JP5449970B2 - Piezoelectric film forming method, piezoelectric element, liquid ejection device, and piezoelectric ultrasonic transducer - Google Patents

Description

  The present invention relates to a method of forming a piezoelectric film containing a lead-containing perovskite oxide by a sputtering method, a piezoelectric element using the piezoelectric film formed by the film forming method, a liquid ejection apparatus, and a piezoelectric type The present invention relates to an ultrasonic transducer.

  A piezoelectric element having a piezoelectric material having a piezoelectric property that expands and contracts as the electric field application intensity increases and decreases and an electrode that applies an electric field to the piezoelectric material are mounted on an ink jet recording head or a piezoelectric ultrasonic transducer. It is used for applications such as piezoelectric actuators. In an ink jet recording head, it is necessary to increase the density of piezoelectric elements in order to realize high-definition and high-speed printing. Therefore, thinning of the piezoelectric element has been studied, and a thin film is preferable as a form of the piezoelectric body used for the piezoelectric element in view of processing accuracy.

  In addition, for high-definition printing, it is necessary to use a highly viscous ink as the ink. In order to be able to eject high viscosity ink, the piezoelectric element is required to have higher piezoelectric performance. As a material having high piezoelectric performance in a piezoelectric thin film (hereinafter referred to as a piezoelectric film), lead-containing perovskite oxides such as lead zirconate titanate (PZT) are widely used.

  When this lead-containing perovskite oxide is used as a material for a piezoelectric film, it is known that the driving durability is greatly influenced by the lead composition, although the piezoelectric performance is high. Since lead is an element that easily causes ion migration when voltage is repeatedly applied during driving, if excessive lead is contained in the piezoelectric film, lead ion migration is likely to occur, and piezoelectric elements such as abnormal discharge It tends to cause a phenomenon that lowers the durability.

  When forming a lead-containing perovskite oxide by a sputtering method that facilitates the film formation process, it is necessary to make the amount of lead in the target excessive in order to form a perovskite oxide with good crystallinity. It is known that if the amount of lead supplied is reduced, a pyrochlore phase having no piezoelectricity is likely to grow in preference to perovskite crystal growth. Therefore, there is a demand for a method for forming a piezoelectric film having a small amount of lead and having good perovskite crystallinity.

  Patent Document 1 discloses a piezoelectric film made of a lead-containing perovskite oxide having a molar ratio of lead to a B-site element of 0.8 to 1.0 and having good piezoelectric characteristics. Patent Document 2 discloses a dielectric element in which the durability of a ferroelectric capacitor having a PZT-based piezoelectric film is improved by changing the lead composition between the vicinity of the electrode and the central portion. . In Patent Document 2, as a method for controlling the amount of lead in the sputtering method, a method of introducing a plurality of targets having different compositions and a method of changing a gas pressure or high-frequency power during film formation are described.

JP 2005-150491 A JP-A-6-21337

  Patent Document 1 describes that a piezoelectric film made of a lead-containing perovskite oxide having a molar ratio of lead to B-site element of 0.8 to 1.0 is preferably formed by a sputtering method. However, the film forming conditions of the sputtering method are not described at all, and it is unclear how to obtain them.

  In Patent Document 2, the molar ratio of lead to B-site element is changed from 1.2 to 1.0 by a method of introducing a plurality of targets having different compositions and a method of changing a gas pressure during film formation. However, it is unclear whether a perovskite oxide film having a good crystallinity can be obtained with a composition in which the molar ratio of lead to the B-site element is less than 1.0 by either method. . In particular, the method of introducing a plurality of targets having different compositions requires a plurality of sputtering chambers, and therefore the apparatus configuration is complicated.

  The present invention has been made in view of the above circumstances, and provides a method for easily forming a piezoelectric film made of a lead-containing perovskite oxide having excellent piezoelectric characteristics and durability by a sputtering method. It is intended to do.

  Another object of the present invention is to provide a piezoelectric element having excellent durability, a liquid ejection apparatus including the piezoelectric element, and a piezoelectric ultrasonic transducer.

  When forming a piezoelectric film made of a lead-containing perovskite oxide (which may contain unavoidable impurities) by sputtering, the present inventors have found that the lead composition in the film formed becomes higher as the substrate potential is higher. The substrate potential is increased at a substrate potential capable of supplying a lead amount sufficient for perovskite-type crystal growth in the initial stage of film formation, and then the lead composition is reduced with the film as a base. It was found that a piezoelectric film having a perovskite-type crystal structure with a small pyrochlore phase can be formed by forming a film with the above method.

  That is, the film forming method of the present invention is a method in which a piezoelectric film (which may contain inevitable impurities) made of one or more lead-containing perovskite oxides is formed on a substrate by sputtering. In the course of film formation, the substrate potential is changed from the first substrate potential Vsub1 to the second substrate potential Vsub2 so that the lead composition of the piezoelectric film becomes a desired composition. Is.

  In the film forming method of the present invention, the piezoelectric film is made of one or more perovskite oxides containing lead zirconate titanate (may contain unavoidable impurities) (PZT piezoelectric). The film can be preferably applied.

In the case where the piezoelectric film is made of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P), Forming a crystal nucleus of a perovskite type oxide having a Pb composition a greater than that of the perovskite type oxide at a substrate potential Vsub1, and a composition of the piezoelectric film having a Pb composition of the following general formula (P): Preferably, the second substrate potential (Vsub2) is set so that the step (B) of forming the piezoelectric film is sequentially performed. In the step (A), Vsub1 preferably satisfies the following formula (1), and more preferably satisfies the following formula (2). Furthermore, it is preferable that the following expressions (3) and (4) are satisfied.
General formula Pb _a B _b O ₃ (P)
(Wherein B is an element of the B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, and At least one element selected from the group consisting of Ni, O is oxygen, a is a value smaller than 1.0 within a range where a perovskite structure can be taken, and b is a perovskite type although 1.0 is standard. It may deviate within the range that can take the structure.)
−10 ≦ Vsub1 (V) (1),
−10 ≦ Vsub1 (V) ≦ 25 (2)
(Where Vsub1 is the first substrate potential)
−20 <Vsub2 (V) <5 (3),
450 ° C. <T (° C.) <600 ° C. (4)
(Where Vsub2 is the second substrate potential, and T is the substrate temperature in steps (A) and (B)).

