JP2007237417A - Electrostatic actuator, liquid droplet jet head, and method for manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the driving durability of an electrostatic actuator without generating a delay of driving of the electrostatic actuator. <P>SOLUTION: An inkjet head 10 having the electrostatic actuator comprises an elastically deformable diaphragm 22 which is one of opposing members, a discrete electrode 31 which is the other opposing member and is disposed to be opposite to the diaphragm 22 with an insulation film 26 and a prescribed gap G therebetween, and a driving control circuit (a driving means) 4 for generating an electrostatic force by applying a drive voltage across the discrete electrode 31 and the diaphragm 22. A hydrophobic film 29 consisting of a primary surface treatment film and a secondary surface treatment film combined by siloxane bond is formed on the surface of the insulation film 26 by using a plurality of treatment agents having different hydrophobic group structures, the insulation film 26 being formed on the lower face of the diaphragm 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic actuator that is driven by utilizing electrostatic force, a droplet discharge head including the electrostatic actuator, and a method of manufacturing the same.

  2. Description of the Related Art An actuator having a microstructure formed by using a semiconductor microfabrication technique is used in an inkjet head of an inkjet printer. As this micro-structure actuator, an electrostatic drive type using an electrostatic force as a drive source is known (see, for example, Patent Document 1).

An ink jet head provided with an electrostatic actuator is formed as a vibration plate whose bottom surface of an ink chamber communicating with an ink nozzle can be elastically deformed. A substrate is disposed opposite to the diaphragm at a constant interval. A counter electrode is disposed on each of the diaphragm and the substrate, and a space between the counter electrodes is sealed. When a voltage is applied between the opposing electrodes, the bottom surface (vibrating plate) of the ink chamber is vibrated by electrostatic attraction or electrostatic repulsion toward the substrate by electrostatic force generated between them. Ink droplets are ejected from the ink nozzles due to fluctuations in the internal pressure of the ink chamber that occur with the vibration of the bottom surface of the ink chamber. By controlling the voltage applied between the counter electrodes, ink droplets are ejected only when necessary for recording.
Here, when the driving of the ink jet head is repeated by repeatedly applying a voltage between the counter electrodes, a phenomenon in which the electrostatic attraction characteristic or the electrostatic repulsion characteristic deteriorates is observed. In order to avoid such an adverse effect, it is conceivable to hydrophobize the actuator surface.

  As the electrostatic actuator subjected to the hydrophobization treatment, techniques disclosed in Patent Documents 2 and 3 are known.

JP-A-5-50601 (FIGS. 1 and 2) Japanese Patent Laid-Open No. 7-13007 (FIGS. 2 and 3) Japanese Patent Laid-Open No. 10-181028 (FIGS. 3 and 4)

In Patent Document 2, by forming an alignment monomolecular layer of perfluorodecanoic acid (PFDA) on the surface of the counter electrode in the micromechanical device that is an electrostatic actuator, these are in a stuck state during driving, etc. I try to prevent it.
In Patent Document 3, a hydrophobic film made of hexamethyldisilazane (HMDS) is formed on the opposing surface of the electrostatic actuator to prevent them from becoming stuck during driving.

In the future, in consideration of improving the durability of inkjet printers, it is necessary to increase the number of times the actuator is driven. However, the conventional electrostatic actuator has a problem that the driving durability is not sufficient. That is, in the hydrophobization treatment using perfluorodecanoic acid (PFDA), there is a problem in the adhesion strength of the PFDA layer, and the PFDA layer may be peeled off by repeated operation of the actuator. On the other hand, in the hydrophobizing treatment using hexamethyldisilazane (HMDS), the formation of a uniform hydrophobic film is inhibited by the generation of ammonia gas in the minute gap between the counter electrodes in the hydrophobizing treatment step. There was a fear.
Therefore, the present applicant has proposed a method of hydrophobizing using a compound that does not generate ammonia gas, for example, a trialkylalkoxysilyl compound (Japanese Patent Application No. 2005-362986). However, this method has a problem that although the hydrophobic effect is good, there is a delay in driving the electrostatic actuator.

  The present invention relates to an improvement of the above-mentioned prior application, and an object thereof is to improve drive durability without causing a drive delay of an electrostatic actuator.

  In order to solve the above-described problems, an electrostatic actuator according to the present invention has a counter-displaceable counter member arranged opposite to each other at a predetermined interval, and generates an electrostatic force between the counter members to make the counter member relatively In an electrostatic actuator having a driving means for displacing, a plurality of treatment agents having different hydrophobic group structures are bonded to a surface of at least one of the facing members facing the other member using a plurality of treatment agents having different hydrophobic group structures. A hydrophobic film composed of a primary surface treatment film and a secondary surface treatment film is formed.

