JP2006212992A - Liquid jetting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid jetting device which solves the problem of non-linearity or hysteresis resulting from ferroelectric characteristics of a piezoelectric body in a relationship between a driving voltage and a displacement amount, and the problem that a piezoelectric driving element has to be manufactured at a high temperature, and which attains the improvement in the high precision and the speeding up. <P>SOLUTION: This liquid jetting device comprises a liquid injecting port 5 for injecting a liquid, a liquid storage section 6 for storing the injected liquid, and a liquid jetting port 7 for jetting the stored liquid. The liquid jetting device also has the piezoelectric driving element 1 for pressurizing the liquid in order to jet the liquid being stored in the liquid storage section from the liquid jetting port 7, and a vibrating plate 3 which is vibrated by the piezoelectric driving element. The piezoelectric driving element has a piezoelectric body sheet 20B of non-ferroelectricity for the liquid jetting device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a liquid ejecting apparatus that intermittently ejects fine liquid particles by the inverse piezoelectric effect of a piezoelectric drive element, represented by a head of an inkjet printer or a fuel injection apparatus of a diesel engine.
In particular, the present invention relates to a liquid ejecting apparatus that is increased in speed and accuracy.

In recent years, development of personal computers, digital cameras, and the like has progressed, and high-capacity and high-quality image data has been handled.
For this reason, printers are also required to have high resolution, multi-gradation, high-speed printing, etc. In particular, inkjet printers are the most popular printer type.
The performance of an ink jet printer is mainly determined by the printer head, and two types of printer heads are currently put into practical use: a piezoelectric method and a thermal method.

The piezoelectric method is one in which ink particles are intermittently ejected from a nozzle using a reverse piezoelectric effect that deforms a piezoelectric film by applying a voltage to a piezoelectric driving element, and there are a bimorph type and a laminated type.
On the other hand, in the thermal method, ink particles are ejected intermittently using the force of bumping of liquid by heating of a thin film heater.
For high resolution and multi-tone printing, the ink particle size is small, the particle size can be accurately controlled, and the ink particles need to be accurately ejected to a predetermined position.
For high-speed printing, it is conceivable to increase the ejection speed and to integrate the liquid ejection nozzles.

Incidentally, the technology for ejecting the ink particles can be used for engraving or drawing on a product in a manufacturing process of a diesel engine fuel injection device or an industrial product, supplying a liquid raw material, and the like other than the ink jet printer.
In addition, in the fields of medical relations and biotechnology, a technique for delivering a minute amount of liquid is required.
As described above, a high-precision and high-speed liquid ejecting apparatus is required in many fields.

However, the conventional thermal and piezoelectric liquid ejecting apparatuses have the following problems in order to achieve high accuracy and high speed.
The conventional thermal type liquid ejecting apparatus has an advantage that the structure is simple and can be manufactured at low cost. However, since the liquid is ejected by utilizing the force of the liquid boiling due to the heating of the thin film heater, Control of the injection amount is difficult, and heating and cooling are repeated every time the liquid is injected, so that it takes time to raise and lower the temperature, and there is a limit to speeding up.
Also, the use of heat-sensitive liquid is inevitably difficult.

On the other hand, the piezoelectric liquid ejecting apparatus ejects liquid by utilizing the inverse piezoelectric effect of the piezoelectric body, so that the ejection amount can be controlled relatively easily and the ejection repetition time can be shortened as compared with the thermal system.
However, the piezoelectric drive element used in the piezoelectric liquid ejecting apparatus generally uses a ferroelectric piezoelectric ceramic such as PZT, and the displacement with respect to the drive voltage is non-linear.

When a voltage is repeatedly applied to the piezoelectric drive element, a so-called hysteresis loop is formed.
That is, when the drive voltage applied to the piezoelectric drive element determines the amount of displacement of the piezoelectric film, and thus the liquid injection amount, and when noise is applied to the voltage while the drive voltage is being applied, the liquid injection amount is affected by the noise applied history. However, it becomes different from time to time, causing variations and making it difficult to control the injection amount with high accuracy.

