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As the power consumption of modern electronics and wireless circuits decreases to a few hundred microwatts, it becomes possible to power these electronic devices by using ambient energy harvested from the environment. Mechanical vibration is among the more pervasive ambient available energy forms. Recent works in vibration-to-electrical energy harvesters have been centered on high frequency vibration applications. Although high-frequency mechanical vibrations are more energy rich, for some situations the local ambient environmental vibrations tend to occur at lower-frequencies. For example, the highway vibration frequencies are mainly between 10 ~ 20 Hz. This paper discusses the development of a miniature vibration-to-electrical energy harvester based on electromagnetic methods using MEMS technology, targeted on the low vibration frequency regime in the 15 ~ 20 Hz range for potential use in highway structural health monitoring (HSHM) purposes or in other applications. Innovative design considerations need to be addressed to achieve this goal in a miniature package. For example, a highly pliant material and a heavy seismic mass are needed. In our design, SU-8 is chosen as a part of the composite material for the cantilever beam, micro-coil, and seismic mass fabrication. The mechanical characteristics of the energy harvester are simulated. The power generation capability of the designed energy harvester is calculated.

In this research, first a modular polymer-based (PMMA) injection micromixer prototype has been designed, fabricated and tested. This micromixer is easy to be integrated into biochemical microfluidic systems under development for BioMagnetICs DARPA funded project at CAMD. To improve the mixing efficiency, layout of micronozzles of the mixer was optimized according to the simulation results. Also because SU-8, an epoxy-based negative photoresist, has high chemical resistance, an SU-8 injection mixer was designed and fabricated to run some biochemical sample liquids. Internal stress in patterned SU-8 structures has been reduced and multi-layer SU-8 processing has been successfully developed to fabricate SU-8 injection mixer.

Fluorescence calibration is usually done by preparing bio-samples with a series of concentrations and measuring their corresponding fluorescence intensities. A simplified approach is studied by using a microfluidic chip and microspheres. The fluorescence calibration can be carried out on the chip with only one concentration of the microspheres. Microspheres with the diameter of 1~5μm are very useful in bio-detection research. These microspheres are manufactured using high-quality, ultraclean polystyrene microspheres and loaded with a variety of proprietary dyes. They can be labeled with biotin-, NeutrAvdin-, streptavidin- and protein, which can be used as tracers for bio-detections. A microfluidic chip was successfully fabricated for the experiment, and preliminary experimental results have proved the feasibility of the approach for fluorescence calibration.

A series of polymer-based Polydimethylsiloxanes (PDMS) ball valves with different opening pressures have been developed for biomedical applications. By tuning different weight ratios of the two components (the base and the curing agent) of PDMS, the valves will have different opening pressures because of different stiffness of the PDMS materials. The curing conditions and mechanical properties of the PDMS material with different ratios have been thoroughly studied. The compressive Young's modulus of the material can be tuned from 310 KPa to 2.0 MPa. Such kind valves can be fabricated by injection molding, one of the cheapest fabrication techniques. Also such kind valve has no dead volume and easily to be integrated into micro-total analysis systems (μTAS).

This paper presents recent results on the microstructural evolution and the resulting mechanical property changes as a function of elevated temperature exposure of two types of electroplated nanocrystalline LIGA Ni. Electroplated Ni structures are the main candidates for LIGA-based MicroElectroMechanical System (MEMS). Initial studies have been conducted to correlate microstructure of electroplated Ni and resulting mechanical properties. A major drawback is that upon exposure to elevated temperatures, electroplated Ni MEMS components suffer dramatic reductions in strength mainly due to grain coarsening. This kind of strength deterioration at elevated temperatures can be detrimental to many MEMS applications, especially to micro-engines and molding inserts. Thus, in order to improve the high temperature performance of LIGA Ni, knowledge of the underlying mechanism is needed. At present, there is very limited understanding of processing-microstructure-property relationship for LIGA Ni at both room and elevated temperatures. The current research is focused on temperature effects on the microstructure of LIGA Ni and the resulting mechanical properties. Two types of sulfuric acid-based solutions were used to produce electroplated Ni samples with different microstructural characteristics. The DSC technique was used to study the stability of plated Ni at elevated temperatures. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to examine the microstructural changes of plated Ni samples as a function of annealing temperature. Nanoindentation tests were performed to study the effects of the evolved microstructures on mechanical properties. The underlying mechanism correlating microstructure and mechanical properties of LIGA Ni at elevated temperatures is discussed.

The normal process to fabricate an x-ray mask involves two steps: make an optical mask by using an optical pattern generator (OPG), and form the pattern on the x-ray mask membrane with the optical mask by UV lithography. The sole function of the optical mask is the pattern transfer from source to target. It is always possible that pattern distortion would happen during its transference. In this paper we present a new process to fabricate deep x-ray lithography (DXRL) mask by direct pattern writing on the first layer of resist of an x-ray mask membrane. A thin layer of gold (1 ~ 2 μm) is deposited on the revealed plating base of the membrane and serves as the absorber for a following x- ray exposure of the second (thicker) layer of resist. Finally a thick (5-10 μm) gold layer is plated in the stencil formed by developed second layer of resist. This process has been demonstrated with Kapton membranes (Polyimide foil). The principle of the process can be applied to other x-ray mask membrane materials and to make ultra deep x-ray lithography (UDXRL) mask as well. In this paper the initial results of the new process are presented. The performance of the fabricated mask is evaluated and the alternative approaches will be discussed.