As a result of examining the cause of the drive delay of the electrostatic actuator, the present inventor has found that the larger the molecule of the treatment agent that is bonded to the surface of the opposing member by a siloxane bond, the more unreacted points, that is, unreacted hydroxyl groups are generated. I came up with it. When unreacted hydroxyl groups exist, moisture in the air forms hydrogen bonds, and electric charges are accumulated when driven by electrostatic force. As a result, driving delay (also called response delay) occurs.
Therefore, by using a plurality of treatment agents having different hydrophobic group structures as described above, the secondary surface treatment film is formed so as to fill the unreacted hydroxyl groups of the primary surface treatment film, thereby delaying the driving of the electrostatic actuator. The drive durability can be improved without causing any problems.

In the electrostatic actuator of the present invention, the hydrophobic film is formed using a trialkylalkoxysilyl compound or a dialkyldialkoxysilyl compound as a first treatment agent and silazane as a second treatment agent. Is.
By using silazane as the second treatment agent, unreacted hydroxyl groups generated in the primary surface treatment film can be filled. In this case, the second treating agent is preferably hexamethyldisilazane (HMDS). Since HMDS has a short chain length of an alkyl group as a hydrophobic group, it is suitable for filling unreacted hydroxyl groups generated in the primary surface treatment film.

  The alkyl group of the first treating agent contains a functional group selected from a methyl group, an ethyl group, an n-propyl group, and an n-butyl group. By constituting the alkyl group with a group having a small number of carbon atoms, it is possible to form a treated surface having a sufficiently low surface energy because it has a sufficient hydrophobizing ability and has little treatment unevenness.

Further, among the trialkylsilyl groups of the first treating agent, at least two alkyl groups are dimethylalkylsilyl groups composed of methyl groups.
In the case of a dimethylalkylsilyl group, the first treatment agent does not become a bulky alkyl group, but penetrates deeply into a minute gap between the opposing members, and forms a uniform hydrophobic film on the opposing surface of the opposing member. be able to.

  A droplet discharge head according to the present invention includes any one of the electrostatic actuators described above as a droplet discharge mechanism. Thereby, a uniform hydrophobic film can be formed on the facing surface of the facing member, and a droplet discharge head with improved driving durability without driving delay can be provided.

  The method for manufacturing an electrostatic actuator according to the present invention includes a counter-displaceable counter member arranged to face each other at regular intervals, and a driving unit that generates an electrostatic force between the counter members to relatively displace the counter member. And at least one of the opposing members of the electrostatic actuator is hydroxylated on the surface facing the other member, and then the alkoxyl group is used as the first treatment agent. And a compound having a trialkylsilyl group or a compound having an alkoxyl group and a dialkylsilyl group to form a primary surface treatment film bonded to the surface with a siloxane bond, and a sub-surface generated in the surface treatment step. Bonded to the surface with a siloxane bond using a post-treatment step to remove the product and silazane as the second treatment agent And having a step of forming a secondary surface treatment film which has.

  By using the first and second treatment agents as described above, it is possible to manufacture an electrostatic actuator with no driving delay and improved driving durability.

In addition, a primary surface treatment film is formed using a trialkylalkoxysilyl compound or a dialkyldialkoxysilyl compound as the first treatment agent.
By using such a compound, it is possible to form a primary surface treatment film having a hydrophobic property bonded to the opposing surface of the opposing member with a siloxane bond.

Moreover, a secondary surface treatment film is formed using hexamethyldisilazane (HMDS) as the second treatment agent.
Since HMDS has a short chain length of an alkyl group as a hydrophobic group, it is suitable for filling unreacted hydroxyl groups generated in the primary surface treatment film. Further, ammonia gas may be generated in this surface treatment process, but it is considered that there are few unreacted points, and therefore it is considered that the driving durability of the electrostatic actuator is not adversely affected.

Further, the alkyl group of the first treatment agent contains a functional group selected from a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.
By constituting the alkyl group with a group having a small number of carbon atoms, it is possible to form a treated surface having a sufficiently low surface energy because it has a sufficient hydrophobizing ability and has little treatment unevenness.

Moreover, it is desirable that at least two alkyl groups among the trialkylsilyl groups are dimethylalkylsilyl groups composed of methyl groups.
In the case of a dimethylalkylsilyl group, the first treatment agent does not become a bulky alkyl group, but penetrates deeply into a minute gap between the opposing members, and forms a uniform hydrophobic film on the opposing surface of the opposing member. be able to.

