Internal Cell Resistance as the Origin of Abrupt Reset Behavior in HfO2-Based Devices Determined from Current Compliance Series

Abstract

The resistive switching behavior in different HfO2/TiO2 nano crossbar structures of 100 x 100 nm² size is analyzed by means of DC voltage sweeps. The devices fabricated from 3 nm thin ALD layers of HfO2 and TiO2 sandwiched between Pt and Hf or Ti electrodes show VCM-type bipolar resistive switching after electroforming. For increased compliance current (cc) during set from 50 µA to 800 µA, the set current runs into self- limitation while the reset behavior changes from gradual to abrupt. A model is defined with an internal resistance being in series with the local resistive switch. A recursive algorithm is applied to the cc series for calculation of the series resistor and evaluation of the intrinsic switching characteristic of HfO2-based cells. The intrinsic LRS turns out to be current compliance controlled and to follow the universal switching rule. Supported by compact modelling, we show that an abrupt reset behavior might arise even for materials with a gradual intrinsic reset characteristic in consequence of an internal series resistor.