JP7067085B2 - Piezoelectric element and liquid discharge head - Google Patents

Description

The present invention relates to a piezoelectric element and a liquid discharge head.

The piezoelectric element generally has a piezoelectric layer having electromechanical conversion characteristics and two electrodes sandwiching the piezoelectric layer. Such a piezoelectric element is used, for example, in a liquid discharge head mounted on an inkjet recording head.

As a material used for the piezoelectric layer, various materials such as lead zirconate titanate (PZT) are known, and most of them have a perovskite type crystal structure. When the piezoelectric layer is a thin film, the piezoelectric layer has a structure in which a large number of crystals (crystal grains) are arranged, and the polarization directions of the crystals are often not aligned in a certain direction.

In Patent Document 1, the direction of spontaneous polarization is aligned in a certain direction by applying an electric field in a direction parallel to the direction in which spontaneous polarization is desired to occur in the piezoelectric thin film to crystallize the precursor of the piezoelectric thin film. It is disclosed that a piezoelectric thin film is formed.

Japanese Unexamined Patent Publication No. 2000-294844

The method for producing a piezoelectric thin film described in Patent Document 1 has a problem that the process becomes complicated because it is necessary to crystallize while applying an electric field. Further, although the piezoelectric element containing the piezoelectric thin film obtained by the method for producing the piezoelectric thin film described in Patent Document 1 has high piezoelectric characteristics, pinning or the like is likely to occur and there is still a point to be improved.

One aspect of the piezoelectric element according to the present invention is
The first electrode provided above the substrate and
A piezoelectric layer having a direction of spontaneous polarization similar to the direction of spontaneous polarization of the perovskite structure of rhombohedral crystals and provided above the first electrode.
A second electrode provided above the piezoelectric layer and
Equipped with
When the crystal structure of the crystal is regarded as a pseudo-cubic crystal, 2σ of the signal intensity distribution of the locking curve of the X-ray diffraction signal attributed to (100) is within 7.0 °.

In the piezoelectric element according to the present invention
The piezoelectric layer may have a plurality of layers.

In the piezoelectric element according to the present invention
The piezoelectric layer may contain bismuth, iron and titanium.

In the piezoelectric element according to the present invention
A positive potential is applied to the first electrode,
A ground potential may be applied to the second electrode.

In the piezoelectric element according to the present invention
The first electrode may include a laminated structure in which a platinum layer and a titanium layer are laminated from the side close to the second electrode.

In the piezoelectric element according to the present invention
The second electrode may have a laminated structure in which an iridium layer, a titanium layer, an iridium layer, and a titanium layer are laminated from the side close to the first electrode.

One aspect of the liquid discharge head according to the present invention includes the above-mentioned piezoelectric element.

The schematic diagram of the cross section of the piezoelectric element which concerns on embodiment. The exploded perspective view which shows typically the liquid discharge head which concerns on embodiment. The plan view which shows typically the liquid discharge head which concerns on embodiment. The cross-sectional view which shows typically the liquid discharge head which concerns on embodiment. The locking curve of the sample according to the embodiment. PE curve before and after pulse application of the sample which concerns on Example. PE curve before and after pulse application of the sample which concerns on a comparative example. The schematic diagram explaining the sign of bending in an Example and a comparative example. The schematic diagram explaining the sign of bending in an Example and a comparative example. The table which shows the measurement result before and after the pulse application of the bending and the radius of curvature of the sample of an Example and a comparative example. Plot of the amount of deflection with respect to the number of pulses of the samples of Examples and Comparative Examples. Plot of the amount of deflection with respect to the number of pulses of the samples of Examples and Comparative Examples. Schematic diagram for explaining the relationship between orientation fluctuation and polarization.

Hereinafter, some embodiments of the present invention will be described. The embodiments described below describe an example of the present invention. The present invention is not limited to the following embodiments, and includes various modifications implemented without changing the gist of the present invention. Not all of the configurations described below are essential configurations of the present invention.

1. 1. Piezoelectric element The piezoelectric element according to this embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the piezoelectric element 100 according to the present embodiment. The piezoelectric element 100 of the present embodiment includes a first electrode 10, a piezoelectric layer 20 provided above the first electrode 10, and a second electrode 30 provided above the piezoelectric layer.

1.1. First Electrode The first electrode 10 is one electrode for applying a voltage to the piezoelectric layer 20. The first electrode 10 can also be referred to as a lower electrode provided under the piezoelectric layer 20. In the illustrated example, the first electrode 10 is provided on the substrate 2 (diaphragm 230).

The shape of the first electrode 10 is, for example, a layer. The film thickness (thickness) of the first electrode 10 is, for example, 3 nm or more and 300 nm or less. The material of the first electrode 10 is not limited as long as it has conductivity, but is, for example, a metal, a conductive oxide, or the like. The first electrode 10 may have a structure in which a plurality of layers of the illustrated materials are laminated.

