Microfabrication Overview

The most widely adopted method for making Microfluidics devices for chemical and biological applications is named soft-lithography, a Microfabrication process combining photolithography and micro-molding techniques using a soft, biocompatible, polymeric material – PDMS (polydimethylsiloxane). The Microfabrication room of our facility offers all the equipment and tools needed for photolithography and soft-lithography process.

To obtain closed channels or multi-layer fluidic systems, the next steps is to bond structured layers of PDMS together. We provide two different methods and tools for bonding – oxygen plasma and corona treatment.

Oxygen plasma – Plasma ashing is a standard procedure in semiconductor manufacture, used to remove photoresist from substrate wafer. Oxygen is introduced to the vacuum process chamber as the reactive gas. The plasma is formed by exposing the reactive gas to electromagnetic radiation such as microwave or radio frequency. Free radicals generated in the plasma state react with the photoresist and substrate material. In addition to using the oxygen plasma to clean the surface (stripping photoresist), we also use the system to facilitate the PDMS bonding process. The process usually takes 5~10 minutes to achieve permanent irreversible bonding. Because the bonding takes effect immediately, it is suitable for quick fabrication of devices. It is less than suitable if the device requires careful alignment of multiple layers  

Corona treatment – Corona treatment uses the same principles as oxygen plasma except that instead of igniting plasma in the vacuum process chamber, the corona discharger creates arc plasma out of atmosphere. It is a hand-held tool does not require a vacuum pump and gas supply. Although its control is not as quantitative as oxygen plasma system, the result is equally reliable. The corona bonding process takes a much longer time (65 degree C overnight), but this slow process allows adjustment if precise alignment of several layers needs to be achieved. 

Making multi-layer devices – Making complex designs such as three–dimensional fluidic networks and membrane valving systems requires precision alignment between different layers, each with its own pattern. The facility contains an OAI alignment bonder specialized for PDMS multi-layer bonding, which allows large clearance between sample-holder and substrate-chuck and adjustable leveling to accommodate uneven PDMS slabs.