Patent ID: 11158371

Abstract:
A novel memory device is provided.The memory device including a plurality of memory cells arranged in a matrix, and each of the memory cells includes a transistor and a capacitor. The transistor includes a first gate and a second gate, which include a region where they overlap with each other with a semiconductor layer therebetween. The memory device has a function of operating in a “writing mode”, a “reading mode”, a “refresh mode”, and an “NV mode”. In the “refresh mode”, data retained in the memory cell is read, and then the read data is written to the memory cell again for first time. In the “NV mode”, data retained in the memory cell is read, the read data is written to the memory cell again for second time, and then a potential at which the transistor is turned off is supplied to the second gate. The “NV mode” operation enables data to be stored for a long time even when power supply to the memory cell is stopped. The memory cell can store multilevel data.