Study Of AlN Based MEMS Deformable Mirror

Deformable mirror(DM),which works as a wavefront corrector in the adaptive optics(AO)system,has now been extensively applied into astronomy,retinal imaging,beam shaping and other fields.In order to obtain DM demonstrating low-cost and simple fabrication process,excellent aberration correcting performance and environment friendly advantage,a novel design of piezoelectric continuous-surface MEMS DM based on AlN is proposed in this paper.Compared with the electrostatic DMs,the DM proposed in this paper has the advantages of excellent linear control and larger deflection.Compared with the traditional piezoelectric DMs based on PZT and PMN,the DM designed in this paper has the advantages of good CMOS compatibility,simple fabrication process and no environment contamination concern.In this paper,the structure of AlN MEMS DM is optimized by theoretical analysis and finite element simulation.It is found that when the ratio of the thickness of the AlN to that of the Si reaches 0.45,the maximum deflection of the DM can be obtained under the same applied electric field.At the same time,the driving performance of the DM is also systematically studied.The results show that the square membrane combined with SU8 restraint structure demonstrates similar performance as the circular membrane structure with the same size.In addition,focusing on the aberration correction ability of the DM,the results show that the DM can fit the first 14 orders of Zernike aberrations better when compared with previous studies.Finally,the preparation process of the DM is preliminarily discussed.In addition,a discrete piezoelectric micromirror based on AlN is also proposed in this paper.The good linear relationship between the motion modes of this micromirror and the control signals is studied through theoretical analysis and finite element simulation.The results show that the linearities for piston movement and tilt movement are 5.40nm/V and0.009deg/V,respectively.At the same time,a prototype has been successfully fabricated using silicon on insulator(SOI)based micro-electro-mechanical system(MEMS)process.Excellent linear relationship between the control signals and the motion modes of thismicromirror under both of the static and dynamic actuation conditions has been experimentally validated.The detailed data are listed as follows: the linearity of 3.10nm/V for piston movement and 0.005deg/V for tilt movement at the static state,the linearity of200.78 nm/V for piston movement(22.13kHz)and 0.200deg/V for tilt movement(63.25kHz)at the dynamic state.