Moreover, it is desirable to include a pretreatment process for removing moisture adhering to the facing surface prior to the surface treatment process for the facing surface.
By this pretreatment step, moisture adhering to the facing surface can be removed prior to the surface treatment step, so that the adhesion state of the treatment agent can be stabilized. Furthermore, the pretreatment step is preferably a vacuum heating step in which the inside of the treatment tank containing the workpiece is evacuated and heated.

  Since the 1st processing agent used by this invention produces alcohol or water as a by-product, it is necessary to post-process in order to remove these by-products. In this case, it is desirable that the post-treatment process is a vacuum heating process in which the inside of the treatment tank containing the workpiece is evacuated and heated.

  Moreover, it is desirable that the post-treatment process is a vacuum heating process in which the inside of the treatment tank containing the object to be processed is evacuated and heated, similarly to the pre-treatment process.

A method for manufacturing a droplet discharge head according to the present invention is a method for manufacturing a droplet discharge head using any one of the above-described electrostatic actuator manufacturing methods.
As a result, it is possible to provide a liquid droplet ejection head such as an ink jet head having a high driving durability.

  Hereinafter, embodiments of a droplet discharge head including an electrostatic actuator according to the present invention will be described with reference to the drawings. Here, as an example of a droplet discharge head, a face discharge type inkjet head that discharges ink droplets from ink nozzles provided on the surface of a nozzle substrate will be described with reference to FIGS. The present invention is not limited to the structure and shape shown in the following drawings, and can also be applied to an edge discharge type inkjet head that discharges ink droplets from ink nozzles provided at the end of a substrate. It is.

  FIG. 1 is an exploded perspective view showing an exploded schematic configuration of the ink jet head according to the present embodiment, and a part thereof is shown in cross section. FIG. 2 is a cross-sectional view of the ink jet head showing a schematic configuration in an assembled state. FIG. 3 is an enlarged sectional view in the longitudinal direction of the electrostatic actuator portion in this ink jet head, and FIG. 4 is an enlarged sectional view in the width direction of the electrostatic actuator portion. 1 and 2 are shown upside down from a state in which they are normally used.

  As shown in FIGS. 1 and 2, an inkjet head (an example of a droplet discharge head) 10 according to the present embodiment includes a nozzle substrate 1 having a plurality of ink nozzles (nozzle holes) 11 provided at a predetermined pitch, The cavity substrate 2 in which an ink supply path is provided independently of the ink nozzle 11 and the electrode substrate 3 on which the individual electrode 31 is disposed facing the vibration plate 22 of the cavity substrate 2 are bonded together. ing.

The electrostatic actuator in the present embodiment includes the diaphragm 22 that is one opposing member that can be elastically deformed, and the other that is disposed to face the diaphragm 22 via an insulating film 26 and a certain gap (gap) G. The above-mentioned individual electrodes 31 that are opposing members, and a drive control circuit (driving means) 4 that generates a static force by applying a driving voltage between the individual electrodes 31 and the diaphragm 22 are further provided. As shown in FIG. 2, a hydrophobic film 29 made of primary and secondary surface treatment films is formed on the surface of the insulating film 26 formed on the lower surface of the diaphragm 22 using the first and second treatment agents of the present invention. Has been.
Hereinafter, the configuration of each substrate constituting the inkjet head 10 will be described.

The nozzle substrate 1 is made of, for example, a silicon substrate having a thickness of 100 μm, and a plurality of ink nozzles 11 are formed. As shown in FIG. 2, each ink nozzle 11 has a cylindrical ejection port portion 11a perpendicular to the surface of the nozzle substrate 1, and is provided coaxially with the ejection port portion 11a and has a diameter larger than that of the ejection port portion 11a. An inlet part 11b having a large (or cross-sectional area) is provided. Thus, by making the ink nozzle 11 have a two-stage hole, the ink droplet ejection direction can be aligned with the central axis direction of the ink nozzle 11, and stable ink ejection characteristics can be exhibited. . That is, there is no variation in the flying direction of the ink droplets, there is no scattering of the ink droplets, and variations in the ejection amount of the ink droplets can be suppressed.
Further, in FIG. 2 of the nozzle substrate 1, a narrow groove-like orifice 13 that forms a part of the ink flow path is provided on the lower surface (the surface on the bonding side with the cavity substrate 2).

