One of a challenging issue in developing brain-inspired hardware is to implement nonvolatile analog synaptic devices in a compact structure. Various types of volatile (capacitor-based) analog synaptic devices have been developed [1–3], whereas types of nonvolatile analog synaptic devices are limited so far. Present nonvolatile synaptic devices use flash-based or its alternative technologies [4–6], however, they had difficulties in designing compact circuits for electron injection and ejection as well as in establishing the high reliability.