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In this research, a rapid prototype hydrodynamic focusing module with three multi-fluidic speed-modulating (MFSM) micropumps in micro-fluidic flow has been designed, fabricated, and characterized. The module comprises of three MFSM micropumps having the dimension of 33 � 25 � 5 mm to achieve hydrodynamic focusing and the stream modulation. Each micropump consists of top, middle and bottom including actuation/modulation source, PDMS/nickel-particle composite (PNPC) diaphragm and Tesla-type valve/chamber, respectively. Three MFSM micropumps share one pneumatic actuation source and two individual permanent magnet modulation sources which are located above the right and left diaphragms. Each permanent magnet is manually controlled by a screw. The PNPC diaphragm deflection is obtained by the external pneumatic force, and the permanent magnet limits the displacement resulting from the interaction between the magnetic field and the nickel particles of the PNPC diaphragm. Hydrodynamic focusing is realized by the flow rate control of two side micropumps with magnetic diaphragm displacement modulation. Analyses of the magnetic modulation field, the flow rate of the MFSM micropump, and the hydrodynamic focused stream modulation are presented. The individual micropump can pump DI water with a flow rate of about 107 μl/min, and the hydrodynamic focusing channel can achieve a flow rate of about 321 μl/min, under the frequency of 2 Hz. This research examines the modulation feasibility of hydrodynamic focused center stream by controlling the neighboring stream flow rate and this technique can be utilized for possible applications in lab-on-a-chip, micro total analysis system and point of care testing system.

Integration of electronic wiring with microfluidic chips is an important process as it allows electrical interactions with the fluidic media, for example required for resistive and capacitive sensing. It is also necessary in order to implement various actuation and control mechanisms such as pumping, electrophoresis and temperature control. Typically electrical wire traces are added to microfabricated fluidic chips using metal deposition processes that are carried out after the fluidic chip has been fabricated. The process for adding the wiring is complicated and is limited to select metals that can be deposited by evaporation or sputtering. We present a single step method for integrating electrical wires into polymer microfluidic chips that are fabricated by a hot embossing process. This process can flexibly embed any kind of commercially available metal wire with a microfluidic chip and the wiring may be integrated to come into surface contact with the fluid or may be embedded in close proximity to (but insulated from)the fluid paths for example for local heating purposes. This method significantly reduces total processing time and is thus a valuable method for wire integration into polymer chips. We demonstrate two applications—a microelectrolysis chip and a heater chip that were fabricated using this methodology. The design, fabrication process and the initial test results are presented.

A novel fabrication method involving two-step sequential backside exposures utilizing Fraunhofer diffraction is developed in this work to overcome some of the limitations of the current micro-nozzle fabrication techniques in controlling the shape and the size of micro-nozzles. Shape and size of the fabricated micro-nozzles are compared with simulation results. Micro-nozzles with tip diameters varying from 0 to 158.1 μm and the base diameter varying from 167.2 to 360 μm are fabricated simultaneously side-by-side on the same substrate by varying the total exposure dosage from 3 to 6 J/cm2 utilizing multiple backside exposures through designed circular aperture and zone plate masks.

We present on a carbon nanoparticle-filled SU-8 photosensitive polymer nanocomposite for use in microelectromechanical systems (MEMS) or microsystems. Exposure and fabrication of the material was carried out using X-ray lithography. The polymer nanocomposite was studied for its electrical, thermal and mechanical characteristics. It was found that at low filler weight percentages, the SU-8 polymer became electrically and thermally conductive. A comparative study of the lithography performance of this functionalized SU-8 to pure SU-8 was also performed. It was determined that UV lithography of the PNC was not suitable for thick films and that by using X-rays, thick film high-aspect-ratio microstructures were achievable. Such results are favorable for many applications such as monolithically integrated polymeric micro-resistive heating elements and polymeric micro-heat sinks.

Polymeric microfluidic chips are an enabling component for cost-effective, point of care analytical devices for pharmaceutical, agriculture, health, biological and medical applications. The microfluidic structures can be completed with active elements like pumps and valves as well as sensor components for more complex so called total analysis systems. Often, systems are designed as reader and disposable cartridge where the fluidic structures are simple devices that will be inserted into the reader, which executes the analytical protocol and displays the information in digital form, and disposed after completion of the analysis. In this paper, a hybrid fabrication approach was employed to build a polymeric microfluidic device, so-called sweatstick, suitable for collecting small, precise amounts (600 μl) of human sweat, which were further analyzed for the amount of calcium ions indicating bone mass loss. The device was assembled from different parts fabricated by ultra deep X-ray lithography, precision micro-milling, and molding. Surface treatment of liquid exposed surfaces by oxygen plasma ensures hydrophilic behavior and proper capillary action. Preliminary testing of the device was performed by collecting defined amounts of sweat simulant and determining the calcium ion content using a fluorescent technique. The results for low calcium ion concentration typical for human sweat were excellent and repeatable with variation less than 5% demonstrating the ability to perform indirect bone loss measurements.

