Resistive memory (ReRAM) based on a solid-electrolyte insulator is a promising nanoscale device and has great potentials in nonvolatile memory, analog circuits, and neuromorphic applications. The underlying resistive switching (RS) mechanism of ReRAM is suggested to be the formation and rupture of nanoscale conductive filament (CF) inside the solid-electrolyte layer. However, the random nature of the nucleation and growth of the CF makes their formation difficult to control, which is a major obstacle for ReRAM performance improvement. Here, we report a novel approach to resolve this challenge by adopting a metal nanocrystal (NC) covered bottom electrode (BE) to replace the conventional ReRAM BE. As a demonstration vehicle, a Ag/ZrO(2)/Cu NC/Pt structure is prepared and the Cu NC covered Pt BE can control CF nucleation and growth to provide superior uniformity of RS properties. The controllable growth of nanoscale CF bridges between Cu NC and Ag top electrode has been vividly observed by transmission electron microscopy (TEM). On the basis of energy-dispersive X-ray spectroscopy (EDS) and elemental mapping analyses, we further confirm that the chemical contents of the CF are mainly Ag atoms. These testing/metrology results are consistent with the simulation results of electric-field distribution, showing that the electric field will enhance and concentrate on the NC sites and control location and orientation of Ag CFs.
The Au/ Cr/ Zr +-implanted-ZrO 2 / n +-Si sandwiched structure exhibits reversible bipolar resistive switching behavior under dc sweeping voltage. The resistance ratio ͑R ratio ͒ of high resistive state and low resistive state is as large as five orders of magnitude with 0.5 V readout bias. Zr +-implanted-ZrO 2 films exhibit good retention characteristics and high device yield. The impact of implanted Zr + ions on resistive switching performances is investigated. Resistive switching of the fabricated structures is explained by trap-controlled space charge limited current conduction.
We report the direct electrical measurement of multiple resistance steps in the ZrO2-based solid electrolyte nonvolatile memory device using the refined dc I-V method with a very small voltage increasing rate. The results demonstrate that multiple conductive filaments are formed successively between the bottom and top metal electrodes through the insulating layer while increasing the bias voltage, which are consistent with the electrical field simulation results based on the solid electrolyte theory. The inverse relationship between resistance steps and the filament formation sequence are obtained, which helps understand the switching mechanism of the multiple conductive filaments.
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