Charge and Discharge of Floating-Gate Amorphous Silicon Thin-Film Transistor Nonvolatile Memories

Charge and discharge phenomena of the floating-gate amorphous silicon thin-film transistor have been studied. The amount of charges stored in the transistor depends on the gate bias voltage and the stress time. Charges are stored in deep and shallow states, depending on the properties of the embedded a-Si:H layer and the gate bias condition. Most of the stored charges can be released using methods such as thermal annealing, negative gate bias, or light exposure. The discharge efficiency is a function of operation parameters, such as annealing temperature, the magnitude of the negative gate bias voltage, or the light intensity. A small number of deeply trapped charges remain in the structure, which may be related to defect states in the embedded gate dielectric layer. The floating-gate amorphous silicon thin-film transistor is a potentially viable nonvolatile memory device that can be fabricated at a low temperature on various type of substrates.