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 (

Molding technologies associated with fabricating macro scale polymer components such as injection molding and hot embossing have been adapted with considerable success for fabrication of polymer microparts. While the basic principles of the process remain the same, the precision with which the processing parameters need to be controlled especially in the case of molding high aspect ratio (HAR) polymer microparts into polymer sheets is much greater than in the case of macro scale parts. It is seen that the bulk effects of the mold insert fixture and molding machine have a dominant influence on the molding parameters and that differences in material parameters such as the glass transition temperature (Tg) of polymer sheets are critical for the success and typically differ from sheet to sheet. This makes it very challenging to establish standard processing parameters for hot embossing of sheet polymers. In the course of this paper, a methodology for developing a hot embossing process for HAR microstructures based on known material properties and considering the cumulative behavior of mold, material, and machine will be presented. Using this method force–temperature–deflection curves were measured with the intent of fine tuning the hot embossing process. Tests were carried out for different materials using a dummy mold insert yielding information that could be directly transferred to the actual mold insert with minimum development time and no risk of damage to the actual microstructures.

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.

Surface modification of silicon-containing fluorocarbon (SiCF) films achieved by wet chemical treatments and through x-ray irradiation is examined. The SiCF films were prepared by plasma-enhanced chemical vapor deposition, using gas precursors of tetrafluoromethane and disilane. As-deposited SiCF film composition was analyzed by x-ray photoelectron spectroscopy. Surface modification of SiCF films utilizing n-lithiodiaminoethane wet chemical treatment is discussed. Sessile water-drop contact angle changed from 95°±2° before treatment to 32°±2° after treatment, indicating a change in the film surface characteristics from hydrophobic to hydrophilic. For x-ray irradiation on the SiCF film with a dose of 27.4kJ∕cm3, the contact angle of the sessile water drop changed from 95°±2° before radiation to 39°±3° after x-ray exposure. The effect of x-ray exposure on chemical bond structure of SiCF films is studied using Fourier transform infrared measurements. Electroless Cu deposition was performed to test the applic...

In the last years the fabrication of micro components made from ceramic materials became more and more evident with respect to the pronounced chemical stability and the outstanding thermomechanical properties in comparison to plastics and metals. The aim of this work is the lithographic generation of ceramic microstructures avoiding an intermediate molding step using SU8 as pronounced sensitive resist matrix filled with fine ceramic powder in the submicron range. Focus of the research was to investigate the composite formation, patterning by x-ray lithography, developing, debinding and sintering to form stable ceramic parts. The addition of fine ceramic particles to low viscous liquids like SU8-10 leads to an increase of the viscosity. For a successful debinding and sintering a volume content of at least 40% ceramic is required resulting in a change of the viscosity from around 2 Pas up to a value of 1000 Pas at 25 °C and low shear rates. A modified casting procedure was developed for the formation of uniform resist films with a thickness around 300 μm. Optimized exposure and development parameters allow the fabrication of good quality resist structures that can be further transformed into ceramic structures by sintering. Details of the work and results will be presented and discussed in this paper.

A micro corona motor was fabricated using a membraneless built-on X-ray mask. Sharp stator electrodes of this motor ionize air molecules and ionized charges transfer onto the rotor surface, resulting in rotating rotor motions by Coulomb forces. For good performance, the stator’s electrodes should be wide (axial) and have sharp tips. Therefore, X-ray lithography was adopted for precise, high aspect ratio characteristics. To avoid the fabrication difficulty of a membrane X-ray mask, a built-on X-ray mask (conformal mask) technique was employed with negative toned SU-8 photoresist. SU-8 features X-ray fabrication compatibility, X-ray transparency and a large range of thickness. This technique may be suitable for fast fabrication of prototypes or very tall structures, which can be largely affected by printing gaps. For the X-ray built-on mask, 20 μm SU-8 was patterned and 8 μm gold absorber was electroplated on top of the 300 μm PMMA resist. Tests showed good quality pattern transfer from the SU-8 pattern and smooth sidewalls.

Micro bearing systems for Micro Electromechanical Systems (MEMS) have drawn attention for several decades as critical components for micro rotating machinery. Ideally, frictionless bearings are needed, and in practice, micro gas bearings approach the ideal. Typically, bearings function as a separate component, assembled onto sliding counterparts. However, in micro scale devices, assembly procedures are known to be very tedious and time consuming. This leads to the pursuit of single material monolithic structures. Critical issues arising from these approaches include: limitation of materials, friction, and reliability, among others. In this paper, new approaches have been pursued. Micro gas bearings were fabricated as a single component through X-ray lithography. A stainless steel gauge pin, machined to ultra precision, was used as a journal shaft. Simple and very easy assembly processes using self-aligning concepts were developed as an alternative method to conventional assembly. This article presents the design, fabrication, assembly, and testing of micro gas bearings.

