Ni-ZrO2 cermet film systems developed on Si or Al2O3 substrates by metallo-organic deposition (MOD), exhibit high figures of merit, superior to the Ni and Pt films used in hybrid sensors. This sensitivity reflects a complex percolative structure in which nanoscale Ni particles and pathways are modulated by the ceramic phase. The Ni-ZrO2 cermet provides an excellent model, therefore, for study of the relevant material parameters (grain size, grain size ratio, composition, doping and phase distribution), which crucially affect percolation and sensor properties. The control of microstructural features will be exercised through the above parameters and by rapid thermal-infrared heat treatment. The planned property measurements include resistive responses to temperature and applied stress, as well as mechanical tests relating to tribology and thermal barrier layer characteristics. Microstructural and interfacial analyses will be performed using a variety of EM techniques. The intellectual merit of this proposal is the deeper understanding to be gained from development of analytical relationships linking process variables to material properties, percolation and sensor characteristics. Since percolation in thin films such as cermets is quite new, the study is expected to have broad relevance to a wide range of composite/particulate systems based on particle morphology and mixing, potentially leading to a new class of sensor materials. The research will impact significantly on the training of graduate, undergraduate and high school students, who will benefit from hands-on exposure to the innovative processing techniques and state-of-the-art measurement and characterization methods that will be used in this research.
A cermet is a composite material consisting of a metal conducting phase dispersed in a non-reactive ceramic or glassy matrix. These materials can exhibit a wide range of interesting and useful properties, including controllable resistance change (percolation), environmental ruggedness and marked catalytic activity. The nickel-zirconia cermet system, as thick films, has been utilized as fuel cell anodes, in high temperature catalysts, and for sensing gases such as ammonia. In thin film form, these materials exhibit significant resistance change with small temperature changes (TCR), a useful attribute for gas flow, gas detection and thermistor control. The films exhibit also a like resistance change to pressure (piezoresistance), making them attractive materials for pressure switching and strain gauge use. Furthermore, they adhere well to the silicon substrates, providing a durable and low friction (tribology) surface. These very desirable attributes, plus the drive for miniaturization and integration of passive devices with silicon technology, justify public support for the proposed research on these systems. The research will involve undergraduate and high school students, working together with graduate students and faculty on a broad range of materials processing and characterization issues related to these sensor devices. The students will gain valuable hands-on experience also in working with available sophisticated equipment. This outreach will extend also to K-12 students and their teachers in a focused effort to inspire and train future scientists. The research findings from this study will be broadly disseminated to the public and scientific community.
