Ag Alloy Films Research Articles

Comparison of texture evolution in Ag and Ag(Al) alloy thin films on amorphous SiO2

The thermal stability of Ag metallization on SiO2 was improved by using Ag(Al) alloy films instead of pure Ag thin films which agglomerate at high temperature. X-ray diffraction techniques were used to study the texture evolution of Ag and Ag(Al) films. Different behaviors were observed in texture evolution of Ag and Ag(Al) films. Detailed information about the texture of Ag and Ag(Al) films was obtained by performing pole-figure analysis. Two different changes in texture are explained using a grain-growth mechanism and an agglomeration phenomenon, both of which work to reduce the total free energy of the system at high temperature. Based on the data obtained in this study, the texture evolution of Ag film, induced by agglomeration, and Ag(Al) film is discussed.

Enhanced adhesion and performance of the source/drain electrode using a single-layered Ag(Cu) film for an amorphous silicon thin-film transistor

The feasibility of using a Ag(Cu) alloy film as a source/drain electrode for thin-film transistor (TFT) liquid-crystal displays has been investigated. The annealing of a Ag(Cu)/Si structure, for 30 min at 200 °C, produced a uniform Cu3Si layer at the Ag(Cu)–Si interface, as a result of the reaction of the segregated Cu with Si. This lowered the resistivity from 5.3 to 3.2 μΩ cm, which also led to improved adhesion properties. A hydrogenated amorphous silicon (a-Si:H) TFT was fabricated using a single layer of Ag (19 at. % Cu) alloy film as the source/drain metal. The subthreshold slope, mobility, and threshold voltage obtained from the fabricated a-Si:H TFT were 0.78 V/dec, 0.79 cm2/V s, and 2 V, respectively, revealing a reduction in the process steps, with excellent performance.

Feasibility of an Ag-alloy film as a thin-film transistor liquid-crystal display source/drain material

The Ag-alloy films have been investigated as source/drain materials applicable to thin-film transistor liquid-crystal displays (TFT-LCDs). The Ag-alloy consisting of 0.9at.%Pd, 1.7at.%Cu (designated APC) showed a resistivity that was lower than one-half that of AlNd. It also had good contact characteristics with amorphous Si (a-Si). In addition, the Ag/Si was stable after heating to above 700°C, requiring no diffusion barrier to prevent reaction between Ag and Si. Pure Ag films deposited on glass by DC magnetron sputtering showed severe hillock formation, hole growth, and agglomeration upon annealing in air. In comparison, the APC-alloy film exhibited improved resistance to agglomeration. Further, inverted-staggered back-channel-etch hydrogenated amorphous silicon (a-Si:H) TFTs using an APC-alloy film as a source/drain material had a threshold voltage of 4 V. A structure of single layers of gate-APC alloys and source/drain-APC alloys leads to lower costs and productivity improvements of large-area, high-resolution, active-matrix LCDs, such as 40-in. size panels through process simplification.

Optical and electrical properties of pure Ag and Ag-based alloy thin films prepared by RF magnetron sputtering

Ag and Ag–(0.9 wt%)Pd–(1.0 wt%)Cu (APC) alloy films were deposited on glass substrates by RF magnetron sputtering. The reflectance of Ag films deposited at room temperature was 98% at a wavelength of 600 nm. However, it decreased with increasing substrate temperature due to crystal grain growth and film surface roughening. The resistivity of pure Ag films with thickness of 100 nm was about 2 μΩ cm, which is almost equivalent to that of bulk Ag (1.6 μΩ cm), while 95% of reflectance and 3 μΩ cm of resistivity were obtained in the case of APC film.

