| 摘要 |
<p>PROBLEM TO BE SOLVED: To enable one non-volatile memory cell to store quarternary information. SOLUTION: Writing operation is performed by applying different three kinds of voltage to a word line successively at the time of verifying operation, and threshold voltage of a memory cell is controlled. At the time, writing data of binary (1 bit) corresponding to information of quarternary (2 bits) to be written are synthesized by a writing data conversion circuit (1) every three writing operations, information of quarternary (2 bits) is written in one memory cell, thereby doubling storage capacity of a flash memory. In reading out information, different three kinds of voltage is applied to a word line, read out three kinds of information of binary (1 bit) are synthesized by a read-out conversion circuit (2), and storage information of a memory cell is converted to information of two bits.</p> |
