A Microstructure for In Situ Determination of Residual Strain

Abstract — This work presents a new strain sensor with a compact structure. The strain sensor comprises of a pair of cantilever beams with different lengths connected by a short tip. The residual strain causes two beams to deflect each other, thereby magnifying the deflection, which is measured by the tip. The displacement is independent of both Young’s modulus and the film’s thickness. An analytical model is derived to relate the measured displacement to residual strain. Finite-element modeling is also used to analyze the model. This work also thoroughly considers other factors that influence the designs and the implicit limitations of the strain sensors. Experimental results with an SiO 2 film as well as undoped LPCVD polysilicon films are used to demonstrate the effectiveness of the proposed structure. [250] Index Terms—Residual strain, thin film. I