Enhancing the overwriting characteristics of phase-change optical disks by doping in dielectric layers

Abstract

In this work, we studied the enhancement of overwriting characteristics of phase-change optical disks by doping in the dielectric layers. The doping elements included chromium (Cr), molybdenum (Mo), nickel (Ni), tantalum (Ta), titanium (Ti), tungsten (W), vanadium (V), and nitrogen (N-2) Dynamic test showed that doping with a certain amount of W and N-2 in dielectric layers enhanced the disk overwriting characteristics. Up to fortyfold improvement in disk cycleability was observed when N-2 gas was introduced during sputtering deposition of the upper dielectric layer at the gas flow rate of N-2/Ar = 25%. Tungsten was the best among the doping metallic elements resulting in fivefold improvement in disk cycleability. Optical property measurement revealed that the refractive index (n) decreased with increasing N-2 doping percentage, while the relatively small amount of metallic element doping negligibly changed the optical constants. Subsequent modulation simulation showed that such an optical property change is beneficial to disk overwriting characteristics. Nanoindentation test showed that N-2 doping was the most effective method for increasing the hardness of the dielectric layer. This implies that, with increasing mechanical strength, the dielectric layer possesses better resistance to thermal deformation resulting from laser heating, thereby enhancing the cycleability of optical disks.