Solid oxide fuel cells need a diffusion barrier layer to protect the zirconia-based electrolyte if a cobalt-containing cathode material like lanthanum strontium cobalt ferrite (LSCF) is used. This protective layer must prevent the direct contact and interdiffusion of both components while still retaining the oxygen ion transport. Gadolinium-doped ceria (GDC) meets these requirements. However, for a favorable cell performance, oxide ion conducting films that are thin yet dense are required. Films with a thickness in the sub-micrometer to micrometer range were produced by the dry room temperature spray-coating technique, aerosol deposition. Since commercially available GDC powders are usually optimized for the sintering of screen printed films or pressed bulk samples, their particle morphology is nanocrystalline with a high surface area that is not suitable for aerosol deposition. Therefore, different thermal and mechanical powder pretreatment procedures were investigated and linked to the morphology and integrity of the sprayed films. Only if a suitable pretreatment was conducted, dense and well-adhering GDC films were deposited. Otherwise, low-strength films were formed. The ionic conductivity of the resulting dense films was characterized by impedance spectroscopy between 300 °C and 1000 °C upon heating and cooling. A mild annealing occurred up to 900 °C during first heating that slightly increased the electric conductivity of GDC films formed by aerosol deposition.

The work describes a fast and flexible micro/nano fabrication and manufacturing method for ceramic Micro-electromechanical systems (MEMS)sensors. Rapid prototyping techniques are demonstrated for metal oxide sensor fabrication in the form of a complete MEMS device, which could be used as a compact miniaturized surface mount devices package. Ceramic MEMS were fabricated by the laser micromilling of already pre-sintered monolithic materials. It has been demonstrated that it is possible to deposit metallization and sensor films by thick-film and thin-film methods on the manufactured ceramic product. The results of functional tests of such manufactured sensors are presented, demonstrating their full suitability for gas sensing application and indicating that the obtained parameters are at a level comparable to those of industrial produced sensors. Results of design and optimization principles of applied methods for micro- and nanosystems are discussed with regard to future, wider application in semiconductor gas sensors prototyping.

In order to prevent detrimental reaction during manufacturing and enable the use of high performing La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode in electrolyte supported solid oxide cells, Ce0.8Gd0.2O2-δ (GDC) barrier layer is implemented between the cathode and the electrolyte. It is of great interest to manufacture thin and dense GDC layer at low temperature to avoid unfavorable reactions. GDC layers deposited through Electron-Beam Physical Vapor Deposition (EB-PVD) were investigated to address this challenge. Dense GDC barrier layers of different thickness were deposited onto yttria-stabilized zirconia (YSZ) electrolyte. Samples coated with GDC thin-film, with and without LSCF cathode, were thermally treated to simulate further cell and stack processing steps. XRD and SEM were applied to evaluate the phase composition, thermomechanical stability, morphology and microstructural changes. It is found that the 0.5 µm GDC layer remains crack-free and adherent to the substrate after the simulated thermal cycles.

Introduction The progress of the Internet of Things stimulates the development of sensors of small size and low power consumption. Miniaturized metal-oxide semiconductor (MOX) gas sensors (e.g. methane, hydrogen or carbon monoxide detection) can be integrated into agro-industrial facilities such as livestock facilities, fish farming, forestry, food-storage and horticulture, where they support future-oriented plant production (smart agriculture). The central part of a MOX gas sensor is a micro-hotplate, which is mainly responsible for the sensor power consumption at operating temperatures of 450 to 600°C. Under harsh environmental conductions, ceramic materials are the best choice for the micro-hotplate substrate and sensor housing (ceramic MEMS) in combination with platinum metallization for the heater. To realize such gas sensors with low power consumption (< 200 mW@4500C) the development of miniaturized printable heaters on ultra-thin ceramic membranes is needed. Methods Yttria-stabilized zirconia (3YSZ) powders were evaluated for the preparation of casting slurries and tape casting of thin tapes < 40 µm (present on Fig.1). After thermal treatment the substrates were characterized by density, thickness, flatness, roughness and mechanical bending stability. To reduce the thermal mass of the hotplate, the ceramic substrate was cut by a developed micro-milling process to realize free standing membranes of 280 µm size in diameter (present on Fig.2). Platinum particle (20 wt.-% and 30 wt.-%) as well as Pt-SiO2-composite inks were synthesized and ink properties like viscosity, surface tension and sedimentation stability characterized. Printing tests of miniaturized heater layouts (2.0x0.5 mm2 and 40 µm line width in hot spot) were performed by aerosol-jet (Optomec M3D 150 µm nozzle) and piezoDoD inkjet (Dimatix DMP 10 pL). The printed microheater were characterized (photo of experiment present on Fig.5) after sintering by film thickness, resistivity and microstructure (SEM). The applicability is demonstrated by heating tests, where temperature and power consumption is monitored in dependence of the heater driving voltage. The all parts of gas sensor was fabricated by totally digital technological flow with using pre-developed in STL format 3D model like as is customary in rapid prototyping way. For material of sensor package was used inexpensive Al2O3 monolithic ceramics. As a form factor for sensor was using SOT-23 package (3.0x1.4x1.0 mm), which give possibility to dissipate 350 mW heating power at room temperature. Parts of sensor package was fabricated by 20W fiber laser with a wavelength of 1.064 μm and tunable pulse duration from 50 to 200 ns with using especially developed software (present on Fig.7) combined process of micronilling and on-line comparisons fabricating geometrical parameters with 3D model. Results and Conclusions Mechanical flexible 3YSZ substrates of 5x5 cm2 size with thickness of 20 to 40 µm and a high density of 6.1 g/cm3 (equals theoretical density) were achieved (Fig.1a). The choice of raw material powders correlates to the substrates surface roughness (250 to 600 nm) and mechanical stability. The developed Pt-particle inks show a good print compatibility and a high sedimentation stability of < 0.2 mm per month. Miniaturized heater layouts with a narrow line width down to 40 µm were only achieved by aerosol-jet printing (Fig.4). Too large ink droplets and a pronounced ink wetting on the substrates leads to line width > 100 µm by using inkjet. The sintered Pt-heater show a suitable resistance of 10 to 30 Ohm and were successfully evaluated by heating tests up to 450-600°C by micro melting technique [1] with using micro powder of polyamide with dependence of power consumption vs. working temperature on surface of microhotplate present on Fig.6. Acknowledgement This research was sponsored by the Federal Ministry of Education and Research (BMBF) in Germany founding No. 02P15B520, the Israel Innovation Authority and the Ministry of Science and Higher Education of the Russian Federation founding with unique identifier RFMEFI58718X0054 in frame of MANUNET project MNET17/ADMA-1147. References [1] Biró, F., Dücso, C., Hajnal, Z., Riesz, F., Pap, A.E., Bársony, I. Thermo-mechanical design and characterization of low dissipation micro-hotplates operated above 500 °c (2015) Microelectronics Journal, 45 (12), pp. 1822-1828. Figure 1

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