This dissertation presents the development and applications of high fill factor (HFF), small footprint micromirror and micromirror array (MMA) devices based on microelectromechanical systems (MEMS) technology. The individual micromirror devices developed in this dissertation are motivated by biomedical imaging, especially endoscopic biomedical imaging applications, where the micromirror serves as the lateral scan engine. The MMA devices presented in this dissertation are mainly focused on the application of optical phased arrays (OPAs), where the individual optical apertures in the MMA device are combined to imitate a much larger optical aperture for a wide range of steering state while maintaining the large steering angle and fast steering speed of each individual optical aperture.;Among the various actuation mechanisms of the micromirrors, this dissertation focuses on the electrothermal (E-T) and piezoelectric (P-E) bimorph actuation methods with E-T method being the primary choice of solution and the P-E method being the secondary. A novel bimorph actuator design will be proposed to solve the drawbacks with existing micromirror designs. Based on this bimorph actuator, three generations of E-T micromirror devices and one generation of P-E micromirror devices has been developed, among which the 2nd-generation E-T micromirror has been successfully implemented for a prototype imaging probe (phi=4.2mm) for commercial dental optical coherence tomography application. The 3rd-generation E-T micromirror devices can offer the highest area fill factor (∼60%) among the existing micromirror designs. The footprint of the micromirror devices is also among the smallest (1.45mmx1.55mm). Hence they can be applied for further miniaturization of the imaging probe. The P-E micromirror has been developed based on the Sol-gel PZT fabrication method. They also demonstrated considerably large scanning range at resonance frequency. However, the large residual thermal stress of the PZT layer caused undesired deformation of the bimorph actuator and thus limited the device performance. The HFF MMA devices presented in this dissertation are based on the design of the 3rd-generation E-T micromirror. They provide the largest sub optical aperture size ever reported (1.50mmx1.50mm) and thus can achieve a large equivalent optical aperture (e.g. 1.4cmx1.4cm) with only a small number ( e.g. 64) of sub apertures, which simplifies the control electronics dramatically. This has made the MMA device quite suitable for OPA applications.;Unlike traditional HFF micromirror and MMA devices with single-crystal silicon (SCS) supported optical aperture, the fabrication method of the 3 rd-generation HFF micromirror and MMA devices is based on a single Silicon-on-Insulator (SOI) wafer without the need for any bonding transfer processes, which simplified the fabrication, enhanced the yield, and reduced the cost. The design of the 3rd-generation micromirror and MMA device also provides surface mounting and flip chip bonding integration capabilities without the need of through wafer vias, which can further reduce the size of the imaging probe or the OPA system. This design, fabrication and packaging method has applied US patent and is currently being processed.;The dissertation consists of seven chapters. Chapter 1 gives a review of micromirror and MMA devices, their applications and the goal of this work. Chapter 2 first discusses the principle and the modeling methods of electrothermal bimorph actuator. Then, the drawbacks with the existing micromirror designs will be summarized followed by the proposal of the novel bimorph actuator design. Chapter 3 presents the development of the 1st-, 2 nd- and 3rd-generation of the E-T micromirror devices based on the proposed bimorph actuator. Chapter 4 focuses on the development of the MMA devices. Chapter 5 discusses the current and future application of the developed micromirrors and MMA devices. Chapter 6 presents the development of P-E micromirror device. Finally, Chapter 7 summarizes the work completed and gives the future research plan.
展开▼