The first electrode 10 preferably contains a platinum group element. Platinum group elements are elements located in the 8th, 9th, and 10th groups in the 5th and 6th periods in the periodic table, and specifically, ruthenium, rhodium, palladium, and osmium. Refers to iridium and platinum. Further, it is more preferable that the first electrode 10 includes a laminated structure in which a platinum layer and a titanium layer are laminated from the side of the piezoelectric layer 20 (from the side close to the second electrode 30). Here, the titanium layer is a layer containing titanium as a main component, and the platinum layer is a layer containing platinum as a main component. The "main component" means that the ratio of a specific element to the total amount of elements constituting a certain member is 80% or more, preferably 90% or more, more preferably 95% or more, still more preferably 98% or more. Refers to being. By including the laminated structure in which the platinum layer and the titanium layer are laminated from the side of the piezoelectric layer 20 (from the side close to the second electrode 30), the first electrode 10 can enhance the barrier property of the first electrode 10. , It is possible to further suppress the metal element from penetrating through the first electrode 10 and diffusing.

1.2. Piezoelectric layer The piezoelectric layer 20 is provided above the first electrode 10. In the illustrated example, the piezoelectric layer 20 is provided on the first electrode 10. The film thickness of the piezoelectric layer 20 is, for example, 100 nm or more and 3 μm or less. The piezoelectric layer 20 can be deformed by applying a voltage (electric field) between the first electrode 10 and the second electrode 30. The piezoelectric layer 20 contains a perovskite-type crystal structure, and exhibits an electromechanical conversion effect when a voltage is applied.

As the material having piezoelectricity, the piezoelectric layer 20 can use, for example, a composite oxide having a perovskite-type crystal structure. Examples of the metal element contained in the piezoelectric layer 20 include Pb, Ba, Ca, Nb, La, Li, Sr, Bi, Na, K, Fe, Ti, Ta, Mg, Mo, Ni, Mn, Zr, Zn. W, Yb and the like can be mentioned.

Among such materials, a composite oxide containing Ti, Zr, and Pb (lead zirconate titanate (PZT)), a composite oxide containing potassium (K), sodium (Na), and niobium (Nb) (KNN). , Bi, Fe-containing composite oxide (bismuth iron acid (BFO)), lead zirconate titanate niobate (Pb (Zr, Ti, Nb) O ₃ : PZTN), etc. are likely to obtain better piezoelectric properties. Therefore, it is more preferable.

Further, the piezoelectric layer 20 may have a laminated structure of a plurality of layers. In this case, each layer to be laminated may be made of the same kind of material, or may be made of different kinds of materials. When the piezoelectric layer 20 has a laminated structure of a plurality of layers, it may include a layer containing bismuth, iron and titanium. Examples of the material of the layer containing bismuth, iron and titanium include bismuth bismuth ironate (BFT), which may contain crystals having a perovskite-type crystal structure.

Further, when the piezoelectric layer 20 has a layer containing bismuth, iron and titanium, the layer containing bismuth, iron and titanium may function as a seed layer. Here, the seed layer means a layer for controlling the orientation of crystals generated when the piezoelectric layer is crystallized. Therefore, in this case, when the layer containing bismuth, iron and titanium is provided on the first electrode 10, the orientation of crystals such as PZT formed above the layer can be controlled more efficiently. Further, when the layers containing bismuth, iron and titanium are arranged in this way, a positive potential is applied to the first electrode 10 and a ground potential is applied to the second electrode 30 in the direction in which the voltage is applied to the piezoelectric layer 20. It is more preferable to make it applied. By doing so, since the electrons are injected into the piezoelectric layer from the second electrode 30 side, deterioration of the interface between the first electrode 10 and the piezoelectric layer 20 can be further suppressed. That is, since electrons do not flow into the layer containing bismuth, iron, and titanium on the first electrode 10, it is easy to maintain a good interface between the first electrode 10 and the piezoelectric layer 20. When a layer containing bismuth, iron, and titanium is arranged in the vicinity of the second electrode 30 for the same reason, a ground potential is applied to the first electrode 10 and a positive potential is applied to the second electrode 30. It is more preferable to be done.

The piezoelectric layer 20 contains crystals in which the direction of spontaneous polarization is similar to the direction of spontaneous polarization of the perovskite structure of rhombohedral crystals. Since the above-mentioned composite oxide has a perovskite-type crystal structure, it can be a crystal having a direction of spontaneous polarization similar to the direction of spontaneous polarization of the perovskite structure of rhombohedral crystals. Here, "the two directions are similar" means that when the two directions are drawn on the same plane, they are within ± 10 °, preferably within ± 5 °, and more preferably within ± 2 °. Point to that.

When a composite oxide having a perovskite-type crystal structure is used, in general, the raw material of A site is often charged (excessively) in a larger amount (excessive) than the stoichiometric composition (stoichiometry) and calcined. For example, in the case of PZT, lead can be contained in a ratio of, for example, 1.0 or more and 1.30 or less, where 1 is the total number of moles of zirconium and titanium. Some of the lead atoms in excess of 1.0 enter the B site of the perovskite-type structure represented by ABO ₃ . Here, the B site refers to an atomic site in which oxygen is coordinated to six. In addition, a part is unevenly distributed at the crystal grain interface and the like. In addition, part of it volatilizes into the atmosphere during firing.

