Amorphous silicon transistors on ultrathin steel foil substrates

Thin-film transistors of hydrogenated amorphous silicon (a-Si:H) were fabricated on foils of stainless steel with thickness ranging down to 3 μm, which is less than three times the thickness of the deposited films. Transistors made on foils from 3 to 200 μm thick exhibit comparable electrical performance. Two factors account for the feasibility of such thin device/substrate structures. One is that the built-in stress and the differential thermal contraction stress nearly cancel each other in steel/a-Si:H structures. The other is that on very thin foils the transistor structure offloads part of its strain to the steel foil.