JP2002144562A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a droplet ejection characteristic is varied. SOLUTION: There is provided an electrode 24 for extracting a substrate voltage which is connected to a second substrate 2 through a connection hole 23 for drawing a substrate voltage formed on an insulation film 21 on the second substrate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head, and more particularly to an electrostatic ink jet head.

[0002]

2. Description of the Related Art An ink jet head used in an image recording apparatus such as a printer, a facsimile, a copying apparatus, a plotter or the like which is used as an image forming apparatus includes a nozzle for discharging ink droplets and a liquid chamber communicating with the nozzle. (Also referred to as an ink flow path, a pressure chamber, a discharge chamber, a pressurized liquid chamber, etc.), a diaphragm forming at least a part of a wall surface of the liquid chamber, and a counter electrode facing the diaphragm. The electrostatic force generated by applying a voltage between the diaphragm and the counter electrode deforms and displaces the diaphragm, and changes the pressure / volume in the liquid chamber to discharge ink droplets from the nozzles. An electric inkjet head is known.

As such an electrostatic ink jet head, for example, as described in JP-A-6-71882, a first substrate composed of a silicon substrate having a diaphragm and a liquid chamber, a silicon oxide film, A second substrate made of a silicon substrate having a counter electrode formed on the bottom surface of the concave portion, and a third substrate having a nozzle formed thereon.
There has been known a method of bonding by a direct bonding method of -Si and defining a gap length between the diaphragm and the counter electrode by a depth of a step of the concave portion and a thickness of the counter electrode. There is also a structure in which the concave portion is provided also on the first substrate side on which the diaphragm is formed.

[0004]

When an opposing electrode is formed on a conductive substrate such as a silicon substrate via an insulating film as in the above-mentioned electrostatic ink jet head, if the conductive substrate is in a floating state, the opposing electrode is formed. When a voltage is applied to the electrode, the phenomenon that the substrate potential fluctuates and the ejection characteristics fluctuates due to capacitive coupling between the counter electrode and the conductive substrate. There is a problem that the effect is increased when attempting to discharge.

[0005] The present invention has been made in view of the above problems, and has as its object to provide an ink jet head in which variations in ink droplet ejection characteristics are reduced.

[0006]

In order to solve the above-mentioned problems, an ink jet head according to the present invention is connected to a second substrate through a connection hole for taking out a substrate potential formed in an insulating film of the second substrate. It has a configuration having a substrate potential extracting electrode.

Here, it is preferable that the opening width of the connection hole for taking out the substrate potential does not exceed twice the value obtained by adding the thickness of the insulating film to the thickness of the electrode. In addition, it is preferable to form a connection hole for taking out the substrate potential and an electrode for taking out the substrate potential also in a region between the adjacent counter electrodes. Furthermore, it is preferable that the surface of the insulating film covering the electrode surface of the second substrate is subjected to CMP polishing and directly joined to the first substrate.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view of an inkjet head according to a first embodiment of the present invention in the longitudinal direction of the diaphragm, FIG.
FIG. 3 is an explanatory plan view of an electrode pattern of the head.

This ink jet head includes a first substrate 1 using a silicon substrate, a second substrate 2 which is a conductive electrode substrate using a silicon substrate provided below the first substrate 1, and a first substrate 1. A nozzle unit 3 provided on an upper side of the substrate 1, the nozzle unit 3 includes a flow path forming plate 4, a common ink chamber forming plate 5 and a nozzle plate 6, a nozzle hole 7 for discharging a plurality of ink droplets, and each nozzle The liquid chambers 8 are ink flow paths to which the holes 7 communicate, the common ink chamber 10 communicates with each of the liquid chambers 8 via a fluid resistance portion 9 also serving as an ink supply path, and the nozzle holes 7 communicate with the liquid chambers 8. The nozzle communication passage 11 and the like are formed.

