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Woo, Hyunsuk,Vishwanath, Sujaya Kumar,Jeon, Sanghun Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.753 No.-
<P><B>Abstract</B></P> <P>Atomic switches are well-known promising candidates for future application in non-volatile logic memory devices. The resistive switching characteristics of these devices depend on the formation of a conductive filament (CF) by active metal electrodes. However, the formation of a stable CF is still a challenge owing to filament overgrowth in the solid electrolyte. To achieve controlled CF growth, we have used a modified active electrode with different Cu<SUB>x</SUB>Se<SUB>1−x</SUB> composition ratios (0.01 < x < 0.45) and a titanium (Ti) buffer layer. The optimum composition was determined to be Cu<SUB>0.11</SUB>Se<SUB>0.89</SUB>/Ti (2.5 nm) for which excellent resistive switching properties were observed, such as a high on/off ratio of 10<SUP>4</SUP>, low operating voltage, uniform resistance distribution, ten-year data retention at 85 °C, and <B>uniform endurance</B> (2000 cycles). The improvement is can be described from the high controllability of the oxidation-reduction reaction rate of the optimized CuSe modified active electrode by the means of Ti buffer layer and the TiO bond formation at the Ti/Al<SUB>2</SUB>O<SUB>3</SUB> interface. In addition, depth profiles of the conductive filament based on Cu<SUB>0.11</SUB>Se<SUB>0.89</SUB> with a Ti buffer layer were studied by performing current atomic force microscopy (I-AFM) to evaluate the enhancements in electrical performance and reliability resulting from the insertion of the Ti buffer layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First report on CuSe based atomic switch. </LI> <LI> Improved reliability depends on interface reaction at Ti/Al<SUB>2</SUB>O<SUB>3</SUB>. </LI> <LI> CuSe/Ti/Al<SUB>2</SUB>O<SUB>3</SUB>/Pt device showed highly stable retention at 102 °C for ten years. </LI> <LI> 860 nm<SUP>2</SUP> area of cross section of conductive filament is observed from I-AFM. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Resistive switching characteristics of CuSe/Ti-based atomic switch with controlled filament.</P> <P>[DISPLAY OMISSION]</P>
Woo, Hyunsuk,Vishwanath, Sujaya Kumar,Jeon, Sanghun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.9
<P>The next-generation electronic society is dependent on the performance of nonvolatile memory devices, which has been continuously improving. In the last few years, many memory devices have been introduced. However, atomic switches are considered to be a simple and reliable basis for next-generation nonvolatile devices. In general, atomic switch-based resistive switching is controlled by electrochemical metallization. However, excess ion injection from the entire area of the active electrode into the switching layer causes device nonuniformity and degradation of reliability. Here, we propose the fabrication of a high-performance atomic switch based on Cu<SUB><I>x</I></SUB>-Se<SUB>1-<I>x</I></SUB> by inserting lanthanide (Ln) metal buffer layers such as neodymium (Nd), samarium (Sm), dysprosium (Dy), or lutetium (Lu) between the active metal layer and the electrolyte. Current-atomic force microscopy results confirm that Cu ions penetrate through the Ln-buffer layer and form thin conductive filaments inside the switching layer. Compared with the Pt/Cu<SUB><I>x</I></SUB>-Se<SUB>1-<I>x</I></SUB>/Al<SUB>2</SUB>O<SUB>3</SUB>/Pt device, the optimized Pt/Cu<SUB><I>x</I></SUB>-Se<SUB>1-<I>x</I></SUB>/Ln/Al<SUB>2</SUB>O<SUB>3</SUB>/Pt devices show improvement in the on/off resistance ratio (10<SUP>2</SUP>-10<SUP>7</SUP>), retention (10 years/85 °C), endurance (∼10 000 cycles), and uniform resistance state distribution.</P> [FIG OMISSION]</BR>
Kang, Dong-Ho,Choi, Woo-Young,Woo, Hyunsuk,Jang, Sungkyu,Park, Hyung-Youl,Shim, Jaewoo,Choi, Jae-Woong,Kim, Sungho,Jeon, Sanghun,Lee, Sungjoo,Park, Jin-Hong American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.32
<P>In this study, we demonstrate a high-performance solid polymer electrolyte (SPE) atomic switching device with low SET/RESET voltages (0.25 and -0.5 V, respectively), high on/off-current ratio (10(5)), excellent cyclic endurance (>10(3)), and long retention time (>10(4) s), where poly-4-vinylphenol (PVP)/poly(rnelamine-co-formaldehyde) (PMF) is used as an SPE layer. To accomplish these excellent device performance parameters, we reduce the off-current level of the PVP/PMF atomic switching device by improving, the electrical insulating property of the PVP/PMF electrolyte through adjustment of the number of cross-linked chains. We then apply a titanium buffer layer to the PVP/PMF switching device for further improvement of bipolar switching behavior and device stability. In addition, we first implement SPE atomic switch-based logic AND and OR circuits with low operating voltages below 2 V by integrating 5 X 5 arrays of PVP/PMF switching devices on the flexible substrate. In particular, this low operating voltage of our logic circuits was much lower than that (>5 V), of the circuits configured by polymer resistive random access memory. This research successfully presents the feasibility of PVP/PMF atomic switches for flexible integrated circuits for next generation electronic applications.</P>
Single-Atom Switches and Single-Atom Gaps Using Stretched Metal Nanowires
Wang, Qingling,Liu, Ran,Xiang, Dong,Sun, Mingyu,Zhao, Zhikai,Sun, Lu,Mei, Tingting,Wu, Pengfei,Liu, Haitao,Guo, Xuefeng,Li, Zong-Liang,Lee, Takhee American Chemical Society 2016 ACS NANO Vol.10 No.10
