MEMS-based Optical Focusing and Micromechanical Testing

Micro-Electro-Mechanical Systems (MEMS) have been applied to various technological areas due to their superiority in miniaturization and stable fabrication process. When applying MEMS to solve problems in different fields, the innovative and effective design of the architecture and fabrication process is one of the most essential and important challenges. This dissertation presents two novel applications of MEMS technology: an optical path length modulator for compact space optical focusing and a force domain analog-to-digital converter (F-D ADC) for microscale materials testing.;In order to effectively shrink the size of traditional optical focusing system, a novel MEMS based optical path length modulator is presented in the first part of this dissertation. This optical path length modulator is composed of a microstage, two reflective micromirrors, and two vertical micromirrors which are electrostatically driven by a comb drive. It proposes a stable microstructure and provides a precise optical length control in a limited distance. The prototype of this optical path length modulator is completely fabricated by using bulk micromachining techniques on three different silicon substrates which are assembled together afterward. A MEMS based focusing system which consists of the proposed optical path length modulator, a lens, and an image sensor is further designed and simulated. The focusing function is achieved by continuously adjusting the focal distances with the proposed modulator. The preliminary testing of the prototype shows a capability of optical path length modulation of up to 16 µm with a driving voltage up to 21 volts and overall optical reflectivity of 70% for the whole modulator.;A force domain analog-to-digital converter (F-D ADC) and its application to micro-scale tensile testing of thin films are presented in the second part of this dissertation. Mechanical characterization of sub-micron thin films or similar small scale structures have been a continuous challenge to the mechanics community due to the difficulty in accurately quantizing the applied load and the resulted deformation. In this part, a new F-D ADC created from the concept of Flash ADC in electronics is developed to perform thin film tensile tests. The key component of the F-D ADC is a quantizer-array of microfabricated buckling beams of pre-determined length. During the testing, the applied force is quantized using the critical load of the increasing number of buckling beams and the deformation of the specimen is controlled by the piezoelectric actuator. The resolution and accuracy of the current method can be significantly improved by increasing the number of buckling beams. The successful testing of (110) single crystal silicon and Ti/Ni multilayer thin film specimens using the proposed F-D ADC tensile test chip demonstrated the feasibility of this novel F-D ADC concept.