SU-8 Mold Research Articles

Metal foundation construction to consolidate electroplated structures for successful removal of SU-8 mould

For integrating thick microstructures with microfabricated circuitry on the same chip, a metal foundation method to consolidate adhesion of the electroplated microstructures to the substrate for successful removal of SU-8 mould is proposed. Along with multilevel interconnections microfabrication or other required metal deposition, the metal foundations are constructed and then tamped by interlevel dielectric. With metal foundations formed along with fabrication of interconnections and thin film electrodes, the electroplated Ni structures of an electrostatically levitated rotational microgyro, with thickness of 200 µm after lapping the whole wafer, are successfully released by removing the SU-8 mould using the fuming sulphuric acid oxidising method.

Swelling of SU-8 structure in Ni mold fabrication by UV-LIGA technique

UV-LIGA technique is used to fabricate hot embossing mold of PMMA microfluidic chip. Pre-polished Ni plate serves as electroforming substrate and the micro channel is the only structure to be electroformed in the fabricated mold. The precision of the micro channel strongly depends on the process parameters. Experiments show that the width of micro channel varies with the electroforming time. With the electroforming time of 108, 140 and 160 min, the width of micro channel reduces to 89, 86 and 82% of patterned SU-8 mold respectively, which is caused by swelling of SU-8 in acidic, high temperature electroforming solution. This swelling is the key answer to the slope of the sidewalls of the electroformed structure. This study is beneficial to optimizing microfluidic chip mold design.

Design and Fabrication of a Micro Reciprocating Engine

This paper presents an ongoing project of developing a micro reciprocating internal combustion engine. The engine is designed on the basis of a two stroke piston engine, but heavy modifications have been made to suit the 2D MEMS fabrication. All the engine parts are located in two layers. Piston seals are not used and leakage is prevented by the introduction of microgrooves on the piston, tight tolerance control and an extended contact area between the piston and the cylinder. With the assistance of a film of lubrication oil, these measures prove effective in preventing leakage. A new approach has been developed to fabricate high temperature resistant engine components at low cost. The approach relies on the UltraThick SU-8 Process (UTSP) to make micromoulds; then ceramic and metallic engine components can be produced based on the moulds. The UTSP is a UV lithography process for producing up to 1000 ?m thick SU-8 layers and the quality of the fabrication results can be compared with those made by using X ray exposure process in the same thickness. A complete microengine has been fabricated in SU-8 using the UTSP for test drive. High quality ceramic and metallic components have been produced based on the SU-8 moulds, proving the new approach is feasible for building

Fabrication of barrier ribs of PDP via powder injection molding

In this paper, an attempt was made to explore a possibility of powder micro injection molding process in manufacturing ceramic microstructures such as barrier ribs of plasma display panel. The barrier ribs are glass matrix composites with ceramic powder (alumina and/or titania) filler. In this molding process, a thermosetting paste was molded into polydimethlsilosane soft molds prepared by replication of thick film resist (SU-8) molds. The SU-8 mold was patterned with UV-lithography. The effects of powder content in the paste on paste viscosity and sintering characteristics of molded samples were examined. In addition, effect of molding speed on pore trapping in the microstructure was studied. These results indicated that the powder micro injection molding process at ambient temperature has merits of low-pressure injection molding process with superior mold release characteristics.

Sol−Gel Modified Poly(dimethylsiloxane) Microfluidic Devices with High Electroosmotic Mobilities and Hydrophilic Channel Wall Characteristics

Using a sol-gel method, we have fabricated poly(dimethylsiloxane) (PDMS) microchips with SiO2 particles homogeneously distributed within the PDMS polymer matrix. These particles are approximately 10 nm in diameter. To fabricate such devices, PDMS (Sylgard 184) was cast against SU-8 molds. After curing, the chips were carefully removed from the mold and sealed against flat, cured pieces of PDMS to form enclosed channel manifolds. These chips were then solvated in tetraethyl orthosilicate (TEOS), causing them to expand. Subsequently, the chips were placed in an aqueous solution containing 2.8% ethylamine and heated to form nanometer-sized SiO2 particles within the cross-linked PDMS polymer. The water contact angle for the PDMS-SiO2 chips was approximately 90.2 degrees compared to a water contact angle for Sylgard 184 of approximately 108.5 degrees . More importantly, the SiO2 modified PDMS chips showed no rhodamine B absorption after 4 h, indicating a substantially more hydrophilic and nonabsorptive surface than native PDMS. Initial electroosmotic mobilities (EOM) of (8.3+/-0.2)x10(-4) cm2/(V.s) (RSD=2.6% (RSD is relative standard deviation); n=10) were measured. This value was approximately twice that of native Sylgard 184 PDMS chips (4.21+/-0.09)x10(-4) cm2/(V.s) (RSD=2.2%; n=10) and 55% greater than glass chips (5.3+/-0.4)x10(-4) cm2/(V.s) (RSD=7.7%; n=5). After 60 days of dry storage, the EOM was (7.6+/-0.3)x10(-4) cm2/(V.s) (RSD=3.9%; n=3), a decrease of only 8% below that of the initially measured value. Separations performed on these devices generated 80,000-100,000 theoretical plates in 6-14 s for both tetramethylrhodamine succidimidyl ester and fluorescein-5-isothiocyanate derivatized amino acids. The separation distance was 3.5 cm. Plots of peak variance vs analyte migration times gave diffusion coefficients which indicate that the separation efficiencies are within 15% of the diffusion limit.

