Impact of Dielectric Resistive Heater, Bottom Contact and Reading Scheme on the Reliability of Nanoscale Low Power Phase Change Memory (PCM) Cell: 3-D-ADI Modeling

摘要

This paper discusses the impact of silicon nitride dielectric resistive-heater, copper bottom contact, and reading scheme on the reliability of a precycled nanoscale phase change memory cell. Through the calibrated run-time efficient 3-D—alternating direction implicit (ADI), numerical modeling we have found that due to the presence of nitride heater, RESET power saving can be significantly achieved with a 1.1-nA RESET current pulse of 75-ps duration mitigating excessive heating within the heater, but at the same time, downsizing amorphous-Ge2Sb 2Te5 (GST) thickness to 2 nm. In contrast, we found that low resistance offered by such 2-nm-thin amorphous-GST is inappropriate for conventional reading used for sensing both SET and RESET states. Furthermore, we found that for having low thermal conductivity, nitride heater tends to store heat for a long time following RESET, which has been identified as a major reliability concern in the cell, although the benefit of the nitride heater toward RESET current scaling has been found prevalent. In this respect, we have demonstrated that the read current window can be reliably maintained to 0.14 mA through a novel in-plane reading in a thin-film GST cell, with 2-nm amorphous-GST. Furthermore, through 3-D-ADI modeling, we have demonstrated that reverse heat relaxation time can be significantly reduced to 30 ps using copper bottom contact, when supported by a nitride heater.