Investigation On Fabrication, Characterization And Properties Of Nanosized Ni-Cr Thin Film

With the development of modem science and technology, thin-filmtechnology has been incorporated with manufacturing processes ofpiezoresistive pressure transducers. Piezoresistive pressure transducers withhigh precision and good stability in a severe environment are needed innational defense, aviation, spaceflight, modem industry manufacture andauto-control. By far, the fabrication of Ni-Cr thin films with stable electricalproperties, higher resistance and lower temperature coefficient of resistance(TCR) is still a challenge issue for manufacturing processes of piezoresistivepressure transducers, which is much important for the films with high strainsensitivity in severe environment. Aiming at these demands, Ni-Cr thin filmswith high performance and dense microstructure were fabricated when thelower energy ion beam sputtering technique was adopted. The fabricationtechnique of Ni-Cr thin films have been investigated in detail in this thesis.The surface topography, microstructure, composition and electricalproperties have been characterized.The Ni-Cr quasi-amorphous broadinterface scattering conductivity mechanism, the samdwich-gradient-diffusion model and the layer oxidized model in Ni-Cr thin film have beenproposed. On the basis of these mechanisms, the experimental data wereanalyzed.The main conclutions are summuried as follows:Firstly, on the basis of the fundamental theory of condensed physics,deposition knowledge of alloy thin film and the dependences of sputteringratio on sputtering energy and binding energy, a composition design principleand film fabrication technique of Ni-Cr thin film were proposed and a simpleformula for calculation and prediction of composition in Ni-Cr thin filmderived. Ni-Cr thin film with different compositions and differentthicknesses were fabricated by this technique. The intersectant experimentmethod was used to investigate the magnetron sputtering rules, thedependence of composition on sputtering physics parameter and the mainfactor affecting the composition, the thickness, the resistivity, the TCR andthe gauge factor of Ni-Cr thin films.A layer oxidized model of Ni-Cr filmwas proposed.The optimized composition, thickness, TCR, gauge factor andthermal annealing technique of Ni-Cr thin film were determined. It has beenconfirmed that it is viable to fabricate nanosized Ni-Cr thin film with different composition by the magnetron co-sputtering technique aftercalculation and prediction of the composition.Secondly, on the basis of the fundamental theory of the thermodynamics.the Daken formula is extended by taking into account the influence of threekinds of elements. A samdwich-gradient-diffusion model in the Ni-Cr filmwas proposed for the first time. Therefore, a calculation method of elementaldiffusion including more than three elements was derived by Fick's secondlaw with a Pile-up law model. In the same time, the diffusions of Ni, Fe andCr were revealed and the diffusion coefficients and diffusion distances of Niand Cr are calculated. The calculation results are well consistent with theexperimental ones.Thirdly, by controlling the lower energy ion beam bombardment andstep-couplet collision effect, a new technique in which kinetic energy can betransformed and target atoms can be moved and this has been utilized tofabricate Ni-Cr thin films with excellent properties in double ion beamsputtering deposition equipment. The sputtering rules and the main factoraffecting the properties of Ni-Cr thin film were investigated in detail. Apredigest formulae to express the dependence of Ni, Cr atoms surfacedensity on the re-sputtering atoms flux ratio in the Ni-Cr thin film wereproposed and derived. The dependence of film composition on the sputteringconditions and target composition can be simply expressed by this model.The selectivity sputtering phenomena was revealed and the sputteringcondition to fabricate Ni-Cr thin film with desired composition by an alloytarget investigated. The surface topography and roughness have beenanalyzed. The deposition process of film was revealed and the structures offilms were determined.The microstructural evolution, crystalline latticeconstants, residual stresses were determined under the sputtering conditionsat thermal annealing temperature. The electrical conductivity and strainsensitivity of Ni-Cr thin films fabricated by lower energy ion beamsputtering was fixed and affecting factors were investigated. The defects andgrain growth can be avoided efficiently; Ni-Cr thin films with highperformance and dense microstructure were fabricated when the lowerenergy ion beam sputtering technique was adopted. The variation thresholdvalues of film thicknesses associating with several kinds of electricalconductivity mechanism in nano Ni-Cr thin films were revealed. Thelimitations in Fuchs-Sondheimer model, Fuchs-Namba model and Mayadas-Shatzkes have been explored when they are applied in interpretingelectrical conductivity mechanism in Ni-Cr thin film. It was first proposedthat quasi-amorphous interface scattering was the main factors that lead tothe increase of resistivity.On the basis of the fundamental theory of the thinfilm physics and the experimental data, a Ni-Cr quasi-amorphous broadinterface scattering model was proposed and its corresponding electricalconductivity mechanism of Ni-Cr thin film analyzed. The variationmechanism was interpreted by this model based on the thin film physics,thermodynamics and kinetics. Meanwhile, it was found that there exists athreshold temperature for the structure stability of Ni-Cr thin film and thethermal annealing temperature should be higher than this value in order toobtain quasi-amorphous structure where the atoms in near-range-orderedmicrostructure transform to the crystalline structure. After an appropriatethermal annealing, Ni-Cr thin films with dense microstructure, low TCR,good temporal stability and good uniformity in sheet resistance and thicknessmake them prime candidates for strain gauge applications.