JP3837901B2 - Piezoelectric thin film element, ink jet recording head using the same, and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the structure of a piezoelectric film constituting a piezoelectric thin film element. Specifically, the piezoelectric film including the transition layers formed at unequal intervals in the film thickness direction so that the distance between the transition layers is narrower at least on the upper electrode side than on the lower electrode side. Related to the structure. In particular, the present invention relates to a piezoelectric thin structure suitable for an ink discharge drive source of an ink jet recording head.
[0002]
[Prior art]
Conventional ink jet recording heads include a piezoelectric thin film element that functions as a drive source for ink ejection. The piezoelectric thin film element has an electromechanical conversion effect that causes a volume change by applying an electric field or a voltage change by applying pressure. Since many ceramics having a perovskite crystal structure exhibit this effect remarkably, they are used as materials for piezoelectric films. The piezoelectric thin film element includes a piezoelectric film, and an upper electrode and a lower electrode that sandwich the piezoelectric film.
[0003]
By the way, since high-definition printing has been increasingly required for recent ink jet recording heads, the volume of the pressurizing chamber is becoming smaller. In order to eject an appropriate amount of ink in a pressurizing chamber having a small volume, it is necessary to generate a larger pressure on the piezoelectric thin film element. Since this pressure appears as an accumulation of minute strains in individual crystal structures, it is considered that a larger pressure can be obtained as the thickness of the piezoelectric film is increased. In addition, by increasing the thickness of the piezoelectric film, it is possible to prevent a decrease in piezoelectric characteristics due to the generation of a strong electric field in the layer. For this reason, attempts have been made to increase the thickness of the piezoelectric film by various film forming methods.
[0004]
The piezoelectric film generally used is a two-component system mainly composed of lead zirconate titanate (hereinafter sometimes referred to as “PZT”), or a third component of PZT in this two-component system. The composition has a three-component system to which is added. As a method for forming this piezoelectric film, a sol-gel method is known.
[0005]
In this sol-gel method, a hydroxide hydrate complex (sol) of a metal component of a PZT piezoelectric film is dehydrated to form a gel, and the gel is heated and fired to form an inorganic oxide (piezoelectric film). It is a method to adjust. According to this method, since the precursor of the PZT-based piezoelectric film can be formed by repeating coating / drying / degreasing several times until a predetermined thickness is obtained, the composition control is excellent. Suitable for adjusting the thickness. Patterning using a photoetching process is also possible, and application to an ink jet recording head has been put into practical use.
[0006]
When a PZT film having a thickness of about 0.5 μm to 1 μm is formed by the sol-gel method, several steps (for example, four steps) of spin coating the sol of the PZT film and drying / degreasing are performed. , RTA (Rapid Thermal Annealing) heat treatment (pre-annealing), spin coating with sol, drying / degreasing step (for example, 4 steps), followed by RTA heat treatment (final annealing) step Obtainable.
[0007]
Thus, conventionally, the amount of sol applied is determined by the relationship between the film thickness of the piezoelectric film and the number of times of application, and the amount of each applied is almost equal. For this reason, no consideration has been given to appropriately changing the coating amount in accordance with the number of coatings.
[0008]
[Problems to be solved by the invention]
However, the present inventor, when forming a piezoelectric film by the sol-gel method described above, attempts to increase the film thickness to some extent, and when growing crystal grains in the degreasing process or the RTA process, It was found that residual stress acts on the film surface and cracks may occur on the film surface. This phenomenon is considered to be because thermal stress acts in a complex manner when the molecular structure that was in an amorphous state in the piezoelectric film degreasing process or RTA process becomes a dense crystal structure. For this reason, it is impossible to form a piezoelectric film having a thickness greater than a certain level, and technical restrictions have been imposed on the high definition of the ink jet recording head.
[0009]
Therefore, the present invention can increase the thickness of the piezoelectric film by providing a piezoelectric film that does not cause stress breakdown such as cracks even if the thickness generated by relaxing the stress generated in the piezoelectric film is increased. The first problem is to provide a piezoelectric thin film element that causes a large volume change and an ink jet recording head using the piezoelectric thin film element.
[0010]
Another object of the present invention is to provide a method for manufacturing these piezoelectric thin film elements and an ink jet recording head.
[0011]
[Means for Solving the Problems]
A first subject of the present invention is a piezoelectric thin film element configured by sandwiching a piezoelectric film formed of a piezoelectric material between an upper electrode and a lower electrode, wherein the piezoelectric film is n in the film thickness direction. Solved by a piezoelectric thin film element comprising n transition layers (n is a natural number of 2 or more), and the distance between the transition layers being at least smaller on the upper electrode side than on the lower electrode side Is done.
