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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.

A novel approach to integrate densely packed CMOS devices with three-dimensional (3-D) microfluidic systems created at the wafer level using low temperature processes is introduced. The approach is based on low temperature (

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.

Since 1995 CAMD has been offering exposure services, so called print shop for a variety of users interested in making precision High-Aspect-Ratio Microstructures (HARMST) for various application. Services have been expanded beyond only the print shop service in recent years and now include x-ray mask fabrication, substrate preparation for PMMA and SU- 8 resists, electroplating, finishing and molding. Metallic and polymeric parts are now routinely fabricated for precision engineering, micro-fluidic and micro-optic applications. This paper presents a brief overview of the actual status of LiGA services provided at CAMD including ongoing research efforts and examples of LiGA components for different applications.

This paper describes a process to fabricate monolithic multilevel high-aspect-ratio microstructures (HARMs) for ferromagnetic devices built on silicon wafers using aligned X-ray lithography in conjunction with electrodeposition. Two X-ray masks were fabricated, each consisting of gold (Au) absorber structures on a transparent polyimide membrane. One mask was used to print a polymethyl methacrylate (PMMA) resist layer. Then, a second PMMA layer was applied to the same wafer, and the second mask was used to pattern it. Transparent alignment windows in the second mask, combined with a piezoelectrically controlled X-ray aligner, allowed for high alignment accuracy between the two print patterns over large areas (>4 inch in diameter). Au circuits were electroplated into first PMMA layer from a sulfite-based electrolyte, and nickel-iron (NiFe) ferromagnetic HARMs were formed in second PMMA resist from a sulfate-based bath. The deposition resulted in well-defined NiFe structures with aspect-ratios up to 67:1 as well as smooth sidewalls and top surfaces. Chemical composition measurements with energy X-ray dispersive spectroscopy (EDS) and wavelength X-ray dispersive spectroscopy (WDS) showed that Fe content increased during the electrodeposition process. To electrically isolate the NiFe posts and Au circuits, both wet chemical etching and sputter etching were explored to remove the exposed seed layer, and the latter approach completely removed the seed layers without damaging the electroplated features.

In this work, an electroplated Ni material made from sulfuric acid-based plating solution has been studied. Differential scanning calorimetry (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 samples as a function of annealing temperature. Microhardness tests were performed to study the effects of the evolved microstructures on surface mechanical properties. The activation energy for the grain growth was determined by using isothermal kinetics analysis. In order to improve the performance of LIGA/MEMS components at high temperature, it is crucial to understand the grain coarsening processes of electroplated Ni materials at elevated temperature.

The concentration of photoacidgenerator (PAG) in SU-8 determines the UV absorption and, therefore, is a limiting factor of the applicable SU-8 thickness. The motivation of this work is to improve SU-8 process control and expand the application scope of SU-8 by modifying its PAG concentration. In this paper we present the experimental results on lithographic properties of SU-8 as the function of PAG concentration (varying up to 2 orders of magnitude). It includes determining the minimum bottom dose and minimum effective energy density for x-ray and UV lithography of SU-8, respectively, and the UV absorption spectra of SU-8. It is fund that as the PAG concentration reduced, SU-8 has lower sensitivities in UV and x-ray lithography, and lower UV absorption coefficients. By using PAG diluted SU-8 taller microstructures with vertical sidewall can be obtained with UV lithography. Based on the large difference in lithographic sensitivities between normal and PAG diluted SU-8, we have developed a new process concept for making 3D microstructures. The 3D microstructures fabricated based on this new process, including microcantilever and microchannel, will be presented.

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.

An alignment system has been developed to address the special needs for deep X-ray lithography (DXRL). The system is based on optical registration method of mask and wafer prior to insertion into the X-ray beam. A simple fixture allows for translation of the mask and rotation of the wafer. The fabrication of masks with optically transparent windows specially developed for that purpose at MCNC, a description of the fixture, and the alignment tests at CAMD will be reported. Results demonstrated +/− 5 micron alignment tolerances. The fixture also allows exposure of mask/wafer systems tilted with respect to the X-ray beam for fabrication of multi-level devices with tapered walls. First tests of dynamic X-ray exposures have been performed using rotation of a resist sample in the X-ray beam during exposure using a modified microlathe.