The first substrate 1 is provided with a liquid chamber 8 and a recess 16 for forming a diaphragm 15 which also serves as an electrode forming a part of the wall of the liquid chamber 8. The first substrate 1 is formed, for example, by injecting boron into a silicon substrate in advance to a thickness of a diaphragm to form a high-concentration boron layer serving as an etching stop layer and joining the second substrate 2 side. KO for the recess 16
Anisotropic etching is performed using an etchant such as an aqueous H solution. At this time, the diaphragm 15 and the like are formed with the high-concentration boron layer serving as an etching stop layer.

On the other hand, an insulating film 21 made of a silicon oxide film or the like is formed on the second substrate 2, and an individual counter electrode 22 facing the diaphragm 15 with a predetermined gap 17 is arranged on the insulating film 21. , The diaphragm 15 and the counter electrode 22
Thus, an electrostatic actuator for deforming the diaphragm 15 by an electrostatic force is configured. Further, a connection hole 23 for taking out a substrate potential is opened in a part of the insulating film 21, and an electrode 24 for taking out a substrate potential which is electrically connected to the second substrate 2 via the connection hole 23 from the surface of the insulating film 21 is formed. are doing.

The electrode 24 for taking out the substrate potential is shown in FIG.
As shown in FIG. 2, the electrode pad 22 is arranged in a donut shape surrounding the counter electrode 22, and the counter electrode 22 and the substrate potential extracting electrode 24 are substantially coplanar with each other.
a and 24a are respectively formed. Then, a silicon oxide film 25 is formed on the counter electrode 22 and the substrate potential extracting electrode 24 except for the electrode pad portions 22a and 24a, and a concave portion 26 for forming the gap 17 is formed in the silicon oxide film 25. Thus, a portion other than the concave portion 26 is formed as a bonding portion 27 for bonding to the first substrate 1 and a gap space wall 28 also serving as a bonding portion.

Here, as shown in FIG. 4, the opening width of the connection hole 23 for taking out the substrate potential is S, the thickness of the silicon oxide film 21 is Tox, and the thickness of the electrode 24 for taking out the substrate potential and the counter electrode 22 is Tce. Then, S <2 (Tox + T
ce) is established, that is, the opening width S of the substrate potential connection hole 23 is formed so as not to exceed twice the value obtained by adding the thickness To of the insulating film 21 to the thickness Tce of the electrode 24. I have.

As described above, the connection hole 23 for taking out the substrate potential
By defining the opening width S of the insulating film (silicon oxide film), the step of the connection hole 23 formed in the insulating film (silicon oxide film) 21 can be almost completely filled with the electrode material and the silicon oxide film 25, In the case where a flattening process (for example, a CMP process) for directly bonding to step 28 is performed, rounding of the corner of the step can be reduced.

The passage forming plate 4 of the nozzle unit 3 has a through hole for forming an ink supply path (fluid resistance portion) 9 and a through hole for forming a nozzle communication passage 11, and the common ink chamber forming plate 5 has a common ink. Through hole and nozzle communication passage 1 forming chamber 10
No. 1 is formed, and a nozzle plate 7 is formed with a nozzle hole 7. Then, the flow path forming plate 4 of the nozzle unit 3 is joined to the first substrate 1 with an adhesive 30.

The surface of the nozzle plate 6 is subjected to a water-repellent treatment. The nozzle unit 3 is provided with an ink supply port (not shown) for supplying ink to the common ink chamber 10 from outside. Further, the liquid chamber 8 and the diaphragm 1
A structure in which a nozzle plate 6 in which nozzle holes are formed on a flow path substrate in which nozzles 5 are formed may be employed.

In this ink jet head, when a driving voltage is applied between the diaphragm 15 and the counter electrode 22, the diaphragm 15 is displaced toward the electrode by electrostatic force generated between the diaphragm 15 and the counter electrode 22. As a result, the ink is supplied from the common ink chamber 10 to the liquid chamber 8 through the fluid resistance portion 9. After that, when the voltage is returned to 0, the diaphragm 15 displaced when the voltage is returned to 0 returns to the original position by the elastic force, and the ink droplet is ejected from the nozzle hole 7.

