Past REU Participants & Project Pages

2006 REU Porjects
2006 REU Projects
2006 Participant: Christina J. Stamper
Project Title: MEMS Prototyping by Micro-Contact Printing

Faculty Advisor: Robert Hull
Introduction:
Micro-Contact Printing (µCP) is a microfabrication technique which, among other applications, can be used to prototype MEMS (Micro-Electro-Mechanical Systems) quickly, efficiently, and economically. First, a pattern is fabricated onto a silicon (Si) wafer using Focused Ion Beam (FIB) technology. Then, elastomer molds are cast from the wafer, eventually creating a negative imprint identical to the original pattern. After coating with Self-Assembled Monolayers (SAMs), this mold is used as the stamp. It is placed in contact with a target substrate which is then immersed in etch solution. Etching then produces the replicated pattern on the substrate. The purpose of this work is to use µCP techniques to develop reactive ion etch (RIE) masks for rapid prototyping of MEMS devices. This specific research is based on work conducted in the UVA Materials Science and Engineering department and documented as Development of a Deep Submicron Printing Technology (2001) by David Longo. More recently, the µCP project has developed through the work of Tim Herlihy and Bob Benoit. This work is done in conjunction with Zyvex Corporation, and funded by NIST-ATP (award #70NANB1H3021).
An optimal range of Ag thickness on target substrates was narrowed to between 150 and 300 nm Ag on top of Si wafer. Prints were conducted on 75 nm (A, D), 300 nm (B), and 500nm Ag (C), with the 500 appearing too grainy and rough, and the 75 so etched through that the silver would be a poor protector in the RIE process (discussed in the Future Works section).

An important aspect to consider when fabricating patterns on the FIB is to ensure that all the features are milled deep enough. The PDMS mold is not rigid enough to support shallow features, thus under-milled patterns result in sagging of the mold during inking. It is for this reason that in (A), the side bars are absent, whereas in (D) the side bars are evident.
Conclusion:
Significant progress has been made while discovering and learning more about µCP technology. The first discovery was that using PDMS worked well as the elastomer for both molds. Previous work was conducted using the elastomer APS-B, which has problems molding to fine features and degassing. PDMS alleviated these problems. This change in the quality of mold features made for much better prints, with more distinguished features and less distortion from surrounding imperfections.
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