A Single-Mask Process for 3-D Microstructure Fabrication in PDMS

This paper reports a single-mask process technique to develop 3-D structures in polydimethylsiloxane (PDMS) finding a wide variety of applications in microfluidics. This technique enables the fabrication of channels and cavities having round corners and many other customized shapes in PDMS in a predictable manner. The process relies on reactive-ion-etching lag to form 3-D channels and cavities in silicon in a single-etch process. The negative replica of patterns is then transferred from the silicon substrate to a glass master by using anodic bonding under vacuum, glass reflowing at temperatures above 700
^°
C for about 5 h, and complete removal of silicon in KOH. Finally, soft lithography is exploited to transfer the structures to PDMS maintaining the same aspect ratio and feature sizes of the original patterns in silicon. As a case example, an insulator-based dielectrophoresis (iDEP) device with 3-D constrictions has been developed that can operate at lower applied potentials compared with previously reported 2-D iDEP designs. Using the 3-D iDEP device, trapping of 2-μm and 500-nm polystyrene beads was achieved with an applied potential of 150 and 350 V, respectively, with more than 80% trapping efficiency.