CN1983464B - Ferroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric element, semiconductor element - Google Patents

Abstract

A ferroelectric film, represented by the general formula of AB _1-X Nb _X O ₃ , wherein at least Pb is contained as the A element, and at least one of Zr, Ti, V, W, Hf, and Ta is used as the B element The above constitution, 0.1≤x≤0.4.

Description

Ferroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric element, semiconductor element

The parent case of this divisional application is:

Title of Invention: Ferroelectric film, capacitor and their manufacturing method, ferroelectric memory

International filing date: October 23, 2003

International application number: PCT/JP03/13556

National application number: 200380101906.2

technical field

The invention relates to a ferroelectric film, a ferroelectric capacitor, a ferroelectric memory, a piezoelectric element, a semiconductor element, a method for manufacturing a ferroelectric film, and a method for manufacturing a ferroelectric capacitor. the

Background technique

In recent years, research and development of ferroelectric films such as PZT and SBT, ferroelectric capacitors, ferroelectric memory devices, and the like using them have been actively conducted. The configuration of ferroelectric memory devices can be roughly classified into 1T type, 1T1C type, 2T2C type, and simple matrix type. Among them, since the 1T type generates an internal electric field in the capacitor structurally, the retention (data retention) is as short as 1 month, and cannot meet the 10-year guarantee generally required by semiconductors. The 1T1C type and 2T2C type have almost the same configuration as DRAM, and the manufacturing technology of DRAM can be applied in order to have selection transistors. In addition, since the 1T1C type and 2T2C type have realized the writing speed of SRAM, so far, small-capacity products of 256 KB or less have been commercialized. the

So far, Pb(Zr,Ti)O ₃ (PZT) has been mainly used as a ferroelectric material. In the case of PZT, a Zr/Ti ratio of 52/48 or 40/60, a rhombohedral crystal and a tetragonal crystal mixed region and its vicinity are used. In addition, in the case of PZT, elements such as La, Sr, and Ca are also used for doping. This area is used to ensure the most required reliability of memory elements. The hysteresis shape is good for a tetragonal crystal region rich in Ti, but produces Schottky defects due to the ionic crystal structure. Therefore, the leakage current characteristic and the imprint characteristic (the degree of deformation of the so-called hysteresis) are not good, and it is difficult to ensure reliability.

On the other hand, the cell size of the simple matrix type is smaller than that of the 1T1C type and the 2T2C type, and capacitors can be multilayered, so high integration and cost reduction are expected. the

In addition, conventional simple matrix ferroelectric memory devices are disclosed in Japanese Patent Application Laid-Open No. 9-116107 and the like. This publication discloses a driving method of applying a voltage of 1/3 of the write voltage to non-selected memory cells when writing data to the memory cells. the

However, this technique does not specifically describe the hysteresis loop of the ferroelectric capacitor necessary for operation. In order to obtain a practically operable simple matrix ferroelectric memory device, a hysteresis loop with good squareness is indispensable. As a compatible ferroelectric material, Ti-rich tetragonal PZT is considered as a candidate, but as with the 1T1C and 2T2C type ferroelectric memories described above, securing reliability is the most important issue. the

In addition, although the PZT tetragonal crystal has square-shaped hysteresis characteristics suitable for memory applications, it lacks reliability and has not been put into practical use. The reason for this is as follows. the

First, the crystallized PZT tetragonal thin film tends to increase the leakage current intensity as the Ti content increases. In addition, when a so-called static impression test was performed in which data was written only once in either the + or - direction, and the data was read after being heated and kept at 100 degrees, after 24 hours (h), substantially no writing remained. The data. These are essential characteristics of PZT which is an ionic crystal and Pb and Ti which are constituent elements of PZT, and are the biggest problems of a PZT tetragonal thin film whose constituent elements are mostly composed of Pb and Ti. This problem is large when the PZT perovskite is an ionic crystal, and is an essential problem of PZT. the

