A two-step sealing-and-reinforcement SU8 bonding paradigm for the fabrication of shallow microchannels

Abstract

Adhesive bonding is a key technique to create microfluidic devices when two separate substrates are used to form microchannels. Among many adhesives explored in microchannel fabrication, SU8 has been widely used as an adhesive layer for sealing the microchannel sidewalls. The majority of the available SU8-based bonding methods, however, suffer from the difficulties associated with sealing of two important types of the microchannel architecture: (1) shallow microchannels with small patterns on a large area, and (2) microchannels with ultra-low aspect ratios (e.g. 6 mm in width and m in height). In this paper, a new bonding paradigm based upon the low-temperature and low-pressure SU8 bonding, consisting of two steps of sealing using a thin-SU8-coated PET film and bonding reinforcement using a SU8-coated glass slide, is proposed to resolve the aforementioned difficulties. Since it does not need complicated instruments such as a wafer bonding machine and a lamination device, the developed bonding paradigm is convenient and economical. We successfully demonstrate the compatibility of the proposed bonding paradigm with the two microchannel fabrication approaches based on the glass wet etching and the SU8 photo-lithography, where small microchannels with the innermost surfaces fully made of SU8 are obtained. A theoretical model is employed to better investigate the flow characteristics and the structural behavior of the microchannel including the PET film deformation, strain and von Mises stress distributions, bonding strength, etc. Moreover, we demonstrate the fabrication of the multi-height deep–shallow microchannel sidewalls and their sealing using the SU8-coated PET film. Finally, as a proof-of-concept device, a microfluidic filter consisting of the double-height deep–shallow microchannel is fabricated for separation of 3 µm and 10 µm particles.

Experimental and theoretical investigation of a low-Reynolds-number flow through deformable shallow microchannels with ultra-low height-to-width aspect ratios

“…3. The procedure is similar to what we described in our previous work [26] with the difference that the flexible membrane is allowed to deform even after the reinforcement step. Briefly, the patterns of the microchannel sidewalls are created through the glass wet etching procedure.…”

“…In this work, we experimentally and mathematically investigate the volumetric flow rate-pressure difference relationship for the shallow deformable microchannels with ultra-low height-to-width-ratios. The microchannels of few millimeters in width and few microns in height are fabricated by modifying our previously reported fabrication protocol [26] to enable the membrane to freely deform, while the bonding reinforcement allows the high pressure differences to be applied. This fabrication method enables us to uncover new fluid-solid behavioral characteristics for the low-Reynolds-number flow, i.e.…”

A passive Stokes flow rectifier for Newtonian fluids

“…The reinforcement glass was bonded to the bare side of the membrane using a 16 µm SU8 layer (E ∼ 2 GPa) 23 . The blank glass slides were used for reinforcement of rigid channels to avoid membrane deformations 24 . Capturing adhesive layers in the model.…”

Properties of Indium Tin Oxide Films Grown on Microtextured Glass Substrates

“…Cross-linked and hard baked SU8 possesses excellent adhesion and mechanical properties for temperatures up to ∼340 °C, enabling the possibility of being a permanent part of the system/device, with appreciable chemical and thermal stability. , In a thermal study by Lian et al, commercial SU8 is subjected to TGA (thermogravimetric analysis) and showed a weight loss of only 5% up to a temperature of 310 °C . Because of these prospective characteristics of SU8, it is widely utilized as a dielectric insertion layer in organic solar cells to enhance the efficiency, adhesion layer for bioelectrodes, microfluidic devices, , MEMS/NEMS devices, , fuel cells, and so on.…”