JPH11277741A - Electrostatic actuator for inkjet head and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize an advantage of mixing p-type impurity atoms (boron atoms) at a high density (forming the thickness of a diaphragm with good control) in an ink jet head, and to make use of the mixing. The present invention suppresses and suppresses the residual stress of the diaphragm and the generation of crystal defects, which are disadvantages. The vibration plate includes a nozzle, a vibration plate provided in a part of an ink flow path communicating with the nozzle, and an individual electrode provided to face the vibration plate.
In an inkjet head that applies a driving voltage between the common electrode attached to the individual electrode 5 and the individual electrode, deforms the vibration plate by electrostatic force, and discharges ink droplets from the nozzles, the vibration plate 35 is And the diffusion region 34 of the p-type impurity atoms is limited to a region having a thickness of 1/3 or less of the thickness from the flow path side of the diaphragm 35, and only the p-type impurity atoms (boron) are formed in this region. atom)
At a high density (1 × 10 ¹⁹ / cm ³ or more).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic actuator for an on-demand type ink jet printer head and a method of manufacturing the same.

[0002]

2. Description of the Related Art In an ink-jet printer that ejects ink droplets directly from a nozzle onto a recording medium to perform recording, an on-demand method that ejects ink only when necessary does not require a mechanism for collecting the ink, so that the cost is low. It has features that it can be downsized and downsized, and can easily cope with colorization. The method of ejecting ink includes an electromechanical conversion method that generates a pressure wave in the ink chamber by the displacement of the piezo element and ejects ink from the nozzle, and a bubble that is generated in the ink chamber by a heater that is heated to high temperature in a short time Then, there is an electrothermal conversion method in which ink is ejected by volume expansion of bubbles.

On the other hand, an electrostatic actuator type ink jet head which generates a pressure wave in an ink chamber by displacing a vibration plate by electrostatic force can be manufactured by a wafer process, and therefore, it is easy to increase the density. In addition, elements with stable characteristics can be manufactured in large quantities. Further, it has an advantage that it can be easily miniaturized because it is based on a planar structure. In Japanese Patent Application Laid-Open Nos. Hei 2-289331, Hei 5-50601, Hei 6-71882, etc., monocrystalline silicon is used. Many structures have been disclosed as materials. In these electrostatic heads, a parallel plate electrode is formed at a position facing a diaphragm that forms the bottom surface of the liquid chamber, and suctions and discharges ink by vibration due to electrostatic attraction and rigidity of the diaphragm.

In an electrostatic head, it is necessary to form the thickness of the diaphragm of the electrostatic actuator with good control. Japanese Patent Application Laid-Open No. 6-71882 discloses a method for forming a diaphragm.
As disclosed in JP-A-9-234873, a boron-doped region is formed in a silicon substrate by utilizing the low etching rate of a p-type impurity layer, and the boron-doped region is etched with a potassium hydroxide solution. A thin film serving as a diaphragm can be formed by leaving only the film.

[0005]

Utilizing the fact that the etching rate of the p-type impurity layer is low, a boron-doped region is formed in a silicon substrate, and etching is performed with a potassium hydroxide solution to leave only the boron-doped region. In the vibrating plate, residual stress is generated due to the high concentration of boron atoms, and there are many crystal defects induced by the mixing of boron atoms. These residual stresses and crystal defects deteriorate the vibration characteristics of the diaphragm, and crystal defects may grow to form fine holes in the diaphragm.

An object of the present invention is to solve the disadvantage of such a diaphragm containing high-concentration boron.

[0007]

According to a first aspect of the present invention, a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and a vibration plate provided facing the vibration plate are provided. An ink jet that has an individual electrode provided thereon, applies a drive voltage between the common electrode attached to the diaphragm and the individual electrode, deforms the diaphragm by electrostatic force, and discharges ink droplets from the nozzles In the head, the diaphragm is formed of silicon single crystal, and a region in which p-type impurity atoms are diffused is formed only in a part of the thickness from the flow path side of the diaphragm. It is an electric actuator.

According to a second aspect of the present invention, in the vibration plate of the inkjet head actuator according to the first aspect, the p-type impurity atom concentration is 1 × 10 ¹⁹ atoms / cm ^3.
The above is the electrostatic actuator for an inkjet head.

