Simulation of non-volatile memory cell using chalcogenide glasses

J.ROCCA; M. FONTANA; B. ARCONDO

Gijon

Simposio; 18th International Symposium on Metastable, Amorphous and Nanostructured Materials (ISMANAM 2011); 2011

Chalcogenide amorphous films are widely used in rewritable compact disks (CD-RW), digital versatile disks (DVD-RW) and are found to be suitable for electrical memories (i.e.: non-volatile memories). This is based on the optical and electrical switching between two states: the amorphous and the crystalline state. In its applications as electrical memories, the material has a high electrical resistivity in the amorphous state, while it has a low resistivity in the crystalline state.In this paper, a non-volatile memory cell is proposed and modeled. It is formed by layers of three materials: an insulating material, a conductor and a sensitive material: chalcogenide glass. The thermal effect generated by applying an electric pulse was calculated and analyzed. A 2D model using a finite element method has been developed for the simulation of the thermal behaviour of the cell. Temporal evolution of temperature maps is obtained. The model is applied to alloys of the Ge-Sb-Te system. Two compositions corresponding to two different zones of the Ge-Sb-Te equilibrium phases diagram were chosen: one is close to binary eutectic Ge15Te85, the other, in the pseudo-binary GeTe-Sb2Te3 system. Experimentally determined temperature dependence of electrical conductivity was used for each state and for each composition. It presents a big change at the glass-crystal transition temperature.The computed results allow us to understand the role played by the variables involved (thickness of different layers, cell radius, composition of the chalcogenide glass) in order to optimize the cell structure. The analysis of the results indicates that alloys with compositions in the pseudo-binary GeTe-Sb2Te3 system present better characteristics for their application in memory cells.