Micro-contact printing of OTFT on polymer foils

In the emerging field of large area electronics polymer foil substrates play a key role in large area and flexible electronic, illumination and display systems. Compared to silicon, however, coatings on polymer substrates and in particular foils are challenging to pattern on a scale below 10 µm due to surface roughness and surface defects caused by industrial manufacturing processes. The presentation shows the latest results of patterning gold and copper metallised plastic films with micro-contact printing technology in the micron and submicron dimension. Considered are fabrication of the moulding master with a reactive ion deep etching process, stamp moulding, thiol-based resist transfer by a stamping process and finally etching of metal layers with cyanide and natriumpersulfate etchants. One benefit of micro-contact printing is the roughness-tolerant flexible PDMS stamp compensating particles and other surface defects. Although most of the experiments have been realised under conventional laboratory conditions the achieved critical dimension is below 1 µm. Polymer transistors have been prototyped to demonstrate the capabilities of the µCP-process for flexible electronic. Source drain electrodes were defined by the stamping process on polyimide foil. Top gate configurations with PEDOT as gate electrode as well as bottom gate configurations with silicon gate electrode have been successfully established. Electrical measurements of transistors with different channel length show performance of the transistor and transition towards short channel effects in organic devices. The results show that micro-contact printing is a valuable tool in organic and large area flexible systems, especially the selective processing of high resolution areas are beneficial for future applications.