  The cavity substrate 2 is made of, for example, a silicon substrate having a thickness of 140 μm. By performing anisotropic wet etching on the silicon substrate, recesses 24 and 25 for forming the ink chamber (discharge chamber) 21 and the reservoir 23 of the ink flow path are formed. A plurality of recesses 24 are independently formed at positions corresponding to the ink nozzles 11. Therefore, when the nozzle substrate 1 and the cavity substrate 2 are joined as shown in FIG. 2, each concave portion 24 constitutes an ink chamber 21 and communicates with the ink nozzle 11 respectively, and the orifice 13 serving as an ink supply port. Both communicate with each other. The bottom wall of the ink chamber 21 (recess 24) serves as the diaphragm 22. The diaphragm 22 can also be constituted by a boron-doped layer formed by diffusing high-concentration boron in a silicon substrate with a required thickness. By configuring the diaphragm with a boron-doped layer, the etching stop sufficiently works on the surface of the boron-doped layer, so that the surface roughness of the diaphragm can be suppressed and the thickness thereof can be processed with high accuracy.

  The other concave portion 25 is for storing liquid material ink, and constitutes a common reservoir (common ink chamber) 23 for each ink chamber 21. The reservoirs 23 (recesses 25) communicate with all the ink chambers 21 through the orifices 13, respectively. Further, a hole penetrating the electrode substrate 3 described later is provided in the bottom of the reservoir 23, and ink is supplied from an ink cartridge (not shown) through the ink supply hole 34 of the hole.

An insulating film made of SiO ₂ or TEOS (Tetraethylorthosilicate Tetraethoxysilane) is formed on the entire surface of the cavity substrate 2 or at least the surface facing the electrode substrate 3 by thermal oxidation or plasma CVD (Chemical Vapor Deposition). 26 is applied with a film thickness of 0.1 μm. This insulating film 26 is provided for the purpose of preventing dielectric breakdown and short circuit when the ink jet head is driven. Further, on the surface of the insulating film 26, as will be described later, a hydrophobic film 29 surface-treated with the treating agent of the present invention is formed.
On the upper surface of the cavity substrate 2, that is, the surface facing the nozzle plate 1 (including the inner surfaces of the ink chamber 21 and the reservoir 23), an ink protection film (not shown) is similarly formed of a SiO ₂ film (including a TEOS film). This ink protective film is provided to prevent corrosion of the flow path by ink.

  The electrode substrate 3 is made from a glass substrate having a thickness of about 1 mm, for example. Among them, it is suitable to use a borosilicate heat-resistant hard glass having a thermal expansion coefficient close to that of the silicon substrate of the cavity substrate 2. This is because when the electrode substrate 3 and the cavity substrate 2 are anodically bonded, the thermal expansion coefficients of the two substrates are close to each other, so that the stress generated between the electrode substrate 3 and the cavity substrate 2 can be reduced. This is because the electrode substrate 3 and the cavity substrate 2 can be firmly bonded without causing the above problem. The electrode substrate 3 may be a silicon substrate made of the same material as the cavity substrate 2.

  The electrode substrate 3 is provided with a recess 32 at a position on the surface of the cavity substrate 2 facing each diaphragm 22. The recess 32 is formed to a depth of about 0.2 μm by etching. In each recess 32, an individual electrode 31 made of, for example, ITO (Indium Tin Oxide) is formed by sputtering with a thickness of, for example, 0.1 μm. Therefore, the gap (gap) G formed between the diaphragm 22 and the individual electrode 31 is determined by the depth of the recess 32 and the thickness of the insulating film 26 covering the individual electrode 31 and the diaphragm 22. . This gap G greatly affects the ejection characteristics of the inkjet head. In the above example, the gap G between the insulating film 26 on the lower surface of the diaphragm 22 and the individual electrode 31 after the cavity substrate 2 and the electrode substrate 3 are joined is 0.1 μm. The open end of the gap G is hermetically sealed by filling a sealing through hole 28 provided at the rear end of the cavity substrate 2 with a sealing material 27 made of, for example, TEOS or epoxy adhesive. The Thereby, moisture, dust and the like can be prevented from entering the gap, and the reliability of the inkjet head 10 can be kept high.

  The individual electrode 31 has a lead part 31a and a terminal part 31b connected to a flexible wiring board (not shown). The terminal portion 31b is exposed in the electrode extraction portion 35 in which the rear end portion of the cavity substrate 2 is opened in order to facilitate connection of the flexible wiring board.

  Here, the diaphragm 22 formed by the bottom wall of each ink chamber 21 functions as a common electrode on each ink chamber side. As shown in FIGS. 3 and 4, the surface of the insulating film 26 formed on the lower surface of the diaphragm 22 is subjected to surface treatment with the treatment agent of the present invention to form a hydrophobic film 29. Individual electrodes 31 made of ITO are formed on the concave surface of the electrode substrate 3 so as to face the diaphragm 22 as the common electrode. The counter electrode of the electrostatic actuator is formed by the diaphragm 22 on the bottom wall of each ink chamber, which is a common electrode, and the individual electrodes 31 corresponding to the insulating film 26 and the gap G.

