Quantifying the performances of SU-8 microfluidic devices: high liquid water tightness, long-term stability, and vacuum compatibility

TL;DR

This paper demonstrates that SU-8 microfluidic devices can achieve high water tightness, long-term stability, and vacuum compatibility using a simple, non-aggressive fabrication process, making them reliable for various microchip applications.

Contribution

The study introduces a novel SU-8 based sealing process that ensures leak-tightness, stability, and vacuum compatibility without aggressive chemicals or high-energy treatments.

Findings

SU-8 walls withstand 1.5 to 5.5 bar water pressure

No water porosity after 2 months aging

Sustainable under $10^{-5}$ mbar vacuum

Abstract

Despite several decades of development, microfluidics lacks a sealing material that can be readily fabricated, leak-tight under high liquid water pressure, stable over a long time, and vacuum compatible. In this paper, we report the performances of a micro-scale processable sealing material for nanofluidic/microfluidics chip fabrication, which enables us to achieve all these requirements. We observed that micrometric walls made of SU-8 photoresist, whose thickness can be as low as 35 $\mu$m, exhibit water pressure leak-tightness from 1.5 bar up to 5.5 bar, no water porosity even after 2 months of aging, and are able to sustain under $10^{-5}$ mbar vacuum. This sealing material is therefore reliable and versatile for building microchips, part of which must be isolated from liquid water under pressure or vacuum. Moreover, the fabrication process we propose does not require the use of aggressive chemicals or high-temperature or high-energy plasma treatment. It thus opens a new perspective to seal microchips where delicate surfaces such as nanomaterials are present.