A piezoelectric microjet has been fabricated and its working mechanism has been investigated. Considering different physical effects, the coupling models of the device are established and the key characteristics of the microjet are simulated by finite-element method. The dynamic displacement responses of the transducer under liquid-loading and unloading are calculated and compared. From numerical results, the coupling interactions dramatically damp the vibration amplitude of the transducer. However, the effects on the resonant frequencies of the structure are negligible, which will save much calculation work during further design optimization of the device. Based on the optimal design rules, the device has been fabricated and characterized.

With a view to meeting the requirements of high resolution microelectromechanical system applications, we studied high resolution (submicron scale) and high aspect ratio pattern fabrication through x-ray lithography. As a critical part of the x-ray lithography, an x-ray mask should have the properties of high resolution and being a thick absorber. To decrease the scattering effect, a 100 keV e-beam lithography system was used for the fabrication of the high resolution x-ray mask. 3 ?m thick PMMA (polymethylmethacrylate) resist was patterned and 2 ?m thick gold was electroplated onto the patterned resist to form the x-ray mask. Scanning electron microscopy analysis showed that the sidewall and pattern uniformity were sufficient and that the proximity effect did not play a significant role for the selected test patterns. 6 ?m thick PMMA resist was exposed by the x-ray mask; the experimental results proved the feasibility of reproducing submicron features. 0.5 ?m nested patterns with an aspect ratio of 12 were fabricated by this approach.

We have developed two fabrication routes for functional micro devices using SU-8/nanoparticle composites. In the first route, patterning of a 0.5% nanoparticle/SU-8 composite resulted in magnetic and luminescent polymeric microstructures. In the second route, a 42% nanoparticle/SU-8 composite was patterned followed by sintering to obtain free standing ceramic microstructures with aspect ratios as high as 16.

In this paper, a process for 200 μm high-aspect-ratio micro-optical (HARM) structures fabricated by deep X-ray lithography (DXRL) of polymethylislesuioane-based spin-on glass (SOG) thick films is presented. The SOG material used in the whole procedures is polymethylsilsesquioxane (GR650), which is a kind of sol-gel derived material and can be cured at a reasonable low temperature (75 °C). A technique to cast thick GR650 films was established in the overall process. After consolidation, the GR650 thick films were machined to reach 200 μm uniformly. Then, as negative resists, the GR650 thick films were patterned directly by DXRL. X-ray irradiated regions can be selectively retained with high structural resolution by development in an organic solvent, such as methanol. Parameter screening was done to find minimum and maximum doses needed for patterning/cross-linking, to vary development time, and to explore different film thickness. The whole process is a novel of technique to create HARM structures based on SOG materials without using molds. This technique can be extended to considerably larger structural heights. Surface and bulk compositions of the irradiated films were measured by XPS and Fourier transform infrared spectroscopy. Surface quality by roughness testing system (WYKO RST) was investigated to fabricate the microstructure with a high-accuracy surface.

Room and elevated temperature tensile, creep and high-cycle fatigue properties of electrodeposited LIGA Ni microsamples have been measured and are being used to predict the reliability of LIGA Ni MEMS structures. Tensile specimens with dimensions of hundreds of microns have been LIGA fabricated and characterized in terms of their underlying microstructure, elevated temperature tensile and creep strength and their high-cycle fatigue performance. The stiffness of these LIGA Ni structures was found to be reduced by the introduction of porosity during the plating process. The strength of these structures was observed to decrease dramatically at temperatures above 200 °C. At stresses significantly below the yield strength, substantial creep deformation was observed at moderately elevated temperatures. The fatigue life of the LIGA Ni microsamples increased with decreasing stress amplitude in a manner comparable to what has been reported for wrought Ni. An apparent fatigue limit was observed for the LIGA Ni microsamples, but the importance of underlying microstructure and component geometry on the fatigue life was also highlighted.

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.

Micromechanical milling has been shown to be a rapid and direct method for fabricating masks for deep x-ray lithography with lateral absorber features down to 10 micrometers. Conventional x-ray mask fabrication requires complex processes and equipment, and a faster and simpler method using micromechanical milling was investigated for larger microstructures for mesoscale applications. Micromilled x-ray masks consisting of a layered architecture of gold and titanium films on graphite yielded exposures in PMMA with accuracy and repeatability suitable for prototype purposes. A method for compensating milling tool radial runout was adapted, and the average accuracy of mask absorber features was 0.65 micrometers, with an average standard deviation of 0.55 micrometers. The milling process leaves some absorber burrs, and the absorber wall is tapered, which introduces an additional process bias. Mask fabrication by micromilling is fast and, therefore, less costly than conventional mask fabrication processes.

