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 (BaTiO3), material diffusion of phase change layer and recording mark degradation were greatly improved during high power (Pr=2.0mW) readout process up to 1X105 times.
Inserting germanium nitride thin films between Sb-Te (for super-resolution readout) and ZnS-SiO2 layers was effective
to improve super-resolution readout durability of a super-RENS disc using a PtOx-SiO2 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
Selecting a binary compound (Sb-Te, Zn-Sb and Ge-Te) with its composition at around a eutectic point generated a
better super-resolution effect. The thickness optimization of the super-resolution readout layer was also effective for the
property improvement. The temperature estimation indicated thinner the layer thickness is better as far as the readout
laser can easily increase its temperature.