JP2002254636A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable ink jet head which reduces fluctuations of an ink drop ejection property. SOLUTION: A first substrate 1 provided with a diaphragm 15 and a second substrate 2 provided with an electrode 22 are bonded together via a silicon oxidized film 25, so that a width W of a groove 24 for electrode separation between electrodes 22 is made to be not greater than double the thickness (t) of the silicon oxidized film 25.

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 vibration plate and a liquid chamber, and 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 step depth of the concave portion and a thickness of the counter electrode. The above-mentioned publication also discloses that a diffusion layer in a silicon substrate is used as an electrode.

[0004]

As in the above-mentioned conventional electrostatic ink jet head, a concave portion is formed in the silicon oxide film of the second substrate, and the gap length between the diaphragm and the counter electrode is reduced by the step depth of the concave portion. When the gap length is large and the electrode thickness is thin with respect to the depth of the recess, the gap length accuracy is almost determined by the accuracy of the depth of the recess. There is a problem that if the size is reduced, the variation in the gap length increases.

In this case, if the thickness of the electrode is reduced, the variation in the gap length can be suppressed. However, since the resistance of the electrode is increased, there is a problem that the driving voltage cannot be increased.

More specifically, gap length = 1.
In the case of 8 μm (each tolerance is 10%), recess depth = 2.0 μm ± 0.2 μm, electrode thickness = 0.2 μm
When ± 0.02 μm, gap depth = 1.8 μm
± 0.22 μm, and the variation in gap depth is ±
12%. On the other hand, when the gap length is reduced while keeping the electrode thickness unchanged, for example, the gap length =
In the case of 0.2 μm (each tolerance is 10%),
Depth of recess = 0.4 μm ± 0.04 μm, electrode thickness = 0.
When 2 μm ± 0.02 μm, gap depth = 0.
This is 2 μm ± 0.06 μm, and the variation in the gap depth is ± 30%.

In this case, when the electrode thickness is reduced, for example, when the electrode thickness is set to 0.02 μm, the gap length = 0.
In the case of 2 μm (each tolerance is assumed to be 10%), recess depth = 0.4 μm ± 0.04 μm, electrode thickness = 0.02
μm ± 0.002 μm, gap depth = 0.2μ
m ± 0.0024 μm, and the variation in the gap depth can be maintained at ± 12%, but the electrode thickness increases, and the resistance of the electrode increases.

In this case, as described above, by employing a structure using a diffusion layer in a silicon substrate as an electrode,
Although the accuracy of the gap (Gap) does not decrease due to the thickness of the electrode, the electrode and the substrate are separated by the pn junction, so that only one side voltage can be applied and the process for securing the withstand voltage becomes complicated. Another problem is that it is difficult to secure the yield of the pn junction when the electrode has a relatively large area such as an electrode of an electrostatic inkjet head. Further, since the periphery of the vibration chamber (a chamber including a space in which the diaphragm is deformed) is not completely sealed, it is necessary to separately seal with a sealing material in order to prevent foreign matter from entering during operation. However, there is a possibility that foreign matter may enter the gap during the manufacturing process (between the opening of the diaphragm of the pad portion and the sealing thereof).

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to obtain a highly reliable ink jet head with reduced variation in ink droplet ejection characteristics.

[0010]

In order to solve the above-mentioned problems, an ink-jet head according to the present invention comprises a first substrate provided with a diaphragm and a second substrate provided with a counter electrode, which are joined via an insulating film. The width of the electrode separating groove between the opposing electrodes is set to a width not exceeding twice the thickness of the insulating film.

Here, the insulating film is preferably a silicon oxide film. Preferably, the bonding surface of the silicon oxide film is flattened by chemical mechanical polishing. Further, it is preferable that the first substrate and the second substrate are bonded by direct bonding via a silicon oxide film.

[0012]

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 ink jet head according to a first embodiment of the present invention in the longitudinal direction of the diaphragm, FIG.
FIG. 3 is an enlarged explanatory view of a main part of FIG.

This ink-jet head has 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 has an oxide film 1 on a base substrate 12.
SOI (Silicon On I
Using the substrate, the base substrate 12 of the SOI substrate is etched to form the liquid chamber 8, and the vibration plate 15 composed of the active layer 23 covered with the oxide film 22 on the liquid chamber 8 side is formed. . Here, the portion of the base substrate 12 where the liquid chamber 8 is not formed serves as a partition 16 between the liquid chambers.

The first substrate 1 is formed, for example, by injecting boron to a diaphragm in advance into a silicon substrate to form a high-concentration boron layer serving as an etching stop layer.
After joining to the side, the concave portion serving as the liquid chamber 8 is anisotropically etched using an etching solution such as a KOH aqueous solution. At this time, even when the high-concentration boron layer serves as an etching stop layer and the diaphragm 15 is formed. Good.