Fig. 44 is a list of main energies related to the bonding of each constituent element of PZT. It is known that PZT contains many oxygen vacancies after crystallization. That is, from FIG. 44 , it is predicted that Pb—O has the smallest binding energy among PZT constituent elements, and is easily cut off during firing heating or polarization inversion. That is, when Pb escapes (escapes), O escapes according to the principle of charge neutrality. the

Next, during heating and holding such as an imprint test, each constituent element of PZT vibrates and repeatedly impacts, but Ti is the lightest among PZT constituent elements, and easily escapes due to vibration shock during high temperature holding. Therefore, if Ti escapes, O will escape according to the principle of charge neutrality. In addition, since the maximum valence number of Pb:+2 and Ti:4 contributes to the combination, charge neutrality does not hold except for escaped O. That is, PZT tends to form so-called Schottky defects in which two anions such as O are easily released from one cation such as Pb and Ti. the

Here, the principle of leakage current generation due to oxygen deficiency in the PZT crystal will be described. 45A to 45C are diagrams illustrating the generation of leakage current in an oxide crystal having a Brownmillerite-type crystal structure represented by the general formula ABO _2.5 . As shown in FIG. 45A , the lignite-type crystal structure is a crystal structure having oxygen deficiency relative to a perovskite-type crystal structure having a PZT crystal represented by the general formula ABO ₃ or the like. In addition, as shown in FIG. 45B , since oxygen ions are in the vicinity of cations in the lignite-type crystal structure, cation deficiency is unlikely to cause an increase in leakage current. However, as shown in FIG. 45C , oxygen ions are connected in series throughout the entire PZT crystal, and when the crystal structure changes to a chrysanthemum crystal structure due to oxygen deficiency, the leakage current also increases.

In addition to the generation of the leakage current described above, defects of Pb and Ti and accompanying O defects are also so-called lattice defects, which cause the space charge polarization shown in FIG. 46 . At this time, in the PZT crystal, the electric field formed by the polarization of the ferroelectric generates a counter electric field caused by lattice defects, and a so-called offset potential is applied. As a result, the hysteresis is shifted or polarized. And, the higher the temperature, the more this phenomenon occurs. the

The above are the essential problems of PZT, and it is considered difficult to solve the above-mentioned problems in pure PZT, and up to now, memory elements using tetragonal PZT have not realized elements with sufficient characteristics. the

In addition, in the ferroelectric memory, the crystallization state of the ferroelectric film included in the ferroelectric capacitor is one of the important factors for determining device characteristics. In addition, in the manufacturing process of the ferroelectric memory, there is a process of forming an interlayer insulating film or a protective film, and a process that generates a large amount of hydrogen is used. At this time, since the ferroelectric film is mainly formed of oxides, reduction of the oxides by hydrogen generated in the manufacturing process undesirably affects the characteristics of the ferroelectric capacitor. the

Therefore, in the conventional ferroelectric memory, in order to prevent the characteristics of the ferroelectric capacitor from deteriorating, the ferroelectric capacitor is covered with a barrier film such as an aluminum oxide film or an aluminum nitride film to ensure the reduction resistance of the capacitor. However, these barrier films require an extra occupied area for high integration of the ferroelectric memory, and from the viewpoint of productivity, a method of manufacturing the ferroelectric memory with a simpler process is desired. the

Contents of the invention

An object of the present invention is to provide 1T1C, 2T2C and simple matrix ferroelectric memories including ferroelectric capacitors having hysteresis characteristics which can be used for any of 1T1C, 2T2C and simple matrix ferroelectrics. In addition, another object of the present invention is to provide a ferroelectric film suitable for the above-mentioned ferroelectric memory and a method of manufacturing the same. Furthermore, another object of the present invention is to provide a piezoelectric element and a semiconductor element using the above-mentioned ferroelectric film. Another object of the present invention is to provide a ferroelectric capacitor capable of securing sufficient characteristics by a simple process that does not require a barrier film, a method of manufacturing the same, and a ferroelectric memory using the ferroelectric capacitor. the

