Growth of Ca_xCoO₂ thin films by phase transformation from CaO-CoO thin films deposited by rf-magnetron reactive cosputtering

The layered cobaltates A_xCoO₂ (A: alkali metals and alkaline earth metals), due to their good electronic and thermoelectric properties, are of interest, in the area of energy harvesting and electronic applications. However their future widespread applicability depends on the simplicity of the growth technique and the production cost. Here, we investigated the sputtering/annealing technique for the growth of Ca_xCoO₂ (x=0.35) thin films. In this approach CaO-CoO film is first deposited by rf-magnetron reactive cosputtering from metallic targets of Ca and Co, second the as-deposited film is reactively annealed under O₂ gas flow to form the final phase of Ca_xCoO₂. The advantage of the present technique is that, unlike conventional sputtering from oxide targets, the sputtering is done from the metallic targets of Ca and Co, and so the deposition rate is high. Further, the composition of the film is controllable by controlling the power at the targets. The present technique, being simple and lower in cost, is potentially suitable for industrial upscaling. The present sputtering/annealing technique may also be applicable for the growth of other member compounds of layered cobaltates A_xCoO₂.(author)