Sumio Ashida

Global models of pulse-power-modulated high-density, low-pressure discharges

Global (volume-averaged) models of high-density, low-pressure electropositive and electronegative discharges are described both for continuous wave (CW) and for pulsed-power excitation. Argon and chlorine discharges are treated. The particle and energy balance equations are applied to determine the charged particle and neutral dynamics. For argon just after the power has been turned on, the analysis shows an initial very sharp rise in electron temperature , followed by a decay of and an increase in the electron density to steady state values during the pulse-on time. Just after the power has been turned off, decays rapidly and decays more slowly. The time-average can be considerably higher than that for CW discharges for the same time-average power. For chlorine, a CW discharge is highly dissociated and the negative ion density is lower than . For a pulsed discharge, the initial rise and subsequent decay of just after the power has been turned off are determined analytically. A pulsed discharge can have the same neutral radical (Cl) flux to the walls for a reduced average power. The analytical models are compared to more complete global model simulations and to experimental observations. We find that global models can provide considerable insight into the discharge dynamics.

Spatially averaged (global) model of time modulated high density argon plasmas

The behavior of argon plasmas driven by time modulated power in ‘‘high density’’ plasma reactors is investigated using a global model. The time evolution of the electron temperature and the plasma density is calculated by solving the particle and energy balance equations. In the first stage of power application during the ‘‘on’’ time, the electron temperature rapidly increases above the steady state value. In this region, charged particles accumulate in the plasma due to the relatively higher power applied than for the continuous wave (cw) case. In the first stage of the ‘‘off’’ time, the electron temperature drops quickly, yielding a smaller particle loss (Bohm) velocity. These effects give rise to higher time‐average plasma densities than for the cw plasma driven by the same average power. The highest average plasma density obtained was more than twice the density of the cw plasma for a duty ratio of 25%. Even higher plasma densities were obtained for shorter duty ratios. The possibility of controlling ...

Measurements of pulsed‐power modulated argon plasmas in an inductively coupled plasma source

The behavior of pulsed‐power (square wave) modulated argon plasmas generated by an inductively coupled plasma (ICP) source is experimentally investigated. The apparatus is an ICP source with a flat coil geometry equipped with a cylindrical Langmuir probe on the axis of the cylindrical chamber. The evolution of the plasma density is determined from the wave forms of ion saturation currents. The rise and fall of the density had a time scale of a few tens of microseconds. The time average plasma density is also measured as a function of pulse frequency and duty ratio, holding the average absorbed power constant. When the plasma is modulated, the density is larger than that for a continuous wave excitation of the same average power. Larger densities are obtained for smaller duty ratios. The density increases monotonically as the period is decreased down to 100 μs. This agrees qualitatively with the modeling result, which accounts for the higher density by the difference of time scales for the generation and t...

Recording Characteristics of Ge Doped Eutectic SbTe Phase Change Discs with Various Compositions and Its Potential for High Density Recording

We describe the recording characteristics of discs having Ge doped eutectic SbTe alloy recording films with various compositions. The recording characteristics are fairly sensitive on the film composition. For our recording condition, the Sb/Te ratio of around 4 and the Ge content of about 5 at.% were preferable to obtain good carrier to noise ratio (CNR). A disc with eutectic recording film of that composition is compared with one with a GeTe–Sb2Te3 pseudo-binary alloy recording film, varying the mark length and the track pitch. The eutectic disc showed better CNR for the shorter mark lengths than the pseudo-binary disc. The cross-erase ratio of the eutectic disc is substantially higher than that of the pseudo-binary disc. The result suggests that the eutectic disc is suitable for higher linear bit density and the pseudo-binary disc is suitable for higher track density.

Super-Resolution Effect of Semiconductor-Doped Glass

Semiconductor-doped glass is proposed as a super-resolution layer for future ultra-high-density optical disc systems. It was confirmed that this material system showed very fast response and large transmittance change by laser-beam irradiation when CdSSe-doped glass was used. The rise time of the transmittance change was less than 10 ns and the transmittance change reached 30%. These optical responses were obtained at a power density of the pumped laser beam of 1 MW/cm2. This power density corresponds to the readout power in digital versatile disk-read only memory (DVD-ROM) and digital versatile disk-random access memory (DVD-RAM) discs. This material system is regarded as a potential candidate for a super-resolution readout layer that is applicable to both ROM and RAM discs.

