Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-03
2002-06-18
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06406133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an ink jet head and a method of producing the same. More particularly, the present invention relates to an ink jet head that discharges ink droplets by driving a diaphragm with electrostatic force between electrodes on the diaphragm side and electrodes that face the diaphragm-side electrodes, and to a method of producing such an ink jet head.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 7-125196 discloses an electrostatic ink jet head that comprises a diaphragm, a substrate integrally formed with the diaphragm, and individual electrodes that face the diaphragm, with a gap being interposed between the diaphragm and the individual electrodes. In this ink jet head, the individual electrodes are formed in concave portions formed in an insulating member, and the gap is defined as: (the depth of each concave portion of the insulating member (or the height of each step portion))−(the thickness of each individual electrode). The individual electrodes and the diaphragm electrodes can be pulled out on the same planes, respectively, so that electric voltage can be applied to them.
Japanese Patent Application No. 9-148062 discloses an electrostatic ink jet head that comprises a diaphragm and individual electrodes which face the diaphragm, with a gap being maintained between the diaphragm and the individual electrodes. In this ink jet head, the individual electrodes are formed in concave portions formed in a glass substrate, and the gap is defined as: (the height of each step of the glass substrate)−(the thickness of each individual electrode). Through holes for embedding conductors in the glass substrate are formed, and conductors are embedded in the through holes. The individual electrodes are pulled onto the bottom surface of the glass substrate through the conductors, and are mounted via bump-like conductors. A voltage is then applied.
Japanese Patent Application No. 10-61308 discloses an electrostatic ink jet head in which individual electrodes are formed by a diffusion layer in a silicon substrate. Through holes for pulling out the electrodes onto the silicon substrate are formed, so that the potential of the individual electrodes can be taken out onto the bottom surface of a supporting substrate. After the formation of the through holes, the electrodes are formed by the diffusion layer.
Japanese Laid-Open Patent Application No. 5-50601 discloses an electrostatic ink jet head in which the diaphragm is deformed by electrostatic force generated by a voltage applied between the diaphragm and electrodes facing the diaphragm, thereby discharging ink droplets. Each diaphragm chamber (gap) is formed by a concave portion in a diaphragm substrate. A lower substrate (electrode substrate) also has concave portions. The individual electrodes are placed in the concave portions, so as to prevent short-circuiting with the diaphragm.
Japanese Laid-Open Patent Application No. 6-71882 discloses an electrostatic ink jet head in which the gap between the diaphragm and each facing electrode is in the range of 0.05 &mgr;m and 2.0 &mgr;m, so that the ink jet head can be driven at a low voltage. More specifically, electrodes are place din concave portions formed in at least one of an electrode substrate or a diaphragm substrate. Accordingly, the gap length is determined by the difference between the depth of each concave portion and the thickness of each electrode. The electrodes are formed by a diffusion layer in a silicon substrate. In this case, the gap length is determined by the thickness of an oxide film formed as a gap spacer.
Japanese Laid-Open Patent Application No. 9-193375 discloses an electrostatic ink jet head in which each gap between the diaphragm and electrodes facing the diaphragm has a non-parallel shape so as to restrict variations of the discharging amount and the discharging rate of ink droplets. Furthermore, the diaphragm and the individual electrodes facing the diaphragm are bonded via an insulating coating layer, so that a collision between the diaphragm ad the individual electrodes can be avoided. Each gap is formed between a step portion or a concave portion in the diaphragm substrate and a non-parallel step portion of the electrode substrate.
An ink jet head of an electrostatic actuator type in which the diaphragm is deformed by electrostatic force so as to generate pressure wave in an ink chamber can be produced by a wafer process. Accordingly, the ink jet head can have high density and a large number of stable devices can be produced. The ink jet head having a planar structure can be made smaller, as disclosed in Japanese Laid-Open Patent Application No. 7-125196 and others. The diaphragm is vibrated by electrostatic force caused by a voltage applied between the diaphragm and the individual electrodes and by the rigidity of the diaphragm. With the vibration of the diaphragm, ink is sucked in and discharged.
The pulling out of the individual electrodes disclosed in Japanese Laid-Open Patent Application 7-125196 is carried out on parts of the surface of the electrode substrate, with which neither liquid chamber nor diaphragm substrate is in contact. As disclosed in Japanese Patent Application Nos. 9-148062 and 10-61308, the individual electrodes are pulled out from the bottom side of the electrode substrate, so that the chip area and the number of mounting steps can be reduced.
As disclosed in Japanese Laid-Open Patent Application No. 7-125196 and Japanese Patent Application No. 9-148062, concave portions are formed in an insulating substrate, and electrodes made of a conductive material such as metal are placed in the respective concave portions, thereby obtaining the individual electrodes. As disclosed in Japanese Patent Application 10-61308, the individual electrodes may also be constituted by conductive impurity (dopant) diffusion regions formed in a silicon substrate.
The displacement ä(m) of the diaphragm of the electrostatic ink jet head is determined by the equation (1), and the electrostatic attraction P (N/m
2
) is determined by the equation (2).
ä
=k×
12(1−
v
2
)/
Eh
3
×Pa
4
(1)
P: electrostatic attraction (N/m
2
)
a: short side length (m)
h: diaphragm thickness
v: Poisson's ratio
E: Young's modulus
k: constant
P=
½
×{dot over (å)}
×(
V/G
eff
)
2
(2)
{dot over (å)}: dielectric constant (F/m)
V: voltage (V)
G
eff
: effective gap length (m)
In accordance with the above equations, the displacement of the diaphragm due to electrostatic force is inversely proportional to the square of the effective gap length G
eff
. Therefore, it is important to form the gaps at high precision. Also, the effective gap length G
eff
needs to be made smaller so as to have a low driving voltage. In other words, it is necessary to form narrow gaps at high precision.
On the other hand, in the case where the individual electrodes are formed in the concave portion in an insulating substrate (or in an insulating film on a conductor or a semiconductor substrate), as disclosed in Japanese Laid-Open Patent Application No. 7-125196 and Japanese Patent Application No. 9-148062, the effective gap length G
eff
can be expressed as:
G
eff
=(concave depth−individual electrode thickness) (3)
In this equation, the passivation film or insulation film on the individual electrodes is no taken into consideration. As is apparent from the equation (3), the effective gap length G
eff
is influenced by both variations of the depth of the concave portions and the thickness of the individual electrodes. If the following relationship (4):
concave depth>individual electrode thickness (4)
is satisfied, the effective gap length G
eff
is determined mainly by the concave depth, which is relatively controllable. If the effective gap length G
eff
is small, the relationship (4) can be satisfied, as long as the thickness of the individual electrodes is very small. How
Cooper & Dunham LLP
Gordon Raquel Yvette
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