Actuators

A wide range of actuators are designed and fabricated at the Institute MNT, including actuators for handling small objects, for gas flow switches, and for modulating electrical signals. Two actuators are demonstrated as examples below. 

Capacitive comb drive

The capacitive comb drive is one of the most commonly used actuators in microsystems. 

Principle

The comb drive consists of two electrodes, one of which is suspended on springs. In this example, each electrode has 600 fingers structured in the form of a comb. The two combs are interdigitated.  

When a potential is applied between the two electrodes, the movable electrode will be pulled and deflected as a result of the Coulomb forces in action. 

Typical Values

  • Fingers per electrode:    ca. 600
  • Finger width:                 16 µm
  • Finger length:                300 µm
  • Finger height:                300 µm
  • Force at 50 V:                1 mN
  • Deflection at 50 V:         30 µm
Comb drive as fabricated
Close-up image of a finger

Thermal actuator

Silicon thermal actuators fabricated through microsystems technology are exceptionally well suited to movements in-plane movements. Depending on the geometry and the maximum allowed temperature, deflections in the 10 to 40 μm are possible. Forces of a few mN can be reached in this way. 

Principle

The actuator is based on a double-clamped structure with legs, through which heat can be transferred. Heating up the legs leads to thermal expansion of the material, which is translated into a lateral movement using an appropriate design strategy. 

A good thermal contact to a heat sink and decoupling structures are the main limiting factors to locally reaching very high temperatures on the actuator. 

Typical Vaues

  • Heating current:                       1 … 100 mA
  • Electric potential:                      1 … 10 V
  • Maximum local temperature:     120 … 300°C
  • Length of the legs:                   1 … 3 mm
  • Maximum force:                         1 … 5 mN
  • Maximum deflection:                 10 … 40 µm
FEM simulation
SEM image