Stress Sensitive Capacitive Transducers 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.