No abstract

Highly reproducible bipolar resistance switching was recently demonstrated in a composite material of Pt nanoparticles dispersed in silicon dioxide. Here, we examine the electrical performance and scalability of this system and demonstrate devices with ultrafast (<100 ps) switching, long state retention (no measurable relaxation after 6 months), and high endurance (>3 × 10(7) cycles). A possible switching mechanism based on ion motion in the film is discussed based on these observations.

TaO(x)-based memristors have recently demonstrated both subnanosecond resistance switching speeds and very high write/erase switching endurance. Here we show that the physical state variable that enables these properties is the oxygen concentration in a conduction channel, based on the measurement of the thermal coefficient of resistance of different TaO(x) memristor states and a set of reference Ta-O films of known composition. The continuous electrical tunability of the oxygen concentration in the channel, with a resolution of a few percent, was demonstrated by controlling the write currents with a one transistor-one memristor (1T1M) circuit. This study demonstrates that solid-state chemical kinetics is important for the determination of the electrical characteristics of this relatively new class of device.

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...

We present resistive switching model for TaOx memristors, which demonstrates that the radius of a tantalum rich conducting filament is the state variable controlling resistance. The model tracks the flux of individual oxygen ions and permits the derivation and solving of dynamical and static state equations. Model predictions for ON/OFF switching were tested experimentally with TaOx devices and shown to be in close quantitative agreement, including the experimentally observed transition from linear to non-linear conduction between RON and ROFF. This work presents a quantitative model of state variable dynamics in TaOx memristors, with direct comparison to high-speed resistive switching data.