As described above, the nozzle substrate 1, the cavity substrate 2, and the electrode substrate 3 are bonded to each other as shown in FIG. That is, the cavity substrate 2 and the electrode substrate 3 are generally bonded by anodic bonding, and the nozzle substrate 1 is bonded to the upper surface (the upper surface in FIG. 2) of the cavity substrate 2 by adhesion or the like.
Finally, as shown in a simplified manner in FIGS. 1 and 2, a drive control circuit (drive means) 4 such as a driver IC is provided on the terminal portion 31 b of each individual electrode 31 and the common electrode (on the cavity substrate 2). The flexible wiring board (not shown) is connected to the terminal (not shown).
Thus, the ink jet head 10 is completed.

Next, the operation of the inkjet head 10 configured as described above will be described.
The drive control circuit 4 is an oscillation circuit that controls the supply and stop of charges to the individual electrodes 31. This oscillation circuit oscillates at, for example, 24 kHz, and supplies electric charges by applying pulse potentials of, for example, 0 V and 30 V to the individual electrodes 31. When the oscillation circuit is driven and charges are supplied to the individual electrode 31 to be positively charged, an electrostatic force (Coulomb force) is generated between the individual electrode 31 and the diaphragm 22. Therefore, the diaphragm 22 is attracted to the individual electrode 31 by this electrostatic force and bends (displaces). As a result, the volume of the ink chamber 21 increases. When the supply of electric charges to the individual electrodes 31 is stopped, the diaphragm 22 returns to its original state due to its elastic force, and at this time, the volume of the ink chamber 21 is rapidly reduced. Part of the ink is ejected from the ink nozzle 11 as ink droplets. Next, when the vibration plate 22 is similarly displaced, ink is supplied from the reservoir 23 through the orifice 13 into the ink chamber 21.
The ink used in the inkjet head 10 is prepared by dissolving or dispersing a surfactant such as ethylene glycol and a dye or pigment in a main solvent such as water or alcohol.

  Next, with reference to FIG. 5, the manufacturing method of the inkjet head 10 provided with the electrostatic actuator of this embodiment is demonstrated.

FIG. 5 is a schematic flowchart showing an outline of the manufacturing process of the inkjet head 10. As shown in this figure, first, in step S1, the nozzle substrate 1, the cavity substrate 2, and the electrode substrate 3 constituting the inkjet head 10 are each processed from a wafer and manufactured.
Next, in step S2, as shown in FIG. 6, the wafer assembly having a large number of ink-jet heads 10 (referred to here as the main body of the ink-jet head 10) is formed by bonding the three-member wafers to each other. 100 is formed. That is, the electrode substrate 3 is bonded to the bottom surface side of the cavity substrate 2 by anodic bonding so that the gap G is formed. Then, the nozzle substrate 1 is bonded and bonded to the upper surface of the cavity substrate 2 with an adhesive. Note that the inkjet head 10 in the wafer assembly 100 has an electrode extraction portion 35 formed by etching at the rear end of the cavity substrate 2 as described above. Processing is performed.

Next, in the pretreatment step of Step S3, the surface to be processed (the inner surface of the gap G) of the inkjet head 10 is dried. That is, in this step, moisture adhering to the surface to be processed of the wafer assembly (object to be processed) 100 is removed. For example, using a processing apparatus as shown in FIG. 7, the wafer assembly 100 is placed in the processing tank 201, for example, nitrogen is used as an inert gas, and the nitrogen introduction valve 202 is opened to supply nitrogen from the nitrogen introduction port. The exhaust valve 203 may be opened at the same time as supplying into the processing tank 201 to replace the inside of the processing tank 201 with a nitrogen gas atmosphere. At this time, the inside of the electrostatic actuator, that is, the gap G is similarly replaced with the nitrogen gas atmosphere. When such a pretreatment process is performed, the surface treatment state of the surface to be treated can be stabilized. In other words, it is possible to remove the adhering moisture from the surface of the insulating film 26 formed on the lower surface of the vibration plate 22 and avoid the occurrence of variations in the state of adhesion of the processing agent in the next step. In FIG. 7, reference numeral 204 denotes a heater.
Further, in this pretreatment step, vacuum heat treatment can be employed in order to remove moisture adhering to the surface to be treated. The conditions of the vacuum heat treatment are, for example, that the treatment tank 201 containing the wafer assembly 100 of the inkjet head is held at a temperature of 340 ° C. and a vacuum degree of 10 ⁻³ Torr for 9 minutes, and then held in a nitrogen gas atmosphere for 1 minute. This cycle is repeated for a total of 12 cycles.

