Experimental Investigation of Threshold Voltage Temperature Effect During Cross-Temperature Write–Read Operations in 3-D NAND Flash

Reading data at a temperature which different from writing can cause a large number of failed bits in 3D NAND Flash memory. In this work, the threshold voltage (Vth) temperature effect of 3D NAND flash memory cell was investigated and a method was proposed to optimize its temperature coefficient (Tco). The results suggested that the Tco of low temperature programmed high temperature read is larger than high temperature programmed low temperature read and this difference is about 2-3mv/°C, which makes against the temperature compensation of reading voltage and lead to irreparable data errors even there is error correction codes. Furthermore, the critical factor of this difference was demonstrated that is the charge loss during low temperature programmed high temperature read and the Vth shift caused by charge loss is up to 30 percent. Based on this, we proposed to optimize the Tco consistency by shortening the interval time of erase to program in endurance cycling stage and confirmed that this method is effective by experiment. As the time interval becomes smaller, the difference of the Tco decreases as well, which have great reference signification for improving the reliability of 3D NAND flash memory.