Search

A resistive-switching solid-state brain-neocortex-like device for advanced non-volatile logic applications was developed. This device can be used as a reconfigurable logic device that is operated by electrically connecting and disconnecting pairs of electrodes. This paper reports for the first time the experimental evaluation results of a three-terminal test element group as the unit for a solid state brain neocortex-like device. The solid-state brain-neocortex-like device was experimentally evaluated as unit in a three-terminal test element group. The evaluation results show that the neocortex-like reconfigurable switching, in particular, fringe-electric-field-induced switching is possible in the device.

To obtain minimum overwrite jitter after 104 overwrites, the cause of degradation of readout waveforms after 104 overwrites was investigated by transmittance electron microscopy (TEM). To decrease the temperature of the recording film at the track center during recording, an Al-alloy double-reflective-layer structure is proposed. Two relationships, one between the thermal conductivity of the first reflective layer and the temperature of the recording film during recording and the other between the thermal conductivity and the readout waveforms after overwrites of more than 105 times, were investigated using thermal simulation and a digital versatile disk (DVD) disk tester. The optimized disk has a minimum overwrite jitter after 105 overwrites at a linear velocity of 6 m/s.

A Ag–Ge–Sb–Te recording film was developed, and its chemical composition was optimized to minumize overwrite jitter. The cause of the jitter was investigated by measuring the crystallization ratios and by transmission electron microscopy. It was found that the overwrite jitter increased with a shortage of Ge or Ag because the crystallization speed increased when these elements were added, while it increased with an excess of Ge or Ag because the crystallization speed decreased when these elements were added. A model based on the atomic bond distance and the strength of interatomic interactions in the crystal was devised. The model can be used to explain the mechanism by which a slight change in the chemical composition of recording films changes the crystallization speed. It was confirmed that the proposed disk with recording film having a small amount of Ag had the minimum overwrite jitter (under 10%).

We have introduced a tungsten oxide film to a layer-selection-type recordable optical disk (LS-R) as an inorganic electrochromic (EC) film. The EC film showed a large transmittance change in a wide wavelength range. Layer selection was demonstrated with a dual-layer disk whose spacing was 0.3 µm, and the capacity of a 20-layer LS-R was estimated to be 1 TB.

A multi-information-layer optical disk system using electrochromism for layer selection has been studied. The advantages of this disk system are its large capacity, high sensitivity in recording, and use of a relative simple hardware. Reading and writing on an electrochromic information layer were successfully performed, and the results suggested an increase in transmittance and the degradation of electrochromism in the recorded area. This fact demonstrates the feasibility of recording on electrochromic layers and the electrical layer selection in the proposed multilayer disk. Also a disk evaluation apparatus was developed by installing an apparatus using ball bearings for voltage transfer to a multilayer disk, and voltage application to a disk was confirmed.

The signals obtained from dual-layer optical disks were analyzed experimentally and theoretically with emphasis on reducing layer cross talk (LCT) and spherical aberration (SA). Using the dual-layer phase change optical disk, the DC element of the LCT was measured and phase change marks were written on both layers. Diffraction calculations were used to explain the experimental results and to determine the amount of LCT and signal degradation caused by SA as functions of spacer layer thickness and optical detector size. Analytical methods to estimate LCT and SA were proposed, and their predictions turned out to agree well with the experimental and diffraction calculation results. These findings indicate that for a blue laser, the conventional techniques cannot simultaneously keep the LCT and SA to within practical values. Accordingly, designs for disks and drives for dual-layer optical disks are discussed.

We have applied the blue-violet laser in developing several technologies for the next-generation digital versatile disk (DVD). We are convinced that four items, i.e., large capacity, high data-transfer-rate, cyclability, and portability, are equally important. We have set targets for capacity and data-transfer-rate. Separate development processes have been carried out in the fields of optical heads, systems (servo-mechanisms, read/write channel and signal processing) and basic subjects and combined the results to achieve our targets. Basic subjects that cross these technical fields and have previously been neglected were studied to find solutions to new problems that arise with next-generation requirements.

