Time Voltage Dependency in Resistance Switching TiO 2
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Time Voltage Dependency in Resistance Switching TiO2 Christian Nauenheim1,2, Dominique Drouin2, Rainer Waser3 and Andreas Ruediger1 1
Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, 1650 blvd. Lionel Boulet, Varennes, QC J3X 1S2, Canada 2 Département de génie électrique et informatique, Université de Sherbrooke, 2500 blvd. Université, Sherbrooke, QC J1K 2R1, Canada 3 Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich, 52425 Jülich, Germany ABSTRACT Resistively switching TiO2 thin films show a multitude of resistance states, which are achieved during the programming and erasing of a memory cell. These resistance states depend on the applied voltage and the allowed current. Additionally, the operation time has a relevant influence on the adjusted resistance. This parameterization points out a potential application in future multi-level cell memory systems, but also determines the persistence of the non-volatile nature and provides an additional insight into the physics of the resistance switching. Our devices consist of metal-insulator-metal stacks made of Pt/TiO2/Ti/Pt, which are built up in crosspoint junctions. The maximum programming current and the maximum erase voltage amplitude were used to tune in the low resistance and high resistance state, respectively, in combination with the operation time. The corresponding dependencies were determined by quasi-static voltage sweeps, pulse bursts and single pulses of up to 4 V and down to 10 ns. INTRODUCTION Resistively switching TiO2 is a common prototype material for the application in future Resistance Random Access Memories (RRAM), often referred to as ‘memristor’ [1, 2]. The resistance of a corresponding thin film can be toggled by overstepping a threshold voltage for a programming or erasing transition, each with a pertinent polarity. ‘Programming’ and ‘erasing’ are analogies to the nomenclature of Flash-Memory operation, in which programming corresponds to an increase and erasing to a decrease of the resistance [3]. For operation voltages between these thresholds, resistance states are maintained, which classifies the respective memory device as non-volatile. In addition, this range is used for the non-destructive read-out of the memorized information. However, recent publications show that TiO2 thin films offer more than two distinctive states between a maximum high resistance state (HRS) and a minimal low resistance state (LRS) [4, 5]. As a number of certain resistances present a corresponding number of logical states, this condition allows the application of multi-bit data storage in a single cell. Besides the non-volatile nature, resistively switching materials are suitable for the application in future memory cells due to their potentially high integration density based on a simple twoterminal configuration. This makes an active setup with a serial transistor for each cell [6] or passive crossbar array possible [7]. Finally, the examined combination of TiO2 and Ti sandwiched between two Pt electr
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