Mechanics of rollable and foldable film-on-foil electronics

The mechanics of film-on-foil devices is presented in the context of thin-f ilm transistors on steel and plastic foils. Provided the substrates are thi n, such transistors function well after the foils are rolled to small radii of curvature. When a substrate with a lower elastic modulus is used, small er radii of curvature can be achieved. Furthermore, when the transistors ar e placed in the neutral surface by sandwiching between a substrate and an e ncapsulation layer, even smaller radii of curvature can be attained. Transi stor failure clearly shows when externally forced and thermally induced str ains add to, or subtract from, each other. (C) 1999 American Institute of P hysics. [S0003-6951(99)03608-6].