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Spring suspended corrugated membranes

A spring suspended membrane (SSM) is essential for many devices based on micro-electro-mechanics (MEM). The difficulty in fabricating SSMs has been the stress and the stress gradient created in the film during its formation. SSMs are different from membranes stretched over a cavity, where a small tensile stress in the film is sufficient to hold the membrane flat over the cavity. Since the membranes in SSMs are free, the relaxation of the stress causes membrane bending and distortion. It is possible to minimize the net stress created in the film by optimizing the film deposition conditions. Unfortunately it is hard to control the gradient in the stress through the thickness of the film. We have developed a general concept for stiffening the membranes in an SSM configuration by film corrugation. In this concept the film is sputtered onto a corrugated sacrificial layer. The film surface follows the corrugation of the sacrificial layer. After the SSM structure is shaped the sacrificial layer is removed to yield a corrugated stiff membrane. To demonstrate the corrugated film concept we have characterized and fabricated 0.3 mu m to 1 mu m thick TiW SSMs, in fixed-fixed and fixed-free configurations.