Monolithic Three-Dimensional Integration of Micro-Fluidic Channels and Optical Waveguides in Fused Silica
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Monolithic Three-Dimensional Integration of Micro-Fluidic Channels and Optical Waveguides in Fused Silica Yves Bellouard1, Ali Said2, Mark Dugan2, and Philippe Bado2. 1
Center for Automation Technologies, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180-3590, U.S.A. 2 Translume Inc., 755 Phoenix Drive, Ann Arbor, MI 48108-2222, U.S.A. ABSTRACT This paper presents dramatic improvements in the micro-fabrication of threedimensional microfluidic channels and high-aspect ratio tunnels within the bulk of a fused silica substrate. We also report the fabrication of optical waveguides within the same substrate, which is a major step towards the integration of sensing capabilities within microfluidic networks. This integrated device, which combines both fluidic channels and optical waveguides, opens new opportunities in bio- and chemical sensing. The flexibility of the improved manufacturing process offers substantial new design capabilities, especially for single channel probing and massively parallel processing and sensing.
INTRODUCTION For the past decade, Lab-on-a-Chips and Biochips have gained increasing attention as a way to obtain faster, more reliable and more efficient chemical analysis. Fluidic channels are an essential component of these systems, playing a role equivalent to that of data-buses in computers. In this paper, we propose a new approach to manufacture high-aspect ratio microfluidic channels and tunnels in fused silica. The microfabrication process is carried out in two steps: (i) a predefined pattern is written with femtosecond laser pulses inside the volume (bulk) of fused silica substrate glass. (ii) This is followed by an etching step in a low-concentration (typ. 5%) aqueous solution of HF acid. Kondo et al. [1] have first proposed a related process for photo-etchable glass. However this material processing is more complex, requiring an additional heat treatment to precipitate crystallites before the etching step. Marcinkevičius et al. [2] described a similar process to manufacture microholes in fused silica. In these pioneering works, the microfluidic tunnel cross-section geometry is equivalent to the laser beam shape. As a result, only very small structures (the typical cross-section was a few microns) have been obtained. This is often undesirable for micro-fluidics applications. Our approach solves this problem. We use a scanning process (referred as “painting” [3]) to create fluidics channels and tunnels of virtually any shape. We have also explored the opportunity of combining optical waveguides and fluidic channels with the same manufacturing process.
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Figure 1. Illustration of the painting process [5]: by moving the substrate in three directions, one can connect laser-affected zones, thus forming large volumetric patterns. The pictures on the right show two optical refractive index maps: the top is produced with a single exposure while the bottom one is produced by “painting” multiple lines enough close to each othe
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