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 ${\text{8F}}^2$ memory cell structure $\text{(F=0.15\hspace{0.17em}μ}\mathrm{m}\mathrm{).}$ 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 ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5,$ 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 ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ layers, for which the electrical resistivity ${\rho }_{\mathrm{elec}}$ is higher than ${10}^5\mathrm{\hspace{0.17em}\mu \Omega }\mathrm{cm},$ and the thermal conductivity κ and specific heat c are as low as those of ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5.$ 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 $\text{(κ=0.2\hspace{0.17em}}\mathrm{W/m K}$ and ${\rho }_{\mathrm{elec}}{\text{=10}}^6\mathrm{\hspace{0.17em}\mu \Omega }\mathrm{cm})$ 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.