This paper reports a resistive switching device of Au/ZnO/stainless steel (SS) and its applicability as a flexible resistive random access memory (ReRAM). The Au/ZnO/SS structure was fabricated by radio frequency sputtering deposition of a ZnO thin film on the SS substrate. The fabricated device showed stable unipolar and bipolar resistive switching behaviors with reliable switching responses over 100 cycles. The device performance was not degraded upon bending, which indicates high potential for flexible ReRAM applications.

This paper reports the coexistence of unipolar and bipolar resistive switching (BRS) in an Ag/ZnO/Pt structure fabricated by sputtering deposition at room temperature. The structure shows reproducible and stable unipolar resistive switching after electroforming with high compliance current $\left(I_{\text{c}}\right)=40\text{mA}$ , regardless of the applied voltage polarity. With low $I_{\text{c}}=5\text{mA}$ at electroforming, BRS was also observed; this phenomenon depended on the voltage polarity. Both states were stable and reproducible over 100 cycles. The switching mode was changed with adjusting $I_{\text{c}}$ but the transition was irreversible. Based on the results, switching mechanism based on filament theory is proposed to explain both resistive switching.

Resistive switching memory devices are promising candidates for emerging memory technologies because they yield outstanding device performance. Storage mechanisms for achieving high-density memory applications have been developed; however, so far many of them exhibit typical resistive switching behavior from the limited controlling conditions. In this study, we introduce photons as an unconventional stimulus for activating resistive switching behaviors. First, we compare the resistive switching behavior in light and dark conditions to describe how resistive switching memories can benefit from photons. Second, we drive the switching of resistance not by the electrical stimulus but only by the modulation of photon. ZnO nanorods were employed as a model system to demonstrate photo-stimulated resistive switching in high-surface-area nanomaterials, in which photo-driven surface states strongly affect their photoconductivity and resistance states.

Resistive switching characteristics of hafnium oxide were studied for possible nonvolatile memory device applications. The <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Hf</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>HfO2 films were grown by metallorganic chemical vapor deposition (MOCVD) at <mml:math display="inline"><mml:mrow><mml:mn>400</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>400°C using tetrakis(diethylamido)hafnium <mml:math display="inline"><mml:mrow><mml:mo>[</mml:mo><mml:mi mathvariant="normal">Hf</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi mathvariant="normal">N</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow></mml:math>[Hf(N(C2H5)2)4] as a precursor and oxygen gas as an oxidizing agent. The film was polycrystalline and had gradational compositions of Hf and O atoms. Current-voltage characteristics of the films were investigated with <mml:math display="inline"><mml:mrow><mml:mn>1</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>mA</mml:mi></mml:mrow></mml:math>1mA compliance. A reproducible resistance switching behavior was observed with high resistance ratio of about <mml:math display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup><mml:mo>–</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>9</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>104–109 , which is higher than other comparable materials, such as <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ti</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>TiO2 and <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Zr</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>ZrO2 . SET and RESET voltages were measured about 0.8 and <mml:math display="inline"><mml:mrow><mml:mn>1.5</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">V</mml:mi></mml:mrow></mml:math>1.5V , respectively, indicating that the device can be operated below <mml:math display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">V</mml:mi></mml:mrow></mml:math>2V . The devices were operated in ohmic conduction mechanism. During the forming process, characteristics of Schottky emission were observed, which indicates that conduction mechanisms between SET and forming processes are different. The bipolar resistance switching behavior was also observed as well as unipolar resistance switching behavior.