Fluidic self-assembly of silicon microstructures

Fluidic self-assembly is a new technique which makes possible the integration of devices fabricated using dissimilar materials and processes. The integration is accomplished by fluidically transporting trapezoidally shaped blocks made of one material into similarly shaped holes in a receptor substrate. In this paper, a systematic study of the FSA integration efficiency is presented. Blocks and holes were formed from silicon using anisotropic etching. Two different sizes were considered: large blocks of dimension 1.0 mm/spl times/1.2 mm, and small blocks of dimension 150 /spl mu/m/spl times/150 /spl mu/m. FSA was performed in either water or methanol using a bubble pump apparatus to recirculate blocks. FSA of large blocks resulted in 100% filling of a substrate containing 191 holes within 2.5 minutes. Similar experiments with small blocks and a substrate with a 64/spl times/64 array of holes yielded a fill ratio of 70%, due to undesirable adhesion of blocks to the substrate surface. Roughening the substrate resulted in a fill ratio of 90%. Also presented is a simple rate equation model of the FSA process, along with a discussion of which process parameters are important and how they can be optimized.