On the other hand, harmful substances such as lead and heavy metals are used in many ferroelectrics.
Furthermore, since ferroelectric piezoelectric ceramics require a high-temperature firing process when formed, it is difficult to process parts with high accuracy when the number of nozzles is increased.
In addition, the ferroelectric piezoelectric material has a problem that the polarization state gradually changes due to the effect of self-heating during operation and the applied voltage.
In order to overcome these problems, a proposal using a single crystal piezoelectric material that does not exhibit ferroelectricity in the piezoelectric drive element (see, for example, Patent Document 1), and the displacement of the drive voltage is optimized by optimizing the drive signal. There has been a proposal for making it less susceptible to non-linearity (for example, see Patent Document 2).

JP 11-48478 A (paragraph 0026 of the specification) JP 2001-138551 A (paragraph 0081 of the specification)

However, when the single crystal piezoelectric material as described above is used, there is a problem that it is necessary to polish the single crystal material thinly, which increases the man-hours in the manufacturing process and consequently increases the material cost.
In addition, the method of adjusting the drive signal not only makes the electric circuit complicated and expensive, but also has a risk of disadvantageous for speeding up due to a long electric processing time.
In any case, these proposals have yet to overcome essential problems such as non-linearity, hysteresis, aging of polarization state and generation of high temperature manufacturing processes characteristic of ferroelectric piezoelectric materials. Absent.

  The present invention has been made in view of such a problem. The relationship between the driving voltage and the displacement amount causes problems of nonlinearity and hysteresis caused by the ferroelectric characteristics of the piezoelectric body, and the piezoelectric driving element at a high temperature. An object of the present invention is to provide a liquid ejecting apparatus that overcomes the problem of having to be manufactured and is improved in accuracy and speed.

  Thus, as a result of earnest research on the background of such problems, the present inventor unexpectedly uses the non-ferroelectric piezoelectric material for the piezoelectric driving element of the liquid ejecting apparatus, thereby The present invention has been completed based on this finding.

  That is, the present invention includes (1) a liquid injection port for injecting a liquid, a liquid storage unit for storing the injected liquid, a liquid injection port for injecting the stored liquid, and the liquid A piezoelectric drive element for applying pressure to the liquid to inject the liquid stored in the storage unit from the liquid injection port; and a vibration plate vibrated by the piezoelectric drive element, the piezoelectric drive The element exists in a liquid ejecting apparatus having a non-ferroelectric piezoelectric film.

  Further, the present invention resides in (2) the liquid ejecting apparatus according to the above (1), wherein the piezoelectric film includes a compound having a wurtzite crystal structure as a main component.

  The present invention resides in (3) the liquid ejecting apparatus according to (2), wherein the compound having the wurtzite crystal structure is aluminum nitride, gallium nitride, indium nitride, zinc oxide, or zinc sulfide.

  The present invention also resides in (4) the liquid ejecting apparatus according to the above (3), wherein the wurtzite crystal structure compound is uniaxially oriented.

  According to the present invention, (5), the piezoelectric driving element includes an upper electrode film and a lower electrode film formed above and below the piezoelectric film, and the lower electrode is bonded to the diaphragm (1) ).

  In addition, as long as the objective of this invention is met, the structure which combined said (1) to (5) suitably is also employable.

According to the present invention, since the piezoelectric drive element, which is a means for inflating and contracting the volume of the liquid storage unit and ejecting the liquid from the liquid ejection port, is made non-ferroelectric, the amount of displacement with respect to the drive voltage has a linear response. In addition, since no hysteresis is shown, highly accurate liquid ejection is possible.
In addition, the polarization state does not change, and a highly accurate and stable liquid ejection characteristic can be maintained over a long period of time.

Furthermore, piezoelectric materials having a wurtzite crystal structure such as aluminum nitride, gallium nitride, and indium nitride can be formed at a low temperature by sputtering or the like, and can be manufactured in an ultra-small and precise manner using existing semiconductor process technology. Is possible.
Accordingly, integration of nozzles at the micro level is facilitated, and high-speed liquid ejection is also possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing a cross section of a basic structure of a piezoelectric driving element used in an embodiment of a liquid ejecting apparatus of the invention.
As shown in the figure, the piezoelectric driving element 1 is composed of a lower electrode film 2A, a piezoelectric film 2B, and an upper electrode film 2C.
That is, the piezoelectric driving element 1 includes an upper electrode film 2C and a lower electrode film 2A formed above and below the piezoelectric film 2B, and the lower electrode film 2A is bonded to the diaphragm 3.
When the piezoelectric drive element 1 vibrates, the diaphragm 3 vibrates in synchronization therewith.
The lower electrode film 2A is not necessarily provided when the diaphragm 3 is a conductor because the diaphragm 3 serves as an electrode.

