Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-07-28
2003-01-07
Nghiem, Michael (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06502928
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an ink jet recording head wherein a piezoelectric element is formed via a diaphragm in a part of each of pressure generating chambers communicating with nozzle orifices for jetting ink drops and ink drops are jetted by displacement of the piezoelectric element, and an ink jet recording apparatus comprising the ink jet recording head.
The following two types of ink jet recording heads, each wherein a part of a pressure generating chamber communicating with a nozzle orifice for jetting an ink drop is formed of a diaphragm and the diaphragm is deformed by a piezoelectric element for pressurizing ink in the pressure generating chamber for jetting an ink drop through the nozzle orifice, are commercially practical: One uses a piezoelectric actuator in a vertical vibration mode in which the piezoelectric element is expanded and contracted axially and the other uses a piezoelectric actuator in a deflection vibration mode.
With the former, the volume of the pressure generating chamber can be changed by abutting an end face of the piezoelectric element against the diaphragm and a head appropriate for high-density printing can be manufactured, but a difficult step of dividing the piezoelectric element like comb teeth matching the arrangement pitch of the nozzle orifices and work of positioning and fixing the piezoelectric element divisions in the pressure generating chambers are required and the manufacturing process is complicated.
In contrast, with the latter, the piezoelectric element can be created and attached to the diaphragm by executing a comparatively simple process of putting a green sheet of a piezoelectric material matching the form of the pressure generating chamber and baking it, but a reasonable area is required because deflection vibration is used; high-density arrangement is difficult to make.
On the other hand, to solve the problem of the latter recording head, Japanese Patent Publication No. 5-286131A proposes an art wherein an even piezoelectric material layer is formed over the entire surface of a diaphragm according to a film formation technique and is divided to a form corresponding to a pressure generating chamber according to a lithography technique for forming a piezoelectric element separately for each pressure generating chamber.
This eliminates the need for work of putting the piezoelectric element on the diaphragm and the piezoelectric element can be created by the lithography method, an accurate and simple technique. In addition, the piezoelectric element can be thinned and high-speed drive is enabled.
In this case, with the piezoelectric material layer provided on the whole surface of the diaphragm, at least only upper electrodes are provided in a one-to-one correspondence with the pressure generating chambers, whereby the piezoelectric element corresponding to each pressure generating chamber can be driven. However, it is desirable that each active part of piezoelectric element consisting of a piezoelectric layer and upper electrode is formed so as not to be beyond the pressure generating chamber because of problems of the displacement amount per unit drive voltage and stress placed on the piezoelectric layer in the portion straddling the portion facing the pressure generating chamber and the outside thereof.
Then, a structure is proposed wherein the piezoelectric element corresponding to each pressure generating chamber is covered with an insulation layer and the insulation layer is formed with windows each for forming a connection part to a lead electrode for supplying a voltage for driving each piezoelectric element, which will be hereinafter referred to as contact holes, in a one-to-one correspondence with the pressure generating chambers, and the connection part of each piezoelectric element and lead electrode is formed in the contact hole.
However, in the structure wherein the contact holes for connecting the upper electrodes and the lead electrodes are made, the whole film of the portion where the contact hole is made becomes thick and the displacement characteristic is degraded.
With the ink jet recording head as described above, a structure wherein the diaphragm in the portion corresponding to both sides of the piezoelectric element is thinned is proposed to improve the displacement efficiency provided by drive of the piezoelectric element. However, if large displacement is thus provided, particularly the tendency of destruction of a crack, etc., to easily occur in the proximity of the contact hole is promoted.
Further, the problems easily occur particularly if a piezoelectric material layer is formed according to a film formation technique, because the piezoelectric material layer formed according to the film formation technique is very thin and thus has low rigidity as compared with a layer where a piezoelectric element is mounted.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ink jet recording head for preventing destruction of a piezoelectric layer in the boundary between a pressure generating chamber and a peripheral wall, and an ink jet recording apparatus comprising the ink jet recording head.
In order to achieve the above object, according to a first aspect of the present invention, there is provided an ink jet recording head comprising: pressure generating chambers communicating with associated nozzle orifices; and piezoelectric elements provided in a one-to-one correspondence with the pressure generating chambers, each of the piezoelectric elements comprising a lower electrode provided in an area corresponding to the pressure generating chamber via an insulating layer, a piezoelectric layer provided on the lower electrode, and an upper electrode provided on the piezoelectric layer, each active area of the piezoelectric elements provided in an area facing the pressure generating chamber, and each inactive part of the piezoelectric elements not to be driven even having the piezoelectric layer continued from the active part.
In the first aspect, when the active part of piezoelectric element is driven, displacement in the boundary between the pressure generating chamber and the peripheral wall is suppressed by the inactive part of piezoelectric element and peeling of the piezoelectric film, occurrence of a crack, and the like are prevented.
In a second aspect of the present invention, crystal directions of the piezoelectric layer are oriented.
In the second aspect, the piezoelectric layer is formed in a thin film process, so that the crystal directions are oriented.
In a third aspect of the present invention, the piezoelectric layer has a columnar crystalline structure.
In the third aspect, the piezoelectric layer is formed in a thin film process, so that piezoelectric layer has a columnar crystalline structure.
In a fourth aspect of the present invention, the inactive part is extended from the inside of the area facing the pressure generating chamber to the outside of the area.
In the fourth aspect, the upper electrode of the active part or the lead electrode can be extended to the outside of the area facing the pressure generating chamber without forming a contact hole; wiring can be formed comparatively easily.
In a fifth aspect of the present invention, in the ink jet recording head in any of the first to fourth aspects, the lower electrode is removed to form the inactive part, and either the upper electrode or a lead electrode connected thereto is extended to the top of a peripheral wall of the pressure generating chamber through the inactive part.
In a sixth aspect of the present invention, in the ink jet recording head in any of the first to fourth aspects, an end portion of the upper electrode is positioned inside from an end portion of the lower electrode to be an end portion of the active part. The piezoelectric layer is provided on the lower electrode projecting to the outside from the end portion of the upper electrode, forming the inactive part, and is also provided outside the end portion of the lower electrode.
In the sixth aspe
Miyata Yoshinao
Moriya Souichi
Sakai Shinri
Shimada Masato
Feggins K.
Nghiem Michael
Seiko Epson Corporation
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