Next, in step S <b> 4, surface treatment inside the electrostatic actuator is performed with the first treatment agent to form a primary surface treatment film 29 a on the surface of the insulating film 26. In the present invention, a plurality of treatment agents having different hydrophobic group structures are used as the surface treatment agent.
Here, the surface treatment method of the insulating film 26 in the present embodiment will be described with reference to FIG. FIG. 8A schematically shows the surface of the insulating film 26 made of SiO ₂ before processing. FIG. 8B is a schematic diagram when surface treatment is performed using n-butyldimethylmethoxysilane as the first treatment agent, and FIG. 8C is a diagram using hexamethyldisilazane (HMDS) as the second treatment agent. It is a schematic diagram when surface treatment is performed. FIG. 8D is a schematic diagram showing a chemical structure of n-butyldimethylchlorosilane as a first treating agent, and FIG. 8E is a schematic diagram showing a chemical structure of HMDS as a second treating agent.

  In order to reduce the surface energy, it is desirable to use a treating agent having a long chain length of the hydrophobic alkyl group as the treating agent. However, when a treating agent having a long chain length of the alkyl group is used, FIG. As shown, there is a high possibility that unreacted hydroxyl groups (OH groups) remain on the surface of the insulating film 26. If unreacted hydroxyl groups are present, after treatment, hydrophilic by-products and moisture in the air are hydrogen-bonded to the hydroxyl groups, and charges accumulate on the surface of the insulating film with repeated driving of the electrostatic actuator. It will be. As a result, the drive delay (response delay) of the electrostatic actuator occurs, and the ejection performance of the inkjet head may become unstable.

Therefore, in the present invention, after the surface treatment with the first treating agent having a long chain length of the hydrophobic alkyl group as the first treating agent, the alkyl group having a shorter chain length, preferably an alkyl group is preferably used. The surface treatment is performed again with the second treating agent that is entirely composed of methyl groups.
As the first treating agent usable in the present invention, a compound having both a functional group for reacting with the insulating film surface and a functional group for reducing the surface energy of the insulating film surface is used.
For example, an alkoxyl group can be used as a functional group for reacting with the insulating film surface. There are many compounds having an alkoxyl group, or a hydroxyl group and an alkyl group in the chemical structure, but in the present invention, a trialkylalkoxysilyl compound comprising one alkoxyl group, three alkyl groups and one silicon atom, or 2 It is desirable to use a dialkyl dialkoxysilyl compound comprising one alkoxyl group, two alkyl groups, and one silicon atom.
Here, it is desirable that the alkyl group contains a fluorinated alkyl group in which hydrogen of the alkyl group is substituted with fluorine. Since the fluorinated alkyl group has a smaller surface energy than the alkyl group, the driving durability of the electrostatic actuator is improved.
Moreover, it is desirable that at least two alkyl groups among the trialkylsilyl groups are dimethylalkylsilyl groups composed of methyl groups. This is because when the treatment agent is composed of a bulky alkyl group, the entire insulating film is hardly uniformly surface-treated depending on the type of the alkyl group, and the driving durability of the electrostatic actuator is not improved.

  In addition, the surface treatment can be either a liquid phase treatment or a vapor phase treatment, but it is desirable to use a vapor phase treatment that can easily obtain a uniform treatment surface. In this embodiment, by reacting at a normal temperature for 30 hours using a 300 μL processing agent, that is, n-butyldimethylmethoxysilane shown below, for a 7 L processing tank and a 4-inch wafer assembly by vapor phase processing, A surface treatment film 29 a was formed on the bottom surface of the insulating film 26. In the gas phase treatment, it is necessary that the vapor pressure of the treatment agent is an appropriate value. Accordingly, among the treating agents represented by the above general formula, a compound having a relatively low vapor pressure at room temperature, specifically, a compound having 4 or less carbon atoms constituting one alkyl group of the treating agent is used. Is desirable.

  In the case of the alkoxysilane compound used in the present invention, when an alkoxyl group reacts with a hydroxyl group on the surface of the insulating film, alcohol is generated as a by-product. If the by-product adheres to the surface of the insulating film of the actuator part, it causes sticking of the actuator. Therefore, in the manufacturing method of this embodiment, the post-processing process which removes the alcohol which generate | occur | produces in a surface treatment process is needed. Although the post-treatment process will be described later, it is desirable to use a lower alkoxide, preferably a linear alkoxide having 3 or less carbon atoms, from which the generated alcohol can be easily removed.

  As specific first treatment agents satisfying the above conditions, the following compounds are commercially available, and an appropriate one may be selected and used.

