Abstract
Electron-beam-evaporated tantalum films were bombarded at normal incidence with a collimated beam of 40 keV argon ions to doses of up to 3 × 10 17 ions cm -2. The conduction mechanism in the as-deposited films (for thickness greater than 200 Å) appears to be a combination of metallic and activated tunnelling with some evidence for an increase in the latter component with increasing oxygen concentration. There is also evidence for the existence of at least two activation energies. After bombardment with low doses of argon the resistivity and temperature coefficient of resistivity (TCR) shift markedly towards values expected for very pure tantalum films, probably as a result of radiation-enhanced diffusion and preferential sputtering of oxygen combined with rearrangement of the film to form large precipitates of b.c.c. tantalum. There is also a significant increase in the strain gauge factor γ from an average of 3 up to a value of 5.2 at similar doses, possibly as a result of microstructural changes enhancing strain-induced changes in the metallic conduction paths of the film. The metallic phase appears to be metastable as resistivity increases with time (up to 2 years) at room temperature, probably because of reaction with oxygen near the film-substrate interface. For higher doses the resistivity rises (but not in a way expected for sputter etching), the TCR changes from a large positive value to a small negative one and γ drops towards a value of 2 which is the predicted value for tantalum on glass. These results indicate that for high doses of argon a single-phase stable compound with a low sputtering rate is formed, probably by reaction with the glass substrate. This compound has a mixture of activated tunnelling and metallic conduction with the strain gauge factor apparently determined by the metallic component of conduction.
Published Version
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