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6688747 
Journal Article 
Tantalum oxide thin films as protective coatings for sensors 
Christensen, C; De Reus, R; Bouwstra, S 
1998 
248-251 
INSPEC:6449832 
Reactively sputtered tantalum oxide thin-films have been investigated as protective coating for aggressive media exposed sensors. Tantalum oxide is shown chemically very robust. The etch rate in aqueous potassium hydroxide with pH 11 at 140degC is lower than 0.03 Aring/h. Etching in liquids with pH values in the range from pH 2-11 generally gives small etch rates. On the other hand etching is possible in hydrofluoric acid. Further, the passivation behaviour of amorphous tantalum oxide and polycrystalline Ta2O5 is different in buffered hydrofluoric acid. By ex-situ annealing in O2 the residual thin-film stress can be altered from compressive to tensile and annealing at 450degC for 30 minutes gives a stress-free film. Sputtered tantalum oxide exhibits also other favourable properties: high dielectric strength and good step coverage.