| 摘要 |
PURPOSE:To increase erasure rate and the power margin of erasure by changing the constituent of a second protection layer from that of a first protection layer and then increasing thermal conductivity. CONSTITUTION:A first protection layer 2, a recording thin-film layer 3, a second protection layer 4, and a reflection layer 5 are formed successively on one surface of a transparent substrate 1. The first protection layer 2 and the second protection layer 4 are formed by a mixed material of ZnS and SiO2 and then the optical state of the recording thin film 3 is thermally changed by applying laser beams, etc., for recording and erasing information. The SiO2 ratio of the second protection layer 4 is made larger than that of the first protection layer 2, thus increasing the erasure rate at a region with a higher lineal speed. As the SiO2 ratio of the second protection layer 4 is made larger, thermal conductivity is increased, thus preventing heat due to application of laser beams etc. from escaping easily and minimizing the temperature difference between the center and the edge of a recording mark part. Therefore, the erasure rate can be increased by gradually increasing temperature by heating and then gradually cooling. |
