A micro vertically-allocated SU-8 check valve and its characteristics

This paper proposes and develops a novel fabrication method to realize a micro vertically-allocated SU-8 check valve. The ordinary vertically-allocated SU-8 check valve formed by the photolithography has a limited overlap between an SU-8 cantilever and its valve seat, resulting in the low diodicity (i.e. the ratio of the forward flow to reverse flow rates). This overlap prevents the leakage through a bottom gap (a gap between a substrate and the SU-8 cantilever) and a top gap (a gap between a cover plate and the SU-8 cantilever) in the backward flow. These gaps, which are necessary for the movement of the SU-8 cantilever in the forward flow, must cause the leakage of check valves in the backward flow. To reduce the leakage and improve the diodicity, we propose to fabricate a novel fully-overlapped valve seat composed of channel walls, a bottom block, and a top block. To keep the advantages on the batch process of vertically-allocated SU-8 check valves, these blocks are desirable to be fabricated by the multi-layer process. We propose a multi-layer process for the bottom block and a novel beam forming process (a dose-controlled UV exposure) for the top block. In this paper, we design two types of check valves: (a) the ordinary partially-overlapped check valve; and (b) the proposed fully-overlapped check valve, to compare their diodicity. By investigating their flow rate characteristics experimentally, we conclude that the fully-overlapped check valve can reduce the leakage of 53.6% compared with the partially-overlapped check valve and increase the diodicity from 1.7 to 3.5 (about 2 times) at the supplied pressure of 18kPa. We also demonstrate that the novel check valve exhibits higher performance and also show that our fully-overlapped check valve can be potentially applied to various microfluidics.