Microstructure to substrate self-assembly using capillary forces

We have demonstrated the fluidic self-assembly of micromachined silicon par ts onto silicon and quartz substrates in a preconfigured pattern with submi crometer positioning precision, Self-assembly is accomplished using photoli thographically defined part and substrate binding sites that are complement ary shapes of hydrophobic self-assembled monolayers. The patterned substrat e is passed through a film of hydrophobic adhesive on water, causing the ad hesive to selectively coat the binding sites. Next, the microscopic parts, fabricated from silicon-on-insulator wafers and ranging in size from 150 x 150 x 15 mum(3) to 400 x 400 x 50 mum(3), are directed toward the substrate surface under water using a pipette, Once the hydrophobic pattern on a par t comes into contact with an adhesive-coated substrate binding site, shape matching occurs spontaneously due to interfacial free energy minimization, In water capillary forces of the adhesive hold the parts in place with an a lignment precision of less than 0.2 mum Permanent bonding of the parts onto quartz and silicon is accomplished by activating the adhesive with heat or ultraviolet light. The resulting rotational misalignment is Within similar to0.3 degrees. Using square sites, 98-part arrays have been assembled in l ess than 1 min with 100% yield. The general microassembly approach describe d here may be applied to parts ranging in size from the nano- to milliscale , and part and substrate materials including semiconductors, glass, plastic s, and metals.