Method and System for Capillary Force Actuators

For micro-electromechanical systems (MEMS) and bio-MEMS (e.g., micro total analysis systems, or MTAS), a variety of force actuation methods have been used to either move structures or to induce stress in stationary structures, including electromagnetic, electrostatic, pneumatic, thermal, piezoelectric, magnetostrictive, among others. Each of these actuation technologies has advantages, disadvantages and trade-offs in terms of performance metrics such as force capability, total displacement, actuation bandwidth, ease of integration to particular applications, and manufacturability. Electrostatic actuation is the most commonly employed technology in commercial applications with actuation forces produced typically within the lateral plane of the lithographically fabricated device. Electrostatic actuation is also employed to tilt objects about a pivot in some applications, notably mirrors in Texas Instruments' Digital Light Processor chip.

The present invention is a Capillary Force Actuator (CFA), which employs the capillary force of a conducting liquid bridge between surfaces to aid in applying a force to those surfaces. The CFA has several significant advantages in comparison to other technologies:

1. The force capability is much greater than (10−100 times) that of a similarly sized electrostatic actuator when voltage levels used are restricted to those commonly employed in integrated circuits;
2. Significantly lower power consumption than thermal actuators;
3. The total movement allowable is greater than that typically achieved with electrostatic or piezoelectric actuators employed in MEMS;
4. Out-of-plane forces can be easily achieved. Many optical and microfluidic applications require forces normal to the device plane; however, this is difficult to achieve with electrostatic actuators that have significant force capability;
5. No mechanical wear occurs unlike in some MEMS actuation technologies, such as scratch actuators;
6. No side snap instability, unlike comb drives, allowing greater achievable stroke.

CFAs provide a new means to create forces for microscale devices, either to provide movement to a part or to apply stress to a structure. As such they are useful for a variety of applications including miniature gratings or switches in micro-optoelectromechanical systems (MOEMS), pumps and actuated valves in Lab-on-a-Chip devices, miniature actuators within medical devices such as catheters, variable capacitances and inductances for telecommunication, and microactuators for hard disk drives.