Finite-difference time-domain (FDTD) simulation was used to determine the amount of absorption of light propagating inside a land/groove optical disk. The results showed that three-dimensional geometry influenced absorption. Furthermore, heat conduction inside the disk depended on its geometry, so the temperature profiles of land and groove tracks were not equal. Therefore, the spatial and historic profiles of temperature must be investigated in three dimensions. These temperature profiles can then be input into a phase-change simulator in order to carry out a simulation of the process of writing marks in land and groove tracks. To predict the optical and thermal effects of a land/groove structure on the writing process, we integrated an FDTD and phase-change simulation. The integrated simulation effectively evaluated the differences between the marks formed in land and groove tracks. As well, we applied the FDTD simulation to a blue-laser recording and found that groove-track recording showed higher light convergence than land-track recording. This inclination was explained the convex/concave effect of the structure of the disk surface.

Nanostructures of sputtered thin films consisting of cobalt oxide and soda lime glass were analyzed. Transmission electron microscope showed the thin film including 9.0 mol.% Co3O4 had nanosize lamellar structure consisting of two amorphous phases. The thin film containing 82.5 mol.% Co3O4 consisted of nanosize columned Co3O4 particles with an amorphous grain boundary phase. Average grain size was 10.3 nm and standard deviation of the grain size was 1.97 nm. A relation between nanostructure and composition of the films, and a mechanism of formation of the nanostructures were discussed in terms of solvability of cobalt ion in the glass matrix.

Simulations of the movement of the crystalline/amorphous boundary during the writing process were performed. The movement of the boundary was traced by drawing arrows representing the crystallization direction and speed. The lines traced by these arrows made a good match with streamlines of crystal growth shown in a transmission electron microscope (TEM) image. We have also introduced the idea of a "recrystallization ring" to explain the mark-formation mechanism by investigating the temperature dependency of the crystallization growth rate. The simulations for GeSbTe and Ag–InSbTe recording materials illustrate the differences in the crystallization mechanisms of these materials.

DVD-RAM is a rewritable DVD disk which has a capacity of 5.2GB. DVD-RAM disk can be recorded an MPEG2 compressed digital movie that is 2.5 hours in length, and is planned to be readable in DVD-ROM drive. DVD-RAM drive can also read CD-ROM disk and DVD-ROM disk.

The formation and observation, with reflected light, of 60‐nm‐diam phase‐changed domains in a thin GeSbTe film using a scanning near‐field optical microscope with a 785 nm wavelength laser diode is demonstrated. The dependence of the domain size on incident laser power was obtained, and the size changed from 150 to 60 nm in diameter with incident power of 8.4–7.3 mW in the probe. At the threshold power of 7.3 mW, the film temperature rose to around 180 °C to partially phase change the local area of the film from amorphous to crystalline. A detected reflectivity increase due to phase change in the formed domain was 8%–2%. The observing (reading) was performed with an incident laser power of 0.2 mW, which corresponds to 10−2–10−3 times less than in a magneto‐optical recording. The incident laser power shows that the phase change reading using the reflection scanning near‐field optical microscope has the potential to read the recorded bit at a speed over 10 MHz.

We demonstrate 80 nm diameter bit recording for the first time using a phase change recording film and a reflection scanning near-field optical microscope with a 785 nm wavelength laser diode. The sample structure was a 20 nm thick ZnS-SiO 2 protection layer/30 nm thick Ge 2 Sb 2 Te 5 recording film/150 nm thick ZnS-SiO 2 protection layer/polycarbonate substrate. Writing was performed with pulsed laser light of 8.4 mW for 5 ms and 0.5 ms, and 8.0 mW for 5 ms. Written bits were observed in reflection by illuminating a small light of 0.2 mW. In this form of recording, a formation of phase change domains of about 50 nm in diameter is expected if the surface deformation is suppressed. Our results indicate the possibility to achieve an ultra-high recording density of more than 100 Gb in -2 .

