Even in today's industries that are predominated by solid-state switching devices, electromechanical devices with electrical contacts are still widely used for switching and/or conveying electrical signals and power. In this paper, some interesting topics in the investigation of electrical contacts, which were selected mainly from those presented at recently held international conferences or submitted to the related Transactions of IEEE and IEICE, are introduced. Specifically, some topics related to investigation regarding contact materials, new techniques for evaluating electrical contact phenomena, new understanding of the contact phenomena, and new applications of electrical contacts are briefly explained.

In this paper, the distributions of two spectral intensities along the axis of an arc column of the breaking arc are measured by using a combination of a CCD color camera and an additional filter, and arc temperature and metal-vapor quantity are calculated, when copper electrodes interrupt circuits of dc 50 V/3.3 A and 5.0 A. As results; The spectral intensities of excited copper atoms are the strongest near the cathode and become weaker with distance from the cathode in the small number of breaking arcs. The spectral intensities become strong near the anode in the large number of breaking arcs. The average arc temperature in the cross-section of an arc column is high near both the cathode and the anode, and the temperature distribution in the cross-section of the arc column is high at the axis of the arc column, and the arc temperature along the axis of the arc column is high near both the cathode and the anode. The metal-vapor quantity is low near both the cathode and the anode, and it is much at the center of the arc column.

Some experimental results on the contact phenomena that have been observed with electrical contacts operated to break an inductive DC load current in nitrogen atmosphere and in air (laboratory atmosphere) are presented. When Ag, Pd and Cu contacts were operated to break an inductive DC load current in the range of 1.0 A to 3.0 A in nitrogen atmosphere, more stable contact resistance characteristics were obtained, as compared to the case where operated in air, or at least the occurrence of unstableness and increase in contact resistance was delayed. The arc duration in nitrogen atmosphere became shorter in general than in air, especially with the Pd and Cu contacts. Voltage waveforms of arc discharges in the Ag and Pd contacts operated in nitrogen atmosphere showed a relatively clear step-like transition from the metallic phase to the gaseous phase as compared to the case where operated in air, while the Cu arcs did not show such significant differences due to the surrounding atmosphere. Although any apparent differences on the contact surface conditions in connection with the surrounding atmosphere were not clearly observed after the switching operations, the anode mass change characteristics were found to be more significantly affected by the difference of surrounding atmospheres than the cathode mass changes. The obtained experimental results suggest that the difference in the surrounding atmosphere introduce some difference in the anode surface morphology, possibly through the deposition of arc products in different deposition patterns, which will then result in differences in the contact resistance characteristics.

At the sliding contact of brush and rotating slip-ring or commutator, it has been recognized that the brush wear is influenced by brush pressure, current density and atmosphere nearby contact part. However, little is known about the relation between brush wear and atmosphere condition in detail. In this paper, the experiments are carried out with a great attention to the effect of surrounding temperature and humidity on brush wear. The sliding part of brush and slip-ring is put on the sealed box and the atmosphere in the sealed box is kept on the specified condition by temperature and humidity control system. The brush wear, contact voltage drop and slip-ring surface morphology are observed after the sliding test. From these results, in both cases of the high humidity (nearby 80%) and low humidity (nearby 20%), the brush wear are large. And the brush wear rate is the lowest around 60% relative humidity. However, the characteristics of brush wear under the 15C is not similar to others. When the surrounding temperature is changed, in case of the 20% humidity, the brush wear increases with increasing surrounding temperature. On the other hand, in case of 80% humidity, the brush wear increases with decreasing surrounding temperature. Consequently, the results clearly shows that the temperature and humidity not only affect the brush wear but also change the condition of the film formation on slip-ring.

