JP2000015800A - Ink-jet head using surface elastic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet head which has a highly stable surface elastic wave generation means with a long service life without generating migrations and in which a wide range of inks can be used. SOLUTION: In an ink-jet head having a piezoelectric substrate 1 for generating surface elastic waves, a comb-shaped electrode 2 set on the piezoelectric substrate 1 for generating an a.c. voltage and an ink liquid chamber for supplying an ink in a propagation direction of surface elastic waves if desired, a metallic oxide film or metallic nitride film is formed on a front face of the comb-shaped electrode 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave generator and an output unit for an image forming apparatus such as a printer, a facsimile, a copying machine, etc., which records an image by flying particularly fine ink droplets. And an inkjet head using a surface acoustic wave.

[0002]

2. Description of the Related Art As an ink jet recording method, a bubble jet method in which a bubble is formed in ink by a heater and the ink is ejected by this pressure, or ink is ejected by using a bulk electromechanical displacement of a piezoelectric element. Continuous or on-demand piezo jet systems have been widely commercialized.

[0003] These types of ink jet heads are:
Fine nozzle, so that fine pixel dots can be formed
It is manufactured by processing a heater or a fine piezoelectric element. Therefore, ink clogging with fine nozzles is likely to occur. In the bubble jet method,
Ink may be scorched on the heater, and there is a limit to the ink material that can be used to avoid scorching. Further, in the piezo method, it is difficult to manufacture a high-density, long, multi-head due to the problem of mounting a driver and supplying energy to a nozzle.

On the other hand, in recent years, for example, a microfluidic device utilizing a streaming phenomenon of a surface acoustic wave (Technical Report of the Institute of Electronics, Information and Communication Engineers,
U.S. Pat. No. 89-51, P41-46, Shiokawa, etc.) and a droplet jet apparatus that emits surface acoustic waves into ink to make the ink fly (Japanese Patent Application Laid-Open No. 2-269058).

FIG. 7 is a schematic view of an ink jet apparatus (droplet jet apparatus) using surface acoustic waves. This FIG.
The device shown in FIG. 1 converts an electric signal from an AC electric signal generator 34 for generating a high-frequency signal of several MHz to several hundreds Mz and a pulse signal generator 35 for intermittently making the AC electric signal into an input comb-shaped electrode (IDT) 32. , A surface acoustic wave is excited in the piezoelectric substrate 31, and a surface acoustic wave filter electrode that causes the liquid 33 on the propagation surface to fly by a traveling wave of the surface acoustic wave.

As shown in FIG. 7, an ink jet device using surface acoustic waves can eliminate nozzles. Therefore, there is no ink clogging and no scorching occurs. Further, compared with the piezo jet method using the bulk displacement of the piezoelectric element, elastic wave energy concentrated on the surface of the elastic body can be supplied to the ink with high efficiency, which is advantageous in terms of input power. However, such an ink jet device requires one tenth to several watts as high-frequency power to be input to the IDT 32.
The DT 32 is likely to cause migration and disconnection or the like.

On the other hand, there has been proposed an ink jet apparatus in which an IDT is provided in ink and a surface acoustic wave is emitted into the ink to fly the ink (Japanese Patent Laid-Open No. 62-66943). FIG. 8 is a schematic sectional view of the ink jet device. In the apparatus shown in FIG. 8, a piezoelectric substrate 43 is provided in an ink liquid chamber 41 for storing ink.
By applying a high-frequency voltage to the IDT 42 formed concentrically on the surface 3 to generate a surface acoustic wave, the vibration pressure from the leaky Rayleigh wave is concentrated in the ink in a cone shape, and the focus 44 of the vibration pressure Ink droplets 45 are ejected from a nearby ink surface and recorded on a recording medium 46.

In the ink jet apparatus as shown in FIG. 8, since the IDT 42 is in direct contact with the ink, if the conductive ink is used, it leaks between the electrodes, making it impossible to obtain a surface acoustic wave efficiently. There is a problem that the constraint of becomes large. Further, there is a problem that the material of the IDT 42 is etched by the reaction between the ink and the IDT 42.