<P>Utilizing individual atoms or molecules as functional units in electronic circuits meets the increasing technical demands for the miniaturization of traditional semiconductor devices. To be of technological interest, these functional devices should be high-yield, consume low amounts of energy, and operate at room temperature. In this study, we developed nanodevices called quantized conductance atomic switches (QCAS) that satisfy these requirements. The QCAS operates by applying a feedback-controlled voltage to a nanoconstriction within a stretched nanowire. We demonstrated that individual metal atoms could be removed from the nanoconstriction and that the removed metal atoms could be refilled into the nanoconstriction, thus yielding a reversible quantized conductance switch. We determined the key parameters for the QCAS between the 'on' and 'off' states at room temperature under a small operating voltage. By controlling the applied bias voltage, the atoms can be further completely removed from the constriction to break the nanowire, generating single-atom nanogaps. These atomic nanogaps are quite stable under a sweeping voltage and can be readjusted with subangstrom accuracy, thus fulfilling the requirement of both reliability and flexibility for the high-yield fabrication of molecular devices.</P>
Lim, Seokjae,Woo, Jiyong,Hwang, Hyunsang Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.9
<P>Bipolar-threshold switching was demonstrated using volatile-atomic switches (VAS) for cross-point selector applications. The VAS (Cu/Cu<SUB>2</SUB>S/W) exhibits asymmetric current–voltage (I–V) characteristics. An abrupt conductance change occurs by the formation of a Cu filament when a positive voltage is applied to the Cu electrode. Meanwhile, nonlinear I–V characteristics are observed because of the high concentration of vacancy of Cu under a negative voltage. We thus introduce the complementary-VAS configuration for the self-compliance characteristics at both polarities. Furthermore, the increased the switching voltage at a fast sweeping rate allows the VAS to show a strong immunity to electrical disturbance.</P>
Epitaxial Brownmillerite Oxide Thin Films for Reliable Switching Memory
Acharya, Susant K.,Nallagatla, Raveendra Venkata,Togibasa, Octolia,Lee, Bo W.,Liu, Chunli,Jung, Chang U.,Park, Bae Ho,Park, Ji-Yong,Cho, Yunae,Kim, Dong-Wook,Jo, Janghyun,Kwon, Deok-Hwang,Kim, Miyoung American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.12
<P>Resistive switching memory, which is mostly based on polycrystalline thin films, suffers from wide distributions in switching parameters including set voltage, reset voltage, and resistance in their low- and high-resistance states. One of the most commonly used methods to overcome this limitation is to introduce inhomogeneity. By contrast, in this paper, we obtained uniform resistive switching parameters and sufficiently low forming voltage by maximizing the uniformity of an epitaxial thin film. To achieve this result, we deposited an SrFeOx/SrRuO3 heteroepitaxial structure onto an SrTiO3 (001) substrate by pulsed laser deposition, and then we deposited an Au top electrode by electron-beam evaporation. This device exhibited excellent bipolar resistance switching characteristics, including a high on/off ratio, narrow distribution of key switching parameters, and long data retention time. We interpret these phenomena in terms of a local, reversible phase transformation in the SrFeOx film between brownmillerite and perovskite structures. Using the brownmillerite structure and atomically uniform thickness of the heteroepitaxial SrFeOx thin film, we overcame two major hurdles in the development of resistive random-access memory devices: high forming voltage and broad distributions of switching parameters.</P>
Young-Min Kim,Sang-Heon Park,Yoongu Lee,Jong-Souk Yeo 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
Understanding the switching mechanism of Ovonic threshold switch (OTS) is necessary to improve device performance. Tt is hard to observe the switching region since it is usually localized in nanoscale dimension. To elucidate switching phenomenon, slice-and-view technique using conductive atomic force microscopy (C-AFM) is a direct approach as an advanced analysis technique. This can help us identify localized switching region by measuring the current using a nanoscale tip. Process conditions such as slice depth and pressure can be optimized for analysis to provide insight on OTS mechanism.
Lin Chen,Qing-Qing Sun,Jing-Jing Gu,Yan Xu,Shi-Jin Ding,David Wei Zhang 한국물리학회 2011 Current Applied Physics Vol.11 No.3
Resistive switching behavior of Nb_2O_5 prepared by atomic layer deposition was investigated as a promising candidate for next generation nonvolatile memory technology. The crystalline structure of deposited film at 300 ℃ was found to be polycrystalline by X-ray diffraction (XRD) and the film was estimated to be oxygen deficient by X-ray photoelectron spectroscopy (XPS). The low resistance ON state and high resistance OFF state can be reversibly altered under low voltage about ±1 V. More than 1000reproducible switching cycles by DC voltage sweep were observed with a resistance ratio above 10,which was large enough to read out for memory applications. Moreover, the HRS and LRS of the devices are stable for more than 5 × 10^4 s and does not show any degradation during the test.