Induced pyroelectricity in sputtered lead scandium tantalate films and their merit for IR detector arrays

Abstract

Thin films of lead scandium tantalate have been prepared by rf magnetron sputtering. The process involves two deposition steps. In the first, scandium tantalate is sputtered onto a heated sapphire substrate using a metal Sc/Ta target. This film is annealed before replacing in the sputtering chamber where a film of lead oxide is sputtered onto the surface. The composite film is annealed, and after diffusion a pale yellow film of lead scandium tantalate Pb(Sc_1/2Ta_1/2)O₃ is formed. The films are close to 100% of the ferroelectric perovskite phase with only 1% to 2% of the pyrochlore phase.

Electrical characterisation has been performed to assess the Merit Figures of the films for use in IR detection. Permittivity, dielectric loss and field induced pyroelectricity have been measured against field and temperature. Film annealing conditions have been identified to produce films displaying sharp first order transitions. Under the bias field, very high values of the properties have been found, peak permittivities of 8000, and induced pyroelectric coefficients of 6 × 10⁻³ C/m²K. The merit for use in infrared detection indicates a performance equivalent to the conventional pyroelectric wafers prepared by the slicing, lapping and polishing of bulk ceramics.