Class I: accelerometers, pressure sensors, inkjet print heads, and strain gauges
Failure mechanism description: unknown to fail due to operation. Particulate contamination can and typically will induce failure. Particles can be difficult to detect because they may not electrically interfere with the operation of a device. Particulate contamination may serve to mechanically obstruct the device while its electrical integrity is maintained.
Class II: gyroscopes, comb drives, resonator, and filters
Failure mechanism description: these devices have intentionally designed moveable parts that interact with the rest of the device to perform a given function, they are susceptible to fatigue, fracture, or particulate contamination.
Class III: relays and valves
Failure mechanism description: MEMS devices with impacting surfaces have the potential to create debris, fracture components, induce cracks, and so forth. Impact failures are very dependent upon the force exerted on the opposite MEMS structure.
Class IV: shutters, scanners, and optical switches
Failure mechanism description: these devices have moving, impacting structures with the addition of rubbing surfaces. Rubbing creates friction and often will result in the creation of wear material or debris. The formation of this material may result in several different failure mechanisms. These are failure by particle contamination binding the device, particles causing third body wear changing the motion tolerance, particulate contamination preventing or obstructing motion, and adhesion of rubbing or contacting surfaces. The mechanism for wear may depend on the temperatures reached during rubbing.
