Bendable Ultra-Thin Silicon Chips on Foil

This work presents research towards obtaining ultra-thin silicon chips (flex-chips) on flexible foils through post-processing steps. The flex-chips are obtained by chemically thinning down the silicon and then transferring the chips to polyimide foils. The transfer printing approach that has thus far been used to transfer quasi 1-D structures such as wires and ribbons, has been adapted in this work to transfer various large sized (width of chips ranging from 4.5 mm to 1.5 cm and the length ranging from 8 mm to 3.6 cm) and ultra-thin (thickness approximate to 15 mu m) chips. The flex-chips contain passive devices, whose resistances do not show any appreciable change on bending, at least in the testing range of radius of curvature 9 mm and above. The distinct advantages of the work presented here are attaining bendability through post-processing of chips, low-cost of fabrication, and east transferring of chips to the flexible substrates without using conventional and sophisticated equipment such as pick-an-place set up.