Design, fabrication, and characterization of hemispherical glass optics for MEMS mirror packaging applications

This paper presents an improved chemical foaming process (CFP) for fabricating uniform hemispherical glass arrays on 8-inch glass wafers for MEMS mirror optical packaging. Firstly, analytical and simulated models are constructed to predict the parameters of hemispherical glass. The fabrication processes of hemispherical glasses and stable foaming agents are also detailed. Then, we found that temperature distribution during cooling was the key factor in glass height using statistical analysis. By fixing the mass of the sheet and using a copper board to heat it together, the height uniformity is improved from 20.2% to 16.6%. A method to further improve height uniformity is proposed through simulation and experiment. Finally, the fabricated hemispherical glasses are tested. The thickness difference is less than 2% between CT (computed tomography) and simulation. The outer roughness is 0.622 nm. The compressive strength is larger than 200 MPa, demonstrating that the glass can package the MEMS mirror with a high vacuum level inside and defend it from harsh environments. These glasses can eliminate the light spot and ghost image problems of the flat glass in MEMS mirror encapsulation, proving the great advantages of hemispherical glass.