JP2010173080A - Electrostatic actuator, liquid droplet delivering head, and liquid droplet delivering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic actuator capable of obtaining a large amount of displacement of an oscillating plate by achieving low voltage driving, and a liquid droplet delivering head and a liquid droplet delivering device including the electrostatic actuator. <P>SOLUTION: The electrostatic actuator includes: the oscillating plate 4 functioning as a first electrode; an individual electrode 11 opposed to the oscillating plate 4 through a gap G and functioning as a second electrode where voltage is applied between the oscillating plate 4 and the individual electrode 11; an insulating film 4a formed on an opposed surface of the oscillating plate 4 to the individual electrode 11; and an insulating film 11a formed on an opposed surface of the individual electrode 11 to the oscillating plate 4, and the insulating film 4a and the insulating film 11a are formed of material of the same kind, and made to be an electret. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrostatic actuator, a droplet discharge head, and a droplet discharge device that are used as a drive mechanism for an inkjet head or the like.

  Conventionally, as a droplet discharge head, there are a thermal method using a heat generating element or the like as a driving unit and an actuator drive method droplet discharge head. As an actuator driving method, there are a so-called electrostatic driving method using electrostatic force as a driving means and a so-called piezoelectric driving method using a piezoelectric element (piezo element).

  In an actuator-driven droplet discharge head, a diaphragm constituting a part of the discharge chamber is elastically displaced by electrostatic force or the piezoelectric effect of a piezoelectric element, and a droplet is discharged from the nozzle by generating pressure in the discharge chamber. I am doing so. In this type of droplet discharge head, in recent years, the number of nozzles has been increased in order to cope with high-speed printing, and a minute actuator has been demanded from the demand for higher resolution. However, when the actuator is downsized and densified, the amount of displacement of the diaphragm becomes insufficient, which causes a problem that sufficient pressure is not generated in the discharge chamber and the required droplet discharge amount cannot be obtained. there were.

  Therefore, in the piezoelectric drive type actuator, an inorganic electret layer is multilayered on the vibration plate to obtain a large mechanical driving force to increase the displacement amount of the vibration plate (see, for example, Patent Document 1). .

  Further, in an electrostatic drive type actuator, an insulating film is provided on one of opposing surfaces of a diaphragm and a counter electrode (individual electrode) disposed opposite to the diaphragm, and the insulating film is electretized ( The dielectric film having a permanent electric polarization) is charged in advance so as to secure a large diaphragm displacement by low voltage driving (see, for example, Patent Document 2). In a droplet discharge head to which an electrostatic actuator is applied, generally, the diaphragm and the individual electrode come into contact when the diaphragm is displaced.

JP 2004-255605 A (page 4, FIG. 1) JP2007-105971A (6th page, FIG. 2)

  In the technique of Patent Document 1, since the inorganic electret layer is multilayered on the diaphragm, it is necessary to increase the thickness of the diaphragm in order to support it. For this reason, the mechanical resistance is increased, and it is actually difficult to obtain a diaphragm displacement sufficient for stable ejection of droplets. Accordingly, there is a problem that it is necessary to increase the drive voltage in order to obtain a sufficient diaphragm displacement. In addition, the manufacturing process is complicated and requires a manufacturing cost.

  Further, in the technique of Patent Document 2, since the contact surface between the diaphragm and the individual electrode has a structure formed of a different material, unintentional charging is caused when contact and separation between the diaphragm and the individual electrode are repeated by driving. Will occur. In other words, the electric charge remains in the insulating film, and the diaphragm is bent by the electric field created by the residual charge and the characteristics change from the initial stage (decrease in driving characteristics), or the diaphragm and the individual electrodes are stuck together and cannot operate ( There has been a problem that inconvenience such as reduction in driving durability occurs.

  The present invention has been made in view of these points, and an object of the present invention is to provide an electrostatic actuator that can be driven at a low voltage and can obtain a large displacement of the diaphragm. It is another object of the present invention to provide a droplet discharge head and a droplet discharge apparatus provided with this electrostatic actuator.

