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The silicon nitride membrane is the structural layer, the chromium hinge is the stress layer, and the silicon substrate is the release layer. The fold angle of each device is proportional to the length of the chromium hinge. Data from the pictures are listed as (hinge length, fold angle): (a) , 20°, (b) , 45°, (c) , 70°, and (d) , 90°. The width of the membranes is in (a) and in (b)–(d). The length is in (a), in (b) and (c), and in (d).
(a) Each of the four hinges is long and has folded to 45°. The total fold angle is 180°. The entire membrane is long and wide. (b) A single fold to almost 180°. The hinge is long. (c) A partially folded corner cube structure. The membranes are folded to approximately 60°.
A membrane folded to 45° with a grating patterned in the center. The fold angle was measured within the scanning electron microscope by rotating the membrane parallel to the electron beam. The grating period is 200 nm and it is etched 80 nm into the silicon nitride membrane. The bending radius of the hinge was .
Three identical hinges ( long) curled to approximately 120° to form this triangular shape. The lengths of the two folded faces of the triangle are and they are both patterned with 200 nm period gratings in the circular regions. The bending radius was .
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