All plastic microfluidic device with built-in 3-D fine microstructures

Abstract

This paper presents the fabrication of all plastic microfluidic devices with built-in 3-D fine microstructures. The built-in micromeshes in the microchannel were formed by the combination of the multi-angle inclined backside exposure and top side exposure of thick Epon SU-8 photoresist on a glass substrate. The lift off method, using LOR (Lift-off Resist) as a sacrificial layer, was utilized to remove the all SU-8 device from the substrate. The monolithic plastic structures realize uniform physical and chemical properties required in microfluidic devices for practical applications. Fragmentation of a water droplet in organic carrier formed by two phase flow was demonstrated.Fabrication process A 3-D micromesh fabrication method and its application for the in-channel microfilters were already reported [1] [2]. These in-channel microfilters consisted of glass, Cr and SU-8. PDMS (polydimethylsiloxane) was used as a cover plate of the microchannel [1]. In this paper, we realized SU-8 in-channel micromeshes fabricated in a SU-8 microchannel. Fig.! shows the fabrication process of a monolithic SU-8 microchannel with built-in micromeshes. The Cr mask layer was patterned on the glass substrate ( Fig.! (a)). LOR was spin-coated as a sacrificial layer to remove the SU-8 devices from the substrate in later step ( Fig.1 (b)). After spin-coating of the first SU-8 ( Fig.1 (c)), UV was exposed through the photomask from front side to form the bottom floor of the SU-8 device (Fig.! (d)). The thickness of the SU-8 second layer defined the depth of the microchannel (Fig.! (e)). During the soft baking of this SU-8 layer, an SU-8 top-cover which was fabricated by single mask photolithography followed by the lift off process was placed on surface of the SU-8 substrate and bonded ( Fig.! (f)). In order to fabricate the in-channel micromesh, UV was irradiated from top to form the channel structure and from bottom to fabricate micromeshes as shown in Fig.! (g) and (h). The irradiation angle conditions were 450 and -450. After development (Fig.! (i)), since LOR was etched by SU-8 developer, the SU-8 monolithic microfluidc chip was removed from the glass substrate ( Fig.1 (j)). Fig.2 shows a photograph of the all SU-8 device fabricated by this method. The chip size is 2cm x 2cm. In order to visualize built-in micromeshes with SEM, the SU-8 top cover structure was partly removed. Fig.3 shows SEM photomicrograph of the fabricated micromeshes. This indicates the fine in-channel micromesh structures were formed successfully. The channel width and height were 800 ,um and 200 ,um, respectively. The thickness of the bottom floor and the top-cover was about 30 jm and 50 gm. Fig.4 shows the magnified view of the micromesh structure. The diameter of the inclined micropillars was I0 ,um.Fragmentation of a droplet formed by two phase flow Using fabricated all SU-8 microfluidic device, fragrnentation of a water droplet in organic carrier formed by two phase flow was performed (Fig.5). The organic phase of butyl acetate was introduced from the two sid...

Polydimethylglutarimide (PMGI) as a sacrificial material for SU-8 surface-micromachining

“…Polydimethylglutarimide (PMGI) is a commercially available deep-UV (DUV) positive resist used mainly for bilayer lift-off processes [3]; however, PMGI has found some use as a sacrificial material for surface-micromachining with metal structural layers [4][5][6]. The lift-off-resist (LOR) formulation of PMGI has also been used as an unpatterned lift-off layer for SU-8 based microfluidics [7][8][9], and as a sacrificial layer with isotropically patterned anchors for SU-8 based cantilevers [10]. However, the PMGI-SF series has a lower solubility than LOR, which allows higher selectivity during photopatterning and less interstitial mixing during SU-8 deposition.…”