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 (AR heater ) and active material, Ge 2 Sb 2 Te 5 (AR GST ) 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 (I RESET ) of the reference device (100 nm heater diameter) consisting of elliptical cross-sections increases significantly to ∼67% when AR heater = 2 and 1 ≤ AR GST ≤ 2, whereas for the scaled-down devices of 20 nm and 10 nm heater diameter with elliptical cross-sections, the I RESET increases to ∼35% and ∼38% when AR heater = 2 and AR GST = 1, and further I RESET increases to ∼54% and ∼63% when AR heater = 2 and AR GST = 2 leading to high-power RESET programming. In the case of the reference device, the AR GST did not play any significant role on I RESET . However, in the scaled-down devices, both AR heater and AR GST significantly affect the I RESET . Furthermore, the device employing a vertically-oriented elliptical heater and horizontally-oriented elliptical GST (where AR heater = 2 and AR GST = 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.