JP2009124840A - Electrostatic actuator, droplet discharge head, and droplet discharge device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic actuator that obtains a larger displacement of diaphragm at a lower voltage, and to provide a droplet discharge head using the actuator. <P>SOLUTION: The actuator includes the diaphragm 101 having flexibility, a counter electrode 103 confronted with the diaphragm 101 across a gap 102 and an insulating film formed in a facing part of the diaphragm 101 with the counter electrode 103. The insulating film is a film 104 of a piezoelectric material which has a higher dielectric constant compared to silicon oxides and warpages in accordance with a voltage applied between the diaphragm 101 and the counter electrode 103. The droplet discharge head uses the electrostatic actuator. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrostatic actuator used for an inkjet head or the like, a droplet discharge head and a droplet discharge device including the electrostatic actuator.

  An ink jet recording apparatus has many advantages such as high-speed printing, extremely low noise during recording, high degree of freedom of ink, and use of inexpensive plain paper. In recent years, so-called ink-on-demand ink jet recording apparatuses, which eject ink droplets only when recording is necessary, have become mainstream among ink jet recording apparatuses. This ink-on-demand ink jet recording apparatus has an advantage that it does not require collection of ink droplets unnecessary for recording.

  In this ink-on-demand ink jet recording apparatus, as a method for ejecting ink droplets, a so-called electrostatic drive system using an electrostatic actuator having a vibration plate and an individual electrode facing the drive means as a drive means. There is an ink jet recording apparatus. In addition, there are so-called piezoelectric drive type ink jet recording apparatuses that use piezoelectric elements (piezo elements) as driving means, and so-called bubble jet (registered trademark) type ink jet recording apparatuses that use heating elements and the like.

  The inkjet head of the electrostatic drive type recording device charges the diaphragm and the individual electrodes, attracts the diaphragm to the individual electrode side and bends it, and then stops charging to return the diaphragm to its original state. The ink discharge pressure is obtained by returning to. At this time, an insulating film for preventing a short circuit is formed between the diaphragm and the individual electrode so that the diaphragm does not stick to the individual electrode.

In an electrostatic drive type ink jet head, it is efficient to discharge a large number of liquid droplets by largely displacing the diaphragm with a voltage as low as possible. For this reason, by forming individual electrodes for driving the diaphragm stepwise along the short side or the long side direction of the diaphragm, an invention such as obtaining a larger displacement of the diaphragm at a relatively low voltage, etc. Has been conventionally proposed (see, for example, Patent Document 1).
JP 2000-318155 A (the second page, FIG. 2 etc.)

  However, forming individual electrodes in a stepped manner as in Patent Document 1 requires forming a plurality of steps in advance on the electrode substrate on which the individual electrodes are formed, which complicates the structure.

  In view of the above problems, the present invention proposes an electrostatic actuator that can obtain a larger displacement of a diaphragm at a lower voltage while having a simple configuration, and further, a droplet discharge head and a liquid using the electrostatic actuator. It aims at obtaining a droplet discharge device.

An electrostatic actuator according to the present invention includes a flexible diaphragm, a counter electrode facing the diaphragm with a gap therebetween, and an insulating film formed on a facing portion of the counter electrode of the diaphragm. The insulating film is a piezoelectric film having a relative dielectric constant higher than that of silicon oxide and distorted according to the voltage applied between the diaphragm and the counter electrode.
In the electrostatic actuator having this configuration, when a voltage is applied between the diaphragm and the counter electrode, the piezoelectric film is distorted. The gap between is narrowed. Furthermore, an electrostatic force acts on the narrow gap, and the diaphragm bends toward the counter electrode. Since the electrostatic force is inversely proportional to the square of the gap, the diaphragm can be displaced with a smaller voltage as the gap becomes narrower. Thereby, it is possible to obtain a large displacement of the diaphragm at a voltage lower than that conventionally required.