[0012]
Here, the transition layer refers to a state in which the crystal structure constituting the piezoelectric film is partly disordered and atoms are partially lost (in this specification, sometimes referred to as a lattice defect). Since stress during film formation of the piezoelectric film acts strongly on the surface (upper electrode side), the piezoelectric film includes many transition layers in the vicinity of the surface by the above configuration. The stress in can be effectively relieved. Accordingly, it is possible to increase the thickness of the piezoelectric film.
[0013]
In this case, the n transition layers are formed as a first transition layer, a second transition layer,..., An nth transition layer in order from the transition layer closer to the lower electrode side. D is the distance between layers ₁ , The distance between the first transition layer and the second transition layer is d ₂ , ..., the distance between the (n-1) th transition layer and the nth transition layer is d _n Then d ₁ > D ₂ >...> d _n It is desirable to form the transition layer so as to satisfy the relational expression. However, even if this relational expression is not strictly satisfied, the problem of the present invention can be solved if the distance between the transition layers is gradually narrowed from the lower electrode side to the upper electrode side.
[0014]
Further, if the number of transition layers is too large, the piezoelectric characteristics of the piezoelectric film may be deteriorated. Therefore, the number n of the transition layers is determined in relation to the thickness of the piezoelectric film. For example, it is desirable that the thickness is in the range of 2 to 6 for a piezoelectric film having a thickness of 2.0 μm.
[0015]
The dislocation density in this dislocation layer is 10 ¹³ Thru 10 ¹⁴ / Cm ² It is desirable to form in the range. Dislocation density is 10 ¹⁴ / Cm ² If it is above, the structural strength of the piezoelectric film is lowered and the dislocation density is 10 ¹³ / Cm ² This is because the stress generated in the piezoelectric film cannot be relieved if it is below.
[0016]
The dislocation layer is preferably formed to a thickness of 5 nm to 15 nm, particularly 10 nm, in the thickness direction of the piezoelectric film. This is because if the thickness is 5 nm or less, the stress generated in the piezoelectric film cannot be relaxed, and if the thickness is 15 nm or more, the structural strength of the piezoelectric film is lowered.
[0017]
The piezoelectric thin film element according to the present invention is applied to an ink jet recording head used in an ink jet printer that obtains a visible image by selectively flying and fixing ink droplets on a recording paper according to input print data. Can do. A first object of the present invention is to provide a pressurization chamber substrate in which the piezoelectric thin film element according to the present invention is disposed on a vibration plate that forms at least one surface of a pressurization chamber for filling ink. This can be realized by the ink jet recording head provided.
[0018]
A second object of the present invention is to provide a method for manufacturing a piezoelectric thin film element according to the present invention. The object is to provide a piezoelectric thin film element comprising: a step of forming a lower electrode; a step of forming a piezoelectric film on the lower electrode; and a step of forming an upper electrode on the piezoelectric film. In the manufacturing method, the piezoelectric film forming step includes heat-treating a first film formed by applying a sol for forming a piezoelectric film precursor at least once and then heat-treating the sol on the first film. M is a step of forming a transition layer in the second film in the vicinity of the interface between the first and second films by heat-treating the second film formed by coating at least once. The above natural number) times are repeated, and m transition layers formed in the film thickness direction of the piezoelectric film are arranged such that the distance between the transition layers is at least smaller on the upper electrode side than on the lower electrode side. Solved by a method of manufacturing a piezoelectric thin film element, characterized in that That.
[0019]
In this case, the problem of the present invention can be solved by making the thickness of the second film smaller than the thickness of the first film. The thicknesses of the first and second films can be adjusted by the number of times of application with the amount of sol applied being constant. Further, the number of times of application can be made constant and the concentration of the applied sol can be adjusted.
[0020]
Further, the m transition layers are formed as a first transition layer, a second transition layer,..., An mth transition layer in order from the transition layer closer to the lower electrode side, and the lower electrode and the first transition layer are formed. D is the distance between layers ₁ , The distance between the first transition layer and the second transition layer is d ₂ ..., the distance between the m-1st transition layer and the mth transition layer is d _m Then d ₁ > D ₂ >...> d _m It is preferable to form the transition layer so as to satisfy this relationship.
[0021]
In this case, the value of m is preferably in the range of 2 to 6 for a piezoelectric film having a thickness of 2.0 μm, and the dislocation density in the dislocation layer is 10 ¹³ Thru 10 ¹⁴ / Cm ² It is preferable to set it as the range. The dislocation layer is preferably formed to a thickness of 5 nm to 15 nm in the thickness direction of the piezoelectric film.
