Investigation Of Threshold Voltage Temperature Effect In 3D NAND Flash

The development of 3D NAND flash memory greatly meets with the demand of storage capacity,but the temperature reliability becomes an important reference index for its reliability evaluation because of its sensitivity to temperature.In this paper,based on the cross temperature read and write test,the temperature reliability of the 3D NAND Flash memory and the temperature effect of the threshold voltage of the memory cell are studied.The research conclusion has important theoretical significance and application value for improving the reliability of the memory.The first part of the paper studied the effect of temperature changes on the threshold voltage of 3D NAND Flash memory cells.After research,it was found that if the temperature changes during the use of the memory,the threshold voltage distribution of the memory cells will be shifted and widened,which will significantly reduce the reliability of flash memory.And in further research,it is found that even if the read voltage is compensated when the temperature changes,the phenomenon of reading error and reading error rate increasing due to temperature change still exists.After analyzing the principle and method of reading voltage temperature compensation,it is clear that this is related to the defects of current reading voltage temperature compensation technology.The second part of the paper studied the diversity of the threshold voltage temperature coefficient of the 3D NAND Flash memory in different situations,which provided a theoretical basis for improving the temperature compensation technology of the read voltage.It is found that if the direction of temperature change is different when use the memory,its influence on the threshold voltage of the memory cell is also different.Specifically,there is a difference in the temperature coefficient between low temperature program high temperature read and high temperature program low temperature read.Then we further studied the different characteristics of the threshold voltage temperature coefficient of the memory under different block filling program methods,different memory cell program states and the memory cell undergoing different erasure cycles based on the cross temperature read and write test.These research results provide an important theoretical basis for optimizing the temperature compensation of the read voltage.The third part of the paper started from optimizing the temperature coefficient itself.firstly,an experiment is designed to study the reason why the temperature coefficient of the threshold voltage of the memory cell is different between the high temperature program low temperature read and the low temperature program high temperature read and the improvement scheme is proposed.The improvement of temperature coefficient consistency will improve the reliability of memory essentially.Secondly,the reason for the difference of threshold voltage temperature coefficient in different block filling and memory cell program states are also studied.The research content and results of this paper have important significance and value for optimizing the temperature compensation technology of the read voltage,improving the consistency of the temperature coefficient of the threshold voltage of the memory cell,reducing the read errors and improving the temperature reliability of the 3D NAND Flash memory.