Microstructure Of Thick Films Research Articles

Particle deposition and deformation from high speed impaction of Ag nanoparticles

The impaction of a single Ag nanoparticle onto an (001) Ag substrate was studied as a function of particle diameter (2–9 nm) and impaction velocity (10–1500 m/sec) using molecular dynamics simulations. The final crystallographic structures were observed to transition from a polycrystalline to an epitaxial morphology as impaction velocity was increased and the velocity required to achieve epitaxy increased with particle size. To understand how the crystallographic structures evolved to their final state, the deformation mechanisms were then studied over a range of time scales, beginning immediately upon impaction. The observed mechanisms included disordering of the atoms and the initiation and propagation of partial dislocations. Deformation increased with impaction velocity due to increases in the degree of disordering and the partial dislocation density. At longer time scales, relaxation of the disordered particles produced epitaxial morphologies, whereas polycrystalline morphologies were observed following incomplete disordering. These results suggest that the microstructures of thick films produced by high speed impaction of nanoparticle aerosols are strongly influenced by processing parameters.

Enhanced dielectric properties of Bi1.5ZnNb1.5O7 thick films via cold isostatic pressing

Dense Bi1.5ZnNb1.5O7 thick films were prepared on Ag/Al2O3 substrates using screen-printing technology at a lower temperature of 825 °C. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of thick films. After cold isostatic pressing prior to sintering, the microstructure of thick films was improved with a more compact morphology and better dielectric properties, and the permittivity and dielectric loss of thick films sintered at 900 °C were about 160 and 0.006. The obvious tunability of thick films was also observed, and the tunability value reached about 3 % for thick films sintered at 900 °C under 400 kV/cm. The enhanced properties and low-temperature sintering made this compound a potential candidate for Low Temperature Co-fired Ceramic (LTCC).

Investigation of PNN-PZT Thick Films Fabricated by Electrophoretic Deposition

0.2Pb(Ni1/3Nb2/3)O3-(0.8−x)PbTiO3-xPbZrO3 (PNN-PZT) dense piezoelectric thick films with the thickness of about 50 μm were fabricated by electrophoretic deposition(EPD) on Pt wire. Effects of different dispersants to the Zeta potential of the suspension and the microstructures of the PNN-PZT thick films were evaluated. The results shows that suspension with polyethyleneglycol 10000 is more stable than the suspension with polyethyleneglycol 6000, and the thick films deposited from suspension with polyethyleneglycol 10000 is more denser. The effects of different dispersants on the stability of the suspension and the influences of different deposition methods on the microstructures of the thick films were discussed. The result shows that dense thick films can be fabricated by stepwise deposition. The effect of different sintering temperatures to the dielectric constant and the dielectric loss of PNN-PZT thick films at room temperature were investigated. The dielectric constant and the dielectric loss at room temperature of the PNN-PZT thick film sintered at 1180°C for 30 min are 988 and 3.7% respectively. The electric induced displacement (E-D) curve and hysteresis loop of the PNN-PZT thick films were measured. The effective piezoelectric constant and the residual polarization of the PNN-PZT films are 90 pm/V and 6.00 kV/cm, respectively.

Effect of dispersibility of silver powders in conductive paste on microstructure of screen-printed front contacts and electrical performance of crystalline silicon solar cells

Effect of dispersibility of silver powders in conductive paste on microstructure of screen-printed front contacts and electrical performance of crystalline silicon solar cells was investigated. Two different dispersed degree silver powders were experimented. It is found that the dispersibility of the silver powders strongly affects the microstructure of thick film and electrical performance of solar cells and highly dispersed silver powders can form even compact thick film and exhibit higher open-circuit voltage (V oc ), short-circuit current (I sc ), shunt resistance (R sh ), maximum power (P max ), optimum operating voltage (V mp ), optimum operating current (I mp ), fill factor (FF) and photoelectric conversion efficiency (Eff) than seriously agglomerated silver powders under otherwise identical conditions.

Termination of BME–MLCC Using Copper–Nickel Bimetallic Powder as Electrode Material

Microstructure of termination of a base metal electrode multilayer ceramic capacitor (BME-MLCC) using copper-nickel bimetallic powder as electrode material was investigated. Thick film paste containing nonagglomerated monodispersed copper-nickel bimetallic powder was applied in preparing the termination electrode of a BME-MLCC. Influence of an inorganic binder on the microstructure of the termination of BME-MLCC was studied. The distribution of metallic copper on the surface of glass bubbles in termination was investigated by energy dispersive X-ray. A scanning electron microscope and a polarized light microscope were applied to discuss the microstructure of thick film. The results show that suitable binder and firing temperature result in the excellent connection between internal and termination electrode, as well as one between termination electrode and green chip. The BME-MLCCs with a dense surface of end termination, high adhesion, and qualified electrical behavior were obtained. The rough interface from interfacial reaction between glass and chip gives high adhesion

