JP4519810B2 - Ferroelectric element and manufacturing method thereof, ferroelectric memory, and ink jet recording head - Google Patents

Description

  The present invention relates to a ferroelectric element, a manufacturing method thereof, a ferroelectric memory (FRAM) using the same, and an ink jet recording head.

A ferroelectric element having a laminated structure of a lower electrode, a ferroelectric film, and an upper electrode is a ferroelectric memory (FRAM (Ferroelectric Random Access Memory)) expected as a next generation memory, an ink jet recording head, etc. It is an element used for the actuator etc. which are mounted in. As the ferroelectric material, perovskite oxides such as lead zirconate titanate (PZT) are known.
In the above application, it is preferable that the ferroelectric film has a high crystal orientation. For example, in a ferroelectric memory, since the remanent polarization value Pr is large and the coercive electric field Ec is low, a (111) orientation film of PZT is preferable.

As described in paragraph [0003] of Patent Document 1, conventionally, it has been said that a PZT (111) alignment film needs to be formed at a film formation temperature of 700 ° C. or higher.
However, in a ferroelectric memory, since a ferroelectric element is usually formed on a substrate on which a driving transistor is built, in order to reduce the influence of heat on the transistor, the ferroelectric film is kept at a temperature as low as possible. It is preferable that a film can be formed. When the film formation temperature is increased, stress is applied to the ferroelectric film during the temperature lowering process during film formation or after film formation due to the difference in thermal expansion coefficient between the substrate and the ferroelectric film, and the film has cracks. There is also a risk of it occurring. In the PZT film, there is also a problem that when the film forming temperature becomes high, Pb loss is likely to occur.

  Patent Document 1 describes a method of obtaining a PZT (111) alignment film by a sol-gel method. In this document, it is proposed to perform the first heat treatment at 250 to 350 ° C. (this temperature is lower than the temperature at which the perovskite crystal structure grows) and the second heat treatment at 500 to 600 ° C. It is described that a PZT (111) alignment film can be obtained at a relatively low temperature by this method.

In Patent Document 2, an amorphous or crystalline thermodynamic metastable phase oxide film is formed at a substrate temperature of 450 ° C. or lower (this temperature is lower than the temperature at which the perovskite crystal structure grows), An oxide film manufacturing method is disclosed in which this film is phase-transformed into a thermodynamically stable phase crystal by heat treatment in a reducing atmosphere gas. In this document, as a thermodynamic metastable phase oxide film, a PZT film having an amorphous structure or a pyrochlore structure is formed by RF sputtering, and then heat treatment in a reducing atmosphere gas is performed. It is described that a PZT film having a perovskite crystal structure can be formed at a relatively low temperature by phase transition to a perovskite crystal. It is also described that a PZT film having a desired crystal orientation can be obtained by controlling the crystal orientation of the previously formed thermodynamic metastable phase oxide film.
Japanese Unexamined Patent Publication No. 2000-243920 JP 2001-139313 JP

The methods described in Patent Documents 1 and 2 are complicated processes. In any of the methods, film formation is first performed at a temperature below the temperature at which the perovskite crystal structure grows, and then the crystallinity of the film is increased, so that it is difficult to control crystallinity and crystal orientation. Therefore, it is difficult to obtain a highly crystalline film, and it is difficult to obtain a high-performance ferroelectric element.
It is known that a PZT film having excellent crystal orientation can be formed by using an MgO single crystal substrate as a substrate, but since an MgO single crystal substrate is expensive, the manufacturing cost increases, which is not preferable.

The present invention has been made in view of the above circumstances, and a ferroelectric film excellent in crystallinity and crystal orientation is obtained at a relatively low temperature without using an expensive substrate or through a complicated process. It is an object of the present invention to provide a manufacturing method of a ferroelectric element capable of forming a film and a ferroelectric element manufactured by the manufacturing method.
In particular, the present invention makes it possible to form a (111) -oriented ferroelectric film excellent in crystal orientation at a relatively low temperature without using an expensive substrate or through a complicated process. It is an object of the present invention to provide a method for manufacturing a ferroelectric element and a ferroelectric element manufactured by the manufacturing method.
It is another object of the present invention to provide a ferroelectric memory including the ferroelectric element, an ink jet recording head including the ferroelectric element, and an ink jet recording apparatus.

The ferroelectric element manufacturing method of the present invention has a laminated structure of a lower electrode, a ferroelectric film, and an upper electrode, and an electric field is applied to the ferroelectric film by the lower electrode and the upper electrode. In the manufacturing method of the ferroelectric element,
A step (A) of sequentially forming a seed layer containing Zr and the lower electrode;
Diffusing Zr contained in the seed layer to deposit the element on the surface of the lower electrode;
(C) sequentially forming the ferroelectric film on the lower electrode.
In the manufacturing method of the present invention, it is preferable that Zr is contained in the constituent element of the ferroelectric film.

In the step (C), the ferroelectric film is preferably formed at a film formation temperature of 400 ° C. or higher and lower than 600 ° C.
In the step (A), it is preferable that the seed layer and the lower electrode are sequentially formed with the seed layer having a thickness of 5 to 50 nm and the lower electrode having a thickness of 50 to 500 nm.
In the step (B), it is preferable to thermally diffuse Zr by heat treatment at 400 to 700 ° C. In this case, the thermal diffusion is preferably performed for 10 minutes to 2 hours.