Silicone contamination due to SiO₂ caused by decomposition of silicone vapor is recognized as an undesirable phenomenon in electrical contact applications. The effects of silicone vapor adsorbed on the contact surface were examined by using micro relay contacts. The amount of SiO₂ formed by the decomposition of silicone vapor is expected to depend on the amount of silicone vapor adsorbed on the contact surface. Hence, first of all, an increase in the thickness of the film from the adsorbed silicone vapor as a function of exposure time was clarified for the static state of the surface. The thickness of the film of adsorbed silicone vapor increased in proportion to exposure time and saturated at a thin monolayer. Moreover, in this exposure period, the thickness was affected by the concentration of the silicone vapor. After the thickness of the molecular layer saturated, the thickness of the layer was not influenced by the concentration of the silicone vapor. Next, from these results obtained by examination of exposure in the static state, the following is deducible. The silicone molecule adsorbs easily on the contact surface during the opening period of making and breaking contacts as well as in the static state. As the time the contacts are open determines the exposure time, the amount of adsorbed silicone molecules depends on the switching rate (operation per second). Contact failure due to increases in contact resistance might be affected by the switching rate in a silicone environment. Accordingly, contact resistance characteristic was examined over a wide range of switching rates. It was found that number of operations up to contact failure was affected markedly by the switching rate. Namely, the number of operations up to contact failure decreases as the switching rate increases. However, once a very thin layer such as the monolayer has formed, the film thickness ceases to grow. Accordingly, after the very thin layer is formed, the occurrence of contact failure does not depend on the concentration of silicone and the switching rate.

The constriction resistance of an electric contact has frequently been obtained using a model of only one circular contact spot of radius a. However, cases of a single contact spot are extremely rare as the interface of the electrical contact actually consists of numerous micro-contact spots. A contact is therefore regarded as the aggregate of several micro-contact spots, which are referred to collectively as a cluster. The constriction resistance of the cluster can be calculated as the sum of the self-resistance and mutual resistance of individual micro-contact spots. In the present study, this model is expanded slightly for practical application by normalizing a previous theoretical formula. In order to obtain the constriction resistance for contacts between composite materials and mating metals, EPMA analysis is applied so as to determine real micro-contact spots. Theoretical calculations of the constriction resistance of multiple contact spots is shown to be reasonably consistent with experimental results. In addition, the contact of a composite material and a mating metal is shown to be made up of multispots. The current was recognized experimentally to flow more easily at micro-contact spots in the cluster periphery. These experimental findings coincide with simulation results obtained by theoretical calculations.

Sticking is one of dominant characteristics of reliability in relays for medium current loads from several amperes to several dozen amperes, which are used for relays for automobiles, industrial control units or power supplies of household electrical appliances. Correlations between the release failures due to sticking and contact characteristics such as arc discharges, material parameters and design factors in relays have never been always made clear. This puts difficulty in the way of reasonable development of contact materials and rational design of relays. So, dependence of electrical load conditions on sticking characteristics are investigated, using the Ag-CdO contacts which have had high practical use to relays for medium current loads. Furthermore, relationship among the sticking characteristics, arc discharge characteristics and contact surface properties after operations are studied. Mechanism of sticking is considered on the basis of those data. The results are as follows: (1) Sticking phenomenon occurs intermittently from initial operations and lasts to the end. (2) The µ + 2 σ value (the sum of the mean value and the integral multiple of the standard deviation of sticking force) increases in proportion to the circuit current. On the other hand, it has the maximum value at a circuit voltage, slightly less than the minimum arc voltage. (3) Factors causing the sticking are considered to be divided into direct factors and its root factors. It is considered that a dominant direct factor is welding, and that its root factor is bridge or welding by Joule's heat. On the other hand, the sticking force becomes rather lower as the circuit voltage increases, in the circuit voltage range where regular arc discharge occurs.

Using LiTaO₃ and LiNbO₃ single crystals, we wish to miniaturize a powerful ultrasonic vibrator. We studied the method of measuring mechanical fractures of resonators with good reproducibility and collected data on mechanical fractures of crystals due to high input electric power. Chip resonators with a 4 MHz and 8 MHz shear mode were selected for the test samples. The driving frequency was swept near the resonance frequency, the duration time was short enough to raise the resonant vibrations and the driving voltage increased in one-volt increments. The method is free from unstable temperature increases. Values of the fracture limit for the driving current were measured and transformed to mechanical vibration velocities. These showed a nearly normal distribution. It was a surprise that concavity in the crater was observed at the center of the 16 MHz LiNbO₃ resonator due to high input power. It was confirmed that the elastic fracture limit was latently very high for LiNbO₃ and LiTaO₃ single crystals.

