Silver content effect on rheological and electrical properties of silver pastes

The novelty of this work is laboratory formulation of environmentally friendly, water-based silver inks adapted for screen printing. The challenge was also to elaborate inks that can withstand temperatures as high as 900 °C. Indeed, when printed on ceramic substrate, they were sintered at these high temperatures. These inks can replace conductive silver pastes present in the market, today, and containing irritant solvents such as terpineol and other aromatic solvents. Besides, screen printing is considered as an additive technique, thus allowing reducing wastes. Furthermore, only with 72.5% silver, considered as low content compared to commercial inks (≥75%), prepared inks presented good electrical resistivity, 23 nΩ m, close to that of bulk silver resistivity, 16 nΩ m. Formulation of silver inks with spherical particles, 2–3 μm mean diameter, was performed. The aim of the study was to determine silver content effect on pastes rheological behaviour, lines properties (width, thickness and roughness) and electrical properties. Therefore, rheological behaviour of inks was studied; in particular, Casson and Bingham models were applied in order to determine the yield stress. Viscosity evolution as a function of shear rate was also determined. Besides, the thixotropic behaviour of inks was highlighted. Inks were then screen printed on alumina sintered substrates and cured at different temperatures during 15 min. Topography measurements were performed. Line resistivity as small as 35 nΩ m was measured on cured lines. These inks, printed on ceramic tapes, can be used to print microwave transmission lines, for which resistivities lower than 1 mΩ m are requested.     

Novel thermoelectric materials based on boron-doped silicon microchannel plates

The thermoelectric properties of boron-doped silicon microchannel plates (MCPs) were investigated. The samples were prepared by photo-assisted electrochemical etching (PAECE). The Seebeck coefficient and electrical resistivity at room temperature (25 °C) were measured to determine the thermoelectric properties of the samples. In order to decrease the very high resistivity, boron doping was introduced and by modulating the doping time, a series of samples with different resistivity as well as Seebeck coefficient were obtained. Boron doping changed the electrical resistivity of the samples from 1.5 × 10⁵ Ω cm to 5.8 × 10⁻³ Ω cm, and the absolute Seebeck coefficient deteriorated relatively slightly from 674 μV/K to 159 μV/K. According to the Seebeck coefficient and electrical conductivity, the power factor was calculated and a peak value of 4.7 × 10⁻¹ mW m⁻¹ K⁻² was obtained. The results indicate that silicon MCPs doped with boron are promising silicon-based thermoelectric materials.     

Strain dependence electrical resistance and cohesive strength of ITO thin films deposited on electroactive polymer

Transparent, conducting, indium tin oxide (ITO) films have been deposited, by pulsed dc magnetron sputtering, on glass and electroactive polymer (poly(vinylidene fluoride)—PVDF) substrates. Samples have been prepared at room temperature by varying the oxygen partial pressure. Electrical resistivity around 8.4 × 10^− 4 Ω cm has been obtained for films deposited on glass, while a resistivity of 1.7 × 10^− 3 Ω cm has been attained in similar coatings on PVDF. Fragmentation tests were performed on PVDF substrates with thicknesses of 28 μm and 110 μm coated with 40 nm ITO layer. The coating's fragmentation process was analyzed and the crack onset strain and cohesive strength of ITO layers were evaluated.     

Organic thin film transistor using silver electrodes by the ink-jet printing technology

We have developed a conductive ink containing silver nanoparticles from which the electrodes for organic thin film transistor were directly patterned by ink-jet printing. Nano-sized silver particles having ∼ 20 nm diameter was used for a direct metal printing. Silver conductive ink was printed on the heavily doped n-type silicon wafer with 200-nm thick thermal SiO₂ layer as a substrate. To achieve a high line resolution and smooth conductive path, the printing conditions such as the inter-drop distance, stage moving velocity and temperature of the pre-heated substrates were optimized. After the heat-treatment at temperatures of 200 °C for 30 min, the printed silver patterns exhibit metal-like appearance and the conductivity. To fabricate a coplanar type TFTs, an active material of semiconducting oligomer, α,ω-dihexylquaterthiophene (DH4T) in a chlorobenzene was deposited between the ink-jet printed silver electrodes by drop casting. The OTFT with the ink-jetted source/drain electrodes shows general performance characteristics with good saturation behavior and no significant contact resistance as compared to the one with vacuum deposited electrodes. The electrical characteristic parameters of OTFT show the mobility of 1.3 × 10^− 3 cm² V^− 1 s^− 1 in the saturation regime, on/off current ratio over 10³, and threshold voltage of about − 13 V.     

