We report fabrication technology for micro fluidic filter device with fine and high aspect ratio filtration gap using single-mask and CMOS compatible process flow. Advantage of Si based Microfabrication platform technology has been fully exploited by adopting manufacture-able process flow. A novel approach of combining silicon deep reactive ion etch (RIE) capability with subsequent gap-fill engineering enabled achieve wide range of filtration gaps of deep sub-micron size with high aspect ratios of >200. This approach eliminated the need to use high-end lithography techniques in order to achieve deep sub-micron gaps after pattern transfer. Si deep RIE etch process was optimized by applying dual passivation technique which enabled to realize sub-micron gap pillar-type filter structures and large reaction chambers simultaneously using single-mask process. Wide range of filtration gap sizes demonstrated in this work offer versatile applications for fine cell trapping such as protozoa and bacteria. Fluid injection channels for the device were realized through wafer backside Si wet etch processing to complete the filter device chip fabrication.
We have developed a deep ultraviolet (DUV) lithography technique for fabricating super dense silicon based photonic crystals. Binary mask is used to create nano scale patterns of very high density. Based on the simulation, photonic crystals with both square and triangular lattice of air cylinders are designed and fabricated to work in communication frequency range (λ within 1.3 to 1.55μm) on amorphous silicon. In order to pattern circular hole we designed different kind of polygons on the mask and layout pattern was under sized at constant pitch. Bottom anti reflection coating (BARC) recipe was developed to improve circularity of the pattern and reduce interhole spacing.
To miniaturize optical passive components or to have optical interconnects replace the current copper/low k interconnects for clock distribution, super high index contrast optics are needed because they allow optical waveguides with small bending radius, ie. < 50um. Silicon nitride core on oxide cladding has loss of <0.1dB/180° for 20um bending radius. However, coupling loss from the fiber to SiN waveguides, with 0.7umx0.7um cross section for single mode, is very large, > 20dB. To reduce the coupling loss, our approach is to have a double-core architecture, where fiber is first coupled to fiber matched waveguide, and then coupling from fiber match waveguide to SiN waveguide through a spot size mode converter. We have found the mode converter loss is reduced by 8dB by reducing the tip of the taper from 0.35um to 0.15um. In this paper, we are reported results of tips with less than 0.1um. We also describe the fabrication technology that enables us to make such fine tip with smooth surfaces.