Functional and Electronic Materials, IUMRS-ICA2010

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Authors: Ying Li, Gao Yang Zhao, Xiao Fei Zhou, Li Ning Pan, Yang Ren
Abstract: Amorphous SiO2 thin films were fabricated at different temperatures using sol-gel technique. The unipolar resistive switching behavior was observed in Cu/ SiO2/ ATO (SnO2: Sb) sandwiched structure when the SiO2 thin film annealed at 500°C. The average ratio of Roff /Ron is 102. We investigated the successful device using HRTEM and XPS. It shows that the Cu defuses into the SiO2 thin film and it forms CuSiO3 in the interface between SiO2 and ATO films according to the high resolution images.
Authors: Zhi Mei Sun, Yuan Chun Pan, Bai Sheng Sa, Jian Zhou
Abstract: On the basis of ab initio total energy calculations, we have performed an extensive study on the stacking sequence and random occupation of Ge and Sb to make the same layer in stable hexagonal Ge2Sb2Te5 (h-GST), an excellent candidate for phase change random memory applications. The results demonstrate that the atomic arrangements have great effects on lattice parameter c and electronic properties of h-GST. h-GST changes from semiconductor to metallic behavior as varying the atomic sequence.
Authors: Hai Lang Ju, Xiong Li, Bao He Li, Bi Hun Hou
Abstract: Using electro-optic sampling technique and THz time-domain spectroscopy-transmission equipment, the reference THz wave and the sample THz wave has been measured from 0.3 THz to 3.0 THz and the absorption index has been obtained. Absorption peaks of β-Zn3BPO7 crystal sample were found in four points. The important condition of direct interaction between lattice and light is that they must have the same frequency and wave vector, also lattice vibration mode should be transverse because the light is electromagnetic wave. The absorption peaks are found multiple of the optical phonon basically after calculation. The sample shows great resonance absorption.
Authors: Li Meng Yin, Jian Wei Xian, Zong Xiang Yao
Abstract: The wetting properties of four typical Sn-based solders, i.e., Sn-37Pb, Sn-3.0Ag-0.5Cu, Sn-0.7Cu and Sn-9Zn, on copper (Cu) and aluminum (Al) substrates at 250 °C, 260 °C and 270 °C were evaluated and compared by wetting balance method. The experimental results show that the wetting time of all solders on Cu substrate is shorter than that on Al substrate, but the wetting force of the solders with Cu substrate is bigger than that with Al substrate except Sn-9Zn solder. In addition, the wettability of the solders on Al substrate increases with increasing soldering temperature, and the wetting force of Sn-9Zn increases most obviously among four solders and reach 3.68 mN at 270 °C. The results also show that the wettability of the solders on Cu substrate mainly depends on surface tension of solder alloy, however, it depends on both surface tension and interaction with Al on Al substrate. Due to the active element Zn riches on the surface of Sn-9Zn solder, and Zn solid solutes into Al more easily, the wettability of Sn-9Zn solder on Al substrate is better than other three solders.
Authors: Jian Feng Zhu, Guo Quan Qi, Hai Bo Yang, Fen Wang
Abstract: ZnO-based varistor ceramics were prepared by sintering ZnO powders with minor additives that were synthesized by standard ball milling, high energy ball milling for 10 h, and pyrogenic decomposition of nitrate. The microscopic structure and composition were analyzed by SEM and XRD respectively, and the electrical properties were investigated by a DC parameter instrument for varistors. Influences of composite additives on composition, microstructure, and electrical properties of ZnO-based varistors were studied. The ZnO varistor with optimum performance is prepared by the pyrogenic decomposition method and it has an average grain size of 5 µm and possesses a varistor voltage of about 561 V/mm, non linear coefficient of 75, and leakage current of 0.45 µA.
