Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-09-14
2002-11-12
Barlow, John (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06478412
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a piezoelectric thin film element including a piezoelectric thin film having a specific shape for use in a micro pump, an ink jet recording head, a micro mirror device, a micro mechanical device, a micro machine, an ultrasonic vibrator or the like. Furthermore, the present invention relates to a process for producing the piezoelectric thin film element including the piezoelectric thin film having the specific shape by the use of a photosensitive composition capable of forming a ferroelectric thin film. Moreover, the present invention relates to an ink jet recording head having the piezoelectric thin film element.
The present invention relates to a piezoelectric thin film element of a bending mode called a bimorph or a unimorph.
In a piezoelectric thin film element of a bending mode, a lower electrode, a piezoelectric thin film and an upper electrode are laminated in this order on a substrate. Although the piezoelectric thin film is to be expanded or contracted in a direction parallel to the substrate with the application of a voltage, it is restricted by the substrate on a side of the lower electrode, to be thus flexed in a direction perpendicular to the substrate in the same manner as a bimetal.
Such a piezoelectric thin film element of a bending mode is applied to various kinds of products. The piezoelectric thin film element according to the present invention is an element suitable for, in particular, an ink jet recording head.
The ink jet recording head generally comprises ink chambers, nozzles communicating with the ink chambers and ink supplying means communicating with the ink chambers, wherein a capacity of the ink chamber is varied by the use of a piezoelectric element so that ink is discharged from the nozzle under pressure generated at that time.
BACKGROUND ART
In order to efficiently produce a fine piezoelectric thin film element, a piezoelectric thin film for a piezoelectric thin film element has been recently formed by applying piezoelectric paste including a starting material of ferroelectric oxide onto a substrate by a thick film method such as a screen printing, followed by firing, as disclosed in, for example, Japanese Laid-open Patent Publication No. 7-60960/1995. A method typified by the screen printing is advantageous in very efficient production of the piezoelectric thin film, but at the same time, involves some deficiencies.
One of the deficiencies is that there easily occurs variations in shape of an obtained piezoelectric thin film.
FIG. 6
is a sectional view schematically showing a typical piezoelectric thin film element formed by a screen printing. In
FIG. 6
, a lower electrode (
12
), a piezoelectric thin film (
13
) and an upper electrode (
14
) are laminated in this order on a substrate (
15
). The upper surface of the piezoelectric thin film (
13
) is curved, and therefore, the bottom surface of the thin film (
13
) is not parallel to the upper surface thereof. Furthermore, the piezoelectric thin film (
13
) is thick at the center thereof but thin at the periphery thereof. The cross-sectional shape of the piezoelectric thin film (
13
) is ark-shaped, and therefore, each of the angles defined between a lower side and both lateral sides is acute. The shape of this piezoelectric thin film (
13
) depends on various conditions of an applying process, a firing process and the like, thereby variations in the shape are liable to occur. Therefore, variations in displacement characteristics are liable to occur even in elements of the same design.
Another deficiency is non-uniformity caused by easy concentration of an electric field density at the periphery of the piezoelectric thin film where an electrode interval is narrow since an distance between the upper electrode (
14
) and the lower electrode (
12
) is not fixed in the case where a voltage is applied to the piezoelectric thin film element, in the piezoelectric thin film having the sectional shape shown in FIG.
6
.
Furthermore, a region contributory to a displacement of an actuator is limited, so that the displacement cannot be increased in the piezoelectric thin film having the cross-sectional shape shown in FIG.
6
. That is, a region effective in the displacement of the actuator is a portion sandwiched between the upper electrode (
14
) and the bottom surface of the piezoelectric thin film (
13
) out of the entire area of the thin film. In the element shown in
FIG. 6
, only a portion considerably narrower than the bottom surface of the piezoelectric thin film (
13
) is the region effective in the displacement. If the area of the upper electrode (
14
) is enlarged to widen the region effective in the displacement, short-circuiting is liable to occur between the lower electrode (
12
) and the upper electrode (
14
). In view of this, it is necessary to make the area of the upper electrode (
14
) narrower than that of the upper surface of the piezoelectric thin film (
13
) so as to allow a considerable portion having no electrode to remain at the peripheral edge portion at the upper surface of the piezoelectric thin film (
13
). Consequently, it is impossible to effectively use the entire region of the piezoelectric thin film, thereby making it difficult to provide sufficient element characteristics.
In this manner, in the case where the piezoelectric thin film produced by the screen printing is used as an actuator for an ink jet recording head, there arises a problem that it is impossible to provide an ink jet recording head having nozzles arrayed at a high density since ink cannot be accurately discharged caused by great variation in displacement or an insufficient displacement due to a non-uniform electric field (i.e., poor conversion efficiency), as described above.
In the meantime,
FIG. 7
is a sectional view schematically showing a conventional piezoelectric thin film element which has been publicly known. In
FIG. 7
, a lower electrode (
22
), a piezoelectric thin film (
23
) and an upper electrode (
24
) are laminated in this order on a substrate (
25
). The cross-sectional shape of the thin film (
23
) is rectangular, the thickness thereof is fixed and the distance between the upper electrode (
24
) and the lower electrode (
22
) is fixed, thus obtaining a uniform electric field. In order to enlarge a region effective in displacement, it is preferable that the upper electrode (
24
) should have a larger area. However, like the element shown in
FIG. 6
, it is necessary to make the area of the upper electrode (
24
) narrower than that of the upper surface (i.e., the area of the bottom surface) of the piezoelectric thin film (
23
) so as to avoid any short-circuiting between the lower electrode (
22
) and the upper electrode (
24
). That is, it is impossible to effectively use the entire area of the bottom surface of the piezoelectric thin film. Thus, there arises a problem that it is impossible to provide an ink jet recording head having nozzles arrayed at a high density.
DISCLOSURE OF THE INVENTION
Objects of the Invention
Accordingly, an object of the present invention is to solve the above-described problems in the prior art and to provide a piezoelectric thin film element including a piezoelectric thin film having a specific shape. Furthermore, another object of the present invention is to provide a process for producing the piezoelectric thin film element including the piezoelectric thin film having the specific shape according to the present invention by the use of a photosensitive composition capable of forming a ferroelectric thin film. Moreover, a further object of the present invention is to provide an ink jet recording head provided with the piezoelectric thin film element having the specific shape according to the present invention.
SUMMARY OF THE INVENTION
As a result of earnest study, the present inventor has accomplished a piezoelectric thin film having a specific sectional shape according to the present invention. A piezoelectric thin film element according to the present invention is featured by a greater displacement and
Barlow John
Feggins K.
Kansai Research Institute
Rader & Fishman & Grauer, PLLC
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