Optical Modulator Based On Moems Technology Research

The fusion of MEMS and Optics(Micro-Opto-Electro-Mechanic Systems) brings up new methods for designing and fabricating optical components. It has the advantages of low-cost, small size, mass production and smart function. The research focuses on optical modulators based on MOEMS in this project. The main contents in this paper are as follows:The optical and mechanical properties of thin films, such as optical constants, residual stress and stress gradient are vital for the MOEMS devices in surface micromachining technology. A simple method to determine the optical constants and physical thickness are presented. The modified Simplex method is used to fit the measured transmission curve based on appropriate dispersion model. The optical constants of various films deposited by evaporation and sputtering are measured using this method. The errors of the results are less than 4% compared with other methods. The SiN_x and SiO_xN_y films are deposited by reactive magnetron sputtering. The optical properties, optical band gap and the chemical composition are analyzed under various process conditions(deposition pressure, gas flow ratio, et.al.). A micro-rotating structure on wafer to determine the residual stress and stress gradient of films is designed. The measured stress of Polysilicon and Si₃N₄ films deposited by LPCVD are -47.8Mpa and +530MPa respectively and the stress gradient are +267.43MPa and +44.2MPa.Microcavity devices are the most common used structures in MOEMS. The relation between the air gap thickness and peak wavelength in short cavity MOEMS Fabry-Perot filter are analyzed with Transfer Matrix Method. The analytical expression for the phase shift coefficient is deduced and a new linear relationship is presented during tuning process. A micro-display component based on induced reflection is designed and the optical properties of dielectric-metal air gap system are computed. Using Purcell effect, a wavelength tunable microcavity organic light emitting diode based on MEMS is designed and the emitting spectrums with variousvoltages actuated are analyzed. A self-consistent arithmetic is introduced to analyzing the coupling problem in MEMS devices which are actuacted by electrostatic force. The deformations of the square, rectangle, bow structures are compared using this method.The variable optical attenuator based on grating light valve is a diffractive MOEMS device. The optical properties, relation between the deformation and voltage and dynamic properties such as resonant frequency, response time are analyzed. Using surface micromachining technology, various material combinations are reseached and the key processes, the stiction and buckling phenomena, are studied. A good-release structure with polysilicon film as sacrificial layer and SiaN4 films as structure layer deposited by LPCVD is fabricated by supercritical CO2 dryer and residual stress control. The optical properties of the device are measured. The zero-order reflectivity decreases from 86.6% to 59.7% when the voltage increases from OV to 30.8V. The response time of the device is l²ms. To improve the properties, anodic bonding between Si and SIMOX SOI wafers with Schott 8329 glass film as an intermediate layer deposited by e-beam evaporated is introduced. The bonding current, bonding strength and bonding area ratio is analyzed under various condition. The structure with thick glass film and thin device layer is achieved with KOH solution etching back. It is a good base for fabrication of some MEMS devices.At last, a summary of this paper is included and the prospect of this project is given together.