The crystal contained in the piezoelectric layer 20 of the present embodiment has a ± 2σ section of the signal intensity distribution of the locking curve of the X-ray diffraction signal attributed to (100) when the crystal structure is regarded as a pseudo-cubic crystal. It is within 0.0 °.

Here, the "X-ray diffraction signal attributed to (100) when the crystal structure is regarded as a pseudo-cubic crystal" is a tetragonal crystal or an oblique crystal when the crystal is distorted in the X-ray diffraction pattern. Peaks attributed to (100), (010), and (001) may appear corresponding to crystals, monoclinic crystals, etc., and the peaks may be complicated. It refers to an X-ray diffraction signal attributed to (100) when it is considered to be present.

The locking curve is a kind of measurement method also called ω (omega) scan, and when the 2θ of the crystal is constant, the orientation (orientation) of the crystal perpendicular to the substrate is reflected in the measurement result. The method. Therefore, the signal intensity distribution of the locking curve represents the fluctuation of the plane orientation of the crystal with respect to the direction perpendicular to the substrate. Since the shape of the locking curve is theoretically a Gaussian distribution (normal distribution), the signal intensity distribution of the obtained locking curve can be fitted with a Gaussian distribution to obtain its standard deviation (σ).

As described above, the piezoelectric layer 20 of the present embodiment has a thin film shape having a diameter of 100 nm or more and 3 μm or less. Therefore, the crystals contained in the piezoelectric layer 20 are difficult to align in orientation due to the shape of the thin film, and are likely to be distorted due to the influence of an external field (external factor) such as substrate stress. Therefore, when the locking curve is measured, the peak has a spread in the direction along the ψ axis of the locking curve.

In the crystal contained in the piezoelectric layer 20 of the present embodiment, the signal intensity distribution of the locking curve of 2σ is within 7.0 °, more preferably within 5.0 °, and further preferably within 3.0 °. be. The distribution of the locking curve is the slope from the direction perpendicular to the substrate. Since the crystals described herein do not consider in-plane orientation, plus and minus are equivalent to the median distribution (corresponding to the perpendicular to the substrate). From this, half of the distribution width is the tilt angle. For example, the distribution width of the tilt angle in the ± 2σ interval, which is the range in which 95.45% of the total intensity exists, is 2σ. Therefore, when 2σ is within 7.0 °, 95.45% of the profile of the X-ray diffraction signal attributed to (100) in the direction along the ψ axis when the crystal structure is regarded as a pseudo-cubic crystal. It means that the strength is within the tilt angle of 7.0 °.

1.3. Second electrode The second electrode 30 is provided above the piezoelectric layer 20. In the illustrated example, the second electrode 30 is provided on the piezoelectric layer 20. The second electrode 30 is the other electrode for applying a voltage to the piezoelectric layer 20. The second electrode 30 is an upper electrode provided on the piezoelectric layer 20.

The shape of the second electrode 30 is, for example, a layer. The film thickness of the second electrode 30 is, for example, 50 nm or more and 300 nm or less. The second electrode 30 is, for example, a metal layer such as an iridium layer or a platinum layer, a conductive oxide layer thereof (for example, an iridium oxide layer), a strontium ruthenate layer, or the like. The second electrode 30 may have a structure in which a plurality of the layers exemplified above are laminated.

The second electrode 30 preferably contains a platinum group element. Platinum group elements are elements located in the 8th, 9th, and 10th groups in the 5th and 6th periods in the periodic table, and specifically, ruthenium, rhodium, palladium, and osmium. Refers to iridium and platinum.

Further, it is more preferable that the second electrode 30 includes a laminated structure in which an iridium layer, a titanium layer, an iridium layer and a titanium layer are laminated from the side of the piezoelectric layer 20 (from the side close to the first electrode 10). Here, the iridium layer is a layer containing iridium as a main component, and the titanium layer is a layer containing titanium as a main component. The "principal component" is as already defined.

By including the laminated structure in which the iridium layer, the titanium layer, the iridium layer and the titanium layer are laminated from the side of the piezoelectric layer 20, the second electrode 30 can enhance the barrier property of the second electrode 30, and the metal element can be removed. It is possible to further suppress the permeation and diffusion through the second electrode 30.

1.4. Other configurations The piezoelectric element 100 is formed on, for example, the substrate 2. The substrate 2 is, for example, a flat plate made of a semiconductor, an insulator, or the like. The substrate 2 may be a single layer or may have a structure in which a plurality of layers are laminated. The internal structure of the substrate 2 is not limited as long as the upper surface has a flat shape, and the substrate 2 may have a complicated structure such that a space or the like is formed inside.