Texture and Resistivity of Cu and Dilute Cu Alloy Films

AbstractAnnealing of dilute binary Cu(Ti), Cu(In), Cu(Al), Cu(Sn), Cu(Mg), Cu(Nb), Cu(B), Cu(Co) and Cu(Ag) alloy films resulted in the strongest <111> fiber texture for Cu(Ti) and the lowest resistivity for Cu(Ag). The behavior of the alloy films was compared and contrasted with that for a pure evaporated Cu film. Electron beam evaporated films with compositions in the range of 2.0-4.2 at% and thicknesses in the range of 420-560 nm were annealed at 400°C for 5 hours. Two different approaches were used to derive volume fractions of texture components, namely fiber plots and orientation distributions. It is argued that for polytextured films such as the copper alloys studied here, orientation distributions derived from pole figures provide the most reliable basis for quantitative characterization.

Pd–Ag alloy films prepared by metallorganic chemical vapor deposition process

Palladium–silver alloy films were prepared by a hot-wall metallorganic chemical vapor deposition process, using a mixed inlet stream of two precursor vapors, palladium acetate and silver acetate. The Pd–Ag alloy film was obtained at a deposition temperature below 500°C and was composed of 20–40 nm grains as determined from the X-ray diffraction data. On top of the dense Pd–Ag film, there was found sub-micrometre aggregates of nano-sized primary particles, resulting from a gas-phase reaction of precursor vapors and subsequent coagulation and partial sintering of nano-sized primary particles. The Ag content of the film was found to be decreasing from the film surface into the film itself. Separate placement of the two precursors gave a stronger control on the film composition, than adjusting the mixing ratio of the two precursors for the mixed precursor practice. The deposition flux and Pd content of the film decreased with increasing distance from the reactor entrance.

Hydrogen Gas Sensing Using a Pd-Coated Cantilever

A cantilever consisting of a thin glass plate coated with an evaporated Pd thin film can be utilized as a hydrogen gas sensor because the Pd film expands upon absorption of hydrogen, resulting in the bending of the free end of the cantilever. A comparison has been made between the response obtained experimentally from 100–1000-nm-thick Pd-coated glass plate cantilevers in the presence of 0.1–600 Torr hydrogen and the response calculated from the data of the Pd lattice expansion due to hydrogen absorption and the elasticity theory. It is shown that the Pd-coated cantilever can detect hydrogen at least from 0.1 to 10 Torr with good reproducibility. The use of a Pd–Ag alloy film instead of a pure Pd film was found to be effective both in enhancing the hydrogen sensitivity at low hydrogen pressures and in extending the hydrogen responsivity up to 600 Torr.

Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd–Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H 2 permeation measurement. Commercial microfiltration ceramic membrane were coated with γ-Al 2O 3-based layer by the sol–gel method and used as substrate of Pd and Pd–Ag alloy film. Both the as-prepared membranes were shown to be He gas-tight at room temperature with a thickness of <1 μm. Permeation results showed that H 2 permeation through these composite membranes is mainly dominated by the surface chemistry of H 2 on or/and in the membranes. The membranes exhibited a high permeation rate of H 2 and a H 2/N 2 permselectivity of higher than 60 in the optimized operation conditions .

Encapsulation of silver by nitridation of AgTi alloy/bilayer structures

Thin encapsulated silver films have been prepared on oxidized silicon. As a preparatory step, silver was deposited either as ∼ 200 nm thick Ag-χ%Ti alloys (where χ = 6−26 at.%) or Ag(120 nm)/Ti(22 nm) bilayers. Subsequent encapsulation was formed by Ti reactions during anneals between 300 and 700 °C in an ammonia ambient. This process has been studied in detail by Rutherford backscattering, scanning Auger, secondary ion mass spectrometry and X-ray diffraction, which showed that Ti nitride and Ti oxide-silicide formation take place at the surface and interface, respectively. Kinetic studies showed that the Ti reactions take place within the first 10 min. This self-limiting behavior occurs for all annealing temperatures, but the extent to which the encapsulation reaction takes place increases with temperature. Four-point probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼3 μΩ cm were measured in encapsulated Ag alloy films with low initial Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as-deposited Ag (∼2.5 μΩ cm).

