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In contact UV lithography, a pair of cantilever beams fabricated by two inclined exposures at ±45° in SU-8 using a single mask will form a connected end on the top of SU-8 layer. These beams made of SU-8 with fixed-end have been used as optical fiber holders (Ling and Lian in Microsyst Technol 13(3–4):245–251, 2007). Recently, a two-mask, two-step process to fabricate free-end cantilever beams from SU-8 using inclined UV lithography has been developed (Ling et al. in Microsyst Technol 15(3):429–435, 2009), which has been successfully applied to fabricate SU-8 optical fiber holders with long free-end cantilever beams. In this process, two masks are needed in order to obtain free-end beams and the alignment between two exposures is always time consuming with limited accuracy. Two new techniques, inclined UV shadow mask lithography and inclined UV proximity lithography, have been illustrated here for fabricating free-end SU-8 cantilever beams, which eliminate the precise alignment step required in our previous work (Ling et al. in Microsyst Technol 15(3):429–435, 2009). In the inclined UV shadow mask lithography approach, the SU-8 cantilever beams without connected ends are formed by using one main mask and two shadow masks. Each shadow mask is used to selectively transfer one of the two separated patterns on main mask into SU-8 layer at +45° and −45°, respectively. In the inclined UV proximity lithography approach, a proper proximity gap between mask and SU-8 surface is obtained by using a 50 μm thick Mylar sheet, so that the exposing light paths that formed connected beam ends will fall inside the proximity layer instead of the SU-8. In this way, the desired open-end cantilever structures can be achieved. In this paper, the principles and the fabrication procedures of the proposed techniques are demonstrated and the preliminary results are discussed.

The optic alignment module containing out-of-plane 3D micro lenses, and micro optic fiber holders have been fabricated using tilted UV lithography technique in water with SU-8 photoresist (Ling and Lian in Proc SPIE 4979:402–409, 2007). Each holder is a circumscribed quadrilateral formed by a V-groove and pairs of fixed microclips, which will hold the fiber in position through the elastic deformation when the fiber is inserted. Since these microclips were fixed cantilever beams and its effective beam length, the distance between the fixed end of the beam and beam–fiber contact point, is very short (~62.5 μm), the stress on the beam is high even under a small (few microns) deformation. The inserted optical fiber was either too loose to lose its alignment accuracy, or too tight causing the clips to break because of dimensional tolerance. It becomes very difficult, if not impossible, to use them in practical applications. Therefore, the key issue of fabricating optical alignment module is to have a suitable stiffness of microclips with an appropriate deformation during the fiber insertion, which can provide enough force to hold the fiber for accurate alignment and avoid introducing neither significant viscous deformation nor the damage to the clips. In this paper, a novel technique to fabricate SU-8 cantilever beam as elastic clamping device in optical fiber holder is proposed. Simulation based on SU-8 material properties indicates that for a 250-μm-long, 50-μm-thick SU-8 beam the clamping force per unit beam width will range from 10 to 100 Newton/m as the deflection increased from 1.4 to 14 μm. This predicted performance is comparable to or even better than that of existing silicon nitride microclips in optical fiber holding application [Bostock et al. in J Micromech Microeng 8(4):343–360, 1998]. By using a two-mask process, we have fabricated free-end cantilever beams as fiber holding clips. In order to have longer beams over V-groove, the slots in the V-groove were introduced, which allow the beams extended deeper into the sloped V-groove walls. The micro alignment module with 250-μm-length cantilever beams as microclips for housing 125-μm-diameter optical fibers has been successfully fabricated using a 300-μm-thick SU-8 photoresist layer by a two-mask UV lithography processes. This approuch offers significant advantages over other techniques with respect to costs of material, simple in equipment, and easy in manufacture. These optical fiber holders with elastic microclips combined with pre-aligned out-of-plane 3D micro lenses make it possible that to build an integrated micro optic system with precise alignment accuracy on a wafer-scale.

This paper presents the important results of enhancing the boiling heat transfer of the pressurized water reactors (PWRs) by using LIGA or LIGA-like techniques to add microstructures on the surface of heater elements. The heater elements were made of 10 mm × 80 mm silicon strips with different in-line square micro-pin-fin configurations of 200 μm fin width, 35 μm fin height, and different inter-fin spacing values of 200, 400, 600, 800, 1000 μm and infinity. The experiments were conducted in de-ionized water at the atmospheric pressure. The input power, heater temperature, steam generation rate and video images of boiling phenomena were continuously recorded. Their relationships was studied and used to evaluate the total boiling heat transfer performance. The optimized microstructures can then be mass-fabricated on PWR tubes by using LIGA or LIGA-like technology. The experimental results suggest that by adding micro-sized in-line pin-fin arrays on heater surface and modifying heater surface morphology, the boiling process can be greatly enhanced through the improvements of vapor nucleation and vapor evolution processes at heater surface, which yields a low wall superheat and achieves a higher boiling heat transfer efficiency. The video images showed that the bubble nucleation sites are located immediately on top of each micro-pin fins. At current experimental setup, the 200 μm-spacing heater has the highest steam generation efficiency.

