Open Access proceedings Journal of Physics: Conference series



Dilute Electrodeposition of TiO2 and ZnO Thin Film Memristors on Cu SubstrateF B Fauzi1, M H Ani1,S H Herman2, M A Mohamed31Department of Manufacturing and Materials Engineering, International Islamic University Malaysia (IIUM), Jalan Gombak, 53100 Kuala Lumpur, Malaysia2 NANO-Electronic Centre (NET), Faculty of Electrical Engineering, UniversitiTeknologi MARA, 40450 Shah Alam, Selangor, Malaysia3Institute of Microengineering and Nanoelectronics, UniversitiKebangsaan Malaysia, 43600 UKM-Bangi, Selangor, MalaysiaEmail:mhanafi@iium.edu.myAbstract. Memristor has become one of the alternatives to replace the current memory technologies. Fabrication of titanium dioxide, TiO2 memristor has been extensively studied by using various deposition methods. However, recently more researches have been done to explore the compatibility of other transition metal oxide, TMO such as zinc oxide, ZnO to be used as the active layer of the memristor. This paper highlights the simple and easy-control electrodeposition to deposit titanium, Tiand zinc,Zn thin film at room temperature and subsequent thermal oxidation at 600 oC. Gold, Au was then sputtered as top electrode to create metal-insulator-metal, MIM sandwich of Au/TiO2-Cu2O-CuO/Cu and Au/ZnO-Cu2O-CuO/Cu memristors. The structural, morphological and memristive properties were characterized using Field Emission Scanning Electron Microscopy, FESEM, X-Ray Diffraction, XRD and current-voltage, I-V measurement. Both Au/TiO2-Cu2O-CuO/Cu and Au/ZnO-Cu2O-CuO/Cu memristivitywere identified by the pinched hysteresis loop with resistive ratio of 1.2 and 1.08 respectively. Empirical study on diffusivity of Ti4+, Zn2+and O2-ions in both metal oxides show that the metal vacancies were formed, thus giving rise to its memristivity. The electrodeposited Au/TiO2-Cu2O-CuO/Cu and Au/ZnO-Cu2O-CuO/Cu memristors demonstrate comparable performances to previous studies using other methods.IntroductionMemristor is a promising alternative for the next generation non-volatile memory system. The limitations on size and manufacturing cost of the current memory storage especially for dynamic random access memory, DRAM has closely reached their maximum limit and has driven a tremendous amount of research on memristor. Memristor was first discovered as the fourth fundamental element by Chua ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Chua", "given" : "Leon O.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "IEEE Transations On Circuit Theory", "id" : "ITEM-1", "issue" : "5", "issued" : { "date-parts" : [ [ "1971" ] ] }, "page" : "507-519", "title" : "Memristor-The missing circuit element", "type" : "article-journal", "volume" : "CT-18" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[1]", "plainTextFormattedCitation" : "[1]", "previouslyFormattedCitation" : "[1]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[1] in 1971 and it was experimentally demonstrated in 2008 by William et al. ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "ISSN" : "1476-4687", "PMID" : "18451858", "abstract" : "Anyone who ever took an electronics laboratory class will be familiar with the fundamental passive circuit elements: the resistor, the capacitor and the inductor. However, in 1971 Leon Chua reasoned from symmetry arguments that there should be a fourth fundamental element, which he called a memristor (short for memory resistor). Although he showed that such an element has many interesting and valuable circuit properties, until now no one has presented either a useful physical model or an example of a memristor. Here we show, using a simple analytical example, that memristance arises naturally in nanoscale systems in which solid-state electronic and ionic transport are coupled under an external bias voltage. These results serve as the foundation for understanding a wide range of hysteretic current-voltage behaviour observed in many nanoscale electronic devices that involve the motion of charged atomic or molecular species, in particular certain titanium dioxide cross-point switches.", "author" : [ { "dropping-particle" : "", "family" : "Strukov", "given" : "Dmitri B", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Snider", "given" : "Gregory S", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Stewart", "given" : "Duncan R", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Williams", "given" : "R Stanley", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Nature", "id" : "ITEM-1", "issue" : "7191", "issued" : { "date-parts" : [ [ "2008", "5", "1" ] ] }, "page" : "80-83", "title" : "The missing memristor found.", "type" : "article-journal", "volume" : "453" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[2]", "plainTextFormattedCitation" : "[2]", "previouslyFormattedCitation" : "[2]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[2]. Memristor is a non-volatile memory whichis also known as a resistive random access memory, RRAM made from a simple structure ofMIM sandwich. The advantages of memristor are its fast switching speed, low power consumption and high density ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Chua", "given" : "Leon O.