TiO₂-based memristors and ReRAM: materials, mechanisms and models (a review)

Abstract

The memristor is the fundamental non-linear circuit element, with uses in computing and computer memory. ReRAM (Resistive Random Access Memory) is a resistive switching memory proposed as a nonvolatile memory. In this review we shall summarise the state of the art for these closely-related fields, concentrating on titanium dioxide, the well-utilised and archetypal material for both. We shall cover material properties, switching mechanisms and models to demonstrate what ReRAM and memristor scientists can learn from each other and examine the outlook for these technologies.

Effect of write voltage and frequency on the reliability aspects of memristor-based RRAM

“…This is due to fact that the different physical mechanisms such as ionic [29], electrochemical [30], Joule heating [31], raising and lowering Schottky barriers [32] etc are getting associated with the memristor device. The detailed discussion of various conduction mechanisms can be found in [20,33,34].…”

Overview of emerging memristor families from resistive memristor to spintronic memristor

“…2, 3 clearly shows that the resistive material when operated in the bipolar switching mode exhibits an analogous I-V curve to that of the theoretical memristor. As a consequence, considerable research efforts have been recently dedicated to the development of the memristor using resistive materials such as TiO 2 [9,11,29], ZnO [30], and TaO x [31,32], thus triggering a presence of some resistive materials-based memristor prototypes.…”

“…In addition to the thermochemical effect and the ionic effect, other possible mechanisms that include metalsemiconductor transition [29,40], crystalline TiO 2 -amorphous TiO 2 phase transition via conduction heating and breaking [29,41], raising and lowering Schottky barriers via bulk or interface transport of the oxygen [29,42], and conductance heating causing lateral transport of conducting filaments [29,43], have also been proposed to account for the resistance switching of the resistive memristor. The presence of various switching mechanisms is possibly due to the fact that the resistive materials were fabricated and measured differently among the aforementioned literatures.…”

“…Therefore, ReRAM can not be strictly recognized as a memristor. In spite of such a difference, scientists still believe that there is at least convergence between them and some researchers even use these two terms interchangeably [29].…”

A model for the voltammetric behaviour of TiO2 memristors

“…Typically, it takes the form of a very thin (tens of nm) layer of TiO 2 sandwiched between two electrodes which can be Pt, Al or Au. While there have been many examples of memristors [1], based on a variety of systems [2], there has not been a great deal of work understanding how the charge is passed through the device. In the paper by Strukov et al [3], there is a diagram of a TiO 2 layer which shows an image of a memristor which is converted from an undoped (highresistance) form to a doped (low-resistance) form by means of a passage of charge.…”