Micromachined parallel plate structures for Casimir force measurement and optical modulation

Abstract

In microelectromechanical systems (MEMS), parallel plate structures with submicron separation have been of much use in various types of sensors and actuators. In this thesis such parallel plate structures are employed for two applications viz. the Casimir force measurement and to develop a mechanooptical modulator. Both research studies are focused on realizing parallel plate structures with a separation distance in the order of 1 μm or less. In this thesis, a methodology to measure the Casimir force using parallel plate structures is described, in which MEMS technology is used to improve the parallelism at sub-micrometer separations. The fabrication of these parallel plate structures is described and a dynamic measurement methodology to determine Casimir force using a scanning laser vibrometer is developed. To realize the parallel plates separated at ~1 μm distance, two fabrication processes based on two different substrates, namely -oriented silicon, providing a very smooth surface, and silicon-on-insulator (SOI) wafers. Only devices based on the SOI process were suitable for performing measurements. So far, no successful Casimir force measurements have been performed, however the obtained results do indicate that the measurement strategy is feasible and the research along this route should be continued. The second part of the thesis deals with the design and realization of an IONM (Integrated Optical Nano-Mechanical) based mechano-optical modulator. The mechanical structure and the optical waveguide are realized on separate chips and then assembled together resulting hybrid integration. The major part of this research study is focussed on the design and optimisation of the light-weight mechanical element that can be integrated with any optical waveguide. The integrated mechano-optical modulator device is characterized for both the electrical and optical measurements. The Capacitance-Voltage (CV) measurements successfully demonstrated the bidirectional electrostatic actuation of the device. This measurement also confirmed the movement of the mechanical beam in close vicinity of the waveguide core. From these results, it is shown that the mechanical structure can be actuated towards and away from the waveguide, demonstrating successful self-aligned assembly.