Micro-actuator with extended analog deflection at low drive voltage

Abstract

Electrostatic Micro-actuators are being increasingly used for a wide variety of applications such as spatial light modulators, scanning mirrors, optical cross connects, micro-valves, and others. Usually the electrical forces operate in one direction and are balanced by a mechanical spring. The resulting deflection is then either defined by a mechanical stop, or it is only a meta-stable equilibrium position: at an additional external force or deflection it will snap to a different position, frequently again defined by a mechanical stop. This issue is well known and is often called 'pull-in'. In the often used parallel-plate capacitor actuator, the instability already begins at a deflection of only on third of the original capacitor plate separation. For safety reasons and due to the steep response-curve one can only use an even smaller fraction of the mechanically possible movement. This means, that the gap below the actuator has to be designed very much larger than the required maximum deflection. To get the pre-described force and deflection, a much higher voltage is needed than for potential smaller gap widths. The useable range of deflection for many types of micro-actuators can be extended without the penalty of large drive voltage or low shock resistivity, by employing springs with steeper-than-linear restoring force. Alternatively, the voltage needed for a given range of deflection may be reduced. This paper shows the benefits and how to design and dimension these types of springs.

Heterogeneous 3D integration of hidden hinge micromirror arrays consisting of two layers of monocrystalline silicon

“…The unique feature of this flexure design is a large strain that is created in the material during operation. With increasing displacement, the flexure behaves less like a cantilever spring but increasingly behaves like a string with nonlinear displacement-force characteristics [38].…”