  The piezoelectric element of the present invention includes a piezoelectric film formed by the film forming method of the present invention and an electrode for applying an electric field to the piezoelectric film.

  The liquid ejection apparatus of the present invention includes the piezoelectric element of the present invention and a liquid ejection member provided integrally or adjacent to the piezoelectric element, and the liquid ejection member stores liquid. The liquid storage chamber and a liquid discharge port through which the liquid is discharged from the liquid storage chamber.

  A piezoelectric ultrasonic transducer according to the present invention includes the piezoelectric element according to the present invention, an AC power source that applies an AC current to the electrode, and a diaphragm that vibrates by expansion and contraction of the piezoelectric body. .

  In the present invention, when a piezoelectric film made of a lead-containing perovskite oxide (which may contain inevitable impurities) is formed on a substrate, the potential of the substrate is changed to the first substrate potential during the film formation in the sputtering method. The film is formed by changing the lead composition of the piezoelectric film from Vsub1 to the second substrate potential Vsub2 so as to have a desired composition. According to such a film forming method, a substrate is formed at a substrate potential capable of supplying a lead amount sufficient for perovskite crystal growth in the initial stage of film formation, and then the lead composition is reduced with the film as a base. Since the film is formed by changing the potential, a piezoelectric film having a perovskite crystal structure with a small pyrochlore phase can be formed even though the lead composition is small.

  According to the present invention, in the sputtering method, it is possible to form a piezoelectric film made of a perovskite oxide having a low lead composition simply by changing the substrate potential during film formation. It is possible to easily form a piezoelectric film made of a lead-containing perovskite oxide that suppresses the ion migration of lead, which is a cause of lowering the lead, and has excellent piezoelectric characteristics and driving durability.

Schematic sectional view of RF sputtering equipment The figure which shows typically the mode during film-forming in RF sputtering device of FIG. 1A Sectional drawing which shows the structure of the piezoelectric element of embodiment which concerns on this invention, and an inkjet recording head (liquid discharge apparatus) 2 is a diagram illustrating a configuration example of an ink jet recording apparatus including the ink jet recording head (liquid ejection apparatus) of FIG. Partial top view of the ink jet recording apparatus of FIG. Sectional drawing which shows the structure of the piezoelectric ultrasonic transducer | vibrator of one Embodiment which concerns on this invention The figure which shows the time-dependent change of the substrate potential at the time of film-forming of Example 1. The figure which shows the XRD pattern of the PZT film | membrane obtained in Example 1 The figure which shows the time-dependent change of the substrate potential at the time of film-forming of Example 2. The figure which shows the XRD pattern of the PZT film | membrane obtained in Example 2 The figure which shows the relationship between the film quality of the PZT film | membrane obtained in Example 3, and substrate potential (substrate temperature 475 degreeC) The figure which shows the relationship between the film quality of the PZT film | membrane obtained in Example 3, and substrate potential (substrate temperature of 500 degreeC) The figure which shows the XRD pattern of the PZT film | membrane obtained in the comparative example 1 The figure which shows the XRD pattern of the PZT film | membrane obtained in the comparative example 2

"Method for forming piezoelectric film"
The film forming method of the present invention is a method of forming a piezoelectric film (which may contain inevitable impurities) made of one or more lead-containing perovskite oxides on a substrate by sputtering. In the course of film formation, the substrate potential is changed from the first substrate potential Vsub1 to the second substrate potential Vsub2 so that the lead composition of the piezoelectric film becomes a desired composition.

  As described in the “Background Art” section, the piezoelectric film made of lead-containing perovskite oxide has high piezoelectric performance, but it causes abnormal ion migration of lead due to repeated application of voltage during driving. A phenomenon that lowers the durability of the piezoelectric element such as electric discharge is likely to occur (Comparative Examples 1 and 2 described later). Therefore, it is preferable that the amount of lead in the piezoelectric film is small. On the other hand, if the amount of lead supplied during film formation is reduced, a pyrochlore phase that does not have piezoelectricity grows in preference to perovskite crystal growth. This becomes easy (see Comparative Examples 3 and 4 below).

  The film forming method of the present invention is a simple method in which, in the film formation of lead-containing perovskite oxides by sputtering, the lead composition increases as the substrate potential increases, and the substrate potential is simply changed during the film formation. Thus, it has been found that a piezoelectric film made of a perovskite oxide having a small pyrochlore phase can be formed even though the lead composition is small.

  Therefore, the film forming method of the present invention is not particularly limited as long as it is a sputtering method, and can be applied. Examples of the sputtering method include a normal sputtering method in which a target having a composition corresponding to the composition of the film to be formed is disposed opposite to the substrate, a reactive sputtering method, etc., but considering the simplicity of the apparatus configuration. Then, it is preferable to apply the film forming method of the present invention to a normal sputtering method.

  Here, the target composition having a composition corresponding to the composition of the film to be formed means a composition in consideration of the property that elements having a high vapor pressure easily escape from the film surface by reverse sputtering or the like during film formation.

  The present invention forms a lead-containing perovskite oxide, and it is generally known that lead has a high vapor pressure and can easily escape from the film surface. For example, Table 8.1.7 of “Vacuum Handbook” (published by ULVAC, Inc., published by Ohm) shows that the sputtering rate of PZT is Pb = 0.75, Zr = 0. 48, Ti = 0.65. Reverse sputtering is more likely to occur for elements that are more easily sputtered.

  In consideration of reverse sputtering, it is preferable that the lead composition of the target is larger than the film composition to be formed in the formation of the lead-containing perovskite oxide.

  A configuration example of the normal sputtering apparatus shown in FIG. 1 will be described. FIG. 1A is a schematic cross-sectional view of an RF sputtering apparatus, and FIG. 1B is a diagram schematically showing a state during film formation.