Micromechanical milling has been shown to be a rapid and direct method for the fabrication of structures with the geometry and size suitable for use as x-ray mask absorbers. While the micromilling process can not duplicate the size and resolution of absorber patterns created by high energy electron beam or optical lithography methods, micromilling can repeatedly create absorber line widths down to 10 micrometers, or less, with a one-sigma tolerance of 0.5 micrometers. A method for easily characterizing milling tool run out has been adapted so tool change out can be more routine. The milling process leaves some absorber burrs and the absorber is apparently tapered at the machined wall which introduce process biases, both of which add to exposure degradation. Nevertheless, based on work to date, it appears both of these effects can be reduced to acceptable limits.

The size evolution of gold nanoparticles in a millifluidic reactor is investigated using spatially resolved transmission electron microscopy (TEM). The experimental data is supported by numerical simulations, carried out to study the residence-time distribution (RTD) of tracers that have the same properties as Au ions. Size and size distribution of the particles within the channels are influenced by the mixing zones as well as the RTD. However, the Au nanoparticles obtained show a broader size distribution even at the shortest investigated residence time of 3.53 s, indicating that in addition to surface growth reaction kinetics also plays an important role. The comparison of time resolved particle growth within the millifluidic channel with flask-based reactions reveals that the particle size can be controlled better within millifluidic channels. Overall, the results indicate potential opportunities to utilize easy to fabricate millifluidic reactors for the synthesis of nanoparticles, as well as as for carrying out time resolved kinetic studies.

The focus of this paper is on the use of SUEX Thick Dry Film Sheet (TDFS) laminates which DJ DevCorp is developing as a thick resist material in optical and X-ray lithography. Preliminary thick dry film sheets up to 1mm thickness were successfully prepared and patterned at the CAMD X-ray beamlines and presented at HARMST 2007. Recently, new results have been published using SUEX resist sheets in UV lithography showing great market potential including plating molds for metal microparts, polymer MEMS, multilayer microfluidics structures, BioMEMS, medical devices, wafer level packaging processes, and displays. The SUEX TDFS are available in a range of thicknesses from 100μm to 1mm or more and are pre-cut into a number of standard wafer sizes. This new material is a modified epoxy formulation containing an antimony-free photo acid generator (PAG) prepared under a highly controlled solvent-less process which provides uniform coatings between two throw-away layers of protective polyester film. As part of our initial studies resist layers of 250, 500 and 1000μm were laminated onto regular silicon wafers using a hot roll laminator at a speed of 1ft/min at 75°C. The entire substrate preparation takes about 1 hour and with practice users can prepare up to 10 substrates in this time which are typically ready to use within 2 hours. In our efforts to develop a commercially viable product we have conducted experiments using standard equipment available at CAMD (Quintel UV aligner and CAMD XRLM 1 and 4 beamline). Initial X-ray exposure tests were done with a bottom dose ranging between 100 and 400 J/cm3 and a top/bottom dose ratio of less than 3 for sheets up to 2mm in thickness. Exposure time for typical conditions of the CAMD storage ring (ring current ranging between 100 and 160mA, beam lifetime of about 10hrs at 100mA ring current) is about 10-15min for a 4' wafer. After exposure the samples were immediately post exposure baked between 70°C and 110°C using a convection oven, taken out and cooled to RT then relaxed up to 3 days before development to reduce stress. Development was done in PGMEA for up to 3 hours for the 1000μm thick samples followed by a short IPA rinse and drying in air. Very high aspect ratios of 100 or more have been routinely patterned with nearly perfectly straight sidewalls (~1-1.5μm deviation for a 1mm tall structure) and excellent image fidelity.

The fabrication and characterization of a novel cyclic olefin copolymer (COC) waveguide embedded in a poly(methyl methacrylate), PMMA, fluidic chip configured in a multi-channel format with an integrated monolithic prism for evanescent fluorescence excitation are reported. The fabrication approach allowed the embedded waveguide to be situated orthogonal to a series of fluidic channels within the PMMA wafer to sample fluorescent solutions in these channels using the evanescence properties of the waveguide. Construction of the device was achieved using several fabrication techniques including high precision micromilling, hot embossing and stenciling of a polymer melt to form the waveguide and coupling prism. A waveguide channel was fabricated in the fluidic chip's cover plate, also made from PMMA, and was loaded with a COC solution using a pre-cast poly(dimethylsiloxane), PDMS, stencil containing a prism-shaped recess. The PMMA substrate contained multiple channels (100 microm wide x 30 microm deep with a pitch of 100 microm) that were situated orthogonal to the waveguide to allow penetration of the evanescent field into the sampling solution. The optical properties of the waveguide in terms of its transmission properties and penetration depth of the evanescent field in the adjacent solution were evaluated. Finally, the device was used for laser-induced fluorescence evanescent excitation of a dye solution hydrodynamically flowing through multiple microfluidic channels in the chip and processed using a microscope equipped with a charge-coupled device (CCD) for parallel readout. The device and optical system were able to image 11 channels simultaneously with a limit-of-detection of 7.1 x 10(-20) mol at a signal-to-noise ratio of 2. The waveguide was simple to manufacture and could be scaled to illuminate much higher channel numbers making it appropriate for high-throughput measurements using evanescent excitation.