Therefore, a surface acoustic wave filter using a SiO ₂ film (Japanese Patent Laid-Open No. 5-22067) has been proposed as a protective film for a surface acoustic wave electrode. FIG. 9 is a schematic sectional view showing an example of the electrode section. The electrode section shown in FIG. 9 has an Al-layer on an adhesion layer 51 made of Cr or the like.
An electrode 52 made of a Cu alloy or the like and a protective film 53 made of SiO ₂ are sequentially laminated. However, in this structure, since there is no protective film 53 on the side surface of the electrode 52, the reaction with the ink cannot be suppressed.

FIG. 10 is a schematic sectional view showing another example of the electrode section. The electrode section shown in FIG. 10 is configured so that the side surface of the electrode 52 is also covered with the protective film 53. However, even in this structure, the protective film 5 made of SiO _{2 is used.}
Since it is difficult to form the electrode 3 uniformly, an exposed portion of the electrode 52 occurs, and a reaction occurs with the ink. If the side surface protective film 53 is formed thick to prevent this, the surface acoustic wave will be attenuated.

That is, the method of forming the protective film 53 made of SiO ₂ is performed by using a few tens of n
It is very difficult to uniformly form the uneven surface of the IDT 52 with a thickness of less than m, which is not practical. In addition, a separate step of forming the protective film 53 made of SiO ₂ is required, and the number of manufacturing steps increases.

When the Al electrode is patterned by RIE, the gas is switched to N ₂ / CO ₂ after etching to form a C-AlN protective film around the Al electrode (Japanese Patent Laid-Open No. 9-199967). Publication). FIG. 11 is a schematic sectional view showing an example of the electrode section. The electrode portion shown in FIG. 11 is obtained by forming an electrode 52 made of an Al-Cu alloy or the like on a piezoelectric substrate 54, and further forming a protective film 53 made of C-AlN so as to cover the electrode 52. It is. According to this structure,
Carbon is isolated from the outside atmosphere by covering a considerable amount of Al surfaces. However, when the protective film 53 comes into contact with the ink, carbon constituting the protective film 53 is eluted, and the exposed Al reacts with the ink, which again causes a problem that the electrode is disconnected.

[0013]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned drawbacks of the prior arts and has a surface acoustic wave generating means which has no migration, has a long life, and has a high stability. An object of the present invention is to provide an inkjet head having a wide range of ink.

[0014]

According to the present invention, there is provided a piezoelectric substrate for generating a surface acoustic wave, and a comb-shaped electrode provided on the piezoelectric substrate for applying an AC voltage, and the direction of propagation of the surface acoustic wave is provided. In an ink jet head that ejects ink to
An inkjet head, wherein a metal oxide film or a metal nitride film is formed on a surface of the comb-shaped electrode.

In the ink jet head of the present invention, since the metal oxide film or the metal nitride film is formed on the surface of the comb-shaped electrode, no migration occurs, and the electrode portion is not etched even when the ink is in direct contact. It is possible to efficiently obtain surface acoustic waves.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

In the present invention, as the piezoelectric substrate as a means for generating a surface acoustic wave, for example, a piezoelectric substrate made of a piezoelectric material for generating a surface acoustic wave and a cut surface may be used. Specifically, for example, LiNbO ₃ , LiTa
O ₃ , piezoelectric single crystal such as quartz; piezoelectric ceramics such as PZT, PLZT; Zn on glass or silicon wafer
One formed with a piezoelectric thin film of O, AlN, PZT or the like can be given.

An input comb-shaped electrode (IDT) for applying an AC voltage is provided on the piezoelectric substrate, and a high-frequency signal voltage in the range of about 10 MHz to 1 GHz is applied to the IDT using an AC electric signal generator or the like. Then, a surface acoustic wave is generated from the piezoelectric substrate.

The surface of the surface acoustic wave propagation may be the surface of a piezoelectric single crystal, a piezoelectric ceramic, or a piezoelectric thin film, which is a piezoelectric substrate. When using a piezoelectric thin film,
A piezoelectric thin film is formed only on the part that generates surface acoustic waves,
It is also possible to separate the propagation surface from the portion that generates the surface acoustic wave. In this case, a substrate surface such as glass or a silicon wafer is used as a propagation surface.