Here, in this ink jet head, since the substrate potential extracting electrode 24 is provided,
By fixing the potential of the second substrate 2 at a constant level via the substrate potential extracting electrode 24, the potential of the second substrate 2 is prevented from fluctuating due to capacitive coupling between the counter electrode 22 and the second substrate 2. Therefore, even when multi-drive for ejecting ink droplets from a large number of nozzle holes 7 is performed, variations in the characteristics of droplet ejection from each nozzle hole 7 are reduced.

The structure for disposing the substrate potential extracting electrode is not limited to the above example. For example, as shown in FIG. 5, the connection hole 23 for taking out the substrate potential may be almost filled only with the electrode material, or as shown in FIG. 6, a plurality of connection holes 23 for taking out the substrate potential (three in FIG. 5). The contact resistance between the electrode 24 and the second substrate 2 can also be reduced by forming the electrodes 24 side by side and forming the electrodes 24 for extracting the substrate potential through the respective connection holes 23. Also, the planar arrangement structure of the substrate potential extracting electrode 24 may be a line shape, a hole shape, or the like, in addition to the donut shape shown in FIG.

Next, the manufacturing process of the ink jet head will be described with reference to FIGS. First,
As shown in FIG. 7A, an insulating film 2 having a thickness of about 1.0 μm is formed on a second substrate 2 made of a silicon wafer as an insulating film.
A silicon oxide film as No. 1 is formed by thermal oxidation. Then, as shown in FIG. 1B, a connection hole 23 for taking out the substrate potential is formed in a part of the insulating film 21 by a photolithography / etching process.

At this time, including the conditions for forming the insulating film 21 on the second substrate 2, S ≦ 2 (Tox + Tc
The connection hole 23 for taking out the substrate potential is opened in the insulating film 21 with the opening width S so that the relationship of e) is satisfied. here,
The opening width S was about 1.2 μm.

Next, as shown in FIG. 1C, an electrode material film 31 serving as the counter electrode 22 and the substrate potential extracting electrode 24 is formed. Here, as the electrode material film 31,
A film composed of two layers of WSi / poly-Si was formed, and the thickness was 0.2 μm / 0.15 μm, respectively. The poly-Si is doped with phosphorus by phosphorus deposition.

Then, as shown in FIG. 2D, the electrode material film 31 is separated into individual patterns of the individual counter electrode 22 and the substrate potential extracting electrode 24 by a photolithography / etching process. At this time, the width T of the separation groove 32 between each counter electrode 22 and between the counter electrode 23 and the substrate potential extracting electrode 24 was about 0.5 μm.

Subsequently, as shown in FIG.
LP-CVD under the conditions of a pressure of 13 Pa and a temperature of about 850 ° C. using SiH ₄ gas and N ₂ O gas on layers 2 and 24
A silicon oxide film 25 is formed by a method. here,
The thickness Tox of the silicon oxide film 25 was set to about 0.7 μm.

At this time, the relationship of S ≦ 2 (Tox + Tce) is satisfied, and the silicon oxide film 25 formed under the above conditions has very good step coverage, so that each of the opposing electrodes 22
The separation groove 32 between the counter electrode 22 and the substrate potential extracting electrode 24 and the groove 33 formed by the substrate potential extracting connection hole 23 are substantially buried.

Thereafter, as shown in FIG.
The surface of the silicon oxide film 25 is polished and flattened. Here, the amount of decrease in the thickness of the silicon oxide film 25 is set to 0.
Polishing was performed so as to have a thickness of about 1 μm, that is, the remaining film thickness of the silicon oxide film 25 was 0.6 μm. By this step, the HTO surface can be directly bonded to a level (surface roughness R
a <about 5 nm).

