Mechanical and material characterization of bilayer microcantilevers for MEMS-based IR detector applications

Uncooled micro-electro-mechanical systems (MEMS)-based infrared radiation (IR) detectors have received extensive attention for wide use in military and civilian applications such as for night vision, environmental monitoring, biomedical diagnostics, remote sensing, and thermal probing of active microelectronic devices. These detectors utilize the bending of bilayer microcantilevers upon absorption of IR to form thermal images. While these MEMS-based IR detectors have many benefits over photon detectors, the residual stress-induced curvature after fabrication and inelastic deformation greatly compromise their performance. Recently, a composite material, silicon oxynitride (SiON), which has a unique tunability in IR absorption spectrum, has been proposed to replace the conventional IR absorption material such as silicon nitride (Si3N4) in IR detectors. This composite material enhances the sensitivity to selective targets, which emit IR at particular wavelength. However, the mechanical properties of the composite material have seldom been studied. Accurate mechanical and material characterization is crucial to ensure performance and reliability.;This dissertation addresses three important fundamental technical issues for the next-generation of high-sensitivity and tunable MEMS-based IR detectors: (1) planarization; (2) long-term behavior prediction of Si3N 4/AI bilayer microcantilevers; and (3) mechanical and material properties characterization of silicon oxynitride thin films. This research provides a comprehensive mechanical and material characterization of the temperature- and time-dependent thermomechanical responses of the Si3N 4/AI bilayer microcantilever beams under different thermal loading. Experimental methodologies, theoretical models and finite element analysis (FEA) models are developed to achieve flattened bilayer microcantilevers, and to predict the temperature- and time-dependent deformation of MEMS-based IR detectors in short- and long-term operation. In addition, the mechanical and material properties of the silicon oxynitride thin films are systematically studied using nanoindentation for mechanical characterization, energy dispersive X-ray analysis (EDX) for material composition, and Fourier transform infrared spectrometry (FT-IR) for optical characterization.;The experimental methodologies and theoretical framework developed in this research can be readily applied to study the thermomechanical behavior of various bilayer microcantilever structures, and to improve the fundamental understanding required to design high-sensitivity and tunable MEMS-based IR detectors.