This paper presents the status and the operation conditions of the 1.3 GeV storage ring at the Center for Advanced Microstructures and Devices (CAMD). An overview of existing beamlines with their relevant parameters is given and four beamlines that came into operation over the last two years are discussed in some detail.

The goal of this research is to enhance the heat exchanger efficiency of pressurized water reactor (PWR) by using LIGA or LIGA-like technique made microstructures. The heat transfer inside the boiler is a complex combination of different physical phenomena, which, besides the traditional convection, conduction, and radiation, includes liquid to vapor phase change, vapor nucleation and evolution, surface tension between the liquid and heating element, and so on. This paper presents the updated total heat transfer enhancement results of the boiling process by adding microstructures on the surface of the heating elements. Different types of microstructure configurations were tested. The power input, temperature of the heating element, and boiling phenomena were recorded. The behavior of increase in power versus rise in temperature of testing coupon is used to evaluate the heat transfer efficiency of the heating element. The steam generating efficiency at fixed input power and fixed temperature have been used to assess the performance of heating elements with different microstructure configurations. The preliminary results show that by simply adding micro-sized poles on the surface of the heating element, the power input can be increased almost 100% higher than that without poles on the surface at 360°C. The current results suggest that the main factors leading to the enhanced boiling process are the surface morphology and configuration of the microstructures. These provide enhanced vapor nucleation sites at heating surface, which result in a better vapor evolution processes, and yield a low superheat temperature. It ultimately results in a higher boiling heat transfer efficiency.Copyright © 2007 by ASME

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.

A method to fabricate a high precision X-ray mask for Ultra Deep X-ray Lithography (UDXRL) is presented in this paper by use of a single substrate. Firstly, an 8-μm layer of positive photoresist is patterned on a 500 μm thick beryllium substrate by use of UV lithography and 5 μm gold is electroplated out of a sulfite based commercial plating solution. Secondly, the photoresist is removed and 15 μm of SU-8 is spincoated and baked. The layer of SU-8 is patterned by use of an exposure from the backside of the substrate with a soft X-ray source, followed by post-exposure bake and development. An additional 5 μm layer of gold is electroplated on top of the first gold pattern thereby increasing the total thickness of the absorber on the X-ray mask to 10 μm. After the removal of the SU-8 resist, the second step of the process is repeated by use of a thicker layer of SU-8 (up to 100 μm) to obtain the high-precision and high-aspect ratio absorber pattern. Using this method, the maximum dimensional error of the fabricated gold pattern remains under 1 μm, while the smallest absorber feature size is 10 μm.

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.

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 describes a process to fabricate three-dimensional multilevel high-aspect-ratio microstructures (HARMs) for magnetoelectronic devices using aligned x-ray lithography in conjunction with electrodeposition. In this process, x-ray masks were constructed on a seed layer coated polyimide membrane with ultraviolet (UV) patterned and electrodeposited gold absorbers. The optically transparent polyimide allows one to align and print large areas (>4 inch in diameter) with high alignment accuracies. Patterns that contain 5-10 μm diameter posts and 7-10 μm wide lines were printed to 100-120 μm polymethyl methacrylate (PMMA) resist prepared on silicon wafers using x-ray lithography. Nickel-iron was electroplated to form ferromagnetic HARMs, while electroplated gold formed circuits. The composition profile measured with an electron probe x-ray microanalyzer (EPMA) suggested that iron content increases as NiFe plating proceeds inside the recess. The electrodeposition resulted in well-defined NiFe structures with aspect-ratios up to 20:1, smooth sidewalls and top surfaces. To isolate the magnetic structures and circuits, both wet chemical etching and sputter etching were explored to remove seed layer, and the latter yielded complete removal without noticeable damage to the features. A complete aligned x-ray exposure and electrodeposition protocol applicable to universal multilevel microstructures was established.

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.

The X-ray lithography and micromachining facility at CAMD hosts the `print-shop' for the development and prototype exposures in LIGA-like processing techniques for the HI-MEMS Alliance. A simple fixture with alignment, tilt, and rotation modules has been developed. It allows for multiple level exposures with registration. More complex shapes can be achieved by rotating and tilting the mask/wafer assembly with respect to the incident X-ray beam. The alignment system is based on optical registration using an X-ray mask with targets on optically transparent windows. The masks were fabricated at MCNC. The alignment tests and off-axis exposures were performed at CAMD. Overlay accuracy of +/- 5 micrometers has been demonstrated.