JP3552013B2 - Ink jet recording head - Google Patents

Description

[0001]
[Field of the Invention]
According to the present invention, a part of a pressure generating chamber communicating with a nozzle opening for discharging ink droplets is formed of an elastic plate, a piezoelectric layer is formed on a surface of the elastic plate, and the ink droplet is formed by displacement of the piezoelectric layer. The present invention relates to an ink jet recording head for discharging.
[0002]
[Prior art]
A part of the pressure generating chamber communicating with the nozzle opening for discharging the ink droplet is constituted by an elastic plate, and the elastic plate is deformed by a piezoelectric vibrator to pressurize the ink in the pressure generating chamber and discharge the ink droplet from the nozzle opening. Two types of ink jet recording heads have been put into practical use, one using a longitudinal vibration mode piezoelectric vibrator that expands and contracts in the axial direction of the piezoelectric vibrator, and the other using a flexural vibration mode piezoelectric vibrator. I have.
[0003]
In the former case, the volume of the pressure generating chamber can be changed by contacting the end face of the piezoelectric vibrator with the elastic plate, and a head suitable for high-density printing can be manufactured. In addition, there is a problem that a complicated process of dividing the piezoelectric vibrator into the pressure generating chamber and fixing the divided piezoelectric vibrator in the pressure generating chamber is required, which complicates the manufacturing process. .
[0004]
On the other hand, in the latter case, the piezoelectric vibrating body can be formed on the elastic plate by a relatively simple process of sticking a green sheet of a piezoelectric material according to the shape of the pressure generating chamber and firing the green sheet. Due to the use of vibration, a certain area is required, and there is a problem that high-density arrangement is difficult.
[0005]
In order to solve the latter disadvantage of the recording head, a uniform piezoelectric material layer is formed by a film forming technique over the entire surface of the elastic plate as disclosed in Japanese Patent Application Laid-Open No. 5-286131. Has been proposed in which a piezoelectric vibrator is formed so as to be separated into respective shapes corresponding to the pressure generating chambers by a lithography method so as to be independent for each pressure generating chamber.
According to this, the work of attaching the piezoelectric vibrator to the elastic plate becomes unnecessary, and not only can the piezoelectric vibrator be manufactured by the precise and simple method of lithography, but also the thickness of the piezoelectric vibrator can be reduced. There is an advantage that it can be made thin and can be driven at high speed.
[0006]
[Problems to be solved by the invention]
On the other hand, since the piezoelectric material layer is very thin, its rigidity is lower than that of the piezoelectric vibrator attached, stress tends to concentrate near the boundary of the pressure generating chamber, and the elastic plate, the piezoelectric vibrator, and the electrode There are inconveniences such as a shortened life.
Also, the piezoelectric constant is about 1/3 to 1/2 lower than that of a piezoelectric vibrator formed by sticking and firing a green sheet, and requires driving at a high voltage. A creeping discharge occurs through the side of the material layer, which tends to cause a leak current between the upper and lower electrodes, making the ejection of ink droplets unstable, and the piezoelectric vibrator corresponding to each pressure generating chamber In such a case, the area of the side surface exposed to the air becomes large, and there is a problem that the piezoelectric vibrator is easily deteriorated by the moisture in the air.
[0007]
The invention It is an object of Teso was made in view of such problems, as well as prevent damage to the upper electrode to reduce the stress concentration near the boundary of the pressure chamber, the piezoelectric material layer It is an object of the present invention to provide an ink jet recording head capable of preventing the occurrence of a leak current between upper and lower electrodes sandwiching the ink, stably ejecting ink droplets, and preventing deterioration due to moisture in the atmosphere .
[0009]
[Means for Solving the Problems]
In order to achieve the first object, according to the present invention, a lower electrode formed on a surface of an elastic plate constituting a pressure generating chamber communicating with a nozzle opening, and a piezoelectric layer formed on a surface of the lower electrode are provided. A piezoelectric vibrator comprising a piezoelectric vibrator comprising: a surface of the piezoelectric layer; and an upper electrode formed in a region facing the pressure generating chamber, wherein the upper electrode faces the pressure generating chamber. It formed independently in a region, and only the region of the side surface of the piezoelectric layer from the peripheral portion of the surface of the upper electrode so as to expose the other peripheral surface of the upper electrode are covered with an insulator layer .
As a result, since the upper electrode is located inside the pressure generating chamber, it can be prevented from being destroyed without being subjected to abrupt displacement at the boundary of the pressure generating chamber, and the upper electrode and the insulating layer can be used to prevent the piezoelectric body from being damaged. The displacement amount can be secured by preventing the insulating layer from increasing the rigidity of the piezoelectric layer while protecting the layer from the external environment and preventing the occurrence of leakage current.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Therefore, the details of the present invention will be described below based on the illustrated embodiment.
