Electrical analysis of filamentary resistive switching behaviors based on tantalum oxide material for nonvolatile memory

Abstract

This doctoral dissertation describes an experimental study on various types of resistive switching behaviors and corresponding switching mechanisms of Ta2O5-x based devices, such as single layer with different metals, pillar-type electrode and poly-crystalline tantalum oxide fabricated with annealing.

In the first place, the influence of variable oxygen concentration in TaOx active layers upon the forming process and bipolar resistive switching (BRS) features of TaOx-based resistive switching cells. TaOx active layers prepared using various rf sputtering powers were systematically analyzed to identify the relation between initial compositions and BRS behavior. Proper control of oxygen vacancy concentration was clearly identified as a basic factor in ensuring typical BRS features without affecting the structural properties. The possible origins about the conduction and switching origins were described based on the variation of oxygen concentrations initially provided by growth conditions

Secondly, a clear evidence of multiple filaments in TaOx-based resistive switching devices is demonstrated using a pillar-type electrode with equivalent circuit analysis. Using the pillar-type electrode, the switching area of the tested devices are varied by the state of the device. On the initial state, the effective cell area is equal to the large top electrode, on the other hands, the switching area after the forming process is restricted to the small area of the pillar type electrode. By observing a current and switching characteristics of the device, the creation of multiple filaments is demonstrated.

Thirdly, the resistive switching characteristics of Pt/TaOx/CuTe devices were investigated with CuTe bottom electrodes deposited under different working pressure. The CuTe bottom electrode was prepared using a magnetron radio-frequency sputtering. The resistance and distribution of HRS were decreased with increasing deposition pressure of CuTe bottom electrode and then the resistance of LRS was increased however the distribution of LRS was unchanged. Furthermore, the CuTe bottom electrode was systematically analyzed to identify the effect of deposition condition on resistive switching behavior and identifying the mechanism of above phenomenon. As a result, the intermixing between the TaOx layer and CuTe bottom electrode was clearly identified as an active factor causing the variation of resistive switching parameters. Furthermore, conical filaments creation was successfully demonstrated by electrical analysis.