For an optical electronic device and method that forms cavities through an interposer wafer after bonding the interposer wafer to a window wafer, the cavities are etched into the bonded interposer/window wafer pair using the anti-reflective coating of the window wafer as an etch stop. After formation of the cavities, the bonded interposer/window wafer pair is bonded peripherally of die areas to the MEMS device wafer, with die area micromechanical elements sealed within respectively corresponding ones of the cavities.