Phase Change Memory Operation Research Articles

The geometric effect and programming current reduction in cylindrical-shaped phasechange memory

This study conducts a three-dimensional electro-thermal time-domain simulation fornumerical analysis of cylindrical-shaped phase change memories (PCMs). The influence ofchalcogenide material, germanium antimony telluride (GeSbTe or GST), structure on PCMoperation is explored. GST with vertical structure exhibits promising characteristics. Thebottom electrode contact (BEC) is advanced to improve the operation of PCMs, where a25% reduction of the required programming current is achieved at a cost of 26% reducedresistance ratio. The position of the BEC is then shifted to further improve theperformance of PCMs. The required programming current is reduced by a factor of 11,where the resistance ratio is only decreased by 6.9%. However, the PCMs with alarger shift of BEC are sensitive to process variation. To design PCMs with lessthan 10% programming current variation, PCMs with shifted BEC, where theshifted distance is equal to 1.5 times the BEC’s radius, is worth considering.This study quantitatively estimates the structure effect on the phase transitionof PCMs and physically provides an insight into the design and technology ofPCMs.

Analysis of Temperature in Phase Change Memory Scaling

We analyze constant-voltage isotropic and non-isotropic scaling issues for phase change memory (PCM) based on electrothermal physics. Various analytical and simulation models of general and typical PCM cells that support the analysis is also provided. The analysis shows that the maximum temperature in the PCM cell, which is a key parameter for PCM operation, is independent of geometrical sizes and depends only on the voltage and material properties. This leads to the minimum programming voltage concept, which is determined by material properties of the phase change material. Constant-voltage scaling, electrothermal modeling, ovonic unified memory (OUM), phase change memory (PCM, phase change random access memory, PRAM), proximity disturbance, thermal disturbance.

Low power and high speed phase-change memory devices with silicon-germanium heating layers

The switching speed and the reliability of the phase-change memory (PCM) device employing a SiGe film as a heating layer were compared with those of the control device employing a conventional TiN heating layer. The influence of the semiconducting nature of the SiGe film on PCM operation was investigated. The critical pulse width for the onset of a set process was reduced to less than about 50% by substitution of SiGe for TiN. The cycling endurance value for the PCM device with a SiGe heating layer was comparable to that of the control device, which indicated that the introduction of a SiGe film did not induce reliability degradation. The heterojunction between the GeSbTe and SiGe layers was so leaky that the effect of the semiconduction type of SiGe was negligible. The reset current was saturated at a minimum value with increasing resistivity of a SiGe film, which was attributed to the resistance lowering of SiGe at high temperature. The PCM device with a SiGe heating layer was successively fabricated using Si complementary metal oxide semiconductor technology, and its reset current decreased drastically compared to that of the control device.