A novel MEMS stage for in-situ thermomechanical testing of single crystal silicon microbeams under bending

Abstract

We present a novel silicon MEMS stage for in-situ bending test of micro/nanoscale samples at high temperature. The stage minimizes uniaxial state of stress in the sample, but maximizes the bending stress over a small volume such that high stresses can be reached without a premature failure by flaw induced fracture. A test setup is designed to carry the stage inside an SEM which enables to heat the sample up to 450 °C. A piezoactuator of the setup stretches the stage which translates into bending the sample. Sample is co-fabricated with the stage to avoid handling and misalignment problems. Analytical and finite element (FE) models are developed to predict the behavior of the bending stage and calculate the stresses in the sample. Single crystal silicon (SCS) micro-beams oriented along [0 1 1] are tested at room temperature under bending. They showed higher strength compared to the uniaxial tension test results. The calculated modulus of elasticity of the samples matches the value reported in literature. In addition samples with thickness 2–5μm exhibited brittle-to-ductile transition (BDT) at 400 °C, about 150 °C below the bulk BDT temperature.