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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.

High aspect ratio nickel microfluidic columns were fabricated using the LiGA technique. The 2-m-long 50-mum-wide high aspect ratio columns will be the separation component of a handheld gas chromatograph device for detecting semivolatile and volatile compounds. As a first step, 600-mum-deep electrodeposited nickel columns were fabricated. The serpentine columns were sealed and pressure-flow rate characteristics compared with the theoretical values. The response of the sealed columns was studied by running methane gas plugs through uncoated columns with a flame ionization detector at the exit. Negligible flow-induced dispersion was observed in the sealed metal columns. Unretained peak widths of ~15 ms were measured, and the experimental pressure and flow rate distributions matched those predicted by established analytical models within plusmn2.5%. Columns were coated with OV-1 stationary phase using static coating methods. A mixture of four hydrocarbons C6, C8, C10, and C12 was separated in a coated 50 mum by 600 mum by 0.5 m column in less than 2 s at 70 degC

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.

Gas chromatography (GC) is one of the most widespread techniques used in laboratories as a way to separate and analyze complex mixtures of volatile and semi-volatile compounds. The main advantage of miniaturization of these systems is the increased performance due to the reduced time for analysis and reduced fabrication cost of the complex pneumatic flow system. In this paper advanced design ideas and fabrication processes to facilitate integration of the sample concentrator and the column will be presented. Using the LIGA process, 0.5- and 2-m-long, 50-μm-wide, and up to 600-μm-high aspect ratio metal GC separation columns with on-chip integrated sample injection and detection were fabricated. Initial experiments of coating these high aspect ratio columns show promising results when compared to simple tubular columns.

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.

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.

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.

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 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.

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.

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).

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

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.

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.

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.

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).

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.

Deep etch lithography of PMMA by the LIGA-technique or H+ lithography is a powerful tool for the fabrication of very high refractive microprisms. We have realized a microintegrated optical imaging system using microprisms fabricated by the LIGA-process and microlenses with a diameter of 250 micrometers . Thus the size of the imaging system is less than 2 mm+.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Deep-etch x-ray lithography allows the fabrication of micro-optical components with critical lateral dimensions of a few micrometers and structural heights up to several hundred micrometers. Using interferometric methods, the structural tolerances of the side walls of fabricated microstructures are shown to be about 0.3 micrometers per 300 micrometers of structural height. A parallel HeNe laser beam is easily passed through several microprisms, which is evidence for the high precision achievable in positioning micro-optical components on a baseplate. Focussing a light beam by cylinder lenses is also possible. The free two- dimensional shape and the high precision achievable in positioning allow fabrication of micro- optical components with integrated fiber fixing grooves in which multi-mode fibers are precisely positioned. Simple fiber connectors, e.g., fiber forks or Y-couplers, can be achieved. By using a light-guiding resist system, divergence losses can be diminished.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.