In the method for manufacturing a ferroelectric element of the present invention, a ferroelectric film having a tetragonal and / or rhombohedral crystal structure and having crystal orientation on the (111) plane can be formed. .
In this specification, the term “having crystal orientation” for a ferroelectric film is defined as an orientation degree F measured by the Lottgering method being 80% or more.
The degree of orientation F is represented by the following formula.
F (%) = (P−P0) / (1−P0) × 100 (i)
In formula (i), P is the ratio of the total reflection intensity from the orientation plane to the total reflection intensity. In the case of (001) orientation, P is the sum ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the sum ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (00l) / ΣI (hkl)}). For example, in the case of (001) orientation in the perovskite crystal, P = I (001) / [I (001) + I (100) + I (101) + I (110) + I (111)].
P0 is P of a sample having a completely random orientation.
In the case of completely random orientation (P = P0), F = 0%, and in the case of complete orientation (P = 1), F = 100%.

Examples of the ferroelectric film include a film (which may contain inevitable impurities) made of one or more perovskite oxides represented by the following general formula. ◎
General formula ABO ₃
(In the formula, A: an element at the A site, at least one element selected from the group consisting of Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K;
B: B site element, at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb,
O: oxygen atom,
The standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0. )
Here, the number of moles of the A site element and the number of moles of the B site element in the formula are the number of moles of the A site element atom and the B site element atom when the number of moles of oxygen atoms is ₃ in the general formula ABO ₃ . Means.

The ferroelectric element of the present invention is manufactured by the above-described method for manufacturing a ferroelectric element of the present invention.
According to the present invention, the ferroelectric element has a laminated structure of a lower electrode, a ferroelectric film, and an upper electrode, and an electric field is applied to the ferroelectric film by the lower electrode and the upper electrode. In the above, it is possible to provide a ferroelectric element in which the lower electrode has a precipitate containing Zr on the surface of the electrode.

A ferroelectric memory according to the present invention includes the ferroelectric element according to the present invention.
The ink jet recording head of the present invention comprises the above ferroelectric element of the present invention,
And an ink storage and discharge member having an ink discharge port through which the ink is discharged from the ink chamber to the outside.
An ink jet recording apparatus of the present invention includes the above ink jet recording head of the present invention.

In the method for manufacturing a ferroelectric element of the present invention, after sequentially forming a seed layer containing Zr and a lower electrode, Zr contained in the seed layer is diffused to deposit the element on the surface of the lower electrode, Thereafter, a configuration in which a ferroelectric film is formed on the lower electrode is adopted.
According to the manufacturing method of the present invention having such a configuration, a ferroelectric film excellent in crystallinity and crystal orientation at a relatively low temperature without using an expensive substrate such as MgO or through a complicated process. Can be formed. According to the manufacturing method of the present invention, a (111) -oriented ferroelectric film excellent in crystal orientation can be naturally grown with high selection.
According to the present invention, a high-quality ferroelectric film can be formed, so that a high-performance ferroelectric element can be provided.

"Ferroelectric capacitors (ferroelectric elements), ferroelectric memories"
With reference to FIG. 1 and FIG. 2, the structure of a ferroelectric element according to an embodiment of the present invention and a ferroelectric memory (FRAM) including the same will be described. FIG. 1 is a cross-sectional view of a main part of a ferroelectric memory, and FIG. 2 is a diagram showing a circuit configuration example. In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The ferroelectric memory 1 is a storage device in which a ferroelectric capacitor (ferroelectric capacitor) 30 forming a memory cell and a transistor 20 for controlling the ferroelectric memory 1 are formed on a semiconductor substrate 11. is there. As the semiconductor substrate 11, a silicon substrate or the like is preferably used.

Examples of the transistor 20 include a thin film transistor (TFT), a metal-oxide-semiconductor field effect transistor (MOSFET), and the like. In the present embodiment, a case where the transistor 20 is formed of a MOSFET will be described.
The transistor 20 includes diffusion layers 21 and 22, one of which is a source region and the other is a drain region, a gate insulating film 23, and a gate electrode 24. An electrode 25 is formed on one of the diffusion layers 21 and 22, and a plug electrode 26 is formed on the other 22. The plug electrode 26 is electrically connected to the lower electrode 32 of the ferroelectric capacitor 30.

  On the semiconductor substrate 11, an element isolation film 27 for isolating each memory cell is formed. An interlayer insulating film 28 made of silicon oxide or the like is formed on the semiconductor substrate 11 on which the transistor 20 and the element isolation film 27 are formed. The interlayer insulating film 28 includes a first interlayer insulating film 28A and a second interlayer insulating film 28B.

  A contact hole penetrating the first interlayer insulating film 28A is opened on the diffusion layer 21, and the electrode 25 is formed across the surface of the first interlayer insulating film 28A from within the contact hole. A contact hole penetrating the first interlayer insulating film 28A and the second interlayer insulating film 28B is opened on the diffusion layer 22, and the plug electrode 26 is formed in the contact hole.

A ferroelectric capacitor 30 is formed on the transistor substrate 10 on which the transistor 20, the plug electrode 26, the interlayer insulating film 28, and the like are formed on the semiconductor substrate 11.
In this embodiment, the ferroelectric capacitor 30 is an element having a laminated structure of a seed layer 31, a lower electrode 32, a ferroelectric film 33, and an upper electrode 34, and the ferroelectric is formed by the lower electrode 32 and the upper electrode 34. An electric field is applied to the body film 33.