Recently the applications of MEMS (micro electro mechanical systems) have made remarkable progress in many filelds. The optical application of MEMS is one of the most promising because it provides micro mechano optical devices, the key components for high-perfromance systems in optical communication networks and data storage devices. This paper disucces the impacts of MEMS techologies on optical systems. Furthermore, state-of-the-art exmaples of micro optical switches, pig-tailed tunable filters and two-dimensional MEMS optical scanners are described.

A tunable optical Fabry-Perrot filter was designed by setting a single-mode optical fiber normal to the diaphragm of a capacitive pressure sensor. The silicon diaphragm is deflected by the electrostatic force generated by applying a voltage to the capacitive electrodes. According to the movement of the diaphragm, the peak wavelength changed from 1546 to 1551 nm when applied voltage was increased from 20 to 50 V. The relationship of the wavelength change to the applied voltage was derived from the silicon diaphragm deflection theory. That measured change of the wavelength agrees well with the wavelength change calculated from this relationship. The commercial pressure sensors are expected to be able to be used as a tunable optical filter.

Several packaging methods for athermalization of Fiber Bragg Grating (FBG), which is equipped with negative expansion substrates, have been proposed. However, those methods have some deficiency resulted from the substrates such as complex structure or poor thermal expansion characteristics. In order to provide a suitable substrate for the athermalization of FBG, the authors have developed a Negative Expansion Ceramic Substrate (NECS) which has simple structure and suitable thermal expansion characteristics. NECS consists of polycrystalline β-quartz solid solution (Li₂O-Al₂O₃-nSiO₂, n>2), and has thermal expansion coefficient of about -65 to -85 10^-7/C, which is sufficient large enough for total compensation of the Bragg wavelength shift. No difference in the thermal expansion was observed between the specimen as prepared and the one on which an epoxy adhesive was applied. NECS is produced by means of a sintering method, which enables flexible design of the chemical composition. It was found that the hysteresis in thermal expansion of the NECS depends upon the chemical composition and crystalline structure. We decreased thermal expansion hysteresis by controlling the SiO₂ ratio in the composition and the crystal grain size. We confirmed that the temperature dependence of the FBG mounted on the NECS with an epoxy adhesive was decreased to -2.3 10^-3 nm/C from 10.0 10^-3 nm/C, in good agreement with the calculated value of -2.6 10^-3 nm/C. The hysteresis in Bragg wavelength shift was less than 0.03 nm, that is sufficiently small enough for practical use. It was confirmed that NECS has suitable thermal expansion characteristics for the athermalization of FBG.

Aiming at lower cost and further miniaturization, we developed a new optical coupling system for use as an optical interface of a parallel optical interconnect module, called ParaBIT-1. It consists of a new-structure 24-fiber bare fiber (BF) connector whose main parts are made of molded plastic and a 24-channel optical coupling component using new polymeric optical waveguide film. To prevent bare fibers from breaking, the BF connector plug has a fiber protector. This BF connector can be joined by direct physical contact between bare fibers in fiber guide holes with a 250-µm pitch. The buckling forces of the fibers themselves secure the physical contacts. The average measured insertion loss of the 24-fiber BF connector was 0.05 dB, and the return losses were over 35 dB. The optical coupling components are composed of a 24-ch polymeric optical waveguide film with 45 mirrors and the 24-fiber BF connector interface, and can be assembled by passive alignment. The high thermal stability of the film allows soldering, and the film is fabricated by direct photo patterning. The average insertion losses of the components for transmitter and receiver modules were 1.28 and 1.35 dB, respectively.

We report a directly deposited dielectric multilayer onto an end face of a fluorinated polyimide optical waveguide by ion beam sputtering process. This dielectric multilayer (Ta₂O₅/SiO₂) acts on a wavelength separation filter which passes 1310 nm wavelength signal and reflects 1550 nm wavelength signal.