Indium tin oxide films deposited by thermionic-enhanced DC magnetron sputtering on unheated polyethylene terephthalate polymer substrate

Indium tin oxide thin films were deposited onto polyethylene terephthalate substrates via thermionic enhanced DC magnetron sputtering at low substrate temperatures. The structural, optical and electrical properties of these films are methodically investigated. The results show that compared with traditional sputtering, the films deposited with thermionic emission exhibit higher crystallinity, and their optical and electrical properties are also improved. Indium tin oxide films deposited by utilizing thermionic emission exhibit an average visible transmittance of 80% and an electrical resistivity of 4.5 × 10⁻⁴ Ω cm, while films made without thermionic emission present an average visible transmittance of 74% and an electrical resistivity of 1.7 × 10⁻³ Ω cm.     

Comparative studies on thermal and laser sintering for highly conductive Cu films printable on plastic substrate

Compound-based Cu paste was synthesized to prepare electrically conductive films on plastic substrate. The Cu pastes screen-printed onto polyimide were annealed inside a furnace and also by an ultraviolet laser beam and the effects of annealing conditions on the microstructures and electrical properties were investigated. Both of thermal and laser processes were carried out under N₂ gas flow, which was very effective in preventing oxidation. The minimum resistivity available with thermal sintering was 1.30 × 10^− 5 Ω cm and a slightly higher resistivity was obtained by laser sintering. This value is several orders of magnitude lower than that reported for the copper nanoparticle paste thermally sintered under N₂ atmosphere. The variation of microstructure and electrical property with the laser power was very similar to the temperature dependence of these factors in thermal sintering.     

Inkjet printing of conductive patterns with an aqueous solution of [AgO2C(CH2OCH2)3H] without any additional stabilizing ligands

The use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate, [AgO₂C(CH₂OCH₂)₃H], and its application as an aqueous metal-organic decomposition (MOD) inkjet ink is reported. The chemical and physical properties of the silver carboxylate and the ink formulated thereof are discussed. The ink meets all requirements of piezo driven inkjet printing. The printed features were converted into electrically conducting silver patterns by thermal or photo-thermal treatment. The conversion of [AgO₂C(CH₂OCH₂)₃H] to elemental silver follows a two-step decomposition as demonstrated by thermogravimetry-mass spectrometry (TG-MS) measurements. The measured conductivities of the printed features on glass and polyethylene-terephthalate (PET) are 2.7 × 10⁷ S m⁻¹ and 1.1 × 10⁷ S m⁻¹, respectively, which correspond to 43% (glass) and 18% (PET) of the bulk silver conductivity.     

Fabrication of conductive silver micropatterns on an organic-inorganic hybrid film by laser direct writing

This paper describes fabrication of silver (Ag) micropatterns on a double-decker-shaped polysilsesquioxane (DDPSQ) hybrid film by laser-induced pyrolysis (LIP) of a film prepared from liquid-dispersed Ag nanoparticles. The line width of Ag micropatterns fabricated by LIP can be controlled flexibly by changing the numerical aperture (NA) value of an objective lens and the focusing point. By changing NA value of an objective lens, line widths of Ag micropatterns can be varied flexibly from 75 μm to 5 μm. The Ag micropatterns show an excellent adherence to DDPSQ surface as evaluated by adhesive tape test. The resistivity of the Ag micropattern is determined to be 4.3 × 10^− 6 Ω cm, which is comparable to that of bulk Ag (1.6 × 10^− 6 Ω cm).     

Comparative study of ITO and FTO thin films grown by spray pyrolysis

Tin doped indium oxide (ITO) and fluorine doped tin oxide (FTO) thin films have been prepared by one step spray pyrolysis. Both film types grown at 400 °C present a single phase, ITO has cubic structure and preferred orientation (4 0 0) while FTO exhibits a tetragonal structure. Scanning electron micrographs showed homogeneous surfaces with average grain size around 257 and 190 nm for ITO and FTO respectively.The optical properties have been studied in several ITO and FTO samples by transmittance and reflectance measurements. The transmittance in the visible zone is higher in ITO than in FTO layers with a comparable thickness, while the reflectance in the infrared zone is higher in FTO in comparison with ITO. The best electrical resistivity values, deduced from optical measurements, were 8 × 10⁻⁴ and 6 × 10⁻⁴ Ω cm for ITO (6% of Sn) and FTO (2.5% of F) respectively. The figure of merit reached a maximum value of 2.15 × 10⁻³ Ω⁻¹ for ITO higher than 0.55 × 10⁻³ Ω⁻¹ for FTO.     