Scanning near-field optical microscopy (SNOM) was applied to phase-change (PC) mark writing to investigate the potential of ultrahigh density data storage. GeSbTe, one of the typical PC media, was used as a recording layer. Using a laser diode (LD) with a wavelength of 785 nm as light source, crystalline marks with a minimum size of ∼ 80 nm in diameter were successfully written in the amorphous GeSbTe film with pulse conditions of 5 ms and 0.5 ms and 8.4 mW inside the probe. The detected power in observation of the marks was 10 2 –10 3 times as high as that in magneto-optical (MO) observation.

再生時間10ns/bitでSN比20を得るという実用的条件での光化学ホールパーニングメモリーの実現可能な記録密度を,理論と実験を併用して求めた。1度,深くあいたホールが,多重ホール形成により埋まる現象(レーザー誘起ホールフィリソグ)の程度が記録密度を決める主要な要因であった。ホール間隔が狭まるにつれて,ホールフィリングは著しくなった。このようなホールフィリングは今まで知られていない。この現象のため,記録密度を最大にする多重度(あるいはホール間隔)と,1ホールあたりの記録光量の組み合わせが存在することがわかった。最もホールフィリソグが起きにくいとされるポリビニルアルコール中に分散させたスルホン酸塩置換型ポルフィリンを記録媒体として,この最大記録密度を求めた。温度20Kのときには多重度130(ホール間隔0.21nm),記録光量29mJ/cm2/holeで最大記録密度1.OGbit/cm2が得られる計算となった。これをもとに液体ヘリウム温度(42K)で現状で最も適当と思われる材料を用いた場合の記録密度を換算すると,20Gbit/cm2弱になる。ここで見られたレーザー誘起ホールフィリングのより起きにくい材料を探すことが,記録密度を上げるためには最も重要である。

We report a novel resistive switching ion-plug memory (IPM) with a dual-layered structure containing a solid electrolyte layer (supply layer) that has Cu ions and a resistive switching layer (memory layer). By adopting this structure, IPM achieved higher endurance and longer retention time compared to previously reported solid electrolyte memory because excess Cu deposition was prevented. The conductive path of Cu with a 20 nm was observed by a cross sectional transmission electron microscope analysis. Generation/rupture of the path enables local resistance switching at diameters smaller than 32 nm. A set/reset operation that takes 30 ns and an endurance of 109 cycles were presented. IPM is a promising candidate for high-density memory for 32-nm technology node and beyond.

We have fabricated a phase change memory using doped In-Ge-Te to improve the data retention required for industrial and automotive use. This chalcogenide features higher thermal stability as well as denser texture and improved adhesion. The memory cell using doped In-Ge-Te provided a larger read margin and better data retention than conventional Ge2Sb2Tes, and we demonstrated 10-year retention at temperatures above 150degC, which is the highest temperature ever reported.

Phase-change memory is promising because it has a simple structure and has scalability that originates from its unique operating mechanism. However, the programming current should be reduced in accordance with the scaling of cell size [1,2]. We previously reported PCM (Phase Change Memory) cells that operate under 1.5-V/100-μA writing pulses [3, 4]. This PCM had a cell structure composed of 180-nm-W (tungsten) bottom contact to an O-GST (Oxygen-doped GeSbTe) film. Its low-power characteristic is suitable for 0.13-μm generation embedded applications. In the present study, we introduced a new W/O-GST/TaO/W cell structure and found further decrease of programming current the improved stability in the fabrication process. We analyzed the mechanism by which oxygen in GST and the additional TaO layer reduce the power consumption during SET/RESET operations.