<Trialkylalkoxysilyl compound>
* (3,3,3-trifluoropropyl) dimethylmethoxysilane
* N-propyldimethylmethoxysilane
* N-butyldimethylmethoxysilane
<Dialkyl dialkoxysilyl compound>
* Dimethyldimethoxysilane
* Dimethyldiethoxysilane
* Diethyldiethoxylsiane
* Di-n-butyldimethoxysilane
* Isobutylmethyldimethoxysilane

Next, the post-treatment step of step S5 is performed in order to reliably remove the lower alcohol generated in the surface treatment step.
The post-treatment step is not particularly limited as long as it is a method capable of removing lower alcohol and water. For example, after the surface treatment, a method of removing the alcohol by placing the wafer assembly 100 of the inkjet head 10 under vacuum, preferably under heating vacuum, is desirable.

  Next, the surface treatment process of step S6 performs surface treatment inside the electrostatic actuator with the second treatment agent. As the second treating agent that can be used in the present invention, a compound having both a functional group for reacting with the insulating film surface and a functional group for reducing the surface energy of the insulating film surface is used. For example, a secondary amine or the like can be used as the functional group for reacting with the insulating film surface. A compound having a secondary amine group and a silylalkyl group in the chemical structure is called silazane. Although there are many silazanes, in this embodiment, as shown in FIG. 8E, hexamethyldisilazane (HMDS) having two trimethylsilyl groups consisting of three alkyl groups and one silicon atom is used. Is desirable. By surface-treating the surface of the insulating film again using HMDS as the second treatment agent, it is possible to eliminate the unreacted hydroxyl group due to the first treatment agent as shown in FIG. 8C. The unreacted hydroxyl group does not appear regularly.

  As described above, the hydrophobic film 29 including the primary and secondary surface treatment films is formed on the surface of the insulating film 26 by performing the two-step surface treatment using a plurality of treatment agents having different hydrophobic group structures.

  Next, the post-processing step of step S7 is performed as necessary. That is, when the surface of the insulating film 26 is surface-treated again by the second treatment agent, this gas is not necessary when a gas is generated as a by-product as in HMDS. Since it occurs, post-processing is necessary. In addition, since it is considered that there are few unreacted points due to the first treatment agent, the amount of gas generated as a by-product is small, and its influence is not a problem. Post-processing is required to affect the drive characteristics of the electrostatic actuator. In this post-processing, as in step S5, the by-product can be easily removed regardless of whether it is a gas or a liquid by placing the wafer assembly 100 under a vacuum, preferably a heating vacuum.

  Next, in the hermetic sealing process of step S8, the wafer assembly 100 of the inkjet head 10 is taken out from the treatment tank replaced with nitrogen, and the space between the insulating film 26 and the individual electrode 31 is used with the sealing agent 27. And hermetically seal. Thereby, a predetermined sealed gap G is formed, and an electrostatic actuator is formed. Then, the inkjet head 10 is completed by cutting the wafer assembly 100 into individual heads by dicing.

  Further, as a result of examining the durability of the hydrophobic film 29 of the present embodiment formed by the method as described above, the number of driving cycles of the electrostatic actuator was 4 billion cycles in the case of the hydrophobic film composed only of HMDS. On the other hand, in the case of the hydrophobic film | membrane 29 of this embodiment, it was 5.8 billion cycles.

  Therefore, according to the ink jet head manufacturing method of the present embodiment, the surface treatment is performed in two stages using the first and second treating agents having different hydrophobic group structures, and therefore the drive delay of the electrostatic actuator is reduced. Drive durability can be improved without generating.

In the above embodiment, the electrostatic actuator, the inkjet head, and the manufacturing method thereof have been described. However, the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the idea of the present invention. it can. For example, by changing the liquid material ejected from the ink nozzles, in addition to inkjet printers, the production of color filters for liquid crystal displays, the formation of light-emitting portions of organic EL display devices, the microarray of biomolecule solutions used for genetic testing, etc. It can be used as a droplet discharge device for various uses such as manufacture of
In addition, although the vibration plate has been described as a thin plate type in which both ends are supported or a substantially rectangular whole circumference is fixed, a cantilever type may be used. Further, the shape of the diaphragm is not particularly limited. For example, it may be circular, and an electrostatic actuator having a circular diaphragm can be used, for example, in a diaphragm portion of a micropump. Furthermore, it can be used for an optical switch, a wavelength tunable device or the like depending on the structure of the support beam.