  The RF sputtering apparatus 200 includes a heater 211 capable of heating the mounted substrate B to a predetermined temperature and a plasma electrode (cathode electrode) 212 for generating plasma. The vacuum vessel 210 is generally configured. The heater 211 and the plasma electrode 212 are spaced apart so as to face each other, and a target T having a composition corresponding to the composition of the film formed on the plasma electrode 212 is mounted. The plasma electrode 212 is connected to a high frequency power source 213.

A gas introduction pipe 214 for introducing a gas G necessary for film formation into the vacuum container 210 and a gas discharge pipe 215 for exhausting the gas V in the vacuum container 210 are attached to the vacuum container 210. As the gas G, Ar, Ar / O ₂ mixed gas, or the like is used. As schematically shown in FIG. 1B, the gas G introduced into the vacuum vessel 210 by the discharge of the plasma electrode 212 is turned into plasma, and positive ions Ip such as Ar ions are generated. The generated positive ions Ip sputter the target T. The constituent element Tp of the target T sputtered by the positive ions Ip is emitted from the target and deposited on the substrate B in a neutral or ionized state. In the figure, the symbol P indicates the plasma space.

  In the plasma space, the substrate B is usually an insulator and is electrically insulated from the ground. Therefore, the substrate B is in a floating state, and its potential (Vsub) becomes a floating potential. The target constituent element Tp between the target T and the substrate B has a kinetic energy corresponding to the acceleration voltage of the potential difference between the potential of the plasma space P and the potential of the substrate B (Vsub), and the substrate B being formed It is thought that it will collide with.

  In other words, the lower the potential Vsub of the substrate B, the greater the kinetic energy of the constituent element Tp of the target. Therefore, it is considered that reverse sputtering is likely to occur by lowering the substrate potential Vsub. That is, by reducing the substrate potential Vsub, lead from the formed film surface can be easily removed, and the lead composition in the formed film can be reduced.

  Therefore, in the present invention, the substrate potential Vsub is set to an appropriate range during the film formation in order to reduce excess Pb in the film that causes deterioration. The method for changing Vsub is not particularly limited, but may be changed by applying a bias to the substrate B, or may be changed by installing a ground between the substrate and the target. Also, the substrate potential can be effectively changed by changing the impedance of the substrate and the chamber wall.

  In the sputtering method, factors that affect the characteristics of the film to be formed include the film formation temperature, the type of substrate, the type of substrate if there is a film previously formed on the substrate, the surface energy of the substrate, and the film formation pressure. The oxygen amount in the atmospheric gas, the input electrode, the substrate / target distance, the electron temperature and electron density in the plasma, the active species density in the plasma and the lifetime of the active species are considered.

  The present inventor pays attention to the importance of the underlying crystal structure as an important factor for the growth of the perovskite type crystal among many film formation factors, and the perovskite type oxide layer composed of the same element, at least of the perovskite type oxide. It has been found that if a crystal nucleus is formed, a perovskite-type crystal growth is possible even if the film composition formed thereon is not necessarily a film composition capable of growing a perovskite-type oxide crystal. Furthermore, by combining that the lead composition can be controlled by changing the substrate potential Vsub, a simple method of changing the substrate potential in the middle of the film formation does not allow a normal perovskite structure, and a lead-containing perovskite type oxidation with a low lead composition. The present invention has been made to enable the formation of an object.

  As shown in the examples described later, by optimizing the first substrate potential Vsub1 at the initial stage of film formation and the second substrate potential Vsub2 after that, a piezoelectric material made of a high-quality perovskite oxide with a low lead composition is used. A body film can be formed.

  The first substrate potential Vsub1 is a substrate potential capable of supplying a sufficient amount of lead for perovskite crystal growth. In the island growth phase at the initial stage of film formation, lead is more easily removed because the surface area of the formed perovskite oxide is large. Therefore, it is preferable that Vsub1 is set so that the amount of lead supply increases in consideration of the ease of removal.

  The timing for changing from Vsub1 to Vsub2 is not particularly limited as long as at least crystal nuclei of the perovskite oxide are formed by the film formation in Vsub1, but considering the homogenization of the film composition, the film formation time by Vsub1 is as long as possible. The shorter one is preferable. In order to make it possible to form a highly crystalline perovskite oxide in the film formation with Vsub2, it is only necessary that one piezoelectric film is formed in Vsub1, and the film thickness of the piezoelectric film is about 150 nm. Is preferred.

  The film forming method of the present invention can be preferably applied to film formation of one or more kinds of lead-containing perovskite oxides, and one or more kinds of perovskite oxides (PZT-based perovskite type) containing lead zirconate titanate. (Oxide) can be preferably applied.

In the case of forming a piezoelectric film made of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P), The step (A) of forming crystal nuclei of the perovskite oxide at the substrate potential Vsub1 of the second substrate potential and the second substrate potential (Vsub2) so that the composition of the piezoelectric film becomes the Pb composition of the following general formula (P) It has been found that it is preferable to perform the step (B) of setting and forming the piezoelectric film in sequence to form the film.
General formula Pb _a B _b O ₃ (P)
(Wherein B is an element of the B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, and At least one element selected from the group consisting of Ni, O is oxygen, a is a value smaller than 1.0 within a range where a perovskite structure can be taken, and b is a perovskite type although 1.0 is standard. It may deviate within the range that can take the structure.)

In the step (A), Vsub1 preferably satisfies the following formula (1), and more preferably satisfies the following formula (2).
−10 ≦ Vsub1 (V) (1),
−10 ≦ Vsub1 (V) ≦ 25 (2)
(Where Vsub1 is the first substrate potential)

  Examples of the perovskite oxide represented by the general formula (P) include lead titanate, lead zirconate titanate (PZT), lead zirconate, and lead niobate zirconium titanate. The piezoelectric film may be a mixed crystal system of perovskite oxides represented by the above general formula (P).