Metallic large area mold inserts (LAMIs) are essential for the replication of polymer microfluidic devices. Successful molding of micro- or nanoscale features over large areas is dependent on improving the dimensional control of the mold inserts, particularly those fabricated by electrodeposition using the LIGA or UV-LIGA processes. A systematic approach to controlling the internal stress of the nickel deposits, which was essential for predicting the final flatness of the LAMIs prior to electroplating, was carried out. The internal stress of the nickel deposits from a nickel sulfamate solution was estimated using a bent strip stress measurement method after maintaining electroplating chemicals and conditions and reducing contamination. Over-electroplating of the nickel LAMIs was performed on SU-8 electroplating molds on 150 mm diameter Si wafers. Detailed characterization of the nickel LAMIs to determine the relationship between the overall flatness of the LAMIs and the internal stress identified a suitable process window in terms of the current densities (10–20 mA/cm2) and the internal stress (−8.3 ∼ −3.0 MPa) for the high quality nickel LAMIs with an overall flatness of 100 μm.

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.

Simple design of CAMD’s new infrared microspectroscopy beamline is presented. A pair of mirrors, planar and toroidal, is utilized for extracting infrared radiation from the conventional bending magnet port to a diamond window located outside of the shielding wall. Infrared radiation passed through the diamond window is then collimated by a small parabolic mirror, and fed into a Michelson interferometer. The Nicolet Nexus 670 FT‐IR spectrometer and the Continuum microscope serve as the end station for this infrared microspectroscopy beamline.

The purpose of this work is to establish a standard sensitivity calibration protocol for GMR (Giant MagnetoResistive) spin valve sensors using superparamagnetic particle embedded microprobes (SPEM). Comparing to other calibration methods, such as the use of MFM (Magnetic Force Microscope), sealed fluidic flow cells, current lines, etc., the proposed SPEM method has four major advantages: no magnetic background, a precisely controlled number of particles which is mostly single-layered, pristine GMR surface after calibration, and mass fabrication. The SPEM is made from a superparamagnetic particle embedded SU-8 post and a glass cantilever. It can calibrate the magnitude of GMR signals to the number of superparamagnetic particles by bringing a known number of single-layered particles close to the GMR surface while still keeping the GMR surface pristine for future biofunction.

The objective of this effort was to fabricate a waveguide integrated in a polymer microfluidic chip in order to deliver excitation light to fluorescent probes contained in a fluidic channel. Instead of exciting the volume at a certain point along a fluidic channel, the goal herein was to excite all the probes contained along the length of the fluidic channel. An air-waveguide structure was designed and integrated into a polymer microfluidic chip. Fabrication of the microfluidic chip was carried out by double-sided hot embossing of poly methyl methacrylate (PMMA) in sheet form. The efficacy of the waveguide was evaluated by coupling light from a laser into it and testing the fluorescence intensity from dye contained in the microfluidic channel. The results demonstrate illumination of the entire length of the microfluidic channel with excitation wavelength light from the waveguide. Details of the design, fabrication process and initial experimental results are presented in the course of this paper.

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 piezoelectric microjet has been fabricated and its working mechanism has been investigated. Considering different physical effects, the coupling models of the device are established and the key characteristics of the microjet are simulated by finite-element method. The dynamic displacement responses of the transducer under liquid-loading and unloading are calculated and compared. From numerical results, while the coupling interactions dramatically damp the vibration amplitude of the transducer, the effects on the resonant frequencies of the structure are negligible, which is very important for further design optimization of the device. Based on the optimal design rules, the device has been fabricated and characterized.

Two advanced processes have been developed for fabricating ultra thick and ultra high aspect ratio (HAR) microstructures. One is the SU-8 based deep X-ray lithography (SU-8 based DXRL) process which uses the normal deep X-ray beam to expose the negative SU-8 resist. Another one is wave length shifter(WLS) based Ultra deep X-ray lithography (WLS-UDXRL) process which uses special ultra deep X-ray beam from wave length shifter to expose the positive PMMA resist. For SU-8 based DXRL process, the typical exposure time of a layer of SU-8 is about 1% of that of PMMA. Even for a few millimeters thick resists the exposure time are just a few minutes. In WLS-UDXRL process, the X-ray beam is strengthened by a wave length shifter(WLS) so the required exposure time for ultra thick PMMA is reduced greatly. In the paper, the characteristic of the these two processes are discussed and the examples of the ultra thick and ultra HAR microstructures fabricated by these processes are presented (ultra thick up to 3600 /spl mu/m and HAR up to 360).

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.