1 is an exploded perspective view showing a schematic configuration of an ink jet head provided with an electrostatic actuator of the present invention. FIG. 2 is a schematic cross-sectional view showing an assembled state of the inkjet head of FIG. 1. FIG. 3 is an enlarged cross-sectional view in the longitudinal direction of an electrostatic actuator portion in the inkjet head of FIG. 2. The expanded sectional view of the width direction of the electrostatic actuator part of FIG. FIG. 3 is a schematic flowchart of a manufacturing process showing an example of a method for manufacturing the ink jet head of FIG. 2. The fragmentary sectional view of a wafer assembly. BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the processing apparatus used in this invention. Structural schematic diagram of insulating film before surface treatment (A), structural schematic diagram of primary surface treatment film formed with first treatment agent (B), secondary surface treatment film formed with second treatment agent Structural schematic diagram (C) and structural schematic diagrams (D, E) of the first and second treatment agents.

Explanation of symbols

1 nozzle substrate, 2 cavity substrate, 3 electrode substrate, 4 drive control circuit (drive means), 10 ink jet head, 11 ink nozzle, 13 orifice, 21 ink chamber, 22 vibration plate, 23 reservoir, 26 insulating film, 27 sealing 28, through-hole for sealing, 29a primary surface treatment film, 29 hydrophobic film (secondary surface treatment film), 31 individual electrode, 32 recess, 34 ink supply hole, 35 electrode take-out part, 100 wafer assembly, 201 Processing tank.

Claims (15)

In an electrostatic actuator having a relatively displaceable facing member arranged to face each other at a fixed interval, and a driving unit that generates an electrostatic force between these facing members to relatively displace the facing member.
A surface of at least one of the facing members facing the other member is composed of a primary surface treatment film and a secondary surface treatment film bonded with siloxane bonds using a plurality of treatment agents having different hydrophobic group structures. An electrostatic actuator characterized by forming a hydrophobic film.   2. The static film according to claim 1, wherein the hydrophobic film is formed using a trialkylalkoxysilyl compound or a dialkyldialkoxysilyl compound as a first treatment agent and silazane as a second treatment agent. Electric actuator.   3. The electrostatic actuator according to claim 2, wherein the alkyl group of the first treatment agent includes a functional group selected from a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.   The electrostatic actuator according to claim 2, wherein the second treatment agent is hexamethyldisilazane.   4. The electrostatic actuator according to claim 2, wherein at least two alkyl groups among the trialkylsilyl groups of the first treating agent are dimethylalkylsilyl groups composed of methyl groups.   A droplet discharge head comprising the electrostatic actuator according to claim 1 as a droplet discharge mechanism. A method of manufacturing an electrostatic actuator comprising: a relatively displaceable facing member disposed facing each other at a fixed interval; and a driving unit that generates an electrostatic force between the facing members to relatively displace the facing member. ,
Of the opposing members of the electrostatic actuator, after hydroxylating the surface of at least one member facing the other member, a compound having an alkoxyl group and a trialkylsilyl group as a first treatment agent, or an alkoxyl group And a step of forming a primary surface treatment film bonded to the surface with a siloxane bond using a compound having a dialkylsilyl group, a post-treatment step of removing a by-product generated in the surface treatment step, a second step And forming a secondary surface treatment film bonded to the surface with a siloxane bond using silazane as a treatment agent.   8. The method for manufacturing an electrostatic actuator according to claim 7, wherein the primary surface treatment film is formed using a trialkylalkoxysilyl compound or a dialkyldialkoxysilyl compound as the first treatment agent.   9. The method of manufacturing an electrostatic actuator according to claim 7, wherein a secondary surface treatment film is formed using hexamethyldisilazane as the second treatment agent.   The alkyl group of the first treatment agent includes a functional group selected from a methyl group, an ethyl group, an n-propyl group, and an n-butyl group. Manufacturing method of electrostatic actuator.   The method for producing an electrostatic actuator according to claim 7, wherein at least two alkyl groups among the trialkylsilyl groups are dimethylalkylsilyl groups composed of methyl groups.   The method for manufacturing an electrostatic actuator according to any one of claims 7 to 11, further comprising a pretreatment step of removing moisture adhering to the facing surface prior to the surface treatment step of the facing surface.   13. The method of manufacturing an electrostatic actuator according to claim 12, wherein the pretreatment step is a vacuum heating step in which the inside of the treatment tank containing the object to be treated is evacuated and heated.   The method of manufacturing an electrostatic actuator according to claim 7, wherein the post-processing step is a vacuum heating step in which the inside of a processing tank containing an object to be processed is evacuated and heated. A method for manufacturing a droplet discharge head, wherein the droplet discharge head is manufactured using the method for manufacturing an electrostatic actuator according to claim 7.

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