According to a third aspect of the present invention, in the actuator for an ink jet head according to the first or second aspect, the density of the diaphragm is 1 × 10 ¹⁹ / cm ³ or more.
The region where the type impurity atoms are diffused is an electrostatic actuator for an inkjet head having at least １ ／ or less of the thickness of the diaphragm.

According to a fourth aspect of the present invention, in the actuator for an ink jet head according to the first or second aspect, the vibration plate has a surface oriented to a crystal plane (100) of single crystal silicon. It is an electrostatic actuator.

According to a fifth aspect of the present invention, in the actuator for an ink jet head according to the first or second aspect, the surface of the vibration plate is oriented to a crystal plane (110) of single crystal silicon, and The long side direction is an electrostatic actuator for an inkjet head, which is formed along the <111> direction of the crystal orientation of the single crystal silicon.

According to a sixth aspect of the present invention, in the actuator for an ink jet head according to the fourth or fifth aspect, the vibration plate is formed integrally with the ink flow path.
This is an electrostatic actuator for an inkjet head.

According to a seventh aspect of the present invention, there is provided a method of manufacturing an actuator for an ink jet head according to the first aspect, wherein a boron diffusion layer, which is a diffusion layer of p-type impurity atoms, is formed on the surface of the single crystal silicon substrate. Forming a single-crystal silicon layer on the boron diffusion layer, bonding the single-crystal silicon substrate to a support substrate having individual electrodes via the single-crystal silicon layer, and controlling the etching rate to be equal to the concentration of the p-type impurity atom. And forming a flow path by etching the single crystal silicon substrate with an etchant depending on the method.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and manufacturing method of the present invention will be described with reference to examples. FIG. 1 shows a configuration of an electrostatic actuator for an ink jet head according to the first to fifth aspects of the present invention. In the figure, reference numeral 35 denotes a diaphragm made of single crystal silicon. Silicon (100) as single crystal silicon material
Wafers or silicon (110) wafers can be used. The thickness of the diaphragm can be determined from the amount of displacement of the electrostatic actuator and the voltage applied between the common and counter electrodes, but is usually in the range of 2.0 to 5.0 μm. This diaphragm is formed by epitaxial growth of silicon after forming a p-type impurity atom diffusion region on the surface of the silicon substrate.

A region 34 in which p-type impurity atoms are diffused is formed on the side of the diaphragm facing the flow path 33.
Since a boron atom is generally used as a p-type impurity atom, the term boron atom will be used hereinafter in place of the term p-type impurity atom. The object of the present invention can be achieved if the thickness of the diffusion region 34 is 1/3 or less of the thickness of the diaphragm 35, but the thickness is desirably as thin as possible. The object of the present invention can be achieved if the concentration of boron atoms in the diffusion region 34 is 1 × 10 ¹⁹ atoms / cm ³ or more.

In the drawing, reference numeral 33 denotes a member forming a flow path.
Although various materials such as metal, glass, silicon, and organic materials can be used as the material, an appropriate material should be selected from the requirement of reliability as a liquid chamber flow path of the ink jet head. A nozzle plate 32 on which nozzles 31 for discharging ink droplets are formed is joined to a member 33 constituting the flow path. The dimensions of the member 33, the nozzle 31, and the nozzle plate 32 that constitute these flow paths are designed to be optimal dimensions when an inkjet head is formed using the electrostatic actuator of the present invention.

The vibration plate 35 is a member for forming the flow path.
The surface on the opposite side joined to 3 is joined to a support substrate 37 on which the individual electrodes 36 are formed. When glass is selected as the material of the supporting substrate, it is necessary to select glass which has a similar expansion coefficient to that of the single crystal silicon forming the diaphragm 35 and can be anodic-bonded to the single crystal silicon. For example, Pyrex glass # 7740 manufactured by Corning, SW3 manufactured by Iwaki Glass, and SD2 manufactured by Hoya are suitable as glass materials for the support substrate. In this embodiment, the diaphragm 35 and the individual electrode 3
Gap G required to generate an electrostatic force between
Is formed on the glass substrate side, but the gap G may be formed on the diaphragm 35 side. The size of the gap G can be determined from the displacement amount t of the electrostatic actuator and the voltage applied between the common and counter electrodes, but is usually in the range of 0.2 to 1.0 μm. A wet / dry etching method of glass is used as a gap forming method. As the individual electrode, a single metal thin film of Pt, Ni, Ti, Al or the like and an alloyed thin film thereof can be used. As a method of forming a thin film, a sputtering method, a vacuum deposition, or the like can be used. The glass supporting substrate 37 thus formed
Are joined to the diaphragm 35 by an anodic bonding method.