The amount of gap between the diaphragm and the counter electrode before voltage application is determined by the amount of deflection of the diaphragm due to the piezoelectric film's piezoelectric power when a predetermined voltage is applied to the diaphragm and the counter electrode. It is preferable to add the amount of deflection of the diaphragm due to the electrostatic force generated between the diaphragm and the counter electrode.
Thereby, when a predetermined voltage is applied to the diaphragm and the counter electrode, the diaphragm comes into contact with the counter electrode, and a large displacement amount of the diaphragm can be secured.

In addition, the diaphragm is formed on the silicon substrate, the counter electrode is formed on the glass substrate, the piezoelectric film is formed only on the opposite side of the counter electrode of the diaphragm, and the silicon substrate and the glass substrate are It is preferable that anodic bonding is performed at a portion where no piezoelectric film is present.
In this way, if the piezoelectric film is disposed only at the opposite portion of the diaphragm with respect to the counter electrode, and the silicon substrate and the glass substrate are anodically bonded at the portion without the piezoelectric film, the bonding quality is improved. And the quality of the electrostatic actuator is improved.

A droplet discharge head according to the present invention includes any one of the electrostatic actuators described above, and the vibration plate constitutes one surface of a discharge chamber in which a pressure fluctuation is generated for liquid discharge.
Furthermore, a liquid droplet ejection apparatus according to the present invention includes the above liquid droplet ejection head in a liquid ejection unit.
Since these droplet discharge heads and droplet discharge devices include the electrostatic actuator, a large displacement of the diaphragm can be generated with a relatively low applied voltage. Can do a lot.

Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing the configuration and operation of the electrostatic actuator of the present invention.
As shown in FIG. 1A, the electrostatic actuator 100 includes a diaphragm 101 having flexibility, a counter electrode 103 facing the diaphragm 101 with a gap 102 therebetween, and a counter electrode of the diaphragm 101. And a piezoelectric film 104 which is an insulating film formed on a portion facing the substrate 103. The piezoelectric film 104 is a material that is distorted in response to application of a voltage. For example, lead zirconate titanate (PZT) can be used.
The diaphragm 101 is formed from a silicon substrate 110, and the counter electrode 103 is formed of a conductor (for example, ITO) in a recess formed in the glass substrate 120. A gap 102 is formed between the diaphragm 101 and the counter electrode 103 due to the recess.

  In this example, the silicon film 110 and the glass substrate 120 are disposed in a portion where the piezoelectric film 104 is not provided so that the piezoelectric film 104 is disposed only on a portion facing the counter electrode 103 of the vibration plate 101. Anodic bonding is performed through a silicon oxide film 105 which is silicon oxide. Anodic bonding is well known as a bonding method suitable for precision bonding.

  In the electrostatic actuator 100 of FIG. 1A, when a voltage is applied between the diaphragm 101 and the counter electrode 103, an electric field is applied to the piezoelectric film 104 as shown in FIG. The piezoelectric film 104 is distorted and deformed, and the diaphragm 101 bends in accordance with the deformation. Thereby, the gap 102 between the diaphragm 101 and the counter electrode 103 is narrowed.

Further, as shown in FIG. 1C, the vibration plate 101 is attracted to the counter electrode 103 side by the electrostatic force and bent, and comes into contact with the counter electrode 103 through the piezoelectric film 104.
As described above, the vibration plate 101 is displaced as shown in FIGS. 1A to 1C, so that the vibration plate 101 is in the state shown in FIGS. The diaphragm 101 can be displaced by the same amount or more with a lower voltage compared to the case of displacing it.

  Therefore, when a predetermined voltage is applied to the diaphragm 101 and the counter electrode 103, the vibration due to the piezoelectric power of the piezoelectric film 104 is determined between the diaphragm 101 and the counter electrode 103 before voltage application. When the amount of bending of the plate 101 and the amount of bending of the vibration plate 101 due to the electrostatic force generated between the vibration plate 101 and the counter electrode 103 are added, the most efficient displacement with respect to the vibration plate 101 is obtained. Is possible.

