1. Field of the Invention
The present invention relates to a piezoelectric actuator, a liquid-jetting apparatus, and a method for producing the piezoelectric actuator.
2. Description of the Related Art
Conventionally, for example, the following piezoelectric actuator for an ink-jet head is known as a piezoelectric actuator in which an objective is driven by piezoelectrically deforming a piezoelectric layer by applying an electric field. The piezoelectric actuator is provided on a channel unit (base member) of the ink-jet head provided with a plurality of pressure chambers communicated with a plurality of nozzles respectively. The piezoelectric actuator has a vibration plate which is arranged to cover the plurality of pressure chambers of the channel unit therewith, a piezoelectric layer which is stacked on the vibration plate, and a plurality of individual electrodes (driving electrodes) which are provided opposingly to the plurality of pressure chambers on a surface of the piezoelectric layer. The individual electrode is led to a portion which does not face the pressure chamber, and a contact portion is formed at a forward end portion thereof. The upper surface of the vibration plate functions as a common electrode which is provided commonly with respect to the plurality of individual electrodes.
The plurality of individual electrodes are arranged in two arrays corresponding to the plurality of pressure chambers. The direction, in which the contact portion is led for the individual electrode belonging to one array, is mutually opposite to the direction in which the contact portion is led for the individual electrode belonging to the other array. The electric potential is applied to the individual electrode via a leading electrode led from the individual electrode by applying the electric potential to the contact portion.
When the voltage is applied between the individual electrode and the common electrode, then the electric field is generated at a portion of the piezoelectric layer facing the individual electrode (portion of the piezoelectric layer interposed between the individual electrode and the common electrode, hereinafter referred to as “active portion”), and the portion is piezoelectrically deformed. In this situation, it is a matter of course that the electric field is also generated to cause the piezoelectric deformation in relation to a portion of the piezoelectric layer facing the leading electrode (portion of the piezoelectric layer interposed between the leading electrode and the common electrode, hereinafter referred to as “leading portion”), when the leading electrode is also formed of the same material as that of the individual electrode.
In the piezoelectric actuator for the ink-jet head as described above, for example, when the plurality of individual electrodes are formed at once and/or when the piezoelectric layer, on which the plurality of individual electrodes are formed, is arranged while being positionally deviated with respect to the channel unit, then the plurality of individual electrodes are formed while being positionally deviated in an identical direction in the in-plane direction of the piezoelectric layer with respect to the channel unit in some cases.
Even when the plurality of individual electrodes are arranged while being positionally deviated in the identical direction in the in-plane direction of the piezoelectric layer with respect to the channel unit, the areal sizes of the portions of the plurality of active portions facing the pressure chambers (facing areal sizes of the active portions) are identical with each other. On the other hand, the plurality of leading electrode are led in the opposite directions in relation to each of the arrays. If the directions, in which the plurality of leading electrode are led, are different from each other, the areal sizes of the portions of the leading portions of the piezoelectric layer facing the pressure chambers (facing areal sizes of the leading portions) are different from each other in relation to each of the arrays of the plurality of leading portions. In the following description, the area of the piezoelectric layer facing the pressure chamber, which is included in the active portion or the leading portion, is referred to as “driving area”.
On this assumption, the facing areal sizes of the plurality of active portions of the piezoelectric layer do not mutually disperse. On the contrary, the facing areal sizes of the plurality of leading portions of the piezoelectric layer disperse. As described above, when the active portions are driven, the leading portions, which correspond to the active portions, are also driven. If the facing areal sizes of the plurality of leading portions of the piezoelectric layer mutually disperse, the total amount of the facing areal size of the active portion of the piezoelectric layer and the facing areal size of the leading portion disperses. In other words, all of the driving areas of the piezoelectric layer (active portions and leading portions) disperse, and the piezoelectric deformation amounts disperse in the driving areas of the piezoelectric layer.