  The seed layer 31 is a layer containing Zr. The ferroelectric capacitor 30 diffuses (preferably thermally diffuses) Zr contained in the seed layer 31 to deposit the element on the surface of the lower electrode 32, and then forms a ferroelectric film 33. It is manufactured. The seed layer 31 can also function as an adhesion layer that satisfactorily adheres the transistor substrate 10 and the lower electrode 32.

The main component of the lower electrode 32 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. Any lower electrode 32 having the exemplified composition can diffuse Zr contained in the seed layer 31 to deposit the element on the surface of the lower electrode 32.
The main component of the upper electrode 34 is not particularly limited, and examples thereof include materials exemplified for the lower electrode 32, electrode materials generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof.
In the present specification, the “main component” is defined as a component having a content of 90% by mass or more.

The composition of the ferroelectric film 33 is not particularly limited, and a film made of a perovskite oxide (which may contain inevitable impurities) is preferable.
Examples of the ferroelectric film 33 include a film made of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula.
General formula ABO ₃
(In the formula, A: an element at the A site, at least one element selected from the group consisting of Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K;
B: B site element, at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb,
O: oxygen atom,
The standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0. )

Perovskite oxides represented by the above general formula include lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead zirconium titanate titanate niobate Lead-containing compounds such as lead nickel titanate niobate and mixed crystal systems thereof;
Non-lead-containing compounds such as barium titanate, bismuth sodium titanate, bismuth potassium titanate, sodium niobate, potassium niobate, lithium niobate, and mixed crystal systems thereof may be mentioned.
The film thickness of the ferroelectric film 33 is not particularly limited, and is usually 50 nm or more, for example, 100 to 300 nm.

  The thickness of the seed layer 31 and the lower electrode 32 is not particularly limited as long as Zr contained in the seed layer 31 can be diffused and the element can be deposited on the surface of the lower electrode 32. The seed layer 31 preferably has a thickness of 5 to 50 nm, and the lower electrode 32 preferably has a thickness of 50 to 500 nm. If the thickness of the seed layer 31 and the lower electrode 32 is too small, it is difficult to form these films, and if too large, the film formation time and film formation cost are unnecessary. In addition, if the seed layer 31 is too thin, it may be difficult to stably supply the element to the lower electrode 32 side. If the thickness of the lower electrode 32 is excessive, it is difficult to diffuse Zr contained in the seed layer 31 so that the element reaches the surface of the lower electrode 32.

In the present embodiment, the ferroelectric film 33 is formed after the Zr contained in the seed layer 31 is diffused to deposit the element on the surface of the lower electrode 32. In this method, the ferroelectric film 33 excellent in crystallinity and crystal orientation can be formed by using the precipitate deposited on the surface of the lower electrode 32 as a nucleus. This effect can be obtained regardless of the type of the substrate 11.
In particular, it is preferable that Zr is contained in the constituent element of the ferroelectric film 33. For example, the ferroelectric film 33 is preferably a PZT film. In such a case, the ferroelectric film 33 having good compatibility between the precipitate and the ferroelectric film 33 and excellent in crystallinity and crystal orientation can be formed.

In PZT, etc., there are three types of crystal systems, cubic, tetragonal and rhombohedral, and in barium titanate, etc., cubic, tetragonal, orthorhombic and rhombohedral There are four types of crystal systems. Since the cubic system is a paraelectric material and does not exhibit ferroelectricity, the ferroelectric film 33 needs to have a crystal structure of any one of tetragonal system, orthorhombic system, and rhombohedral system. .
The ferroelectric film 33 is preferably a film having a tetragonal and / or rhombohedral crystal structure and crystal orientation on the (111) plane. In this case, the electric field-polarization curve shows good hysteresis, the residual polarization value Pr is large, the coercive electric field Ec is low, and a high-performance ferroelectric memory 1 can be obtained.

  The inventor diffuses Zr contained in the seed layer 31 to deposit the element on the surface of the lower electrode 32, and then forms the ferroelectric film 33, whereby the (111) orientation film is selected. It is found that it can be obtained.

With reference to FIGS. 2A and 2B, a circuit configuration example of the ferroelectric memory 1 of the present embodiment will be described.
FIG. 2A is a circuit configuration example of a so-called 1T1C cell system in which one memory cell is configured by a combination of one transistor 20 and one ferroelectric capacitor 30. In the 1T1C cell system, the memory cell is located at the intersection of the word line WL and the bit line BL, one end of the ferroelectric capacitor 30 is connected to the bit line BL via the transistor 20, and the other end of the ferroelectric capacitor 30 is connected. Is connected to the plate line PL. The gate electrode 24 of the transistor 20 is connected to the word line WL. The bit line BL is connected to a sense amplifier A that amplifies signal charges.

Hereinafter, an operation example in the 1T1C cell will be briefly described.
In the read operation, after the bit line BL is fixed to 0V, a voltage is applied to the word line WL to turn on the transistor 20. Thereafter, by applying the plate line PL from 0 V to about the power supply voltage _Vcc , the polarization charge amount corresponding to the information stored in the ferroelectric capacitor 30 is transmitted to the bit line BL. By amplifying the minute potential change caused by the polarization charge amount by the differential sense amplifier A, the stored information can be read out as two pieces of information of _Vcc or 0V.
In the write operation, a voltage is applied to the word line WL, the transistor 20 is turned on, a voltage is applied between the bit line BL and the plate line PL, and the polarization state of the ferroelectric capacitor 30 is changed and determined. be able to.