Authors: Ou Yang Yao, Qiang Hu, Fu Wen Zhang, Zhi Gang Wang
Abstract: The effects of phosphorous on the anti-oxidation of SnPb solder and the mechanism were investigated. The surface oxidation behavior of Sn63Pb37 solder in the liquid state was observed by comparing the color of the molten solder and the effects of the temperature on the oxidation resistance of solder Sn63Pb37-P is conduced by skimming and weighting the oxidation dross. OM, SEM and EDS were used to analyze the anti-oxidation performance and mechanism. The results show that Sn63Pb37 solder with 0.019wt.% P can maintain smooth and brightly longer under 260°C, and produce less oxide slag. It is found that phosphorous is needle-like and concentrate on the surface of the solder and oxide film. At 260 °C, the additional element P suppresses impurity element Fe forming oxide. The additional element P will engage in the forming of oxide film, and improve the structure and mechanical property of oxide film to achieve the antioxidant effect. If heated to 380°C, the oxidation resistance of molten Sn63Pb37-P alloy was greatly worsen, instead.
Authors: Tian Guo Wang, Qun Qin, Dong Jian Zhou
Abstract: TiO2 varistors doped with 0.1 mol% Ta and different concentrations of Pr3+ were obtained by ceramic sintering processing at 1400 °C and their properties were characterized by XRD, SEM, I-V and impedance spectroscopy. The effect of Pr on the microstructure, nonlinear electrical behavior and dielectric properties of the Ta-doped TiO2 ceramics were investigated. It is found that Pr affects the grain size, electrical properties and the dielectric properties of the TiO2-based varistors. The samples have the nonlinear coefficients (α) values of (3.0-5.0) with low breakdown voltages (4-30 V/mm). A small quantities of Pr can improve the nonlinear properties of the samples significantly. It was found that an optimal doping composition of 0.5 mol% Pr3+ leads to a low breakdown voltage of 9.2 V/mm, a high nonlinear constant of 4.9 and an ultrahigh electrical permittivity of 8.38×104 (at 1 kHz), which is consistent with the highest grain boundary barriers of the ceramics. In view of these electrical characteristics, the TiO2-0.5 mol% Pr3+ ceramic is a viable candidate for capacitor-varistor functional devices. The defects theory was introduced to explain the nonlinear electrical behavior of Pr-doped TiO2 ceramics.
Authors: Yao Li Wang, Gai Hong Dong, Chen Yang Li, Zhi Wei Wu, Jing Sun
Abstract: Creep property is one of the most important factors to affect the reliability of soldered joints. The effect of rare earth(RE) on the creep rupture life of Sn2.5Ag0.7Cu solder joints were investigated under constant temperature and stress using creep specimens with a 1mm2 cross sectional area. The results show that adding tiny RE in Sn2.5Ag0.7Cu solder alloy can effectually affect the size and configuration of the intermetallic compound (IMC) of interfacial layer. The IMC of Sn2.5Ag0.7Cu interfacial layer is thinner and its thickness is homogeneous with adding 0.1% RE, and the creep rupture life of solder joints is longest, which is apparently superior to that of Sn2.5Ag0.7Cu and commercial used Sn3.8Ag0.7Cu solder alloy.
Authors: Fu Xiang Huang, Ming Li, Ping Ying, Yong Hong Xu, Ying Zhang
Abstract: It is well known that the rare-earth elements (RE) have exhibited favorable microalloying effects on the microstructure and properties of silver alloys. In the present investigation, a detailed description of the microstructure of a Silver-4wt.%Copper-0.3wt.% Nickle as–cast alloy containing 0.2wt. % of a cerium element was presented. Particles types occurring and their distribution in the microstructure, as well as the distribution of elements in the phases were described. The result show that the second phase in Ag-Cu-Ni Alloy is Cu-Ni-rich solution phase, some of which forms interdendritic segregation in Ag matrix as eutectic colonies. Trace additions of cerium to the alloy decrease eutectic proportion and size of the Cu-Ni-rich phase, result in finer and more uniform secondary phases distributed in the α-Ag matrix. Besides Cu-Ni-rich phase, the Ni-Cu-Ce-rich and Ag-Cu-Ce-rich phases were found in the alloy. The Ni-Cu-Ce-rich should be the (NiCu)5Ce, which is distributed as dispersive particle in the Ag matrix, and Ag-Cu-Ce-rich phases should be (AgCu)4Ce, which is distributed as fibrous particle of eutectic colonies. Some of (AgCu)4Ce phases are located at the interface between α-Ag matrix and Cu-Ni-rich phases, which indicate that Ce could be segregated at the frontier of Cu-Ni-rich phases during the growth, causing Cu-Ni-rich phase refinement.

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