The substrate 2 may be a diaphragm 230 that is flexible and can be deformed (displaced) by the operation of the piezoelectric layer 20, or has a higher-order configuration including the diaphragm 230. May be. The diaphragm 230 is, for example, a silicon oxide layer, a zirconium oxide layer, or a laminate thereof (for example, a laminate in which a zirconium oxide layer is provided on the silicon oxide layer). Although not shown, an adhesion layer for improving the adhesion between the first electrode 10 and the substrate 2 may be provided. The adhesion layer is, for example, a titanium layer, a titanium oxide layer, a zirconium layer, or the like. Further, when a conductive close contact layer such as a titanium layer or a zirconium layer is provided, the close contact layer may be regarded as a part of the first electrode 10.

In the present specification, as shown in the illustrated example, the member composed of the substrate 2 (diaphragm 230) and the piezoelectric element 100 may be referred to as an actuator 110. The actuator 110 can bend or vibrate when the piezoelectric element 100 is deformed. Further, the diaphragm of the actuator 110 constitutes a part of the wall that divides the pressure generating chamber of the liquid discharge head, which will be described later, so that the volume of the pressure generating chamber can be changed according to the input signal. .. Further, the diaphragm 230 and the first electrode 10 may be collectively referred to as a diaphragm.

The actuator 110 may be used, for example, as a piezoelectric actuator that pressurizes the liquid in the pressure generating chamber, such as a liquid discharge head or a printer using the liquid discharge head. Further, the piezoelectric element 100 may be used for a piezoelectric sensor (ultrasonic sensor, gyro sensor) or the like that detects deformation of the piezoelectric layer as an electric signal.

1.5. Action effect, etc. In the piezoelectric element 100 of the present embodiment, the signal strength of the locking curve of the X-ray diffraction signal attributed to (100) when the crystal contained in the piezoelectric layer 20 is regarded as a pseudo-cubic crystal structure. The ± 2σ interval of the distribution is within 7.0 °. Therefore, the orientations of the crystals contained in the piezoelectric layer 20 are arranged in a state where the variation is small. Therefore, pinning is unlikely to occur, and as a result, for example, when the piezoelectric element 100 is used to displace the diaphragm 230, the displacement bias due to the polarization treatment can be suppressed.

2. 2. Method for Manufacturing Piezoelectric Element Next, a method for manufacturing the piezoelectric element 100 according to the present embodiment will be described.

First, the substrate 2 is prepared. Specifically, a silicon oxide layer is formed by thermally oxidizing a silicon substrate. Next, a zirconium layer is formed on the silicon oxide layer by a sputtering method or the like, and the zirconium oxide layer is thermally oxidized to form the zirconium oxide layer. By the above steps, the substrate 2 can be prepared.

Next, the first electrode 10 is formed on the substrate 2. The first electrode 10 is formed by, for example, a sputtering method or a vacuum vapor deposition method.

Next, the piezoelectric layer 20 is formed on the first electrode 10. The piezoelectric layer 20 is formed by, for example, a liquid phase method (chemical solution method) such as a sol-gel method or a MOD (Metal Organic Deposition). More specifically, a metal complex containing a metal contained in the piezoelectric layer 20 is dissolved or dispersed in an organic solvent to prepare a precursor solution, and the precursor solution is applied onto the first electrode 10 by a spin coating method. And the like to form a precursor layer (coating step). Next, the precursor layer is heated at, for example, 130 ° C. or higher and 250 ° C. or lower and dried for a certain period of time (drying step), and the dried precursor layer is further heated at, for example, 300 ° C. or higher and 450 ° C. or lower for a certain period of time. Degreasing by holding (defatting step). Next, the degreased precursor layer is heated at, for example, 650 ° C. or higher and 800 ° C. or lower, and held at this temperature for a certain period of time to crystallize (calcination step).

By the above steps, the piezoelectric layer 20 is formed on the first electrode 10. If necessary, the piezoelectric layer 20 composed of a plurality of layers may be formed by repeating the series of steps from the coating step to the firing step a plurality of times. Further, when the piezoelectric layer 20 is formed by a plurality of layers, the layer formed first may be used as a seed layer. The material of the seed layer is, for example, a layer containing bismuth, iron and titanium, and can be similarly formed by selecting the material.

Examples of the heating device used in the drying step, the degreasing step, and the firing step for forming the piezoelectric layer 20 include an RTA (Rapid Thermal Annealing) device that heats by irradiation with an infrared lamp.

Next, the piezoelectric layer 20 is patterned. As a result, as shown in FIG. 1, the piezoelectric layer 20 and the first electrode 10 having a predetermined shape can be formed. Patterning is performed, for example, by photolithography and etching. The patterning may be performed after the film to be the second electrode 30 is formed.

Next, the second electrode 30 is formed on the piezoelectric layer 20. The second electrode 30 is formed by, for example, film formation by a sputtering method, a vacuum vapor deposition method, or the like, and patterning by photolithography and etching.

By the above steps, the piezoelectric element 100 can be manufactured. When the substrate 2 is the diaphragm 230, or when the substrate 2 is further processed into the diaphragm 230, the actuator 110 can be manufactured by adding an appropriate step to these steps. Although the example of forming the piezoelectric layer 20 by the liquid phase method has been described above, the method of forming the piezoelectric layer 20 is not particularly limited, and for example, a CVD method, a sputtering method, or the like may be used.

