Hopping Conduction in Intermediate Resistance State of Tantalum Oxide Resistive Switching Memory

Abstract

Resistive switching memory with a simple MIM (metal-insulator-metal) structure has the characteristics of high operation speed, high retention time, low operation voltage. Generally, the resistance switching mechanism is strongly related to defect states in oxide and the electrode/oxide interface. Based on I-V sweeping curves, Ta/TaOx/Pt device can be operated in bipolar mode, with writing at positive bias and erasing at negative bias. Different resistance states are achieved in the device by controlling the reset stop voltage under bipolar mode operation. According to the I-V measurement at various temperatures, it is observed that conduction mechanisms are different in three resistance states of the device. The low resistance state (LRS) shows ohmic conduction with a semiconductor-like behavior. This situation can be interpreted by the existence of the oxygen vacancy filament connecting the top and bottom electrodes. The high resistance state (HRS) is governed by Schottky emission conduction. The intermediate resistance state (IRS) shows hopping conduction. It can be regarded as changing of interior state of the active layer between HRS and IRS. To characterize separate contribution to the total resistance from individual component, complex impedance spectroscopy is used to study three resistance states of the device. It is shown that HRS and IRS can be described with an equivalent circuit consisting of the major components R 1, R 2, R3, C1and C 2, and LRS can be characterized with an equivalent circuit consisting of the major components R 1, R 2, R3, C1. These components show a strong dependence on the reset stop voltage, which can be explained in the framework of oxygen vacancy model and conductive filament concept. According to results of temperature-dependent I-V measurement and complex impedance analysis, different current conduction mechanisms and values of major components in equivalent circuit in three resistance states can be attributed to changing of the filament structure and the oxygen vacancy distribution.