Single crystal silicon can also be used as a material for the support substrate 37. In this case, as the individual electrode 36, a method of forming a metal thin film between the silicon substrate and the silicon substrate via an insulating layer, or a method of diffusing an impurity having a conductivity type opposite to that of the substrate into the substrate is used. In this case, the support substrate 37 is joined to the vibration plate 35 by a silicon / silicon direct joining method.

FIG. 2 shows the structure of an electrostatic actuator for an ink jet head according to the present invention. In the drawing, the diaphragm 45, the boron atom diffusion region 44, the nozzle 41, the nozzle plate 42, the individual electrode 46, and the support substrate 47 are respectively the vibration plate 35, the boron atom diffusion region 34,
This is the same as the nozzle 31, the nozzle plate 32, the individual electrodes 36, and the support substrate 37. In the configuration of FIG. 2, members (43 in the figure) constituting the flow path are formed integrally with the diaphragm 45.

FIG. 3 is a view for explaining a specific manufacturing process of the electrostatic actuator shown in FIG. A silicon (100) wafer was used as a single crystal silicon substrate (FIG. 3A). An ion implantation method using BF3 as a source gas was used to form a p-type impurity atom diffusion region 52 on the substrate surface. Acceleration voltage during ion implantation is 4
0 KeV, a dose of 1.5 × 10 ¹⁵ atoms / cm ² , and then 800 ° C., 30 ° C. in a nitrogen atmosphere in an electric furnace.
Heat treated for minutes. With the above processing, the single crystal silicon substrate 5
A diffusion region 52 having a boron atom concentration of 1.2 × 10 ¹⁹ atoms / cm ³ was formed from the surface of Sample No. 1 to a position at a depth of 0.7 μm (FIG. 3B).

Next, a single crystal silicon 53 serving as a vibration plate is formed on the boron atom diffusion region 52 of the single crystal silicon substrate 51. Single crystal silicon is formed using silicon H4 (100%) as a source gas at a temperature of 950 ° C.
By a silicon epitaxial growth method. The thickness of the epitaxially grown single crystal silicon 53 is 1.8.
Microns (FIG. 3 (C)).

The supporting substrate 55 on which the individual electrodes 54 are formed
Corning Pyrex glass # 7740 was used. A gap having a depth of 0.5 μm and a width of 100 μm was formed on Pyrex glass # 7740 by a dry etching method using etching gases CF4 and H2. Next, the Pt film was formed to a thickness of 2000 angstroms and T
a205 film is continuously formed at 1000 Å,
The individual electrode 54 was formed in the gap by using the photolithography and the dry etching.

The single crystal silicon substrate 51 and the individual electrode support substrate 55 are joined by an anodic bonding method. Wiring is performed so as to be negative on the glass support substrate side 55 by a needle electrode and positive on the base electrode on which the silicon substrate 51 is placed. Heat to 400 ° C. in air at atmospheric pressure or in an inert gas such as Ar, N ₂ , He, and apply 800 V to the electrode to the polarity. Thus, the glass support substrate 55 and the silicon substrate 51 are anodically bonded (FIG. 3D).