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "IEEE Transations On Circuit Theory", "id" : "ITEM-1", "issue" : "5", "issued" : { "date-parts" : [ [ "1971" ] ] }, "page" : "507-519", "title" : "Memristor-The missing circuit element", "type" : "article-journal", "volume" : "CT-18" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[1]", "plainTextFormattedCitation" : "[1]", "previouslyFormattedCitation" : "[1]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[1]. 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Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. This paper describes the development of NOR type flexible resistive random access memory (RRAM) with a one transistor-one memristor structure (1T-1M). By integration of a high-performance single crystal silicon transistor with a titanium oxide based memristor, random access to memory cells on flexible substrates was achieved without any electrical interference from adjacent cells. The work presented here can provide a new approach to high-performance nonvolatile memory for flexible electronic applications.", "author" : [ { "dropping-particle" : "", "family" : "Kim", "given" : "Seungjun", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Jeong", "given" : "Hu Young", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Kim", "given" : "Sung Kyu", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Choi", "given" : "Sung Yool", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Lee", "given" : "Keon Jae", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Nano Letters", "id" : "ITEM-2", "issue" : "12", "issued" : { "date-parts" : [ [ "2011" ] ] }, "page" : "5438-5442", "title" : "Flexible memristive memory array on plastic substrates", "type" : "article-journal", "volume" : "11" }, "uris" : [ "" ] }, { "id" : "ITEM-3", "itemData" : { "ISBN" : "978-1-4673-3136-4", "abstract" : "This paper presents the fabrication and characterization of ZnO-based Memristor devices with Platinum (Pt) electrodes. Properties of ZnO/ZnOx strongly depends upon the sputtering conditions and heat treatment (annealing) done by rapid thermal process (RTP). Annealing creates the vacancies which provide hysteresis or in other words memory in I-V characteristics of the device. Experimental results show high current density 0.015\u03bcA/\u03bcm2 and Roff/Ron ratio of 2.5 is achieved with Pt electrode. This paper also presents C-V behaviour of the fabricated Memristor without annealing and with annealing. Maximum value of the capacitance is 5.7\u00d710-8 F/cm2 obtained at 0V without annealing. With annealed Memristor, the maximum capacitance 2.3\u00d710-7 F/cm2 is obtain at 0V.", "author" : [ { "dropping-particle" : "", "family" : "Kumar", "given" : "Ashish", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Rawal", "given" : "Yaksh", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Baghini", "given" : "Maryam Shojaei", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "2012 International Conference on Emerging Electronics", "id" : "ITEM-3", "issued" : { "date-parts" : [ [ "2012", "12" ] ] }, "page" : "1-3", "publisher" : "IEEE", "publisher-place" : "Mumbai", "title" : "Fabrication and characterization of the ZnO-based memristor", "type" : "paper-conference" }, "uris" : [ "" ] }, { "id" : "ITEM-4", "itemData" : { "ISBN" : "978-1-4244-5308-5", "abstract" : "We report on the fabrication and electrical characterisation of memristors with TiO2/TiO2+x active layer. This active layer is deposited at room temperature with RF-sputtering and consists of two sub-layers, the top one of which contains excess oxygen atoms. Electrical characterisation of the devices demonstrates similar switching characteristics as previously reported for nano-scale memristors with TiO2/TiO2-x active cores.", "author" : [ { "dropping-particle" : "", "family" : "Prodromakis", "given" : "T", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Michelakis", "given" : "K", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Toumazou", "given" : "C", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "International Symposium on Circuits and Systems (ISCAS)", "id" : "ITEM-4", "issued" : { "date-parts" : [ [ "2010" ] ] }, "page" : "1520-1522", "publisher" : "IEEE", "publisher-place" : "Paris", "title" : "Fabrication and electrical characteristics of memristors with TiO2/TiO2+x active layers", "type" : "paper-conference", "volume" : "2" }, "uris" : [ "" ] }, { "id" : "ITEM-5", "itemData" : { "ISBN" : "1748-3395 (Electronic) 1748-3387 (Linking)", "ISSN" : "1748-3387", "PMID" : "18654568", "abstract" : "Nanoscale metal/oxide/metal switches have the potential to transform the market for nonvolatile memory and could lead to novel forms of computing. However, progress has been delayed by difficulties in understanding and controlling the coupled electronic and ionic phenomena that dominate the behaviour of nanoscale oxide devices. An analytic theory of the 