FIG. 2B shows a so-called 2T2C cell circuit configuration example in which one memory cell is configured by a combination of two transistors 20 and two ferroelectric capacitors 30.
In the 2T2C cell system, the memory cell has a structure in which two 1T1C cells are combined, and has a structure for holding complementary information. That is, in the 2T2C cell system, as two differential inputs to the sense amplifier A, complementary signals can be input from two memory cells in which data is written in a complementary manner, and data can be detected.

"Manufacturing method of ferroelectric memory"
A method for manufacturing the ferroelectric capacitor 30 will be described with reference to FIG. FIG. 3 is a process diagram and is a cross-sectional view corresponding to FIG.

<Process (A)>
First, as shown in FIG. 3A, the transistor substrate 10 having the above-described structure is manufactured, and a seed layer 31 containing Zr and a lower electrode 32 are sequentially formed on substantially the entire surface of the substrate. As shown in the enlarged drawing in FIG. 3A, the surface of the lower electrode 32 at this point is substantially flat, and the average surface roughness Ra is, for example, less than 0.5 nm.

  The method for forming the seed layer 31 and the lower electrode 32 is not particularly limited, and examples thereof include a sputtering method. The formation of the seed layer 31 and the lower electrode 32 may be performed using the same apparatus or may be performed using different apparatuses. In this step, it is preferable to perform film formation with the seed layer 31 having a thickness of 5 to 50 nm and the lower electrode 32 having a thickness of 50 to 500 nm.

<Process (B)>
Next, as shown in FIG. 3B, Zr contained in the seed layer 31 is diffused to deposit the element on the surface of the lower electrode 32. Reference numeral 31 a is attached to the precipitate deposited on the surface of the lower electrode 32. The diffusion of Zr contained in the seed layer 31 can be performed by thermal diffusion by heating. The heating may be normal heat treatment using a heater or the like, or heating by light irradiation or the like.

Hereinafter, examples of thermal diffusion conditions will be described.
The thermal diffusion temperature and the thermal diffusion time are not particularly limited, and may be set within a range in which Zr contained in the seed layer 31 can be favorably thermally diffused and no problem such as deterioration of the transistor substrate 10 occurs.
The thermal diffusion temperature is preferably 400 to 700 ° C, particularly preferably 450 to 650 ° C. If the thermal diffusion temperature is set equal to the film formation temperature of the ferroelectric film 33, it is not necessary to change the set temperature at the start of the film formation of the ferroelectric film 33.
The heat diffusion time depends on conditions such as the heat diffusion temperature and the thickness of the lower electrode 32, but is preferably 10 minutes to 2 hours.

The inventor has found that fine irregularities are generated on the surface of the lower electrode 32 after the step (B) is finished, as shown in the enlarged view in FIG. The lower electrode 32 after the completion of the step (B) has, for example, a surface shape in which a large number of gentle mountains are connected, and a structure in which island-like precipitates 31a are deposited in the valleys between the gentle mountains and the mountains. Become.
The present inventor conducted the crystal orientation in the subsequent step by diffusing Zr under the condition that the average surface roughness Ra of the lower electrode 32 after the completion of the step (B) is, for example, 0.5 to 30.0 nm. It has been found that an excellent ferroelectric film 33 can be formed.
“Average surface roughness Ra” in the present specification is an arithmetic average roughness Ra determined based on JIS B0601-1994.

<Process (C)>
Next, as shown in FIG. 3C, a ferroelectric film 33 and an upper electrode 34 are sequentially formed on substantially the entire surface of the transistor substrate 10 on which the lower electrode 32 having the precipitate 31a is formed. A method for forming the ferroelectric film 33 is not particularly limited, and a vapor phase growth method such as a sputtering method, an MOCVD method, and a pulsed laser deposition method is preferable. As a method for forming the ferroelectric film 33, a chemical solution deposition method (CSD) such as a sol-gel method and an organometallic decomposition method, or an aerosol deposition method may be used. Examples of a method for forming the upper electrode 34 include a sputtering method.

  Finally, as shown in FIG. 3D, the stacked body of the seed layer 31 to the upper electrode 34 is patterned and separated into a plurality of memory cells by a known method such as dry etching. As described above, the ferroelectric capacitor 30 and the ferroelectric memory 1 are manufactured.

  In the present embodiment, Zr contained in the seed layer 31 is diffused to deposit the element on the surface of the lower electrode 32, and the ferroelectric film 33 is formed thereon. In this configuration, the ferroelectric film 33 having excellent crystallinity and crystal orientation can be formed by using the precipitates 31a scattered on the surface of the lower electrode 32 as the nucleus of crystal growth.

  In the present embodiment, the Zr-diffused lower electrode 32 is dotted with precipitates 31a containing Zr on the surface, and the entire surface of the lower electrode 32 has moderate surface irregularities. The lower electrode 32 after Zr diffusion has, for example, a surface structure in which a large number of gentle peaks are connected, and a surface structure in which island-like precipitates 31a are deposited in the valleys between the gentle peaks and peaks. It becomes. The lower electrode 32 having such a surface structure has an appropriate surface irregularity as a whole, and has a surface structure in which the precipitate 31a is formed in the recessed portion. Therefore, the precipitate 31a formed in the recessed portion is a nucleus. Thus, the ferroelectric film 33 grows. The lower electrode 32 having such a surface structure is considered to be more suitable as a base for the growth of the ferroelectric film 33 than the lower electrode having a substantially flat surface.

