Shinichi Tatsuta

Temperature Compensation Servo Algorithm for Holographic Data Storage

Photopolymers are widely used as media for holographic data storage because of their high dynamic range, high photosensitivity and availability. However, the most photopolymers have a large coefficient of linear thermal expansion. Therefore, it is known that the temperature changes cause deterioration of readout image under the Bragg-mismatch conditions. This paper proposes a new servo algorithm which includes both the servo error signals detection method and the automatic compensation procedures with feedback servo for the holographic data storage system. Experimental results for the proposed technique are demonstrated for temperature changes of up to +25 K successfully.

The effect of boundary thermal resistance on HD DVD-ARW optical recording media

Thermal conductivities and boundary thermal resistances of thin films having the thickness of the order of ten nanometers were measured by using the thermo-reflectance method at room temperature. A thermal simulation of HD DVD-ARW (the next-generation advanced rewritable DVD) media was carried out to clarify the effect of boundary thermal resistance at the interface of those films. The thermal conductivity of thin films greatly depends on film thickness. The result of the thermal simulation depends significantly on whether the boundary thermal resistance is considered or not. Thus it is important to consider the boundary thermal resistances and using thermal properties of thin films to perform more accurate calculation for the phase change recording media. The results of the thermal simulation also suggested that the boundary thermal resistances dominate the thermal diffusion and response of the medium.

Construction of holographic data storage system with dual-reference beam

A novel holographic data storage (HDS) system with dual-reference beam is proposed. Several servo techniques that construct a read and write procedure of the HDS system are introduced and experimentally confirmed.

Computational Analysis of Cross-Erase Phenomenon for High-Density Phase-Change Recording

In order to increase the recording density and decrease the track pitch of the digital versatile discs (DVD) media using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure of the recorded marks. A computational analysis to estimate the mark and erasure shapes was carried out, and comparisons with the experimental results have shown good agreement. The cross-erasure was reduced under the conditions given in this paper by increasing the duty ratio of land width to groove width (L/G) while keeping the groove pitch constant.

Computational analysis of cross-erase phenomena for high-density phase-change recording

In accordance with the increase of the recording density of DVD media, the track pitch is required to be smaller and the cross-erase phenomena becomes more prominent. In order to realize large capacity by using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure. In this paper, the computational analysis to estimate the mark and erasure shapes is described and the cross-erase phenomenon obtained from the analysis is discussed in terms of the duty ratio of land width to groove (L/G). The computational analysis mainly consists of two parts, the electromagnetic analysis and thermal analysis. The former computes the electromagnetic field induced from the incident beam by using the finite difference time domain (3D-FDTD) method. The latter simulates the temperature distributions by the finite volume method (3D-FVM). The cross-erase phenomenon is observed by mapping the mark and erasure areas that are obtained from the transient results of temperature distributions.

Acceleration of CVD Step Coverage Simulation Applied to DSMC Method.

This paper describes acceleration of the numerical simulation for chemical vapor deposition (CVD) step coverage problems. The CVD process is used to deposit thin films during LSI production. The thin film deposition process is generally simulated using a combination of the direct simulation Monte Carlo (DSMC) method and trench profile evolution, but much time is required to compute a trench filling shape when sticking probability is small. In the present work, reduction of the computation time was achieved by parallel processing using an engineering workstation (EWS) network system and stick-at-all-the-reflection-points (SARP) method which was newly developed. In the former case, more than 85% parallel efficiency on a 20-EWS system was achieved. In the latter case, computation was more than 780000 times faster than by the conventional method when an experimental poly-Si deposition process was considered.

Simulation of CVD Step Coverage for SiH4 using Parallel Processing of DSMC Method

This paper describes the basic study of the simulation of chemical vapor deposition (CVD) step coverage that is used to estimate the deposition of thin films in LSI production. Given the trend toward extremely high density in the semiconductor manufacturing process, such as that of LSIs, the deposition process of silicon thin film on the circuit pattern needs to be accurate. To optimize the deposition of thin film around the trench of the order of less than a micron, computer simulations of the step coverage and of the film growth rate in the process are very important. In this simulation reported in this paper, the thin film deposition process, whose reaction is modeled as silicon from silane (SiH4) and silylene (SiH2), is solved using the direct simulation Monte Carlo (DSMC) method. The DSMC method is usually adopted in this case, but, since 1) this method solves the Boltzmann equation with a huge amount of molecular collisions and free motions and 2) sticking probability of molecules is of the order of 10-5 [1], even a high performance computer needs much time for this calculation. Although the performance of supercomputers and other types of computers is improving, the DSMC method as conventionally applied seems to be reaching its limit in terms of practicality.