Effects of water adsorption on conductive filaments of a Ta₂O₅ atomic switch investigated by nondestructive electrical measurements

Atomic switches based on a metal/oxide/metal structure have attracted considerable attention for application in nonvolatile switching memory devices. In atomic switches, the formation and rupture of atomic-scale conductive metal filaments can be controlled via an applied voltage, which is central to the optimization of the resistive switching of such switches. Because the high-resistance (OFF) state is determined by the previous rupture (RESET) process and affects the subsequent formation process, it is important to know the filament structure and the electronic states in the OFF state. However, direct observation of the structure and electronic states is exceedingly difficult in the case of filaments embedded in the oxide matrix. In this paper, we propose a nondestructive methodology to evaluate the filament structure and electronic states in the OFF state based on current–voltage measurements. Using this method, the OFF states of a Ag/Ta₂O₅/Pt atomic switch were characterized, and changes in the size and potential barrier of a ruptured filament were estimated according to the introduction and evacuation of water molecules. The results clarify the effects of moisture, which are important for the operation of oxide-based resistive memories under ambient conditions.