PDMS microchannels with slanted grooves embedded in three walls to realize efficient spiral flow

This paper presents functional three-dimensional microchannels whose top and side walls have slanted microgrooves. These microchannels can generate short pitch spiral flow for efficient chaotic mixing. We proposed a novel fabrication method for 3-D SU-8 molds using two-step inclined backside exposures and additional two-step top side exposures. The width and depth of the SU-8 microchannel are 100 μm. Slanted grooves of 50 μm in width and 30 μm in depth were patterned on the top and the side walls of the microchannel. Their orientation angle was 63.5° with the microchannel axis. It was demonstrated that the microchannel with slanted grooves on three walls achieved short pitch spiral flow compared to the microchannel with slanted grooves on one wall. Since liquid in the channel flows along the grooves on the walls, optimum design of the pitch and placement of the slanted grooves enables efficient spiral flows in the channel.

Fabrication of large SU-8 mold with high aspect ratio microchannels by UV exposure dose reduction

Fabrication of large SU-8 mold with high aspect ratio microchannels by UV exposure dose reduction

Fabrication of large SU-8 mold with high aspect ratio microchannels by UV exposure dose reduction

Patterned SU-8 can be used as a master mold for soft lithography. Fabrication of SU-8 molds with high aspect ratio microchannels for this purpose is non-trivial due to the contrary imperatives of mold hardness and faithful replication of the photomask pattern. Increased UV exposure time, which improves resist hardness, is found to result in overexposure of the shadowed resist and unresolved pattern structure in the wafer center. We have found that reduction of UV exposure dose from the resist manufacturer’s recommendation of 500–600mJ/cm2 to 350mJ/cm2 permits the successful fabrication of dense SU-8 gratings with relatively wide (80μm) SU-8 bars separated by narrow (10μm) microchannels with aspect ratio of 10 over the entire 100mm-diameter wafer. The underexposed SU-8 was rather soft but could be sufficiently hardened to attain a useable hardness (Vickers hardness (VH) number of 25) by hard baking at a relatively low temperature (95°C). A hard baking time of 20min resulted in saturation of the hardness; further increase of hard baking time resulted in no significant increase in hardness. The hard-baked SU-8 gratings were successfully used for replication of soft silicone rubber. Without hard-baking, the silicone rubber broke cohesively within the SU-8 gratings during demolding. A method of fabricating 100mm-diameter SU-8 mold consisting of 80μm wide SU-8 bars separated by 10μm narrow channels with aspect ratio of 10 for soft lithography has been demonstrated.

Experimental investigation of an embedded root method for stripping SU-8 photoresist in the UV-LIGA process

In much previous research it has been popular to use SU-8 photoresist as a mold for electroplating, facilitating the production of low-cost microelectromechanical systems. However, the thickness of the electroplated structures standing on the substrate could only reach 50 µm or less due to the internal force and deformation of the photoresist in the final stripping process. In order to fabricate thicker structures, an embedded root method has been proposed to consolidate the adhesion of the metal structures to the substrate during the SU-8 removal process. In this paper, an experimental investigation of this method is conducted to characterize the relationship between the root depth, the linewidth and the achievable thickness of the electroplated structures. Some test patterns with embedded roots have been designed and fabricated to estimate the possible size of various structures associated with different depths of niches, which are completely defined through the SiO2 masking and KOH etching processes. Based on the established relationship between the root depth and the geometric sizes, a three-dimensional Ni coil, with a thickness of 200 µm, a width of 80 µm and a root depth of 4 µm, is successfully released by the SU-8 mold, which has a height of 400 µm. This cannot be achieved by the standard SU-8 molding process. The process parameters presented herein may be applied to the fabrication of other thick metal microstructures with similar needs.

