Gas in-diffusion contribution to impedance in tin oxide thick films

The ac electrical resistance and capacitance of SnO2 thick films under vacuum and air atmosphere were analyzed using the Cole–Cole plot. To fit the experimental results, a simple circuit model that considers a capacitance and a resistance in parallel was employed. An explanation for the resistance variation considering spherical grains with different characteristics is proposed. A careful analysis of the resulting depletion layers and doping levels gives evidence for gas diffusion into the grain

Thick film microsensors based on nanosized Titania sol-gel powder

Thick films of nanostructured TiO2 and tantalum--doped TiO2 have based fabricated by screen--printing technology starting from pure titania and tantalum--doped titania powders prepared by sol--gel method. The titania powders, obtained via sol--gel, show crystalline anatase structure and the particles are homogeneous and nanosized (30 ÷ 50 nm). Two series of films each one composed by pure and Ta--doped titania samples have been obtained by firing the pastes in air atmosphere at the temperatures of 650°C and 850°C, respectively. SEM observations and electrical characterizations showed that the firing temperature strongly influences the nanostructure and the gas response of the pure titania samples. The addition of tantalum inhibits the grain sintering at the higher temperature. Moreover the electrical data show that the tantalum addition (10 at.%) does not affect the conductance of the films in air while significantly enhances the response towards CO and leaves almost unaltered or enhances its ability to sense NO2 depending on the thermal treatments

UV-Cured Composite Films Containing ZnO Nanostructures: Effect of Filler Shape on Piezoelectric Response

In this work, a facile aqueous sol-gel approach was exploited for synthesizing different ZnO nanostructures; these latter were employed at 4 wt% loading in a UV-curable acrylic system. The piezoelectric behavior of the resulting UV-cured nanocomposite films (NCFs) at resonance and at low frequency (150 Hz, typical value of interest in energy harvesting applications) was thoroughly investigated and correlated to the structure and morphology of the utilized ZnO nanostructures. For this purpose, the NCFs were used as active material into cantilever-shaped energy harvesters obtained through standard microfabrication technology. Interesting piezoelectric behavior was found for all the prepared UV-cured nanostructured films; the piezoelectric response of the different nanofillers was compared in terms of RMS voltage measured as a function of the applied waveform and normalized to the maximum acceleration applied to the cantilever devices. The obtained results confirmed the promising energy harvesting capability of such ZnO nanostructured films. In particular, flower-like structures showed the best piezoelectric performance both at resonance and 150 Hz, gaining a maximum normalized RMS of 0.914 mV and a maximum peak-peak voltage of about 16.0 mVp-p corresponding to the application of 5.79 g acceleration

UV-Cured Composite Films Containing ZnO Nanostructures: Effect of Filler Shape on Piezoelectric Response

In this work, a facile aqueous sol-gel approach was exploited for synthesizing different ZnO nanostructures; these latter were employed at 4 wt% loading in a UV-curable acrylic system. The piezoelectric behavior of the resulting UV-cured nanocomposite films (NCFs) at resonance and at low frequency (150 Hz, typical value of interest in energy harvesting applications) was thoroughly investigated and correlated to the structure and morphology of the utilized ZnO nanostructures. For this purpose, the NCFs were used as active material into cantilever-shaped energy harvesters obtained through standard microfabrication technology. Interesting piezoelectric behavior was found for all the prepared UV-cured nanostructured films; the piezoelectric response of the different nanofillers was compared in terms of RMS voltage measured as a function of the applied waveform and normalized to the maximum acceleration applied to the cantilever devices. The obtained results confirmed the promising energy harvesting capability of such ZnO nanostructured films. In particular, flower-like structures showed the best piezoelectric performance both at resonance and 150 Hz, gaining a maximum normalized RMS of 0.914 mV and a maximum peak-peak voltage of about 16.0 mVp-p corresponding to the application of 5.79 g acceleration

Comparison between normal and reverse thin crystalline silicon solar cells

The newly developed ingot growing techniques, as the three-grain and the columnar multigrain ingot processes, are now offering the possibility of slicing thinner wafers (=< 100 m). In this paper we present the results obtained on p type large area (=< 100 cm2) and 100 m thick wafers by using both conventional and reverse cell manufacturing technologies.The conventional cells are provided with aluminium or boron BSF plus screen-printed silver mirror or a silver-aluminium net; the reverse cells have a FSF and the deep back junction completely covered by a screen-printed or CVD silver layer.The constructing parameters have been chosen on the base of one and two dimensions modeling and both raw material and devices have been completely characterized.This work shows that very thin wafers do not introduce serious problems for the conventional manufacturing of solar cells. The efficiencies of the normal and of the reverse cells are found to be comparable and are of the same order than those of thicker cells, however at a significant lower cost. The main obtained result has to be related to the demonstration of a cell manufacturing feasibility starting from very thin wafers

Synthesis of pure and loaded powders of WO3 for NO2 detection through thick film technology

Nanopowders of pure and of Mn-, Ta- and Zr-loaded (5 wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric WO3 was prepared by a modified sol–gel synthesis while loading was carried out by impregnation with Mn(II), Ta(V) and Zr(IV) chlorides. Addition of Ta resulted in grain coalescence and phase transition inhibitions in the layers with respect to pure WO3 films, being the effect strongly enhanced in the filmsfired at 850 °C. The Ta-doped films turned out to be the most sensitive films with a response extending down to the sub-ppm domain

Development of a low-power thick-film gas sensor deposited by screen-printing technique onto a micromachined hotplate

We report on the design, implementation and characterisation of a thick-film gas sensor deposited for the first time by screen-printing technique onto a micromachined hotplate, the microheater maintains a film temperature as high as 400°C with <30 mW of input power. The microheater consists of a dielectric stacked membrane equipped with embedded polysilicon resistors acting as heating element as well as temperature sensing elements. Extensive finite-element computer simulations were carried out during the design step to optimise the radial temperature gradient up to 1200°C/mm. A newly developed scheme for temperature measurement was adopted for on-line adjustment of the film temperature through aconventional low-power proportional integral (PI) regulator. Deposition of sensing layers based on semiconductor oxides, such as SnO2 was achieved by computer-aided screen-printing. The films were then fired through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH4 and NO2 at concentrations typical for indoor and outdoor applications was recorded by measuring the film resistance through ultra high impedance CMOS circuit

Membrane-type Gas Sensor with Thick Film Sensing Layer: Optimization of Heat Loses

We report the results of application of combined technology for the manufacturing of metal oxide gas sensors. This technology includes the manufacturing of micromachined thin dielectric membrane with microheater used as a support for thick film metal oxide gas sensing layer. The optimization of geometry of the membrane performed by means of finite-element computer simulation enabled the fabrication of methane gas sensor with power consumption of ~35 mWatt at optimal temperature equal to about 500°C. The microheater and the sensing layer have satisfactory long-term stability