'memristor' (memory-resistor) was first developed from fundamental symmetry arguments in 1971, and we recently showed that memristor behaviour can naturally explain such coupled electron-ion dynamics. Here we provide experimental evidence to support this general model of memristive electrical switching in oxide systems. We have built micro- and nanoscale TiO2 junction devices with platinum electrodes that exhibit fast bipolar nonvolatile switching. We demonstrate that switching involves changes to the electronic barrier at the Pt/TiO2 interface due to the drift of positively charged oxygen vacancies under an applied electric field. Vacancy drift towards the interface creates conducting channels that shunt, or short-circuit, the electronic barrier to switch ON. The drift of vacancies away from the interface annilihilates such channels, recovering the electronic barrier to switch OFF. Using this model we have built TiO2 crosspoints with engineered oxygen vacancy profiles that predictively control the switching polarity and conductance.", "author" : [ { "dropping-particle" : "", "family" : "Yang", "given" : "J. Joshua", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Pickett", "given" : "Matthew D.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Li", "given" : "Xuema", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ohlberg", "given" : "Douglas A. 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Bipolar resistive switches based on metal oxides such as TiO2 have been identified as memristive devices primarily based on the \u201cpinched hysteresis loop\u201d that is observed in their current-voltage i-v characteristics. Here we show that the mathematical definition of a memristive device provides the framework for understanding the physical processes involved in bipolar switching and also yields formulas that can be used to compute and predict important electrical and dynamical properties of the device. We applied an electrical characterization and state-evolution procedure in order to capture the switching dynamics of a device and correlate the response with models for the drift diffusion of ionized dopants vacancies in the oxide film. The analysis revealed a notable property of nonlinear memristors: the energy required to switch a metal-oxide device decreases exponentially with increasing applied current.", "author" : [ { "dropping-particle" : "", "family" : "Pickett", "given" : "Matthew D.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Strukov", "given" : "Dmitri B.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Borghetti", "given" : "Julien L.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Yang", "given" : "J. 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Such devices are of particular interest if they are compatible with back-end-of-line processing for CMOS integrated circuits. A variety of resistance-change technologies show promise in this respect, but a new approach that is based on switching in copper-doped silicon dioxide may be the simplest and least expensive to integrate. This paper describes the characteristics of W-(Cu/SiO2)-Cu programmable metallization cell (PMC) devices formed by the thermal diffusion of Cu into deposited SiO2. PMC devices operate by the electrochemical control of metallic pathways in solid electrolytes. Both unipolar and bipolar resistive switching could be attained in these devices. Bipolar switching, which is identical to that seen in PMC devices based on other solid electrolytes, was observed for low bias (a few tenths of volts) and programming currents in the microampere range. The resistance ratio between high and low states was on the order of 103, and a multibit storage is considered possible via the strong dependence of ON-state resistance on programming current. The low and high resistance states were stable for more than 5 x 104 s. The devices could be made to exhibit unipolar switching using a negative bias on the order of -1 V combined with erase currents of hundreds of microampere to a few milliampere. 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The drop coated aluminium foil memristors compare favourably with the sputter-coated ones, demonstrating an expansion in the accessibility of memristor fabrication. A comparison between aluminium and gold for use as the sputter-coated electrodes shows that aluminium is the better choice as using gold leads to device failure. The devices do not require a forming step.", "author" : [ { "dropping-particle" : "", "family" : "Gale", "given" : "Ella", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Mayne", "given" : "Richard", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Adamatzky", "given" : "Andrew", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Costello", "given" : "Ben de Lacy", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Materials Chemistry and Physics", "id" : "ITEM-1", "issue" : "2", "issued" : { "date-parts" : [ [ "2014", "1" ] ] }, "page" : "524-529", "title" : "Drop-coated titanium dioxide memristors", "type" : "article-journal", "volume" : "143" }, "uris" : [ "" ] }, { "id" : "ITEM-2", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Gergel-Hackett", "given" : "Nadine", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hamadani", "given" : "Behrang", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Dunlap", "given" : "Barbara", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Suehle", "given" : "John", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Member", "given" : "Senior", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Richter", "given" : "Curt", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Member", "given" : "Senior", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hacker", "given" : "Christina", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Gundlach", "given" : "David", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "IEEE Electron Device Letters", "id" : "ITEM-2", "issue" : "1", "issued" : { "date-parts" : [ [ "2009" ] ] }, "page" : "2-4", "title" : "A flexible solution-processed memristor", "type" : "article-journal" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[6], [23]", "manualFormatting" : "[6], [23], ", "plainTextFormattedCitation" : "[6], [23]", "previouslyFormattedCitation" : "[6], [23]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "ISSN" : "02540584", "abstract" : "The fabrication of memristors by drop-coating sol\u2013gel Ti(OH)4 solution onto either aluminium foil or sputter-coated aluminium on plastic is presented. The gel layer is thick, 37 \u03bcm, but both devices exhibit good memristance I\u2013V profiles. The drop coated aluminium foil memristors compare favourably with the sputter-coated ones, demonstrating an expansion in the accessibility of memristor fabrication. A comparison between aluminium and gold for use as the sputter-coated electrodes shows that aluminium is the better choice as using gold leads to device failure. The devices do not require a forming step.", "author" : [ { "dropping-particle" : "", "family" : "Gale", "given" : "Ella", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Mayne", "given" : "Richard", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Adamatzky", "given" : "Andrew", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Costello", "given" : "Ben de Lacy", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Materials Chemistry and Physics", "id" : "ITEM-1", "issue" : "2", "issued" : { "date-parts" : [ [ "2014", "1" ] ] }, "page" : "524-529", "title" : "Drop-coated titanium dioxide memristors", "type" : "article-journal", "volume" : "143" }, "uris" : [ "" ] }, { "id" : "ITEM-2", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Gergel-Hackett", "given" : "Nadine", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hamadani", "given" : "Behrang", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Dunlap", "given" : "Barbara", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Suehle", "given" : "John", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Member", "given" : "Senior", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Richter", "given" : "Curt", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Member", "given" : "Senior", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hacker", "given" : "Christina", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Gundlach", "given" : "David", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "IEEE Electron Device Letters", "id" : "ITEM-2", "issue" : "1", "issued" : { "date-parts" : [ [ "2009" ] ] }, "page" : "2-4", "title" : "A flexible solution-processed memristor", "type" : "article-journal" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[6], [23]", "plainTextFormattedCitation" : "[6], [23]", "previouslyFormattedCitation" : "[6], [23]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[6], [23], atomic layer deposition, ALD ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "ISBN" : "1748-3395 (Electronic)\\r1748-3387 (Linking)", "ISSN" : "1748-3387", "PMID" : "20081847", "abstract" : "Resistance switching in metal oxides could form the basis for next-generation non-volatile memory. It has been argued that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only indirectly, limiting our understanding of the switching mechanism. Here, we use high-resolution transmission electron microscopy to probe directly the nanofilaments in a Pt/TiO(2)/Pt system during resistive switching. In situ current-voltage and low-temperature (approximately 130 K) conductivity measurements confirm that switching occurs by the formation and disruption of Ti(n)O(2n-1) (or so-called Magn\u00e9li phase) filaments. Knowledge of the composition, structure and dimensions of these filaments will provide a foundation for unravelling the full mechanism of resistance switching in oxide thin films, and help guide research into the stability and scalability of such films for applications.", "author" : [ { "dropping-particle" : "", "family" : "Kwon", "given" : "Deok-Hwang", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Kim", "given" : "Kyung