One-dimensional heat conduction model for an electrical phase change random access memory device with an 8F2 memory cell (F=0.15 μm)

Abstract

A one-dimensional heat conduction model is developed for a phase change random access memory device with an 8F2 memory cell structure (F=0.15 μm). The required current level for a reset operation, which corresponds to the phase switching from a crystalline (“1” state) to an amorphous phase (“0” state) of Ge2Sb2Te5, was investigated by calculating one-dimensional temperature profiles for the memory cell structure. It is revealed that a reset operation is not achieved at the current level (2 mA) reported for existing devices with a subquarter micron plug size when only TiN is used as a resistive heater. However, it is possible when an additional heating layer of 5 nm thickness is inserted between the TiN and Ge2Sb2Te5 layers, for which the electrical resistivity ρelec is higher than 105 μΩ cm, and the thermal conductivity κ and specific heat c are as low as those of Ge2Sb2Te5. In addition, it is shown that a reset operation at a low current level of 1 mA can be realized in this memory cell when amorphous carbon (κ=0.2 W/m K and ρelec=106 μΩ cm) is used as an additional heating layer. It is believed that this relatively simple one-dimensional heat conduction model is a useful tool for analyzing the device operation of phase change random access memory devices and for selecting the proper conditions for an additional heating layer allowing for low-current operation.