Growth of Ca_xCoO₂ Thin Films by A Two-Stage Phase Transformation from CaO⁻CoO Thin Films Deposited by Rf-Magnetron...

The layered cobaltates A_xCoO₂ (A: alkali metals and alkaline earth metals) are of interest in the area of energy harvesting and electronic applications, due to their good electronic and thermoelectric properties. However, their future widespread applicability depends on the simplicity and cost of the growth technique. Here, we have investigated the sputtering/annealing technique for the growth of Ca_xCoO₂ (x = 0.33) 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; thus, the deposition rate is high. Furthermore, the composition of the film is controllable by controlling the power at the targets.