Optimized screen-printing and SEM-FIB characterization of YSZ thin films for Solid Oxide Fuel Cells and gas sensors devi
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Optimized screen-printing and SEM-FIB characterization of YSZ thin films for Solid Oxide Fuel Cells and gas sensors devices A. Morata, A. Tarancón, G.Dezanneau, F. Peiró and J. R. Morante. Electronics Materials and Engineering (EME), Department of Electronics, University of Barcelona, Spain. ABSTRACT In the present work, the screen printing technique has been used to deposit thick films of Zr0.84Y016O1.92 (8YSZ). In order to control the final porosity in view of a specific application (SOFCs or gas sensor), an experimental design based on analysis of variances (ANOVA) has been carried out. From this, we were able to determine the influence of several technological parameters on films porosity and grain size. The films obtained have been analysed with both Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) combined with SEM. We show that only the combination of experimental design and advanced observation technique such as Focused Ion Beam allowed us to extract significant information for the improvement of the deposition process. INTRODUCTION Yttria stabilized zirconia thin films is the most used electrolyte material in the field of solid state electrochemical devices. Depending on the target application i.e. SOFCs or gas sensors, these films need to be, respectively, dense (with no possibility of permeation) or porous with a controlled porosity. Also the control of thickness is of strong importance since, as demonstrated for Solid Oxide Fuel Cells, a low thickness allows to enhance significantly the device efficiency, by diminishing electrolyte ohmic losses. Among the numerous techniques available for zirconia deposition, some (CVD, ESD…) are able to produce very thin and dense layers, but suffer problems of cost or are hardly able to produce several microns thicknesses. Conversely, cheaper methods, like tape casting and slip casting, fail in the achievement of low thickness. In the view of lowering production cost and of increasing devices efficiency, one of the main actual limitations of Solid Oxide Fuel Cells, there is a need to investigate new deposition technologies or to improve known ones [1]. Among the available deposition techniques, screen printing has been traditionally used for the deposition of porous layers, in particular for semiconducting oxide gas sensors [2]. Much less common is the use of such technique for obtaining dense ceramic films. Recently, Xia et al. [3] proposed the use of screen-printing for gadolinium-doped ceria thin electrolyte deposition and showed that such technique combine the possibility of controlling the film thickness and density with a very low cost of production. The aim of the present work is to investigate yttria-stabilised zirconia deposition by screen-printing. By the use of an experimental design for deposition combined with Focused Ion Beam technology for cross-section characterization, we determined the most significant technological parameters for the control of film density and grain size. From this, we were able to produce films with controlled
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