Ferromagnetic Co₇₇Cr₂₀Ta₃ layers were deposited on a Pt seed layer by a facing targets sputtering apparatus. The Co-Cr-Ta and Pt crystallites revealed better c-axis orientation at a substrate temperature T_s above 200C. Relatively high perpendicular coercivity H_c⊥ of 2.5 kOe was obtained for the bilayered film with a Co-Cr-Ta layer thickness, δ_Co, of 50 nm deposited at T_s of 250C. Although the Co-Cr-Ta/Pt medium with δ_Co of 100 nm exhibited lower recording density than a Co-Cr-Ta/Cr longitudinal one, its noise level became small at the high-density recording range. Measurement of the anomalous Hall voltage clarified that the bilayered film with δ_Co as small as 30 nm revealed larger perpendicular magnetization than the single layer. The Pt seed layer is effective for depositing thin ferromagnetic Co-Cr-Ta layers below 100 nm in thickness.

Magnetic layer thickness dependences of magnetic properties are investigated for Co-Cr-Pt polycrystalline thin films with different Cr-alloy underlayers (Cr-Ti, Cr-W, Cr-Mo, Cr-V, Cr-Mo-V). The specimens with Cr-Ti, Cr-V, and Cr-Mo-V underlayers show higher coercivities by about 30% and lower activation magnetic moments than those with Cr-Mo underlayer. The effective diameter of activation volume increases by 10-20% when the magnetic layer thickness is decreased from 12 to 8 nm. Temperature dependences of magnetic properties are also determined and discussed by referring to the data obtained using single crystal magnetic thin films with similar composition.

Post annealing treatment for CoCrPt magnetic thin films were tried in different thermal conditions, by changing the time of annealing procedure. Coercivity (H_c) improvement was achieved in annealed sample compared with those as deposited, in which as high as 5.2 kOe has been attained. To clarify the mechanism of annealing treatment on the magnetic properties, X-ray diffraction (XRD) spectrums of those samples and their magnetic properties were carefully studied. Co and Cr lattice parameters were separately calculated from different crystal lattice plane. It was found that a axis lattice spacing of Co hexagonal structure increases monotonically with increased annealing time. Variation of Co hcp peaks significance may due to Cr or Pt redistribution in the crystal grains and its boundaries. Combined with the grain size analysis of Co-rich area by X-ray diffraction peak broaden width, which was not very consistent with the result obtained from other's TEM and AFM studies, Cr diffusion was suggested to be the governing factor at short annealing time region. Co-rich grain growth should also be applied to explain the variation of magnetic properties in longer post annealing.

Triple-layer CoCrPt magnetic thin films with different bias configurations were fabricated by DC magnetron sputtering on CrV and glass substrate. In-plane coercivity (H_c) showed an increase for those films with bias sputtered CoCrPt layer. The in-plane coercivity (H_c) was optimized in NB-B-NB type film prepared with substrate heating at 300C (NB: no bias and B: rf bias applied in sputtering). Better in-plane crystal texture was observed in NB-B-NB type film by XRD and this is believed to be the main reason for the coercivity improvement. The other resource for the coercivity improvement was due to the decoupling of intergrain magnetic interactions. This was discussed accordingly to the results obtained from TEM, MFM and SIMS depth profiling.

Co-ferrite thin films have been fabricated on Corning glass substrates by a chelating sol-gel process. Structural and magnetic properties of the films have been studied as a function of annealing temperature using an X-ray diffraction (XRD) and a vibrating sample magnetometer. XRD results revealed that most of the Co-ferrite grains were randomly oriented. Rapid annealing (RA) and standard annealing (SA) processes were used for the variation of heat treatment and the characteristic comparison. Coercivity was changed with the thermal condition and the magnetization increased with the soaking time. With prolonged soaking time, however, the coercivity decreased due to the diffusion of cations from the glass substrate. RA in the preparation of Co-ferrite thin films was effective for preventing interdiffusion at interfaces and for forming a single phase in the case of reduced soaking time. A yttria stabilized zirconia (YSZ) buffer layer between the Co-ferrite layer and the substrate was effective for improving the magnetic properties of the films at higher temperatures. It was observed that Co-ferrite thin films were composed of grains typically 35 nm in size and their rms roughness was approximately 1.3 nm. The saturation magnetization of the thin films by subjected to rapid annealing at 900C for 150 seconds was 400 emu/cm³ and the coercivity of the films was approximately 3000 Oe.

