Two-dimensional micro-self-assembly using the surface tension of water

Several self-assembling microstructures have been fabricated, and approximately 100 units floating on the surface of water have been self-assembled two-dimensionally. The basic assembly units are 400 mu m in diameter, and consist of both polyimide and polysilicon thin films. Surface tension is used as the bonding force in this system. The surface tension is the local interaction between the units, and is dominant on the microscale. Each unit is bonded selectively by employing the following characteristics of the surface tension: (1) objects located at equal heights are attracted to each other; (2) large attractive forces act on sharp parts; and (3) objects located at different heights are mutually repulsed. The curling-up property of the thin films is used to obtain the different heights. We control the curling-up curvature by the thickness of the polysilicon layer. Self-assembling behaviour is also predicted by using a rate equation.