This application is the U.S. national phase of International Application No. PCT/CN2017/093064 filed Jul. 15, 2017 which designated the U.S. and the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a piezoelectric device and more particularly to a thin film piezoelectric actuator for MEMS (Micro Electro Mechanical System) membrane structure.

BACKGROUND OF THE INVENTION

Piezoelectric elements are widely used as drive elements and applied in various fields such as MEMS structure inkjet, micro pump, micro mirror and PMUT (Piezo Micromachined Ultrasonic Transducer), because the piezoelectric elements may be deformed when an electrical field is applied.

For example, a vibration plate of an inkjet printing head may constitute a part of a wall of an ink chamber, and the ink chamber may be in communication with a nozzle orifice that ejects ink droplets. In the case that a thin film piezoelectric element is arranged on the vibration plate, the thin film piezoelectric element may be deformed to expand or contract when an electrical field is applied, thereby driving the vibration plate to move and changing the volume of the ink chamber to eject ink droplets through the nozzle orifice.

However, in existing devices with such structure, undesired displacements in the opposite direction at the edge of the chamber are detected. As shown inFIGS. 1A and 1B, since the edge of the vibration plate102is constrained by the chamber forming layer104and thus cannot be displaced, in the case that the thin film piezoelectric element103is deformed to expand or contract when an electrical field is applied, the vibration plate102which constitutes a part of a wall of the chamber101will move upwards or downwards. In such case, during the upward or downward movement, since the vibration plate102is not strong enough to hold the edge of the thin film piezoelectric element103disposed in the center, the edge of the thin film piezoelectric element103can move freely when the thin film piezoelectric element103is deformed to expand or contract, which results in undesired displacements105in the opposite direction at the edge portion of the vibration plate102around the thin film piezoelectric element103, i.e., at the edge portion of the vibration plate102which is not covered by the thin film piezoelectric element103, as shown inFIG. 1C.

Such undesired displacements can affect the reliability of the device, make it difficult to achieve precise control of the change amount of the chamber volume, and disturb the accuracy of both ink jetting position and ink jetting amount. Thus, it is desired to provide a piezoelectric device which can eliminate undesired displacements of the vibration plate in the opposite direction.

SUMMARY OF THE INVENTION

The present invention aims to provide a piezoelectric device, which can efficiently actuate the vibration plate, eliminate undesired displacements of the vibration plate in the opposite direction at the edge of the chamber, and provide higher displacement sensitivity to driving voltage.

To this end, the present invention provides a piezoelectric device, which comprises a pressure chamber forming layer, a vibration plate disposed on and connected with the pressure chamber forming layer to form a pressure chamber, and a piezoelectric element disposed on the vibration plate and used for driving the vibration plate to move and thus changing a volume of the pressure chamber, wherein the piezoelectric element is disposed on the vibration plate in such a manner as to cover a portion of the pressure chamber, the piezoelectric element has two opposite ends respectively extending beyond an edge of the pressure chamber and covering the pressure chamber forming layer.

When an electrical field is applied, the piezoelectric element is deformed to expand or contract, thereby driving the vibration plate to move upwards or downwards. In such case, since two opposite ends of the piezoelectric element cover the pressure chamber forming layer, the two opposite ends of the piezoelectric element and the vibration plate can be efficiently held by the pressure chamber forming layer located below. In this way, when the piezoelectric element is deformed to expand or contract, the two ends of the piezoelectric element have no displacement in the direction opposite to the direction in which the middle portion or main portion of the piezoelectric element is displaced, and the piezoelectric element can be integrally displaced in the same direction, whereby the whole vibration plate can be integrally driven to move upwards or downwards depending on the expansion or contraction deformation of the piezoelectric element. In such case, undesired displacements of the vibration plate in the opposite direction can be eliminated, and the displacement sensitivity can be increased.

Preferably, the pressure chamber may have a length greater than a width thereof, and a connecting line connecting two opposite ends and a width direction of the pressure chamber form an angle greater than zero. Since the movement performance of the whole vibration plate is more of longitudinal feature dominated, in the case that the piezoelectric element is disposed in such a manner that a connecting line connecting two opposite ends thereof and a width direction of the pressure chamber form an angle greater than zero and the two ends respectively extending beyond an edge of the pressure chamber and covering the pressure chamber forming layer can be efficiently held by the pressure chamber forming layer, undesired displacements of the vibration plate in the opposite direction can be better eliminated, and the displacement sensitivity can be increased.

Furthermore, the connecting line connecting two opposite ends and the length direction of the pressure chamber form an angle A less than 20 degrees. With such arrangement, undesired displacements of the vibration plate in the opposite direction may be better eliminated, and the displacement sensitivity can be increased.

Furthermore, the connecting line connecting the two opposite ends is parallel to the length direction of the pressure chamber. Since the movement performance of the whole vibration plate is more of longitudinal feature dominated, in the case that the piezoelectric element is disposed in such a manner that the connecting line connecting the two opposite ends is parallel to the length direction of the pressure chamber and the two ends respectively extending beyond an edge of the pressure chamber and covering the pressure chamber forming layer can be efficiently held by the pressure chamber forming layer, undesired displacements of the vibration plate in the opposite direction are eliminated to a great extent, and the displacement sensitivity can be increased.

In particular, the pressure chamber may be elongated or oval shaped.

Alternatively, the pressure chamber may have a length equal to a width thereof. In particular, the pressure chamber may be a square or a circle.

Preferably, the piezoelectric element may cover a central point of the pressure chamber. In such case, undesired displacements of the vibration plate in the opposite direction may be better eliminated, and higher displacement sensitivity can be provided.

Preferably, the vibration plate may be made from anyone or a combination of more materials selected from Si, SiO2, Si3N4, poly-Si, PZT. Preferably, the vibration plate may form a membrane structure. In this way, the vibration plate has increased vibration efficiency.

Preferably, the piezoelectric element may be a single layer of thin film piezoelectric element, or two or more layers of thin film piezoelectric elements disposed in a laminated manner. Preferably, the thin film piezoelectric element may have a thickness of less than 5 μm. Preferably, the two or more layers of thin film piezoelectric elements may be configured to actuate the vibration plate in the same direction. In this way, with the combination of the two or more layers of thin film piezoelectric elements, the vibration plate has increased vibration efficiency.

Preferably, the piezoelectric element may comprise a piezoelectric layer and electrodes arranged on upper and lower sides of the piezoelectric layer. In other words, the piezoelectric layer and the electrodes are alternately disposed, such that the device can be driven by a drive voltage. Preferably, the piezoelectric element may comprise at least two piezoelectric layers, and any two adjacent piezoelectric layers share the electrode disposed there-between.

Preferably, the piezoelectric element may further have at least one extending portion extending beyond an edge of the pressure chamber and cover the pressure chamber forming layer.

Preferably, the piezoelectric element may further have at least two extending portions oppositely arranged.

Preferably, the pressure chamber may have a length greater than a width thereof, and the extending portion extends in a direction parallel to the width direction of the pressure chamber.

The piezoelectric device of the present invention can be widely applied to MEMS structure inkjet, micro pump, micro mirror, PMUT and the like as the drive element, taking the piezoelectric element as the actuator for driving the vibration plate to displace so as to change the volume of the pressure chamber. The piezoelectric device of the present invention can efficiently actuate the vibration plate, eliminate undesired displacements of the vibration plate in the opposite direction at the edge of the chamber, and provide higher displacement sensitivity to driving voltage.