Investigation of gas sensitivity of Sb-doped ZnO nanoparticles

Undoped and Sb-doped ZnO nanoparticles were successfully synthesized by vapor condensation method from pure Zn and Zn–Sb alloy with different mole ratios (50:1, 15:1 and 6:1) as raw materials in a flowing gas mixture of Ar + O 2. The morphological characteristics, phase structure, composition and chemical state of nanoparticles were measured by TEM, HRTEM, XRD, EDX and XPS, respectively. The microstructures of thick films based on nanoparticles were investigated by SEM. The gas sensitivity of thick film based on Sb-doped ZnO nanoparticles to volatile organic compounds (VOCs), benzene, toluene, xylene, acetone and alcohol, as a function of temperature were measured, and compared to undoped ZnO thick film. After doping with Sb, the morphology of ZnO nanoparticles is modified from the needle-shape to the polygon; the gas sensitivity of the thick films is greatly improved, wherein the sensitivity of Sb-doped ZnO nanoparticles produced from alloy with Zn/Sb = 15:1 is maximal and response-recovery time is short. The gas sensitivity of the ZnO-based nanoparticles maybe depended on the content and chemical state of Sb in the ZnO lattices.

Microstructure and electronic properties of InGaN alloys

AbstractThe InxGa1−xN system has electronic band gaps extending from under 1eV to 3.4 eV, and as such they are used as the active layer in commercially available visible‐light emitting devices. There are many interesting features that make these nitride semiconductor alloys especially useful for efficient light emitters. It has been conjectured that the combination of piezoelectric fields and local composition inhomogeneities may be responsible for the observed high emission efficiencies, in spite of their characteristic high dislocation densities. But it is very difficult to grow InxGa1−xN layers with high indium composition. This paper presents an overview of the properties of InxGa1−xN epilayers based on a systematic study of thick layers and of quantum well structures. We find that the microstructure of thick films varies significantly with indium composition. For x < 0.08, the composition is uniform and unperturbed by dislocations. For 0.10 < x < 0.20, secondary phases nucleate at threading dislocations. For x > 0.20, spontaneous phase separation occurs resulting in a polycrystalline, inhomogeneous layer. A correlation between optical properties and microstructure is presented. It is observed that the misfit strain is affected by threading dislocations. Mechanisms of misfit strain relaxation are presented for InxGa1−xN layers grown on standard GaN on sapphire and on epitaxial‐lateral‐overgrowth GaN layers. In addition, we have studied the properties of quantum well structures using several novel techniques. The electrostatic fields across the wells have been profiled using electron holography in the TEM. The effect of well thickness on the strength of the fields is reported. The effects of localization by compositional fluctuations and of internal field screening have been studied using time‐resolved cathodoluminescence spectroscopy. In spite of significant progress that has been made in the last ten years, much work remains ahead in order to master the science and technology of these alloys. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Barium titanate screen-printed thick films

Barium titanate (BT) thick films were prepared from mechanically activated powders based on BaCO 3 and TiO 2. After homogenization and milling in a high-energy vibro mill, the powders were calcined at 700 °C for 2 h by slow heating and cooling rates. A thick film paste was prepared by mixing BT fine powders with small amount of low temperature sintering aid and organic binder. The thick films were screen-printed on alumina substrates electroded with Ag-Pd. The BT films were sintered at 850 °C for 1 h. The thickness was 25–75 μm depending of number of layers. The microstructure of thick films and the compatibility between BT layers and substrate were investigated by SEM .Results of dielectric property measurements are also reported.

Interfacial adhesion and microstructure of thick film metallized aluminum nitride substrates

The adhesive strength and fractured microstructure of aluminum nitride (AlN) substrate metallized with resistor thick-films followed by firing at 850 oC have been investigated via a pull-out rupture test loaded in tension. The AlN substrate used includes the as-received form and an oxidized form that was thermally treated at 1450 oC prior to the metallization. The thick-film paste includes both the as-received form (which is an RuO 2-based resistor) and a mixture of the paste with varying fractions of submicrometer alumina powder (5–20 wt.%) for comparison purposes. When the as-received AlN is used as the substrate, rupture strength decreases monotonically from 1.2 to ∼0.1 MPa as the alumina loading (in the film) increased from 0 to 20 wt.%. The strength, however, remains relatively constant (∼0.5 MPa) for the pre-oxidized AlN case, i.e. the adhesion is found insensitive to the change of alumina loading. This strength dependency has been compared with their fractured microstructure and the possible fracture mechanism that caused the failure is discussed.