3. 3. Liquid Discharge Head Next, the liquid discharge head according to the present embodiment will be described with reference to the drawings. FIG. 2 is an exploded perspective view schematically showing the liquid discharge head 200 according to the present embodiment. FIG. 3 is a plan view schematically showing the liquid discharge head 200 according to the present embodiment. FIG. 4 is a sectional view taken along line IX-IX of FIG. 3 schematically showing the liquid discharge head 200 according to the present embodiment. In FIGS. 2 to 4, the X-axis, the Y-axis, and the Z-axis are shown as three axes orthogonal to each other.

The liquid discharge head according to the present invention includes the above-mentioned piezoelectric element 100 or the above-mentioned actuator 110. Hereinafter, as an example, the liquid discharge head 200 including the piezoelectric element 100 will be described.

As shown in FIGS. 2 to 4, the liquid discharge head 200 includes, for example, a piezoelectric element 100, a flow path forming substrate 210, a nozzle plate 220, a diaphragm 230, a protective substrate 240, and a circuit board 250. Includes compliance board 260 and. For convenience, FIG. 3 omits the illustration of the circuit board 250 and the connection wiring 204.

The flow path forming substrate 210 is, for example, a silicon substrate. The flow path forming substrate 210 is provided with a pressure generating chamber 211. The pressure generating chamber 211 is partitioned by a plurality of partition walls 212.

An ink supply path 213 and a communication passage 214 are provided at the end of the flow path forming substrate 210 on the + X axis direction side of the pressure generating chamber 211. The ink supply path 213 is configured to reduce the opening area of the pressure generating chamber 211 by narrowing the end portion on the + X-axis direction side from the Y-axis direction. The size of the communication passage 214 in the Y-axis direction is, for example, the same as the size of the pressure generating chamber 211 in the Y-axis direction. A communication portion 215 is provided on the + X-axis direction side of the communication passage 214. The communication portion 215 constitutes a part of the manifold 216. The manifold 216 serves as a common ink chamber for each pressure generating chamber 211. As described above, the flow path forming substrate 210 is formed with a liquid flow path including the pressure generation chamber 211, the ink supply path 213, the communication passage 214, and the communication portion 215.

The nozzle plate 220 is provided on one surface (the surface on the −Z axis direction side) of the flow path forming substrate 210. The material of the nozzle plate 220 is, for example, SUS (Steel Use Stainless). The nozzle plate 220 is joined to the flow path forming substrate 210 by, for example, an adhesive or a heat welding film. Nozzle openings 222 are arranged side by side on the nozzle plate 220 along the Y axis. The nozzle opening 222 communicates with the pressure generating chamber 211.

The diaphragm 230 is provided on the other surface (the surface on the + Z axis direction side) of the flow path forming substrate 210. The diaphragm 230 is composed of, for example, a first insulating layer 232 formed on the flow path forming substrate 210 and a second insulating layer 234 provided on the first insulating layer 232. The first insulating layer 232 is, for example, a silicon oxide layer. The second insulating layer 234 is, for example, a zirconium oxide layer.

The piezoelectric element 100 is provided on the diaphragm 230, for example. A plurality of piezoelectric elements 100 are provided. The number of piezoelectric elements 100 is not particularly limited.

In the liquid discharge head 200, the diaphragm 230 and the first electrode 10 are displaced due to the deformation of the piezoelectric layer 20 having the electromechanical conversion characteristic. That is, in the liquid discharge head 200, the diaphragm 230 and the first electrode 10 substantially have a function as a diaphragm. The diaphragm 230 may be omitted so that only the first electrode 10 functions as the diaphragm. When the first electrode 10 is directly provided on the flow path forming substrate 210, it is preferable to protect the first electrode 10 with an insulating protective film or the like so that the ink does not come into contact with the first electrode 10.

The first electrode 10 is configured as an independent electrode for each pressure generating chamber 211. The size of the first electrode 10 in the Y-axis direction is smaller than the size of the pressure generating chamber 211 in the Y-axis direction. The size of the first electrode 10 in the X-axis direction is larger than the size of the pressure generating chamber 211 in the X-axis direction. In the X-axis direction, both ends of the first electrode 10 are located outside the both ends of the pressure generating chamber 211. A lead electrode 202 is connected to the end of the first electrode 10 on the −X axis direction side.

The size of the piezoelectric layer 20 in the Y-axis direction is, for example, larger than the size of the first electrode 10 in the Y-axis direction. The size of the piezoelectric layer 20 in the X-axis direction is larger than, for example, the size of the pressure generating chamber 211 in the X-axis direction. The end portion of the piezoelectric layer 20 on the + X-axis direction side is located, for example, outside (on the + X-axis direction side) of the end portion of the first electrode 10 on the + X-axis direction side. That is, the end portion of the first electrode 10 on the + X axis direction side is covered with the piezoelectric layer 20. On the other hand, the end portion of the piezoelectric layer 20 on the −X axis direction side is located inside (on the + X axis direction side) of the end portion of the first electrode 10 on the −X axis direction side, for example. That is, the end portion of the first electrode 10 on the −X axis direction side is not covered by the piezoelectric layer 20.

