Project 2: Novel Microstructures Fabricated Using Grayscale Lithography (Prof. Kevin Walsh, ECE)
Complex three-dimensional microstructures are traditionally very difficult to produce using conventional microfabrication techniques. They are commonly made by depositing and patterning subsequent thin films on top of one another to build up the 3D structure layer by layer, much like 3D printing. This research will explore a fast and efficient alternative strategy for producing 3D MEMS microstructures using a relatively new technology called “grayscale lithography”. Lithography has traditionally been a binary process where the thin film layers are either spatially etched or not. With the advent of new laser-based direct write systems, such as the Heidelberg 150, one now has the capability of finely controlling the intensity of the laser beam as it scans over the substrate surface. Using a photo-polymer base material, one can spatially vary the exposure intensity of the finely-focused laser beam and produce true 3D structures in a single pass. Some of the interesting 3D MEMS structures we have produced at UofL using this technology is shown in the figure. In this 10-week research project, the REU student will learn about grayscale lithography and how to operate the Heidelberg system. The student will work closely with the UofL cleanroom staff to design patterns, characterize the process, understand the process and its limitations, fabricate a variety of interesting 3D MEMS microsctructures, and image them using scanning electron microscopy and profilometry.
Micro and nano-structures fabricated in photosensitive resist and polyimide using direct grayscale lithography. (a,b) 8 um tall hemispherical structures in photoresist using laser direct write. (c) 70 nm step pyramid in photoresist using laser direct write. (d) 2 um step staircase in photo-patternable HD-8820 polyimide using DMD projection printing.
By Kevin Walsh, Shamus McNamara, and Curt McKenna
J. H. Lake, S. D. Cambron, K. M. Walsh, and S. McNamara, "Maskless Grayscale Lithography Using a Positive-Tone Photodefinable Polyimide for MEMS Applications", Journal of Microelectromechanical Systems, Vol. 20, Number 6, pp. 1483-1488, Dec. 2011.
James Loomis, Curt McKenna, Kevin Walsh, and Mark Crain, "Advanced MEMS Grayscale Lithography Mask Generation Software", 2011 Joint Conference 7th Kentucky Innovation and Entrepreneurship Conference and 16th Kentucky EPSCoR Conference, Louisville, KY, May 26, 2012.
Curtis McKenna, Shamus McNamara and Kevin Walsh, "Grayscale Lithography using the Heidelberg Laser pattern Generator", Advanced Lithography Workshop, Nanoscale Research Facility, University of Florida, Dec 2011.