A ferroelectric film represented by the general formula of AB _1-x Nb _x O ₃ , containing at least Pb as an A element, and composed of at least one of Zr, Ti, V, W, Hf, and Ta as a B element , where 0.1≤x≤0.4

Description of drawings

FIG. 1 is a cross-sectional view schematically showing a ferroelectric capacitor. the

Fig. 2 is a flowchart showing the formation of a PZTN film by the spin coating method. the

FIG. 3 is a graph showing a P (polarization)-V (voltage) hysteresis curve of a ferroelectric capacitor. the

4A to 4C are diagrams showing the surface structure of the PZNT film of Example 1. FIG. the

5A to 5C are graphs showing the crystallinity of the PZNT film of Example 1. FIG. the

6A to 6C are graphs showing the relationship between the film thickness of the PZNT film of Example 1 and the surface structure. the

7A to 7C are graphs showing the relationship between the film thickness and crystallinity of the PZNT film of Example 1. FIG. the

8A to 8C are graphs showing the film thickness and hysteresis characteristics of the PZNT film of Example 1. FIG. the

9A to 9C are graphs showing the film thickness and hysteresis characteristics of the PZNT film of Example 1. FIG. the

10A and 10B are graphs showing leakage current characteristics of the PZNT film of Example 1. FIG. the

FIG. 11A is a graph showing the fatigue characteristics of the PZTN film of Example 1. FIG. 11B is a graph showing the static image characteristics of the PZTN film of Example 1. FIG. the

12 is a diagram showing the structure of a ferroelectric capacitor in Example 1 in which a SiO ₂ protective film is formed using ozone TEOS.

13 is a graph showing hysteresis characteristics of a ferroelectric capacitor after forming a SiO ₂ protective film using ozone TEOS in Example 1. FIG.

FIG. 14 is a graph showing leakage current characteristics of a conventional PZT film of Example 1. FIG. the

FIG. 15 is a graph showing fatigue characteristics of a ferroelectric capacitor using a conventional PZT film according to Example 1. FIG. the

FIG. 16 is a graph showing static image characteristics of a ferroelectric capacitor using a conventional PZT film according to Example 1. FIG. the

17A and 17B are graphs showing hysteresis characteristics of the PZTN film of Example 2. FIG. the

18A and 18B are graphs showing hysteresis characteristics of the PZTN film of Example 2. FIG. the

19A and 19B are graphs showing hysteresis characteristics of the PZTN film of Example 2. FIG. the

FIG. 20 is a diagram showing an X-ray diffraction pattern of a PZTN film of Example 2. FIG. the

21 is a graph showing the relationship between the amount of Pb defects and the composition ratio of Nb in the PZTN crystal of Example 2. FIG. the

Fig. 22 is a diagram illustrating the crystal structure of WO ₃ which is a perovskite crystal.

23A to 23C are cross-sectional views schematically showing the steps of forming the PZTN film in Example 3. FIG. the

24A and 24B are graphs illustrating changes in the lattice constant of the PZTN film in Example 3. FIG. the

FIG. 25 is a graph illustrating changes in lattice mismatch ratios between the PZTN film and the Pt metal film in Example 3. FIG. the

Fig. 26 is a flow chart for forming a conventional PZT film in a reference example by spin coating. the

27A to 27E are diagrams showing the surface structure of the PZT film in the reference example. the

28A to 28E are diagrams showing the crystallinity of the PZT film in the reference example. the

29A and 29B are diagrams showing hysteresis of a tetragonal PZT film in a reference example. the

FIG. 30 is a graph showing hysteresis of a conventional tetragonal PZT film in a reference example. the

31A and 31B are graphs showing the results of outgassing analysis of the tetragonal PZT film in Reference Example. the

32A to 32C are views showing the manufacturing process of the ferroelectric capacitor. the

33A and 33B are graphs showing hysteresis characteristics of ferroelectric capacitors. the

Fig. 34 is a graph showing electrical characteristics of a ferroelectric capacitor. the