[0022]
A second subject of the present invention is a pressure chamber substrate configured by arranging the piezoelectric thin film element according to the present invention on a vibration plate that forms at least one surface of a pressure chamber for filling ink. An ink jet recording head comprising: a step of forming a diaphragm on a substrate; a step of forming a pressure chamber on the substrate; and a method of manufacturing a piezoelectric thin film element according to the present invention. This is realized by the manufacturing method of the recording head.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS. In this embodiment, the thickness of the piezoelectric film can be increased by forming it at unequal intervals in the film thickness direction so that the distance between the transition layers gradually decreases from the lower electrode side to the upper electrode side. The present invention relates to a piezoelectric thin film element.
[0024]
Here, FIG. 1 is an explanatory view of the piezoelectric thin film element according to the present embodiment, FIG. 2 is a sectional view of a manufacturing process when the piezoelectric thin film element shown in FIG. 1 is formed on a substrate, and FIG. It is manufacturing process sectional drawing which showed the manufacturing process shown to B) in detail.
[0025]
(Structure of piezoelectric thin film element)
As shown in FIG. 1, the piezoelectric thin film element includes a piezoelectric film 40 sandwiched between an upper electrode 50 and a lower electrode 30. Although details of the manufacturing process will be described later, the piezoelectric film 40 includes a piezoelectric layer 40A obtained by pre-annealing four layers of piezoelectric film precursors, a piezoelectric layer 40B obtained by pre-annealing three layers, and two layers. The piezoelectric layer 40C is pre-annealed in an overlapping manner, and the piezoelectric layer 40D is pre-annealed with one layer.
[0026]
In this way, by performing the pre-annealing treatment on the piezoelectric film precursor, the transition layer 40b can be formed at each film interface, for example, at the interface between the piezoelectric layer 40A and the piezoelectric layer 40B. That is, by pre-annealing the piezoelectric film precursor of the piezoelectric layer 40A, the lattice array near the surface of the piezoelectric film precursor is sintered and crystallized in a disordered state. Therefore, by pre-annealing the piezoelectric film precursor of the piezoelectric layer 40B formed thereon, it is sintered and crystallized under the influence of the disordered lattice array. Accordingly, a transition layer (first transition layer) 40b in which a lattice of the perovskite crystal is partially lost is formed in the piezoelectric layer 40B in the vicinity of the interface between the piezoelectric layer 40A and the piezoelectric layer 40B. Similarly, for the piezoelectric layer 40C and the piezoelectric layer 40D, the second transition layer 40c and the third transition layer 40d are formed. This transition layer can relieve internal stress when the piezoelectric film 40 is formed.
[0027]
Usually, cracks generated during the formation of the piezoelectric film 40 are generated from the film surface (upper electrode side) toward the inside of the film, and therefore, the internal stress generated on the film surface is considered to be the strongest. The inventor paid attention to this point, and formed it at unequal intervals in the film thickness direction so that the interval between the transition layers gradually narrowed from the lower electrode side to the upper electrode side.
[0028]
That is, the distance from the upper surface of the lower electrode to the first transition layer 40b is defined as d. ₁ , The distance from the first transition layer 40b to the second transition layer 40c is d ₂ , The distance from the second transition layer 40c to the third transition layer 40d is d ₃ Then,
d ₁ > D ₂ > D ₃ ... (1)
It becomes a relationship. However, the number of transition layers is not limited to three, and an arbitrary number, for example, n (n = 2, 3, 4,...) Layers may be formed. Further, if the number of transition layers is increased too much, the piezoelectric characteristics of the piezoelectric film may be deteriorated, so the number of transition layers is determined by the relationship with the thickness of the piezoelectric film. For example, it is desirable that the number of transition layers is 4 in a piezoelectric film having a thickness of 3.0 μm. In this case, d ₁ Is in the range of 0.6 μm to 1.4 μm, and d ₂ Is in the range of 0.4 μm to 1.2 μm, and d ₃ Is in the range of 0.2 μm to 1.0 μm, and d ₄ Is preferably in the range of 0.01 μm to 0.8 μm.
[0029]
Moreover, even if it does not satisfy | fill the conditions of Formula (1) exactly | strictly, it should just be formed so that the space | interval of transition layers may become narrow on the film | membrane surface. For example, if there are four transition layers,
d ₁ = D ₂ > D ₃ > D ₄ ... (2)
Relationship
d ₁ > D ₂ = D ₃ > D ₄ ... (3)
The relationship may be The distance between the transition layers and the number thereof can be appropriately changed in accordance with the method of forming the piezoelectric film, the thickness of the piezoelectric film, and other conditions.
[0030]
(Manufacturing process of piezoelectric thin film element)
Next, a manufacturing method for forming a piezoelectric thin film element using this piezoelectric film on a substrate will be described with reference to FIGS.
