Adhesion of copper electroplated to thin film tin oxide for electrodes in flat panel displays

The performance of large area and high resolution flat panel displays is contingent upon the conductivity of the transparent electrodes. Copper busbars plated to the sidewalls of the conventional SnO2 electrode structure provide an order of magnitude enhancement in electrode conductivity while minimizing the loss in transmittivity to less than 3%. Essential to the above is sufficient adhesion between the copper and the SnO,. Previous work identified the need for an electrolytic reduction process, before copper plating, for adhesion to reach an acceptable strength, as observed by qualitative rubbing and peel tests. In this work, the electrochemical process conditions required for an adhesion strength of at least 100 kg/cm(2) are identified. Our results show that while both the current density and the electrical charge should be carefully chosen for optimum copper layer properties, the parametric selection can be made from a relative wide range of values. The suitable charge Q(R), Q(Cu), (C/cm(2)) and current densities J(R), J(Cu) (mA/cm(2)) for the reduction and copper plating stages of the process are: 0.3 < Q(R) < 0.5, 0.3 < Q(Cu) < 0.5, 31 < J(R) < 93, and 31 < J(Cu) < 125. Under these conditions, the copper thickness is between 300 and 500 nm.