Comparison of synaptic properties considering dopant concentration and device operation polarity in Cu/SiN/SiO₂/p-Si devices for neuromorphic system

In this study, we characterize Cu/SiN/SiO₂/Si devices with different dopant concentrations in the silicon surface for use as synaptic devices in neuromorphic systems. We verified the device stack by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). An abrupt change is observed in Cu/SiN/SiO₂/p⁺⁺-Si at positive SET and negative RESET values, where Cu diffusion is involved in the conducting path. On the other hand, abrupt SET and gradual RESET values are observed in Cu/SiN/SiO₂/p⁺⁺-Si at negative SET operation and positive RESET operation, when intrinsic resistive switching occurs in SiN. The Cu/SiN/SiO₂/p⁺-Si device shows gradual bipolar resistive switching with negative SET and positive RESET. Lower current switching and more gradual switching is possible in the Cu/SiN/SiO₂/p⁺-Si device due to the series resistance. Potentiation and depression of the Cu/SiN/SiO₂/p⁺-Si device can be more accurately controlled by pulses than is the case for the Cu/SiN/SiO₂/p⁺⁺-Si device. Moreover, we reveal that the Cu/SiN/SiO₂/p⁺-Si device is more suitable for use as a synaptic device than the Cu/SiN/SiO₂/p⁺⁺-Si device according to the MNIST pattern recognition test.