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

Abstract

An electrostatic actuator, a liquid droplet ejection head, and a liquid droplet ejection device which have a good response and are driven by a small drive voltage includes a vibration plate as a sheet-shaped movable electrode and an individual electrode acting as a rectangular fixed electrode confronting the vibration plate and having stepped portions or an inclined portion in a long side direction with respect to the vibration plate, wherein the thickness of the vibration plate is reduced according to an order by which the vibration plate is made to abut against the individual electrode by electrostatic attracting force generated between the vibration plate and the individual electrode. Methods of manufacturing the above devices are also disclosed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a liquid droplet ejection head according to an embodiment 1 by exploding it;

FIG. 2 is a sectional view of the liquid droplet ejection head;

FIG. 3 is a longitudinal sectional view showing the relation among a recessed portion 11, an individual electrode 12A, and a vibration plate 22;

Parts A to C of FIG. 4 are views (1) explaining the relation between a drive voltage and a gap length;

Parts D to G of FIG. 5 are views (2) explaining the relation between the drive voltage and the gap length;

FIG. 6 is a graph showing an example of the relation between electrostatic attracting force and restoring force with respect to displacement;

Parts A to I of FIG. 7 are views showing an example of steps of manufacturing an electrode substrate 10;

Parts A to I of FIG. 8 are views showing steps of forming a boron diffused layer according to the embodiment 1;

Parts A to F of FIG. 9 are views showing steps of manufacturing a liquid droplet ejection head;

Parts A to G of FIG. 10 are views showing steps of forming a boron diffused layer according to an embodiment 2;

FIG. 11 is an outside appearance view of a liquid droplet ejection device using the liquid droplet ejection head;

FIG. 12 is a view showing an example of main means constituting the liquid droplet ejection device; and

FIG. 13 is a view showing an optical switch using an electrostatic actuator of the present invention.

Claims

1. An electrostatic actuator comprising a sheet-shaped movable electrode and a rectangular fixed electrode confronting the movable electrode and formed to have stepped portions in a long side direction with respect to the movable electrode, wherein the thickness of the movable electrode is reduced according to an order in which the movable electrode is made to abut against the fixed electrode by electrostatic attracting force generated between the movable electrode and the fixed electrode.

2. 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.

3. The electrostatic actuator according to claim 1, wherein the movable electrode is formed of stepped portions as many as those of the fixed electrode.

4. A liquid droplet ejection head comprising the electrostatic actuator according to claim 1, wherein a liquid is pressurized by the movable electrode and ejected from nozzles as droplets.

5. A liquid droplet ejection device on which the liquid droplet ejection head according to claim 4 is mounted.

6. An electrostatic driving device on which the electrostatic actuator according to claim 1 is mounted.

7. 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; anda step of forming the movable electrode by wet etching the silicon substrate while remaining only the boron diffused layer.

8. The method of manufacturing an electrostatic actuator according to claim 7, wherein when boron is diffused, a boron diffused layer having a different depth is formed by sequentially increasing selected positions from a position at which a boron diffused layer is formed thickest.

9. The method of manufacturing an electrostatic actuator according to claim 7, wherein when boron is diffused, a boron diffused layer is formed at one time at a selected position.

10. The method of manufacturing an electrostatic actuator according to claim 7, wherein the electrode substrate is formed by carrying out: (1) a step of forming an etching mask on a substrate acting as an electrode substrate;(2) a step of forming a rectangular opening portion having short sides and long sides by etching the etching mask;(3) a step of forming a rectangular recessed portion having short sides and long sides to a portion confronting the opening portion of the etching mask by etching the substrate;(4) a step of forming an opening portion longer than the previous opening portion in a long side direction by expanding the opening portion at both edges in the long side direction by etching the etching mask;(5) a step of forming a stepwise recessed portion to a portion of the substrate confronting the longer opening portion of the mask, by etching the substrate;(6) a step of forming a recessed portion having a desired number of stepped portions to the substrate by carrying out the steps (4) and (5) once or a plurality of times; and (7) a step of forming the fixed electrode so that its thickness is made uniform in the recessed portion.

11. A method of manufacturing a liquid droplet ejection head by applying the method of manufacturing an electrostatic actuator according to claim 7.

12. A method of manufacturing a liquid droplet ejection device by applying the method of manufacturing a liquid droplet ejection head according to claim 11.

13. A method of manufacturing an electrostatically driven device by applying the method of manufacturing an electrostatic actuator according to claim 7.

14. The electrostatic actuator according to claim 2, wherein the movable electrode is formed of stepped portions as many as those of the fixed electrode.