SiO₂-added Ba ferrite (BaM:SiO₂) films were prepared using BaFe₁₂Si_0.18O_x targets. BaM:SiO₂ films exhibited perpendicular coercivity H_c⊥ of over 4.2 kOe and squareness ratio of 0.83, although saturation magnetization M_s decreased by about 15%. The angular dependence of coercivity H_c and remanent coercivity H_r were investigated to explain the magnetization reversal mechanism. Intergranular interactions in the films were also evaluated. The magnetization reversal mode of Ba ferrite films with and without SiO₂ additives is not coherent rotation but appears to be the curling mode. The origin of the high coercivity of BaM:SiO₂ films is different from that of Al-substituted Ba ferrite films. It seemed that SiO₂ additives and the defects caused by them decreased M_s and prevented the expansion of reversed domains in the magnetization reversal process, similarly to some pinning effects, and caused high H_c⊥ of 4.2-5.1 kOe in BaM:SiO₂ films.

Medium noise is the dominant noise in ultrahigh density disk recording systems. The peak, width and jitter noise are analyzed by micromagnetic simulations. Four different media, with a fixed grain size of 135 and a coercivity of 2900 Oe, are chosen for medium noise analysis. The linear recording density is increased from 340 KFCI (Kilo flux-changes per inch) to 750 KFCI, while the area density goes up from 14.3 Gb/in² to 31.5 Gb/in². The peak-amplitude noise is studied by the distribution of the peak magnetization M_p in each bit. The distribution of M_p develops from a delta-function around the remanence M_r at low densities to a flat distribution at extremely high densities. It is found that the transition a-parameter is no longer proportional to the square root of M_rδ, as given in the William-Comstock approximation. The peak-jitter noise in the read back voltage is analyzed by the percentage of the transition jitter in a bit length.

As the track becomes narrower, the effects of track edge become more significant. These effects, such as the amplitude reduction, variations in the shape of the isolated pulse, the partial erasure and the amplitude asymmetry, are dependent on head/disk combination and the off-track position. These relationships are discussed in detail in this paper. More importantly, an off-track model is proposed to study the off-track BER performance for the head with narrow track width. The BER performances of EPRML channel for different off-track cases and different head/media combinations are studied based on this model. Simulation results have proved that this model is a useful tool for simulation of system performance.

It is known that amorphous continuous media such as TbFeCo have extremely low noise characteristics because of the structure of the continuous grainless medium. There is great interest in the use of amorphous media in magnetic recording. This study investigated the recording characteristics of the amorphous continuous medium by computer simulation using the Landau-Lifshitz-Gilbert equation. It was shown that the transition of the continuous medium is very sharp and the noise level very low. It was also shown that the recorded magnetization patterns of the continuous medium are distinct at the high recording density of 380 Gbit/inch². We concluded that the continuous medium has great potential for use in ultra-high density recording.

A Co/Pd multilayer film with perpendicular coercivity of 2.2 kOe and remanence ratio (SQ) of unity was prepared by electron beam evaporation in vacuum. In the MFM image of signal patterns of 4 kFRPI recorded using a ring-type MIG head, many reversed domains were observed. However, when the film was magnetized along the film normal direction using an electromagnet (H = -13 kOe), only few reversed magnetic domains were observed, which was consistent with SQ = 1. Therefore, the reversed domains in the signal patterns were induced in the recording process. dc erasing was also studied with the magnetic field inclined to the film normal. The domain structures were almost the same when the perpendicular component of the field was kept constant while the in-plane component was varied, implying that the in-plane field component did not contribute to the formation of the reversed domains. It was found that reversed magnetic domains were easily induced even by a weak reversing magnetic field applied along the film normal. Hence, although the possibility of an insufficient recording head field was not excluded, it seemed more likely that the reversed magnetic domains in the signal patterns were caused by some erasing effect of the ring-type MIG head. For a Co/Pd multilayer medium with a negative nucleation field in the perpendicular M-H loop, a stronger reversing field was needed to induce the reversed magnetic domains. No reversed magnetic domains were observed in the MFM image for signal patterns of 4 kFRPI in this medium, indicating that a negative nucleation field was effective to suppress the formation of reversed magnetic domains.

