Patent ID: 9042179
Filing Date: 2015-05-26
Classification: G11C

Abstract:
1. A method for writing in and reading data from a semiconductor storage device, the semiconductor storage device including a plurality of memory cells each including: a gate electrode on a semiconductor substrate which has a first impurity region and a second impurity region with a channel region interposed therebetween; a first charge accumulation portion between the first impurity region and the gate electrode; and a second charge accumulation portion between the second impurity region and the gate electrode, the plurality of memory cells being divided into both of a main storage region consisting of a majority of the memory cells for storing main data; and a sub storage region consisting of at least one of the memory cells for storing reference data, the method comprising: writing, in the first and second charge accumulation portions of each memory cell in the sub storage region, the reference data distinguishing both of a value of a readout current that flows when no charge is accumulated in the main storage region and the value of a readout current that flows when a large amount of charge is accumulated the main storage region, the reference data being stored so as to accumulate charge through both of: a first write step of accumulating charge in the first charge accumulation portion of each memory cell in the sub storage region by applying a positive voltage to the first impurity region and the gate electrode and applying a voltage lower than the positive voltage to the second impurity region; and a second write step of accumulating charge in the second charge accumulation portion of each memory cell in the sub storage region by applying a positive voltage to the second impurity region and the gate electrode and applying a voltage lower than the positive voltage to the first impurity region, wherein the charge accumulated in the first and second charge accumulation portions prevents electrons from moving towards the gate electrode during a readout of the reference data from the memory cell in the sub storage region; and a step of reading data from the main storage region while comparing a readout current fed from each memory cell in said main storage region with a readout current fed from each memory cell in said sub storage region.