Mechanical Performance of Microcantilevers in Liquids

Abstract

Microelectromechanical systems (MEMS) are exposed to a variety of liquid environments in applications such as chemical and biological sensors and microfluidic devices. Environmental interactions between liquids and microscale structures can lead to unpredictable performance of MEMS in liquid environments. In this paper, the mechanical performance of microcantilevers in liquid environments was investigated through a series of experiments: Microcantilever beams were placed in a liquid-filled enclosure and cyclically actuated for ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cycles. Silicon, silicon with titanium coating, silicon with a polymeric coating (SU-8), and silicon nitride microcantilevers were evaluated in deionized water, saline, and glucose. Microcantilever materials, liquid environments, and load levels (0-5 ± 0.5 MPa) were selected to be representative of sensor applications. The mechanical performance of the microcantilevers was evaluated by periodically monitoring changes in resonant frequency. All specimens performed reliably in air. Significant changes in resonant frequency, often exceeding 1%, were observed for uncoated silicon and titanium-coated microcantilevers immersed in saline and for SU-8-coated microcantilevers immersed in water. The changes in resonant frequency were attributed to mineral deposition for uncoated silicon microcantilevers in saline, corrosion fatigue for titanium-coated silicon microcantilevers in saline, and water absorption for SU-8-coated microcantilevers in water.