Min", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Jang", "given" : "Jae Hyuck", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Jeon", "given" : "Jong Myeong", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Lee", "given" : "Min Hwan", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Kim", "given" : "Gun Hwan", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Li", "given" : "Xiang-Shu", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Park", "given" : "Gyeong-Su", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Lee", "given" : "Bora", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Han", "given" : "Seungwu", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Kim", "given" : "Miyoung", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hwang", "given" : "Cheol Seong", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Nature Nanotechnology", "id" : "ITEM-1", "issue" : "2", "issued" : { "date-parts" : [ [ "2010" ] ] }, "page" : "148-153", "publisher" : "Nature Publishing Group", "title" : "Atomic structure of conducting nanofilaments in TiO2 resistive switching memory.", "type" : "article-journal", "volume" : "5" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[24]", "plainTextFormattedCitation" : "[24]", "previouslyFormattedCitation" : "[24]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[24] and electrodeposition ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Yusoff", "given" : "Marmeezee Mohd.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ani", "given" : "Mohd. Hanafi", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Suryanto", "given" : "", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Advance Materials Research", "id" : "ITEM-1", "issued" : { "date-parts" : [ [ "2013" ] ] }, "page" : "172-175", "title" : "Synthesis and characterization of ZnO thin film memristor", "type" : "article-journal", "volume" : "701" }, "uris" : [ "" ] }, { "id" : "ITEM-2", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Fauzi", "given" : "Fatin Bazilah", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Othman", "given" : "Raihan", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Mohamed", "given" : "Mohd Ambri", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Herman", "given" : "Sukreen Hana", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Zahirani", "given" : "Ahmad", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Azhar", "given" : "Ahmad", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hana", "given" : "Mohd", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "id" : "ITEM-2", "issued" : { "date-parts" : [ [ "0" ] ] }, "page" : "2-6", "title" : "Transition Metal Oxide (TMO) Thin Film Memristor on Cu Substrate Using Dilute Electrodeposition Method", "type" : "article-journal" }, "uris" : [ "" ] }, { "id" : "ITEM-3", "itemData" : { "DOI" : "10.1088/1757-899X/99/1/012002", "ISSN" : "1757-8981", "author" : [ { "dropping-particle" : "", "family" : "Fauzi", "given" : "F B", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ani", "given" : "M H", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Othman", "given" : "R", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Azhar", "given" : "A Z A", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Mohamed", "given" : "M A", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Herman", "given" : "S H", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "IOP Conference Series: Materials Science and Engineering", "id" : "ITEM-3", "issued" : { "date-parts" : [ [ "2015" ] ] }, "page" : "012002", "title" : "Fabrication of Flexible Au/ZnO/ITO/PET Memristor Using Dilute Electrodeposition Method", "type" : "paper-conference", "volume" : "99" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[7], [8], [25]", "plainTextFormattedCitation" : "[7], [8], [25]", "previouslyFormattedCitation" : "[7], [8], [25]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[7], [8], [25]. Recently, ZnO has attracted a lot of attention due to its non-toxicity and prevalence in semiconductor material for electronic devices applications such as light emitting diodes, LED, photodetectors, sensors, and solar cells. In this paper, thin films of TiO2 and ZnOwere fabricated on copper, Cu substrate by using electrodeposition and thermal oxidation methods thatyields comparable results to the expensive, complex and time consuming existing methods. Cu substrate has been chosen due to its resistance to corrosion, high electrical conductivity and its wide use in electronic devices. The memristive performance of Au/TiO2-Cu2O-CuO/Cu and Au/ZnO-Cu2O-CuO/Cu samples were compared and evaluated.Experimental procedures The electrodeposition setup consists of working electrode and counter electrode placed in a dilute solution of 0.06M titanium trichloride, TiCl3 and 0.005M zinc chloride, ZnCl2 electrolytic baths. The supporting precursor hydrogen peroxide, H2O2 was added to the TiCl3 to pre-oxidize Ti3+ to Ti4+.TiCl3electrolyte bath was prepared as reported by Chang et al. ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.1149/2.026207jes", "ISSN" : "0013-4651", "abstract" : "Cathodic deposition of titanium dioxide (TiO2) from two plating solutions with H2O2 and NaNO3 as their respective oxidants for converting Ti(III) into Ti(IV) are systematically compared. From the electrochemical quartz crystal microbalance (EQCM) and mass loading studies, the deposition solution containing H2O2, denoted as bath A, exhibits a higher rate of TiO2 deposition in comparison with the solution containing NaNO3, denoted as bath B, probably due to the formation of Ti(IV) oxy-hydroxyl species in bath A. However, the surface morphology and crystalline structure of annealed TiO2 deposits are not significantly affected by using different deposition baths. TiO2 deposits have been successfully electroplated onto Ti substrates from both baths under the dual-electrode deposition mode. The surface morphology of TiO2 is significantly influenced by the deposition methods including galvanostatic, potentiostatic, and pulse-rest modes. Finally, uniform porous morphologies of TiO2 in cm2 scale are controllable by varying the pulse-rest deposition variables (e.g., pulse frequency and duty percentage) due to its unique advantages such as excellent adhesion, good uniformity, and controllable particle size of TiO2.", "author" : [ { "dropping-particle" : "", "family" : "Hu", "given" : "C.C.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Hsu", "given" : "H.C.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Chang", "given" : "K.H.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Journal of the Electrochemical Society", "id" : "ITEM-1", "issue" : "7", "issued" : { "date-parts" : [ [ "2012" ] ] }, "page" : "D418-D424", "title" : "Cathodic Deposition of TiO2: Effects of H2O2 and Deposition Modes", "type" : "article-journal", "volume" : "159" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[26]", "plainTextFormattedCitation" : "[26]", "previouslyFormattedCitation" : "[26]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[26] by adding 0.075M of hydrochloric acid followed by addition of H2O2. 1M ZnCl2stock solution was made by dissolving 13.65g of ZnCl2from Ajax Finechem in 100 ml distilled water. Then, it was diluted to 0.005M. A fixed voltage of 1 V was used during the electrodeposition process for Zn deposition, but a higher voltage of 10 V was needed for Ti deposition. The acrylic cell holder was used to clamp the plates with a fixed spacing, d of 20mm and deposition diameter, a of 12 mm shown in Figure 1 (a) and schematic diagram of the electrodeposition setup shown in Figure 1 (b).Figure SEQ Figure \* ARABIC 1. Schematic diagram for electrolytic cell holder (a) and electrodeposition setup (b)The working electrode was Cu foil for both cases, while the counter electrode was Ti plate for Ti/Cu sampleand Zn foil for Zn/Cu sample. Both thin films were deposited for 1 minute deposition time atits respective voltage. After the deposition, the samples underwent thermal oxidation process at a temperature of 600oC for 60 minutes ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.3390/molecules17055021", "ISSN" : "1420-3049", "PMID" : "22552155", "abstract" : "In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 \u00b0C to 650 \u00b0C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 \u00b0C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 \u00b0C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.", "author" : [ { "dropping-particle" : "", "family" : "Khanlary", "given" : "Mohammad Reza", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Vahedi", "given" : "Vahid", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Reyhani", "given" : "Ali", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Molecules (Basel, Switzerland)", "id" : "ITEM-1", "issue" : "5", "issued" : { "date-parts" : [ [ "2012", "1" ] ] }, "page" : "5021-9", "title" : "Synthesis and characterization of ZnO nanowires by thermal oxidation of Zn thin films at various temperatures.", "type" : "article-journal", "volume" : "17" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[27]", "plainTextFormattedCitation" : "[27]", "previouslyFormattedCitation" : "[27]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[27]. It was then coated with Au to form a simple MIM junction by using an auto fine coater (JEOL JFC-1600). Both deposited samples then underwentI-V measurements by applying DC voltage from -2V to 2V with a step voltage of 0.1V. FESEM (JEOL JSM-6700F), XRD (SHIMADZU XRD-6000) and potentiostat (PGSTAT302N, AUTOLAB) were used to characterize the thin films for surface morphology, structure and I-V measurement. All experiments and measurements were performed at room temperature.Results and DiscussionThe XRD patterns of both thin films after thermal oxidation were illustrated in Figure 2(a). Miller indices were included at each diffraction peak. Deposited Ti and Zn were fully oxidized to TiO2 andZnO. TiO2 peaks were observed at 25.21° (101), 49.02° (200) and 61.21° (118) conforming to JCPDS Card 21-1272. ZnO peaks also matches the JCPDS Card 36-1451 at 2θ of 35.68° (101) and 44.26° (102). The