[0031]
Oxide film and lower electrode formation process (FIG. 2A)
An oxide film 20 made of silicon dioxide having a desired thickness (for example, 1.0 μm) is formed on a silicon single crystal substrate 10 having a predetermined thickness (for example, 220 μm) by thermal oxidation. In this step, high temperature treatment is performed in an oxidizing atmosphere containing oxygen or water vapor. The oxide film 20 functions as a vibration plate, but is not limited to a silicon dioxide film, and may be a zirconium oxide film, a tantalum oxide film, a silicon nitride film, or an aluminum oxide film. The lower electrode may also serve as a diaphragm. The formation of the oxide film 20 is not limited to the thermal oxidation method, and may be a CVD method.
[0032]
A platinum layer (for example, a film thickness of 500 nm) to be the lower electrode 30 is formed on the surface of the oxide film 20 by a thin film formation method such as a sputtering film formation method. In this case, although not shown, a titanium layer (for example, a film thickness of 20 nm), a titanium oxide layer (for example, a film thickness of 20 nm), a titanium layer (for example, a film thickness of 5 nm) is provided between the lower electrode 30 and the oxide film 20. ) May be sequentially formed, and a titanium layer (for example, a film thickness of 5 nm) may be formed on the lower electrode 30. Thus, the lower electrode 30 having a multilayer structure can improve the adhesion between the lower electrode 30 and the oxide film 20.
[0033]
Piezoelectric film forming process (FIG. 2B)
A piezoelectric film 40 is formed on the lower electrode 30. In the present embodiment, the piezoelectric film 40 is formed by a sol-gel method. As long as the piezoelectric film 40 is a piezoelectric ceramic having piezoelectric characteristics, any composition can be applied. For example, in addition to a PZT piezoelectric material, a material added with a metal oxide such as niobic acid, nickel oxide, or magnesium oxide can be applied. Specifically, lead titanate (PbTiO ₃ ), Lead zirconate titanate (Pb (Zr, Ti) O) ₃ ), Lead zirconate (PbZrO) ₃ ), Lead lanthanum titanate ((Pb, La), TiO) ₃ ), Lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti) O) ₃ ) Or lead zirconium titanate magnesium niobate (Pb (Zr, Ti) (Mg, Nb) O) ₃ ) Etc. can be applied.
[0034]
In the present embodiment, a PZT-based piezoelectric film precursor in which the molar mixing ratio of lead titanate and lead zirconate is 44%: 56% is obtained by a sol-gel method, and the final film thickness is 1 The film is formed by repeating coating / drying / degreasing a desired number of times (for example, 10 times) until it becomes 0.0 μm. The piezoelectric film precursor is
Pb _X Ti _Y Zr _Z O ₃ (Y + Z = 1)
X and Y in the composition formula represented by
1.00 ≦ X ≦ 1.20 and 0.4 ≦ Y ≦ 0.6
If it is selected within the range, piezoelectric characteristics that can withstand practical use can be obtained. In order to make the piezoelectric film 40 have a desired thickness, the sol for forming the piezoelectric film 40 is spin-coated in a desired number of times (for example, 10 times), and a drying / degreasing process is performed. Specifically, the film is formed as shown in FIG.
[0035]
Piezoelectric layer (first layer) formation step (FIG. 3A)
A sol for forming the piezoelectric film 40 on the lower electrode 30 is spin-coated at 1500 rpm for 30 seconds to a film thickness of 0.1 μm, dried at 180 ° C. for 10 minutes, degreased at 400 ° C. for 30 minutes, and piezoelectric A body film precursor 401 is formed. Further, similar processes are repeated three times to form piezoelectric film precursors 402, 403, and 404.
[0036]
In this case, in order to prevent the piezoelectric characteristics from deteriorating as a result of lead in the piezoelectric film precursor evaporating and becoming low dielectric during pre-annealing by RTA (Rapid Thermal Annealing) to be described later, The lead content of the body 404 may be larger than the lead content of the piezoelectric film precursors 401 to 403. For example, the lead content of the piezoelectric film precursors 401 to 403 is 1, and the lead content of the piezoelectric film precursor 404 is 1.15. However, the Pb content in the sol that forms the piezoelectric film precursor 404 may be the same as the Pb content in the sol that forms the piezoelectric film precursors 401 to 403. In this case, a piezoelectric film is formed by a low dielectric layer (a layer having a large composition of O and Ti and a small composition of Zr and Pb as compared with other piezoelectric film precursors) generated in the piezoelectric film precursor 404. Stress generated inside can be relaxed.
[0037]
Next, the piezoelectric film precursors 401 to 404 are subjected to continuous heat treatment (pre-annealing) at 550 ° C. for 5 minutes in an oxygen atmosphere using RTA, and subsequently at 675 ° C. for 1 minute.
A piezoelectric layer 40A is formed. By this pre-annealing, the lattice arrangement near the surface of the piezoelectric layer 40A is sintered in a disordered state and crystallized.
