Electrostatic actuator, liquid droplet ejection head, liquid droplet ejection device and electrostatic driving device as well as methods of manufacturing them

An electrostatic actuator comprising a sheet-shaped movable electrode and a rectangular fixed electrode having stepped portions or an inclined portion formed thereto in a long side direction such that a gap formed by confronting the movable electrode is increased from the edges thereof toward the central portion thereof, the fixed electrode generating electrostatic force in confrontation with the movable electrode, wherein the thickness of the movable electrode is reduced from the edges in the long side direction toward the central portion.

A method of manufacturing an electrostatic actuator comprising:

• a step of forming a boron diffused layer acting as a movable electrode, which is displaced by electrostatic attraction force between the movable electrode and a rectangular fixed electrode formed stepwise or to have an inclined surface in a long side direction, by selectively diffusing boron into a silicon substrate while changing a depth of diffusion depending on a position so that the depth of diffusion is thinned as the width of a gap, which is formed when the movable electrode is caused to confront the fixed electrode, is increased;
• and
• a step of forming the movable electrode by wet etching the silicon substrate while remaining only the boron diffused layer.