On the other hand, on the second substrate 2, an insulating film 21 made of a silicon oxide film or the like formed by a thermal oxidation method or the like using a single crystal silicon substrate is formed. An electrode member 23 that forms an opposing individual opposing electrode 22 is disposed with a gap 17 between the vibrating plate 15 and the opposing electrode 22 to form an electrostatic actuator that deforms the vibrating plate 15 with an electrostatic force. .

Then, each counter electrode 22 (electrode member 23)
By forming a silicon oxide film 25 as an insulating film on the electrode member 23 including the electrode separating groove 24 for separating the silicon oxide film 24 into a concave portion 26 for forming a gap 17 in the silicon oxide film 25, The part not forming
The spacer portion 27 is bonded to the substrate 1 and the opening of the gap 17 is sealed.

As described above, the counter electrode 22 is provided on the second substrate 2.
And a silicon oxide film 25 serving as an insulating film is formed on the counter electrode 22. A concave portion 26 for forming the gap 17 is provided in the silicon oxide film 25. In this structure, the gap between the diaphragm 15 and the counter electrode 22 can be reduced, and the gap 17 can be hermetically closed. 1
7 can be prevented from entering the inside, and long-term stability and reliability can be obtained.

Here, the electrode separating groove 2 of each counter electrode 22
4 is set to a value not exceeding twice the thickness t of the silicon oxide film 25 as an insulating film. Thereby, the surface of the spacer portion 26 formed of the silicon oxide film 25 is
The surface properties when flattened by (chemical mechanical polishing) can be secured, and the joining reliability when joining the first substrate 1 and the second substrate 2 can be secured.

The passage forming plate 4 of the nozzle unit 3 has a through hole for forming an ink supply passage (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 forming plate. 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 bonded onto 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 to the electrode side by an electrostatic force generated between the diaphragm 15 and the counter electrode 22. The ink is deformed, and 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.

In this ink jet head, the gap length between the vibration plate 15 and the counter electrode 22 is determined regardless of the depth of the concave portion 26 formed in the silicon oxide film 25, so that a high precision gap is provided. Can be formed, and variations in the ink droplet ejection characteristics can be reduced.

Next, the manufacturing process of the ink jet head will be described with reference to FIGS. In addition,
FIG. 4 is a cross-sectional explanatory view in the short direction of the diaphragm, and FIG. 5 is an enlarged explanatory view of a main part of the gap spacer portion.

First, as shown in FIGS. 4A and 5A, a silicon oxide film as an insulating film 21 having a thickness of about 1.0 μm is formed on a second substrate 2 made of a silicon wafer as an insulating film. It is formed by thermal oxidation. Then, after forming an electrode material (electrode member 23) to a predetermined thickness on the insulating film 21 by LP-CVD or the like, an electrode separation groove 24 is formed in a photolithography / etching step, so that each of the opposing electrodes 2 is formed.
Separate into 2. In addition, as the electrode member 23, WSi was formed to a thickness of 0.2 μm, and then poly-Si was formed to a thickness of 0.15 μm.
m in a laminated structure. The width W of the electrode separating groove 24 was about 0.8 μm.

Thereafter, as shown in FIG.
A silicon oxide film 25 including the electrode separation groove 24 is formed on the substrate 2 to a thickness t of about 0.7 μm. Silicon oxide film 25
LP-CVD using SiH ₄ + N ₂ O gas
An oxide film formed by the method, that is, a so-called HTO film was used. This H
The TO film has a very good step cover. When the TO film is formed with the above thickness, the electrode separation groove 24 is almost completely buried with the silicon oxide film 25.

That is, like the ink jet head, a counter electrode 22 is provided on the second substrate 2, a silicon oxide film 25 as an insulating film is formed on the counter electrode 22, and a gap 17 is formed in the silicon oxide film 25. Is formed, and portions other than the concave portion 26 are
In the case where the structure 7 is bonded to the first substrate 1, it is necessary to bury the electrode separation groove 24 between the opposing electrodes 22 with the silicon oxide film 25. Therefore, by setting the width W of the electrode separation groove 24 to a value not exceeding twice the thickness t of the silicon oxide film 25, the electrode separation groove 24 is almost completely formed when the silicon oxide film 25 is formed. Can be embedded.

Next, 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, since the electrode separating groove 24 is almost buried with the silicon oxide film 25, the rounding of the stepped portion hardly occurs when the CMP is performed, and the bonding area at the spacer portion 27 is reduced. Almost never.

Subsequently, as shown in FIG. 4D, a concave portion 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 concave portion 26 having a depth of about 0.2 μm was formed. At this time, the silicon oxide film 25 is formed on the electrode 22.
About 0.4 μm in thickness, which is the diaphragm 15 and the electrode 22
It becomes a protective film for preventing short circuit of.