Encapsulation of Ag films on SiO2 by Ti reactions using Ag–Ti alloy/bilayer structures and an NH3 ambient

Thin encapsulated silver films have been prepared on oxidized silicon by nitridation of ∼200-nm-thick Ag–19 at. % Ti alloy films and Ag(120 nm)/Ti(22 nm) at 300–700 °C in an ammonia ambient. The encapsulation process has been studied in detail by Rutherford backscattering, and scanning Auger and secondary-ion-mass spectrometry, which showed that Ti-nitride and Ti-oxide-silicide formation take place at the surface and the Ag–Ti/SiO2 interface, respectively. Four-point-probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼4 μΩ cm were measured in encapsulated Ag alloy films with initial low Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as-deposited Ag (∼3 μΩ cm).

XPS Valence Band and Core Level Spectra of Sputter-Deposited Fe–Cu, Fe–Ag and Fe–Cu–Ag Alloy Films

Valence band and core-level characteristics of sputter-deposited Fe–Cu, Fe–Ag and Fe–Cu–Ag alloy films have been studied by X-ray photoelectron spectroscopy using monochromatized Al Kα radiation. These films are composed of metastable bcc, fcc and amorphous phases depending on the alloy composition. Their valence band spectra consist of well-resolved peaks representative of Fe-, Cu- and Ag-derived d bands in the respective alloy systems, whose spectral features are similar to those of Ni-Cu and Pd–Ag alloys reported by Hüfner et al. The spectral component of the Fe-derived d band near the Fermi level tends to shrink rapidly in Cu- and Ag-rich fcc alloys. This feature is discussed in relation to the variation of the Curie temperature with the Cu or Ag concentration in these alloys. The core-level spectra of Fe 2 p , Cu 2 p and Ag 3 d states reveal that charge transfer among constituent elements is not appreciable. The effects of thermal annealing and the attendant phase separation upon these XPS spectra are also studied.

An ISS / AES study of surface segregation of Cu-Mn and Cu-Ag alloy films in-situ deposited onto low temperature W substrates

The surface composition of Cu-Mn and Cu-Ag alloy films co-deposited in-situ in UHV has been studied by a newly developed ISS/AES analyzer. Cu and Mn, or Cu and Ag are co-evaporated from two evaporation sources, each evaporation rate being changed to prepare specimens with different bulk composition. The substrate is a polycrystalline W sheet and its temperature ( T s) during and after the deposition can be varied. When a Cu-35at%Mn film is deposited at T s=300 K, Mn enrichment can be clearly observed by ISS but not AES. No significant enrichment of Mn takes place, when the deposition is performed at T s=100 K. In contrast, a similar measurement made on a Cu-20at%Ag alloy film shows a significant segregation even at T s=100 K.

Isomerization of alkanes on epitaxially oriented (111) Pd–Cu and Pd–Ag alloy films

The reactions of neopentane and n-butane in the presence of an excess of dihydrogen have been studied on films of Pd–Cu and Pd–Ag evaporated onto mica. The characterization of films showed that they were predominantly (111) oriented. The catalytic activity for isomerization of neopentane and n-butane was higher for ca. 10 at% Cu than for pure Pd, resembling the catalytic behaviour of Pd–Au(111) films. This does not, however, confirm the existence of the ligand effect in alkane isomerization over Pd–IB metal alloys. The catalytic activity of Pd–Ag(111) alloys decreases with increasing silver content, but on the basis of the inferred surface composition of these alloys this agrees with the conclusion drawn for the Pd–Cu system, i.e. the possible absence of the ligand effect.

The structure of vapour-quenched GdAg alloys containing between 0 and 16 at% silver

The structures of non-crystalline vapour-quenched GdAg alloy films containing between 0 and 16 at% silver have been examined by X-ray diffraction techniques. Radial distribution functions calculated from the experimental data, are in general appearance similar to those generated from a binary hard-sphere model derived from random layers of unequal-sized spheres for all compositions except those near 13 at% Ag. A hard-sphere model proposed by Sadoc et al. [13] generated from a seed cluster gives better agreement in the region of 13 at% Ag. Magnetic measurements show a Curie-Weiss behaviour for the magnetic susceptibility with p eff = 7.6 ± 1.9 μ B for these alloys.