The electrode spacing of the IDT may be optimized according to the type of piezoelectric substrate, the excitation frequency, and the like. Here, assuming that the excitation frequency is f, the propagation velocity of the surface acoustic wave is v, and the electrode period of the IDT is d, the excitation is strongest when f = v / 2d. For example, LiNbO
_{3 When} using a piezoelectric substrate at (propagation velocity of surface acoustic wave v = approximately 4000 m / s) and exciting with a high frequency drive circuit of frequency f = 50 MHz, the electrode period d of the IDT is 40 μm.
It is desirable to design with m.

The material of the IDT may be any conductive material that can form an electrode. For example, Ni, Cr, Mo,
Metals such as W, Ti, Cu, Pd, and Ag, or alloys of these metals are preferred. In addition, semiconductors such as polysilicon can also be used. The comb-shaped electrode can be easily formed by using a combination of a film forming technique such as vacuum deposition and a patterning technique such as photolithography and etching. Further, it may be formed by using another method (for example, a printing technique).

In order to form a metal oxide film or a metal nitride film on the surface of the IDT, for example, a comb-shaped IDT is formed on the piezoelectric substrate by the method described above, and then the surface of the IDT is oxidized or nitrided. I just need. Specifically, the ID is determined by using an anodic oxidation method, an oxidation method using O ₃ , a thermal oxidation (nitridation) method, a plasma oxidation (nitridation) method, a photoexcited oxidation (nitridation) method, or the like.
It is possible to oxidize or nitride only the very surface of T. According to these methods, a protective film made of an oxide film or a nitride film of the material constituting the IDT can be easily formed.

The thickness of the oxide film or the nitride film to be formed is usually designed by selecting an appropriate value from the range of several nm to several hundred nm. In particular, the range of 5 nm to 20 nm is preferable. If the thickness of the oxide film or the nitride film is appropriately increased, the problem that the film is dispersed in an island shape hardly occurs. Also,
If the thickness is appropriately reduced, it is difficult to absorb the surface acoustic wave, and efficient propagation becomes possible.

FIG. 1 is a schematic view showing an example of a piezoelectric substrate and a comb-shaped electrode of an ink jet head according to the present invention, and FIG. 2 is a sectional view taken along the line AA 'of FIG. As shown in FIGS. 1 and 2, when an AC voltage is applied to a comb-shaped electrode 2 provided on a piezoelectric substrate 1 that generates a surface acoustic wave using a high-frequency driving circuit (not shown), the surface elasticity of the piezoelectric substrate 1 is increased. Waves are generated and ink jet recording can be performed.

FIGS. 3A to 3D are schematic cross-sectional views showing an example of a method of manufacturing a member having the structure shown in FIGS. 1 and 2 in the order of steps. First, as shown in FIG. 3A, an IDT-forming conductive film 3 is formed on a cleaned piezoelectric substrate 1 by an RF sputtering method or the like. Next, FIG.
As shown in (b), the ID is obtained by photolithography or the like.
A resist 4 for obtaining a pattern of T2 is formed on the conductive film 3. Next, as shown in FIG.
Is dry-etched, and then the resist 4 is removed by ashing to form a pattern of the conductive film 3 having a desired shape. Thereafter, as shown in FIG. 3D, the surface of the conductive film 3 is oxidized or nitrided by the method described above to obtain a desired IDT2.

The oxidation or nitridation may be performed by using various conventionally known processing apparatuses. FIG. 4 is a schematic diagram showing an example of a processing apparatus for performing anodic oxidation. The apparatus includes an anodizing tank 5 for storing an electrolytic solution 6, a motor 7 for stirring the electrolytic solution, a platinum electrode 8, and a DC power supply 9. A piezoelectric substrate 11 with an IDT is placed in the anodizing tank 5, and a platinum electrode 8 and a piezoelectric substrate 1 are
By applying a voltage to one IDT, anodic oxidation of the IDT surface can be performed, and an oxide film can be formed.

FIG. 5 is a schematic diagram for explaining an example of the operation of the ink jet head of the present invention. In FIG. 5, a part of the IDT on the piezoelectric substrate 11 is buried in the ink 13 in the ink liquid chamber 12. Here, high-frequency power from a high-frequency drive circuit (not shown) is
By applying a surface acoustic wave to the piezoelectric substrate 1 by applying a voltage to the DT 2, ink droplets fly from the ink 13 in the ink liquid chamber 12 in the direction of the arrow, land on the recording medium 15, and perform inkjet recording. it can.