An electrostatic actuator according to the present invention includes a diaphragm that functions as a first electrode, a second electrode that faces the diaphragm with a gap therebetween, and a voltage is applied between the diaphragm and the diaphragm. A first insulating film formed on the surface facing the second electrode, and a second insulating film formed on the surface facing the diaphragm of the second electrode. The two insulating films are made of the same material and are electretized.
As described above, since the insulating films made of the same kind of material are provided on both surfaces of the diaphragm and the second electrode facing each other, it is possible to prevent contact charging. Accordingly, it is possible to prevent the drive characteristics from being deteriorated and to improve the drive durability.
In addition, since the first insulating film and the second insulating film are electretized, an electric field is formed between the diaphragm and the second electrode when no voltage is applied, and the electric field is generated by applying a normal voltage. Low voltage driving is possible for the voltage required to achieve this. Accordingly, the amount of displacement of the diaphragm can be increased as much as low voltage driving is possible.

In the electrostatic actuator according to the present invention, the electrets of the first insulating film and the second insulating film have different polarities.
Thereby, the electric field of the same direction is formed in a gap, and an electrostatic attraction force can be generated.

In the electrostatic actuator according to the present invention, the first insulating film and the second insulating film are silicon oxide films.
Thus, a silicon oxide film can be used as an insulating film to be electretized.

In the electrostatic actuator according to the present invention, the first insulating film and the second insulating film are made of a high-k material.
Thus, a High-k material can be used as the insulating film to be electretized. By using a High-k material, it is possible to improve the insulation and operating characteristics of the electrostatic actuator.

Further, a liquid droplet ejection head according to the present invention includes the electrostatic actuator described above, a nozzle from which liquid droplets are ejected, and a liquid flow channel that communicates with the nozzle and has a diaphragm formed in part. It is.
As described above, since the electrostatic actuator is provided, it is possible to obtain a liquid droplet ejection head that can obtain low voltage driving and a large displacement amount of the diaphragm, and is excellent in driving durability.

A droplet discharge apparatus according to the present invention is equipped with the above-described droplet discharge head.
Since the liquid droplet ejection head is provided as described above, a liquid droplet ejection device that exhibits the effects of the liquid droplet ejection head can be obtained.

FIG. 3 is an exploded perspective view of a droplet discharge head including the electrostatic actuator according to the first embodiment. FIG. 2 is a schematic longitudinal sectional view of the droplet discharge head shown in FIG. 1. AA sectional drawing of FIG. The figure which shows the structure of the charging device by corona charging. FIG. 3 is an example diagram of a droplet discharge device including the electrostatic actuator according to the first embodiment.

Embodiment 1 FIG.
FIG. 1 is an exploded perspective view of a droplet discharge head including an electrostatic actuator according to Embodiment 1 of the present invention. FIG. 2 is a schematic longitudinal sectional view of the droplet discharge head shown in FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG.

  The droplet discharge head 100 according to the first embodiment is mainly configured by bonding a cavity substrate 1, an electrode substrate 2, and a nozzle substrate 3. The cavity substrate 1 is made of, for example, a single crystal silicon substrate (hereinafter simply referred to as a silicon substrate), and is subjected to the following predetermined processing. In FIG. 1, for example, a silicon substrate having a (110) plane orientation of about 50 μm in thickness is used as the cavity substrate 1. In the cavity substrate 1, a silicon substrate is anisotropically etched to form a recess 5 a that forms a discharge chamber 5 whose bottom wall is formed as a diaphragm 4, and a reservoir that stores droplets to be supplied to each discharge chamber 5. 6 is formed. A liquid flow path is formed by the discharge chamber 5, the reservoir 6, and an orifice 21 described later.

The diaphragm 4 is formed of a high-concentration boron-doped layer. This boron-doped layer is formed by doping boron at a high concentration (about 5 × 10 ¹⁹ atoms / cm ³ or more). For example, when single crystal silicon is etched with an alkaline aqueous solution, the etching rate is extremely low. This is a so-called etching stop layer that is delayed. Since the boron-doped layer functions as an etching stop layer, the thickness of the diaphragm 4 and the volume of the discharge chamber 5 can be formed with high accuracy. The diaphragm 4 is formed with a thickness of 4 μm in this example. The diaphragm 4 having such a configuration functions as a common electrode (first electrode) on each discharge chamber 5 side.

