Thermal Stress Analysis of $\hbox {Ge}_{1}\hbox {Sb}_{4} \hbox {Te}_{7}$ -Based Phase-Change Memory Devices

Due to the extreme operating conditions in phase-change memory (PCM) cells in terms of temperature and heating/cooling rate, thermal stress is regarded as one of the most critical problems in PCM devices. Here, we report on the thermal stress analysis of Ge₁Sb₄Te₇-based PCM cells using numerical simulations. Thermomechanical properties are measured prior to the thermal stress analysis, where the Young´s modulus, thermal expansion coefficient, and density of (poly)crystalline Ge₁Sb₄Te₇ are measured to be 37.8 GPa, 17.913 × 10^-6 K^-1, and 5685 kg · m^-3, respectively. Transient thermal stress evolution in conventional T-structured and trench depth-varying PCM cells is simulated during the reset process. For the T-structured PCM cell, thermal stress is developed largely in the interface of the phase-change and bottom contact layers (PCL and BCL respectively), which may lead to the delamination of the PCL from the metal electrode. However, we observe that, as the trench depth is increased, the thermal stress along the interface of the PCL and the interlayer dielectric (ILD) also increases. Therefore, in a deep-trenched PCM cell, a possible thermal failure is likely to occur not only at the interface of the PCL and the BCL but also at the interface of the PCL and the ILD.