Effect of clamping conditions and built-in stresses on the thermopneumatic deflection of SiO2/Si membranes with various geometries

Built-in stresses are known to induce deflections in microstructures such as composite membranes. The thermoelastic behaviour of large square SiO 2 /Si membranes with a side length from 3 to 7.5 mm, a Si thickness in the [7.7–50] μm range and a SiO 2 thickness up to 1.5 μm, was studied by optical profilometry. A very satisfactory agreement within 10% has been found between the experimental and the simulated deflections of prestressed SiO 2 /Si membranes. However, clamping conditions have been found to play a major role in built-in stress relaxation. This tendency was confirmed by Finite Element Modelling. Oxidized (up to 1.5 μm) and bare Si membranes with thicknesses from 7.7 to 50 μm were studied under pressure in the [0–1] bar range. We observed that the membrane stiffness is affected by the oxide depending on SiO 2 /Si thickness ratio. Finally, F.E.M. results are in good agreement for various membrane geometries, and the interest of this tool for the design of packaging structures is shown.