The second electrode 30 is continuously provided on the piezoelectric layer 20 and the diaphragm 230. The second electrode 30 is configured as a common electrode common to the plurality of piezoelectric elements 100. Although not shown, the first electrode 10 may be used as a common electrode instead of the second electrode 30.

The protective substrate 240 is joined to the flow path forming substrate 210 by the adhesive 203. The protective substrate 240 is provided with a through hole 242. In the illustrated example, the through hole 242 penetrates the protective substrate 240 in the Z-axis direction and communicates with the communication portion 215. The through hole 242 and the communication portion 215 constitute a manifold 216 which is a common ink chamber of each pressure generating chamber 211. Further, the protective substrate 240 is provided with a through hole 244 that penetrates the protective substrate 240 in the Z-axis direction. The end of the lead electrode 202 is located in the through hole 244.

The protective substrate 240 is provided with an opening 246. The opening 246 is a space for not obstructing the driving of the piezoelectric element 100. The opening 246 may or may not be sealed.

The circuit board 250 is provided on the protective board 240. The circuit board 250 includes a semiconductor integrated circuit (IC) for driving the piezoelectric element 100. The circuit board 250 and the lead electrode 202 are electrically connected to each other via the connection wiring 204.

The compliance board 260 is provided on the protective board 240. The compliance substrate 260 has a sealing layer 262 provided on the protective substrate 240 and a fixing plate 264 provided on the sealing layer 262. The sealing layer 262 is a layer for sealing the manifold 216. The sealing layer 262 has, for example, flexibility. The fixing plate 264 is provided with a through hole 266. The through hole 266 penetrates the fixing plate 264 in the Z-axis direction. The through hole 266 is provided at a position overlapping the manifold 216 in a plan view (viewed from the Z-axis direction).

Since the liquid discharge head 200 includes the above-mentioned piezoelectric element 100, the orientations of the crystals contained in the piezoelectric layer 20 are arranged in a state of small variation. Therefore, pinning is unlikely to occur. As a result, when used to displace the diaphragm 230, the displacement bias due to the polarization process can be suppressed, and for example, the range of volume change of the pressure generating chamber 211 can be made larger, so that the efficiency of discharging the liquid can be improved. expensive.

4. Experimental Examples Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

4.1. Preparation of sample of example <Preparation of BFT solution>
Propionic acid was weighed into a container, then bismuth acetate, iron acetate, and titanium tetra-i-propoxide were weighed and stirred at 140 ° C. for 2 hours. After cooling, a BFT precursor solution was prepared by adjusting the concentration with propionic acid.

<Preparation of PZT solution>
Acetic acid and water were weighed in a container, then lead acetate, zirconium butoxide, titanium tetra-i-propoxide, and polyethylene glycol were weighed, and these were heated and stirred at 90 ° C. to prepare a PZT precursor solution. ..

<Creation of first electrode pattern and piezoelectric film>
A silicon dioxide film was formed on the 6 inch silicon substrate by thermal oxidation. Next, a zirconium film was produced by a sputtering method and thermally oxidized to produce a zirconium oxide film (insulator film). Next, the first electrode was manufactured by manufacturing titanium and platinum in this order by a sputtering method. Then, a photoresist pattern having a predetermined pattern (undisclosed) was prepared, and the first electrode was patterned by ion milling to form the first electrode pattern.

Next, the BFT precursor solution was applied onto the first electrode pattern by the spin coating method, then heated to 350 ° C. on a hot plate, and then heated to 650 ° C. by RTA. (Seed layer) was prepared. Next, the PZT precursor solution was applied by the spin coating method, heated to 140 ° C. and 370 ° C. on a hot plate, and then heated to 737 ° C. by RTA by repeating the process four times to obtain PZT having a film thickness of 700 nm. A piezoelectric layer made of was created.

<Formuator (ACT) and cavity structure (CAV)>
After forming iridium 4 nm and titanium 3 nm on the piezoelectric layer by a sputtering method, a second electrode was produced by baking at 740 ° C. using RTA. Next, the second electrode was produced by forming iridium 40 nm on the second electrode pattern by a sputtering method. A photoresist pattern having a predetermined pattern was produced on the second electrode pattern, and the second electrode was patterned by ion milling to form a second electrode pattern.

The back surface of the second electrode pattern was ground by polishing to reduce the silicon thickness to 400 μm. Then, a Cr hardmask having a predetermined pattern was prepared on the polished surface, and a cavity (CAV) structure was formed by wet etching with a KOH aqueous solution. By the above steps, a flexible vibration type piezoelectric element was formed.

4.2. Preparation of Sample of Comparative Example In the step of forming the first electrode, iridium and titanium were formed by a sputtering method after platinum sputtering, and the step of forming an orientation control layer made of BFT was omitted. A sample of a comparative example was prepared by the same method.

4.3. Structural analysis <X-ray diffraction and locking curve>
The crystal structure and orientation of the examples and comparative examples were measured using "D8 Discover" manufactured by Bruker AXS, a CuKα as a radiation source, and a two-dimensional detector (GADDS) as a detector, and two-dimensional mapping images and diffraction patterns were measured. bottom.