Comb-drive microactuator is widely used in MEMS devices and traditionally is made of silicon as structural material using silicon-based fabrication technology. Recent development in UV lithography of SU-8 has made it possible to fabricate the ultra high aspect ratio microstructures with excellent sidewall quality. In this paper, we report a low cost alternative to the silicon-based comb drive by using cured SU-8 polymer as structural material. The microactuator was designed to have a integrated structure without assembly or bonding. A unique integration fabrication process was successfully developed based on UV lithography of SU-8 and selectively metallizing SU-8 polymer structures. Preliminary experimental results have proved the feasibility of the microactuator and the fabrication technology.

Out-of-plane microlenses and microoptical fiber holder are two of the most important components for building an integrated microoptic system with a precise alignment accuracy. In this paper, a simple and convenient method to fabricate these components from SU-8 by using inclined UV lithography in water is proposed. It consists of two perpendicular exposures in SU-8 at ±45°. DI water possesses a low absorption coefficient and a moderate and stable value of refractive index in near UV. Using water, the exposure angle in SU-8 can be increased to 50° from 35° in air necessary to pattern the desired 45° slope of the sidewalls. The principle of the proposed technique and the detailed fabrication process of the microoptic components will be presented. The integratability of the fabricated components was demonstrated by the fabrication of the microoptical fiber holder with a pre-aligned out-of-plane microlens.

Electroplated nickel is the main material used in LIGA technique for fabricating MicroElectroMechanical System (MEMS) components. This paper presents the recent results regarding LIGA Ni material property enhancement at Center for Advanced Microstructures and Devices at Louisiana State University. The methodology of this study is based on the fundamental materials science paradigm that processing and manufacturing determine the microstructure of materials, which results in specific properties, and governs the performance of the structures that are made from these materials. This paper will focus on results in three aspects of our current research efforts, which are: (1) manipulating the plating parameters to tailor deposited Ni microstructures for different grain size distributions that are in the range of tens nanometer in diameters; (2) analyzing the mechanical properties, such as nano-hardness, micro-hardness, and wearing property as the function of LIGA Ni metallurgical microstructures; (3) estimating the corrosion properties of nanocrystalline LIGA Ni.

One of the major difficulties faced by MEMS researchers today is the lack of data regarding properties of electroplated metals or alloys of which microstructures and microdevices are fabricated, especially in LIGA technology. These mechanical properties cannot be extrapolated from macro-scale data without experimental verification. Therefore, study on material properties of microfabricated structures is of vital importance to the development of LIGA technology and to its industrial applications. This paper reports an experiment scheme and UV-LIGA microfabrication technology to study the fracture toughness of nickel micro specimens. 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 same experiment scheme and sample fabrication technology can be used in future work to study the fracture toughness values for LIGA fabricated samples in various metals and alloys.

SU-8 has received wide attention in recent years because of its application in the fabrication of high aspect ratio microstructures and devices. This negative resist is known for its excellent lithography properties using ultraviolet light source. As the microfabrication technology based on UV-lithography of SU-8 finds wide applications, a good understanding and characterization of cured SU-8 polymer on various substrate materials are therefore very important. A good adhesion on various substrate materials is essential to both the fabrication process and to the functionality of any final products that have cured SU-8 as part of the structural material. There are very limited studies reported in this important area in the literature. This paper presents a theoretical and experimental work to quantitatively study the adhesion properties of cured SU-8 on some of the most commonly used metallic surface materials. The adhesion strengths of cured SU-8 samples on Au, Ti, Cu, Cr, and Ni coated glass substrates were measured following ASTM-C633 standard. A detailed analysis of the experimental results was also provided based on the atomic structures and electron configurations of the respective metals.

Many MEMS applications require multi-level microstructures in which two or more levels have to be aligned to each other in the processing. A passive alignment method based on a mechanical registration concept utilizing reference posts has been described in our early work [1]. An alignment accuracy of 1 μm for a two layers optical lithography has been achieved. In this paper the experimental results on improvement of the alignment accuracy and expanding this alignment method to multi-level X-ray or combined optical/X-ray lithography are presented.

This paper reports a research effort to design, microfabricate and test a DC type magnetohydrodynamic (MHD) micropump using LIGA method (Menz et al., 1991). The micropump is driven using the Lorentz force and can be used to deliver electrically conductive fluids. In operation, a DC voltage is supplied across the electrodes to generate the distributed body force on the fluid in the pumping chamber, and therefore a constant pressure difference along the pumping chamber. The external magnetic field was supplied using permanent magnets. 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, biological and biomedical studies. The test of the DC prototype micropump shows that bubble generation mechanism affect the performance significantly and an AC driving mechanism may be used to improve the performance.