A key building block of electronic circuits is the transistor. The semiconducting layer in a field-effect transistor  might be made of one polymer and the source, drain, and gate electrodes of another, conducting, polymer. A thin film of the semiconducting polymer can be easily applied to the device. The electrodes, however, require patterning and, for inorganics such as metals, that step has traditionally been done with lithographic and etching techniques. For low-cost plastics, however, photolithography is not a good choice because it is relatively expensive, incompatible with some polymers, difficult to apply on uneven substrates such as flexible plastics, and not appropriate for reel-to-reel processing. These drawbacks have motivated the search for alternative printing methods