As a result, it was confirmed that the orientation was (100) in all the examples. It should be noted that the (100) orientation in the present specification is expressed as a plane index when the ABO type ₃ perovskite structure is regarded as a pseudo cubic crystal (pseudo-cubic crystal) as an expression of the orientation orientation, and is actually expressed. It is different from the plane index in the crystal structure of. For example, the one oriented in the (100) plane and the one oriented in the (001) plane of the tetragonal crystal are collectively referred to as the (100) orientation in the pseudo-cubic crystal described in the present specification. The orientation was defined by the area ratio F ^* of each peak shown below.
F ^* = A ₍₁₀₀₎ / {A ₍₁₀₀₎ + A ₍₁₁₀₎ + A ₍₁₁₁₎ }

First, the diffraction pattern was obtained in the region of ψ = ± 10 ° in the two-dimensional mapping with respect to the plane perpendicular direction (direction perpendicular to the substrate plane), and F * was calculated from the peak area. As a result, it was clarified that F ^* = 0.99 in the example and F ^* = 0.91 in the comparative example, both of which are good (100) orientations.

Next, the locking curve of the (100) peak was obtained from the two-dimensional mapping, and the standard deviation σ was calculated by fitting with a Gaussian function. As a result, σ = 3.34 ° in the example and σ = 8.50 ° in the comparative example.

Here, the diffraction intensity in XRD can be regarded as the frequency distribution of orientation. In addition, since the fluctuation angles of + σ and −σ are equivalent, it was clarified that in the examples, 95% or more corresponding to 2σ had a fluctuation angle of 6.7 ° or less. On the other hand, in the comparative example, it was clarified that 35% or more had a fluctuation angle larger than 8.5 °. FIG. 5 shows the locking curve of the embodiment (see also the section “1.2. Piezoelectric layer” for 2σ and the tilt angle).

<Shape observation and length measurement with an optical microscope>
The machined shape and the effective area of the electrodes greatly affect the vibration characteristics of the actuator. Therefore, for the processed shapes of all the examples, shape observation and length measurement were performed using an optical microscope of "OPTIPHOT 200" manufactured by Nikon Corporation. As a result, all the samples had a predetermined shape, and no peculiar abnormality affecting the characteristics was observed. Therefore, it became clear that it is not necessary to consider structural factors in the subsequent measurement results.

<Measurement length of cross-sectional shape by STEM>
Since the measurement length of the cross-sectional shape was measured, an electron microscope observation was performed using a "scanning transmission electron microscope HD2000" manufactured by Hitachi, Ltd. The measurement cross section was prepared by a focused electron beam (FIB). As a result, the film composition was as intended, and no significant difference was observed between the examples.

4.4. Evaluation <Imprint test>
The PE loop after pulse application was measured using the "FCE system" manufactured by Toyo Corporation. For the fatigue waveform, a square wave with low potential VL = + 15V and high potential VH = + 35V is applied with the second electrode as the reference potential (GND), and after applying a predetermined number of pulses, 1 kHz, ± 25 V P-E loop measurement is performed. rice field.

6 and 7 show the results of P-E loop evaluation before the imprint test (as-grown) and after applying 10101100 100 pulses, respectively, in Examples and Comparative Examples. In the following, as an index of imprint, evaluation is performed based on the shift rate of hysteresis (imprint rate: IPR) represented by the following formula (I).
IPR = 100 * {(+ _{VC) + (-VC )} } / {(+ _VC )-(- _VC )}
... Equation (I)

As shown in FIG. 6, in the embodiment, + Vc = 1.62V and −Vc = -1.78V in the initial state, and + Vc = 2.48V and −Vc = −3.00V after the pulse was applied. Therefore, the IPR in the examples remained at 5% on the minus side at the initial stage and at 10% on the minus side even after the pulse was applied. On the other hand, as shown in FIG. 7, in the comparative example, + Vc = 1.85V and −Vc = -2.40V in the initial state, and + Vc = 1.22V and −Vc = -2.40V after the pulse was applied. Therefore, in the comparative example, a large imprint of 13% on the minus side at the initial stage and 33% on the minus side after the pulse was applied was shown. From this result, it was clarified that imprinting was suppressed in the examples according to the present invention.

Generally, the cause of imprint is the immobilization of polarization. As will be described in detail later, the immobilization of the polarization in the piezoelectric element described in the present specification is the immobilization (pinning) of the polarization transition. Therefore, since the IPR of the examples is smaller than that of the comparative examples, it can be seen that pinning is suppressed.

<Flexibility evaluation test>
Before the PE loop measurement of the above-mentioned imprint test, the bending position of the diaphragm and its radius of curvature were evaluated using "optical interference type surface shape roughness measurement system NT9300DMEMS" manufactured by Veeco. In the present specification, as shown in FIGS. 8 and 9, the case of convex bending on the CAV surface is expressed as a plus, and the case of concave bending on the CAV surface is expressed as a minus. The radius of curvature was calculated from the result of the deflection evaluation and the CAV width measured by the above-mentioned STEM.

