Lowering the resistivity of aluminum doped zinc oxide thin films by controlling the self-bias during RF magnetron sputtering

Abstract Transparent conducting thin films based on aluminum-doped zinc oxide are regarded as a viable alternative for low-cost and large-area applications such as solar cells and smart windows. Despite of intensive research, the thin film growth mechanism by magnetron sputtering is under debate concerning the role of energetic oxygen negative ions and the spatial distribution of atomic oxygen during the deposition. As the negative ions energy is directly related to the self-bias during RF driven magnetron sputtering, this work demonstrates a method to lower the thin film resistivity with a factor above 2 by including a tuning electrode between the target and the substrate. The electrode increases the RF coupling, reduces the dc self-bias and improves the electronic properties uniformity over the substrate. Consequently, resistivity below 3 × 10−3 Ωcm is obtained over a substrate area comparable with the target surface for an averaged transmittance above 90% without intentional substrate heating.