FIG. 1 is an assembled perspective view showing one embodiment of the present invention, and FIG. 2 is a view showing a cross-sectional structure in a longitudinal direction of one pressure generating chamber. Then, the silicon single crystal substrate is anisotropically etched so that one surface becomes an opening surface and the other surface forms an elastic plate 2 made of silicon oxide to form a pressure generating chamber 3 and a reservoir 4. The ink supply port 5 is formed by a concave portion for communicating the pressure generating chamber 3 and the reservoir 4 with a constant fluid resistance.
[0012]
In the region of the elastic plate 2 facing each pressure generating chamber 3, a piezoelectric vibrator 6 formed by a film forming method independently for each pressure generating chamber 3 is provided.
[0013]
The piezoelectric vibrator 6 includes a lower electrode 10 formed on the surface of the elastic plate 2 so as to substantially cover the area of the pressure generating chamber 3 and the ink supply port 5, and a region where the elastic plate 2 of the pressure generating chamber 3 is exposed. The piezoelectric layer 11 is formed by laminating the piezoelectric layer 11 formed so as not to protrude and slightly smaller than the width of each pressure generating chamber 3 and the upper electrode 12 formed on the surface of the piezoelectric layer 11.
[0014]
As shown in FIGS. 2A and 2B, the piezoelectric layer 11 and the upper electrode 12 have sides 11a and 12a on the nozzle opening side and sides 11b and 12b on the ink supply port side of the pressure generating chamber 3. It is formed so as to be located inside the longitudinal boundaries 3a and 3b, and is desirably located inside the partition wall of the pressure generating chamber in the width direction.
[0015]
A material that has electrical insulation properties so as to cover at least the periphery of the upper surface of the upper electrode 12 and the side surfaces of the piezoelectric layer 11, and that can be formed by a film forming method or shaped by etching, for example, silicon oxide, silicon nitride, or an organic material Preferably, a thin insulator layer 13 made of photosensitive polyimide having low rigidity and excellent electrical insulation is formed.
[0016]
A window 13a for exposing a part of the upper electrode 12 is formed in a part of the upper electrode 12 of the insulator layer 13 so as to be connected to a conductive pattern 14 described later, and one end of the upper electrode 12 is formed through the window 13a. A conductive pattern 14 that is connected to and extends at the other end to the connection terminal portion is formed. The conductive pattern 14 is formed to have a width as narrow as possible so as to reliably supply a drive signal to the upper electrode 12.
[0017]
Reference numeral 15 denotes a nozzle plate, which is formed by forming a nozzle opening 16 so as to communicate with one end of the pressure generating chamber 3, and is fixed so as to seal the opening of the flow path forming substrate 1. In the drawing, reference numeral 17 denotes a flexible cable for supplying a drive signal to the piezoelectric vibrator 6, and reference numeral 18 denotes a head case.
[0018]
In this embodiment, when a driving signal is supplied from an external driving circuit to the piezoelectric vibrator 6 via the flexible cable 17, the driving signal is applied to the upper electrode 12 through the conductive pattern 14, and the piezoelectric vibrator 6 bends and vibrates to generate pressure. The volume of the chamber 3 is reduced.
[0019]
Part of the ink in the pressure generating chamber 3 pressurized by the change in the volume of the pressure generating chamber 3 is ejected from the nozzle opening 16 as an ink droplet. When the ejection of the ink droplets is completed and the piezoelectric vibrator 6 returns to the original state, the volume of the pressure generating chamber 3 increases, and the ink in the reservoir 4 flows into the pressure generating chamber 3 through the ink supply port 5.
[0020]
By the way, the piezoelectric layer 11 constituting each piezoelectric vibrator 6 is formed in such a size that both ends 11a and 11b are located inside the boundaries 3a and 3b of the pressure generating chamber 3, and the piezoelectric layer 11 and Since the electrode 12 does not exist at the boundary 3b, the electrode 12 is not affected by a sudden displacement gradient, and there is no breakage due to mechanical fatigue.
[0021]
On the other hand, as shown in FIG. 8, the piezoelectric layer 11 'is extended to near the end of the recording head, and the piezoelectric layer 11' is used as an insulating layer between the lower electrode 10 and the upper electrode 12 '. In a recording head of a type in which an extension of the upper electrode 12 'is used as an extraction electrode, the piezoelectric layer 11' is located at the end 3b of the pressure generating chamber 3, and abrupt displacement occurs in a region facing the boundary 3b. There is a disadvantage that a gradient is generated and the piezoelectric vibrator 6 is easily broken.