FIG. 2 is a circuit diagram showing an equivalent circuit of the electrostatic actuator of FIG. In this equivalent circuit, “E” represents an applied voltage, “C1” represents a capacitance (capacitor) caused by the piezoelectric film 104, and “C2” represents a capacitance (capacitor) caused by the gap 102. In this equivalent circuit, the voltage Va applied to the piezoelectric film 104 can be expressed by the following equation.
Va = [(ε _g / d _g ) / ((ε _g / d _g ) + (ε _a / d _a ))] · E
In the above formula, d represents the distance between the diaphragm 101 and the counter electrode 103, and ε represents the relative dielectric constant of the piezoelectric film 104 and the gap 102. The subscript a represents the piezoelectric film 104 and g represents the gap 102.
Here, the thickness of the piezoelectric film 104 is 200 μm, the amount (or width) of the gap 102 when no voltage is applied is 400 nm, the thickness of the diaphragm 101 is 1 μm, and the applied voltage (input voltage) E is 45V. As a trial calculation, the voltage Va applied to the piezoelectric film 104 is about 15V.

If the displacement amount of the diaphragm 101 when a voltage of 15 V is applied to the piezoelectric film 104 is 200 nm, the amount of the remaining gap 102 is narrowed to 200 nm. In this state, a voltage of about 20 V is required to bring the diaphragm 101 into contact with the counter electrode 103 by electrostatic force. In this example, since it can be considered that a voltage of 30 V (45 V-15 V) is applied to the gap 102, the diaphragm 101 can be brought into contact with the counter electrode 103 by electrostatic force.
For this reason, when a predetermined voltage (for example, 45 V described above) is applied to the diaphragm 101 and the counter electrode 103, the gap amount between the diaphragm 101 and the counter electrode 103 before voltage application is applied. The amount of deflection of the diaphragm 101 caused by the distortion due to the piezoelectric power of the membrane 104 and the amount of deflection of the diaphragm 101 due to the electrostatic force generated between the diaphragm 101 and the counter electrode 103 should be added. preferable.

On the other hand, when the distortion of the piezoelectric film 104 is not taken into account, the amount of the gap 102 remains at the initial 400 nm, so that the voltage is 50 V in order to bring the diaphragm 101 into contact with the counter electrode 103. Therefore, a higher applied voltage is required as compared with the structure including the piezoelectric film 104.
Although the piezoelectric body has a lower instantaneous dielectric breakdown strength (TZDB) than a silicon oxide film or the like, application to an electrostatic actuator is possible by sufficiently increasing the film thickness.

In the first embodiment, the piezoelectric film 104 is disposed as an insulating film in a portion facing the counter electrode 103 of the vibration plate 101, and the voltage is lower than that in the case where the piezoelectric film 104 is not provided. A large displacement of the diaphragm 101 can be obtained.
In addition, by arranging the piezoelectric film 104 only on the opposite side of the diaphragm 101 to the counter electrode 103, anodic bonding between the silicon substrate 110 and the glass substrate 120 is also possible.

Embodiment 2. FIG.
FIG. 3 shows a droplet discharge head 1 according to the second embodiment of the present invention, in which the electrostatic actuator having the configuration described in the first embodiment is applied to a droplet discharge portion. The droplet discharge head of the present invention is not limited to the structure and shape shown in FIG. 3 below, and is a four-layer structure in which four substrates each having a discharge chamber and a reservoir portion provided on separate substrates are stacked. The present invention can also be applied to a structure or a liquid droplet ejection head in which nozzle holes are provided at the edge of the substrate. The droplet discharge head 1 is configured by bonding three substrates of a cavity substrate 2, an electrode substrate 3, and a nozzle substrate 4 in three layers. FIG. 3 schematically shows the drive circuit 21 portion.

