Abstract
Electrostatic out-of-plane microactuators have been widely used in applications of variable capacitors, optical attenuators, optical switches and scanning displays due to their small size, low cost, simple and diverse structure, low power consumption and high compatibility with semiconductor process. The large out-of-plane displacement of the microactuator with high reliability is preferred in order to increase the tuning range, tunability and the display size. However, the “pull-in” instability associated with conventional attractive-force electrostatic microactuators significantly limits the out-of-plane displacement and lowers the operation stability. A repulsive-force microactuator has been previously developed which can achieve large out-of-plane rotation and does not suffer from the “pull-in” instability. However, a larger rotation angle of the repulsive-force actuator is highly desired in order to improve its performance in the applications such as increasing the tunability and the scanning angle. In this thesis two novel repulsive-force actuators, i.e., two-row interdigitating-finger and two-width-finger (TWF) actuators are developed which output much larger out-of-plane rotation than the previous repulsive-force actuator without suffering from the “pull-in” instability. The mathematical models are established for both actuators using a hybrid approach. The actuators require only two thin layers and are suitable for surface micromachining process. The measured results show that the two microactuators can achieve rotation angles of 11.5° and 7.5° at 150 V respectively. The improvements are 100% and 35% in comparison to the previous repulsive-force actuator with the same size, stiffness and driving voltage. A 2D scanning micromirror has been developed and fabricated based on the two-row-finger (TRF) actuator. Experimental results show the micromirror has larger rotation angle and faster response speed than those of the micromirror driven by the previous repulsive-force microactuator. The vector scanning display based on the micromirror is demonstrated. An advanced display approach is developed to generate displays with less distortion and higher refreshing rate compared to the previous generic display approach. The automotive Head-up Display (HUD) based on the micromirror and advanced display approach has been constructed for both real and virtual image configurations, which has advantages of small size, low cost, large viewing angle and good visibility over those HUDs in the market.
Highlights
1.1 Out-of-plane microactuator reviewMicroactuator is a microscopic mechanism that provides actuation motion to other micro structures
It is a constitutional device of Microelectromechanical Systems (MEMS)
The in-plane motion indicates that the movement is in a plane parallel to the substrate and the out-of-plane motion means the movement has an angle with the substrate
Summary
Microactuator is a microscopic mechanism that provides actuation motion to other micro structures. If classified by driving principle, microactuators can be categorized into 4 types, i.e., electrostatic, electrothermal, electromagnetic and piezoelectric actuations [1], [2]. A lot of electrostatic microactuators have been developed for optical switches [18]–[20], optical attenuators [21], [22], tunable optical filter [23] and scanning displays [24]–[27] All of those applications require out-of-plane motions, which highly desire large rotation angles in order to increase the switching number of ports, the attenuating range and tunability as well as enlarge the display area for scanning display application. There are two types of conventional out-of-plane electrostatic actuators, i.e., parallel-plate (or gap-closing) and vertical comb-drive actuators, both of which utilize the attractive force to pull the moving electrode toward the fixed electrode
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