the color shutter, such as the color gamut, the average transmittance and the white chromaticity shift, were formulated, and the simulation of evaluation indices was examined, where the spectral transmittance characteristics of the polarizer were changed in steps. It was indicated that there was a tradeoff between the color gamut and the average transmittance of the color shutter, and the shutter configuration that provides 0.096 (63% to NTSC) color gamut and 4.3% average transmittance was selected based on the simulation results. Next, the three-line simultaneous scanning method of the monochrome CRT was improved so that the disturbance due to the raster modulation was eliminated by averaging the distribution of beam luminance apparently. To confirm results of the study, the prototype of 21-inch screen size was produced, and the following display characteristics was obtained: luminance of 71 cd/m2, contrast ratio of 146:1 and color gamut of 0.096 (63% to NTSC) under the standard room lighting environment.

Scattering responses from a dielectric sphere are analyzed in the time-frequency domain by using two types of wavelet transform in order to reveal the scattering mechanisms. In the resulting time-frequency displays, various scattering processes including reflection, refraction, and diffraction can be clearly resolved and identified. The delay time of each scattering process agrees well with that obtained by the ray theory. Furthermore, the natural frequencies that are not easy to extract by the conventional Fourier analysis can be extracted.

This paper describes an estimation method for an antenna current distribution including the interaction between a cellular telephone antenna and a human body. In our experiments, current distributions on a half wavelength dipole antenna at 900 MHz are evaluated by measuring the magnetic field near the antenna, when a human head-sized phantom model is located near the dipole antenna. From the experiments, the antenna current around a feed point is confirmed to increase by 30% due to the interaction effect. This result shows that antennas of portable phones should be designed by considering the effect of a human presence for the development of the higher performance antenna, and our estimation method will contribute to optimizing the design of such antennas.

An analytic equation was derived for the time jitter of digital NRZ signals due to inter-symbol interference in the PCB transmission lines loaded by DRAM chips which are located in uniform spacing. The inter-symbol interference is caused by a low-pass filtering effect of the loaded transmission line. Good agreements were observed between the equation and measurements with an average error of 17.5%.

We derive an efficient and simple analytical expression for estimating maximum simultaneous switching noise (SSN) on ground distribution networks in CMOS systems. In order to estimate maximum SSN voltages, we use α-power law MOS model and Taylor's series approximation. The accuracy of the proposed expression is verified by comparing the results with those of previous researches and HSPICE simulations under the contemporary process parameters and environmental conditions. The proposed method predicts the maximum SSN values more accurately when compared to existing approaches even in most practical cases such that there exist some output drivers not in transition.