Fabrication and characteristics of phase change memory based on block copolymer lithography

Abstract

Phase change memory (PCM) is a promising non-volatile memory device demonstrating high operation speed, low power consumption, robust cycling endurance, and so on. The data program and erase of a PCM device is accomplished by reversible current-induced phase transitions between the high resistive amorphous state (RESET) and the low resistive polycrystalline state (SET). The current state of the art technology for PCM is facing two major technological challenges: i) how to minimize the RESET current for low power switching and ii) how to realize multilevel resistive states for maximum storage capacity. For the first issue of RESET current minimization, research efforts have focused on reducing the cell size, as the electric current required for a phase change is generally proportional to the material volume. Nevertheless, the currently available conventional photolithography is close to the intrinsic resolution limit, destined by the optical diffraction. The development of an alternative nanopatterning technology to complement conventional photolithography is an urgent requirement. Regarding the second issue of multilevel switching, various approaches have been exploited, such as finding new non-GST (Ge2Sb2Te5) material (In3Sb1Te2) showing inherent multilevel resistance property, adapting multilayer of phase change material, crystallinity control, and modulation of pulse condition. In the case of finding new non-GST material, the In3Sb1Te2 (IST) alloy is promising material to realize multilevel PCM. IST material has the advantage of multilevel data storage through a resistance difference that can be attributed to a change in crystal structure. For multilevel switching, the multilayer stacking of different chalcogenide layers may realize the desired multiple resistance levels with high stability. The discrete phase change conditions of different chalcogenide material layers offers clearly distinguishable and highly stable resistive states. This thesis contains t...