Next, in order to form a vibrating plate, a 20 wt% concentration of potassium hydroxide (KOH) is applied to the silicon substrate side.
Etch with solution. The etching temperature was 80 ° C. In the etching using a potassium hydroxide (KOH) solution having a concentration of 20 wt%, the etching rate is reduced in a region where boron is diffused at a high concentration. For example, when the boron concentration increases from 1 × 10 ¹⁸ / cm ³ to 1 × 10 ¹⁹ / cm ³ , the etching rate decreases from 1.7 μm / min to 0.5 μm / min, which is 1/3 or less. When the boron concentration is increased to 1 × 10 ²⁰ / cm ³ , the etching rate is remarkably reduced to 0.1 μm / min. The end point of the etching was easily detected by utilizing the decrease in the etching rate. The thickness of the single crystal silicon diaphragm formed by etching was 2.4 microns. This step completes the electrostatic actuator part (FIG. 3).
(E)). Finally, a member 5 constituting a separately formed flow channel
7. The nozzle plate 58 provided with the nozzle 59 is bonded (joined) to the electrostatic actuator section, and the ink jet head is completed (FIG. 3 (F)).

FIG. 4 is a diagram for explaining a specific manufacturing process of the electrostatic actuator shown in FIG. A silicon (110) wafer was used as the single crystal silicon substrate 61 (FIG. 4A). In order to form a p-type impurity atom diffusion region 62 on the substrate surface, an ion implantation method using BF3 as a source gas was used. Acceleration voltage during ion implantation is 4
It was implanted at 0 KeV and a dose of 1.7 × 10 ¹⁵ atoms / cm ² , and then heat-treated in an electric furnace at 800 ° C. in a nitrogen atmosphere for 30 minutes. With the above processing, the single crystal silicon substrate 61
A diffusion region 62 having a boron atom concentration of 1.2 × 10 ²⁰ atoms / cm ³ was formed from the surface to a depth of 0.7 μm (FIG. 4B).

Next, a single crystal silicon 63 serving as a diaphragm is formed on the boron atom diffusion region 62 of the single crystal silicon substrate 61. Single crystal silicon was formed by a silicon epitaxial growth method at 950 ° C. using SiH ₄ (100%) as a source gas. The thickness of the single crystal silicon 63 epitaxially grown is 1.8.
Microns (FIG. 4C). As the support substrate 65 on which the individual electrodes 64 are formed, a silicon (100) p-type low-resistance wafer was used. Etching gas SF on silicon wafer
6, H ₂ depth 0 by the method of dry etching using.
A 5 micron gap was formed with a width of 100 microns.
Next, phosphorus was implanted into the substrate by an ion implantation method, and an n-type individual electrode 64 was formed in the gap.

The single crystal silicon substrate 61 and the individual electrode support substrate 65 are bonded by a silicon / silicon direct bonding method via an oxide film. A 1000 Å thermal oxide film is formed on the bonding surface of both silicon substrates, and adhered to each other through this oxide film.
C. for 2 hours. Thus, the individual electrode support substrate 65, which is a silicon substrate, and the silicon substrate 61 are joined (FIG. 4D).

Next, in order to integrally form the vibration plate 63 and the member 61a constituting the flow path, a Ta205 film 66 serving as an etching mask was formed to a thickness of 5000 angstroms by a sputtering method and photolithographically etched into a flow path shape. At this time, the wall 61a in the longitudinal direction of the flow path is made of silicon (11
1) The direction of the mask 66 is set so as to be formed on the surface (FIG. 4E). Using the Ta205 film 66 as an etching mask, the silicon substrate 61 side is etched with a potassium hydroxide (KOH) solution having a concentration of 20 wt%. The etching temperature was 80 ° C. The thickness of the single crystal silicon diaphragm 63 formed by etching was 2.5 microns, and the longitudinal wall 61a of the flow path was formed perpendicular to the diaphragm. In this step, an electrostatic actuator integrally formed with a flow path is completed (FIG. 4F). Finally, a nozzle plate 67 provided with a separately formed nozzle 68 is adhered (joined) to the electrostatic actuator section to complete an ink jet head (FIG. 4G).

[0029]

According to the first aspect of the present invention, p is included in the diaphragm.
Since the region where the type impurity atoms are diffused is limited, a diaphragm having small residual stress and few crystal defects can be obtained.

According to the second aspect of the present invention, since the concentration of p-type impurity atoms in which the diffusion region is limited is 1 × 10 ¹⁹ atoms / cm ³ or more, the etching rate is sufficiently reduced, and the controllability of the diaphragm thickness is controlled. Can be higher.