A novel memory cell for phase-change memories (PCMs) that enables low-power operation has been developed. Power (i.e., current and voltage) for the cell is significantly reduced by inserting a very thin Ta2O5 film between GeSbTe (GST) and a W plug. The Ta2O5 interfacial layer works not only as a heat insulator enabling effective heat generation in GST but also as an adhesion layer between GST and SiO2 underneath. Nonetheless, sufficient current flows through the interfacial layer due to direct tunneling. A low programming power of 1.5 V/100 muA can therefore be obtained even on a W plug with a diameter of 180 nm fabricated using standard 0.13-mum CMOS technology. In addition, the uniformity and repeatability of cell resistance are excellent because of the inherently stable Ta2O5 film properties

We demonstrated the operation of phase-change memory cells that enabled 1.5-V/100-muA programming through a tungsten-bottom-electrode contact with a diameter of 180 nm. This is the lowest power ever reported. This was achieved with oxygen-doped GeSbTe, and resulted from the high electric resistance of the germanium oxides in this material. Germanium oxides were also estimated to restrain the growth of crystal in GeSbTe, and our cells maintained a 10-year thermal lifetime at 100 degC

This paper presents a measurement method for 1 transistor-1 resistance (1T1R), phase-change memory (PCM) devices. We fabricated a novel PCM test structure with an internal voltage measurement point, and we monitored the voltage drop between 1T and 1R. The voltage drop was accurately converted to the PCM programming current. This test structure enabled us to measure programming current of less than 100/spl mu/A with a width of 100ns. This method is essential for measuring the low-power operation of PCMs and other nonvolatile memories.

We introduced an inorganic electrochromatic layer for layer selection recordable optical disk (LS-R) by applying voltage. The material showed a large transmittance change in a wide wavelength range. The cross-talk between layers was sufficiently low.

Characteristics of a phase‐change optical disk using a (Ge–Sb–Te)‐(Cr–Te) recording film containing a high‐melting‐point component Cr–Te are studied. The high‐melting‐point component Cr–Te precipitates in the recording film, and prevents a material flow of the recording film during repeated rewrites in which the recording film is melted. There is no drawback such as noise increase by the addition of Cr–Te. Thus the phase‐change optical disk using this recording film shows very small distortion in the reproduced signal wave form even after 2×104 rewrites of high‐density recording signals that are liable to cause the material flow by forming long and short recording marks on the disk. With a phase‐change optical disk, it is easy to overwrite (rewrite without prior erasure) information, which makes it highly suitable for digital recording of motion pictures and sound. They are expected to be used as rewritable compact disks, rewritable CD‐ROM disks, rewritable video disks, and small recording media for personal computers.

A multi-information-layer optical disk using electrochromism for layer selection is proposed. DVD-like write/read has been achieved using the same disk-substrate and optics as DVD on a layer colored by voltage application. Full text article is not available.

High-speed and high-density recording using blue laser appears to be the main stream for the next generation of phase-change optical disks. Sb-rich phase-change recording materials present one option as a medium for high-speed recording. We have estimated the crystal growth rate (CGR) of two variants of the GeSbTe recording material, for 100 Mbps recording (type 1) and Sb-rich material for 300 Mbps recording (type 2), by comparing the simulation and experimental results. We studied the characteristics of the materials in writing and erasing for high-speed recording. We applied our phase-change simulator (PCS) to search for the relationship between the linear velocity of the rotating disk and the formation of amorphous material in the recording layer. In this study, we used the optical system with NA = 0.85, /spl lambda/ = 405 nm and disks with 320 nm track pitch.

This paper discusses a crystallization model that takes difference of covalent bond and ionic bond into consideration. Ionic bond makes crystallization easier than covalent bond because ionic bond is more flexible than covalent bond. The diameter and spaces around large minus-ions should also be taken into consideration. Elements••having electronic negativity far from that of Te or Sb has a tendency to form ionic bonds. For example, Tb and In are considered to make chemical bonds having more ionic characteristics than Ge. In the case of already reported Sn or Bi addition, large ion diameter seems to increase crystallization speed.

Designs of drives and disks for dual-layer optical disks are discussed based on a newly proposed theoretical model to estimate the layer cross talk approximately.