Micro production technologies are a driving factor in today’s continuous effort of developing new, highly functional products. The need for increased functionality is met by decreasing the size of individual components as well as consequently miniaturizing components for non-electronic properties including optical, mechanical, and fluidic functions. An important factor in this approach his the right material for a given task and the ability to shape it into the desired geometry as well as to combine micro components in a cost-effective way to build more complex modules and micro systems. One micro production technology that meet several of the above mentioned needs is the LIGA process, a combination of three major fabrication processes — x-ray based micromachining or deep x-ray lithography (DXRL), electroplating, and molding. In x-ray lithography the unique properties of synchrotron radiation, especially high intensity of collimated x-ray photons, permit patterning of extremely precise, very tall primary microstructures up to several millimeters in height with micrometer lateral dimensions and sub-micrometer details (so-called High-Aspect Ratio Microstructures, HARM). These microstructures are attractive for mechanical and optical components in MEMS (MicroElectroMechanicalSystems) devices. While x-ray lithography is crucial to achieve a primary microstructure with superior features, the use of synchrotron radiation is limiting the material choice to only a few polymer materials, so-called x-ray resists. Additional processes including electroplating and molding, however, open up a huge selection of engineering materials such as metals, ceramics, and also a large number of polymers and allow MEMS engineers to combine structural and material properties to build the next generation MEMS devices. This paper is primarily focusing on the DXRL process. Process fundamentals including equipment and infrastructure, x-ray masks, resists, typical structure geometries as well as patterning accuracy will be discussed. A few examples will illustrate ongoing efforts of commercializing this technology and also indicate future areas of applications.Copyright © 2004 by ASME

Micro gas chromatograph (GC) separation columns were fabricated and tested. Rectangular columns with high aspect ratio have inherent benefits over traditional tubular columns and can easily be integrated into a GC sensor system for rapid chromatographic analysis. The 2 m long, 50 μm wide, 500 μm tall columns were fabricated out of electroplated nickel through deep X-ray lithography using the LIGA technique. Critical fabrication issues including reproducible fabrication of compact footprint, deep columns and sealing of the metal columns were addressed. Experiments were conducted to establish the relationship between column head pressure and flow rate. Methane samples analyzed using hydrogen as a carrier gas on uncoated columns showed very little dispersion suggesting that there was no internal leakage in the columns. The sensor performance data compares well with other micro GC sensor systems.Copyright © 2004 by ASME

Elevated temperature tensile, creep and high cycle fatigue properties of electro-deposited LIGA Ni structures have been measured and are being used to predict the reliability of LIGA based MEMS structures. Microsamples with dimensions of 100's of microns have been LIGA fabricated and characterized in terms of their elevated temperature tensile and creep strength and their high-cycle fatigue performance. The strength of these LIGA Ni structures was found to decrease dramatically at temperatures above 200/spl deg/C. At stresses significantly below the yield strength, substantial creep deformation was also observed at moderately elevated temperatures. The fatigue life of the LIGA Ni microsamples increased with decreasing stress amplitude in a manner comparable to what has been reported for wrought Ni. An apparent fatigue limit was observed for the LIGA Ni microsamples, but the importance of component geometry on the fatigue life was also highlighted.

Challenging requirements in optical and BioMEMS application with high aspect ratios of microstructures in access of 20 and smallest structure details of less than 1 μm have motivated this work to irmpove x-ray mask fabrication. Several approaches to pattern an intermediate x-ray mask with the gold absorber thickness of 1.6-2.2μm using a 1μm thick silicon nitride membrane have been explored. E-beam lithography is employed for primary patterning and experimental results show that high energy (100keV) e-beam lithography is a very promising approach. So-called working x-ray mask can be fabricated from intermediate x-ray mask through x-ray lithography. More than 10μm thick PMMA x-ray resist has been coated on the silicon nitride membrane by multi-coating process without crack. First exposure results indicate that adhesion and stability of sub-micrometer structures wiht these heights is critical. In order to overcome these problems a novel approach has been proposed by coating resist on both sides of the silicon nitride membrane and simultaneous patterning of both sides using x-rays. First successful experimental results have been achieved for proving the feasibility.

The production of X-ray masks is one of the key techniques for X-ray lithography and the LIGA process. Different ways for the fabrication of X-ray masks has been established. Very sophisticated, difficult and expensive procedures are required to produce high precision and high quality X-ray masks. In order to minimize the cost of an X-ray mask, the mask blank must be inexpensive and readily available. The steps involved in the fabrication process must also be minimal. In the past, thin membranes made of titanium, silicon carbide, silicon nitride (2-5μm) or thick beryllium substrates (500μm) have been used as mask blanks. Thin titanium and silicon compounds have very high transparency for X-rays; therefore, these materials are predestined for use as mask membrane material. However, the handling and fabrication of thin membranes is very difficult, thus expensive. Beryllium is highly transparent to X-rays, but the processing and use of beryllium is risky due to potential toxicity. During the past few years graphite based X-ray masks have been in use at various research centers, but the sidewall quality of the generated resist patterns is in the range of 200-300 nm Ra. We used polished graphite to improve the sidewall roughness, but polished graphite causes other problems in the fabrication of X-ray masks. This paper describes the advantages associated with the use of polished graphite as mask blank as well as the fabrication process for this low cost X-ray mask. Alternative membrane materials will also be discussed.

