Study On Novel Micro Piezoelectric Actuators For MOEMS Applications

With the rapid development of Micro-electro-mechanical systems (MEMS) technology, optimizing the structures and performances of actuator materials is highly demanded. MEMS based piezoelectric actuators are becoming increasingly important for optical MEMS applications due to their inherently small size, high speed and high energy density. Thus, optimizing the design of MEMS piezoelectric actuators and applied research on them have great sense to develop MEMS. In this thesis, optimizing the geometries of piezoelectric actuators to improve the actuating qualities is studied. An analytical method for calculating the bending stiffness and blocking force of the optimized structure is proposed; FEA method is used to confirm the validity of the analytical method and the excellent actuating performance of the optimized actuators. Moreover, PMN-PT single crystal giant-piezoelectric materials is utilized in the structure to further enhance the actuating performances. The main contents of the thesis are as following:(1) A "force-focused" mechanism and a "bending-force-focused" mechanism are introduced into a cantilevered piezoelectric unimorph actuator. Based on Euler-Bernoulli theory, the analytical equations of mechanical stiffness of the two mechanisms are derived, of which the equation for calculating the mechanical stiffness of one single layer of the two mechanisms can also be used in other similar structures. With the methods of analytical calculation and FEA (Finite Element Analysis), the features of actuators with the two mechanisms are compared and contrasted. The results show that with the same dimension and the same applied voltage, a bending-force-focused actuator can produce a larger stroke than that of a force-focused actuator by sacrificing its blocking force. FEA simulations are used to confirm the validity of the method of calculating the mechanical stiffness and analyze the actuating performance of the optimized actuators.(2) To further improve the performance of the actuators, the novel PMN-PT single crystal piezoelectric material is used in the designed actuators and the performances are compared with that of the actuators using PZT-5H piezoelectric material. It is shown that with the same geometries, the strokes of PMN-PT actuators are larger than that of PZT actuators for several times, and its blocking forces are also higher than the later apparently. Thus, PMN-PT actuators have better actuating performances.(3) As an application of the proposed actuator, the feasibility of constructing deformable mirrors for adaptive optics utilizing unimorph actuators with force-focused mechanism is studied. The stroke transferability from an actuator to the mirror is analyzed. It is shown that a force-focused actuator has much higher actuation efficiency than that of a simple rectangular cantilevered actuator.(4) A lamellar grating interferometer (LGI) is designed with a PMN-PT/Si unimorph actuator with bending-force-focused mechanism. Under the dimension of2mm×2mm, the specific parameters and resolution of an LGI are presented. The verification of the compactness and high resolution of the designed LGI is provided via FEA simulation.