Characterisation of PMMA microfluidic channels and devices fabricated by hot embossing and sealed by direct bonding

doi:10.1016/j.cap.2009.01.007

Current Applied Physics

Volume 9, Issue 6, November 2009, Pages 1199-1202

https://doi.org/10.1016/j.cap.2009.01.007 Get rights and content

Abstract

In this study we fabricated a silicon-based stamp with various microchannel arrays, and demonstrated successful replication of the stamp micro-structure on poly methyl methacrylate (PMMA) substrates. We used maskless UV lithography for the production of the micro-structured stamp. Thermal imprint lithography was used to fabricate microfeatured fluidic platforms on PMMA substrates, as well as to bond PMMA lids on the fluidic platforms. The microfeature in the silicon-based (silicon wafer coated with SU-8) stamp includes microchannel arrays of approximately 30 μm in depth and 5 mm in width. We produced various channels without pillars, as well as with SU-8 pillars in the range of 50–100 μm wide and 6 μm in height. PMMA discs of 1 mm thickness were utilized as the molding substrate. We found 10 kN applied force and 100 °C embossing temperature were optimum for transferring the micro-structure to the PMMA substrate.

Introduction

The basic requirements for microfluidic devices commercialization are economical fabrication, large scale production and good sensitivity. Microfluidic devices based on silicon, glass, quartz and plastic has been widely studied in the past ten years. The silicon and glass-based material often induces problems, such as lack of optical clarity, low impact strength and poor-compatibility, thus limiting its widespread usage in microfluidic devices. On the other hand, the importance of micro-structures on polymers is increasing, particularly when considered as a low-cost alternative to the silicon- or glass-based MEMS technologies, for single-use disposable biomedical sensors. Additionally, polymer-based materials offer a wide range of physical and chemical properties, such as low electrical conductivity and high chemical stability. In recent years, many polymer-based microfabrication techniques [1] via microinjection molding [2], [3], casting [4], [5], and micro-hot embossing [6], [7] have been developed.

In polymer-based microfabrication techniques, microinjection molding is most popular and generally used for micromolding in the industry. However, compared to the microinjection molding, hot embossing provides several advantages such as a relatively low-cost for embossing tools, simple operation and higher accuracy in the replication of small features. The hot embossing process introduces less residual stress in the polymer because the polymer stretches for a very short distance from the substrate into micro-structure during hot embossing. As a result, the molded parts are well suited for optical components. In addition, the temperature variation range for the polymer is smaller than that required in injection molding, thus can reduce shrinkage during cooling and the friction forces acting on the microfeatures during de-molding. Hot embossing includes several steps and details have been reported elsewhere [1]. The embossing master stamp can be a silicon wafer, glass, electroplated nickel mold or other stamp with microfeatures. Still, micro-hot embossing is facing challenge in terms of process feasibility, since it is difficult to make the polymer to fill completely into microfeatured geometry of high aspect ratio and it is also delicate to separate the embossed structures from the mold without breakage.

In this paper, the correlation between the dimensions of the master stamps features and the corresponding replicated features was analysed along with the fluid flow behaviour in the channel. The bonding between microfluidic structures and lids was leak-tested was carried on these devices by flowing colored dye.

Section snippets

Microchannel stamp fabrication

The maskless UV lithographic technique was employed for the production of the micro-structured stamp. In this study, the SU-8 (SU-8 is a photopatternable epoxy resin) micro-structures were fabricated on a 4 inches silicon wafer. The SU-8 is a viscous and adhesive substance commonly used in lithographic process to create well-defined and stiff pattern. Prior to fabrication the silicon substrate is cleaned first with piranha solution (H₂SO₄ + H₂O₂) and then with acetone and de-ionized water before

Results and discussion

Maskless UV lithography was used to produce micro-structured stamp based on SU-8 photoresist coated on silicon substrate. The microfeature in the silicon stamp includes microchannel arrays of approximately 30 μm in depth and 5 mm in length. The stamp contains various channels without pillars, as well as with SU-8 pillars in the range of 50–100 μm wide and 10 μm in height. PMMA discs of 4 inches diameter and 1 mm thickness were utilized as the molding substrate. One PMMA disc can accommodate at least

Conclusion

In this study, novel microchannel device fabrication process was demonstrated in which a microchannel was formed by hot embossing on PMMA discs and directly bonded with the PMMA lid. It was confirmed by the experiments that the microchannel is suitable for fluid flow without any leak. The transient evolution of meniscus front is experimentally visualized using optical microscope for DI water.

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Characterisation of PMMA microfluidic channels and devices fabricated by hot embossing and sealed by direct bonding

Abstract

Introduction

Section snippets

Microchannel stamp fabrication

Results and discussion

Conclusion

Microelectronic Engineering

Current Opinion in Chemical Biology

Journal of Micromechanics and Microengineering

Analytical Chemistry

Polymer News

Analytical Chemistry