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Unformatted text preview: EE 245: Introduction to MEMS Lecture 14: Beam Bending CTN 10/13/09 1 Copyright © 2009 Regents of the University of California MEMS Material Property Test Structures EE C245 : Introduction to MEMS Design LecM 7 C. Nguyen 9/28/07 41 Stress Measurement Via Wafer Curvature • Compressively stressed film → bends a wafer into a convex shape • ensile stressed film ends etector θ x Slope = 1/R Tensile stressed film → bends a wafer into a concave shape • Can optically measure the deflection of the wafer before and after the film is deposited • Determine the radius of Si-substrate Laser Detector Mirror x Scan the mirror θ t EE C245 : Introduction to MEMS Design LecM 7 C. Nguyen 9/28/07 42 curvature R, then apply: Rt h E 6 2 ′ = σ σ = film stress [Pa] E ′ = E/(1- ν ) = biaxial elastic modulus [Pa] h = substrate thickness [m] t = film thickness R = substrate radius of curvature [m] h R MEMS Stress Test Structure • Simple Approach : use a clamped- clamped beam ª Compressive stress causes...
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This note was uploaded on 10/31/2010 for the course C 218 taught by Professor Clarknguyen during the Fall '09 term at Berkeley.
- Fall '09