Single crystalline silicon optical MEMS with photonic crystal mirrors

Microelectromechanical systems (MEMS) and silicon photonics are two emerging fields in the semiconductor industry. This dissertation studies the intersection of these two fields: optical MEMS with silicon photonics. Our work is focused on using single crystalline silicon to make monolithic optical MEMS devices with integrated photonic crystal sensing mirrors. To learn more about photonic crystals, we studied novel optical properties on photonic crystal mirrors in the first part of this work. Two optical effects based on the phase of complex reflectivity: effective thickness and Goos-Hanchen shift (GHS) were thoroughly studied. Effective thickness, related to group delay, is the gradient of reflected phase over wavenumber. GHS is the gradient of reflected phase over incident angle. Both were studied with temporal coupled mode theory, simulated with numerical methods, and demonstrated experimentally on photonic crystal mirrors. Both negative effective thickness and negative GHS are anomalous that are demonstrated on low-loss material for the first time. Furthermore, the fundamental limitations of these effects and the link between them were theoretically studied. Applications of these novel effects are discussed. Effective thickness can be useful for Fabry-Perot sensing with broadband light sources, and negative GHS on low-loss material can be the key to demonstrating optical rainbow trapping. Next, we combined photonic crystal mirrors with optical MEMS to make two types of sensors: acoustic sensors and pressure sensors. These sensors use the mechanical properties of MEMS structures for sensing and the optical properties of silicon photonics for readout. The sensor readout is based on a Fabry-Perot interferometer between an integrated photonic crystal mirror on MEMS diaphragm as the movable sensing mirror and a metal-coated fiber-tip as the stationary mirror. They are assembled into fiber-tip sensors for remote sensing with a small footprint. New fabrication process flows were also developed to make the sensing devices in a single crystalline form on standard bulk silicon wafers. For the acoustic sensor, a new fabrication process flow and a new simplified assembly process are presented. Optical, mechanical, and acoustic properties of the sensor are studied. The assembled sensors are tested and demonstrated minimum detectable pressure (MDP) close to the thermal-mechanical noise limit. Additionally, the limitations of clamped diaphragm-based sensors are studied. A new type of sensor with MEMS springs are studied, and new advanced process flows are designed. For the pressure sensor, we developed a new process flow called GOPhER silicon-on-nothing (SON) process based on the standard SON process. This new process extended the design space of a single crystalline SON structure, which is a sealed near-vacuum cavity inside a silicon device. Furthermore, it has the capability to add integrated ellipsoidal void photonic crystal onto the top diaphragm of a SON structure. At the end, a fiber-tip pressure sensor is assembled and characterized. The sensor demonstrated good dynamic range and sensitivity.

Keywords: Applied Physics.
Advisor: Fejer Martin M. (Martin Michael) 
Solgaard Olav 
Miller D. A. B.