A layer of TiNi is sputter-deposited on this, then heat treated, and patterned with wet etchants. Finally, the wafer is separated into dies, each containing a single actuator. The result is a frame of silicon with TiNi microribbon supporting an island of silicon. When this island is displaced out of plane, the TiNi ribbon is stretched linearly. The fabrication processes developed for the pneumatic valve are not adaptable to further miniaturization.
Processing requires etching through the wafer.
Anisotropic etchants proceed at an angle of about one radian, so it is difficult to place microribbons arbitrarily close together. Therefore, devices smaller than the thickness of a wafer cannot readily be fabricated by current processing steps, and etching through the wafer makes it weak and subject to breakage. These limitations are being addressed by surface micromachining techniques. We have evolved wet-etch processes by which a void is created in he substrate directly under the TiNi microribbon without damaging the TiNi. A group of actuators each 40 microns wide and 1000 microns long has been released in this manner.