We report the development of a high efficiency magnetic microfluidic mixer based on a novel 3D impellor-shaped ferromagnetic micro-stirrer bar. The 3D impellor-shaped micro-stirrer bar with 31.6º inclined angle is fabricated using titled (55º) SU-8 exposure technique. The 3-D inclined micro-stirrer bar causes 3-D perturbation of fluids resulting in rapid mixing in microscale. When compared with a vertical straight sidewall micro-stirrer bar, approximately 20% of mixing efficiency enhancement is achieved.
The emergence of vertical cavity surface emitting laser (VCSEL) and photo diode (PD) arrays has given scope for the development of many applications such as high speed data communication. Further increase in performance can be obtained by the inclusion of micro-mirrors and microlens in the optical path between these components. However, the lack of efficient assembly and alignment techniques has become bottlenecks for new products. In this paper, we present development of optical sub-assembly and metallic MEMS structures that enable in the massively parallel assembly and alignment of these components to form a single miniature package. VCSEL wafer was processed to have polymer pedestal and polymeric lens on top of it. Such optical sub assembly greatly increases coupling efficiency between the VCSEL and optical fibers. Multiple numbers of suspended MEMS serpentine springs made out of electroplated nickel have been fabricated on ceramic substrates. These springs serve for clamping and alignment of multiple numbers of optoelectronic components. They are designed to be self-aligning with alignment accuracies of less than 3 micron after final assembly. Electrical connection between the bond pads of VCSEL's and PD's to the electrical leads on the substrate has been demonstrated by molten solder inkjet printing into precisely designed MEMS mold structures. This novel massively parallel assembly process is substrate independent and relatively simple process. This technique will provide reliable assembly of optoelectronic components and miniature optical systems in low cost mass production manner.
Electron beam lithography (EBL) is widely used for patterning of sub-micron and nano-scale patterns. Patterns in the order of tens of nano meters have been successfully realized using EBL. There are increasing needs in high aspect ratio structures in sub-micron and nano scales for microelectronics and other applications. Traditionally, high aspect ratio structures in sub-micron and nano scales have been realized by precision lithography techniques and subsequent dry etch techniques. In this work, we present commercially available SU-8 as a potential resist that can be used for direct resist patterning of high aspect ratio structures in sub-micron and nano scales. Such resist pattern can be used as a polymeric mold to create high aspect ratio metallic sub-micron and nano scales structures using electroplating technology. Compared to the most commonly used EBL resist, PMMA (poly methylmethacrylate), SU-8 requires a factor of 100~150 less exposure doses for equal thickness. It results in a significant reduction of EBL processing time. In this paper, characterization results on the patterning of up to 4:1 aspect ratio SU-8 structures with minimum feature size of 500 nm is reported. In addition, preliminary results on high aspect ratio metallic sub-micron structures using electroplating technology are also reported.
It is of great interest to develop an efficient and reliable manufacturing approach that allows for the integration of microdevices each of which is optimally fabricated using a different process. We present a new method to achieve electrical and mechanical interconnects for use in heterogeneous integration. This method combines metal reflow and a self-aligned, 3-D microassembly approach. The results obtained so far include a self-aligned, 3-D assembly of MEMS to MEMS, post-processing which selectively deposited indium on 50 μm-thick MEMS structures, and reflow tests of indium-on-gold samples demonstrating 15-45 mΩ resistances for contact areas ranging from 100 to 625 μm2. 3-D microassembly coupled with metal reflow allows for the batch processing of a large number of heterogeneous devices into one system without sacrificing performance. In addition, its 3-D nature adds a new degree of freedom in system design space. Downward scalability of the method is also discussed.