The basic unit of information in filamentary-based resistive switching memories is physically stored in a conductive filament. Therefore, the overall performance of the device is indissolubly related to the properties of such filament. In this Letter, we report for the first time on the three-dimensional (3D) observation of the shape of the conductive filament. The observation of the filament is done in a nanoscale conductive-bridging device, which is programmed under real operative conditions. To obtain the 3D-information we developed a dedicated tomography technique based on conductive atomic force microscopy. The shape and size of the conductive filament are obtained in three-dimensions with nanometric resolution. The observed filament presents a conical shape with the narrow part close to the inert-electrode. On the basis of this shape, we conclude that the dynamic filament-growth is limited by the cation transport. In addition, we demonstrate the role of the programming current, which clearly influences the physical-volume of the induced conductive filaments.

Germanium possesses higher electron and hole mobilities than silicon. There is a big leap, however, between these basic material parameters and implementation for high-performance microelectronics. Here we discuss some of the major issues for Ge metal oxide semiconductor field effect transistors ͑MOSFETs͒. Substrate options are overviewed. A dislocation reduction anneal Ͼ800°C decreases threading dislocation densities for Ge-on-Si wafers 10-fold to 10 7 cm −2 ; however, only a 2 times reduction in junction leakage is observed and no benefit is seen in on-state current. Ge wet etch rates are reported in a variety of acidic, basic, oxidizing, and organic solutions, and modifications of the RCA clean suitable for Ge are discussed. Thin, strained epi-Si is examined as a passivation of the Ge/gate dielectric interface, with an optimized thickness found at ϳ6 monolayers. Dopant species are overviewed. P and As halos are compared, with better short channel control observed for As. Area leakage currents are presented for pϩ/n diodes, with the n-doping level varied over the range relevant for pMOS. Germanide options are discussed, with NiGe showing the most promise. A defect mode for NiGe is reported, along with a fix involving two anneal steps. Finally, the benefit of an end-of-process H 2 anneal for device performance is shown.

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In this letter, we explore the influence of the CuxTe1-x layer composition (0.2 < x < 0.8) on the resistive switching of CuxTe1−x/Al2O3/Si cells. While x > 0.7 leads to large reset power, similar to pure-Cu electrodes, x < 0.3 results in volatile forming properties. The intermediate range 0.5 < x < 0.7 shows optimum memory properties, featuring improved control of filament programming using <5 μA as well as state stability at 85 °C. The composition-dependent programming control and filament stability are closely associated with the phases in the CuxTe1−x layer and are explained as related to the chemical affinity between Cu and Te.

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Articles you may be interested inDetailed leakage current analysis of metal-insulator-metal capacitors with ZrO2, ZrO2/SiO2/ZrO2, and ZrO2/Al2O3/ZrO2 as dielectric and TiN electrodes J. Vac. Sci. Technol. B 31, 01A109 (2013); 10.1116/1.4768791 Impact of bottom electrode and Sr x Ti y O z film formation on physical and electrical properties of metalinsulator-metal capacitors Appl. Phys. Lett. 98, 182902 (2011); 10.1063/1.3584022 Influence of precursor chemistry and growth temperature on the electrical properties of SrTiO 3 -based metalinsulator-metal capacitors grown by atomic layer deposition J. Vac. Sci. Technol. B 29, 01AC04 (2011); 10.1116/1.3525280 Impact of crystallization behavior of Sr x Ti y O z films on electrical properties of metal-insulator-metal capacitors with TiN electrodes Appl. Phys. Lett. 97, 162906 (2010); 10.1063/1.3505323 Atomic-layer-deposited Al 2 O 3 -Hf O 2 -Al 2 O 3 dielectrics for metal-insulator-metal capacitor applications Appl. Phys. Lett.In this work, the physical and electrical properties of Sr x Ti 1−x O y ͑STO͒-based metal-insulator-metal capacitors ͑MIMcaps͒ with various compositions are studied in detail. While most recent studies on STO were done on noblelike metal electrodes ͑Ru, Pt͒, this work focuses on a low temperature ͑250°C͒ atomic layer deposition ͑ALD͒ process, using an alternative precursor set and carefully optimized processing conditions, enabling the use of low-cost, manufacturable-friendly TiN electrodes. Physical analyses show that the film crystallization temperature, its texture and morphology strongly depends on the Sr/Ti ratio. Such physical variations have a direct impact on the electric properties of Sr x Ti 1−x O y based capacitors. It is found that Sr-enrichment result in a monotonous decrease in the dielectric constant and leakage current as predicted by ab initio calculations. The intercept of the EOT vs physical thickness plot further indicates that increasing the Sr-content at the film interface with the bottom TiN would result in lower interfacial equivalent-oxide thickness.

