The current devices are fabricated by deposition of titanium-nickel SMA film on silicon substrates, which are then micromachined using MEMS photolithography and selective etching techniques. Microribbons of TiNi have been produced, demonstrating repeated recovery of 3 percent strain under 30 ksi stress. Intrinsic materials properties are equal to or superior to those of bulk Nitinol. For multiple valve arrays on a single substrate, this requires that at least one of the dimensions be less than one millimeter. Many applications require time constants less than 100 milliseconds.
Many applications demand a lifetime of at least a million cycles.
This is important because heat is transferred to the surrounding medium. Low average power can be achieved the duty cycle is small or if a bistable actuator is used. With feedback control, it is highly desirable that a valve be capable of partial opening. Our current valves are not microvalves, but 'millivalves' having dimensions in the 0.1 to 10 mm size range. These valves are practical and are used as components in evolving integrated systems.