Surface Modification and Characterization of PMMA Used in the Construction of Microelectromechanical Systems.

Poly(methyl methacrylate), PMMA, is a standard photoresist and is also a popular material out of which microelectromechanical systems are made. Described within is the characterization of the bulk and surface properties of commercial PMMA sheets and their relevance to PMMA as a photoresist. The surface chemical modification and characterization of commercial PMMA sheets is discussed; these modifications and their chemical properties have direct pertinence to the use of PMMA as a substrate for the fabrication of microelectromechanical devices. The molecular masses of pristine and irradiated PMMAs were determined by means of gel-permeation chromatography (GPC) and it was found that the molecular mass of irradiated PMMA is less than that of pristine PMMA. In addition, the glass transition temperatures (Tg) of pristine and annealed PMMA were determined and compared. The surface topography of commercial PMMA sheets was assessed using scanning force microscopy (SFM) and related to the adhesive properties of sheet PMMA to metal surfaces. It was determined that thermally treated PMMA sheets displayed a higher surface area than those sheets not thermally treated, which is due to defects on the surface of the PMMA. The pits were determined, using gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME), to be due to the expulsion of MMA monomer from the matrix of the PMMA during annealing. The surface chemical modification of PMMA sheets to yield primary amine-terminated PMMA surfaces is described. Characterizations of amine-terminated PMMA sheets conclude that the amines are covalently linked to the surface of PMMA and are accessible for further surface reactions; in addition, the amines are present at a surface density of 5 nmol cm-2. Amine-terminated PMMA sheets were used in reactions with isothiocyanates, isocyanates and carboxylic acids. Such functionalized PMMA surfaces can be used to manipulate the electroosmotic flow (EOF) of microcapillary electrophoresis devices and will be used as stationary phases in microcapillary electrophoresis. Amine-terminated PMMA surfaces have been used in the electroless deposition of several metals and for the fabrication of colloidal metal films. Finally, a photopatterning technique was developed that allows for the selective deposition of various organic moieties or metals with micrometer-level resolution