Studies On The Microfabrication Technology For Production Of Microfluidic Chips Based On SU-8 Negative Photoresis

Microfluidics is the science and technology of systems that process or manipulate small(10^-9to 10^-18litres)amounts of fluids,using channels with dimensions of tens to hundreds of micrometres.Compared to macroscale laboratory techniques,microfluidic chip has a number of advantages over conventional chemical processes,which is expected to promote the development of analytical instrumentation to minimization,integration and automation.However,the present microfabrication technology can not follow the rapid development of microfluidics.For example,it is difficult to seal electrodes within glass microchip and tedious to fabricate molds used for replication of plastic chips. The fabrication of high-respect-ratio and 3-dimensional micro structure without using special instrtmaents is still on development.In this dissertation,several new fabrication and sealing techniques using SU-8 negative photoresist are studied and reported as following:In chapter 1,the current status in the field of fabricating microfluidic chip and the fabrication process for SU-8 microstructure was reviewed.In chapter 2,a novel method for adhesive bonding of glass microfluidic chips at room temperature was developed.Channels in an etched glass substrate were filled with a heated sulfur liquid at 120℃that formed a solid sacrificial layer cooled to 95℃.Then,the etched substrate and cover substrate were bonded together utilizing a SU-8 adhesive layer.To avoid any chance ofphotoresist curing inside the channel,the UV light was exposed through sulfur sacrificial layer.Once the sealing step was complete,the sacrificial layer was melted and removed,leaving enclosed microfluidic channels.The chips have been used successfully for the separation of amino acids. Another advantage of this method is the possibility of integration of metal electrodes into a microfluidic glass device.In chapter 3,a simple and inexpensive method to fabricate nickel mold insert for replicating of plastic microfluidic chips was developed.A polished nickel plate was used as a substrate on which a thick SU-8 photoresist layer was coated.Conventional contact UV lithography was applied to pattern the thick SU-8 photoresist layer.After development,electroetching was conducted at a large current density of 16～30 A/dm² for 5 min to clean the nickel surface in the SU-8 recesses where unexposed SU-8 had been lifted up and to form 5～10μm deep root structures for increasing the strength of the nickel insert electroformed later on.By using the fabricated SU-8 microstructure as a template and nickel substrate as an electrode supplying current,nickel mold insert with a sidewall slope of 83°and high aspect ratio were successfully fabricated within 5 h in a conventional chemical laboratory.More than 500 PMMA microfluidic chips were replicated by hot-embossing.The chips have been used successfully for the separation of DNA fragments.In chapter 4,a simple and low cost method to fabricate high aspect ratio metallic microstructures without the requirement of specialized equipments was described. Conventional contact UV lithography was applied to pattern a thin AZ 4620 positive photoresist film coated on the ITO layer of the glass substrate.After development of the photoresist,a nickel film was electrodeposited in the recesses where exposed AZ 4620 had been lifted up.The formed Ni pattern was then functioned as an exposure mask to pattern a thick SU-8 photoresist coated on it.SU-8 microstructures with high aspect ratio were fabricated with reverse-side exposure.By using the fabricated SU-8 microstructure as a template and the nickel pattern on the ITO glass substrate as the seed layer,nickel microstructures with high aspect ratio of about 15 and a sidewall slope of 89°were successfully fabricated in conventional chemical laboratory.In chapter 5,micro fabrication of embedded channels in SU-8 microchip using phase changing sacrificial material sulfur was developed,in which SU-8 open channels were sealed by another coating layer of SU-8 after being filled with liquified sulfur at 120℃and solidified at 95℃to form a sacrificial layer.Based on this new technique,3-dimensional SU-8 microchip was fabricated for first time by photolithography to pattern the top SU-8 photoresist layer sealed on the microchannels.By repeating the above steps,multi-layered structures could be fabricated.Unlike conventional sacrificial layer techniques,this method drastically simplifies and shortens the sacrificial layer removal process,especially for long and complex channel networks.The fabrication process is very flexible and opens new possibilities to construct complex 3-D structures in SU-8,which has very promising applications in electrophoresis microchips,micro-mixers and organic synthesis reactions carried out in microfluidics reactors.