[0022]
In addition, since the conductive pattern 14 connected to the upper electrode 12 is formed on the surface of the insulator layer 13, the gap between the conductive pattern 14 and the lower electrode 10 is large, and the insulation resistance between the lower electrode 10 and the surface is ensured. Is prevented, and the capacitance and the loss of the piezoelectric body are extremely reduced, so that a reduction in response speed and heat generation can be suppressed.
[0023]
Further, the piezoelectric layer 11 whose piezoelectric constant and the like are liable to change due to moisture absorption is cut off from the atmosphere by the upper electrode 12 and the insulating layer 13 on the upper surface and by the insulating layer 13 on the side surface. Therefore, the initial characteristics can be maintained without absorbing moisture for a long period of time.
[0024]
In the above-described embodiment, the conductive pattern 14 is connected only at one end of the upper electrode 12, but as shown in FIGS. A conductive pattern 14 is formed so as to extend, windows 13a, 13b, 13c are formed at a plurality of locations on the insulator layer 13 facing the upper electrode 12, and the upper electrode 12 is connected to the upper electrode 12 through these windows 13a to 13c. Accordingly, a drive signal can be supplied to the upper electrode 12 with a response delay as small as possible.
[0025]
In the above-described embodiment, the windows 13a, 13b, and 13c are formed in the insulator layer in conformity with the shape of the connection portion with the conductive pattern 14. However, as shown in FIG. Even if a window 17 larger than the connection portion of the conductive pattern 14 is formed, leaving only a part of the periphery of the upper surface of the piezoelectric layer 11, ΔL ′, ΔL ′, ΔL ″, the surface of the piezoelectric layer 11 can be formed of a dense material such as platinum. Since it is covered with the upper electrode 12 made of a film and the side surface is covered with the insulator layer 13 and is isolated from the atmosphere, deterioration due to moisture in the atmosphere and creeping discharge along the side surface are prevented.
[0026]
The piezoelectric layer 11 has a window 17 formed in a large part of its displacement region and only the upper electrode 12 is present. Therefore, an increase in rigidity due to the rigidity of the insulator layer 13 is suppressed as much as possible. The displacement per unit voltage can be increased as compared with the above embodiment.
[0027]
By the way, such a recording head is basically manufactured by anisotropic etching using a silicon single crystal substrate as a base material as described below with reference to FIGS.
[0028]
That is, a base material is prepared in which silicon oxide films 21 and 22 are formed on the surface of a silicon single crystal substrate 20 by a thermal oxidation method or the like, and a conductive layer 23 of a lower electrode also serving as a diaphragm is formed on one surface by a sputtering method such as platinum. I do. Then, a piezoelectric material layer 24 such as lead zirconate titanate is formed on the surface of the conductive layer 23, and subsequently, a conductive layer 25 serving as the upper electrode 12 is formed by a sputtering method.
[0029]
Next, the piezoelectric layer 24 and the conductive layer 25 are etched in the same process by photolithography according to the shape of the pressure generating chamber. Further, the conductive layer 23 is patterned by photolithography to form a lower electrode, and then the silicon oxide film 22 on the other surface of the silicon single crystal substrate 20 is patterned by photolithography according to the shape of the pressure generating chamber. I do.
When patterning the lower current, the resist layer 31 functions as a protective layer for the piezoelectric material layer 24 and the conductive layer 23 of the upper electrode. Further, hydrofluoric acid is used as an etchant for patterning the silicon oxide film 21, but by forming the above-described resist layer 31, the piezoelectric material layer 24 can be protected from hydrofluoric acid (see FIG. )).
[0030]
Next, a fluororesin protective film 26 having a thickness of about 6 μm is formed on the surfaces of the piezoelectric material layer 24 and the conductive layers 23 and 25 (FIG. 5 (II)).
This fluororesin protective film is coated on the piezoelectric material layer 24 and the conductive layers 23 and 25 by coating a layer of about 2 μm by a spin coating method and drying the coating at 120 ° C. for 20 minutes three times. 26 can be formed in close contact with each other while increasing the degree of polymerization.
[0031]
Note that, as shown in FIG. (II ′), a method of forming the fluororesin protective film 26 includes attaching a resin film 27 to the other surface of the base material and immersing the whole in a fluororesin liquid to form a piezoelectric film. A resin liquid is applied so as to cover the body material layer 24 and the conductive layers 23 and 25. This may be pre-annealed at a temperature of 100 ° C. for about 30 minutes, and then heated at a temperature of 200 ° C. for 30 minutes to cure the fluororesin 28 until it functions as a protective film. When the resin film 27 is removed at the stage when the formation of the fluororesin protective film 28 is completed, the unnecessary fluororesin protective film 29 is also removed.
