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 x 1.2 mm, and small blocks of dimension 150 p m x 150 pm.FSA wm performed in either water or methanol using a bubble pump apparatus to recirculate blocks. FSA of large blocks resulted in 100% fXng of a substrate containing 191 holes within 2.5 minutes. Similar experiments with small blocks and a substrate with a 64 x 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. BACKGROUND

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A novel reflective surface-micromachined spherical mirror (SMSM), which can be used for focusing, collecting and imaging without chromatic aberration and can be easily integrated into the micro optical bench, has been designed, fabricated and characterized.Summary In order to meet the increasing demand in optical data communication, sensing technology and compact optoelectronic systems, microoptics is driven in very fast growing speed. The surface-micromachined optical bench, which can be monolithically integrated on a single silicon chip, is crucial among several microoptics technologies. In such free-space optical systems, a great deal of effort has been made on reflective, diffractive and refractive micro-optical elements, such as torsional micromirrors, micro-Fresnel lenses and refractive microlenses. What seem to be lacking, however, are reflective micromirrors with three-dimensional profile. For example, only few attempts for surface-micromachined spherical mirrors, which are not intact spherical, have so farbeen made [ 1,2].This work demonstrates a surface-micromachined spherical mirror by using a two-layer surfacemicromachining technique, as shown in Figure 1, where a center-anchored bilayer microstructure of SMSM is placed on the substrate. Due to the bimetallic effect, the SMSM is subjected to residual stresses, generated from the fabrication processes, and thus is usually bent remarkably. However, such great bending frequently results in buckling, as shown in Figure 2 [3]. With the purpose ofpreventing buckling, the original circularplate was sliced up into several sectors [3]. A better solution, which can preserve the intact spherical shape and avoid buckling simultaneously, is the optimization of the geometrical dimensions of the SMSM, especially its thickness.Theoretically, the SMSM is flat, as the thickness of its upper layer equals zero. Assume that the residual stresses of