Special optical sensors require thin film devices with a layer structure of the type glass/Al/Al2O3 with thicknesses of oxide and metal in the range of some nm. Structures comparable with a printed circuit board were written by electrochemical potential control with a scanning droplet device. Dots, lines, or areas of different thickness ratios Al/Al2O3 or even with gradients can be written. Insulating lines become possible by complete oxidation of the Al metal. (C) 2003 Elsevier Science Ltd. All rights reserved.