Isolating the negative stiffness region of a buckled Si/SiO2 membrane

Negative stiffness can provide a method of altering the stiffness of a device without changing its geometry. The silicon/ silicon dioxide (Si/SiO2) membrane presented in this research utilizes buckling resulting from compressive residual stress. A transversely actuated buckled membrane displays properties similar to a linear regressive spring, which include a positive and negative stiffness region. Cantilever beams were used to restrict the outward displacement of the membrane and force it to actuate only in its negative stiffness region. Analytical equations were utilized to estimate the amount of outward deflection by the membrane and to estimate the amount of reduced deflection required for the device to display only negative stiffness characteristics. Devices were tested using a force sensor actuated by a piezo controller. Interferometric imaging confirmed the cantilevers ability to reduce the buckling displacement in the membrane up to 30%.