[0038]
Piezoelectric layer (second layer) formation step (FIG. 3B)
The piezoelectric film precursors 405, 406, and 407 are formed on the piezoelectric layer 40A by the same process as the process of forming the piezoelectric film precursors 401 to 404, and 5 at 600 ° C. in an oxygen atmosphere using RTA. Subsequently, continuous heat treatment (pre-annealing) is performed at 850 ° C. for 1 minute to form the piezoelectric layer 40B. In this case, the thickness of each of the piezoelectric film precursors 405 to 407 is made equal to the thickness of each of the piezoelectric film precursors 401 to 404, so that the thickness of the piezoelectric layer 40B is larger than the thickness of the piezoelectric layer 40A. Can be reduced. As described above, when the amount of sol to be applied is constant, the film thickness of the piezoelectric layer can be adjusted by the number of times of spin coating. The film thickness of the piezoelectric layer can be changed by appropriately adjusting the concentration.
[0039]
Further, as described above, the lead content of the piezoelectric film precursor 407 may be appropriately adjusted. Since the lattice arrangement near the surface of the piezoelectric layer 40A is sintered and crystallized in a disordered state, the lattice arrangement of the piezoelectric layer 40B is influenced by the lattice arrangement near the surface of the piezoelectric layer 40A by this process. It is sintered and crystallized in a state where lattice defects are generated. For this reason, as shown in FIG. 1, a dislocation layer 40b, which is a lattice defect, is formed in the vicinity of the interface between the piezoelectric layer 40A and the piezoelectric layer 40B in the piezoelectric layer 40B.
[0040]
When the dislocation density of the transition layer formed in this step was measured, 10 ¹³ Thru 10 ¹⁴ / Cm ² It was confirmed that the thickness of the transition layer was about 10 nm. The dislocation density of the piezoelectric film having no dislocation layer is 10 ¹¹ Thru 10 ¹² / Cm ² Therefore, there are about 100 times more lattice defects in the dislocation layer. For this reason, it is considered that the transition layer can relieve stress generated in the piezoelectric film.
[0041]
Piezoelectric layer (third layer) formation step (FIG. 3C)
The piezoelectric film precursors 408 and 409 are formed on the piezoelectric layer 40B by the same process as the piezoelectric layer (second layer) forming process described above, and RTA is used in an oxygen atmosphere at 600 ° C. for 5 minutes. Subsequently, continuous heat treatment (pre-annealing) is performed at 850 ° C. for 1 minute to form the piezoelectric film 40C. In this case, the film thickness of the piezoelectric film 40C is smaller than the film thickness of the piezoelectric film 40B. Further, as described above, the lead content of the piezoelectric film precursor 409 may be appropriately adjusted. By this step, as shown in FIG. 1, a transition layer 40c is formed in the piezoelectric layer 40C.
[0042]
Piezoelectric layer (fourth layer) formation step (FIG. 3D)
A piezoelectric film precursor 410 is formed on the piezoelectric layer 40C by the same process as the above-described piezoelectric layer (third layer) forming process, and is continued at 600 ° C. for 5 minutes in an oxygen atmosphere using RTA. A continuous heat treatment (final annealing) is performed at 850 ° C. for 1 minute to form the piezoelectric film 40D. In this case, the film thickness of the piezoelectric film 40D is smaller than the film thickness of the piezoelectric film 40C. Further, as described above, the lead content of the piezoelectric film precursor 410 may be appropriately adjusted. By this step, as shown in FIG. 1, a transition layer 40d is formed in the piezoelectric layer 40D.
[0043]
In this way, the piezoelectric film 40 can be formed on the lower electrode 30. Hereinafter, the next process will be described with reference to FIG.
[0044]
Upper electrode formation process (FIG. 2C)
After forming the piezoelectric film 40, the upper electrode 50 is formed on the piezoelectric film 40. In this step, a platinum film having a thickness of 0.1 μm is formed by a direct current sputtering method, an electron beam evaporation method, or the like. Thereafter, a desired process such as patterning is performed to obtain a piezoelectric thin film element.
[0045]
In the above description, in order to form the piezoelectric film 40, the piezoelectric film precursor (sol) is applied / dried / degreased in 10 times, and then every four layers, three layers, two layers, and one layer. However, the number of times of application of the piezoelectric film precursor can be changed as appropriate so that the film can be formed as long as it can withstand the stress during film formation.
[0046]
(Example)
Piezoelectric constant d of the piezoelectric thin film element according to the present embodiment obtained by the manufacturing method described above. ₃₁ Is 140 pC / N, voltage output coefficient g ₃₁ Was 11 mV · m / N, and the dielectric constant e was 1500. On the other hand, in the piezoelectric film produced by the conventional manufacturing method, if a piezoelectric film having a film thickness of 0.9 μm or more is formed, a crack occurs during the film formation, and the piezoelectric characteristic is not exhibited. The subscript 31 indicates a value in the film thickness direction.
