We report the readout stability improvement results of super-resolution near field structure (Super-RENS) write-once
read-many (WORM) disk at a blue laser optical system. (Laser wavelength 405nm, numerical aperture 0.85) By using diffusion barrier structure (GeSbTe sandwiched by GeN) and high transition temperature recording material (BaTiO<sub>3</sub>), material diffusion of phase change layer and recording mark degradation were greatly improved during high power (Pr=2.0mW) readout process up to 1X10<sup>5</sup> times.
Inserting germanium nitride thin films between Sb-Te (for super-resolution readout) and ZnS-SiO<sub>2</sub> layers was effective
to improve super-resolution readout durability of a super-RENS disc using a PtO<sub>x</sub>-SiO<sub>2</sub> write-once recording layer.
Waveform of 97-nm (that is below the resolution limit of the optics used) and 340-nm combined marks scarcely
changed even after 50,000 times readout. CNR of 100 nm marks was stable (within 3 dB decrease) after 268,000 times
We report the error rate improvement of super-resolution near field structure (Super-RENS) write-once read-many (WORM) disk at a blue laser optical system. (Laser wavelength 405nm, numerical aperture 0.85) We used a disk of which carrier level (CL) of 75nm is improved from -26.3 dBm to -19.0 dBm. We controlled the equalization (EQ) profile characteristics and used the adaptive 5 symbol write strategy and advanced high tap partial-response maximum likelihood (PRML) technique in order to improve the bit error rate (bER) characteristics of the super-RENS random signal. As a result, we obtained bER of 10<sup>-4</sup> level with new signal processing techniques and bit error analysis process. This result shows high feasibility of super-RENS technology for practical use in the near future.
We have developed a novel lithography technique, which we refer to here as Volume-Change Thermal-Lithography (VCTL), for application to the mastering process in a manufacture of next-generation ultra-high density optical ROM disks. Using a visible laser beam and conventional optics, we have succeeded in fabricating minute dots with diameters of under 100 nm and with interdot spacing far beyond the optical diffraction limit at a practical fabrication speed of 3 m/s. The combination of the temperature distribution induced by a focused laser beam with a Gaussian profile and a specially designed multilayer consisting of TbFeCo and ZnS-SiO<sub>2</sub> was utilized for fabricating the aforementioned nano-structures. A focused laser beam with a Gaussian profile can generate a peak temperature area far smaller than its spot size. TbFeCo and ZnS-SiO<sub>2</sub> undergo mutual diffusion when heated, a result of which is that their volume expands. An incident pulsed laser induces mutual diffusion restricted to the highest heated area. As a result, minute convex structures appear as dots on the sample surface. In addition to fabrication of continuous dot patterns, as a demonstration, small letters with dimensions of approximately 1 μm were drawn by specific dot arrangement, confirming the strong possibility of the technique.
We report the random pattern signal characteristics of the super resolution near field structure (Super-RENS) disk in a blue laser optical system. (Laser wavelength 405 nm, numerical aperture 0.85) We introduced new structure for blue laser system, which results in 43 dB carrier to noise ratio (CNR) at the 75 nm mark length signal (which is equivalent to 50 GB capacity with 0.32 micrometer track pitch) and much better readout stability were obtained. The relatively clear eye pattern, phase locked loop (PLL) state and data to clock jitter of around 20% for a 50 GB (2T:75 nm) random pattern signal were realized.