The present invention is particularly preferably applicable to PZT represented by the following general formula (P-1) or a B site substitution system thereof and mixed crystal systems thereof.
Pb _a (Zr _b1 Ti _b2 X _b3 ) O ₃ (P-1)
(In Formula (P-1), X is at least one metal element selected from the group of elements of Group V and Group VI. A> 0, b1> 0, b2> 0, b3 ≧ 0, where a is The value is less than 1.0 within the range where the perovskite type structure can be taken, and b1 + b3 + b3 is 1.0 as a standard, but may be deviated within the range where the perovskite type structure can be taken.

The perovskite oxide represented by the general formula (P-1) is lead zirconate titanate (PZT) when b3 = 0, and when b3> 0, part of the B site of PZT is group V. And an oxide substituted with X which is at least one metal element selected from the group of elements of group VI.
X may be any metal element of Group VA, Group VB, Group VIA, and Group VIB, and is preferably at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, and W. .

  When forming a film made of a perovskite oxide represented by the general formulas (P) and (P-1) (which may include inevitable impurities), first, the first substrate that satisfies the above formula (1) Crystal nuclei of the perovskite oxide are formed at a potential (step (A)).

  In step (A), the target composition is set to a target composition that takes into account lead loss due to reverse sputtering, and is formed at a substrate potential Vsub1 that satisfies the above formula (1). The above formula (1) is a substrate potential condition that can provide crystal nuclei of lead-containing perovskite oxides having good crystallinity, regardless of whether the underlying layer has perovskite crystallinity. .

  In the post-process (B), a perovskite oxide is formed under the condition that the lead composition is less than 1.0. Whether or not a perovskite crystal is obtained in step (B) depends on whether or not crystal nuclei are formed in step (A). Therefore, in step (A), it is important to provide enough lead to form perovskite crystal nuclei.

  Other film forming conditions other than the substrate potential can be set within the technical common sense of those skilled in the art so that good perovskite-type crystal growth is possible (see the examples described later). For example, the substrate-target distance is preferably 30 to 80 mm, and the substrate temperature is preferably in the range of 400 ° C to 800 ° C.

  The implementation time of the step (A) is not particularly limited as long as sufficient crystal nuclei can be formed to perform perovskite type crystal growth under the condition that the lead composition is reduced in the step (B). As described above, it is preferable that the execution time is short in terms of homogenization of the film composition. In Examples 1 and 2 described later, the step (A) is carried out for about 5 minutes to form a piezoelectric film having a film thickness of about 150 nm, and the perovskite oxide having good crystallinity in the step (B). It is possible to form a film.

  After completion of the step (A), a piezoelectric film is formed at a second substrate potential that satisfies the above formula (2) (step (B)). In the step (B), it is sufficient that the lead composition a in the general formula (P) can be reduced to less than 1.0, but as described above, lead ion migration during driving of the piezoelectric film is suppressed as much as possible. Thus, it is preferable to have a composition having good piezoelectric performance while further enhancing the durability of the piezoelectric film.

  On the other hand, when a piezoelectric film made of the perovskite oxide represented by the general formula (P) is formed, a lead-containing perovskite oxide having good crystallinity without lowering the substrate potential in the middle is used. In order to form a film, it is common to form the film under conditions where the amount of lead is slightly larger than the stoichiometric composition a = 1.0. However, as shown in Comparative Examples 1 and 2, a piezoelectric film with an excessive amount of lead has good piezoelectric characteristics but low driving durability.

  In a piezoelectric film composed of PZT represented by the general formula (P-1) or a B site substitution system thereof and a perovskite oxide that is a mixed crystal system thereof (which may contain inevitable impurities), P- E Hysteresis coercive field shows ferroelectricity biased in the positive direction, and a high piezoelectric constant is obtained when a negative voltage is applied. On the other hand, a positive voltage drive has a low piezoelectric constant and is likely to cause a decrease in displacement due to continuous drive. (Comparative Example 2 described later). Considering that the current general-purpose drive driver IC is for positive drive, the piezoelectric film preferably has high piezoelectric performance by positive voltage drive.

  On the other hand, the piezoelectric films of Examples 1 and 2 to be described later have substantially the same piezoelectric constant when a plus voltage is applied and when a minus voltage is applied, and have a high piezoelectric performance of d31 (pm / V) = 200. Has been confirmed.

  Therefore, according to the film forming method of the present invention, it is possible to form a piezoelectric film made of a PZT-based perovskite oxide having high piezoelectric performance in plus voltage driving in addition to high driving durability.

  In the present invention, when a piezoelectric film made of a lead-containing perovskite oxide (which may contain inevitable impurities) is formed on a substrate, the potential of the substrate is changed to the first substrate potential during the film formation in the sputtering method. The film is formed by changing the lead composition of the piezoelectric film from Vsub1 to the second substrate potential Vsub2 so as to have a desired composition. According to such a film forming method, a substrate is formed at a substrate potential capable of supplying a lead amount sufficient for perovskite crystal growth in the initial stage of film formation, and then the lead composition is reduced with the film as a base. Since the film is formed by changing the potential, it is possible to form a piezoelectric film having a perovskite crystal structure with a small pyrochlore phase despite a small lead composition.

  According to the present invention, in the sputtering method, it is possible to form a piezoelectric film made of a perovskite oxide having a low lead composition simply by changing the substrate potential during film formation. It is possible to easily form a piezoelectric film made of a lead-containing perovskite oxide that suppresses the ion migration of lead, which is a cause of lowering, and has excellent piezoelectric characteristics and excellent driving durability.

"Piezoelectric element and inkjet recording head"
With reference to FIG. 2, the structure of a piezoelectric element according to an embodiment of the present invention and an ink jet recording head (liquid ejecting apparatus) including the piezoelectric element will be described. FIG. 2 is a cross-sectional view of the main part of the ink jet recording head (cross-sectional view in the film thickness direction of the piezoelectric element). In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The piezoelectric element 1 of the present embodiment is an element in which a lower electrode 20, a piezoelectric film 30, and an upper electrode 40 are sequentially stacked on a substrate 10, and the lower electrode 20 and the upper electrode 40 with respect to the piezoelectric film 30. Thus, an electric field is applied in the film thickness direction.