  An insulating film 4a is formed on the entire surface of the cavity substrate 1 on the electrode substrate 2 side. The insulating film 4a is provided for the purpose of preventing a short circuit and a dielectric breakdown between the diaphragm 4 functioning as a common electrode on each discharge chamber 5 side and an individual electrode (second electrode) 11 described later. In the present invention, the insulating film 4a is further electretized (a dielectric having permanent electric polarization). The electret has an action of permanently maintaining polarization even in a state where no voltage is applied and no electric field exists outside, and forms an electric field with respect to the surroundings.

The insulating film 4a is formed of a silicon oxide film (SiO ₂ film) by thermal oxidation. As the material of the insulating film 4a, for example, a TEOS (Tetraethylorthosillicate Tetraethoxysilane) film having a thickness of about 0.1 μm may be formed by plasma CVD (Chemical Vapor Deposition method), or silicon oxide. Alternatively, a dielectric material having a higher relative dielectric constant, that is, a so-called High-K (high dielectric constant gate insulating film) material such as alumina may be used. Since the insulating film made of a High-K material has a higher dielectric constant than silicon oxide, it is possible to improve the insulating properties and operating characteristics of the electrostatic actuator. In addition, other films such as silicon oxynitride, tantalum oxide, hafnium nitride silicate, or hafnium oxynitride silicate may be used as long as they are insulating films that can be converted into electrets. The electretization of the insulating film 4a will be described later.

  The electrode substrate 2 is made of, for example, borosilicate glass having a thickness of 1 mm, and is joined to the diaphragm 4 side of the cavity substrate 1. In this electrode substrate 2, an electrode recess 8 having a depth of, for example, 0.2 μm and forming a gap G with the diaphragm 4 is formed by etching. An individual electrode (second electrode) 11 is formed inside the electrode recess 8 so as to face the diaphragm (first electrode) 4. The individual electrode 11 is made of ITO (Indium Tin Oxide) doped with tin oxide or the like, and is formed with a thickness of 0.1 μm by sputtering, for example.

  In addition, an insulating film 11 a is formed on the individual electrode 11 at a portion facing the diaphragm 4. The insulating film 11a is also electreted like the insulating film 4a. The insulating film 4a and the insulating film 11a are made of the same kind of material to prevent contact charging during driving. Further, the insulating film 4a and the insulating film 11a are configured so that the polarities of the electrets are different from each other as shown in FIG. In FIG. 3, the insulating film 4a side has a positive polarity and the insulating film 11a side has a negative negative polarity. Thus, by reversing the polarities of the electret on the diaphragm 4 side and the electret on the individual electrode 11 side, the directions of the electric fields created in the gap G are the same. Therefore, the magnitude of the electric field generated when no voltage is applied is increased, and low voltage driving is possible.

  The electrode substrate 2 is provided with a liquid supply hole 14 for supplying a droplet to the reservoir 6. Further, the individual electrode 11 is connected to the oscillation circuit 23 via the lead portion 12 and the terminal portion 13 (see FIG. 1) by FPC (not shown). The common electrode terminal 7 provided on the oscillation circuit 23 and the cavity substrate 1 is also connected through the FPC. The gap G is sealed with a sealing material 9. The electrode substrate 2 may be formed of a silicon substrate or the like instead of borosilicate glass.

  The nozzle substrate 3 is made of, for example, a silicon substrate having a thickness of 180 μm, and a nozzle 20 penetrating in the thickness direction of the nozzle substrate 3 is formed. In the nozzle 20, the lower surface side of the nozzle substrate 3 communicates with the discharge chamber 5, and the upper surface side of the nozzle substrate 3 is an opening for discharging droplets. The nozzle 20 includes a first groove 20a having a small cross-sectional area on the upper surface side of the nozzle substrate 3, and a second groove 20b having a large cross-sectional area on the lower surface side of the nozzle substrate 3, and is stepped. It is a two-stage nozzle.

