Cheaper microfluidic devices with infrared modification to photolithography process


RESEARCHERS at the A*STAR Singapore Institute of Manufacturing Technology have developed an infrared-based approach which allows the patterning of tiny circuits without high-temperature processing.

Microfluidic devices allow microelectronic engineers to replicate the capabilities of laboratories within a space of a computer-chip. These devices have a series of microscopic channels and reservoirs carved into a flat plate, which reagents flow through.

These microfluidic devices allow researchers to develop new chemical reactions or monitor the cellular effects of drugs on a much smaller scale, potentially saving time and money.

Some microfluidic devices integrate electrical components which work as heaters and sensors. However, the scale of such components means there has been difficulties in developing a rapid, low-cost method for creating the detailed metal patterns that make up these circuits.

Conventional techniques tend to require high-temperature processing, which can damage the transparent polymers typically used to build microfluidic devices. Polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are vulnerable to heat but are preferred for use in microfluidic devices due to their optical properties and the fact that they can be plastic injection moulded, for high volume production.

The new research from Singapore is an alternative process which is used to build complex metal-patterned microfluidic devices while not exposing the polymers to high temperatures.

The researchers covered sheets of PC or PMMA with thin layers of chromium, copper and nickel, and added a coating of a light-sensitive material called a photoresist.

Instead of baking this sandwich at high temperatures in order to remove residual solvents, the researchers used infrared heating elements to eliminate the solvents.

The metal layer acted as a protective barrier, reflecting more than 95% of any infrared radiation that hit it. This meant the photoresist layer was heated to the required temperature, but the polymer beneath was protected from the heat.

The researchers then used standard photolithography processes to create the microfluidic device. They placed a patterned mask over the sandwich and shone ultraviolet light to erode some areas of the photoresist; then, they etched away the exposed areas of metal beneath using a wash of chemicals. Stripping off any remaining photoresist left a clean metal pattern, which had features as small as 10 micrometers in width.

This new process cuts the costs of creating microfluidic devices by more than 90 percent.