SU-8 ON PMMA – A NEW TECHNOLOGY FOR MICROFLUIDICS

International Journal of Computational Engineering ScienceVol. 04, No. 03, pp. 667-670 (2003) Poster PapersNo AccessSU-8 ON PMMA – A NEW TECHNOLOGY FOR MICROFLUIDICST. Q. TRUONG and N. T. NGUYENT. Q. TRUONGSchool of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore Search for more papers by this author and N. T. NGUYENSchool of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore Search for more papers by this author https://doi.org/10.1142/S1465876303002003Cited by:4 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractConventional SU-8 lithography process for fabricating microfluidic devices ofthe uses silicon or glass as wafer materials. Since silicon and glass are hard and brittle, drilling fluid access holes or dicing the wafers into individual devies are difficult. We investigated the use of polymethylmethacrylate (PMMA) as a new wafer material. PMMA, an amorphous thermoplastic, was chosen for being easy to drill or cut, biocompatible, transparent, and much cheaper than silicon or glass wafers. Moreover, is thermal expansion coefficient ideally matches that of SU-8. PMMA poorly resists solvents, and has low glass transition temperature (105°C). Thus, the conventional process needed to be modified. The wafer was only cleaned with isopropyl alcohol and deionized water. The baking temperature was lowered to 90°C. In addition, a "base layer" of SU-8, helping to achieve a high quality structural pattern, was coated before coating the actual structural SU-8 layer. A Tesla valve, a non-moving part microfluidic valve, was successfully fabricated in SU-8 using thr presented process,. However, the PMMA wafer bowed ue to the thermal residual during baking steps. Despite the bowing which can be solved by increasing wafer thickness, we conclude that PMMA is a promising wafer material for a SU-8 process.Keywords:MicrofluidicsSU-8PMMAFabricationPhotolithography References N. T. Nguyen and S. T. Wereley , Fundamentals and Applications of Microfluidics ( Artech House , Boston , 2002 ) . Google ScholarN. T. Nguyenet al., Sensors and Actuators A69, 85 (1998). Google ScholarD. Mailleferet al., Proc. MEMS'99 541 (1999). Google ScholarRebecca J. Jackmanet al., Journal of Micromechanics and Microengineering 11, 263 (2001). Crossref, Google ScholarE. L. Hostiset al., Sensors and Actuators B64, 156 (2000). Google ScholarF. K. Forsteret al., Proc. The ASME Fluids Engineering Division 39 (1995). Google Scholar FiguresReferencesRelatedDetailsCited By 4Microcalorimeter: Design considerations, materials and examplesM.K. Khaw, F. Mohd-Yasin and N.T. Nguyen1 Jun 2016 | Microelectronic Engineering, Vol. 158PMMA as a base material for SU8 mold to fabricate PDMS reliefIrni Hamiza Hamzah, Asrulnizam Abd Manaf and Othman Sidek1 Dec 2010Fabrication technique of a 3 dimensional SU8 mold on PMMA substrateI. H. Hamzah, Asrulnizam Abd Manaf and O. Sidek1 Jan 2009 | IEICE Electronics Express, Vol. 6, No. 24Prototype Development for Chip-Chip Interconnection by Multimode WaveguideB.L.S. Pong, R. Pamidigantham and C.S. Premachandran Recommended Vol. 04, No. 03 Metrics History KeywordsMicrofluidicsSU-8PMMAFabricationPhotolithographyPDF download

Ultrathick SU-8 mold formation and removal, and its application to the fabrication of LIGA-like micromotors with embedded roots

In this study, a novel method to completely remove crosslinked SU-8 without remnants of the resist or destroying the electroplated microstructures was utilized. The LIGA-like fabrication of a side-driven electrostatic micromotor was employed as an example to describe polymerized SU-8 resist removal. Using near-UV light, nickel components of the micromotor were electroplated 160 μm in a 300 μm-thick SU-8 mold. A comparison of various approaches based on a commercial remover was performed during the mold removal process. Experimental results showed that components having 1 μm-deep substructures embedded in the substrate could provide stronger structures to withstand the internal stress due to the photoresist deformation. In addition, when the height of the electroplated structure was below two-thirds of the photoresist mold thickness, the net clamping force on the resist could be effectively reduced to make the removal of SU-8 with heated remover successfully. The rotor and the stator with embedded roots were released cleanly and thereby, assembled to form a high-aspect-ratio micromotor. The technique of SU-8 removal and LIGA-like process presented herein can be applied to the fabrication of other high-powered microactuators.