The material of the diaphragm 3 is carbon steel, tungsten steel, chrome steel, molybdenum steel, stainless steel, copper, phosphor bronze, brass, nickel alloy, aluminum alloy, magnesium alloy, titanium alloy, zinc alloy, platinum, gold, silver Other metal materials can also be used.
In addition to so-called metal materials, semiconductors such as silicon and gallium arsenide, oxides such as aluminum oxide, nitrides such as silicon nitride, boron nitride and titanium nitride, carbides such as silicon carbide and tungsten carbide, polyimide, polyethylene or Organic polymer materials such as vinyl can also be used.

As the material of the lower electrode film 2A, metals such as aluminum, nickel, chromium, platinum, gold, silver, copper, iron, tantalum, tungsten, zirconia, molybdenum, ruthenium, iridium and palladium, and alloys thereof can be used. .
Alternatively, a metal oxide such as ruthenium oxide or a metal nitride such as titanium nitride can be used.
By the way, between the diaphragm 3 and the lower electrode film 2A, it is preferable to laminate Ti, Cr, or the like as a cut synthetic intermediate layer from the viewpoints of the bondability of these layers and further the quality.
The intermediate layer may be other than Ti and Cr as long as it is a conductive metal film. For example, In, Ag, Cu, Zn, Sn, Ge, Ni, Pd, and Pb may be used.

The piezoelectric film 2B is a non-ferroelectric material, and a compound having a wurtzite crystal structure, for example, a material mainly composed of aluminum nitride, gallium nitride, indium nitride, zinc oxide, or zinc sulfide is used. In particular, aluminum nitride is mainly used. It is preferable to use as a component.
This is because aluminum nitride is a promising material for reducing the size and thickness of piezoelectric elements, such as being easy to fabricate and thin.

In order to use aluminum nitride as a piezoelectric element, aluminum nitride uniaxially oriented on the C axis is preferable from the viewpoint that the stronger the C axis orientation, the stronger the piezoelectricity.
The orientation is desired not only for aluminum nitride, but also for indium nitride, gallium nitride, zinc sulfide, zinc oxide and other materials, it is also preferred that the orientation be similarly from the viewpoint of piezoelectricity and the like.

By using a non-ferroelectric material for the piezoelectric film 2B, the graph of the relationship between the drive voltage and the amount of displacement shows a linear response, as shown in the test results described later, from micro vibrations on the order of picometers (pm) to micro. Vibration over a wide range up to vibrations in the order of meters (μm) can be generated with high accuracy and at high speed.
The material of the upper electrode film 2C can be selected from materials that can be used for the lower electrode film 2A.

  The method for forming the piezoelectric film, electrode film, diaphragm, etc. described above includes sputtering, vacuum deposition, laser ablation, ion plating, CVD, MOCVD and MBE, or coating. What is necessary is just to select a preferable thing suitably among them.

FIG. 2 shows a cross section when the liquid ejecting apparatus according to the embodiment of the invention is viewed from the side.
The liquid ejecting apparatus 4 includes a cylindrical apparatus main body 9 and a piezoelectric driving element 1 provided on the outer peripheral surface of the apparatus main body 9.
A liquid inlet 5 for injecting liquid into the apparatus main body 9 is formed on the rear end side of the cylindrical apparatus main body 9.
The shape of the liquid injection port 5 is tapered such that the hole diameter decreases toward the distal end side of the apparatus main body 9.
The liquid injection port 5 communicates with a relatively large space, that is, a liquid storage unit 6 that stores the injected liquid.
Further, a hole penetrating the liquid storage unit 6 and the outer periphery of the apparatus main body 9 is formed in the apparatus main body 9, and the piezoelectric driving element 1 is provided at the hole.