Poly-methylmethacrylate (PMMA), a positive resist, is the most commonly used resist for deep X-ray lithography (DXRL)/LIGA technology. Although PMMA offers superior quality with respect to accuracy and sidewall roughness but it is also extremely insensitive. In this paper, we present our research results on SU-8 as negative resist for deep X-ray lithography. The results show that SU-8 is over two order of magnitude more sensitive to X-ray radiation than PMMA and the accuracy of the SU-8 microstructures fabricated by deep X-ray lithography is superior to UV-lithography and comparable to PMMA structures. The good pattern quality together with the high sensitivity offers rapid prototyping and direct LIGA capability. Moreover, the combinational use of UV and X-ray lithography as well as the use of positive and negative resists made it possible to fabricate complex multi-level 3D microstructures. The new process can be used to fabricate complex multi-level 3D structures for MEMS, MOEMS, Bio-MEMS or other micro-devices.

X-ray lithography is commonly used to build high aspect ratio microstructures (HARMS) in a 1:1 proximity printing process. HARMS fabrication requires high energy X-rays to pattern thick resist layers; therefore the absorber thickness of the working X-ray mask needs to be 10-50 μm in order to provide high contrast. To realize high resolution working X ray masks, it is necessary to use intermediate X-ray masks which have been fabricated using e beam or laser lithographic techniques. The intermediate masks are characterized by submicron resolution critical dimensions (CD) but comparatively lower structural heights (~2 μm). This paper mainly focuses on the fabrication of high resolution X-ray intermediate masks. A three-step approach is used to build the high resolution X-ray masks. First, a so called initial mask with sub-micron absorber thickness is fabricated on a 1 μm thick silicon nitride membrane using a 50KeV e beam writer and gold electroplating. The initial X-ray mask has a gold thickness of 0.56 μm and a maximum aspect ratio of 4:1. Soft X-ray lithography and gold electroplating processes are used to copy the initial mask to form an intermediate mask with 1 μm of gold. The intermediate mask can be used to fabricate a working X-ray mask by following a similar set of procedures outlined above.

Two types of Microfluidic bioanalytical systems were designed and fabricated in polymer substrates using the LIGA process. A continuous flow polymerase chain reaction (CFPCR) Microfluidic device was fabricated in polycarbonate (PC), which utilized isothermal zone and shuttling the sample through each zone to achieve amplification. A 20-cycle PCR amplification of a fragment of a plasmid DNA template was achieved in 5.3 min. The results were comparable to those obtained in commercial laboratory-scale PCR system. The second system consisted of a microchip contating a low-density array assembled into the Microfluidic channel, which was hot-embossed in poly(methyl methacrylate) (PMMA). The detection of low-abundant mutations in gene fragments (K-ras) that carry point mutations with high diagnostic value for colorectal cancer was successfully performed. The array accessed microfluidics in order to enhance the kinetic associated with hybridization.

During the past few years, graphite based X-ray masks have been in use at CAMD and BESSY to build a variety of high aspect ratio microstructures and devices where low side wall surface roughness is not needed In order to obtain lower sidewall surface roughness while maintaining the ease of fabrication of the graphite based X-ray masks, the use of borosilicate glass was explored. A borosilicate glass manufactured by Schott Glas (Mainz, Germany) was selected due to its high purity and availability in ultra-thin sheets (30 μm). The fabrication process of the X-ray masks involves the mounting of a 30 μm glass sheet to either a stainless steel ring at room temperature or an invar ring at an elevated temperature followed by resist application, lithography, and gold electroplating. A stress free membrane is obtained by mounting the thin glass sheet to a stainless steel ring, while mounting on an invar ring at an elevated temperature produces a pre-stressed membrane ensuring that the membrane will remain taut during X-ray exposure. X-ray masks have been produced by using both thick negative- and positive-tone photoresists. The membrane mounting, resist application, lithography, and gold electroplating processes have been optimized to yield X-ray masks with absorber thicknesses ranging from 10 μm to 25 μm. Poly(methyl methacrylate) layers of 100 μm to 400 μm have been successfully patterned using the glass membrane masks.