Comparison of PMMA and SU-8 resist moulds for embossing of PZT to produce high-aspect-ratio microstructures using LIGA process

In this paper results are presented from a range of experiments to explore the feasibility of inserting a ceramic material PZT (lead zirconium titanate) into different kinds of high-aspect-ratio resist moulds. Polymethylmethacrylate (PMMA) and SU-8 on silicon substrates and free-standing SU-8 membranes with micro-cavities or through-holes (defined by X-ray lithography) have been used as moulding medium. Processing conditions for the resist materials including pre-bake, exposure, post-bake, development and stripping have been compared. The advantages of different types of resist mould for the LIGA process has been evaluated. Additionally a comparison of photosensitivity of PMMA and SU-8 has been carried out. Using a range of load pressures (5 to 60 MPa), appropriate conditions for PZT embossing into resist moulds have been determined (ensuring minimum void formation in the final PZT structures). In the final form, SU-8 moulds have been removed by laser ablation. This is the first reporting of high-aspect-ratio ceramic microstructures fabricated using a combination of SU-8 moulds and PZT embossing.

Patterning, electroplating and removal of SU-8 moulds by excimer laser micromachining

The ablation characteristics of the SU-8 photoresist (spun on Siwafers) under 248 KrF excimer pulsed laser radiation have been studied.The variation of etch rate with fluence has been investigated in the range0.05-3.01 J cm-2. The threshold fluence for ablation of SU-8 ismeasured to be about 0.05 J cm-2. The etch rate of SU-8 is found tobe higher than that of polyimide (previously reported) under similarconditions. We have investigated the effects of different prebaketemperatures (90, 110, 120 and 200 °C) on ablation characteristics,which are found to be similar for all temperatures. The effect ofincreasing the number of laser shots (from 10 to 10 000) has beenexamined at different fluences in order to understand the etch-ratevariation near the `end of film' stage of ablation. The results of ouranalysis using scanning electron microscopy, profilometry and opticalmicroscopy reveal the very smooth morphology of the etched surfaces withno significant debris, no noticeable damage to underlying silicon and thegradual build-up of a carbonaceous film outside and around the etch pits.We find SU-8 very suitable for excimer ablation lithography and havedemonstrated this by patterning a gear structure in an SU-8 resist layerwith an aspect ratio of 4.5. For the first time, we have shown that thelaser micromachining technique has the potential to cleanly remove SU-8after electroplating a microstructure with copper.

Electroplated compliant metal microactuators with small feature sizes using a removable SU-8 mould

In the work presented in this article a fabrication process for high aspect ratio metal microstructures has been developed using photoresist EPON SU-8. A smallest feature size of 2 μm with near vertical sidewalls has been achieved on a routine basis. The SU-8 photoresist has been used as mould for electroplating high aspect ratio metal micro actuators. A removal process has also been developed. The removal of the SU-8 mould after plating is done in a plasma asher using an oxygen or oxygen/fluorine plasma with plasma power as low as 200 W. To demonstrate the fabrication process a 10 μm thick nickel, electro-thermal micro actuator has been fabricated.

Evaporation characteristics of materials from an electron-beam gun : E. B. Graper. J. Vac. Sci. Technol.8(1), January–February (1971), p. 333

The fabrication of high-aspect-ratio metal micro device on metal substrate is largely limited by its poor interfacial adhesion strength between metal substrate and thick SU-8 photoresist mould. In this paper, ultrasonic treatment is introduced to improve the interfacial adhesion strength between metal substrate and a high-aspect-ratio inertial switch SU-8 mould. Firstly, a device for ultrasonic treatment was developed, ultrasonic vibration is applied to SU-8 film after post exposure baking in order to improve the interfacial adhesion strength. Compared with the traditional one, SU-8 photoresist mould treated by ultrasonic vibration can effectively improve the interfacial adhesion strength. After 90 min cavitation erosion test, SU-8 film treated by ultrasonic vibration remains 34.4% relative to nothing left of the SU-8 film without ultrasonic treatment. Besides, the mechanisms of ultrasonic treatment on improving interfacial adhesion strength are investigated. Finally, an inertial switch is successfully fabricated on metallic substrate with the ultrasonic treated SU-8 photoresist mould.