A 3-degree-of-freedom low power and large displacement MEMS Lorentz force micro-mirror

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Afsharipour, Elnaz
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Optical equipment such as spectrometers, imaging systems, micro-projectors, and optical telecommunication devices often include a mechanically moving mirror to direct light beams. The performance of an optical system can be therefore limited by the mirror’s scanning area, its overall size, and power consumption to enable motion. Micro-mirrors moved by MEMS actuators have been developed by various groups to improve the directing of light beams. In this thesis, the development of a micro-mirror that can move and direct a light beam in 3 dimensions is presented. This micro-mirror has a large range of motion and consumes lower electrical power compared to its counterparts. The micro-mirror presented in this thesis is actuated by electromagnetic force. It is able to tilt about two axes and has linear motion along a third axis. The size of the mirror is 2 mm x 2 mm and the structure is of gimbal-less type. The performance is first evaluated using finite element simulation. After confirming the design, the fabrication process of the structure is explained, followed by experimental testing of static and dynamic responses. In a magnetic field of 0.1 T and by applying 20 mA of current to the actuators (2.6 mW) during resonant operation, the micro-mirror demonstrated a tilt angle of 13.3° at 292.7 Hz about the x-axis, and 22.8° at 247.5 Hz about the y-axis. With a total dc-drive current of 27.5 mA per actuator, 232-μm linear motion in the z-axis direction was achieved. The results are discussed and compared with simulation results. To explain the dynamic behaviour of the system, Lagrange’s equations were solved, which described the frequency response of the system. Finally, the performance of the presented micro-mirror was compared with micro-mirrors reported in the other works. It is shown that this micro-mirror has a large range of motion and consumes relatively low electrical power, compared to other works in literature. In a secondary study, a process for fabricating Distributed Bragg Reflectors (DBR) is presented. The fabrication process includes predicting the required conditions for depositing a thin layer of SiOx with a specified refractive index by using reactive sputtering technique. Using the developed method, a DBR was fabricated which showed a high reflection of 95% in a wide range of 270 nm bandwidth.
Micro-mirror, MEMS mirror, Lorentz force, 3 degree-of-freedom mirror, Beam steering, Scanning micro-mirror, Large amplitude of motion, Large stroke, Low power consumption, Electromagnetic actuation, Distributed Bragg Reflector, Bragg mirror, Micro-fabrication