existence of CuO (JCPDS Card 80-1917) and Cu2O (JCPDS Card 5-0667) diffraction peaks indicated that the Cu (JCPDS Card 85-1326) was being oxidized as show inFigure 2 (b). Hence, not only TiO2 andZnObut also copper oxides were also possibly functioning as the active layer for the memristor. Figure SEQ Figure \* ARABIC 2. XRD results of deposited thin films after thermal oxidation (a) and Bare Cu substrate before and after thermal oxidation (b)As observed, there were peaks shifted to higher 2θ after thermal oxidation process. Thermal oxidation has resulted in the Cu peaks becoming broader and the intensity was increased. Their peaks also were shifted to a higher angle. This indicates the formation of copper oxides and at the same time inter-diffusion between atoms has occurred. The phase formation during thermal oxidation occurred through solid-state diffusion of ions. The 2θ values of Cu diffraction peaks corresponding to (111), (200) and (220) had shifted towards higher angle value thus indicating the reduction of the lattice parameter of Cu. This is due to the diffusion of Cu which during the formation of oxides. This lattice changes can be calculated by using Bragg’s Law in equation (3.0).nλ=2dsinθ(3.0)where n is equal to 1, ? is the wavelength of the x-ray, d is the lattice distance and θ is the incident angle. The lattice distances, d for corresponding (111), (200) and (220) after the thermal oxidation process was reduced by 2.5 x 10-3, 1.1 x 10-3, and 6.0 x 10-4 nm respectively. From here, the shifted peak shows the reduction in lattice parameter of Cu due to the formation of vacancy defects. This happened during the heat treatment where diffusion of ions occurred. REF _Ref478675257 \h \* MERGEFORMAT Figure 3shows the FESEM micrographs for surface morphologies of (a) TiO2-Cu2O-CuO and (b) ZnO-Cu2O-CuO at high magnification (x60k). The microstructure of TiO2-Cu2O-CuO exhibits granular grainsin contrast to ZnO-Cu2O-CuO that displays a rod-like structure with similar length and diameter. Figure SEQ Figure \* ARABIC 3. Surface morphology of synthesized TiO2-Cu2O-CuO/Cu(a) and ZnO-Cu2O-CuO/Cu (b) after thermal oxidation at x60K magnificationThe I-V measurements of both samples show the pinched hysteresis loops as shown in Figure 4 (a) and (b) which follows the characteristics of a memristor. Higher maximum and minimum current value for Au/ZnO-Cu2O-CuO/Cu was bigger than the Au/TiO2-Cu2O-CuO/Cu sample. The maximum and minimum current measured were52 μA, -61 μA for Au/TiO2-Cu2O-CuO/Cu and 93 μA, -103 μA for Au/ZnO-Cu2O-CuO/Cu respectively.Figure SEQ Figure \* ARABIC 4. I-V hysteresis loops from synthesized Au/TiO2-Cu2O-CuO/Cu (a) and Au/ZnO-Cu2O-CuO/Cu(b) at 1 minute deposition timeThe polarity dependence of the resistance to voltage is called bipolar resistive switching ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Sawa", "given" : "Akihito", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Materials Today", "id" : "ITEM-1", "issue" : "6", "issued" : { "date-parts" : [ [ "2008" ] ] }, "page" : "28-36", "title" : "Resistive switching in transition metal oxides", "type" : "article-journal", "volume" : "11" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[11]", "plainTextFormattedCitation" : "[11]", "previouslyFormattedCitation" : "[10]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[11]. Resistive switching behavior was illustrated in Figure 4where the current changes from high resistance state, HRS to low resistance state, LRS at a set voltage from ‘0V to 2V’ path to ‘2V to 0V’ path. The difference of HRS and LRS creates the hysteresis loop in I-V curve. Calculated HRS and LRS of both samples were tabulates in Table 1. Au/TiO2-Cu2O-CuO/Cu gave greater difference in between HRS and LRS of 8.83 kΩwith HRS/LRS ratio of 1.2. While Au/ZnO-Cu2O-CuO/Cuhave HRS and LRS difference of 2.02kΩ with HRS/LRS ratio of 1.08. Table SEQ Table \* ARABIC 1. Calculated HRS and LRSSampleΔImax (μA)HRS (K?)LRS (K?)HRS – LRS (K?)HRS/LRSAu/ZnO-Cu2O-CuO/Cu21.027.0525.02.021.08Au/TiO2-Cu2O-CuO/Cu5.050.741.98.831.2HRS/LRS ratio of Au/ZnO-Cu2O-CuO/Cu shows results that is within the range of our previous findings reported by Marmezee et al. ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Yusoff", "given" : "Marmeezee Mohd.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ani", "given" : "Mohd. Hanafi", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Suryanto", "given" : "", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Advance Materials Research", "id" : "ITEM-1", "issued" : { "date-parts" : [ [ "2013" ] ] }, "page" : "172-175", "title" : "Synthesis and characterization of ZnO thin film memristor", "type" : "article-journal", "volume" : "701" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[7]", "plainTextFormattedCitation" : "[7]", "previouslyFormattedCitation" : "[7]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[7]. Electrodeposition is suitable to be used as a fabrication method because of its reproducibility and comparable results to other studies reported by other groups.The difference