[0047]
As described above, according to the piezoelectric thin film element according to the present embodiment, the transition layers are arranged at unequal intervals in the film thickness direction of the piezoelectric film, and the distance between the transition layers is reduced on the surface of the piezoelectric film. Since the structure is formed as described above, the reliability of the piezoelectric film can be improved without deteriorating the piezoelectric characteristics. In addition, the piezoelectric film can be made thicker.
[0048]
The piezoelectric thin film element according to the present invention includes a non-volatile semiconductor memory device, a thin film capacitor, a pyroelectric detector, a sensor, a surface acoustic wave optical waveguide, an optical device, as well as a pressure source for an ink jet recording head described later. The present invention can be applied to ferroelectric elements such as a type storage device, a spatial light modulator, and a frequency doubler for a diode laser.
[0049]
<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the piezoelectric thin film element obtained in Embodiment 1 is used as a pressure source for an ink jet recording head.
[0050]
Here, FIG. 4 is an exploded perspective view of the ink jet recording head, and FIGS. 5 and 6 are sectional views of manufacturing steps of the main part of the ink jet recording head. The same reference numerals as those in FIGS. 1 to 3 denote the same parts, and a detailed description thereof will be omitted.
[0051]
Hereinafter, the structure of the ink jet recording head will be described with reference to FIG. 4, and the manufacturing process of the main part of the ink jet recording head will be described with reference to FIGS. 5 and 6.
[0052]
(Configuration of inkjet recording head)
The exploded perspective view of the ink jet recording head shown in FIG. 4 shows a type in which the ink supply flow path is formed in the pressurizing chamber substrate. As shown in the figure, the ink jet recording head mainly includes a pressurizing chamber substrate 1, a nozzle unit 2, and a base 4.
[0053]
The pressurizing chamber substrate 1 is formed on a silicon single crystal substrate and then separated into each. The pressurizing chamber substrate 1 is provided with a plurality of strip-shaped pressurizing chambers 11 and includes a common channel 13 for supplying ink to all the pressurizing chambers 11. The pressurizing chambers 11 are separated by side walls 12. A diaphragm film and a piezoelectric thin film element are formed on the substrate 4 side of the pressurizing chamber substrate 1. Further, the wiring from each piezoelectric thin film element is converged on the wiring board 3 which is a flexible cable and connected to an external circuit (not shown) of the base 4. Print data is supplied to the external circuit from a computer built in a printer (not shown), and the ink jet recording head ejects ink at a predetermined timing.
[0054]
The nozzle plate 2 is bonded to the pressurizing chamber substrate 1. A nozzle 21 for extracting ink droplets is formed at a position corresponding to the pressurizing chamber 11 in the nozzle plate 2.
[0055]
The base 4 is a steel body such as plastic or metal and serves as a mounting base for the pressurizing chamber substrate 1.
[0056]
(Operation principle of ink jet recording head)
Next, the operation principle of the ink jet recording head will be described with reference to FIG. FIG. 2 is a cross-sectional view of the main part of the ink jet recording head.
[0057]
When it is desired to eject ink, a voltage is applied between the upper electrode 50 and the lower electrode 30. This voltage is in the same direction as the polarization direction of the piezoelectric film 40. As a result, the piezoelectric film 40 expands in the thickness direction and contracts in the width direction. This contraction causes a compressive stress to act on the interface between the piezoelectric film 40 and the oxide film 20 (functioning as a diaphragm film), and the oxide film 20 warps to the pressurizing chamber 11 side. Due to this warpage, the volume of the pressurizing chamber 11 changes, and ink droplets are ejected from the nozzle 21. This enables printing.
[0058]
(Manufacturing process in main part of ink jet recording head)
Next, the manufacturing process of the ink jet recording head according to this embodiment will be described with reference to FIGS.
[0059]
5 and 6 correspond to cross-sectional views taken along the line aa of the pressurizing chamber substrate 1 of FIG.
[0060]
Piezoelectric thin film element forming step (FIG. 5A)
An etching protective layer (thermal oxide film) 20 made of silicon dioxide is formed on the entire surface of a silicon single crystal substrate 10 having a predetermined size and thickness (for example, a diameter of 102 mm and a thickness of 220 μm) by a thermal oxidation method or the like.
