Poly-SiGe MEMS actuators for adaptive optics

Abstract

Many adaptive optics (AO) applications require mirror arrays with hundreds to thousands of segments, necessitating a CMOS-compatible MEMS process to integrate the mirrors with their driving electronics. This paper proposes a MEMS actuator that is fabricated using low-temperature polycrystalline silicon-germanium (poly-SiGe) surface-micromaching technology (total thermal budget is 6 hours at or below 425°C). The MEMS actuator consists of three flexures and a hexagonal platform, on which a micromirror is to be assembled. The flexures are made of single-layer poly-SiGe with stress gradient across thickness of the film, making them bend out-of-plane after sacrificial-layer release to create a large nominal gap. The platform, on the other hand, has an additional stress-balancing SiGe layer deposited on top, making the dual-layer stack stay flat after release. Using this process, we have successfully fabricated the MEMS actuator which is lifted 14.6 µm out-of-plane by 290-µm-long flexures. The 2-µm-thick hexagonal mirror-platform exhibits a strain gradient of -5.5×10 -5 µm -1 (equivalent to 18 mm radius-of-curvature), which would be further reduced once the micromirror is assembled.

Experimental Techniques for the Measurement of Mechanical Properties of Materials Used in Microelectromechanical Systems

“…The basic premise behind the concept of MEMS is that the efficiencies of high volume production and low unit cost achieved by the microelectronics industry over the past 50 years can be translated to devices in which the mechanical and electrical/electronic functions are integrated. In addition to the potential economic benefits, unique capabilities can be achieved by such integration to realize devices at very small scales such as sensors [1][2][3][4][5][6] , actuators 1,[7][8][9][10] , power producing devices [11][12][13] , chemical reactors [14][15][16] and biomedical devices [17][18][19][20] . The potential military applications for MEMS 21 include those in personnel systems, inertial guidance systems in precision-guided munitions, health monitoring of aircraft engine and structures, microUAVs, picosatellites, light weight radios, etc.…”