The origins of baseline shift were discussed considering the measured off-track properties using a wide write head with track widths of 97 µm and a narrow read head with track widths of 2.7 µm. The baseline shift increased when the read head was moved close to the track edge. Beyond the track edge, baseline shift decreased to negative values. The impulse response curve of the MR head to the perpendicular magnetization was estimated from the readback waves of the MIG head and the MR head. The response curve depended on the recorded track width. When the recorded track was narrow, the undershoot of the response curve was smaller than that of the head field based on the 2D double-gap ring head model with infinite track width. This small undershoot induces sensitivity of the DC-component of the recorded magnetization and causes the baseline shift. To calculate the readback waves of the MR head for single-layer perpendicular recording media with narrow-track recording, the effect from stray field at the recorded track edge must be included in the impulse response curve of read head.

The medium noise of single-layer perpendicular recording media is known to be suppressed by reducing the magnetic domain size and achieving a higher squareness ratio (M_r/M_s = SQ) in the perpendicular M-H loop. The media with smaller domain sizes exhibit a small slope at H_c in the M-H loop due to exchange de-coupling between adjacent grains, which requires a sharp head field to acquire high recording performances. Reduction of the medium thickness would be effective for recording as only a sharp head field near the head surface could be used. Thus, the effects of reduced recording layer thickness in single-layer perpendicular recording media on read/write performances were investigated using Co/Pd multilayer media with a small loop slope having thickness, δ, of 46, 22 and 10 nm, and with a steeper loop slope having δ of 40 and 10 nm. It was found that the recording performance on small loop slope media could be improved in terms of signal level by reducing the recording layer thickness, which indicated that the recording on the media was sensitive to the recording head field. The results in the simulation analysis were similar to those obtained experimentally, indicating that the change in recording layer thickness could be mainly regarded as that in the head-medium spacing. Thinner media with steeper loop slopes could acquire a narrower dipulse width. The recording resolution of the present media, however, was determined under the influence of the domain structure and the size. Finally, for media with small loop slopes, the same SNR of 38 dB at 100 kFRPI was obtained for thicknesses of 22 and 10 nm, which was larger than that for a thick medium of 46 nm thickness by 8 dB. For both the steep loop slope media, the obtained SNR was 35 dB at 100 kFRPI.

As technology moves at an annual area density increase rate of 80-120% and channel density moves beyond 3, micro-fluctuation of media recording performance and the homogeneity of media's recording capability become serious reliability concerns in future high density magnetic recording systems. Two concepts are proposed in this work for the characterization of the micro-recording performance fluctuation at high bit and channel densities: recording performance roughness analysis and dynamic magnetic roughness analysis. The recording performance roughness analysis is based on an in-situ measurement technique of the non-linear transition shift (NLTS). Relationship between the performance roughness and the roughness of dynamic magnetic parameters are studied. Results of experimental investigations indicate that the NLTS based performance roughness analysis can reveal more details on media's recording capability and the capability fluctuation--the macro and micro fluctuation of recording performance. The dynamic magnetic roughness analysis is read/write operation based and can be used to characterize the macro and micro fluctuation of media's dynamic magnetic properties. The parameters used for the analysis include media's dynamic coercivity and the dynamic coercive squareness. Here, "dynamic" refers to the dynamic performance measured at MHz frequency. The authors also noticed in their technology development process that further methodology development and confirmation are necessary for media's dynamic performance analysis. Therefore, the work also extends to the accuracy analysis of the playback amplitude based methods for the analysis of the dynamic coercive squareness and dynamic hysteresis loop. A method which is of smaller testing error is identified and reported in this work.

Future high density magnetic recording requires a nanometer spaced head-slider interface, high track seeking velocity and high spindle speed. Such a combination greatly increases the likelihood of slider-disk and slider-particle-disk impact. Furthermore, the impact can generate high flash temperature and leads to data reliability problems, such as partial or full data erasure. This work report a method to conduct controlled experimental investigations into the possibility of such a data erasure even when the temperature is far below the Curie temperature. Results indicate that the high density magnetic transitions are of high likelihood of being affected by the flash temperature. Investigations also extended to micromagnetic modeling of the flash temperature effect. Results suggest that thermally induced local stress can play important roll in the data erasure process. Modeling results also exhibit that smaller grain size and higher recording density are also of higher likelihood of getting the transitions being affected by the flash temperature.