[0061]
Next, a piezoelectric thin film element including the lower electrode 30, the piezoelectric film 40, and the upper electrode 50 is formed on the surface of the substrate 10 on the active element side (the side on which the piezoelectric thin film element is formed). The method for forming the piezoelectric thin film element is the same as that of the first embodiment described above, and a description thereof will be omitted. The piezoelectric film 40 has a configuration in which transition layers are formed at unequal intervals in the film thickness direction of the piezoelectric film 40 and the distance between the transition layers is narrowed on the surface of the piezoelectric film 40. Yes.
[0062]
Piezoelectric thin film element separation step (FIG. 5B)
An appropriate resist (not shown) is applied to the upper electrode 50 and the piezoelectric film 40 in accordance with the position where the pressurizing chamber 11 is to be formed, and predetermined separation is performed using ion milling or the like using this resist as a mask. Form into shape. The resist may be formed using a known method such as a spinner method or a spray method. Further, an appropriate resist (not shown) is similarly applied to the lower electrode and formed into a predetermined shape using ion milling or the like.
[0063]
Further, a protective film (not shown) against various chemicals eroded in a later process is applied to the active element side of the substrate 10, and at least a pressurizing chamber or a side surface region including a side wall of the surface of the substrate 10 on the pressurizing chamber side. The thermal oxide film 20 is etched with hydrogen fluoride to form an etching window 14.
[0064]
Pressurization chamber forming recess forming step (FIG. 5C)
The silicon single crystal substrate 10 of the window 14 is etched to a predetermined depth using a wet anisotropic etching solution, for example, a 10% concentration potassium hydroxide aqueous solution kept at 80 ° C. to form the recess 15.
[0065]
This process may be performed by dry anisotropic etching using an active gas such as parallel plate type reactive ion etching.
[0066]
Pressurization chamber forming process (FIG. 6D)
After the silicon dioxide film 20 is formed as an etching protective layer by 1 μm on the substrate 10 on which the recess 15 is formed by a chemical vapor deposition method such as a CVD method, an etching mask is formed in accordance with the position where the pressure chamber is to be formed. And etching with hydrogen fluoride.
[0067]
A sol-gel method may be used as another method for forming the silicon dioxide film 20, but since a piezoelectric thin film element has already been formed on the surface on the active element side, a high temperature of 1000 ° C. or higher. The sol-gel method that requires heating is not preferable because it inhibits the crystallinity of the piezoelectric film.
[0068]
Pressurization chamber forming process (FIG. 6E)
The substrate 10 is anisotropically etched from the pressure chamber side toward the active element side using a wet anisotropic etching solution, for example, a 10% concentration potassium hydroxide aqueous solution kept at 80 ° C. And sidewalls 12 are formed.
[0069]
Nozzle plate joining process (Fig. 6 (F))
A separate nozzle unit 2 is joined to the pressurizing chamber substrate 1 formed by the above steps using an adhesive. The adhesive may be any of epoxy, urethane, silicone, and the like. In the nozzle unit 2, nozzles 21 are formed corresponding to the pressure chambers 11.
[0070]
The pressurizing chamber substrate 1 and the nozzle unit 2 may be integrally formed by etching a silicon single crystal substrate. In this case, this step is unnecessary.
[0071]
As described above, according to the ink jet recording head according to the present embodiment, due to the structure of the piezoelectric film, the transition layers are arranged at unequal intervals in the film thickness direction of the piezoelectric film, and the piezoelectric film Since the surface is formed so that the distance between the transition layers becomes narrow on the surface, it is possible to prevent the occurrence of cracks in the piezoelectric film in the manufacturing process of the ink jet recording head, and to improve the yield. . Therefore, cost can be reduced.
[0072]
Further, since the piezoelectric thin film element can be improved in reliability and the piezoelectric characteristics of the piezoelectric film can be improved, the amount of ink discharged is increased, and clear printing can be performed.
[0073]
In addition, since the piezoelectric film can be made thicker than before, a larger volume change can be generated, and high-definition printing is possible in response to a reduction in the volume of the pressurizing chamber. become.
[0074]
【The invention's effect】
According to the piezoelectric thin film element according to the present invention, the piezoelectric films have unequal intervals with respect to the film thickness direction so that the distance between the transition layers is at least smaller on the upper electrode side than on the lower electrode side. Therefore, it is possible to relieve stress in the manufacturing process of the piezoelectric thin film element and to prevent generation of cracks. With this configuration, the piezoelectric film can be thickened and the piezoelectric characteristics can be improved.
[0075]
Further, according to the ink jet recording head of the present invention, the ink discharge amount is increased due to the improvement of the piezoelectric characteristics of the piezoelectric film, and clear printing can be performed.
[0076]
Moreover, since the generation of cracks in the manufacturing process can be suppressed, the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a piezoelectric thin film element according to an embodiment.
2 is a cross-sectional view of a manufacturing process of the piezoelectric thin film element shown in FIG. 1. FIG.
3 is a manufacturing process sectional view showing the manufacturing process shown in FIG. 2 (B) in more detail; FIG.