When the piezoelectric driving element 1 is driven, that is, when a driving voltage is applied between the lower electrode film 2A and the upper electrode film 2C, the piezoelectric film 2B vibrates, and this vibration is amplified by the diaphragm 3, and the diaphragm 3 Applies pressure to the liquid stored in the liquid reservoir 6.
The liquid to which pressure is applied is ejected from a liquid ejection port 7 formed at the tip of the apparatus main body 9.
By this action, the volume of the liquid storage unit 6 is repeatedly contracted (pressurized) and expanded (depressurized), and droplets 8 are ejected from the liquid ejection port 7 every cycle.

(Linearity confirmation test)
A test was conducted to confirm that when a non-ferroelectric material was used for the piezoelectric film of the piezoelectric drive element, the drive voltage applied to the piezoelectric film and the displacement of the piezoelectric film were almost linear.
As shown in FIG. 3, the structure of the piezoelectric driving element 10 (17 mm × 17 mm) used in this test is a silicon wafer (thickness: 500 μm) as the diaphragm 3 and aluminum nitride (thickness: 1 μm) as the piezoelectric film 20B. The lower electrode film 20A (platinum thin film having a thickness of 100 nm) and the upper electrode film 20C (platinum thin film having a thickness of 100 nm) were formed with the piezoelectric film 20B interposed therebetween.
A sine wave voltage was applied between the lower electrode film 20A and the upper electrode film 20C. The displacement was measured using a laser Doppler vibrometer.

FIG. 4 shows the relationship between the drive voltage and displacement characteristics of the piezoelectric drive element used in the liquid ejecting apparatus of the present invention, and is a test result.
As can be seen from the figure, a graph showing good linearity was obtained.
The driving speed could be 40 kHz or higher.
In this embodiment, since the silicon wafer having a thickness of 500 μm is used as the diaphragm 3, the displacement amount is on the order of nanometers (nm). However, by adjusting the shape and elastic modulus of the diaphragm Naturally, variable adjustment in a wide range from picometer to micrometer is possible.

  Although the present invention has been described above, the present invention is not limited to the above-described embodiment, and various other modifications can be made without departing from the essence thereof. .

FIG. 1 is an explanatory view showing a cross section of a basic structure of a piezoelectric driving element used in an embodiment of a liquid ejecting apparatus of the invention. FIG. 2 is an explanatory diagram illustrating a cross section when the liquid ejecting apparatus according to the embodiment of the invention is viewed from the side. FIG. 3 is an explanatory view showing the structure of the piezoelectric driving element used by the confirmation tester. FIG. FIG. 4 is an explanatory diagram showing the relationship between the drive voltage and displacement characteristics of the piezoelectric drive element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric drive element 2A Lower electrode film 2B Piezoelectric film 2C Upper electrode film 3 Diaphragm 4 Liquid ejector 5 Liquid inlet 6 Liquid storage part 7 Liquid ejector 8 Droplet 9 Apparatus body 10 Piezoelectric drive element 20A Lower electrode film 20B Piezoelectric film 20C Upper electrode film 30 Diaphragm

Claims (5)

A liquid inlet for injecting liquid;
A liquid reservoir for storing the injected liquid;
A liquid ejection port for ejecting the stored liquid;
A piezoelectric drive element for applying pressure to the liquid in order to eject the liquid stored in the liquid storage unit from the liquid ejection port;
A diaphragm that is vibrated by the piezoelectric drive element;
Have
The liquid ejecting apparatus, wherein the piezoelectric driving element has a non-ferroelectric piezoelectric film.   The liquid ejecting apparatus according to claim 1, wherein the piezoelectric layer includes a compound having a wurtzite crystal structure as a main component.   3. The liquid ejecting apparatus according to claim 2, wherein the compound having the wurtzite crystal structure is aluminum nitride, gallium nitride, indium nitride, zinc oxide, or zinc sulfide.   The liquid ejecting apparatus according to claim 3, wherein the compound having the wurtzite crystal structure is uniaxially oriented. The piezoelectric driving element includes an upper electrode film and a lower electrode film formed above and below the piezoelectric film,
The liquid ejecting apparatus according to claim 1, wherein the lower electrode is bonded to the diaphragm.

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