  In addition, on the lower surface of the nozzle substrate 3, a recess 21 a serving as an orifice 21 for communicating the discharge chamber 5 and the reservoir 6 and a recess 22 a for providing the reservoir diaphragm 22 are provided. A portion of the upper surface of the nozzle substrate 3 corresponding to the reservoir diaphragm 22 is a recess. By thinning the reservoir diaphragm 22 in this way, it is possible to stably discharge droplets even when there is a change in the external pressure.

  In practice, a silicon oxide film is formed on the entire outer surface of the nozzle substrate 3, but the illustration thereof is omitted in FIGS. 1 and 2. Further, FIG. 1 shows a droplet discharge head in which the nozzles 20 and the discharge chambers 5 are arranged in two rows, but the nozzles 20 and the discharge chambers 5 may be arranged in one row. In FIGS. 1 and 2, the ejection method has been described by taking the face ejection type of ejecting droplets in parallel to the nozzle substrate 3 as an example, but it may be a side ejection type.

Next, the operation of the droplet discharge head shown in FIGS. 1 and 2 will be described.
The oscillation circuit 23 oscillates at 24 kHz, for example, and supplies a charge to the individual electrode 11 by applying a pulse voltage between the common electrode terminal 7 and the individual electrode 11 of the cavity substrate 1. When a charge is supplied to the individual electrode 11 to be positively charged, the diaphragm 4 is negatively charged, and an electrostatic force is generated between the diaphragm 4 and the individual electrode 11. Due to the suction action of the electrostatic force, the diaphragm 4 is attracted and bent toward the individual electrode 11 side, and the volume of the discharge chamber 5 is increased. As a result, droplets of ink or the like accumulated in the reservoir 6 flow into the discharge chamber 5 through the orifice 21. Next, when the application of voltage to the individual electrode 11 is stopped, the electrostatic attraction force disappears, the diaphragm 4 is restored, and the volume of the discharge chamber 5 contracts rapidly. As a result, the pressure in the discharge chamber 5 rapidly increases, and droplets such as ink are discharged from the nozzles 20 communicating with the discharge chamber 5. Such a method is called pulling, but there is also a method called pushing that discharges droplets using a spring or the like.

  Here, in the droplet discharge head 100 of this example, the insulating film 4a and the insulating film 11a are electretized as shown in FIG. 3, and one is charged to the positive electrode and the other is charged to the negative electrode. For this reason, an electric field is always generated between the diaphragm 4 and the individual electrode 11, and an electrostatic force is generated, and a force that the diaphragm 4 pulls toward the individual electrode 11 side works to such an extent that it does not actually bend. Yes. Therefore, it is possible to drive at a voltage lower than the contact voltage necessary for driving the normal diaphragm 4. Therefore, when a normal contact voltage is applied, the diaphragm displacement can be increased by the amount that enables low voltage driving by the action of the electret portions 4a and 4b.

  As described above, according to the first embodiment, the insulating film 4a and the insulating film 11a made of the same kind of material are provided on both opposing surfaces of the vibration plate 4 and the individual electrode 11. It is possible to prevent contact charging. Accordingly, it is possible to prevent the drive characteristics from being deteriorated and to improve the drive durability.

  In addition, since both insulating films 4a and 11a are electretized and the electrets have different polarities, an electric field in the same direction is formed in the gap G, and an electrostatic attractive force can be generated. For this reason, it is possible to drive at a low voltage by a voltage necessary for generating the electric field by applying a normal voltage. Accordingly, the amount of displacement of the diaphragm can be increased as much as low voltage driving is possible.

  Incidentally, as a charging method for electretizing the insulating film 4a and the insulating film 11a, there are a corona discharge, a thermal electret method, and an electron beam method. In this example, charging is performed by corona discharge. Here, a charging method using corona discharge will be briefly described.

