This invention discloses a configuration of thin-film membrane. This
thin-film membrane is freestanding, movable, and made of multiple layers
of different materials such as silicon nitride, polycrystalline silicon or
the combination of these two. This thin-film membrane can be actuated by
external controlling forces such as electrostatic force. This thin-film
membrane consists of odd number of layers, e.g., 1 layer, 3 layers, 5
layers, . . . , etc. Moreover, the layer profile of this membrane is
symmetric, e.g., the bottommost layer is made to be identical to the
topmost layer, the next bottommost layer is made to be identical to the
next topmost layer, so on and so forth.