The effect corresponding to claim 3 is that the density is 1 × 10
^{Since the} region where p-type impurity atoms of ¹⁹ atoms / cm ³ or more are diffused is 1/3 or less of the thickness of the diaphragm, residual stress and crystal defects of the diaphragm can be sufficiently reduced.

According to the fourth aspect of the present invention, since the surface of the diaphragm is a silicon (100) surface, a smooth surface can be obtained by etching, and a diaphragm with less stress concentration during vibration can be obtained.

According to a fifth aspect of the present invention, since a vertical wall formed by a silicon crystal plane (111) can be formed on the vibration plate integrally with the vibration plate, the range of use of the vibration plate actuator can be expanded. it can.

According to the sixth aspect of the invention, since the ink flow path is formed integrally with the vibration plate, a highly reliable ink jet head without ink leakage can be provided.

Effect on Claim 7: The region where the p-type impurity atoms are diffused in the vibration plate is limited, and an actuator for an ink jet head having a vibration plate with small residual stress and few crystal defects can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an inkjet head using the electrostatic actuator of the present invention.

FIG. 2 is a diagram showing an embodiment of an ink jet head using an electrostatic actuator formed integrally with a flow channel of the present invention.

FIG. 3 is a diagram for explaining an example of a manufacturing process of the electrostatic actuator of the present invention.

FIG. 4 is a view for explaining another example of the manufacturing process of the electrostatic actuator formed integrally with the flow channel of the present invention.

[Explanation of symbols]

31, 41, 59, 68... Nozzles, 32, 42, 58,
67: nozzle plate; 33, 43, 57, 61a: members constituting flow paths, 34, 44, 52, 62: p-type impurity atom diffusion regions (boron atom diffusion regions), 35, 45 ...
Silicon diaphragm, 36, 46 ... individual electrode, 37, 47 ...
Support substrate, 51, 65: silicon (100) substrate, 5
3, 63: epitaxial silicon layer, 54: Ta20
5 / Pt electrode, 55 ... Support substrate (Pyrex glass #
7740), 61 ... silicon (110) substrate, 64 ... n
Diffusion electrode, 66 ... Ta205 mask.

Claims (7)

[Claims] An ink passage communicating with the nozzle, a vibrating plate provided in a part of the flow passage, and an individual electrode provided facing the vibrating plate; A driving voltage is applied between a common electrode attached to a plate and the individual electrodes, the diaphragm is deformed by electrostatic force, and in an ink jet head that discharges ink droplets from the nozzles, the diaphragm is made of silicon single crystal. An electrostatic actuator for an ink jet head, wherein a region in which p-type impurity atoms are diffused is formed only in a part of the thickness from the flow path side of the diaphragm. 2. The electrostatic device according to claim 1, wherein the p-type impurity atom concentration is 1 × 10 ¹⁹ atoms / cm ³ or more. Actuator. 3. The inkjet head actuator according to claim 1, wherein the region in which the p-type impurity atoms having a concentration of the vibrating plate of 1 × 10 ¹⁹ atoms / cm ³ or more are diffused is at least the region. 1/3 of diaphragm thickness
An electrostatic actuator for an ink jet head, characterized in that: 4. The actuator for an ink jet head according to claim 1, wherein a surface of the vibration plate is oriented to a crystal plane (100) of single crystal silicon. Electrostatic actuator. 5. The actuator for an ink jet head according to claim 1, wherein a surface of the vibration plate is oriented to a crystal plane (110) of single crystal silicon, and a long side direction of the vibration plate is: An electrostatic actuator for an ink jet head, wherein the electrostatic actuator is formed along the <111> direction of the crystal orientation of the single crystal silicon. 6. The electrostatic actuator for an ink jet head according to claim 4, wherein the vibration plate is formed integrally with an ink flow path. 7. The method for manufacturing an actuator for an ink jet head according to claim 1, further comprising: forming a boron diffusion layer, which is a diffusion layer of p-type impurity atoms, on a surface of the single crystal silicon substrate; An etching solution in which a single-crystal silicon layer is formed thereon, and the single-crystal silicon substrate and a supporting substrate having individual electrodes are joined through the single-crystal silicon layer, and an etching rate depends on the concentration of the p-type impurity atom. Forming a flow path by etching the single-crystal silicon substrate.