Investigation of Retention Characteristics Caused by Charge Loss for Charge Trap NAND Flash Memory

In this paper, we investigate the retention characteristics cause by loss of trapped charges in charge-trap NAND flash memory. We fabricated silicon-oxide-nitride-oxide-silicon (SONOS) flash memory devices having different widths and lengths for setting up a more accurate retention model. For higher accuracy in the measurement results, we have set up a fast-response measurement scheme to have a closer look at the retention characteristics, using a waveform generator and a fast-measurement unit. Drain current can be measurement immediately after a program operation with a μs-level resolution. Transient analysis on the retention characteristics over a very short time period is performed along with the long-time measurement results. As the result, a more succinct set of clues for understanding the initial charge loss and the charge redistribution are provided.