  In the present embodiment, since the surface structure of the lower electrode 32 is suitable as a base for the growth of the ferroelectric film 33, the ferroelectric film 33 can be formed at a relatively low temperature. Specifically, the ferroelectric film 33 excellent in crystallinity and crystal orientation can be formed at a relatively low temperature of 400 ° C. or higher and lower than 600 ° C. “The ferroelectric film 33 has good crystallinity” means that when the ferroelectric film 33 is made of a perovskite oxide, it is a perovskite crystal having no pyrochlore phase.

  When the ferroelectric film 33 is made of a Pb-containing material such as PZT, the deposition temperature of the ferroelectric film 33 is more preferably 450 to 580 ° C., and particularly preferably 500 to 580 ° C. When the ferroelectric film 33 is made of a Pb-containing material such as PZT, the ferroelectric film 33 having good crystallinity and crystal orientation can be stably formed by performing film formation under such conditions. Moreover, it is possible to form a high-quality ferroelectric film 33 while suppressing the escape of the Pb component.

  It is preferable that the ferroelectric film 33 can be formed at a relatively low temperature because the influence of heat on the transistor 20 and the like can be reduced. Since the ferroelectric film 33 can be formed at a relatively low temperature, the ferroelectric film 33 is formed during or after the film formation due to a difference in thermal expansion coefficient between the substrate 11 and the ferroelectric film 33. It is also possible to prevent stress from being applied to 33 and the occurrence of cracks and the like in the film.

  As described above, in the present embodiment, the lower electrode 32 has a surface structure suitable as a base for the growth of the ferroelectric film 33, and the ferroelectric film 33 can be formed at a relatively low temperature. Combined with the effect, it is considered that a high-quality ferroelectric film 33 excellent in crystallinity and crystal orientation can be formed.

  When the present inventor forms a seed layer containing Ti and diffuses Ti in the seed layer and deposits it on the surface of the lower electrode, a ferroelectric film having a (100) orientation can be selectively obtained. On the other hand, in the method of the present embodiment in which the seed layer 31 containing Zr is formed and the Zr in the seed layer 31 is diffused and deposited on the surface of the lower electrode 32, the ferroelectric film 33 with (111) orientation is formed. It has been found that it can be selectively obtained (see Examples 1 to 3 and Comparative Example 2 below).

  As described above, in the ferroelectric memory 1, the ferroelectric film 33 having the (111) orientation is preferable. Thus, a layer containing Zr is formed as the seed layer 31, and Zr in the seed layer 31 is diffused. It is very useful that the (111) oriented ferroelectric film 33 can be naturally grown with high selectivity simply by depositing it on the surface of the lower electrode 32.

  Note that, in a ferroelectric element having a laminated structure of a lower electrode, a ferroelectric film, and an upper electrode regardless of the presence or absence of the seed layer 31, the lower electrode is a strong element having a precipitate containing Zr on the surface of the electrode. The dielectric element itself is novel.

  As described above, according to the present embodiment, a ferroelectric material excellent in crystallinity and crystal orientation at a relatively low temperature without using an expensive substrate such as MgO or through a complicated process. The film 33 can be formed. According to the manufacturing method of the present invention, the (111) -oriented ferroelectric film 33 having excellent crystal orientation can be naturally grown with high selection. The inventor has also found that the ferroelectric film 33 having a small leakage current can be obtained in this embodiment (see Examples 1 to 3 described later).

  According to the present embodiment, since a high-quality ferroelectric film 33 can be formed, the electric field-polarization curve shows a good hysteresis property, the remanent polarization value Pr is large, the coercive electric field Ec is low, and high performance A ferroelectric capacitor 30 and a ferroelectric memory 1 can be provided.

"Piezoelectric elements (ferroelectric elements) and ink jet recording heads"
In the present invention, since a ferroelectric film having a (111) orientation can be selectively formed, the ferroelectric element of the present invention can be preferably used for a ferroelectric memory. However, the ferroelectric element of the present invention can also be used as a piezoelectric element mounted on an ink jet recording head or the like.

  With reference to FIG. 4, the structure of a piezoelectric element (ferroelectric element) according to an embodiment of the present invention and an ink jet recording head having the same will be described. FIG. 4 is a cross-sectional view of the main part of the ink jet recording head. In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The piezoelectric element 50 of this embodiment is an element in which a seed layer 52 containing Zr, a lower electrode 53, a piezoelectric film (ferroelectric film) 54, and an upper electrode 55 are sequentially stacked on a substrate 51. An electric field is applied to the piezoelectric film 54 in the thickness direction by 53 and the upper electrode 55. In the piezoelectric element 50 of the present embodiment, Zr contained in the seed layer 52 is diffused (preferably thermally diffused) to deposit the element on the surface of the lower electrode 53, and then the piezoelectric film 54 is formed. It is manufactured. The seed layer 52 can also function as an adhesion layer that satisfactorily adheres the substrate 51 and the lower electrode 53.

In the present embodiment, a seed layer 52 and a lower electrode 53 are sequentially laminated on substantially the entire surface of the substrate 51, and line-shaped convex portions 54a extending from the front side to the back side in the figure are arranged in stripes on the lower electrode 53. The piezoelectric film 54 having the above pattern is formed, and the upper electrode 55 is formed on each convex portion 54a.
The pattern of the piezoelectric film 54 is not limited to that shown in the figure, and is designed as appropriate. The piezoelectric film 54 may be a continuous film. However, the piezoelectric film 54 is not a continuous film, but formed by a pattern composed of a plurality of protrusions 54a separated from each other, so that the expansion and contraction of the individual protrusions 54a occurs smoothly, so that a larger displacement amount can be obtained. preferable.