The Center for Advanced Microstructures and Devices (CAMD) at Louisiana State University (LSU) supports one of the strongest programs in synchrotron radiation based microfabrication in particular, in deep X-ray lithography (DXRL) in the USA. For taller microstructures above 500 micrometers height, a harder source has been made available at CAMD using a 5-pole 7T super-conducting wiggler that has been installed in one of the straight sections of the synchrotron ring. A beamline and exposure station designed for ultra deep X-ray lithography (UDXRL) has been constructed and connected to the wiggler. An in-air scanner system has been built and installed at the beamline in approximately 10m distance to the source point. The scanner system features a fully water-cooled mask and substrate assembly to allow accurate patterning of high aspect ratio microstructures. The performance of the entire exposure system has been qualified and being proved compatible to standard exposure tools. Simultaneous exposure of a stack of four graphite substrates with 500 micrometers thick PMMA resist layers illustrate the potential for a cost-effective mass production of LIGA microstructures at hard UDXLR sources. The samples have been exposed using a 600 micrometers thick beryllium mask with 50 micrometers gold absorber. Dose calculations for the stacked exposures and preliminary exposure results as well as measurements of patterning accuracy over structure height and structure quality are presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

For patterning thick photoresist films, x-ray lithography is superior to optical lithography because of the use of a shorter wavelength and a very large depth of focus. SU-8 negative resist is well suited to pattern tall, high-aspect ratio microstructures in UV optical and x-ray lithography with rapid prototyping capability due to its high sensitivity. The negative tone of the SU-8 resist offers advantages in fabricating multi-level and non-planar microstructures using x-ray lithography or a combination of x-ray and UV optical lithography. In this paper, we present a fabrication process for multi-level metallic mold insert by a combination of multi-layer SU-8 patterning, poly-dimethylsiloxane (PDMS) molding, and nickel electroplating to make final nickel mold inserts that are suitable for injection molding and hot embossing of plastics and ceramics.

We are developing microsystems for genetic-based assays, which allow assembling devices with discrete functions to carry out complex assays. Specifically, the microfluidic devices are designed to perform ligase detection reactions (LDR) for identifying mutations in K-ras genes associated with colorectal cancer. The functions of the devices consist of PCR, LDR, and interrogation of LDR products using either micro-electrophoresis or DNA microarrays. The microfluidic devices are fabricated using LIGA to manufacture molding dies (metal electroforms) consisting of high aspect ratio microstructures (>10:1). Our devices are made from polymers, such as PMMA or PC. In this presentation, we will discuss the fabrication and operational characteristics of PCR/LDR thermal cycling modules as well as micro-hybridization units. The thermal cycling devices consist of isothermal zones with fluid packets shuttled through a spiral channel of ∼1.2 m in total length (total number of thermal cycles = 20).

A technology for the direct molding and release of silica micro-optical components in polymethyl methacrylate (PMMA) molds is developed. The objectives of this work are to bypass some of the usual steps in deep x-ray lithography (DXRL) and to determine the suitability of GR650 resin (methylpolysilsequioxane) for molding thick, high aspect ratio structures. The process is initiated by DXRL exposure of PMMA, followed by spin-on glass application, a cure at 85°C to set the shape of the resin, followed by demolding. The cure is below the glass transition temperature of PMMA and the demolding process allows re-use of the mold. There is no need for electroforming in the replication process. PMMA molds with thickness of 250, 350 and 500 um were fabricated by DXRL and standard resist development. A novel metal sacrificial layer technique is used in the release process with initial yield of about 50%. Microoptical elements that were fabricated include lenses, prisms, grating structures and transmission test structures. These components are cured above 400°C after release, to convert the organosilicon polymer to a silica-like material. Weight loss from the high temperature cure was in the range of 15 to 25%, while linear dimensions of the components decreased by about 1%. Composition of the molded, cured structures was measured by XPS depth profiles.

The LIGA process is used to fabricate micro-optical benches which allow to mount hybridically active and passive optical components with very high precision and without active alignment. Moreover, also micro mechanical structures like electro-mechanical actuators are fabricated on the same substrate. To avoid any lateral misalignment al fixing structures in the optical bench are produced in the lithography step. Due to the high precision of x-ray lithography lateral tolerances are in the range of 0.1 to 0.2 micrometers depending on thermal distortions. Thus, optical losses for these components are rather small. The potential of the free space concept based on LIGA technology for the fabrication of devices for optical telecommunication has been demonstrated by a bi-directional transceiver module as well as an optical bypass. In the case of the optical bypass element, a movable mirror is fabricated on the substrate together with the fixing elements. This movable mirror is the end face of an electro-static actuator which allows to move the mirror into the collimated light beam between two fibers and thus, change the direction of the light. For the first prototypes the losses in the beam without mirror are about 1.7 dB, whereas the losses in the deflected beam are about 4.5 dB.

Microtechnology offers the possibility to fabricate photonic devices. Especially the LIGA technique allows the fabrication of micro-optical benches for free-space optical set-ups, with mounts for inserting hybrid components structured to micrometer accuracy well aligned to each other. These optical benches are not only used to build up passive optical devices but also opto-mechanical systems have been realized. Also concepts to integrate active optical components like laser and photo diodes have been tested. In the paper the concept and the technology to fabricate hybrid micro-optical systems is described. Two systems, a bi-directional transceiver module and an opto- mechanical by pass switch have been fabricated and evaluated. Their performance data prove the ability of the concept of micro-optical functioning modules based on free- space micro-optical systems fabricated by LIGA technique and assembly.