FIG. 4 is a diagram illustrating a configuration of a charging device using corona discharge.
The charging device includes a wire electrode 31 made of tungsten and a grid electrode 32 configured in a lattice shape, and a high voltage V1 is applied to the wire electrode 31 and a low voltage V2 is applied to the grid electrode 32, thereby providing a stage. The insulating film 34 a on the silicon substrate 34 placed on the substrate 33 is charged. When positive charging is performed, a positive voltage is applied to the high voltage V1 and the low voltage V2, and when negative charging is performed, a negative voltage is applied to the high voltage V1 and the low voltage V2. The high voltage V1 applies a voltage sufficient for the wire to cause corona discharge, and the low voltage V2 sets a value within a range where the electret does not cause dielectric breakdown. In this example, by using this charging device, a voltage of 2 kV is applied in an atmosphere of 100 ° C. for about 1 hour to charge the insulating film 4a with a charge corresponding to 24V, thereby obtaining an electretized insulating film 4a. Yes. The insulating film 11b is also electreted in the same manner, and is charged by switching the polarity with the insulating film 4a. The insulating film 4a and the insulating film 11a may be electretized at a stage before the cavity substrate 1 and the electrode substrate 2 are bonded.

Embodiment 2. FIG.
FIG. 5 is a view showing an example of a droplet discharge apparatus according to Embodiment 2 of the present invention. FIG. 5 shows an example of an inkjet recording apparatus that discharges ink in particular. An ink jet recording apparatus 110 shown in FIG. 5 is an ink jet printer, and is equipped with a droplet discharge head 100 including the electrostatic actuator of the first embodiment. For this reason, low voltage driving is possible, a large diaphragm displacement can be obtained, and the generated pressure in the discharge chamber 5 can be increased. Therefore, stable discharge characteristics can be obtained, and high-resolution printing can be performed. Therefore, in the second embodiment, it is possible to obtain the ink jet recording apparatus 110 that can stably perform high-quality printing.

  In addition, since an electrostatic actuator with good driving durability is mounted, a highly reliable ink jet recording apparatus 110 can be obtained.

  In addition to the ink jet printer shown in FIG. 5, the droplet discharge head 100 provided with the electrostatic actuator according to the first embodiment can change the liquid to be discharged in various ways, thereby forming a matrix pattern of the color filter, organic The present invention can also be applied to a droplet discharge device that forms a light emitting portion of an EL display device, discharges a biological liquid sample, and the like.

  1 cavity substrate, 2 electrode substrate, 4 diaphragm, 4a insulating film, 5 discharge chamber, 5a recess, 6 reservoir, 6a recess, 7 common electrode terminal, 8 electrode recess, 9 sealing material, 11 individual electrode, 11a insulation Membrane, 12 Lead portion, 13 Terminal portion, 14 Liquid supply hole, 20 Nozzle, 20a First groove, 20b Second groove, 21 Orifice, 21a Recess, 22 Reservoir diaphragm, 22a Recess, 23 Oscillation circuit, 31 Wire electrode , 32 grid electrode, 33 stage, 34 silicon substrate, 34a insulating film, 100 droplet discharge head, 110 inkjet recording apparatus, G gap.

Claims (6)

A diaphragm functioning as a first electrode;
A second electrode that is opposed to the diaphragm with a gap and to which a voltage is applied to the diaphragm;
A first insulating film formed on a surface of the diaphragm facing the second electrode;
A second insulating film formed on a surface of the second electrode facing the diaphragm,
The electrostatic actuator, wherein the first insulating film and the second insulating film are made of the same material and are electretized.   The electrostatic actuator according to claim 1, wherein polarities of electrets of the first insulating film and the second insulating film are different from each other.   The electrostatic actuator according to claim 1, wherein the first insulating film and the second insulating film are silicon oxide films.   The electrostatic actuator according to claim 1, wherein the first insulating film and the second insulating film are high-k materials.   5. An electrostatic actuator according to claim 1, a nozzle from which liquid droplets are ejected, and a liquid flow channel that communicates with the nozzle and in which the vibration plate is partially formed. A droplet discharge head characterized by that.   A liquid droplet ejection apparatus, comprising the liquid droplet ejection head according to claim 5.

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