28 September 2001 Fabrication of the refined MEMS-based compound grating (MCG) based on silicon micromachining
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Proceedings Volume 4557, Micromachining and Microfabrication Process Technology VII; (2001) https://doi.org/10.1117/12.442953
Event: Micromachining and Microfabrication, 2001, San Francisco, CA, United States
Abstract
The MEMS-based Micrograting (MCG) is a basic building component in many optical systems. This paper presents the fabrication technique of a custom MCG whose optical surface can be reconfigured electrostatically. The ruling is made of SiO2 and both the top and the bottom electrodes are made of Cr/Au. A robust three-mask process was designed and developed. The reduced ruling width (1 micrometers ) is not a simple miniaturization of previously reported 3 micrometers and 4 micrometers ruled microgratings. Because of mechanical integrity and fringe effects at the ruling edge during device operation, the design and fabrication of the new 1 micrometers ruled MCG require new material and process integration. To achieve self-alignment between the top electrode and the ruling, the top electrode is patterned first then the pattern is transferred to the ruling material by Reactive Ion Etch (RIE). Experiments show that the lift-off process results in a smoother top electrode than ion milling. Residual stress proves to be an important factor that influences the device performance. Because Ni is used as a hard mask for RIE, the resulting stress gradient causes the rulings to bend up. The actuation voltage is increased as a result of this increased air gap. Annealing experiments are performed to reduce the material residual stress and lower the pull-in voltage. Auger Electron Spectroscopy (AES) data shows that the adhesion layer (Cr) diffuses through the Au and gets oxidized when annealing temperature is higher than 450 degree(s)C. It was found that the optimum annealing condition is at 350 degree(s)C for 1 hour. Finally, optical tests these prototypes show that the diffraction patterns switch at about 11 V, much lower than the devices reported previously.
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Yahong Yao, Yahong Yao, Bai Xu, Bai Xu, James Castracane, James Castracane, } "Fabrication of the refined MEMS-based compound grating (MCG) based on silicon micromachining", Proc. SPIE 4557, Micromachining and Microfabrication Process Technology VII, (28 September 2001); doi: 10.1117/12.442953; https://doi.org/10.1117/12.442953
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