Steadily Decreasing Power Loss of a Double Schottky Barrier Originating from the Dynamics of Mobile Ions with Stable Interface States

A general aging model of the double Schottky barrier was proposed to unveil the long-term aging behaviors of $\mathrm{Zn}\mathrm{O}$ varistor ceramics, especially for those ones with steadily decreasing power loss. For those samples, the barrier height and electrical properties were even enhanced rather than commonly deteriorated, which were beyond the classic ion migration model. In this paper, inspired by the unique reversible aging of them, interface states are proposed to remain stable in those samples. The major mobile ions, which have been in debate, are further identified to be ${\mathrm{Zn}}_{i}^{\ensuremath{\cdot}}$ ions. Based on these assumptions, a quantitative dynamic ion migration-diffusion model is proposed. The calculated power loss steadily decreases with aging time, which well supported our proposal. When the interface states are not combined with those mobile ions, the formation of a ``U-shape'' ion spatial distribution in depletion layers is found to be responsible for the unique aging phenomena, i.e., a reduction in the depletion layer and interfacial charge, a rise in the depletion layer width, and an increase in the barrier height. However, continuously increasing power loss would be generated if the mobile ions combined with the interface states. Therefore, a general mechanism on the aging of the double Schottky barrier is unveiled that it is a competition process between consumption of the interface states and the dynamics of mobile ions in depletion layers.