A study on residual stress measurement using I-V characteristics of bent-beam actuators

Abstract

Develops a new class of sensitive and compact passive stress measurement pattern that use piezoresistivity of polysilicon. The measurement pattern utilizes a pair of bent-beam actuators connected by a central beam. The bent-beam actuators are 15 /spl mu/m wide, 200 /spl mu/m long, and bent 0.1 radians (0.73/spl deg/). The central beam is 5 /spl mu/m wide, 264 /spl mu/m long. The bent-beam actuators amplify and transform deformations caused by residual stress into elongation or contraction of the central beam. The length change causes resistance change of a central beam. We can measure residual stress by measuring the change of resistance. It is shown that tensile and compressive residual stress levels about 10 MPa, corresponding to strains below 6/spl times/10/sup -5/, can be measured in 40 /spl mu/m-thick layer of polysilicon. The pattern is suitable for post-packaging stress measurement because of electrical measurement.