J. Strozier

Spatially extended nature of resistive switching in perovskite oxide thin films

The authors report the direct observation of the electric pulse induced resistance-change effect at the nanoscale on La1−xSrxMnO3 thin films by the current measurement of the atomic force microscopy (AFM) technique. After a switching voltage of one polarity is applied across the sample by the AFM tip, the conductivity in a local nanometer region around the AFM tip is increased, and after a switching voltage of the opposite polarity is applied, the local conductivity is reduced. This reversible resistance switching effect is observed under both continuous and short-pulse-voltage switching conditions. It is important for future nanoscale nonvolatile memory device applications.

Direct resistance profile for an electrical pulse induced resistance change device

We report the direct microscale resistance profile measurements on a symmetric thin-film electrical pulse induced resistance change (EPIR) device composed of a Pa0.7Ca0.3MnO3 (PCMO) active layer, using surface scanning Kelvin probe microscopy. The resistance switching is found to be an integration of the resistance changes from three parts of the device: the two interface regions within ∼1–3μm of the electrical contacts, and the bulk PCMO material. Such a symmetric EPIR device showed a “table leg” resistance switching hysteresis loop under electric pulsing at room temperature. The symmetric EPIR device may be used as a resistive random access memory nonvolatile memory device with different operation modes by controlling electric pulse voltage.

Resistance Non-volatile Memory – RRAM

Electric-pulse induced resistance (EPIR) change effect encompasses the reversible change of resistance of a thin oxide film under the application of short, low voltage pulses. The phenomenon is widely observed in complex and binary oxides, and is the basis for development of non-volatile resistance random access memory (RRAM). A variety of analytical techniques have been employed to understand the origin of the resistance change with recent data yielding a model incorporating oxygen ion/vacancy diffusion and pile-up near the interface region of the oxide at the impervious metal interface. Further efforts are still required to fine tune the model and apply it to the optimization of RRAM device development.

Resistance switching in oxide thin films

Resistance switching in transition metal oxide thin films has been observed in a variety of complex and binary oxides, and is the basis for development of non-volatile resistance random access memory (RRAM). We review here the electric-pulse induced resistance (EPIR) change effect, which is responsible for this switching and encompasses the reversible change of resistance of a thin oxide film under the application of short- and low-voltage pulses. Although the phenomenon has been observed in a number of oxide systems, there is still limited understanding of the origin of the resistance change. A recent model that has found fair acceptability incorporates oxygen ion/vacancy diffusion and pile-up near the interface region of the oxide at the impervious metal interface. Further efforts are still required to fine tune the model and apply it to the optimization of RRAM device development.

A study of the symmetry properties and multi-state nature of perovskite oxide-based electrical pulse induced resistance-change devices

A new model of a symmetric two-terminal non-volatile RRAM device based on Perovskite oxide thin film materials, specifically Pr1-xCaxMnO3 (PCMO), is proposed and analyzed. The model consists of two identical half-parts, which are completely characterized by the same resistance verses pulse voltage hysteresis loop, connected together in series. Even though the modeled device is physically symmetric with respect to the direction of current, it is found to exhibit switching of the resistance with the application of voltage pulses of sufficient amplitude and of different polarities. The apparent breakdown of parity conservation of the device is attributed to changes in resistance of the active material layer near the electrodes during switching. Thus the switching is history dependent, a feature that can be very useful for the construction of real non-volatile memory devices. An actual symmetric device, not previously reported in the literature and based on the proposed model, is fabricated in the PCMO material system. Measurements of the resistance of this new device generated an experimental hysteresis curve that matches well the calculated hysteresis curve of the model, thus confirming the features predicated by the new symmetric model.A new symmetric two-terminal non-volatile electrical pulse induced resistance-change (EPIR) device is fabricated in the Pr0.7Ca0.3MnO3 (PCMO) materials system and analysed. Two actual devices of somewhat different construction are tested. Both consist of two similar half-parts, characterized by similar resistance versus pulse voltage hysteresis loops, which are reversely connected together in series forming a reflection symmetric device. Even though the devices are as physically symmetric as possible, they are found to exhibit resistance-switching under the application of voltage pulses of different amplitude and of different polarities. A symmetric model of the above device is proposed, and its analysis confirms the features noted above. The switching is history dependent and shows multi-intrinsic state resistance switching, which is very useful for developing future multi-bit EPIR devices.

A MICROSCOPIC ANALYSIS ON THE ELECTRICAL PULSE INDUCED RESISTANCE CHANGE EFFECT

ABSTRACT We have carried out microscopic resistance profile measurements by scanning probe microscopy (SPM) and model analyses on a symmetric thin-film electrical pulse induced resistance change (EPIR) device having a Pr0.7Ca0.3MnO3(PCMO) active layer. The film morphology and surface potential distribution has been examined by atomic force microscopy (AFM) and surface scanning Kelvin probe microscopy (SKPM). Resistance distribution profiles across the device indicate contribution to the resistance switching from three parts of the device: the two PCMO interface regions within ∼1–3 μ m around the metal electrode/PCMO contacts, and the bulk PCMO material. Such an EPIR device showed a symmetric resistance switching behavior under electric pulsing at room temperature. This research indicates that the EPIR device may be used as a nonvolatile resistive random access memory (RRAM) device with different operation modes by controlling electric pulse voltage. The result is also important for understanding the resistance switching behavior in the EPIR device.