Synthesis of silver nano particles and fabrication of aqueous Ag inks for inkjet printing

The main problem in preparing stable and printable inks containing nanoparticles for inkjet printing is to overcome the strong agglomeration of the particles in dispersion medium. In this study, the silver particles with diameter around 50 nm were produced by a simple wet chemistry method. Stable aqueous printable inks were formulated by using the combination of a triblock copolymer and high intensity focused ultrasound (HIFU). Various factors that affect the ink stability, such as, copolymer content and time of HIFU treatment, were investigated. The ink containing 5 wt% silver has a viscosity of about 2 mPa s and surface tension 30 mN m⁻¹ at 25 °C, which meet inkjet printer requirements. Such inks have been successfully printed on Al₂O₃ ceramics and low-temperature co-fired ceramics (LTCC) and the printed films show low resistivity.     

The use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate as precursor in the deposition of thin silver layers on float glass by the atmospheric pressure combustion chemical vapor deposition process

The innovative use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate ([AgO₂C(CH₂OCH₂)₃H], 3) as precursor for the deposition of silver on float glass by applying the atmospheric pressure combustion chemical vapor deposition process is described. As nucleation layer tungsten oxide was utilized, conformal, closed and dense silver layers of ca. 70 nm thickness were obtained. They are adhesive and high reflective with a resistivity of 5 ? 10⁻⁸ Ωm.     

Conductive silver patterns via ethylene glycol vapor reduction of ink-jet printed silver nitrate tracks on a polyimide substrate

In this paper, we report using ethylene glycol vapor reduction approach to fabricate conductive silver tracks directly from silver nitrate solution by ink-jet printing. The silver nitrate precursor can be reduced in ethylene glycol vapor to form silver at low temperatures. X-ray diffraction, thermogravimetric analysis, and energy dispersive spectrometric analysis results indicate that the silver nitrate has been converted to silver completely. Using a high concentration silver nitrate solution, continuous silver conductive lines with a resistivity of 7.314 × 10^− 5 Ω cm have been produced, which is relatively close to the resistivity of bulk silver.     

Multifunctional ZnO:V thin films deposited by rf-magnetron sputtering from aerogel nanopowder target material

ZnO:V thin films have been grown onto suprasil substrates by rf-magnetron sputtering at room temperature using nanocrystalline powder synthesized by modified sol-gel method. In our approach the water for hydrolysis used in the synthesis of nanopowder was slowly released by esterification reaction followed by a thermal drying in ethyl alcohol at 250 °C. The effects of V concentration on structural, electrical, morphological and optical properties were studied. The as-deposited films with a thickness of about 0.4 μm were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The films present high optical transmittance in the visible range of approximately 90%, carrier concentration of about 10²⁰ cm^− 3 and electrical resistivity of 10^− 3 Ω cm at room temperature. In the as-prepared state the films also present ferromagnetic properties attributed to the presence of vanadium based secondary phases.     

Influence of Ag thickness of aluminum-doped ZnO/Ag/aluminum-doped ZnO thin films

Highly conducting aluminum-doped ZnO (30 nm)/Ag (5-15 nm)/aluminum-doped ZnO (30 nm) multilayer thin films were deposited on glass substrate by rf magnetron sputtering (for top/bottom aluminum-doped ZnO films) and e-beam evaporation (for Ag film). The transmittance is more than 70% for wavelengths above 400 nm with the Ag layer thickness of 10 nm. The resistivity is 3.71 × 10^− 4 Ω-cm, which can be decreased to 3.8 × 10^− 5 Ω-cm with the increase of the Ag layer thickness to 15 nm. The Haacke figure of merit has been calculated for the films with the best value being 8 × 10^− 3 Ω^− 1. It was shown that the multilayer thin films have potential for applications in optoelectronics.     

Fluorine-doped ZnO transparent conducting thin films prepared by radio frequency magnetron sputtering

Fluorine-doped ZnO transparent conducting thin films were prepared by radio frequency magnetron sputtering at 150 °C on glass substrate. Thermal annealing in vacuum was used to improve the optical and electrical properties of the films. X-ray patterns indicated that (002) preferential growth was observed. The grain size of F-doped ZnO thin films calculated from the full-width at half-maximum of the (002) diffraction lines is in the range of 18-24 nm. The average transmittance in visible region is over 90% for all specimens. The specimen annealed at 400 °C has the lowest resistivity of 1.86 × 10^− 3 Ω cm, the highest mobility of 8.9 cm² V^− 1 s^− 1, the highest carrier concentration of 3.78 × 10²⁰ cm^− 3, and the highest energy band gap of 3.40 eV. The resistivity of F-doped ZnO thin films increases gradually to 4.58 × 10^− 3 Ω cm after annealed at 400 °C for 4 h. The variation of the resistivity is slight.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.     