The piezoelectric film 30 is not particularly limited as long as it is a piezoelectric film made of a lead-containing perovskite oxide (which may contain unavoidable impurities) formed by the piezoelectric film forming method of the present invention. Piezoelectric film made of a lead-containing perovskite oxide represented by the following general formula (P) or (P-1) (which may contain inevitable impurities), which is formed under the conditions satisfying the following formula (1) It is preferable that
General formula Pb _a B _b O ₃ (P),
(Wherein B is an element of the B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, and At least one element selected from the group consisting of Ni, O is oxygen, a is a value smaller than 1.0 within a range where a perovskite structure can be taken, and b is a perovskite type although 1.0 is standard. It may deviate within the range where the structure can be taken).
Pb _a (Zr _b1 Ti _b2 X _b3 ) O ₃ (P-1)
(In Formula (P-1), X is at least one metal element selected from the group of elements of Group V and Group VI. A> 0, b1> 0, b2> 0, b3 ≧ 0, where a is The value is less than 1.0 within the range where the perovskite type structure can be taken, and b1 + b3 + b3 is 1.0 as a standard, but may be deviated within the range where the perovskite type structure can be taken.
−10 ≦ Vsub1 (V) (1)
(In the formula, Vsub1 is the first substrate potential.)

  The lower electrode 20 is formed on substantially the entire surface of the substrate 10, and a piezoelectric film 30 having a pattern in which line-shaped convex portions 31 are arranged in stripes is formed thereon, and the upper electrode 40 is formed on each convex portion 31. Is formed.

  The pattern of the piezoelectric film 30 is not limited to the illustrated one, and is designed as appropriate. The piezoelectric film 30 may be a continuous film. However, the piezoelectric film 30 is not a continuous film, but is formed by a pattern composed of a plurality of protrusions 31 separated from each other, so that the expansion and contraction of the individual protrusions 31 occurs smoothly, so that a larger displacement amount can be obtained. ,preferable.

The substrate 10 is not particularly limited, and examples include silicon, silicon oxide, stainless steel (SUS), yttrium stabilized zirconia (YSZ), alumina, sapphire, SiC, and SrTiO ₃ . As the base material 10, a laminated substrate such as an SOI substrate in which a SiO ₂ film and a Si active layer are sequentially laminated on a silicon substrate may be used.

The composition of the lower electrode 20 is not particularly limited, and examples thereof include metals such as Au, Pt, Ir, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof. The composition of the upper electrode 40 is not particularly limited, and examples thereof include materials exemplified for the lower electrode 20, electrode materials generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof. The thickness of the lower electrode 20 and the upper electrode 40 is not particularly limited and is preferably 50 to 500 nm.

  In the piezoelectric actuator 2, a vibration plate 50 that vibrates due to expansion and contraction of the piezoelectric film 30 is attached to the back surface of the substrate 10 of the piezoelectric element 1. The piezoelectric actuator 2 is also provided with control means (not shown) such as a drive circuit for controlling the driving of the piezoelectric element 1.

  The ink jet recording head (liquid ejecting apparatus) 3 generally includes an ink chamber (liquid storing chamber) 61 in which ink is stored on the back surface of the piezoelectric actuator 2 and an ink discharging port (in which ink is discharged from the ink chamber 61 to the outside). An ink nozzle (liquid storage and discharge member) 60 having a liquid discharge port 62 is attached. A plurality of ink chambers 61 are provided corresponding to the number and pattern of the convex portions 31 of the piezoelectric film 30. In the ink jet recording head 3, the electric field strength applied to the piezoelectric element 1 is increased / decreased to expand / contract the piezoelectric element 1, thereby controlling the ejection of ink from the ink chamber 61 and the ejection amount.

  Instead of attaching the vibration plate 50 and the ink nozzle 60 which are members independent of the substrate 10, a part of the substrate 10 may be processed into the vibration plate 50 and the ink nozzle 60. For example, when the substrate 10 is made of a laminated substrate such as an SOI substrate, the substrate 10 is etched from the back side to form the ink chamber 61, and the vibration plate 50 and the ink nozzle 60 are formed by processing the substrate itself. Can do.

  The piezoelectric element 1 and the ink jet recording head 3 of the present embodiment are configured as described above. In the present embodiment, a piezoelectric film made of a lead-containing perovskite oxide (which may contain inevitable impurities) formed by the film forming method of the present invention is used as the piezoelectric film 30. Therefore, according to the present embodiment, it is possible to provide the piezoelectric element 1 and the ink jet recording head 3 having excellent piezoelectric characteristics and excellent driving durability.

  Furthermore, the lead-containing perovskite oxide represented by the above general formula (P) or (P-1) formed under the conditions satisfying the above formulas (1) and (2) (including inevitable impurities) When the piezoelectric film 30 is used, it is possible to provide the piezoelectric element 1 and the ink jet recording head 3 that have high piezoelectric performance by positive voltage driving and excellent driving durability.

"Inkjet recording device"
With reference to FIG. 3 and FIG. 4, a configuration example of an ink jet recording apparatus including the ink jet recording head 3 of the above embodiment will be described. 3 is an overall view of the apparatus, and FIG. 4 is a partial top view.

The illustrated ink jet recording apparatus 100 includes a printing unit 102 having a plurality of ink jet recording heads (hereinafter simply referred to as “heads”) 3K, 3C, 3M, and 3Y provided for each ink color, and each head 3K, An ink storage / loading unit 114 that stores ink to be supplied to 3C, 3M, and 3Y, a paper feeding unit 118 that supplies recording paper 116, a decurling unit 120 that removes curling of the recording paper 116, and a printing unit An adsorption belt conveyance unit 122 that conveys the recording paper 116 while maintaining the flatness of the recording paper 116, and a print detection unit that reads a printing result by the printing unit 102. 124 and a paper discharge unit 126 that discharges printed recording paper (printed matter) to the outside.
Each of the heads 3K, 3C, 3M, and 3Y forming the printing unit 102 is the ink jet recording head 3 of the above embodiment.

