A positive-feedback (PF) neuron device capable of threshold tuning and simultaneously processing excitatory (G +) and inhibitory (G-) signals is experimentally demonstrated to replace conventional neuron circuits, for the first time. Thanks to the PF operation, the PF neuron device with steep switching characteristics can implement integrate-and-fire (IF) function of neurons with low-energy consumption. The structure of the PF neuron device efficiently merges a gated PNPN diode and a single MOSFET. Integrateand-fire (IF) operation with steep subthreshold swing (SS < 1 mV/dec) is experimentally implemented by carriers accumulated in an n floating body of the PF neuron device. The carriers accumulated in the n floating body are discharged by an inhibitory signal applied to the merged FET. Moreover, the threshold voltage (Vth) of the proposed PF neuron is controlled by using a charge storage layer. The low-energy consuming PF neuron circuit (~ 0.62 pJ/spike) consists of one PF device and only five MOSFETs for the IF and reset operation. In a high-level system simulation, a deep-spiking neural network (D-SNN) based on PF neurons with four hidden layers (1024 neurons in each layer) shows high-accuracy (98.55%) during a MNIST classification task. The PF neuron device provides a viable solution for high-density and low-energy neuromorphic systems.
A positive feedback (PF) mechanism was adopted for the first time in the cell string of a 3-D NAND flash memory where n + and p + regions are formed on both ends of the string to implement a diode-type cell string. The body consists of a tubetype poly-Si channel. To generate the PF in the channel during a read operation, a new read operation scheme is proposed. In this paper, the simulator was calibrated in terms of trap density ( D it ) of a poly-Si channel extracted from fabricated 3-D NAND flash memory cells. By utilizing the PF, a NAND flash memory cell in a cell string has a steep subthreshold swing of <1 mV/decade.
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