FIG. 10 (Table) shows the amount of deflection and the radius of curvature in the examples and comparative examples in the pulse application process described above. As shown in FIG. 10, the radius of curvature before applying the pulse was 3.0 mm in the example and 2.9 mm in the comparative example. From this result, it was clarified that the difference in the radius of curvature between the example and the comparative example was 3%, so that the difference in internal stress due to the difference in the electrode and the seed layer could be ignored.

FIG. 11 shows the amount of deflection for each applied pulse, and FIG. 12 shows the radius of curvature for each applied pulse number. As shown in FIG. 11, in the example, the change in bending is suppressed as compared with the comparative example, and as shown in FIG. 12, the radius of curvature after applying 10101100 100 pulses is 2.6 times longer than that in the comparative example in the example. It became clear that it would be.

4.5. Mechanism and evaluation results The changes in the imprint rate and the amount of deflection in the imprint test are due to the orientation fluctuation of 7.0 ° or less for 95% or more of the components in the examples. FIG. 12 is a diagram for explaining the relationship between orientation fluctuation and polarization. As shown in FIG. 13, (100) when there is no orientation fluctuation (upper part of FIG. 13), the polarization of the rhombohedral crystal in the piezoelectric material crystal is <111> with respect to the plane perpendicular direction (vertical direction in FIG. 13). 4 directions (4 axes) are equivalent. On the other hand, when there is an orientation fluctuation (lower part of FIG. 13), the polarizations are unequal in the four axes. Therefore, when a voltage is applied in the direction perpendicular to the plane, a polarization transition as shown in the figure may occur. When this polarization transition occurs irreversibly (this is called pinning), a change in internal stress occurs, the initial amount of deflection increases (the amount of deflection causes a bias amount), and the resulting energy is given. It is considered that the amount of deflection becomes small and the efficiency decreases. When the diaphragm constitutes one wall of the pressure generating chamber, it is considered that the liquid discharge efficiency is lowered. On the other hand, in the case of the embodiment of the present invention, since pinning is suppressed, it is considered that the efficiency of bending is good and the liquid discharge efficiency is good when used for the liquid discharge head.

In the present specification, when it is referred to as a specific B member (hereinafter referred to as "B") provided "upper" or "lower" of a specific A member (hereinafter referred to as "A"), it is above or above A. It is meant to include a case where B is directly provided below and a case where B is provided above or below A via another member. Further, the case of being on A is the same as the case of being above A. Further, when B exists above or below A, it means that it can be understood that it exists by changing the viewing direction and angle or rotating the field of view, and it is irrelevant to the action direction of gravity.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the present invention includes substantially the same configurations as those described in the embodiments (eg, configurations with the same function, method and result, or configurations with the same purpose and effect). The present invention also includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. Further, the present invention includes a configuration having the same action and effect as the configuration described in the embodiment or a configuration capable of achieving the same object. Further, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

2 ... substrate, 10 ... first electrode, 20 ... piezoelectric layer, 30 ... second electrode, 100 ... piezoelectric element, 110 ... actuator, 200 ... liquid discharge head, 202 ... lead electrode, 203 ... adhesive, 204 ... connection Wiring, 210 ... Flow path forming substrate, 211 ... Pressure generating chamber, 212 ... Bulk partition, 213 ... Ink supply path, 214 ... Communication passage, 215 ... Communication part, 216 ... Manifold, 220 ... Nozzle plate, 222 ... Nozzle opening, 230 ... Vibrating plate, 232 ... First insulating layer, 234 ... Second insulating layer, 240 ... Protective substrate, 242, 244 ... Through hole, 246 ... Opening, 250 ... Circuit board, 260 ... Compliance board, 262 ... Sealing layer 264 ... Fixed plate, 266 ... Through hole

Claims (6)

The first electrode provided above the substrate and
A piezoelectric layer having a direction of spontaneous polarization similar to the direction of spontaneous polarization of the perovskite structure of rhombohedral crystals and provided above the first electrode.
A second electrode provided above the piezoelectric layer and
Equipped with
The piezoelectric layer contains bismuth, iron and titanium.
A piezoelectric element in which 2σ of the signal intensity distribution of the locking curve of the X-ray diffraction signal attributed to (100) when the crystal structure of the crystal is regarded as a pseudo-cubic crystal is within 7.0 °. In claim 1,
The piezoelectric layer is a piezoelectric element having a plurality of layers. In claim 1 or 2 ,
A positive potential is applied to the first electrode,
A piezoelectric element to which a ground potential is applied to the second electrode. In any one of claims 1 to 3 ,
The first electrode is a piezoelectric element including a laminated structure in which a platinum layer and a titanium layer are laminated from a side close to the second electrode. In any one of claims 1 to 4 ,
The second electrode is a piezoelectric element having a laminated structure in which an iridium layer, a titanium layer, an iridium layer, and a titanium layer are laminated from the side close to the first electrode. A liquid discharge head comprising the piezoelectric element according to any one of claims 1 to 5 .

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