Postbuckled micromachined square membranes under differential pressure

We report quantitative results on the load-deflection response of compressively prestressed square membranes under differential pressure. The membranes consist of 1.9 ?m thick silicon nitride films with a compressive prestrain ?0 = ?(1.6 ? 0.1) ? 10?3. For these square membranes we observed a new symmetry transition of the deflection profile from a state without reflection symmetries at small loads to a state with reflection symmetries at sufficiently large loads. The load-deflection response was modeled by finite element simulations covering a wide range of prestrains ?0 and pressures using various geometries. From the symmetry transition process, Young's modulus E = (150 ? 7) GPa of the membrane material was extracted.