Thermoelectric power of gold-silver alloy films

Thermoelectric power, resistivity, and temperature coefficient of resistance of annealed Au−Ag alloy films, covering the entire composition range, have been measured. Using size effects in the electron transport theory, the energy dependence of the mean free path U and the Fermi surface area V have been determined.

The thermal desorption of carbon monoxide from palladium and palladium-silver films

The extent of adsorption at 295 and 78 K and the thermal desorption of CO from Pd, Ag, and PdAg alloy films have been measured in an ultrahigh vacuum system. The adsorption data indicated that the surface of the alloys studied in this paper was enriched by Ag. Desorption spectra revealed several adsorption/desorption states, designed as γ 1, γ 2, α 1, α 2, and β. The nonspecific, most weakly bound γ 1-state was observed with all adsorbents. The γ 2-state, also weakly bound, was observed only on Pd. The α 1- and α 2-states were observed on Pd and PdAg alloys; they were completely missing on Ag. The population of α-states decreased with increasing Ag content. This is explained by assuming that upon alloying of Pd with Ag the number of large ensembles necessary for strong adsorption decreases.

Surface potential measurements of CO chemisorption on clean palladium-silver alloy films

Surface potentials (S.P.) due to CO chemisorption at 0 °C were measured for a series of evaporated PdAg alloy films prepared in ultrahigh vacuum. The S.P. increased from zero (for pure Ag) with increasing Pd content but then increased sharply at ~60% Pd, remaining constant for higher Pd contents up to pure Pd (−0.62 V at 2 × 10 −6 Torr CO). Results for Ag-rich films require a special explanation, e.g., electron activation, if the concept of relating chemisorption capacity to d-band vacancies, a collective property, is to be maintained but the concept of surface Pd atoms acting as individual adsorption centers in an Ag diluent is difficult to generalize across the whole composition range. It is suggested that the viewpoint from which the surface properties of an alloy system such as PdAg are discussed, may depend on the concentration of the Group IB additive because, e.g., the band of surface electron states may not overlap the normal crystal band in Ag-rich alloys (unlike Pd-rich alloys), so that the surface properties need not relate to the electronic structure of the corresponding bulk alloy.

The oxidation of ethylene over evaporated palladium-rhodium alloy films: II. Variation of activity with film composition and structure

Rates of CO 2 formation when ethylene was completely oxidized in a static system over evaporated PdRh alloy films showed a complex variation with alloy composition. This activity pattern generally reflected the variations in activation energy, E, with composition; values of E and log (frequency factor) fell on a linear plot, indicating a compensation effect, with the exception of pure Rh which is discussed. The activity pattern can be interpreted in terms of the film structure and properties occurring in the three composition ranges distinguished as follows: 0–30% Rh; increased activity compared with pure Pd, expected from bulk electronic properties and previous results with PdAg alloy films, was not observed. Instead the activity passes through a minimum at 10–15% Rh. It is believed that at this composition the alloy has a reasonable capacity to dissolve hydrogen (from C 2H 4) which would reduce the activity by filling d-band holes, combined with a decreased ability to effect H 2O 2 combination. An alternative explanation, based on the onset of phase-separation at the surface at lower Rh contents than expected, was tested by CO oxidation. 30–80% Rh; the activity decreased continuously with increasing Rh content in alloys composed of two “phases,” the Rh-rich Phase II is believed to form the kernel of the crystallites, surrounded by a variable-composition Phase I. The activity results were re-plotted assuming that the surface composition can be equated with the composition of Phase I given by X-ray data in Part I. Apparently anomalous results fitted into place and a maximum in activity below 30% Rh, which would occur in the absence of hydrogen solubility, was indicated. 80–100% Rh; some enrichment of the surface by Pd may occur; the decrease in activity between 98% and pure Rh is discussed, as well as its very low absolute activity.

The preparation of homogeneous PdAg alloy films

The preparation of homogeneous PdAg alloy films