The substrate 51 is not particularly limited, and examples thereof include silicon, glass, stainless steel (SUS), yttrium-stabilized zirconia (YSZ), alumina, sapphire, and silicon carbide. As the substrate 51, a laminated substrate such as an SOI substrate in which a SiO ₂ oxide film is formed on the surface of a silicon substrate may be used.

  The composition and film thickness of the seed layer 52, the lower electrode 53, and the upper electrode 55 are the same as those of the ferroelectric capacitor 30 of the above embodiment. The film thickness of the piezoelectric film 54 is thicker than the ferroelectric film 33 of the ferroelectric capacitor 30 and is usually 1 μm or more, for example, 1 to 5 μm.

The ink jet recording head 2 generally includes an ink chamber 71 in which ink is stored and an ink from which ink is discharged to the outside via a vibration plate 60 on the lower surface of the substrate 51 of the piezoelectric element 50 having the above-described configuration. An ink nozzle (ink storage and discharge member) 70 having a discharge port 72 is attached. A plurality of ink chambers 71 are provided corresponding to the number and pattern of the convex portions 54 a of the piezoelectric film 54.
In the ink jet recording head 2, the electric field strength applied to the convex portion 54 a of the piezoelectric element 50 is increased / decreased for each convex portion 54 a to expand / contract, thereby controlling the ejection of ink from the ink chamber 71 and the ejection amount. Is called.

  The piezoelectric element 50 and the ink jet recording head 2 of the present embodiment are configured as described above.

  In this embodiment, similarly to the ferroelectric capacitor 30 of the above embodiment, after the seed layer 52 containing Zr and the lower electrode 53 are sequentially formed, Zr contained in the seed layer 52 is diffused, and the element is diffused. A structure is adopted in which the film is deposited on the surface of the lower electrode 53 and then a piezoelectric film 54 as a ferroelectric film is formed on the lower electrode 53. Zr diffusion conditions, piezoelectric film formation conditions, and the like are the same as in the ferroelectric capacitor 30 of the above embodiment.

  In this embodiment, like the ferroelectric capacitor 30 of the above embodiment, the crystallinity and crystal orientation are excellent at a relatively low temperature without using an expensive substrate such as MgO or through a complicated process. The piezoelectric film 54 can be formed. In this embodiment, the (111) oriented piezoelectric film 54 can be selectively grown.

  In the use of a ferroelectric memory (FRAM), it is possible to obtain a high-performance ferroelectric memory with a large remanent polarization value Pr and a low coercive electric field Ec by setting the ferroelectric film to (111) orientation. Stated. Since the (111) oriented piezoelectric film 54 has a low coercive electric field Ec, it can be polarized with a relatively low electric field. In particular, if a polarization process is performed on the piezoelectric film 54 by applying a high electric field after forming a driving circuit or the like, the piezoelectric film 54 having a low coercive electric field Ec is preferable because the circuit or the like may be affected. .

"Inkjet recording device"
With reference to FIG. 5 and FIG. 6, a configuration example of an ink jet recording apparatus including the ink jet recording head 2 of the above embodiment will be described. FIG. 5 is an overall view of the apparatus, and FIG. 6 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”) 2K, 2C, 2M, and 2Y provided for each ink color, and each head 2K, An ink storage / loading unit 114 that stores ink to be supplied to 2C, 2M, and 2Y, 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.

  The heads 2K, 2C, 2M, and 2Y that form the printing unit 102 are the ink jet recording heads 2 of the above-described 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. 5, 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.

  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, so that the belt 133 is driven in the clockwise direction in FIG. 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 type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 6). Each of the print heads 2K, 2C, 2M, and 2Y is a line-type head in which a plurality of ink discharge ports (nozzles) are arranged over a length that exceeds at least one side of the maximum size recording paper 116 targeted by the ink jet recording apparatus 100. It is configured.

  Heads 2K, 2C, 2M, and 2Y 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 inks from the heads 2K, 2C, 2M, and 2Y while conveying the recording paper 116, respectively.

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.

(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
Using a sputtering apparatus, a 20 nm thick Zr seed layer and a 100 nm thick Ir lower electrode were sequentially formed on substantially the entire surface of the Si substrate under the conditions of a substrate temperature of 200 ° C. and a vacuum of 0.5 Pa.
In order to thermally diffuse Zr in the Zr seed layer, the substrate temperature was raised to 520 ° C. for 1 hour after the formation of the lower electrode and the substrate was placed in a sputtering apparatus in a vacuum atmosphere. Retained.
Thereafter, using the same apparatus, the conditions of an Ar / O ₂ mixed atmosphere (O ₂ volume fraction of 3.0%) with a substrate temperature of 520 ° C. and a vacuum of 0.5 Pa are formed on substantially the entire surface of the substrate on which the lower electrode is formed. Then, a PZT film having a thickness of 200 nm was formed using a Pb _1.3 Zr _0.52 Ti _0.48 O ₃ target.
Using the same apparatus, a Pt upper electrode having a thickness of 100 nm was formed on the PZT film to obtain a ferroelectric element of the present invention.

