Realization of low-stress Au cantilever beams

Abstract

A significant challenge in the fabrication of thin-film (<1 µm) Au MEMS devices is maintaining planarity after removal of the sacrificial layer. Out-of-plane deformations are driven by residual stress gradients in the Au films. It was found that the baking time and temperature of the sacrificial photoresist layer, as well as the thermal history once the Au was deposited, combined to determine the stress gradient within the Au film. In this technical note we provide the complete details of the optimized procedures to fabricate planar thin-film Au devices with unattached ends that are characterized by low residual stresses.

FEM modelling and experimental characterization of microbeams in presence of residual stress

“…Another origin of internal stresses within the gold microbeam is the difference of the coefficient of thermal expansion (CTE) between gold and photoresist, being used as sacrificial layer to build a gap between the suspended microstructures and the ground [37]. This difference may cause a significant stress gradient over the microsystem, anytime at which temperature changes, during the microfabrication process, in particular during sintering and plasma etching.…”

“…Nevertheless, very often it happens that material properties and microspecimen dimensions are known only approximately. This paper contributes to the above mentioned research activity, by investigating effectiveness and computational performance of some numerical models developed and proposed by the authors in [23,[31][32][33][34][35] and already experimentally validated in case of inplane bending tests [36,37]. Present work is aimed to complete the previous investigation by focusing on the outof-plane bending tests.…”

Design optimization of RF-MEMS switch considering thermally induced residual stress and process uncertainties

“…A stress gradient is developed in the microstructures due to the difference in the coefficient of the thermal expansion (CTE) between the gold thin film and the photoresist. The CTE values for the gold and photoresist are 14.7 μm/m/°C and 68.6 μm/m/°C respectively [30]. A tensile residual stress develops at the interface between the gold and photoresist because the sacrificial layer expands at a faster rate than the gold layer.…”

Standalone Tensile Testing of Thin Film Materials for MEMS/NEMS Applications

“…In fact in high temperatures two problems arise; above the glass transition temperature, polymer layer starts a significant flow which causes deformation and wrinkling in the metallic film; on the other hand, the thermal mismatch between the polymer and the metallic film causes significant stresses on the film that, in high temperatures, may result in creep and permanent deformation. (Stance et al, 2007) Tajik, 2008 optimized this process in order to realize free-standing thin film specimens that are free of wrinkle and warpage.…”