[0032]
Only the side of the patterned silicon oxide film 22 is immersed in a 5 wt% to 20 wt% aqueous solution of potassium hydroxide maintained at a temperature of 80 ° C. to perform etching for about 1 to 2 hours. As a result, the silicon single crystal substrate is etched to the other silicon oxide film 21 using the silicon oxide film 22 as a protective layer to form a concave portion 30 serving as a pressure generating chamber. By protecting the piezoelectric material layer 24 with the fluororesin protective film 28 in this etching step, the piezoelectric material layer 24 can be prevented from being damaged by the potassium hydroxide aqueous solution.
[0033]
Next, a region of the silicon oxide film 21 functioning as an etching stopper, which is exposed from the concave portion 30, and the silicon oxide film 22 functioning as an anisotropic etching pattern are formed using a hydrofluoric acid solution or a hydrofluoric acid solution. Remove with a solution mixed with ammonium. Finally, the fluororesin film 26 (28) is removed by etching using oxygen plasma (FIG. 6 (II)).
[0034]
When the window 31 is formed on the upper surface of the conductive layer 25 serving as the upper electrode and forms a connection portion with at least the conductive pattern, while etching is performed so as to remain on the side surface of the piezoelectric layer 24, the fluororesin film 26 is removed. (28) can have the same function as the above-mentioned insulating layer 13 (FIG. 6 (II ′)).
[0035]
Of course, when the fluororesin protective film 26 (28) is completely removed as shown in FIG. 6 (II), a new insulating film 13 may be separately formed as described above.
[0036]
In the above-mentioned embodiment, the nozzle opening 16 is formed in a direction perpendicular to the surface of the recording head to form a face type recording head. However, as shown in FIG. It is apparent that a similar effect can be obtained even if the pressure generating chamber is formed as an edge type by forming a nozzle opening 41 in the end face 40 of the recording head via a flow path in the pressure generating chamber.
[0037]
Further, in the above embodiment, the case where the piezoelectric vibrator is formed by the film forming method has been described. It is apparent that the same effect can be obtained even when the piezoelectric layer is applied to a piezoelectric layer formed by firing.
[Brief description of the drawings]
FIG. 1 is an assembled perspective view showing one embodiment of an ink jet recording head of the present invention.
FIGS. 2 (a) and 2 (b) are diagrams showing a cross-sectional structure of one pressure generating chamber of the above-mentioned ink jet recording head, and conductive patterns in a positional relationship among the pressure generating chamber, an upper electrode, and a lower electrode. It is a figure which shows the arrangement form.
FIGS. 3 (a) and 3 (b) show another embodiment of the ink jet recording head according to the present invention, showing a sectional structure of one pressure generating chamber, and a pressure generating chamber, an upper electrode, FIG. 4 is a diagram showing an arrangement of conductive patterns in a positional relationship with a lower electrode.
FIGS. 4 (a) and 4 (b) show the cross-sectional structure of one pressure generating chamber of the ink jet recording head in the longitudinal direction of the pressure generating chamber and the cross section in the direction in which the pressure generating chambers are arranged. FIG.
FIGS. 5 (I) to (II ′) are views showing the first half of a method of processing a silicon single crystal substrate constituting an ink jet recording head.
FIGS. 6 (I) to (II ′) are views showing the latter half of a method of processing a silicon single crystal substrate constituting an ink jet recording head.
FIG. 7 is a sectional view showing an embodiment of another type of recording head to which the electrode structure of the present invention can be applied.
FIG. 8 is a cross-sectional view illustrating an example of a recording head using a flexural vibrator.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 flow path forming plate 2 elastic plate 3 pressure generating chamber 4 reservoir 5 ink supply port 6 piezoelectric vibrator 10 lower electrode 11 piezoelectric layer 12 upper electrode 13 insulating layer 14 conductive pattern 15 nozzle plate 16 nozzle opening

Claims (5)

A lower electrode formed on the surface of an elastic plate constituting a pressure generating chamber communicating with the nozzle opening; a piezoelectric layer formed on the surface of the lower electrode; and a pressure generating chamber on the surface of the piezoelectric layer. In an ink jet recording head provided with a piezoelectric vibrator consisting of an upper electrode formed in a region facing the
The upper electrode, the formed independently to the pressure generating chamber opposite to the area, and from the periphery of the surface of the upper electrode so as to expose the other peripheral surface of the upper electrode side of the piezoelectric layer An ink jet recording head in which only the area is covered with an insulator layer. 2. The ink jet recording head according to claim 1, wherein a conductive pattern connected to the upper electrode is formed at a position facing a partition of the pressure generating chamber. The ink jet recording head according to claim 1, wherein the insulator layer is formed of an organic material such as silicon oxide, silicon nitride, or polyimide. 2. The ink jet recording head according to claim 1, wherein the insulator layer is formed by an etching protection film used in an etching step. 2. The ink jet recording head according to claim 1, wherein the piezoelectric layer and the upper electrode are formed inside a region facing the pressure generating chamber.

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