Multi-Layer Photopolymer Micromachining
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J11.5.1
Multi-Layer Photopolymer Micromachining J. R. Huang1, B. Bai2, J. Shaw1, T. N. Jackson2, C. Y. Wei1, V. Manivannan1, K. Durocher1 1
GE Global Research Center, One Research Circle, Niskayuna, NY, 12309, USA Center for Thin Film Devices, Electronic Materials and Processing Research Laboratories, Department of Electrical Engineering, Pennsylvania State University, University Park, PA 16801, USA 2
ABSTRACT This paper presents a novel method to create and integrate micro-machined devices and high aspect-ratio (height-to-width ratio) microstructures in which the microstructures are built up using multiple layers of photopolymer film and/or viscous solution. Very high aspect-ratio 2and 3-dimensional (2-D and 3-D) microstructures were constructed by stacking photo-imageable polymer films. Such films may be dry films applied by lamination or solution layers applied by bar coating, or doctor blade coating. Photolithography is used in both cases to define the microstructure. This additive process of thin-film micromachining facilitates high aspect-ratio microstructure fabrication. We have demonstrated structures of up to 12-layers comprising 2-D arrays of deep trenches (180 µm deep and 25 µm wide) and a 2-layer SU-8 micro-trench array with an aspect ratio up to 36 on glass substrates. Miniaturized structures of interconnected reservoirs as small as 50 µm x 50 µm x 15 µm (~38 pico liter storage capacity) are also being fabricated, along with a novel 5-layer microfluidic channel array and a vacuum-infiltration process for fluid manipulation. This method has the potential to create functional large-area micro-devices at low-cost and with increased device flexibility, durability, prototyping speed, and reduced process complexity for applications in optoelectronics, integrated detectors, and biodevices. The novel multi-layer photopolymer dry film and solution process also allows microstructures in micro-electro-mechanical systems (MEMS) to be built with ease and provides the functionality of MEMS integration with electronic devices and integrated circuits (ICs). INTRODUCTION MEMS has emerged as a promising technology for many applications, for example, in bio- and life-sciences, automobile, medical, chemical, communication, and optical equipment engineering [1]-[10]. Many practical and potential uses have flowed from this technology, chief among them being increased miniaturization and process/analysis speed, enhanced functionality, and reduced complexity in system design. To take just two examples, the lab-on-a-chip, or micro total analysis system (µ-TAS) [11] has achieved an increased precision and accuracy in fine-volume liquid dispensing and micro-structured flow channels/separation columns [12] have achieved an increased cell sorting speed and efficiency. However, the requirement for elaborate three-dimensional structures in MEMS devices often leads to quite complicated and difficult processes. Conventional approaches for fabrication of MEMS devices involve numerous additive, subtractive, and patterning processes [1
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