Research On Temperature Characteristic Of 3D Charge-Trap NAND Flash Memory

With the explosive growth of data,the rapidly increasing demand for data storage and data mining brings new challenges to storage technology and greatly promotes the development of the storage industry.Among many choices of storage technologies,three-dimensional(3D)NAND flash memory has become the first choice for large capacity data storage due to its advantages of high performance and low cost.And it gradually replaces planar NAND flash as one of the most widely used nonvolatile storage.However,3D technology makes reliability characteristics of the former significantly different from the latter,resulting in the traditional reliability model of planar flash memory not being applicable in 3D NAND flash memory.In addition,with the complexity of flash memory usage conditions and process technologies,it also needs to face new and more tough reliability issues.Therefore,exploring the factors which affects flash memory reliability has become a significant topic in the storage field.Based on the ultra-multivalued charge trapping 3D NAND flash memory,this paper systematically studies and analyzes the impact of temperature on flash memory reliability,including program and erase(P/E)time,read disturb(RD),data retention(DR).Reveal the laws and mechanisms of environmental temperature how it controls 3D NAND flash reliability characteristic,and provide important basic data for building high-performance flash memory systems and designing reliability optimization strategies.The first part of this paper focuses on the temperature characteristic of flash memory basic parameters,including program time,erase time and raw bit error rate(RBER)of read-write.First of all,through high and low temperature wear experiments of flash in the temperature ranging from-30℃to 85℃,we found that there is a strong temperature correlation between erase time,program time and RBER of read-write,and the basic trend is that erase time,program time and RBER of read-write decreases while temperature increases.Then,in order to verify and explore the mechanism behind this phenomenon,experimental schemes for some fresh blocks at different temperatures are designed.Through analysis of the experimental results,it is found that the sensitivity of fresh and worn-out flash memory to high and low temperature working environments was inconsistent.It seems that:the higher the temperature,the greater the difference in read-write characteristics at fresh and worn-out stage.At last,through cross temperature wear experiments,it is found that P/E cycles at high temperature would bring higher electrical stress damage to storage cell.In the second part of this paper,the relationship between flash memory read operation and temperature is deeply explored.It mainly includes two parts:RD temperature characteristic and cross temperature effect.By analyzing the experimental data of read cycles at different temperatures,we find that the RBER recovery occurs when continuous read operations are performed at high temperatures of fresh stage flash memory,but this phenomenon is not observed after worn-out firstly and the difference of flash RD temperature characteristic between different wearing gears will gradually increase as the temperature increases secondly.Then,by adding a step of returning to write temperature and reading data after the experiment of cross temperature effect,we find that there is a difference in the physical mechanism between high temperature writing and low temperature reading and low temperature writing and high temperature reading cross temperature phenomenon.The phenomenon of the former is mainly caused by changes in the read current,while the later involves a certain proportion of charge loss in the storage cell.The third part of this paper studies the relationship between flash memory data retention(DR)and temperature.Based on a systematic analysis of DR characteristic at high and low temperature,a general conclusion is drawn that the difference between flash memory DR temperature characteristic of fresh and worn-out stage increases as the temperature increases.Then,after analyzing the results of high and low temperature RD and DR at worn-out flash,it is found that the failure mechanisms of the former are different at the two working conditions.And the relationship between the RBER and the number of read cycles and retention time is approximately linear in the latter condition.Finally,the DR result under cross temperature environments indicates that writing at high temperature and maintaining at low temperature looks like the best option for data reliability.In summary,this paper has conducted a systematic research and analysis on the reliability characteristic of 3D NAND flash memory in the temperature field.The main work consists of two parts.One is that the impact of temperature on flash memory RBER has been studied,including RD temperature characteristic,cross temperature characteristic and DR temperature characteristic of flash memory,and the other is the differences in the working modes of flash at high and low temperature conditions are comprehensively compared,and the physical mechanisms are discussed in depth.The research work carries out in this paper provides important basic data for analyzing the temperature characteristics of flash memory,and has an important reference value for constructing high reliability flash memory storage systems which can be applied to complex temperature environments.