Phase-change optical discs are common media for audio-visual equipment and computer peripherals. In such recording media as the DVD-RAM, amorphous marks are written on the crystalline matrix by controlling the power of laser beam pulses. Due to the need for higher capacity optical disc drives, track pitches are becoming narrower, so that the thermal effects of adjacent tracks are no longer negligible. This is also a problem in the track direction. Achieving higher density in drives requires smaller marks on the media, leading to shorter intervals between pulses. The thermal effects of the following pulses change the shape of the amorphous mark made by previous pulse. That is, the trailing boundary of an amorphous mark is re-crystallized by the heat of the following pulses. Close attention to the re-crystallization of the recording material is necessary to control the mark shapes on phase-change optical discs. We have simulated the movement of the crystalline/amorphous boundary during the writing process. We have also developed the concept of a 're-crystallization-ring' to explain the mark-forming process. The movement of the boundary was traced by drawing arrows to represent the crystallization direction and speed. The trace lines of these arrows matched the streamlines for crystal growth as observed by TEM. Simulation was done for both GeSbTe and Ag-InSbTe recording materials.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Phase change mark simulator is investigated. Nucleation, crystal growth, and re-crystallization at amorphous/crystal boundary are taken into consideration. Crystallization is evaluated with 3-dimensional thermal analysis. Mark shapes of experiments and simulation are in good agreement. Amorphous mark forming process was analyzed with the simulator.

High-speed recording and read-out were carried out under the condition of numerical aperture (NA) 0.65 and substrate thickness 0.6 mm using a blue-violet laser of 405 nm. Using a GeSbTe phase change material of the crystal nucleus generation dominant type, we obtained a carrier-to-noise ratio (CNR) of 50 dB with 0.24 µm mark and a DC erase ratio of 30 dB at a velocity of 18 m/s. It was proven that the realization of the 100 Mbps data transfer rate was possible by optimizing record compensation.

Semiconductor blue-multi-laser-diode annealing (BLDA) for amorphous Si film was performed to obtain a film containing uniform polycrystalline silicon (poly-Si) grains as a low temperature poly-Si (LTPS) process used for thin-film transistor (TFT). By adopting continuous wave (CW) mode at the 445 nm wavelength of the BLDA system, the light beam is efficiently absorbed into the thin amorphous silicon film of 50 nm thickness and can be crystallized stably. By adjusting simply the laser power below 6 W with controlled beam shape, the isotropic Si grains from uniform micro-grains to arbitral grain size of polycrystalline phase can be obtained with reproducible by fixing the scan speed at 500 mm/s. As a result of analysis using electron microscopy and atomic force microscopy (AFM), uniform distributed micro-poly-Si grains of smooth surface were observed at a power condition below 5 W and the preferred crystal orientation of (111) face was confirmed. As arbitral grain size can be obtained stably and reproducibly merely by controlling the laser power, BLDA is promising as a next-generation LTPS process for AM OLED panel including a system on glass (SoG).

Thermal deformation is calculated to clarify the cause of material flow due to multiple overwriting in a phase-change optical disk. The results suggest that the molten material of the recording layer moves along the recording track by thermal deformation of layers. Moreover, the direction of the material flow depends on the Al reflective layer thickness.

Phase-change random access memory (PRAM) technology is reviewed. PRAM uses the phase change between the amorphous state and the crystalline state caused by Joule heating as its memory mechanism. A change in electrical resistance owing to a phase change is detected by a small electric current. The merits of this approach are that the resistance change is more than one order of magnitude, and its simple structure decreases the number of steps in the manufacturing process. Suppression of reset current for the change from the low-resistance crystalline state to the amorphous state and an improvement in durability against set-reset cycles and high-temperature operation will ultimately be achieved.

A microcellular recording film is proposed to prevent material flow due to multiple overwriting in phase-change opticaldisks. The GeSbTeCo recording film, divided into cells of approximately 20-30 nm in diameter, is prepared by sputter-etching using a Ti polycrystalline film as a mask. Reversible phase-change occurs in the microcellular GeSbTeCo film.Moreover, single beam overwriting is achieved at a linear velocity of 7 m/s. 1. INTRODUCTION Single-beam overwriting up to 1O times has been achieved in a phase-change optical disk with a GeSbTeCo recording 1 frjor limiting factors of the number of overwriting cycles include local thickness change and void generation in therecording il3 This indicates that the melted recording film material gradually flows along the recording track due to therepeated laser irradiation.To prevent the material flow due to multiple overwriting, we propose a microcellular phase-change film divided into fewtens nm diameter cells surrounded by a protective layer. A cross section of a disk having a microcellular recording film isshown schematically in Fig. 1.