  The nozzle substrate 4 is made of silicon, for example, a cylindrical first nozzle hole 6 and a cylindrical second nozzle hole that communicates with the first nozzle hole 6 and has a larger diameter than the first nozzle hole 6. 7 is formed. The first nozzle hole 6 is formed so as to open on the droplet discharge surface 10 (the surface opposite to the bonding surface 11 with the cavity substrate 2), and the second nozzle hole 7 is bonded with the cavity substrate 2. It is formed so as to open on the surface 11.

  The cavity substrate 2 is made of, for example, single crystal silicon, and a plurality of recesses serving as discharge chambers 13 whose bottom wall functions as the diaphragm 12 (corresponding to the diaphragm 101 in FIG. 1) are formed. It is assumed that the plurality of discharge chambers 13 are formed in parallel from the front side to the back side in FIG. In addition, the cavity substrate 2 has a recess serving as a reservoir 14 for supplying a droplet of ink or the like to each discharge chamber 13 and a recess serving as a narrow groove-like orifice 15 that communicates the reservoir 14 with each discharge chamber 13. Is formed. In the droplet discharge head 1 shown in FIG. 3, the reservoir 14 is formed from a single recess, and one orifice 15 is formed for each discharge chamber 13. The orifice 15 may be formed on the bonding surface 11 of the nozzle substrate 4.

An insulating film is formed on the surface of the cavity substrate 2 on the side where the electrode substrate 3 is bonded. The same material is not uniformly formed in the insulating film, and a piezoelectric film 104 is formed on a portion facing a counter electrode 17 (corresponding to the counter electrode 103 in FIG. 1) to be described later. In other portions, a silicon oxide film 16 (corresponding to the silicon oxide film 105 in FIG. 1) made of silicon oxide is formed and becomes an insulating film.
On the other hand, a droplet-proof protective film 19 is formed on the surface of the cavity substrate 2 on the side where the nozzle substrate 4 is bonded. The droplet-resistant protective film 19 is for preventing the cavity substrate 2 from being etched by droplets inside the discharge chamber 13 and the reservoir 14.

  An electrode substrate 3 made of borosilicate glass, for example, is bonded to the cavity substrate 2 side of the cavity substrate 2. On the electrode substrate 3, a plurality of counter electrodes (also referred to as individual electrodes because they are independent from each other) 17 facing the diaphragm 12 through gaps 20 (corresponding to the gaps 102 in FIG. 1) are formed. The counter electrode 17 is formed by sputtering a conductive material, for example, ITO (Indium Tin Oxide). A liquid supply hole 18 that communicates with the reservoir 14 is formed in the electrode substrate 3. The liquid supply hole 18 is connected to a hole provided in the bottom wall of the reservoir 14, and is provided to supply a discharge liquid such as ink to the reservoir 14 from the outside.

  The bonding method of the electrode substrate 3 and the cavity substrate 2 is not particularly limited. However, when the electrode substrate 3 is made of borosilicate glass and the cavity substrate 2 is made of a silicon substrate, they are anodic bonded through the silicon oxide film 16. Can be joined with high quality.

Next, the operation of the droplet discharge head 1 will be described. A drive circuit 21 is connected to the cavity substrate 2 and each counter electrode 17. When a pulse voltage is applied between the cavity substrate 2 and the counter electrode 17 by the drive circuit 21, the diaphragm 12 is bent toward the counter electrode 17 as shown in FIGS. Then, it comes into contact with the counter electrode 17 through the piezoelectric film 104. As a result, ink droplets or the like that have accumulated in the reservoir 14 flow into the ejection chamber 13. When the voltage applied between the diaphragm 12 and the counter electrode 17 disappears, the diaphragm 12 returns to its original position, the pressure inside the discharge chamber 13 increases, and a droplet such as ink from the nozzle 8. Is discharged.
As described with reference to the action of the electrostatic actuator according to the first embodiment, the droplet discharge head 1 can greatly displace the diaphragm 12 with a lower applied voltage than when the piezoelectric film 104 is not provided. The liquid discharge amount can be stably increased with a relatively low applied voltage.

