Solving stiction in MEMs devices


Microelectromechanical devices were supposed to change the world, so where are they?

A few designs have leaked out, such as the accelerometers in air bags. But most have remained stubbornly, and literally, stuck in the lab.

One of the troubling secrets about MEMs is that many designs simply don’t work because their moving parts become stuck fast and refuse to budge.

Engineers call this “stiction”: a vaguely defined force that affects small parts but not large ones (where inertia plays a greater role in overcoming these forces). Stiction is thought to be caused variously by Van der Waals forces, electrostatic forces, hydrogen bondng and even the Casimir force, perhaps in combination. That’s why it’s so hard to avoid.

Now Raul Esquivel-Sirvent and a buddy at the Universidad Nacional Autonoma de Mexico in Mexico City, have a potential solution based on the acoustic Casimir force, an acoustic analogue of the more famous quantum Casimir force which was discovered 10 years ago by Andres Larraza, then at the Naval Postrgraduate School in Monterey.

Here’s the idea: place a couple of parallel plates close together and blast them with sound waves of a specific frequency range. If the waves are larger than the gap between the plates, they will tend to push them together but if they are smaller, they will squeeze into the gap and tend to push them apart. So changing the wavelength or the distance between the plates switches the direction of the force.

That could be useful for microswitches in MEMs devices, says Esquivel-Sirvent. But more interestingly, it could also be used to separate microcomponents that have become stuck together. Perhaps the promise of MEMs will be realised at last.

Ref: Pull-in Control in Microswitches Using Acoustic Casimir Forces

One Response to “Solving stiction in MEMs devices”

  1. nanoqed says:

    Dear Xivr:

    Sorry to disapoint you, but there is no Casimir force !!!

    In 1947, Casimir after consultation with Bohr, began a folly that has been going on now for over 50 years.

    If Casimir would have conserved EM energy betweeen the plates he would have shown the EM radiation is always constant as the gap changes dimensions, and therefore the force is zero because the gradient of energy with respect to distance vanishes.

    You can think of the plates emitting thermal radiation that is altered because half-wavelengths greater the gap L are excluded from the gap. But as you decrease the gap, the EM energy is conserved, so the frequency simply increases.

    The forces being measured are electrostatic attractive forces caused as the frequency of EM radiation in the UV produces electrons by photolysis, i.e., positive charge is produced in one plate as electrons are emitted and move to the other plate.

    I call this QED induced EM radiation.

    Check out my homepage at link “natural electrification”


    PS: If you bathe the plates in acoustic radiation, you will find an attractive electrostatics force. But the Casimir force is zero.