Semiconductor memory device and method for correctnig reference unit

Abstract

A semiconductor memory device includes a plurality of memory cells (1) each capable of storing and programming N-level data; a reference cell (2) storing a reference level used when reading a data level stored in the memory cells (1); a counter circuit (3) counting number of times of reading of the reference cell (2); a check means (4) for determining whether the reference level stored in the reference cell is within a preset range when the number of times of reading that is counted reaches a specified value; and a correction means (5) for, if the check means (4) determines that the reference level is out of the range, correcting the reference level to fall within the range in accordance with a master reference cell (6). With this constitution, it is possible to provide the semiconductor memory device capable of efficiently correcting the state of the reference cell, preventing the deterioration of the reference cell due to disturbance or the like, and highly accurately maintaining the level of the reference cell.

Description

technical field [0001] The invention relates to a semiconductor storage device and a correction method of a reference unit. Background technique [0002] As a conventional semiconductor memory device, a flash memory (flash memory) will be described as an example. In flash memory, the threshold value is changed by injecting charge into a floating gate. By controlling the amount of charge, the threshold value can be controlled into multiple states to realize multi-valued storage. For example, when the threshold value is stored in a flash memory that can be controlled in 2 states (1 bit), 16 bits of data are stored in 16 flash memories, but when the threshold value can be controlled in 4 states (2 bits) ) in the case of flash memory, 16-bit data can be stored in 8 [0003] in memory. Here, for example, in order to check which of the four states it is in, it can be judged by comparing with a flash memory having a threshold value as a reference. [0004] However, a flash mem...

AI Technical Summary

Problems solved by technology

[0007] The object of the present invention is, in order to solve the problem that the reference cell deteriorates due to repeated read operation, write operation, and erase operation, effectively confirm the state of the reference cell, correct it, prevent the reference cell from being deteriorated due to interference, etc. Accurately maintain the value of the reference unit

Images