Design and fabrication of MEMS optical switches

Abstract

This thesis focuses on the research related to the microelectromechanical systems (MEMS) optical switch consisting of three major areas, micromahined actuator, deep reactive ion etching (DRIE) fabrication, and total internal reflection (TIR) optical switch.Firstly, a stable micromachined actuator with large displacement has been designed and demonstrated. It consists of comb-finger-sets and compliant microstructure to amplify the displacement efficiently and lock the output by bifurcation effect. The amplification obtained is 54.2 when the input displacement is only 0.96 um and it is locked thereafter.Subsequently, a DRIE fabrication process for silicon on insulator (SOI) wafers has been investigated. Based on the study of DRIE process chemically and physically, the notching effect on SOI substrate is eliminated and utilized to realize dry release resolving the station problem by developing a spacer oxide thin film technique.Lastly, a TIR prism optical switch based on the thermo-optic (TO) effect has been studied. It takes the merits of robustness of thermo-optic prism and the precise control and batch fabrication of MEMS. The optical properties including insertion loss, polarization dependent loss and cross-talk are theoretically simulated and proven by experiments.ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library It is a pleasure to offer thanks to those who made this dissertation possible and made my stay in NTU most meaningful and enjoyable. ii ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library 3.3.1 DRIE fabrication 51 3.3.2 Displacement measurement and discussions 53 3.3.3 Resonant frequency measurement and discussion 55 3.4 FABRICATION TOLERANCE ANALYSIS 57 3.4.1 The effect of the beam profile 59 3.4.2 The effect of a comb finger uneven depth 64 3.4.3 Effect of undercut of microbeams 67 3.5 SUMMARY 70 CHAPTER FOUR THE DEEP RIE PROCESS 73 4.1 DRIE FABRICATION PROCESS FLOW 75 4.2 CHEMISTRY-PHYSICS OF DRIE 77 4.2.1 Effect of platen power 80 4.2.2 Effect of gas flow with source power 83 4.2.3 The effect of the duration of the cyclic etch/passivation cycles 86 4.2.4 Effect of process pressure 87 4.3 THE LOADING EFFECT 89 4.3.1 The loading effect dependence on the design of various features. 89 4.3.2 Etch rate along the process 98 4.3.3 Beam verticality 100 4.4 THE NOTCHING EFFECT 101 4.4.