between HRS and LRS in memristor occurred because of the diffusion of defect vacancy in oxide layers when polarized. The formation vacancy defectsduring oxidation in a metal oxide depends on the species diffusivityaccording to Fick’s first law of diffusion (steady-state) in equation (3.1):J= -D ?c?x(3.1)whereJ is the flux, D is the diffusivity coefficient, c is the concentration of each species and x is the displacement (length of diffusion). From experimental data on oxygen ion, O2- diffusivity inZnO compiled by Erhart and AlbeADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Erhart", "given" : "Paul", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Albe", "given" : "Karsten", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Physical Review B", "id" : "ITEM-1", "issue" : "115207", "issued" : { "date-parts" : [ [ "2006" ] ] }, "page" : "1-9", "title" : "First-principles study of migration mechanisms and diffusion of oxygen in zinc oxide", "type" : "article-journal", "volume" : "73" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[28]", "plainTextFormattedCitation" : "[28]", "previouslyFormattedCitation" : "[28]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[28], it can be postulated that at 600 °C the diffusivity of O2- in ZnO is around 10-22 cm2 s-1 and zinc ions, Zn2+in ZnO is about 10-18 cm2 s-1. It shows that the Zn2+ has greater diffusivity compared to O2- in ZnO. For TiO2, the temperature dependence of self-diffusion coefficient fortitanium(IV) ions, Ti4+ and O2-in TiO2are compiled by Pereloma et al. ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.4028/KEM.520.49", "ISBN" : "9783037854686", "ISSN" : "10139826", "author" : [ { "dropping-particle" : "V.", "family" : "Pereloma", "given" : "Elena", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Savvakin", "given" : "Dmytro G.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Carman", "given" : "Andrew", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Gazder", "given" : "Azdiar a.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ivasishin", "given" : "Orest M.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Key Engineering Materials", "id" : "ITEM-1", "issued" : { "date-parts" : [ [ "2012" ] ] }, "page" : "49-56", "title" : "Microstructure Development and Alloying Elements Diffusion during Sintering of Near-\u03b2 Titanium Alloys", "type" : "article-journal", "volume" : "520" }, "uris" : [ "" ] } ], "mendeley" : { "formattedCitation" : "[29]", "plainTextFormattedCitation" : "[29]", "previouslyFormattedCitation" : "[29]" }, "properties" : { "noteIndex" : 0 }, "schema" : "" }[29] and Nowotny [14]. It is postulated that at 600 °C the diffusivity of O2- in TiO2 is around 10-24 cm2 s-1 and Ti4+in TiO2is about 10-19 cm2 s-1. It shows that the Ti4+ has greater diffusivity compared to O2- in TiO2. The order of diffusivity of each species are as follows in (3.2):DZn2+inZnO>DTi4+inTiO2>DO2-inZnO>DO2-inTiO2(3.2)The diffusivity of cation possesses greater value than the diffusivity of anion by a factor of 103 ~ 104 which creates metal vacancies instead of oxygen vacancies. The formation of metal vacancy defects in transition metal oxide produces the pinched hysteresis loop in memristor. We conclude that the ability of memristor to be usedas memory device to store data relies on the existence of metal vacancy defects come from different diffusivities in the metal oxide active layer.ConclusionIn summary, it can be demonstrate that TiO2-Cu2O-CuO and ZnO-Cu2O-CuO thin films are successfully deposited using ultra-dilute solution on Cu substrates through the electrodeposition and thermal oxidation method. Both samples showed the hysteresis loop in the I-V measurements where Au/TiO2-Cu2O-CuO/Cu has bigger HRS-LRS value of 8.83 KΩ compared to Au/ZnO-Cu2O-CuO/Cu of 2.02 KΩ. However based on the HRS/LRS ratio, both Au/TiO2-Cu2O-CuO/Cu and Au/ZnO-Cu2O-CuO/Cu have comparable memristive performancesof 1.2 and 1.08 respectively. From the postulation of diffusivity, the memristive effects occurred due to the formation of metal vacancy defects as the diffusion of each ions are DZn2+ in ZnO> DTi4+ in TiO2> DO2- in ZnO > DO2- in TiO2. The diffusivity of cation greater than anion in 103 ~ 104 factor.Acknowledgement This work was financially supported by the Niche Research Grant Scheme, Ministry of Education Malaysia (600-RMI/NRGS 5/3 (7/2013)) and Research Acculturation Grant Scheme (RAGS13-002-0065), UniversitiTeknologi MARA (UiTM) and International Islamic University Malaysia (IIUM).ReferencesADDIN Mendeley Bibliography CSL_BIBLIOGRAPHY [1]Chua L O 1971 IEEE Transations Circuit TheoryCT-18 507–519[2]Strukov D B, Snider G S, Stewart D R, and Williams R S 2008 Nature453 80–83[3]Williams R S 2008 IEEE Spectr. 45 28–35[4]Li Y T et al 2010 10th IEEE International Conference on Solid-State and Integrated Circuit Technology 1148–1150[5]Yang J J et al 2011 Appl. Phys. A102 785–789[6]Gale E et al 2014 Mater. Chem. Phys. 143 p 524–529[7]Yusoff M M, Ani M H and Suryanto 2013 Adv. Mater. 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