Microstructure and thermoelectric properties of n-type 95%Bi2Te3-5%Bi2Se3 alloy produced by rapid solidification and hot extrusion

n-type SbI₃-doped 95%Bi₂Te₃+5%Bi₂Se₃ compounds were prepared by a rapid solidification and extrusion at the temperature range 420-480 °C using an extrusion ratio of 25:1. The microstructure and thermoelectric properties of the compounds were investigated as a function of extrusion temperature. The fabricated powder consists of homogeneous Bi₂Te₃+Bi₂Se₃ solid solution and the relative density of over 99% was obtained by hot extrusion. The values of Seebeck coefficient for the compounds hot extruded at 420, 450, and 480 °C were −160.8, −170.2, and −165.7 μV K⁻¹, respectively. The values of electrical resistivity (ρ) for the compounds hot extruded at 420, 450, and 480 °C were 0.49, 0.57, and 0.51×10⁻⁵ Ω m, respectively. The maximum power factor value of the compounds hot extruded at 480 °C was 53.8×10⁶ μW cm⁻¹ K⁻².     

Remote plasma sputtering of indium tin oxide thin films for large area flexible electronics

Indium tin oxide (ITO) thin films with a specific resistivity of 3.5 × 10^− 4 Ω cm and average visible light transmission (VLT) of 90% have been reactively sputtered onto A4 Polyethylene terephthalate (PET), glass and silicon substrates using a remote plasma sputtering system.This system offers independent control of the plasma density and the target power enabling the effect of the plasma on ITO properties to be studied. Characterization of ITO on glass and silicon has shown that increasing the plasma density gives rise to a decrease in the specific resistivity and an increase in the optical band gap of the ITO films. Samples deposited at plasma powers of 1.5 kW, 2.0 kW and 2.5 kW and optimized oxygen flow rates exhibited specific resistivity values of 3.8 × 10^− 4 Ω cm, 3.7 × 10^− 4 Ω cm and 3.5 × 10^− 4 Ω cm and optical gaps of 3.48 eV, 3.51 eV and 3.78 eV respectively.The increase in plasma density also influenced the crystalline texture and the VLT increased from 70 to 95%, indicating that more oxygen is being incorporated into the growing film. It has been shown that the remote plasma sputter technique can be used in an in-line process to produce uniform ITO coatings on PET with specific resistivities of between 3.5 × 10^− 4 and 4.5 × 10^− 4 Ω cm and optical transmission of greater than 85% over substrate widths of up to 30 cm.     

Effect of deposition parameters and annealing temperature on the structure and properties of Al-doped ZnO thin films

Transparent conductive films of Al-doped ZnO (AZO) were deposited onto inexpensive soda-lime glass substrates by radio frequency (rf) magnetron sputtering using a ZnO target with an Al content of 3 wt%. The Taguchi method with a L₉ orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to examine the performance characteristics of the coating operations. This study investigated the effect of the deposition parameters (rf power, sputtering pressure, thickness of AZO films, and substrate temperature) on the electrical, structural, morphological and optical properties of AZO films. The grey-based Taguchi method showed the electrical resistivity of AZO films to be about 9.15 × 10⁻³ Ω cm, and the visible range transmittance to be about 89.31%. Additionally, the films were annealed in a vacuum ambient (5.0 × 10⁻⁶ Torr) at temperatures of 400, 450, 500 and 600 °C, for a period of 30 min. It is apparent that the intensity of the X-ray peaks increases with annealing treatment, leading to improved crystallinity of the films. By applying annealing at 500 °C in a vacuum ambient for 30 min, the AZO films show the lowest electrical resistivity of 2.31 × 10⁻³ Ω cm, with about 90% optical transmittance in the visible region and a surface roughness of Ra = 12.25 nm.     

Effects of annealing on optical and electrical characteristics of p-type semiconductor copper (II) oxide electrodeposits

The 1.35-eV-bandgap energy-CuO film with the optical absorption coefficient of 2.2 × 10⁴ cm^− 1 has been prepared on a conductive glass substrate by anodic electrodeposition in an aqueous solution containing copper (II) nitrate and ammonium nitrate at 298 K followed by annealing at 573 K and above in air. The as-deposited CuO film with a monoclinic lattice showed p-type conduction with resistivity of 2.2 × 10⁵ Ω cm and slightly expanded bandgap energy of 1.46 eV with the absorption coefficient of 1.3 × 10⁴ cm^− 1. The annealing induced changes in the grain morphology, bandgap energy, absorption coefficient, and resistivity, and the resistivity of 3.3 Ω cm could be obtained by annealing at 773 K.