As described above, after the individual opposing electrodes 22 are separated, the surface of the silicon oxide film 25 serving as the bonding surface of the second substrate 2 is flattened by performing the CMP polishing, thereby performing the CMP polishing of the bonding surface. The yield of direct bonding is improved and the reliability of bonding is increased, as compared with a later step of separating the electrodes.

Next, as shown in FIGS. 4E and 5D, the silicon oxide film 25 of the second substrate 2 and the first substrate 1 including the vibration plate 15 are directly bonded. afterwards,
The liquid chamber 8 and the diaphragm 15 are formed on the first substrate 1 by masking a portion serving as a partition wall of the liquid chamber 8 with a silicon nitride film or the like, and performing etching with an alkaline aqueous solution such as a KOH aqueous solution. The ink jet head according to the present embodiment is completed by bonding the nozzle unit 3 onto one substrate 1 with an epoxy-based adhesive (adhesive layer) 30 and bonding other members.

As described above, the width W of the electrode separating groove 24 is
Is not more than twice the thickness t of the silicon oxide film 25 which is an insulating film for joining the first substrate 1 and the second substrate 2, so that C
Even when the bonding surface is flattened by MP or the like,
Since the electrode separating groove 24 can be almost completely buried, the rounding of the spacer portion 27 made of the silicon oxide film 25 from the corner can be reduced, and the reduction of the bonding area can be prevented, and the bonding reliability can be reduced. Can be secured.

On the other hand, when the width W of the electrode separating groove 24 exceeds twice the thickness t of the silicon oxide film 25,
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 described in detail with reference to FIGS. 6 and 7. As shown in FIGS. 6A and 6A, the width W of the electrode separating groove 24 between the opposing electrodes 22 is increased (to be described later). If the thickness is more than twice the thickness t of the film 25), the electrode forming groove 24 cannot be buried even if the silicon oxide film 25 is formed, as shown in FIG. Remain.

Therefore, when polishing is performed by CMP in this state, a dent inclined toward the concave portion 41 is generated as shown in FIG. 6C, and the concave portion 26 is formed as shown in FIG. Is formed, a large recess 42 is formed on the joint surface of the spacer portion 27. Therefore, FIG.
As shown in FIG. 7D, when the first substrate 1 including the diaphragm 15 is joined, a large unjoined area is formed in the recess 42 and its peripheral portion, 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, by forming the width W of the electrode separating groove 24 to be equal to or less than twice the thickness of the silicon oxide film 25 as in the present invention, sufficient bonding can be achieved without increasing the chip area. Strength can be secured.

In each of the above-described embodiments, the description has been given of the side shooter type head formed so that the ink droplet is ejected in the direction of displacement of the diaphragm. However, the ink droplet is 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.

[0039]

As described above, according to the ink jet head of the present invention, the first substrate provided with the vibration plate and the second substrate provided with the counter electrode are joined via the insulating film.
Since the width of the electrode separating groove between the opposing electrodes is set not to exceed twice the width of the insulating film, the space between the opposing electrodes can be buried with the insulating film, so that the chip area is not increased and the bonding reliability is improved. Thus, it is possible to obtain a highly reliable head with improved ink droplet ejection characteristics.

Here, since the insulating film is a silicon oxide film, the first substrate and the second substrate can be bonded by direct bonding of silicon. In addition, the reliability of direct bonding is improved by flattening the bonding surface of the silicon oxide film by chemical mechanical polishing. Furthermore, the gap accuracy is improved by joining the first substrate and the second substrate by direct joining via the silicon oxide film.

[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 enlarged explanatory view of a main part of a spacer portion of the head.

FIG. 4 is a schematic sectional explanatory view for explaining a manufacturing process of the head.

FIG. 5 is an enlarged schematic cross-sectional view of a main part explaining a manufacturing process of the head.

FIG. 6 is a schematic sectional explanatory view for explaining a manufacturing process of a head according to a comparative example to be compared with the present invention.

FIG. 7 is an enlarged schematic cross-sectional view of a main part explaining a manufacturing process of a head according to the comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st board | substrate, 2 ... 2nd board | substrate, 8 ... liquid chamber, 15 ... diaphragm, 17 ... gap, 21 ... insulating film, 22 ... counter electrode,
24: an electrode separating groove, 25: a silicon oxide film, 26: a concave portion, 17: a spacer portion.

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 that discharges ink droplets from the nozzles by deforming the first substrate with an electrostatic force, a first substrate provided with the vibration plate and a second substrate provided with the counter electrode are joined via an insulating film, An ink jet head, wherein the width of the electrode separating groove between the electrodes is not more than twice the thickness of the insulating film. 2. The ink jet head according to claim 1, wherein said insulating film is a silicon oxide film. 3. The ink jet head according to claim 2, wherein a bonding surface of said silicon oxide film is flattened by chemical mechanical polishing. 4. The ink jet head according to claim 3, wherein the first substrate and the second substrate are joined by direct joining via the silicon oxide film.