The recording medium 15 is fed and scanned in a fixed direction by the rotation of the roller 14, and the roller is driven by a stepping motor (not shown) to sequentially print and record each line.

In the example shown in FIG. 5, an example is shown in which ink is ejected directly from the ink liquid chamber and printing is performed on a recording medium. However, the present invention is not limited to this. May be provided, and ink may be ejected through a nozzle. Further, in the example shown in FIG. 5, a part of the IDT is buried in the ink in the ink liquid chamber, but the entire IDT may be buried in the ink. Further, as shown in FIG. 7 described as a conventional example, ink and IDT
May be configured so as not to contact with each other, and the ink may fly.
Also in this case, there is obtained an effect that the reaction between the IDT and the ink does not occur and the disconnection due to the migration of the IDT due to the application of the high-frequency power can be suppressed.

FIG. 6 is a perspective view showing a multi-jet ink jet head as an example of the ink jet head of the present invention. The multi-jet ink jet head shown in FIG. 6 includes a plurality of piezoelectric substrates 11 with IDTs arranged on a carriage drive head 21. The recording medium 15 is fed and scanned in the direction of arrow A by the rotation of the roller 14, and the carriage drive head 21 moves in the direction B perpendicular to the transport direction of the recording medium 15. An ink supply tank (not shown) of the carriage drive head 21 contains inks of three colors, yellow, magenta, and cyan, and the inks are ejected by individual driving, respectively, and printing of each line is sequentially performed. Will be

In the example shown in FIG. 6, the recording apparatus having the piezoelectric substrate 11 with IDT for three colors is shown, but the present invention is not limited to this. Alternatively, piezoelectric substrates 11 with IDTs of four or more colors may be mounted. Further, in the example shown in FIG. 6, the plurality of piezoelectric substrates 11 with IDTs are arranged in the moving direction of the carriage, but the plurality of piezoelectric substrates 11 with IDTs may be arranged along the moving direction A of the recording medium 15. .

[0032]

The present invention will be described in more detail with reference to the following examples.

<Example 1> A piezoelectric substrate and a comb-shaped electrode having the structures shown in FIGS. 1 and 2 were manufactured as follows in accordance with the process shown in FIG.

First, an IDT-forming conductive film 3 made of Al was formed to a thickness of about 300 nm on a cleaned piezoelectric substrate 1 made of LiNbO ₃ by RF sputtering [FIG. 3 (a)]. Next, a pattern of a resist 4 for forming a pattern of the IDT 2 was formed by photolithography [FIG. 3B]. Next, the IDT forming conductive film 3 made of Al was dry-etched, and then the resist 4 was removed by ashing to form a pattern of the conductive film 3 having a desired shape [FIG. 3 (c)].

Next, the surface of the pattern of the conductive film 3 made of Al is oxidized by anodic oxidation, and about 50 n
An m-thick Al oxide film was formed [FIG. 3 (f)]. This anodic oxidation is performed by the processing apparatus shown in FIG.
25% (DC) at room temperature using 3% oxalic acid solution
This was performed by applying voltage.

The width W of the IDT 2 was 1 mm, the electrode line width t of the IDT 2 was 20 μm, the electrode period d was 40 μm, the cross width was 500 μm, and the IDT logarithm was 5. As described above, the velocity v of the surface acoustic wave propagating through the piezoelectric substrate 1 made of LiNbO _{3 is} 4000 m / s, and the electrode period d is
By applying a high-frequency voltage having an excitation frequency f = 50 MHz at 40 μm, the most powerful excitation can be achieved.

Next, in the configuration as shown in FIG. 5, a high-frequency driving circuit (not shown) applies a high-frequency power of 1 W at 50 MHz to the IDT 2 to excite a surface acoustic wave on the piezoelectric substrate 1 so as to form an ink. Ink droplets flew from the ink 13 in the liquid chamber 12 in the direction of the arrow. When ink jet recording was performed in this manner, IDT2 did not cause migration and had improved durability. In addition, no matter what kind of ink was used, no leak occurred between the electrodes, surface acoustic waves could be obtained efficiently, and the reaction between the ink and the IDT could be suppressed.