In the decurling unit 120, heat is applied to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction, and the decurling process is performed.
In the apparatus using roll paper, as shown in FIG. 3, a cutter 128 is provided at the subsequent stage of the decurling unit 120, and the roll paper is cut into a desired size by this cutter. The cutter 128 includes a fixed blade 128A having a length equal to or larger than the conveyance path width of the recording paper 116, and a round blade 128B that moves along the fixed blade 128A. The fixed blade 128A is provided on the back side of the print. The round blade 128B is arranged on the print surface side with the conveyance path interposed therebetween. In an apparatus using cut paper, the cutter 128 is unnecessary.

  The decurled and cut recording paper 116 is sent to the suction belt conveyance unit 122. The suction belt conveyance unit 122 has a structure in which an endless belt 133 is wound between rollers 131 and 132, and at least portions facing the nozzle surface of the printing unit 102 and the sensor surface of the printing detection unit 124 are horizontal ( Flat surface).

  The belt 133 has a width that is wider than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. An adsorption chamber 134 is provided at a position facing the nozzle surface of the printing unit 102 and the sensor surface of the print detection unit 124 inside the belt 133 that is stretched between the rollers 131 and 132. The recording paper 116 on the belt 133 is sucked and held by suctioning at 135 to make a negative pressure.

  When the power of a motor (not shown) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, the belt 133 is driven in the clockwise direction in FIG. 3 and is held on the belt 133. The recording paper 116 is conveyed from left to right in FIG.

Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region).
A heating fan 140 is provided on the upstream side of the printing unit 102 on the paper conveyance path formed by the suction belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 102 is a so-called full-line head in which line-type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) perpendicular to the paper feed direction (see FIG. 4). Each of the print heads 3K, 3C, 3M, and 3Y is a line-type head in which a plurality of ink discharge ports (nozzles) are arranged over a length exceeding at least one side of the maximum-size recording paper 116 targeted by the ink jet recording apparatus 100. It is configured.

Heads 3K, 3C, 3M, and 3Y corresponding to the respective color inks are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. ing. A color image is recorded on the recording paper 116 by ejecting the color ink from each of the heads 3K, 3C, 3M, 3Y while conveying the recording paper 116.
The print detection unit 124 includes a line sensor that images the droplet ejection result of the print unit 102 and detects ejection defects such as nozzle clogging from the droplet ejection image read by the line sensor.

A post-drying unit 142 including a heating fan or the like for drying the printed image surface is provided at the subsequent stage of the print detection unit 124. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.
A heating / pressurizing unit 144 is provided downstream of the post-drying unit 142 in order to control the glossiness of the image surface. The heating / pressurizing unit 144 presses the image surface with a pressure roller 145 having a predetermined surface irregularity shape while heating the image surface, and transfers the irregular shape to the image surface.

The printed matter obtained in this manner is outputted from the paper output unit 126. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. In the ink jet recording apparatus 100, there is provided sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 126A and 126B. It has been.
When the main image and the test print are simultaneously printed on a large sheet of paper, the cutter 148 may be provided to separate the test print portion.
The ink jet recording apparatus 100 is configured as described above.

"Piezoelectric ultrasonic transducer (ultrasonic transducer)"
With reference to FIG. 5, the structure of a piezoelectric ultrasonic transducer according to an embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of the main part of the piezoelectric ultrasonic transducer. In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The piezoelectric ultrasonic transducer 5 of this embodiment is an open in which a cavity 81, a diaphragm 82, and a support portion 83 that supports the diaphragm 82 are integrally formed by reactive ion etching (RIE) processing from the back side. The SOI substrate 80 having a pool structure, the piezoelectric element 4 formed on the substrate, and an Rf power source (high frequency AC power source) 90 for applying a high frequency alternating current to the electrodes 71 and 73 of the piezoelectric element 4 are roughly constituted. . The piezoelectric element 4 has a laminated structure of a lower electrode 71, a piezoelectric film 72, and an upper electrode 73 from the substrate 80 side.

  The composition and thickness of the lower electrode 71 and the upper electrode 73 are the same as those of the lower electrode 20 and the upper electrode 40 of the piezoelectric element 1 of FIG. The piezoelectric film 72 is composed of the columnar structure film of the present invention.

  When an electrical AC signal in the ultrasonic region is applied to the electrodes 71 and 73 of the piezoelectric element 4, flexural vibration is generated in the piezoelectric element 4 at the same frequency as the applied electrical AC signal, and the vibration plate 82 is integrated with the piezoelectric element 4. It bends and vibrates. At this time, the vibration plate 82 vibrates in a state where the peripheral portion is supported by the support portion 83, thereby radiating ultrasonic waves having the same frequency as the applied electrical AC signal from the opposite side of the vibration plate 82 to the piezoelectric element 4. Is done.

The piezoelectric ultrasonic transducer 5 of the present embodiment is configured as described above. According to the present embodiment, it is possible to provide the piezoelectric ultrasonic transducer 5 having excellent withstand voltage and excellent driving durability.
The piezoelectric ultrasonic transducer 5 of this embodiment can be used for an ultrasonic motor or the like.
The piezoelectric ultrasonic transducer 5 of the present embodiment can also be used as a sensor or the like that generates an ultrasonic wave of a specific frequency and detects an ultrasonic wave that has been reflected back from an object, and can be used as an ultrasonic probe or the like. Can be used. When the vibration plate 82 vibrates in response to an ultrasonic wave that has been reflected back from the object, the piezoelectric film 72 is displaced according to the stress, and a voltage corresponding to the displacement amount is generated in the piezoelectric element 4. By detecting this, the shape or the like of the object can be detected.

(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate without departing from the spirit of the present invention.

Examples and comparative examples according to the present invention will be described.
Example 1
Pb _1.3 Zr _0.52 Ti having a diameter of 120 mm under the conditions of a vacuum of 0.5 Pa and an Ar / O ₂ mixed atmosphere (O ₂ volume fraction 2.5%) using the sputtering apparatus shown in FIG. _A piezoelectric film made of PZT was formed using a _0.48 O ₃ sintered target. The substrate temperature was 475 ° C.

