| 摘要 |
An object of the present invention is to contribute to increase of storage capacity of a memory and to cope with an nonlinear parasitic resistance. The non-volatile memory have a cell applying to multi-bit data by means of a double layered floating gate architecture. The cell comprises: heavily doped layers (drains 30-32 and source 2) being formed separated from each other along an arrangement direction L in a semiconductor substrate; a first floating gate 4A being disposed along a direction orthogonal to the direction L between the drains and source above the semiconductor substrate; second floating gates 4B1, 4B2 which respectively extend across the first floating gate above the first floating gate and lie along the direction L, close to the drain; program gates 61, 62 disposed correspondingly to one of the second floating gates; and a control gate 5 extending across the gate 4A above the gate 4A and being disposed along the direction L, close to the source. Since the second floating gates individually store carriers corresponding to a data bit and the first floating gate determines a threshold voltage in accordance with a sum amount of carriers stored in all of the second floating gates, two or more bits of data can be saved per one storage cell. It is possible to avoid influence of nonlinear parasitic resistance because a transistor formed by the first floating gate and the control gate is used exclusively for reading.
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