Single-beam overwriting up to 105 times has been achieved in phase-change optical discs with GeSbTeCo recording films.1 Major limiting factors of the number of overwriting cycles include local thickness change and void generation in recording films.2 This indicates that the film's melted material gradually flows along the recording trucks owing to the repetitions of laser irradiation.

not Available.

We experimentally studied an optical disk with a large capacity and high data-transfer rate that can record high-definition television signals. A high rotation speed was used to achieve the high data-transfer rate. Using Ge–Sb–Te phase change material, a carrier-to-noise ratio of about 50 dB was achieved at a linear velocity of 15–30 m/s with a 0.4-µm-long mark. High-speed crystallization was necessary to erase recording marks. Therefore, by appropriately designing layers that assist nucleation, we obtained a DC erase ratio of 29 dB with a 0.4-µm mark and 1-mW power margin for over-25-dB erase ratio at a linear velocity of 18 m/s. Furthermore, the 0.4-µm mark-space repetition jitter was less than 7% even after 1000 cycles. A data transfer rate of 60 Mbps was obtained by optimizing the write strategy using a multi-pulse with an optical system equivalent to that of current digital versatile disk (DVD).

The read-out signal simulation of an optical disk having a cobalt-oxide super-resolution film was performed to find the optimum condition for a higher recording density of the super-resolution disk. A simple model of the complex refractive index change in a super-resolution film due to its temperature was applied, which can explain experimental data. It was found that this type of super-resolution disk must increase its reflectivity as the incident laser-beam intensity rises. To confirm this experimentally, a new super-resolution disk with an added Ge–N layer was prepared, and its read-out signals were measured, which agreed well with the calculated results.

A new super-resolution material for optical disks is proposed which contains cobalt oxide as a main component and shows a refractive index change upon irradiation of a laser beam. This new material is different from the ones already proposed for super-resolution in that it is durable against high-power laser irradiation and thus is applicable to rewritable optical disks as well as read-only (ROM) disks. This paper reports fundamental properties of this material, C/N improvement of ROM and phase-change disks with this material, and its durability against continuous many-time readout. The potential of this technique is discussed.

We present for the first time a nanometer-sized phase-change recording using a scanning near-field optical microscope (PC-SNOM recording). The recording experiments were performed with a SNOM using a 785-nm-wavelength semiconductor laser diode, shear force detection for gap control and reflected light detection for observing the domains (reading). The recording media of ZnS·SiO2(20 nm)/GeSbTe(30 nm)/ZnS·SiO2(150 nm)/polycarbonate substrate were used. The writings were done at laser powers of 8.4–7.3 mW in the probe for pulse widths of 5 or 0.5 ms. As a result, we obtained a minimum recorded domain size of 60 nm in diameter. This size shows a potential to achieve an ultrahigh density PC-SNOM recording with about 170 Gb/in2. A possibility of achieving high speed readout for the future data storage is also discussed.

Double-reflective-layer structure disks with recording film containing a high-melting-point component that does not melt during recording are studied. Cr–Te is chosen for the high-melting-point component to be added to Ge–Sb–Te recording film to suppress a recording film material flow. A Si–Al double-reflective-layer structure has the advantage of increasing the material flow stopping power margin. The structure is also effective in preventing deformation of the recording marks due to the difference in light absorption between the crystallized region and the amorphized recording mark. A Si–Al double-reflective-layer-structure disk with Cr–Ge–Sb–Te recording film shows very little distortion in the reproduced signal waveform even after 104 overwrites of pulse-width modulation (PWM). This makes it suitable for high density recording as a rewritable digital video disk (DVD).