  As a film formation substrate, a substrate with an electrode was prepared in which a 20 nm thick Ti adhesion layer and a 150 nm thick Ir lower electrode were sequentially laminated on a Si wafer. The distance between the substrate and the target was 60 mm.

  In this apparatus, an LCR circuit including a plurality of variable capacitors is connected to an electrically floating substrate. Using this LCR circuit, the impedance of the system including the substrate was changed to control the substrate potential Vsub (V). As shown in FIG. 6A, the substrate potential Vsub1 for 5 minutes from the start of film formation was set to 25V, and the substrate potential Vsub2 after 5 minutes was set to −15V.

  The X-ray diffraction (XRD) pattern of the obtained film is shown in FIG. 6B. As shown in FIG. 6B, it was confirmed that the obtained film had a perovskite crystallinity of (100) preferential orientation.

As a result of the resulting film was carried out composition analysis by XRF (fluorescent X-ray _analysis), it was confirmed that the _{Pb 0.88 Zr 0.52 Ti 0.48 O 3} .

  Further, a 30 nm thick Ti adhesion layer and a 150 nm thick Pt upper electrode were formed on the piezoelectric film by a sputtering method. A driving durability test using a 30 kHz, 20 V peak-to-peak rectangular wave of the piezoelectric film was performed. The drive durability was evaluated by measuring the capacitance Cp of the drive unit (piezoelectric film portion), and when the Cp value suddenly dropped, it was determined as dielectric breakdown. As a result, in 310 billion cycles, the capacitance of the driving unit suddenly dropped and breakdown occurred.

  Next, upper and lower electrodes and a PZT film were formed on the SOI substrate with the same configuration and film formation conditions, and the substrate was further processed to manufacture a piezoelectric element having a diaphragm structure. Next, positive and negative voltages were applied to the obtained piezoelectric element, and the displacement was measured using a laser Doppler vibrometer (manufactured by Ono Sokki). Based on this displacement, d31 was calculated by ANSYS. The piezoelectric constant in the plus voltage drive is d31 (+), and the piezoelectric constant in the minus voltage drive is d31 (−). The piezoelectric constant d31 (+) was measured as a sin wave with Voff = 10V and Vpp = 20V · 1 kHz, and d31 (−) was measured as Voff = −10V. As a result, both d31 (+) and d31 (−) showed high piezoelectric characteristics of 200 pm / V.

(Example 2)
As shown in FIG. 7A, a PZT film was formed in the same manner as in Example 1 except that the second substrate potential Vsub2 was set to −5V. The XRD pattern of the obtained film is shown in FIG. 7B.

  As shown in FIG. 7B, it was confirmed that the obtained film had a perovskite crystallinity of (100) preferential orientation.

As a result of the resulting film was carried out composition analysis by XRF (fluorescent X-ray _analysis), it was confirmed that the _{Pb 0.97 Zr 0.52 Ti 0.48 O 3} .

  Further, when a driving durability test was conducted in the same manner as in Example 1, no dielectric breakdown was observed even after driving for 600 billion cycles.

  In addition, the piezoelectric characteristics in the case of the diaphragm structure were evaluated in the same manner as in Example 1. As a result, like Example 1, both d31 (+) and d31 (−) showed high piezoelectric characteristics of 200 pm / V.

(Example 3)
A piezoelectric film made of PZT was formed in the same manner as in Example 1 in the case where Vsub1 and Vsub2 were changed and the substrate temperatures were 475 ° C. and 500 ° C., respectively. FIG. 8A and FIG. 8B show the results of evaluating the quality of the PZT film with respect to Vsub1 and Vsub2 with respect to the plurality of obtained films. In FIGS. 8A and 8B, the meanings of the symbols in the figure are as follows.
X: Pyrochlore structure is mixed by 50% or more,
* ... Perovskite structure is the main, durability is 30 billion dots or less,
○… The main structure is perovskite and durability is 100 billion dots or more.

When the composition analysis by XRF of the films of * and ◯ in FIGS. 8A and 8B was performed, the films * were all in the above general formula (P-1) and the Pb composition a was a> 1.05. Were all Pb <1.0.

  Since Vsub1 plays a role of forming an initial perovskite nucleus, the perovskite structure does not grow unless it is −10 V or higher regardless of the temperature (within a range where perovskite can be formed) and Vsub2. It is understood that by controlling Vsub2 after satisfying this, the amount of Pb in the film is suppressed to 1.0 or less and high durability can be realized.

  Further, it is known that the Pb amount has a correlation with the film forming temperature. By comparing FIGS. 8A and 8B, it can be confirmed that the appropriate Vsub2 range also changes as the film formation temperature changes. There is a close relationship between the Pb composition of the target and the amount of Pb in the film. Therefore, for example, when a target having a large composition of Pb is used, the amount of Pb in the film also increases, so that the appropriate value of Vsub2 decreases. On the other hand, when a target having a small Pb composition is used, the value of Vsub2 must be increased.

(Comparative Example 1)
A PZT film was formed in the same manner as in Example 1 except that the substrate potential was set to 15 V and was kept constant without being changed during the film formation. The XRD pattern of the obtained film is shown in FIG. As shown in FIG. 8, it was confirmed that the obtained film had a perovskite crystallinity of (100) preferential orientation.

As a result of the resulting film was carried out composition analysis by XRF (fluorescent X-ray _analysis), it was confirmed that the _{Pb 1.04 Zr 0.52 Ti 0.48 O 3} .

  Further, when a driving durability test was performed in the same manner as in Example 1, dielectric breakdown occurred when driven by 40 billion cycles, and the piezoelectric characteristics deteriorated.

  In addition, the piezoelectric characteristics in the case of the diaphragm structure were evaluated in the same manner as in Example 1. As a result, the piezoelectric constant d31 (−) at the time of applying a negative voltage showed a high piezoelectric characteristic of 250 pm / V, but d31 (+) was 60 pm / V, which is less than a quarter of d31 (−). Value.