FIG. 4 is an exploded perspective view of an ink jet recording head.
FIG. 5 is a manufacturing process cross-sectional view of the main part of the ink jet recording head.
FIG. 6 is a manufacturing process cross-sectional view of the main part of the ink jet recording head.
[Explanation of symbols]
1 ... Pressure chamber substrate
2 ... Nozzle unit
3. Wiring board
4 ... Base
10 ... Board
11 ... Pressurizing chamber
12 ... Sidewall
13 ... Common flow path
20 ... Oxide film
21 ... Nozzle
30 ... Lower electrode
40. Piezoelectric film
40A ... piezoelectric layer
40B ... piezoelectric layer
40C ... piezoelectric layer
40D ... piezoelectric layer
40b ... transition layer,
40c ... transition layer
40d ... transition layer
50 ... Upper electrode

Claims (12)

In a piezoelectric thin film element configured by sandwiching a piezoelectric film formed of a piezoelectric material between an upper electrode and a lower electrode,
The piezoelectric film includes n (n is a natural number of 2 or more) transition layers in the film thickness direction, and the distance between the transition layers is at least smaller on the upper electrode side than on the lower electrode side. A piezoelectric thin film element characterized by the above. The n transition layers are formed as a first transition layer, a second transition layer,..., An nth transition layer in order from the transition layer closer to the lower electrode side, and the lower electrode and the first transition layer are formed. The distance between the layers is d ₁ , the distance between the first transition layer and the second transition layer is d ₂ ,..., And the distance between the n−1th transition layer and the nth transition layer is _dn. Then,
d ₁ > d ₂ >...> d _n
The piezoelectric thin film element according to claim 1, satisfying the relationship: 3. The piezoelectric thin film element according to claim 1, wherein n is in a range of 2 to 6 with respect to a piezoelectric film having a thickness of 2.0 μm. 4. The piezoelectric thin film element according to claim 1, wherein a dislocation density in the dislocation layer is in a range of 10 ^{13 to} 10 ¹⁴ / cm ² . 5. The piezoelectric thin film element according to claim 1, wherein the dislocation layer is formed to a thickness of 5 nm to 15 nm in a thickness direction of the piezoelectric film. 6. A pressurizing chamber substrate comprising the piezoelectric thin film element according to claim 1 disposed on a vibration plate that forms at least one surface of a pressurizing chamber for filling ink. An ink jet recording head comprising: In a method of manufacturing a piezoelectric thin film element, comprising: a step of forming a lower electrode; a step of forming a piezoelectric film on the lower electrode; and a step of forming an upper electrode on the piezoelectric film. ,
In the piezoelectric film forming step, a first film formed by applying a sol for forming a piezoelectric film precursor at least once is heat-treated, and then the sol is applied on the first film at least once. The step of forming a transition layer in the second film in the vicinity of the interface between the first and second films by heat-treating the second film is m times (m is a natural number of 2 or more) times. Repetitively, m transition layers formed in the film thickness direction of the piezoelectric film were formed so that the distance between the transition layers was at least narrower on the upper electrode side than on the lower electrode side. A method of manufacturing a piezoelectric thin film element, which is characterized. The m transition layers are formed as a first transition layer, a second transition layer,..., An mth transition layer in order from the transition layer closer to the lower electrode side, and the lower electrode and the first transition layer are formed. d ₁ the distance between the _layers, d ₂ the distance between the first transition layer and the second transition _layer, ..., the distance between the transition layer of the (m-1) of the transition layer and the m d _m Then,
d ₁ > d ₂ >...> d _m
The method for manufacturing a piezoelectric thin film element according to claim 7, wherein the relationship is satisfied. 10. The method of manufacturing a piezoelectric thin film element according to claim 7, wherein m is in a range of 2 to 6 with respect to a piezoelectric film having a thickness of 2.0 μm. 10. The method of manufacturing a piezoelectric thin film element according to claim 7, wherein a dislocation density in the dislocation layer is in a range of 10 ^{13 to} 10 ¹⁴ / cm ² . 11. The method of manufacturing a piezoelectric thin film element according to claim 7, wherein the dislocation layer is formed to a thickness of 5 nm to 15 nm in a thickness direction of the piezoelectric film. The pressurization comprised by arrange | positioning the piezoelectric thin film element of any one of Claims 1 thru | or 6 in the diaphragm which forms at least one surface of the pressurization chamber for filling with ink. In a manufacturing method of an ink jet recording head provided with a chamber substrate,
A method of forming a diaphragm on a substrate, a step of forming a pressure chamber on the substrate, and a method of manufacturing a piezoelectric thin film element according to any one of claims 7 to 11. A method of manufacturing an ink jet recording head.

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