Metal/TiO2 interfaces for memristive switches

Abstract

The interfaces between metal electrodes and the oxide in TiO 2 -based memristive switches play a key role in the switching as well as in the I -V characteristics of the devices in different resistance states. We demonstrate here that the work function of the metal electrode has a surprisingly minor effect in determining the electronic barrier at the interface. In contrast, Ti oxides can be readily reduced by most electrode metals. The amount of oxygen vacancies created by these chemical reactions essentially determines the electronic barrier at the device interfaces.The memristor, the fourth fundamental passive circuit element [1][2][3], has a wide variety of potential applications based on its promising device properties [1][2][3][4][5][6][7], including non-volatility, fast switching (<10 ns), low energy (∼1 pJ/operation), multiple-state operation, scalability and stackability. As suggested by the name, memristors can be used for information storage [8][9][10][11][12][13][14]. Moreover, memristors can function as stateful Boolean logic gates via the material implication operation [15]. In addition, memristors can also be used for neuromorphic computing [16,17] because of their analog switching, and some hybrid circuits due to their ease of stacking [18,19].Among all the kinds of switching materials that have been reported, oxides are the most extensively studied [4]. The interfaces between the metal electrodes and the oxide play a crucial role, especially for bipolar switches [5,6,20]. Under an applied electric field, oxygen vacancies can drift into the interface region, reducing the electronic barrier and resulting in a low-resistance state. Under an electric field with the opposite polarity, the oxygen vacancies are repelled away from the interface region, recovering the electronic barrier to regain the high resistance state [6,21,22]. A family of nanodevices with different switching and currentvoltage (I -V ) characteristics has been demonstrated by manipulating the elemental composition at the two interfaces of a simple metal/oxide/metal device stack [23]. For a crossbar array of memristors in a storage/memory circuit, sneak path currents [24] can be minimized by using memristors with a rectifying I -V characteristic, especially when they are in the low-resistance state. Therefore, interface engineering is critical to obtain the desired switching behavior and electrical properties for memristive devices.From a semiconductor physics point of view, the work function of the electrode metal might be an important factor in determining the electronic barrier at the metal/oxide interface [25]. This barrier in our thin film devices is not a traditional Schottky barrier because the oxide film is amorphous with a large concentration of defects and likely thinner than the depletion region of the semiconducting oxide. We prepared a set of 5 µm × 5 µm cross-point devices with six different top electrode metals (Au, Pt, Ag, Ni, W and Ti) to examine the effect of these contacts on the I -V characteristics, as show...

Electronic and magnetic properties ofTi4O7predicted by self-interaction-corrected density functional theory

“…Furthermore, they predict contradictory electronic structures for the HT phase. Liborio et al used the B3LYP hybrid functional 22 10 when oxygen atoms are removed from TiO 2 as the material switches from a high to a low resistance state.…”

Anatomy of a Nanoscale Conduction Channel Reveals the Mechanism of a High‐Performance Memristor

“…Switching mechanisms in many transition metal oxide based resistance switches [ 5 , 6 , 13 , 46 ] have been extensively studied, and the drift/diffusion of oxygen vacancies [ 47 ] (or anions) driven by an electric fi eld and/or thermochemical reduction/oxidation [ 48 ] are believed to play a key role. Lee et al [ 45 , 49 ] have adopted a drift switching mechanism similar to that introduced for TiO 2 memristive switching [ 13 ] to explain tantalum oxide based devices.…”

Obtaining memristor elements based on non-noble materials

“…in [5][6][7][8], most of them concern the application of TiO 2 films or a TiO 2 /TiO x structure, where TiO x is non-stoichiometric titanium dioxide. The electrodes in these elements are made of only noble metals -Pt or Au.…”