To clarify the potential of photochemical hole-burning memory systems, we study the theoretical recording-density limit of such systems. Shot noise and material noise are considered the principal noises. Material noise originates in fluctuations in the chromophore concentration. The recording-density limit proves to be proportional to (multiplicity)1/2 × (chromophore concentration)1/2 × (hole depth), approximately. It becomes clear that the recording spot diameter can be optimized to maximize the recording density. A molar extinction coefficient for a chromophore can be also optimized, and its value is ∼105 L/(mol cm) under the conditions of a 0.2 hole depth, 1000 multiplicity, and 10−2 mol/L choromophore concentration. When the readout time is 10 ns/bit and the signal-to-noise ratio is 20, in addition to the above conditions, the recording-density limit is calculated to be 26 Gbits/cm2. For this readout time the optimal recording spot diameter is ∼2 μm. When the readout time is less than ∼10 ns/bit, shot noise becomes the dominant noise; when the readout time is more than ∼50 ns/bit, the recording-density limit increases, and the influence of material noise becomes prominent.

The studies on hole formation type optical recording films, which are mainly studies on three Te-based recording films are reviewed. Pb-Te-Se recording films, are deposited by vacuum evaporation or by sputtering. The role of Se in the film is to inhibit the oxidation. By more than 14% of Se addition, film oxidation is completely inhibited even at 60°C relative humidity 95%. A selenium condensed layer is found at the inner part of an oxidized surface layer by Auger electron spectroscopy. The surface Te oxide layer and the Se rich layer inhibit the film inside oxidation. The role of the metallic elements In, Pb, Sn, Bi, and Sb in the film is to inhibit cracking and to decrease noise in reproduced signals by decreasing the size of crystal grains. Lead is found to be the best among these metallic elements, because its recorded hole shape is clean even when recorded after 15 days accelerated oxidation at 60°C relative humidity 95%. A storage life longer than 50 years at room temperature is expected for the Pb-Te-Se optical recording film.Te-C films are deposited by sputtering a Te target in mixed a gas of Ar and CH4. The film structure shows small particles of Te surrounded by organic compounds made from the CH4 gas. CS2-Te films are deposited by plasma polymerizing CS2 gas while vacuum-evaporating Te. The film has a structure in which small particles of Te are surrounded by polymerized CS2. In these films, the organic compounds protect the Te particles from oxidation and a long storage life is expected.

The shapes of holes thermally created by a laser beam in thin films of wide range of materials are studied. The most cleanly shaped holes, which measure up to recent requirements for direct‐read‐after‐write video recordings by submicron dots, are obtained in some compositions of amorphous chalcogenide thin films such as As‐Te system, Ge‐Te system, As‐Se system, Ge‐Se system, and Sb‐S system thin films. The experiments clarify several important conditions helpful in obtaining cleanly shaped holes. The most important condition is that the viscosity of the material in liquid or softened state should be high. The required incident laser‐beam power for recording in an As‐Te system thin film on a polymethyl methacrylate substrate rotating at 1800 min−1 is about 10 mW. Addition of Se to the As‐Te system thin films greatly increases film stability. A signal‐to‐noise ratio of about 45 dB is obtained in reproduced color video signals.

The dependence of oxidation resistance of metal‐Te‐Se optical recording films on film composition is investigated, as well as the effects of oxidation on laser beam recorded hole shape. The films are deposited by vacuum evaporation on substrates with a glass/UV light curing resin/cellulose nitrate structure. The role of Se in the film is to inhibit the oxidation. With at least 14% Se addition, film oxidation is completely inhibited even at 60 °C, relative humidity 95%. Depth profiles of elements in the recording films are analyzed by Auger electron and x‐ray photoelectron spectroscopy to clarify the mechanisms of oxidation inhibition by Se addition. A selenium condensed layer is found at the inner part of an oxidized surface layer. The surface Te oxide layer and the Se‐rich layer should inhibit the film inside from oxidizing. The role of the metallic elements In, Pb, Sn, Bi, and Sb in the film is to inhibit cracking and to decrease noise in reproduced signals by decreasing the size of crystal grains. Lead...