(Comparative Example 2)
A PZT film was formed in the same manner as in Example 1 except that the substrate potential was set to 25 V and was kept constant without being changed during the film formation. As a result of measuring the XRD of the obtained film, it was confirmed that the film had perovskite crystallinity of (100) preferential orientation (not shown).

As a result of the resulting film was carried out composition analysis by XRF (fluorescent X-ray _analysis), it was confirmed that the _{Pb 1.06 Zr 0.52 Ti 0.48 O 3} .

  Further, when a driving durability test was performed in the same manner as in Example 1, dielectric breakdown occurred when driven for 10 billion cycles, and the piezoelectric characteristics deteriorated.

(Comparative Example 3)
A PZT film was formed in the same manner as in Example 1 except that the substrate potential was set to −15 V and was kept constant without being changed during the film formation. The XRD pattern of the obtained film is shown in FIG. As shown in FIG. 9, in the obtained film, the peak of the perovskite structure could not be detected, and it was confirmed that it had a pyrochlore structure.

(Comparative Example 4)
A PZT film was formed in the same manner as Comparative Example 3 except that the substrate potential was −5V. As a result of measuring the XRD of the obtained film, the peak of the perovskite structure could not be detected as in Comparative Example 3, and it was confirmed that the film had a pyrochlore structure (not shown).

(Evaluation)
Table 1 summarizes the results obtained in the above examples and comparative examples. In the substrate potential control method according to the embodiment of the present patent, a substrate potential of 25 V or more could not be realized. However, as the substrate potential becomes higher, Pb is more easily taken in, and a perovskite structure is easily obtained in the initial layer. , Vsub1 may be 25V or more.

  As shown in Table 1, in Examples 1 and 2, a perovskite PZT film having a composition in which the molar amount of lead when the molar amount of oxygen element is 3 is smaller than 1 is obtained. The piezoelectric durability of 200 pm / V and the driving durability of one digit or more higher than the driving durability of the lead-rich PZT films of Comparative Examples 1 and 2 are achieved.

  Further, when Comparative Examples 1 and 2 are compared, in the lead-rich composition, the driving durability increases as the lead composition decreases, and further, when the molar amount with respect to 3 mol of oxygen in Example 2 is less than 1.0. As described above, it is recognized that the durability is remarkably increased (one digit or more). On the other hand, in Example 1, although the lead composition is further reduced, it is also confirmed that durability and piezoelectric performance are lowered. This is thought to be because both the piezoelectric properties and the driving durability were lowered because the pyrochlore phase increased and the crystallinity decreased due to the lead composition becoming too small.

Further, the PZT film of the comparative example has a low piezoelectric d31 constant in the plus voltage drive, whereas the PZT films of Examples 1 and 2 have a high piezoelectric d31 constant equivalent to the minus voltage drive in the plus voltage drive. ing. Therefore, it was confirmed that the PZT films of Examples 1 and 2 are piezoelectric films having high piezoelectric performance and high drive durability that can be driven by a current general-purpose drive driver.

The piezoelectric film forming method of the present invention is mounted on an ink jet recording head, a magnetic recording / reproducing head, a MEMS (Micro Electro-Mechanical Systems) device, a micro pump, an ultrasonic probe, an ultrasonic motor, or the like. The present invention can be preferably applied to the formation of a piezoelectric film used for a ferroelectric element such as a piezoelectric element / piezoelectric ultrasonic transducer / piezoelectric power generation element or the like, or a ferroelectric memory.

1 Piezoelectric element 3, 3K, 3C, 3M, 3Y Inkjet recording head (liquid ejection device)
10 Substrate 20, 40 Electrode 30 Piezoelectric film (columnar structure film)
60 Ink nozzle (liquid storage and discharge member)
61 Ink chamber (liquid storage chamber)
62 Ink ejection port (liquid ejection port)
100 Inkjet recording device 4 Piezoelectric element 5 Piezoelectric ultrasonic transducer (ultrasonic transducer)
71, 73 Electrode 72 Piezoelectric film (columnar structure film)
82 Diaphragm 90 Rf power supply (high frequency AC power supply)

Claims (6)

A piezoelectric film made of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P) is formed on the substrate by sputtering, and the temperature of the substrate 475 ° C. to 500 ° C.
After forming crystal nuclei of perovskite oxide having a Pb composition higher than that of the perovskite oxide at the first substrate potential Vsub1,
The potential of the substrate, from the first substrate potential Vsub1, as Pb composition of the piezoelectric film is Pb composition of one or more perovskite oxides represented by the following general formula (P) The film forming method is characterized in that the piezoelectric film is formed by changing to the second substrate potential Vsub2.
General formula Pb _a B _b O ₃ (P)
(Wherein B is an element of the B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, and At least one element selected from the group consisting of Ni, O is oxygen, a is a value smaller than 1.0 within a range where a perovskite structure can be taken, and b is a perovskite type although 1.0 is standard. It may deviate within the range that can take the structure.)   2. The film forming method according to claim 1, wherein the piezoelectric film is made of one or more perovskite oxides containing lead zirconate titanate (may contain inevitable impurities). . And Step (A) to form a crystal nucleus of the perovskite oxide than Pb composition often perovskite oxide in said first substrate potential Vsub1, Pb composition of the piezoelectric film by the general formula (P) Step (B) of forming the piezoelectric film by setting the second substrate potential (Vsub2) so as to have a Pb composition of one or a plurality of perovskite oxides represented is sequentially performed. The film forming method according to claim 1, wherein: The film forming method according to claim 1, wherein the first substrate potential Vsub1 satisfies the following formula (1).
−10 ≦ Vsub1 (V) (1)
(In the formula, Vsub1 is the first substrate potential.) 5. The film forming method according to claim 4, wherein the first substrate potential Vsub1 satisfies the following formula (2).
−10 ≦ Vsub1 (V) ≦ 25 (2) Furthermore, the following formula (3) is satisfied, The film-forming method of Claim 5 characterized by the above-mentioned.
−20 <Vsub2 (V) <5 (3)
(Where Vsub2 is the second substrate potential)

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