(Example 2)
A ferroelectric element of the present invention was obtained in the same manner as in Example 1 except that the thermal diffusion temperature of Zr was changed to 600 ° C.
(Example 3)
A ferroelectric element of the present invention was obtained in the same manner as in Example 1 except that a stainless steel substrate (SUS430) was used instead of the Si substrate.

(Comparative Example 1)
Immediately after the formation of the lower electrode (specifically, within 5 minutes after the substrate temperature reached 520 ° C.), the same as in Example 1 except that the PZT film was formed and the thermal diffusion of Zr was not performed. Thus, a comparative ferroelectric element was obtained.
(Comparative Example 2)
A comparative ferroelectric element was obtained in the same manner as in Example 1 except that a Ti seed layer was formed instead of the Zr seed layer.

(Comparative Example 3)
The seed layer was not formed, the same sputtering apparatus as in Example 1 was used, and the PZT film was formed by changing only the film formation temperature to 300 ° C. under the same apparatus atmosphere conditions. A comparative ferroelectric element was obtained in the same manner as in Example 1 except that the annealing was performed at 0 ° C. for 1 hour.
(Comparative Example 4)
A comparative ferroelectric element was obtained in the same manner as in Example 1 except that the seed layer was not formed and a PZT film was formed by the sol-gel method (calcination temperature was 700 ° C.).

(Evaluation items and evaluation methods)
<AFM surface observation of lower electrode>
In Example 1 and Comparative Example 1, the surface of the lower electrode at the start of PZT film deposition (after thermal diffusion of Zr in Example 1 and immediately after deposition of the lower electrode in Comparative Example 1) (Microscope).
<TEM cross-sectional observation of lower electrode and PZT film>
In Example 1 and Comparative Example 1, after the PZT film was formed, the interface between the lower electrode and the PZT film and the cross section in the vicinity thereof were observed with a TEM (transmission electron microscope).
<XRD measurement>
In Examples 1 to 3 and Comparative Examples 1 to 4, XRD (X-ray diffraction) measurement of the PZT film was performed after the PZT film was formed, and the crystallinity and crystal orientation of the PZT film were evaluated. Crystallinity was evaluated based on the following criteria.
Criterion for crystallinity: A single phase having a perovskite structure without a pyrochlore phase was obtained. Furthermore, the (111) plane was strongly preferentially oriented, and the degree of orientation was 98% or more.
(Triangle | delta): The single phase of the perovskite structure without a pyrochlore phase was obtained. Furthermore, preferential orientation was performed in the (111) direction, and the degree of orientation was 80% or more and less than 98%.
X A pyrochlore phase was observed.

<Measurement of electric field-polarization curve and remanent polarization value Pr>
In Examples 1 to 3 and Comparative Examples 1 to 4, the electric field-polarization curves of the obtained ferroelectric elements were measured, and the remanent polarization value Pr when the electric field strength = 0 was measured. Since Pr has ±, it was evaluated by comparison with 2Pr.

<Leakage current>
In Examples 1 to 3 and Comparative Examples 1 to 4, leakage currents of the obtained ferroelectric elements were measured. Using a semiconductor parameter measuring device 4155C manufactured by Agilent, a voltage was applied between the upper electrode and the lower electrode of 100 μm square, and the leakage current was measured. The applied electric field intensity was about ± 150 kV / cm.

(result)
Table 1 shows the main element manufacturing conditions and evaluation results for each example.
In Comparative Example 1 in which the Zr seed layer was formed but Zr thermal diffusion was not performed, the AFM observation surface of the lower electrode at the start of the formation of the PZT film was substantially flat. When TEM cross-section observation was performed on the interface between the lower electrode and the PZT film and in the vicinity thereof, no precipitate of Zr was found on the surface of the lower electrode. In the PZT film obtained in Comparative Example 1, a pyrochlore phase was observed, and the perovskite crystallinity was low. The ferroelectric element obtained in Comparative Example 1 had a low hysteresis property of the electric field-polarization curve and a small value of 2Pr, and was not suitable as a ferroelectric memory.

  On the other hand, in Examples 1 to 3, in which a Zr seed layer was formed and thermal diffusion of Zr in the seed layer was performed, AFM observation of the lower electrode at the start of PZT film formation (after thermal diffusion of Zr) Each of the surfaces had a surface shape in which a large number of gentle mountains were connected. When the TEM cross section of the interface between the lower electrode and the PZT film and the vicinity thereof was observed, island-like Zr precipitates were deposited on the surface of the lower electrode in the gentle mountain-to-crest valley portion. It was observed.

  When XRD measurement was performed on the PZT films obtained in Examples 1 to 3, all the PZT films were high-quality perovskite crystals having no pyrochlore phase. All of the obtained PZT films were strongly oriented in the (111) plane, and the degree of orientation was 99.0% or more. As a representative, the XRD pattern of Example 1 is shown in FIG. The prepared PZT film has a composition in the vicinity of the phase transition between the tetragonal system and the rhombohedral system.

  Each of the ferroelectric elements obtained in Examples 1 to 3 had a good hysteresis property of the electric field-polarization curve, a large value of 2Pr, and was suitable as a ferroelectric memory. The value of 2Pr in Examples 1 to 3 was almost twice that of Comparative Example 1. The ferroelectric elements obtained in Examples 1 to 3 were good with a small leakage current. In Examples 1 to 3, similar results were obtained regardless of the substrate.