At this time, the separation grooves 32 between the opposing electrodes 22 and between the opposing electrodes 22 and the substrate potential extracting electrode 24 are formed.
Is almost buried in the silicon oxide film 25, and the portion of the connection hole 23 for taking out the substrate potential is substantially buried in the electrode 24 and the silicon oxide film 25. No reduction in bonding area occurs.

Subsequently, as shown in FIG. 3C, a recess 26 serving as a gap 17 between the diaphragm 15 and the electrode 22 is formed in the silicon oxide film 25 by a photolithography / etching process.
To form Here, the recess 26 having a depth of about 0.35 μm was formed. At this time, the silicon oxide film 2
5 has a thickness of about 0.25 μm, which serves as a protective film for preventing a short circuit between the diaphragm 15 and the electrode 22.

Next, as shown in FIG. 1D, the silicon oxide film 25 of the second substrate 2 is directly bonded to the first substrate 1 including the diaphragm 15 at least partially made of silicon. After that, the first substrate 1 is masked with a silicon nitride film or the like at a portion serving as a partition of the liquid chamber 8 and is etched with an alkaline aqueous solution such as a KOH aqueous solution.
Then, the nozzle unit 3 is bonded to the first substrate 1 with an epoxy-based adhesive (adhesive layer) 30 and other members are bonded to the first substrate 1 to form an ink jet head according to the present embodiment. Complete.

As described above, the opening width S of the connection hole 23 for taking out the substrate potential, the thickness Tox of the silicon oxide film 21,
Thickness T of substrate potential extracting electrode 24 and counter electrode 22
By setting the relationship of ce to S <2 (Tox + Tce), even when the bonding surface is flattened by CMP or the like, the rounding from the corner of the step can be reduced, and the reduction of the bonding area can be prevented. can do.

On the other hand, S> 2 (Tox + Tce)
When the bonding surface is flattened by CMP or the like, rounding occurs from the corner of the step, and the bonding area is significantly reduced. This will be specifically described with reference to FIG. 9. As shown in FIG. 9A, the opening width S of the substrate potential connection hole 23 is increased (> 2 (Tox + Tc).
e)) When formed, even if the silicon oxide film 25 is formed, the connection hole 23 for taking out the substrate potential cannot be buried, and the concave portion 41 remains.

Therefore, when polishing is performed by CMP in this state, a dent inclined toward the concave portion 41 is generated as shown in FIG. 4B, and the diaphragm is formed as shown in FIG. When bonding the first substrate 1 including
In addition, a large unjoined area is formed at the periphery thereof, and the joining strength is reduced. Even if such an unbonded region occurs, if the bonding strength is to be ensured, the chip (head) area must be increased accordingly.

Therefore, as in the present invention, the opening width S of the substrate potential connection hole 23 is formed so as not to exceed twice the value obtained by adding the thickness Tx of the insulating film 21 to the thickness Tce of the electrode 24. Thus, sufficient bonding strength can be ensured without increasing the chip area.

Next, an ink jet head according to another embodiment of the present invention will be described with reference to FIGS. FIG. 10 is an explanatory cross-sectional view of the head in the lateral direction of the diaphragm. FIG. 11 is an enlarged explanatory view of a gap interval wall portion in FIG. 10, and FIG. 12 is a plan explanatory view of an electrode pattern of the head.

In this ink jet head, the gap interval wall (electrode interval wall) 28, that is, the counter electrode 2
A connection hole 23 for taking out the substrate potential and an electrode 24 for taking out the substrate potential are also formed between 2 and 22. The other configuration is the same as the above embodiment.

As described above, the adjacent opposing electrodes 22, 22
The substrate potential extracting electrode 24 is also formed between the substrate potential extracting connection holes 23 near the center of the chip.
The distance between the substrate and the second substrate 2 can be shortened, so that variations in characteristics due to fluctuations in the substrate potential can be reduced even in a channel near the center of the chip. This is particularly effective when the second substrate 2 is formed of a relatively high-resistance substrate material.