Here, an example of a method for manufacturing the droplet discharge head 1 will be briefly described. In addition, the code | symbol in description is a code | symbol corresponding to FIG.
First, for example, after both surfaces of a silicon substrate having a thickness of 525 μm (which will later become the cavity substrate 2) are mirror-polished, the piezoelectric material is obtained by ECR (Electron Cyclotron Resonance) sputtering, plasma CVD, AD method (Aerosol Deposition method), or the like. The film 104 (for example, PZT film) is directly formed on one surface of the silicon substrate, for example, with a thickness of 200 μm. Here, when the AD method is used, a low-stress insulating film can be formed at a relatively low temperature or normal temperature, and when ECR sputtering is used, a dense insulating film can be formed.
Note that before forming the piezoelectric film 104 on the silicon substrate, boron may be diffused on the surface of the formation surface to form a boron doped layer.

Next, resist patterning is performed on the surface of the piezoelectric film 104 by photolithography so that the piezoelectric film 104 remains only in a portion that will face the counter electrode 17 in a later etching process.
Subsequently, the piezoelectric film 104 is wet-etched with, for example, a buffered hydrofluoric acid solution, thereby forming the piezoelectric film 104 in a portion that faces the counter electrode 17. Note that RIE (Reactive Ion Etching) using CHF3 may be used instead of wet etching using a buffered hydrofluoric acid aqueous solution. Then, the resist used for patterning is removed by oxygen plasma or the like.
Thereafter, the surface of the silicon substrate on the side where the piezoelectric film 104 is formed is formed on the entire surface other than the portion where the piezoelectric film 104 is formed by, for example, TEOS (Tetra Ethyl Ortho Silicate) plasma CVD. A silicon oxide film 16 of about 100 nm is formed.

Subsequently, the silicon substrate and the electrode substrate 3 on which the counter electrode 17 is formed are heated to, for example, 360 ° C., an anode is connected to the silicon substrate, and a cathode is connected to the electrode substrate 3 to apply a voltage of about 800 V to perform anodic bonding. Do. The electrode substrate 3 is formed by etching a glass substrate made of borosilicate glass with a hydrofluoric acid aqueous solution or the like using a gold / chromium etching mask, for example, and then forming a recess in the recess by sputtering or the like. For example, the counter electrode 17 made of ITO can be formed.
After anodic bonding of the silicon substrate and the electrode substrate 3, the entire silicon substrate is thinned to a thickness of, for example, 140 μm by, for example, mechanical grinding. After mechanical grinding, it is desirable to perform light etching with a potassium hydroxide aqueous solution or the like in order to remove the work-affected layer.

Then, a silicon oxide film having a thickness of, for example, 1.5 μm is formed on the entire upper surface of the silicon substrate (the surface opposite to the surface to which the electrode substrate 3 is bonded) by TEOS plasma CVD. Then, the silicon oxide film is patterned with a resist for forming a recess serving as the discharge chamber 13, a recess serving as the reservoir 14, and a recess serving as the orifice 15, and the silicon oxide film in this portion is removed by etching.
Thereafter, the silicon substrate is wet-etched with a potassium hydroxide aqueous solution or the like to form a recess serving as the discharge chamber 13, a recess serving as the reservoir 14, and a recess serving as the orifice 15, and then the silicon oxide film is removed. In the wet etching step, the surface roughness of the diaphragm 12 can be suppressed by using, for example, a 35% by weight potassium hydroxide aqueous solution first and then using a 3% by weight potassium hydroxide aqueous solution. it can.
Thereafter, a droplet-proof protective film 19 made of a silicon oxide film or the like is formed with a thickness of, for example, 0.1 μm on the surface of the silicon substrate where the recesses or the like serving as the discharge chamber 13 are formed.