One of the major difficulties faced by MEMS researchers today is the lack of data regarding properties of electroplated metals or alloys at micro-levels as those produced by the LIGA and the LIGA related process. These mechanical properties are not well known and they cannot be extrapolated from macro-scale data without experimental verification. This lack of technical information about physical properties at microscale has affected the consistency and reliability of batch-fabricated components and leads to very low rates of successful fabrication. Therefore, this material issue is of vital importance to the development of LIGA technology and to its industrial applications. The research work reported in this paper focuses on the development of a new capability based on design, fabrication, and testing of groups of UV-LIGA fabricated nickel microspecimens for the evaluation of fracture strength. The devised testing mechanism demonstrated compatibility with the fabricated samples and capability of performing the desired experimentation by generating resistance-to-fracture values of the nickel specimens. The average fracture strength value obtained, expressed with a 95% confidence interval, was 315 ± 54 Mpa. Further data acquisition, especially involving tensile specimen testing, and material analysis is needed to fully understand the implications of the information obtained.

In recent year SU-8 has became the most attractive photoresist in both optical and x-ray lithography. In our early work we have optimized its exposure parameters to improve the patterning quality in UV lithography and concluded that the UV absorption in SU-8 is proportional to the concentration of photoacidgenerator (PAG) and limiting the applicable SU-8 thickness in UV lithography. Actually, the PAG concentration plays an important role in all aspects of SU-8 processing in both optical and x-ray lithography. The motivation of this work is to expand the applicable thickness and application scope and improve processing control of SU-8 by optimizing its PAG concentration. In this paper we present the most recent experimental results on lithographic performance of SU-8 with different PAG concentration (varying up to 2 orders of magnitude). It includes determining the minimum bottom dose and minimum effective energy density in x-ray and UV lithography of SU-8, respectively, observing the dimensional change of SU-8 microstructure at different post exposure bake (PEB) temperature and time and measuring UV absorption spectrum of SU-8 as the function of PAG concentration. The modified SU-8 resists have moderate sensitivities and lower absorption coefficients. The application of the modified SU-8 will be addressed and demonstrated.

This paper reports on a research effort to design, microfabricate and test an optical fiber display switch based on magneto hydrodynamic (MHD) principal. The switch is driven by the Lorentz force and can be used to turn on/off the light. The SU-8 photoresist and UV light source were used for prototype fabrication in order to lower the cost. With a magnetic field supplied by an external permanent magnet, and a plus electrical current supplied across the two inert sidewall electrodes, the distributed body force generated will produce a pressure difference on the fluid mercury in the switch chamber. By change the direction of current flow, the mercury can turn on or cut off the light pass in less than 10 ms. The major advantages of a MHD-based micro-switch are that it does not contain any solid moving parts and power consumption is much smaller comparing to the relay type switches. This switch can be manufactured by molding gin batch production and may have potential applications in extremely bright traffic control,, high intensity advertising display, and communication.

This paper reports on a research effort to design, microfabricate and test an AC-type magnetohydrodynamic (MHD) micropump using UV-LIGA microfabrication. The micropump is driven using the Lorentz force and can be used to deliver electrically conductive fluids. In the AC-type MHD micropump developed in our laboratory, a diffuser/nozzle is integrated with a MHD driving chamber. With a magnetic field supplied by an external permanent magnet, and an AC electrical current supplied across two copper side-walls, the distributed body force generated will produce a pressure difference on the fluid in the pumping chamber. The directional dependence of the flow resistance of the diffuser/nozzle allows for a net output flow in response to the oscillating pressure generated by the sinusoidal current. The major advantage of a MHD-based micropump is that it does not contain any moving parts. It may have potential applications in medicine delivery, and biological or biomedical studies. An AC-driven micropump may be used to improve on the performance obtained in tests of a DC-driven prototype micropump, that showed pumping performance was significantly degraded by bubble generation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Many MEMS applications require multi-level microstructures in which two or more levels have to be aligned to each other in the processing. In this paper a passive alignment system based on a mechanical registration method utilizing reference posts is described. A detailed analysis of the test results was conducted to reveal main error sources and estimate the accuracy of this alignment method. An alignment accuracy of +/- 5(mu) m between 2 layers has been achieved. The further work on improving the alignment accuracy and expending in this alignment method to graphite masks for multi-level X-ray or combined optical/x-ray lithography is proposed.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

SU-8 has great potential in low cost ultra-thick high aspect ratio MEMS applications. Although a broad range of thickness (from micrometer to mm) can be obtained by spin coating, the works about the sidewall profile and dimension control of SU-8 microstructures have not been published in detail. This paper describes the detailed investigations on the effects of processing parameters such as UV wavelength and exposure dose on dimensional change and sidewall profile of SU-8 microstructures. The optimized processing parameters for SU-8 structures with the thickness from 10 to 360 micrometer are presented.