Piezo and Thermal Resistance Sensor Properties of Ni-ZrO2 Cermet Films On Silicon Substrates

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9612122 Buchanan Cermet (metal-oxide composite) films for sensor applications require high temperature coefficient of resistance (TCR), wide resistance range (20-10k(), and high piezoresistive strain sensitivity. Such Ni-ZrO2 cermet films have been successfully prepared on silicon substrates by the MOD process. The formation of molecular clusters during this process offers distinct advantages in achieving homogeneous microstructures in these difficult to fabricate cermet films. Controlled sintering in a reducing atmosphere modulates the Ni phase and the resistive properties of the cermet films. Electrical conduction in cermets is controlled by key microstructural features such as grain size, grain morphology and porosity. In all cases, conductive paths must be formed through the structure in order to have dominant metallic behavior with low resistance and positive TCR. In cermets, both TCR and piezoresistance are of interest near the percolation conductivity threshold composition. At this threshold, as insulator content increaqes, resistance increases several orders of magnitude, TCR changes from positive to negative, and piezoresistive gauge factor increases. Positive TCR, negative TCR (NTC), and piezoresistive sensor materials can all be produced within a tight volume % metal range in this transition region. This behavior will be thoroughly investigated in this study. Ni-ZrO2 represents a 2 phase composite system containing a non-noble metal component that does not react with the insulative component. The thin film MOD Ni-ZrO2 system, therefore, is of interest for several reasons. Increased ZrO2 in the Ni-ZrO2 thin film cermet allows the design of higher resistance films with high TCR. Films fabricated by the author exhibit high TCR of 3000-6800 ppm/(C over Ni volume contents in the 30-80 vol.% Ni range. Advantages of these Ni-ZrO2 thin films are: silicon compatibility, controlled thickness in micron range films (0.2-l(m), high strength, and adherence to Si, SiO2 and A1203 sub strates, and demonstrated pressure sensitivity. Resistive changes indicating piezoresistive gauge factors approaching 50 have been measured for the MOD derived Ni-ZrO2 cermet films. In the proposed work the effects of the deposition process, including the underlying solution chemistry will be investigated. The effects of sintering variables, including rapid thermal annealing(RTA), on resistance properties in the Ni-ZrO2 cermet composite films will also be studied, with a view to developing a model for predicting sensor properties. ***