Solid State Phenomena Vols. 124-126

Abstract: We demonstrated a nonvolatile memory fabricated with the sandwich device structure of Al/Au nano-crystals embedded in the PVK/Al. The bi-stable conduction switching characteristic (Ion/Ioff ratio) was >1x102, depending on Au nano-crystal size. The size and distribution of Au nano-crystals were determined by the inserted Au-layer thickness between PVK layers. The size of Au nano-crystals increased with the inserted Au-layer thickness. The uniform distribution of isolated Au nano-crystals was obtained with 5 nm of the inserted Au-layer thickness.

Abstract: Thermal stress model considering the effect of phase transformation is proposed for Phase-Change Random Access Memory (PRAM). The results of simulation show that the high level of stress is generated on the junction where Ge2Sb2Te5(GST), TiN and SiO2 meet together. The high level of stress can also be observed in the interface between TiN and SiO2. From simulation results, it can be predictable that delamination between GST and TiN can occur during operation of PRAM. It is expected that the simulation model, which has been developed in this research, is very useful tool for PRAM device design.

Abstract: Ru thin films were grown by metalorganic chemical vapor deposition (MOCVD) on TiN and TEOS oxide substrates at 300oC using (2,4-demethylpentadienyl)(ethylcyclopenadienyl) ruthenium [Ru(DMPD)(EtCp)] and oxygen. Instead of conventional single step process, we investigated 2-step CVD process to enhance initial nucleation rate and reduce the incubation time for film formation. This process consisted of a seeding step, where high flow rate of oxygen and low process pressure were used, and a film growth step with low O2 flow rate and high pressure. The deposited Ru films by 2-step process have smooth surface morphologies compared to those by single step process.

Abstract: We investigated the phase transformation and thermal stability of Ni silicides formed in Ni/Si and Ni0.95Ta0.05/Si systems. The sheet resistance values of the silicide in the Ni0.95Ta0.05/Si system were lower than those in Ni/Si system at any temperature. The enhancement of thermal stability is closely related to the phase transformation occurred during post heat-treatment. Microstructure of the phases formed by reaction was investigated by analytical electron microscopy (AEM) and the phase identification of Ni silicide was carried out using convergent beam electron diffraction (CBED) technique. It was found that a Ta rich layer formed on the top of the Ni silicide layer and small amount of Ta dissolved into the silicide layer. By addition of Ta atoms, phase transformation from NiSi to NiSi2 is retarded and thermal stability of Ni silicide is improved.

Abstract: Electroplating of copper in via filling is very important in 3D SiP (System in Packaging). Defect free via filling can be obtained through additive in the electrolyte and current type control. Via in Si wafer were formed by RIE method with 170 &m depth and 50 &m in diameter. Seed layers were deposited by ionized metal plasma (IMP) sputtering; Ta for diffusion barrier, Cu for conductive layer. Via was filled with copper by electroplating method. Different types of additives were used in via filling; PEG, SPS, Cl- and JGB. Defects in via were controlled and eliminated by precise monitoring of additive concentration and input current. The optimum condition of electroplating was determined by getting cross-sectional images of filled vias and by determining the degree of via filling.

Abstract: Langasite (La3Ga5SiO14 or abbreviated as LGS) single crystal is an attractive substrate for surface acoustic wave (SAW) devices requiring good temperature stability and higher electromechanical coupling constant than quartz. AlN thin films are attractive materials that have some excellent characteristics, such as high SAW velocity, piezoelectricity, high-temperature stability, and stable chemical properties. In this study, AlN thin films were deposited on LGS to be a new composite SAW substrate (AlN/LGS) by reactive RF magnetron sputtering method. SAW delay-line device was manufactured on this substrate. The performance of the device was measured by network analyzer (Agilent 8753E).The results exhibited the composite substrate (AlN/LGS) increased the Rayleigh wave velocity, decreased the insertion loss of SAW devices, and suppressed the harmonic response.

Abstract: The band gap anomaly exhibited by ABC2 : A = Cd; B = Si,Ge,Sn; C = P,As pnictides with respect to their binary analogs GaP, Ga0.5In0.5P, InP, GaAs, Ga0.5In0.5As, InAs is studied using Tight Binding Linear Muffin Tin Orbital (TBLMTO) method as an investigating theoretical tool. The influence of the structural parameters, η and u are analyzed to enable one to tune energy gap to make tailor made compounds.

Abstract: The initial GaN growth mode on stepped sapphires by plasma enhanced metal organic molecular beam epitaxy (PEMOMBE) has been analyzed using in-situ, real time synchrotron x-ray diffraction and x-ray absorption. The sapphire substrate annealed at high temperature had flat terraces and regular atomic steps. The crystal quality and the vicinal angle of sapphire substrate had an effect on the width of terraces and the step arrangement. The initial growth mode of the GaN film on the regular atomic step (AS) surface was the layer-by-layer mode and changed to the 3D growth mode within 2 bilayer thickness. In the meanwhile, the growth mode of the GaN film grown on the sapphire with random roughness (RR) surface made the flat surface in the early stage and changed the 3D growth mode. As increasing the film thickness, the nucleation layer grows strain-free hexagonal GaN on stepped sapphires

Abstract: The etching properties of the ZnO thin films in the inductively coupled Cl2/Ar plasma (ICP) were studied in the terms of etch rate and selectivity as functions of gas mixing ratio, ICP coil power and dc bias voltage. The maximum etch rate of 129.3 nm/min was obtained for the mixture of 20% Ar/80% Cl2. The X-ray photoelectron spectroscopy (XPS) analyses of the ZnO surfaces etched at various Cl2/(Cl2+Ar) mixing ratios revealed the formation of the ZnClx and ClOx reaction by-products as a result of the increased etch rate with increasing Cl2 addition, compared with 100% Ar+ sputter etching. From the analysis of these data, it was proposed that the maximum on the etch rate may be explained by the concurrence of chemical and physical pathways in the ion assisted chemical reaction.