Test structures for determining design rules for microelectromechanical-based sensors and actuators

We present two test structures for establishing design rules for minimum spacing of a new class of microelectromechanical-based sensors and actuators fabricated through commercial complementary metal-oxide-semiconductor (CMOS) foundries. The microelectromechanical devices are suspended membranes of passivation glass that encapsulates polysilicon and aluminum layers in the CMOS process. The membranes are suspended by anisotropically etching the silicon substrate through openings in the passivation glass. These test structures measure the lateral undercutting and the rotational misalignment of openings in passivation oxide that are used to make the microelectromechanical devices, and give information for the layout, and proximity to circuits of the microelectromechanical devices. Two test structures are discussed, one optical and one electrical, and results for a 2-μm n- and p-well CMOS process run are presented