Next, the nozzle substrate 4 on which the nozzles 8 are formed is bonded to the surface of the silicon substrate on which the recesses and the like serving as the discharge chambers 13 are formed, using an adhesive or the like.
Finally, the bonded substrate to which the silicon substrate, the electrode substrate 3 and the nozzle substrate 4 are bonded is separated by dicing (cutting), and the droplet discharge in which the cavity substrate 2, the electrode substrate 3 and the nozzle substrate 4 are laminated is performed. The head 1 is completed.

  Through the above steps, a small-sized electrostatic actuator excellent in driving durability can be manufactured in which the withstand voltage is secured between the diaphragm 12 and the counter electrode 17 and the actuator driving voltage is reduced. .

Embodiment 3. FIG.
FIG. 4 is a perspective view of an ink jet printer which is a droplet discharge device in which the droplet discharge head described in the second embodiment is applied to a droplet discharge unit.
The ink jet printer 200 can obtain a larger amount of ejected droplets by using a voltage lower than a conventionally used voltage due to the action of the droplet ejection head applied thereto. Therefore, there is no missing dot and the print quality is improved. Further, it is excellent in durability and discharge stability, and is further small in size and excellent in driving durability.

  In addition to the ink jet printer described above, the droplet discharge head 1 shown in Embodiment 2 can be used to produce a color filter for a liquid crystal display and to form a light emitting portion of an organic EL display device by replacing the discharge liquid. It can also be applied to the discharge of biological liquids.

It is a figure which shows the structure and effect | action of an electrostatic actuator which concern on Embodiment 1 of this invention. FIG. 2 is an equivalent circuit diagram of the electrostatic actuator of FIG. 1. It is sectional drawing of the droplet discharge head which concerns on Embodiment 2 of this invention. It is a perspective view of the inkjet printer which concerns on Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Droplet discharge head, 2 Cavity substrate, 3 Electrode substrate, 4 Nozzle substrate, 6 1st nozzle hole, 7 2nd nozzle hole, 8 Nozzle, 10 Droplet discharge surface, 11 Joining surface, 12 Vibration plate, 13 Discharge chamber, 14 reservoir, 15 orifice, 16 silicon oxide film, 17 counter electrode, 18 liquid supply hole, 19 droplet-resistant protective film, 20 gap, 21 drive circuit, 100 electrostatic actuator, 101 diaphragm, 102 gap, 103 Counter electrode 104 Piezoelectric film, 105 Silicon oxide film, 110 Silicon substrate, 120 Glass substrate, 200 Inkjet printer.

Claims (5)

A diaphragm having flexibility, a counter electrode facing the diaphragm with a gap, and an insulating film formed at a facing portion of the counter electrode of the diaphragm,
An electrostatic actuator characterized in that the insulating film is a piezoelectric film having a relative dielectric constant higher than that of silicon oxide and distorted according to a voltage applied between the diaphragm and the counter electrode.   The diaphragm by the piezoelectric power of the piezoelectric film when a predetermined voltage is applied to the diaphragm and the counter electrode to determine the gap amount between the diaphragm and the counter electrode before voltage application 2. The electrostatic actuator according to claim 1, wherein an amount of bending of the diaphragm and an amount of deflection of the diaphragm due to an electrostatic force generated between the diaphragm and the counter electrode are added.   The diaphragm is formed on a silicon substrate, the counter electrode is formed on a glass substrate, and the piezoelectric film is formed only on a portion of the diaphragm facing the counter electrode, and the silicon substrate 3. The electrostatic actuator according to claim 1, wherein the glass substrate is anodically bonded at a portion of the piezoelectric body where no film is formed.   A droplet discharge head comprising the electrostatic actuator according to claim 1, wherein the vibration plate constitutes one surface of a discharge chamber that causes a pressure fluctuation for liquid discharge.   A droplet discharge device comprising the droplet discharge head according to claim 4 in a liquid discharge portion.

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