Fabrication and material characterization of silver cantilevers via direct surface micromachining

Abstract

Microelectromechanical Systems (MEMS) rely heavily on the semiconductor industry's manufacturing paradigm. While the standardized process model allows semiconductor chips to benefit from economy of scale and be sold at low prices, MEMS devices use specialized processes and subsequently have to be sold at higher prices. This severely hinders MEMS development because it is not economically feasible to research and develop specialized devices where only small volumes are needed. As such, tools and processes which divorce MEMS fabrication from this paradigm are needed. Using Hewlett-Packard thermal inkjet technology mounted to an X-Y microcontroller stage, we present a mask-less, or direct, surface micromachining process flow with a 250°C thermal budget. The process uses Cabot Corp.'s silver-based conductive ink for the structural layer and PMMA for the sacrificial layer. Several other materials were tested for use as sacrificial inks in addition to PMMA. Silver cantilevers with dimensions of 200x50[mu]m and 200x100[mu]m were fabricated as a demonstration of the process. The silver cantilevers were mechanically characterized by using force-deflection measurements made by a P-10 contact profilometer or a Hysitron nanoindentor. We present findings of 21.9±1.50GPa or 22±1.5GPa for the silver ink's Young's modulus of elasticity, depending on the characterization method. These measurements were consistent with results measured by nanoindentating Cabot silver films. We hypothesize that the film's porosity is the cause of the silver's reduced material properties. Some preliminary data supporting this hypothesis is provided, and potential methods of improving the material properties and the surface micromachining process are discussed.