Abstract
The nature and direction of the hysteresis in memristive devices is critical to device operation and performance and the ability to realise their potential in neuromorphic applications. TiO2 is a prototypical memristive device material and is known to show hysteresis loops with both clockwise switching and counter-clockwise switching and in many instances evidence of negative differential resistance (NDR) behaviour. Here we study the electrical response of a device composed of a single nanowire channel Au–Ti/TiO2/Ti–Au both in air and under vacuum and simulate the I–V characteristics in each case using the Schottky barrier and an ohmic-like transport memristive model which capture nonlinear diffusion and migration of ions within the wire. The dynamics of this complex charge conduction phenomenon is obtained by fitting the nonlinear ion-drift equations with the experimental data. Our experimental results support a nonlinear drift of oxygen vacancies acting as shallow donors under vacuum conditions. Simulations show that dopant diffusion under bias creates a depletion region along the channel which results in NDR behaviour, but it is overcome at higher applied bias due to oxygen vacancy generation at the anode. The model allows the motion of the charged dopants to be visualised during device operation in air and under vacuum and predicts the elimination of the NDR under low bias operation, in agreement with experiments.
Highlights
Simulations show that dopant diffusion under bias creates a depletion region along the channel which results in negative differential resistance (NDR) behaviour, but it is overcome at higher applied bias due to oxygen vacancy generation at the anode
Resistive Random Access Memory (RRAM) devices have recently attracted a great deal of attention due to their superior characteristics that include a simple metal–insulator–metal (MIM) structure, high-density integration, and fast write/erase operation.[1,2]
To support all memristive models used to describe the dynamics of the tunnelling and Schottky channels within the Au–Ti/TiO2/ Ti–Au device, we exposed the system to air from which we expect to isolate other aspects that corroborate with the ion dri diffusion picture with recurrent concentration of dopants
Summary
We study the electrical response of a device composed of a single nanowire channel Au–Ti/TiO2/Ti–Au both in air and under vacuum and simulate the I–V characteristics in each case using the Schottky barrier and an ohmic-like transport memristive model which capture nonlinear diffusion and migration of ions within the wire. The dynamics of this complex charge conduction phenomenon is obtained by fitting the nonlinear ion-drift equations with the experimental data. We describe the surprisingly complex electrical behaviour of a simple TiO2 RRAM device under both air and vacuum and apply an extended ion-dri memristance model that accurately describes the device response and provides new insights into its conduction mechanisms
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