The implementation of dense, one-selector one-resistor (1S1R), resistive switching memory arrays, can be achieved with an appropriate selector for correct information storage and retrieval. Ovonic threshold switches (OTS) based on chalcogenide materials are a strong candidate, but their low thermal stability is one of the key factors that prevents rapid adoption by emerging resistive switching memory technologies. A previously developed map for phase change materials is expanded and improved for OTS materials. Selected materials from different areas of the map, belonging to binary Ge-Te and Si-Te systems, are explored. Several routes, including Si doping and reduction of Te amount, are used to increase the crystallization temperature. Selector devices, with areas as small as 55 × 55 nm2, were electrically assessed. Sub-threshold conduction models, based on Poole-Frenkel conduction mechanism, are applied to fresh samples in order to extract as-processed material parameters, such as trap height and density of defects, tailoring of which could be an important element for designing a suitable OTS material. Finally, a glass transition temperature estimation model is applied to Te-based materials in order to predict materials that might have the required thermal stability. A lower average number of p-electrons is correlated with a good thermal stability.

Strontium titanate ͑STO͒ is a promising candidate as a high-k dielectric for dynamic random access memory application. STO thin films are deposited by atomic layer deposition using Sr͑ t Bu 3 Cp͒ 2 , Ti͑OMe͒ 4 , and H 2 O as precursors. Growth and saturation behavior of STO and binary oxides are evaluated by ellipsometry thickness measurements. The precursor pulse ratio controls the amount of Sr and Ti incorporated in STO films. Stoichiometric SrTiO 3 is characterized by the lowest crystallization temperature and largest refractive index, density, and dielectric constant. An excess of Ti or Sr results in an increase in the crystallization onset temperature and contraction or expansion of the cubic cell constant of perovskite SrTiO 3 . Incorporation of more Sr in STO reduces the leakage current density but also increases the capacitance-equivalent thickness.Strontium titanate ͑STO͒ is highly attractive as a high-k dielectric for dynamic random access memory applications in metalinsulator-metal ͑MIM͒ capacitors due to its high storage capacity. SrTiO 3 demonstrates a high ͑Ͼ200͒ dielectric constant with a good stability as a function of temperature and frequency. In view of the three-dimensional structures envisaged for these applications to achieve high capacitance values, the most suitable technique is atomic layer deposition ͑ALD͒, which through its self-limiting growth mechanism ensures conformal growth. This deposition method is based on alternate saturated reactions at the surface, the reactants being consecutively adsorbed, and building up the layer in a controlled manner. ALD offers a simple and accurate way to ensure thickness and uniformity control. For SrTiO 3 , the precursor choice for the two metal components, namely, Sr and Ti, is rather limited. Although titanium halides, such as TiCl 4 , easily form TiO 2 films via an ALD process, they must be avoided due to their reactivity toward strontium. Consequently, titanium alkoxides are mainly used as a source of titanium in SrTiO 3 for their noncorrosive and halide-free properties. The available titanium alkoxides have been studied establishing that the decomposition onset temperature under dynamic conditions of an ALD reactor increases in the order Ti͑O t Bu͒ 4 ഛ Ti͑O i Pr͒ 4 Ͻ Ti͑OEt͒ 4 Ͻ Ti͑OMe͒ 4 . 1 Until now the most preferred alkoxide is Ti͑O i Pr͒ 4 that was used in combination with Sr metallorganic precursors. 2-7 Because of its conveniently high volatility, the drawback of titanium isopropoxide is that it gradually starts to decompose above 250°C. Therefore alternative titanium precursors such as Ti͑O-i Pr͒ 2 ͑thd͒ 2 8 or Ti͑mpd͒͑thd͒ 2 9 have been investigated. Reviewing the available literature data for Sr precursors, they can be divided into two families: Diketonates and cycloalkenyls, with research mostly focused on the first class. [2][3][4][5][6][7][8][9] However, due to their low reactivity toward the most common oxidant sources ͑H 2 O and O 2 ͒, processing temperatures around or higher than 300°C are needed. At these temperatures titanium...