A MEMS capacitive test structure for in-line automatic planar stress characterization

A MEMS (microelectromechanical system) test structure for planar stress characterization of the structural layer in a surface micromachining process is presented. The classical rotating needle design has been adopted and enhanced with electrical capacitive transduction of the rotation angle. The main goal is a device suitable for electrical measurements in order to allow in situ and fast in-line automatic testing. Stress extraction is performed through quantized capacitive transduction, leading to improved robustness versus capacitive parasitic effects which typically impair the analog transduction. The methodology is demonstrated through a comparison between electrical measurements and optical inspections on fabricated prototypes based on a gold electroplated structural layer.