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Due to the thermal mismatch between GaN and Si, GaN grown on Si at elevated temperatures (~1100 °C) usually exhibits large internal residual stress. Therefore, the characterization of residual stress in GaN on Si substrate is of particular importance. In this work, a type of reliable bent-beam strain sensor was used to estimate residual stress in suspended GaN microstructures. The device was modeled by finite element method (FEM) and was fabricated by a dry-etch-only deep-releasing technique featuring a combination of anisotropic and isotropic Si etching. Results were analyzed and an averaged residual stress value of ~575 ± 5 MPa was estimated for the GaN sample used in this work.