Energy-Gap-Induced Super-Resolution (EG-SR) Optical Disc Using ZnO Interference Film

We have developed a super-resolution read-only memory (ROM) disc with a high readout stability using a zinc oxide (ZnO) thin film. Applying the reversible and repeatable change in the optical constants of ZnO induced by heat, we can successfully confirm super-resolution effects that can read out a small mark beyond the optical diffraction limit. By realizing this characteristic in a ROM disc, we obtained a linear bit density twofold higher than that of a conventional disc in the blue-laser optical system. To clarify the origin of ZnO super resolution, we performed two types of test: a test to compare ZnO super-resolution characteristics using blue- and red-laser optical systems, and a test to determine the relationship between the absorption edges of semiconductor films with various energy band gaps and readout laser wavelength.