Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-05-25
2003-04-29
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06554407
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink jet head, a method for producing an ink jet head, and an ink jet type recording apparatus.
BACKGROUND ART
In the prior art, ink jet type recording apparatuses for recording information by utilizing a piezoelectric effect of a piezoelectric element have been used as printers, word processors, facsimiles, and the like. Typically, an ink jet head for use in a recording apparatus of this type includes a plurality of pressure chambers containing ink, a plurality of nozzles communicated to the pressure chambers, respectively, and an actuator for applying a pressure on the ink in the pressure chamber so as to discharge ink through the nozzle. Some of such actuators are made of a large number of thin films layered together, as illustrated in
FIG. 26
, for example.
In an ink jet head as described above, a head body
101
is provided with a plurality of pressure chamber depressions
102
arranged in the direction indicated by X
1
in the figure. A vibration plate
104
is provided on the head body
101
so as to cover the plurality of pressure chamber depressions
102
, so that the vibration plate
104
and the pressure chamber depression
102
of the head body
101
define a pressure chamber
103
, A piezoelectric element
105
made of PZT is provided on the vibration plate
104
so as to correspond to each pressure chamber
103
, and a separate electrode
106
made of Pt (platinum) is provided on the piezoelectric element
105
. Note that the vibration plate
104
is made of Cr (chromium) and functions also as a common electrode of the piezoelectric element
105
. The vibration plate
104
, the piezoelectric element
105
and the separate electrode
106
together form an actuator. When discharging ink, a voltage is applied between the separate electrode
106
and the vibration plate
104
as a common electrode so as to expand/contract the piezoelectric element
105
. Thus, the vibration plate
104
fixed to the piezoelectric element
105
undergoes flexural deformation so as to pressurize the ink in the pressure chamber
103
, thereby discharging the ink through a nozzle (not shown).
In recent years, the thickness of the piezoelectric element
105
has been reduced as the ink jet heads have been downsized. However, as the thickness of the piezoelectric element
105
is reduced, the voltage endurance is reduced. Thus, the reduction in the thickness increases the possibility of dielectric breakdown occurring upon application of a voltage. Dielectric breakdown occurring in the piezoelectric element
105
not only reduces the ink discharging performance, but may also leads to leakage of the ink in the pressure chamber
103
to the outside if the degree of dielectric breakdown is high. In view of this, a technique for preventing dielectric breakdown of the piezoelectric element
105
has been longed for in order to improve the reliability of the ink jet head.
As one of such techniques, there is a technique of improving the voltage endurance of the piezoelectric element itself by modifying the crystal structure of a piezoelectric material, as disclosed in Japanese Laid-Open Patent Publication No. 10-217458.
However, during the formation of the piezoelectric element in the process of producing an ink jet head, a defective portion
107
may occur in the piezoelectric element
105
as illustrated in
FIG. 27
due to impurities in the production apparatus being introduced into the piezoelectric element or due to the influence of the thermal stress of the piezoelectric element. Therefore, even when the voltage endurance of the material of the piezoelectric element
105
itself is high, the presence of such a defective portion
107
makes the piezoelectric element
105
structurally liable to dielectric breakdown. Specifically, in a case where the defective portion
107
is conductive (e.g., where conductive impurities are introduced), the portion of the piezoelectric element
105
corresponding to the defective portion
107
becomes a portion with a locally reduced thickness, thereby significantly reducing the voltage endurance. Moreover, even in a case where the defective portion
107
is insulative, the piezoelectric element
105
has a non-uniform thickness at the defective portion
107
, whereby an electric field localization is likely to occur upon application of a voltage. Therefore, dielectric breakdown is likely to occur in this portion. Particularly, as the thickness of the piezoelectric element is more reduced, the proportion of the defective portion with respect to the piezoelectric element increases. Therefore, the possibility of dielectric breakdown in the piezoelectric element becomes even higher as the thickness of the piezoelectric element is reduced.
Thus, a new technique of preventing the dielectric breakdown of the piezoelectric element in view of the defect which may occur during the formation of the piezoelectric element has been longed for. Moreover, in order to prevent the dielectric breakdown of the piezoelectric element, a new technique of detecting a defect in the piezoelectric element and a new technique of improving the voltage endurance of the piezoelectric element have been longed for.
The present invention has been made in view of the above, and has an object to provide an ink jet head, an ink jet type recording apparatus and a method for producing the same in which the voltage endurance of the piezoelectric element is not reduced even when a defect is included therein.
Moreover, another object is to provide a method for producing an ink jet head in which a defect in the piezoelectric element is detected by a simple method so as to improve the voltage endurance of the piezoelectric element based on the detection. Moreover, another object is to provide an ink jet head and an ink jet type recording apparatus in which the piezoelectric element has a high voltage endurance.
DISCLOSURE OF THE INVENTION
In one embodiment of the present invention, a portion of an upper electrode or a lower electrode corresponding to a defective portion of a piezoelectric element is removed by dielectric breakdown so that an applied voltage is locally absent in the defective portion of the piezoelectric element.
In another embodiment of the present invention, a voltage is applied between an upper electrode and a lower electrode, and a defective portion is detected based on the temperature distribution of the upper electrode or the lower electrode.
In another embodiment of the present invention, a voltage is applied between an upper electrode and a lower electrode to cause minute dielectric breakdown, and a dielectric breakdown portion thereof is detected so as to detect a defective portion.
Specifically, an ink jet head production method according to the present invention is a method for producing an ink jet head for discharging ink by a piezoelectric effect of a piezoelectric element, the method including: a step of, after the piezoelectric element and an upper electrode and a lower electrode of the piezoelectric element are formed, removing, through dielectric breakdown, a portion of the upper electrode or the lower electrode corresponding to a defective portion of the piezoelectric element.
Thus, a portion of the upper electrode or the lower electrode corresponding to the defective portion of the piezoelectric element is removed, whereby at least one of an upper portion or a lower portion overlying/underlying the defective portion of the piezoelectric element becomes an electrode discontinuity portion where the electrode is locally absent. Accordingly, no voltage is applied through the defective portion of the piezoelectric element. Therefore, even if a defect is included in the piezoelectric element, no dielectric breakdown occurs, whereby the voltage endurance of the piezoelectric element does not deteriorate.
The thickness of the piezoelectric element may be 0.5 &mgr;m to 5 &mgr;m.
Thus, the voltage endurance does not deteriorate even though the piezoelectric element is a thin film, whereby the effect of improving the voltage
Ikeda Koji
Takao Shigeyuki
Harness Dickey & Pierce PLC
Vo Anh T. N.
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