In each of the above embodiments, the description has been made of the side shooter type head formed so that ink droplets are ejected in the direction of displacement of the diaphragm. However, ink droplets are ejected in the direction intersecting the direction of displacement of the diaphragm. The present invention can be similarly applied to an edge shooter type head formed to discharge. In addition, the present invention is not limited to a device that discharges ink droplets, and can be applied to a device that discharges droplets of liquid resist or the like.

[0038]

As described above, according to the droplet discharge head of the present invention, the substrate potential connected to the second substrate via the substrate potential connection hole formed in the insulating film of the second substrate. With the configuration having the extraction electrode, it is possible to reduce the variation in the droplet discharge characteristics.

Here, by making the opening width of the connection hole for taking out the substrate potential not more than twice the value obtained by adding the thickness of the insulating film to the thickness of the electrode, the bonding surface is flattened. In this case, the occurrence of unbonded regions can be reduced, and a decrease in bonding strength can be prevented.

Further, by forming a connection hole for taking out the substrate potential and an electrode for taking out the substrate potential also in the region between the adjacent opposing electrodes, it is possible to further prevent the fluctuation of the substrate potential and suppress the variation in the droplet discharge characteristics. Can be.

Further, since the insulating film surface of the second substrate is directly polished by CMP and bonded to the first substrate, a high precision gap can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of an inkjet head according to the present invention in a longitudinal direction of a diaphragm.

FIG. 2 is an explanatory cross-sectional view of the head in a lateral direction of a diaphragm.

FIG. 3 is an explanatory plan view of an electrode pattern of the head.

FIG. 4 is an enlarged sectional explanatory view of a main part of a connection hole portion for taking out a substrate potential of the head.

FIG. 5 is an enlarged cross-sectional view of a main part for explaining another example of the connection hole portion for taking out the substrate potential of the head.

FIG. 6 is an enlarged cross-sectional view of a main part for explaining still another example of a connection hole portion for taking out a substrate potential of the head.

FIG. 7 is a schematic sectional view for explaining a method of manufacturing the head.

FIG. 8 is a schematic sectional explanatory view for explaining a method for manufacturing the head.

FIG. 9 is a schematic cross-sectional explanatory view illustrating the structure of a comparative example used to explain the operation of the embodiment.

FIG. 10 is a schematic cross-sectional explanatory view along a lateral direction of a diaphragm of an inkjet head according to another embodiment of the present invention.

FIG. 11 is an enlarged sectional explanatory view of a main part for describing an electrode spacing wall portion of the head.

FIG. 12 is an explanatory plan view of an electrode pattern of the head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... First substrate, 2 ... Second substrate, 8 ... Liquid chamber, 15 ... Vibration plate, 16 ... Concave part, 21 ... Insulating film, 22 ... Electrode, 23 ... Connection hole for taking out substrate potential, 24 ... For taking out substrate potential Electrodes, 25: silicon oxide film.

Claims (4)

[Claims] 1. A vibration plate having a nozzle for discharging ink droplets, a liquid chamber with which the nozzle communicates, a vibration plate forming a wall surface of the liquid chamber, and a counter electrode facing the vibration plate. In an ink jet head in which a first substrate provided with an electrode and an electrically conductive second substrate formed with an insulating film provided with the electrodes are connected to each other through a substrate potential extracting connection hole formed in the insulating film of the second substrate. An ink jet head having a substrate potential extracting electrode connected to two substrates. 2. The ink jet head according to claim 1, wherein an opening width of the connection hole for taking out the substrate potential is a value obtained by adding a thickness of the insulating film to a thickness of the electrode.
An inkjet head characterized by not exceeding twice. 3. The ink jet head according to claim 1, wherein the connection hole for taking out the substrate potential and the electrode for taking out the substrate potential are formed in a region between the adjacent counter electrodes. Inkjet head. 4. The ink jet head according to claim 1, wherein said second substrate is formed on a substrate potential extracting electrode, and an insulating film surface is polished by CMP and directly joined to said first substrate. An ink jet head characterized in that: