Nanostructured sensors have uses in safety, environmental monitoring, fire detection, and security.
Standard microfabrication techniques can be implemented and scaled to help assemble nanoscale microsensors. Currently nanostructures are often deposited onto materials primarily by adding them to a solution, then applying the solution in a thin film. This results in random placement of the nanostructures with no controlled order, and no way to accurately reproduce the placement. This method changes the means by which microsensors with nanostructures are fabricated. The fundamental advantage to this approach is that it enables standard microfabrication techniques to be applied in the repeated manufacture of nanostructured sensors on a microplatform.
The fundamental steps are first to define a standard metal electrode pattern of interdigitated fingers with parallel fingers that are saw-toothed. Nanostructures are then added to a standard photoresist to form a dilute solution. The photoresist solution is then applied to the microstructure. Before the solution solidifies, alternating electric fields are applied across the electrodes in order to align the nanostructures on the wafer. Once this photoresist later dries into a film and is processsed, a second layer of metal is deposited on top of the first layer. The effect is to remove photoresist from the metal fingers, but leave the nanostructures that bridge the fingers to be held in place by the top metal layer. Longer nanostructures, which are already aligned across the fingers, will be held in place by the top metal.
This buries the contacts of the nanostructures that are bridging the fingers between two layers of metal. The result is a microsensor fabricated using microfabrication techniques with aligned nanostructures bridging the electrodes and buried electrical contacts.
Possible applications include emissions monitoring, leak detection, engine monitoring, security, fire detection, extravehicular-activity (EVA) applications, personal health monitoring, and environmental monitoring. Because this process is compatible with low temperatures and thin-film supports, it can be used in thin films for conductive coatings requiring electrical connections.
A proof-of-concept of this approach was demonstrated using alumina as the substrate, metals such as platinum as the bottom electrode and titanium as the top metal layer, and both multiwalled carbon nanotubes and metal oxide nanowires as the nanostructured material.
This work was done by Gary W. Hunter, Randall L. VanderWal, Laura J. Evans, and Jennifer C. Xu of Glenn Research Center. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Manufacturing & Prototyping category.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18418-1.