Device Structure And Fabrication Process Of Phase Change Memory

Phase change memory(PCM)has been regarded as one of the promising candidates for the next-generation nonvolatile memory to replace the most popular memory nowadays like FLASH memory and Dram,because it has many advantages such as nonvolatility,high storage density,low power consumption,and better reliability.PCM was proposed in 1960s,more than a half of a century has been passed,with the development of semiconductor process,the PCM can be fabricated nowadays.PCM was applied in one style of mobile phone in 2011 by Sumsung corporation,PCM completed the process from theory to reality.But PCM chips have not been mass sold in the market,and the performance of PCM can be further improved,such as write/erase speed,crosstalk.The three main methods of improving the PCM performance are developing new phase change material,PCM structure and process optimization.In this paper the fabrication process of PCM cells and chips have been investigated;a new PCM structure with double electrodes have been proposed which can improve PCM crosstalk,and an asymmetric structure of T-type PCM has also been proposed which has high electric-thermal conversion efficiency;the fabrication process not limited by the lithography resolution has been developed,the above-mentioned investigation lay the function for the practical application of PCM in our country.Firstly we investigated T-type PCM,the mask of PCM cell has been designed,eight independent PCM cells have been fabricated,the process and parameters have been determined,and the test results of PCM cells indicated the fastest write speed was 5 ns.Then the post-integration fabrication of 256 bit and 1 Mb PCM chips using the determined process has been completed,the peripheral circuit and the PCM cells normally worked,and chips can be re-write/erase.Secondly a finite element model of T-type PCM has been established,the electric-thermal characters of PCM have been simulated based on finite element analysis using ANSYS,a PCM structure with double electrodes has been proposed,which marked reduced the thermal crosstalk of PCM.An asymmetric T-type PCM structure has been also proposed based on finite element simulation,the new structure has higher electric-thermal conversion efficiency,comparing with traditional T-type PCM.Finally new process for line-type PCM has been proposed based on angle evaporation,the feature size of PCM was not limited by lithography resolution when using the new process to fabricate PCM cell.A PCM cell whose feature size was 100 nm X 80 nm has been fabricated using micron dimension process.The cell fabricated by the new process had smaller feature size,faster write/erase speed,and lower fabrication cost.From the electric-thermal simulation results,the thermal crosstalk of new PCM cell was reduced.