Impact of process-induced ellipticity on the RESET process of cylindrical phase change memory devices

Abstract

Phase change memory (PCM) is one of the promising candidates for the next-generation high-speed non-volatile memory which exhibits excellent scalability. The cylindrical-type PCM devices entering the nano-scale regime should show their tolerance to the variation in the manufacturing process. However, it is highly challenging to fabricate cylindrical-type nano-scale devices ideally with circular cross-sections. In general, the degree of variation in circular cross-section is dictated by a geometrical parameter called aspect ratio (AR). In this study, the impact of variation in AR of heater (ARheater) and active material, Ge2Sb2Te5 (ARGST) on the RESET programming of the mushroom-type cylindrical PCM device is systematically investigated by using 3D TCAD simulations. The simulation results reveal that the RESET current (IRESET) of the reference device (100 nm heater diameter) consisting of elliptical cross-sections increases significantly to ∼67% when ARheater = 2 and 1 ≤ ARGST ≤ 2, whereas for the scaled-down devices of 20 nm and 10 nm heater diameter with elliptical cross-sections, the IRESET increases to ∼35% and ∼38% when ARheater = 2 and ARGST = 1, and further IRESET increases to ∼54% and ∼63% when ARheater = 2 and ARGST = 2 leading to high-power RESET programming. In the case of the reference device, the ARGST did not play any significant role on IRESET. However, in the scaled-down devices, both ARheater and ARGST significantly affect the IRESET. Furthermore, the device employing a vertically-oriented elliptical heater and horizontally-oriented elliptical GST (where ARheater = 2 and ARGST = 0.5) shows the peculiar re-amorphization among all the cases considered in this study. Hence, the miniaturized cylindrical PCM devices comprising elliptical cross-sections due to process-induced variability require an accurate understanding of the programming characteristics for reliable modeling and simulations.