Stress sensitive capacitive tranducers to verify package models

Abstract

This paper describes MEMS capacitive transducers modified to characterize package stress. Two transducer types were designed: one to measure uniform in-plane strain, the other to measure uniform z-axis bending ("curvature"). These packagestress transducers had the same sensing mechanism as the MEMS acceleration transducers (capacitive output), so they could be used in existing accelerometers to quantify package-induced deformation. These transducers were fabricated in a production MEMS process (Motorola/Freescale 3u thick polysilicon "two poly" flow) and were characterized with capacitive probe and in accelerometer packages. Test data from the two sensor types provided useful data for verifying package models.