Study On Cross Temperature Reliability And System Optimization Of 3D NAND Flash

The huge demand for data storage in the information age has created the prosperity of today’s memory market.3D NAND flash memory has become the mainstream medium in the non-volatile memory market by virtue of innovations and breakthroughs in structures or technologies such as three-dimensional stacking and multi-value storage,continuously improving storage density and reducing production costs,and is widely used in mobile phones,computers and other civilian terminals equipment and special terminal equipment such as flight data recorders.However,the storage characteristics of 3D NAND flash memory are closely related to the operating temperature,and the variable ambient temperature in special scenarios poses a severe challenge to the reliability of flash memory data.Based on the charge-trapping 3D TLC NAND flash memory chip,this paper conducts strict cross-temperature read and write tests,studies the impact of variable temperature characteristics on storage reliability,and proposes a system optimization scheme for the data reading process.The first part of the paper is the research on the storage reliability of 3D NAND flash memory under variable temperature scenarios.First,by studying the cross-temperature characteristics of low-temperature programming,high-temperature reading and hightemperature programming,low-temperature reading in two variable temperature scenarios,the effect of variable temperature operation mode on the threshold voltage distribution of 3D NAND flash memory is clarified,that is,the threshold voltage distribution will increase during the heating process.Left shift,and right shift when cooling down,and the shift amplitudes in the two scenarios are not equal;secondly,modify the test parameters of cross temperature reading and writing and control variables,and explore the temperature difference between reading and writing,reading and writing temperature and The influence of many factors,including the number of erase and write cycles,on the reliability performance of variable temperature scenarios.The study found that the reading and writing temperature difference is the decisive factor affecting the shift of the threshold voltage distribution in the variable temperature scene.When the temperature difference is equal,the temperature changing characteristics in different reading and writing temperature ranges are basically the same.At the same time,the number of erasing and writing cycles and the array structure are different.The performance will also have a certain impact on the performance of variable temperature characteristics.The above research conclusions are of great value for understanding the temperature-variable reliability of 3D NAND flash memory,and provide key data for the proposal of the read optimization scheme and the process design in the follow-up work of this paper.The second part of the thesis is the research on the system optimization scheme of the reading process of 3D NAND flash memory under variable temperature environment.On the basis of the research in the previous part,combined with the optimal reading voltage reading and the flash memory error correction code technology,a systematic reading scheme of variable temperature scene is proposed.In this paper,the preset optimal read voltage temperature offset parameter is used,combined with the reading and writing environment temperature difference to calculate the optimal read voltage gear in the variable temperature environment,and the default read voltage and the calculated optimal read voltage are read in two rounds,and the hard drive The three-level decoding process combined with decoding and soft decoding not only avoids unnecessary read delays and takes into account system efficiency,but also ensures data reliability during variable temperature reading.The research results show that the optimal read voltage level calculated by this scheme has a high accuracy rate.Using this voltage for reading can significantly reduce the read bit error rate in variable temperature scenarios,and the three-level decoding process can maximally correct the remaining Error code ensures the correct reading of data.This paper systematically studies the reliability of 3D NAND flash memory in variable temperature environment.According to the characteristics of threshold voltage distribution and optimal read voltage offset in variable temperature operation mode,combined with error correction code technology,an optimization scheme for variable temperature reading is proposed.The research content and results of this paper are of great significance for understanding and optimizing the temperature-variable reliability of 3D NAND flash memory.