  In Comparative Example 2 in which a Ti seed layer was formed and thermal diffusion of Ti in the seed layer was performed, a (100) -oriented PZT film was obtained. In Examples 1 to 3, the value of 2Pr was larger than that of Comparative Example 2, which was suitable as a ferroelectric memory.

  In Comparative Example 3 in which the PZT film was formed at 300 ° C. and then annealed at 600 ° C., the obtained PZT film exhibited (111) orientation but had poor crystallinity. The ferroelectric element obtained in Comparative Example 3 had a low hysteresis property of the electric field-polarization curve and a small value of 2Pr, and was not suitable as a ferroelectric memory. The obtained ferroelectric element had a large leakage current because the film quality of the PZT film was not good.

  In Comparative Example 4 in which the PZT film was formed by the sol-gel method, high-temperature baking was performed, so that the obtained PZT film was a high-quality perovskite crystal having no pyrochlore phase. However, when the PZT film was observed with a microscope (100 times magnification), a large number of minute cracks were observed. In Comparative Example 4, since high-temperature baking was performed, it is considered that due to the difference in thermal expansion coefficient between the substrate and the PZT film, stress was applied to the PZT film during or after the baking and the cracks were generated.

  The ferroelectric element of the present invention can be preferably used for a ferroelectric memory (FRAM), an ink jet recording head, a pressure sensor, and the like.

Sectional drawing which shows the principal part which shows the structure of the ferroelectric element of embodiment which concerns on this invention, and a ferroelectric memory provided with the same (A), (b) is a circuit configuration example of the ferroelectric memory of FIG. (A)-(d) is process drawing which shows the manufacturing method of the ferroelectric element of FIG. 1 is a cross-sectional view of a principal part showing the structure of a piezoelectric element (ferroelectric element) according to an embodiment of the present invention and an ink jet recording head including the same. The figure which shows the structural example of the ink jet type recording apparatus provided with the ink jet type recording head of FIG. Partial top view of the ink jet recording apparatus of FIG. XRD pattern of the PZT film of Example 1 Electric field-polarization curve of the ferroelectric element of Example 1

Explanation of symbols

1 Ferroelectric Memory 11 Substrate 30 Ferroelectric Capacitor (Ferroelectric Device)
31 Seed layer 31a Precipitate 32 Lower electrode 33 Ferroelectric film 34 Upper electrode 2 Inkjet recording head 50 Piezoelectric element (ferroelectric element)
51 Substrate 52 Seed layer 53 Lower electrode 54 Piezoelectric film (ferroelectric film)
55 Upper electrode 100 Inkjet recording apparatus

Claims (11)

A laminated structure of a lower electrode, a ferroelectric film (which may contain inevitable impurities) made of one or more perovskite oxides represented by the following general formula, and the upper electrode; In a method for manufacturing a ferroelectric element by applying an electric field to the ferroelectric film by a lower electrode and the upper electrode by a sputtering method ,
A step (A) of sequentially forming a seed layer containing Zr and the lower electrode;
Diffusing Zr contained in the seed layer to deposit the element on the surface of the lower electrode;
And (C) sequentially forming the ferroelectric film on the lower electrode at a film forming temperature of 400 ° C. or higher and lower than 600 ° C.
General formula ABO ₃
(In the formula, A: A site element mainly composed of Pb,
B: Element of B site containing Zr,
O: oxygen atom,
The standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0. ) In step (A), wherein the thickness of the seed layer and 5 to 50 nm, according to claim 1, wherein the thickness of the lower electrode as a 50 to 500 nm, characterized by sequentially performing the formation of the seed layer and the lower electrode A method for producing a ferroelectric element as described in 1). 3. The method of manufacturing a ferroelectric element according to claim 1, wherein in the step (B), Zr is thermally diffused by a heat treatment at 400 to 700 ° C. 3. 4. The method for manufacturing a ferroelectric element according to claim 3 , wherein in the step (B), the thermal diffusion is performed for 10 minutes to 2 hours. The ferroelectric film has a tetragonal crystal structure and / or the rhombohedral system, any one of the preceding claims, characterized in that a film having a crystalline orientation in the (111) plane A method for producing a ferroelectric element as described in 1). 6. The method for manufacturing a ferroelectric element according to claim 1, wherein the perovskite oxide contains Ti. The lower _{electrode, Au, Pt, Ir, IrO} 2, RuO 2, LaNiO 3, and any of claims 1-6, characterized in that a main component at least one selected from the group consisting of SrRuO ₃ A method for producing a ferroelectric element as described in 1). Wherein the ferroelectric element, a silicon substrate, a stainless substrate, and a ferroelectric element according to any one of claims 1 to 7, characterized in that formed on either of the substrates of the glass substrate Production method. Ferroelectric element, characterized in that those produced by the production method of a ferroelectric device according to any one of claims 1-8. A laminated structure of a lower electrode, a ferroelectric film (which may contain inevitable impurities) made of one or more perovskite oxides represented by the following general formula, and the upper electrode; In a ferroelectric element in which an electric field is applied to the ferroelectric film by a lower electrode and the upper electrode,
The lower electrode has a precipitate containing Zr in a recessed portion of the surface of the electrode ,
A ferroelectric element characterized in that the ferroelectric film has crystal orientation in a (111) plane .
General formula ABO ₃
(In the formula, A: A site element mainly composed of Pb,
B: Element of B site containing Zr,
O: oxygen atom,
The standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0. ) A ferroelectric memory comprising the ferroelectric element according to claim 9 .

Images