In this embodiment, the case where Al having an Al oxide film formed on the surface by anodization is used as the IDT. However, the Al surface is nitrided by another method, and an Al nitride film is formed on the surface. Similar good results were obtained using the formed IDT.

<Comparative Example 1> An oxide film was not formed on the surface of IDT2, that is, FIG.
(D) The anodic oxidation step was omitted, and all other steps were performed in the same manner as in Example 1, thereby producing an ink jet head.

Using this head, recording was carried out in the same manner as in Example 1. As a result, ink droplets flew in the same manner, but did not fly after several minutes. Therefore, the piezoelectric substrate 1
When the ink was taken out of the ink, disconnection was observed at several points of the IDT.

Example 2 As shown in FIG. 6, a plurality of piezoelectric substrates 11 with IDTs manufactured in Example 1 were arranged on a carriage drive head 21 to manufacture a multi-inkjet head. When the three color inks of yellow, magenta, and cyan were put into the ink supply tank of the carriage drive head 21 and the inks were ejected by individual driving, the same good results as in Example 1 were obtained. Leakage between the electrodes did not occur even when the color ink was used, and the reliability of the ink jet head could be improved even in the case of multiple printing.

[0042]

As described above, in the ink jet head of the present invention, since a metal oxide film or a metal nitride film is formed on the surface of an input comb electrode (IDT) to which an AC voltage is applied, migration occurs. In addition, even if the ink is in direct contact with the ink, the electrode portion is not etched, no leak occurs between the electrodes, and the IDT has a long life and high stability. In addition, it is possible to efficiently obtain a surface acoustic wave. Further, the range of usable inks is widened, good recording is possible even with a multi-head, etc., and a highly reliable multi-inkjet head can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a piezoelectric substrate and comb electrodes of an ink jet head according to the present invention.

FIG. 2 is a sectional view taken along line AA ′ of FIG. 1;

FIG. 3 is a schematic cross-sectional view showing an example of a method for manufacturing a member having the structure shown in FIGS. 1 and 2 in the order of steps.

FIG. 4 is a schematic view showing an example of a processing apparatus for performing anodic oxidation.

FIG. 5 is a schematic diagram for explaining an example of the operation of the inkjet head of the present invention.

FIG. 6 shows an example of the inkjet head of the present invention.
FIG. 3 is a perspective view showing a multi-jet inkjet head.

FIG. 7 is a schematic view of a conventional ink jet apparatus using surface acoustic waves.

FIG. 8 is a schematic cross-sectional view of a conventional ink jet device using a surface acoustic wave.

FIG. 9 is a schematic cross-sectional view illustrating an example of an electrode portion of a conventional inkjet head using surface acoustic waves.

FIG. 10 is a schematic cross-sectional view illustrating an example of an electrode portion of a conventional inkjet head using surface acoustic waves.

FIG. 11 is a schematic cross-sectional view showing an example of an electrode portion of a conventional inkjet head using surface acoustic waves.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric substrate 2 input comb electrode (IDT) 3 conductive film for forming IDT 4 photoresist 5 anodizing bath 6 electrolyte 7 motor 8 platinum electrode 9 DC power supply 11 piezoelectric substrate with IDT 12 ink liquid chamber 13 ink 14 roller 15 recording Medium 21 Carriage drive head 31 Piezoelectric substrate 32 IDT 33 Liquid 34 AC electric signal generator 35 Pulse signal generator 41 Ink liquid chamber 42 Input comb-shaped electrode (IDT) 43 Piezoelectric substrate 44 Focus of vibration pressure 45 Ink droplet 46 Recording medium 51 Adhesion layer 52 Electrode 53 Protective film 54 Piezoelectric substrate

Claims (3)

[Claims] An ink jet head having a piezoelectric substrate for generating a surface acoustic wave, and a comb-shaped electrode provided on the piezoelectric substrate for applying an AC voltage, and ejecting ink in a propagation direction of the surface acoustic wave. An ink jet head, wherein a metal oxide film or a metal nitride film is formed on a surface of the comb-shaped electrode. 2. The ink jet head according to claim 1, wherein the metal oxide film or the metal nitride film formed on the surface of the comb electrode is formed of an oxide film or a nitride film of a material forming the comb electrode. 3. The ink jet head according to claim 1, further comprising an ink liquid chamber for supplying ink.