Dual-layer rewritable phase-change recording media for HD DVD system

We have investigated the recording characteristics of the dual-layer phase-change recording media for a system that uses the blue-violet laser (wavelength of 405 nm), with the numerical aperture of 0.65 and light incidence on 0.6-mm-thick substrate having the land and groove format (HD DVD). In order to achieve higher storage density for its beam spot size, a number of technologies have been incorporated into the media, such as the bismuth-substituted pseudobinary GeSbTe alloy recording film and hafnium oxide-based interface layer material. The feasibility of the user capacity of 36 GB has been successfully demonstrated.

Media Technologies of 20 GB Single-Layer Rewritable Phase-Change Disc for HD DVD System

Sufficient signal amplitude, erase ratio and low amount of cross-erase must be attained to achieve higher recording capacity of rewritable phase-change media. We have developed new media technologies, such as the GeTe-rich GeTe-Sb2Te3 pseudobinary alloy recording film partially substituted with bismuth and an additional layer to control thermal diffusion. The recording layer material enables a high erase ratio with a high signal amplitude. The additional layer also reduces the amount of cross-erase while maintaining a sufficient erase ratio. We have successfully demonstrated rewritable phase-change media having 20 GB capacity by using these media technologies for the HD DVD system with a blue-violet laser diode having the wavelength of 405 nm, a numerical aperture of the objective lens of 0.65 and light incident on a 0.6-mm-thick substrate. In this paper, we describe our new media technologies and the evaluation results, such as tilt margins, uniformity, overwriting cyclability and life durability.

Advanced phase change media for blue laser recording of 18 GB capacity for 0.65 numerical aperture and 30 GB capacity for 0.85 numerical aperture

We attempted to improve phase change media to achieve larger capacity for systems with blue lasers using numerical apertures (NA) of both 0.85 and 0.65. It was found that the Bi-added GeTe-rich pseudo-binary composition promised high erase ratio even when we did not use any interface layers on a recording layer. The use of an absorption control layer (ACL) was also attempted to suppress the cross erase (XE). It was found that the ACL was very effective in suppressing the XE. The advanced phase change media that used the above novel technologies showed good analog performance. The advanced media also showed bER of less than 1.0×10-4, promising 18 GB capacity for an NA of 0.65 and 30 GB capacity for an NA of 0.85.

High-Speed Recording Media for HD DVD Rewritable System

We have developed optical recording media for high-speed operation on the HD DVD rewritable (HD DVD-R) format, which uses a laser wavelength of 405 nm, a numerical aperture of the objective lens of 0.65 and a cover layer thickness of 0.6 mm. In this study, we optimized the amount of bismuth substitution for antimony in pseudo-binary GeTe–Sb2Te3 alloy recording film and inserted interface layers to achieve high-speed recording and sufficient thermal stability in our media. As the amount of bismuth substitution increased, the erase ratio of the media improved. The rewritable media in which all the antimony is substituted by bismuth, i.e., the media having GeTe–Bi2Te3 alloy recording film achieved a sufficient erase ratio at a linear velocity 2.4 times that of the previous study without sacrificing the good thermal stability of amorphous marks. We demonstrate the operation of the media at data transfer rates ranging from 36.55 to 87.72 Mbps.

Evolution of protrusions during sputtering from composite Ag–Si targets

In this paper we describe studies on the effects of the sputtering pressure and power on shape and size of microscopic protrusions formed on a target consisting of a small Ag plate placed on a Si wafer. The influence of the target topography change during sputtering on the composition of the sputter‐deposited film was investigated. It was found that the Ag concentration of the deposited films was considerably reduced with the growth of the target surface protrusion on Ag plates. This is considered to be attributable to the prevention of sputtered atoms from escaping from the target by surface protrusions.In this paper we describe studies on the effects of the sputtering pressure and power on shape and size of microscopic protrusions formed on a target consisting of a small Ag plate placed on a Si wafer. The influence of the target topography change during sputtering on the composition of the sputter‐deposited film was investigated. It was found that the Ag concentration of the deposited films was considerably reduced with the growth of the target surface protrusion on Ag plates. This is considered to be attributable to the prevention of sputtered atoms from escaping from the target by surface protrusions.