Demands for the high storage capacities and rates of data transfer have been overwhelming in the recent years. With the increasing use of multimedia, the rewritable optical phase-change disks, e.g. CD and DVD, have become more popular. The optical PC data storage devices provide relatively short data access rates (∼ 10 MHz) and moderate areal densities. As in other areas of data storage, there has been tremendous demand and pressure, driven by consumer application, for inexpensive high-density PC systems. So far, the optical data storage industry has managed to meet the demands by using lasers with shorter wavelengths and objective lenses with higher numerical aperture (NA). Several strategies such as “multilevel storage layers” [1] and “mark radial width modulation” [2] have been proposed for the next generation of the high-density PC data storage devices. There have been advances in near field optical techniques to increase density (40 Gb/in) using solid immersion lens [3]. Hosaka et al. [4] demonstrated 60 nm domains in phase change media that translates to 170 Gb/in2 using a scanning near-filed optical microscope. Kado and Tohda [5] used an atomic force microscope (AFM) to locally modify the electrical property (×100) of a PC material by applying an electrical pulse between the probe and media. They achieved an areal density near 1 Tbits/cm2.
Phase Change Chalcogenide Materials for Optical Data Storage
