Actuator

An actuator comprising:

• a substrate;
• a lower electrode disposed on the substrate;
• an upper electrode opposed to the lower electrode, a distance between the lower electrode and the upper electrode being variable;
• a support having one end fixed to the substrate and one other end connected to the upper electrode and supporting the upper electrode, the support having a higher creep resistance than the upper electrode;
• and
• a driving unit connected between the lower electrode and the upper electrode and feeding a driving voltage applied between the lower electrode and the upper electrode,
• the driving voltage at which the lower electrode and the upper electrode start to come into contact with each other when an absolute value of a potential difference between the lower electrode and the upper electrode is increased being defined as a pull-in voltage,
• a capacitance between the lower electrode and the upper electrode when the pull-in voltage is applied being defined as a pull-in capacitance,
• there existing a first region where a change rate of a capacitance ratio relative to the pull-in capacitance rapidly changes when the absolute value of the potential difference is increased to the pull-in voltage or larger and a second region where the change rate changes more slowly than in the first region, when the absolute value of the potential difference is further increased, and
• the driving unit feeding the driving voltage in the second region.