Yasuo Hosoda

Multilayer Optical Read-Only-Memory Disk Applicable to Blu-ray Disc Standard Using a Photopolymer Sheet with a Recording Capacity of 100 GB

We have been investigating a multilayer optical disk applicable to Blu-ray Disc (BD) standard using a photopolymer (2P) sheet in order to realize a recording capacity of 100 GB on a 12-cm-diameter disk. We had already developed a 2P sheet utilizing the multilayer disk. In this study, we developed a BD-type quad-layer disk using the 2P sheet, and investigated readout signals from each layer. The jitter values of layer 0 (L0), layer 1 (L1), layer 2 (L2) and layer 3 (L3) in the quad-layer disk were 6.5%, 7.1%, 7.3% and 6.6%, respectively. According to the analysis of the components of jitter values, the main factor behind the deterioration of jitter values is the crosstalk from adjacent layers. However, the jitter value of each layer was sufficient to reproduce the recorded data. From these results, we proved the feasibility of realizing the BD-type multilayer read-only-memory (ROM) disk with the recording capacity of 100 GB.

Inorganic Recordable Disk with More Eco-Friendly Material for Blue

We realized an inorganic write-once disk using a high numerical aperture (NA) objective lens and a blue-violet laser diode. Its recording layer was Bi?Ge nitride alloy which was more environmentally friendly than that of the rewritable disk. The data-to-clock jitter of 5.7% was obtained at 25 GB capacity, using the limit equalizer. In addition, we confirmed that this disk had potential for application as a 1X-2X recordable disk.

Recording Mechanism of High-Density Write-Once Disks Using Inorganic Recording Material

We realized an inorganic write-once disk using a Bi-Ge nitride alloy recording layer for an optical recording system for the Blu-ray disc format. We developed a recording system, which is composed of two types of metal nitride as a recording material. One metal nitride is decomposed easily by the heat of the laser beam during recording. The other metal nitride is not decomposed at that temperature. The recording signal modulation depends mainly on the reflectivity change of the recording layer caused by the decomposition of nitride. The non-decomposing nitride controlled the reaction and prevented deformation of the layer. Thus we could obtain a well-formed minute mark. We confirmed the reliability of our hypothesis on the recording mechanism by using another material, which is composed of Sn-N and Ti-N. By this method, we confirmed that this recording mechanism can be widely applied to any inorganic recording material.

Electron Beam Recording beyond 200 Gbit/in2 Density for Next Generation Optical Disk Mastering

We had developed an electron beam recorder for high-density mastering. The electron beam recorder has a capability to record high-density patterning beyond 200 Gbit/in2 density because it has characteristic of fine beam convergence. The behavior of electron scattering is important to realizing high-density patterning. Scattered electrons degrade patterning resolution and high-density patterning can not be realized. Thus, we adopted a new substrate made of a material that reduces the influence of the electron backscattering and attempted to record high density patterning beyond 200 Gbit/in2 density. As experimental result, 300 Gbit/in2 density patterning could be realized.

Bd-type write-once disk with pollutant-free material and starch substrate

We realized an inorganic write-once disk for an optical recording system of the Blu-ray disk format. We developed a new Al alloy for the reflective layer and a Nb-compound oxide nitride material for the dielectric layer. By adopting these materials for the reflective layer and the dielectric layer of our write-once disk, we achieved complete exclusion of toxic substances specified in the pollutant release and transfer register (PRTR) law. That is, this disk did not contain any substances specified in the PRTR law. We confirmed this disk to be compatible with 1× to 2× recording at the user capacity of 25.0 GB. The bottom jitter values of both 1× and 2× were less than 6.0%. In addition, we developed another kind of substrate, which was made of a natural polymer derived from corn starch. The bottom jitter value was 6.0% at the user capacity of 25.0 GB with the limit equalizer.

Highly efficient photoconductive antennas using optimum low-temperature-grown GaAs layers and Si substrates

We have improved the efficiency of photoconductive antennas (PCAs) using low-temperature-grown GaAs (LT-GaAs). We found that the physical properties of LT-GaAs photoconductive layers greatly affect the generation and detection characteristics of terahertz (THz) waves. In THz generation, high photoexcited carrier mobility and the presence of a few As clusters in the LT-GaAs are two important factors. In detection, short carrier lifetime and the absence of a polycrystalline structure in the LT-GaAs are significant factors. By optimizing these physical properties, we improved the total dynamic range of THz generation and detection by 15 dB over that obtained by conventional commercially available PCAs. In addition, we replaced the semi-insulating GaAs (SI-GaAs) substrate with a Si substrate, which has a low absorption in the THz region. We proposed a new idea of including a highly insulating Al0.5Ga0.5As buffer layer on the Si substrate. Finally, we confirmed the feasibility of manufacturing PCAs using Si substrates.

Nanopattern Profile Control Technology Using Reactive Ion Etching for 100 GB Optical Disc Mastering

We had developed an electron beam recorder (EBR) and studied a process technology for high-density optical disc mastering. In this study, we aimed at controlling a nanopattern profile by adopting inductively coupled plasma reactive ion etching (ICP-RIE) under simple conditions. To control a pattern inclination angle, we introduced an etching power ratio of antenna to bias and investigated the relationship. From the results of our investigation, we confirmed that inclination angle depended on etching power ratio linearly. Furthermore, in the case of a 100 GB read-only memory (ROM) equivalent pattern, we formed two kinds of inclined pattern by adopting ICP-RIE. We evaluated line edge roughness (LER) to determine the difference in pit profile accurately. As the result, we confirmed that LER was improved at a steep inclination angle. In addition, we applied ICP-RIE to a 300 GB ROM pattern.

Low-Noise and Low-Environmental-Impact Reflective Material for High-Density Optical Data Storage

We designed a new reflective material for high-density optical data storage to manage both recording and reproducing properties and environmental impact. We achieved suitable characteristics using an Al based alloy including two additional elements. In the case that AlPdSnO2 was applied in a Blu-ray disc (BD) type write-once disk, recording and reproducing properties equivalent to those for the conventional Ag alloy of AgPdCu were achieved. Moreover, in the case that it was applied for a BD-type read-only disk, jitter was improved compared with the conventional Al alloy of AlTi.

Nano-Pattern Profile Control Technology Using Reactive Ion Etching for 100 GB Optical Disc Mastering

For high-density patterning, we tried to control the nano-pattern profile using a reactive ion etching technology. Line edge roughness could be improved and the line width fluctuation 7 nm could be realized.