Thin-film transistor circuits on large-area spherical surfaces

We report amorphous silicon (a-Si:H) thin-film transistors (TFTs) fabricated on a planar foil substrate, which is then permanently deformed to a spherical dome, where they are interconnected to inverter circuits. This dome subtends as much as 66° (∼1 sr) with the tensile strain reaching a maximum value of ∼6% on its top. Functional TFTs are obtained if design rules are followed to make stiff TFT islands of limited size on compliant substrates. Photoresist patterns for island interconnects are made on the flat structure, are plastically deformed during the shaping of the dome, and then serve to delineate interconnects deposited after deformation by lift-off. We describe the effect of deformation on the TFTs before and after deformation and the performance of TFT inverter circuits. Our results demonstrate that the concept of stiff circuit islands fabricated on deformable foil substrates is a promising approach to electronics on surfaces with arbitrary shapes.