Research On MOEMS Optical Current Sensor

Optical current sensor is an important direction of high-current sensor's future evolving.A solution that combines optical and electrical method to monitor and measure high-voltage grid offers some clear advantages,including better insulation,stronger anti-interference capability,higher precision,etc.Meanwhile,rapid developing MOEMS (Optical MEMS)technology,with its cost-effectiveness and flexibility,provides a new path for the advance of optical current sensor.In this thesis,a novel MOEMS optical current sensor detecting high alternating current is designed based on Grating Light Valve technology,and the fabrication process of the measurement chip is explored.This device features excellent frequency response, temperature stability and sensitivity at high current.The design principle of the device is detailed,the optical and mechanical characteristics are analyzed,and optimal design parameters are achieved.Finite element analysis and numerical calculation reveal that the alternating current with peak value ranging from 500A to 2000A can be detected by the device;1st order resonant frequency is approximately 60kHz and the sensitivity at high current can reach 0.19dB/A;when temperature varies±50K,measurement error is around 0.7%.The stiction problem and residual stress of the structure film which have great impact on the performance of the device are also carefully examined.The critical stiction length of the device beam in different situations is discussed and a solution to solve the stiction problem during drying process of fabrication is presented.Besides,a micro-rotating structure designed to determine the residual stress on the structure layer is introduced. FEM analysis of the structure using ANSYS software is performed,and the result 20MPa is basically in accordance with measured residual stress by fabricated structure on SOI wafer top Si layer.Based on analysis results,the fabrication of device using MEMS surface micromachining technology and SOI material is explored,major fabrication processes are studied,and fully-released structure is accomplished.An optical testing system has been established to measure the optical properties of the device.It is observed that the zero-order reflectivity decreases from 92.6%to 55.1%when the voltage increases from 0V to 24.9V.At last,a summary of this thesis is included and the prospect of this project is given together.