Fig. 35A is a plan view schematically showing a simple matrix type ferroelectric memory device. Fig. 35B is a cross-sectional view schematically showing a simple matrix type ferroelectric memory device. the

36 is a cross-sectional view showing an example of a ferroelectric memory device in which a memory cell array and peripheral circuits are commonly integrated on the same substrate. the

Fig. 37A is a cross-sectional view schematically showing a 1T1C type ferroelectric memory. Fig. 37B is an equivalent circuit diagram schematically showing a 1T1C type ferroelectric memory. the

38A to 38C are views showing the manufacturing steps of the ferroelectric memory. the

Fig. 39 is an exploded perspective view of a recording head. the

Fig. 40A is a plan view of a recording head. Fig. 40B is a sectional view of the recording head. the

Fig. 41 is a cross-sectional view schematically showing a layered structure of a piezoelectric element. the

Fig. 42 is a schematic diagram showing an example of an ink jet recording device. the

FIG. 43A is a graph showing hysteresis characteristics of a ferroelectric film in which Ta is added to PZT. FIG. 43B is a graph showing hysteresis characteristics of a ferroelectric film in which W is added to PZT. the

Fig. 44 is a graph showing various characteristics related to combinations of constituent elements of a PZT-based ferroelectric. the

FIGS. 45A to 45C are diagrams illustrating Schottky defects in the browniite-type crystal structure. the

Fig. 46 is a diagram illustrating space charge polarization of a ferroelectric. the

Detailed ways

(1) The ferroelectric film of this embodiment is represented by the general formula of AB _1-X Nb _X O ₃ , the A element is composed of at least Pb, and the B element is at least one of Zr, Ti, V, W, Hf, and Ta. One or more kinds of constitutions, containing Nb within the range of 0.05≤x<1.

In addition, the A element may be composed of Pb _1-y Ln _y (0<y≦0.2). In addition, Ln may be composed of at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

(2) The ferroelectric film of this embodiment is represented by the general formula of (Pb _1-y A _y )(B _1-x Nb _x )O ₃ , and the A element is La, Ce, Pr, Nd, Pm, Sm, Eu , Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu at least one or more, B element is composed of Zr, Ti, V, W, Hf, and Ta at least one or more, in 0.05≤x< 1 (preferably 0.1≤x≤0.3) contains Nb.

(3) The ferroelectric film of the present embodiment is the following PZT ferroelectric film, the composition of Ti is more than that of Zr, and the Ti composition is more than 2.5 mol % and not more than 40 mol (preferably more than 10 mol % and not more than 30 mol). ) is replaced by Nb. In addition, the PZT-based ferroelectric film may have at least one crystal structure of a tetragonal system and a rhombohedral system. Furthermore, the PZT-based ferroelectric film may contain Si or Si and Ge at 0.5 mol % or more (more preferably 0.5 mol % or more and less than 5 mol %). In addition, the PZT-based ferroelectric film can be formed using a sol-gel solution. the

(4) The ferroelectric film of this embodiment is a PZT-based ferroelectric film represented by the general formula of ABO ₃ , contains Pb as a constituent element on the A side, and contains at least Zr and Ti as constituent elements on the B side. The amount of Pb deficiency on the A side of the PZT-based ferroelectric film is at most 20 mol% or less than the stoichiometric theoretical composition of the ABO ₃ . The ferroelectric film contains Nb on the B side at a composition ratio equivalent to twice the amount of Pb deficiency on the A side. In this ferroelectric film, the Ti composition on the B side is higher than the Zr composition, and may have a rhombohedral crystal structure. In addition, the ferroelectric film can be formed using a sol-gel solution.

(5) The manufacturing method of the ferroelectric film of the present embodiment is a manufacturing method of a PZT-based ferroelectric _film , using a _mixture of a sol-gel solution for PbZrO , a sol-gel solution for PbTiO , and a sol-gel solution for PbNbO ₃ solution as the sol-gel solution.

In the method for producing a ferroelectric film according to this embodiment, a solution obtained by further mixing a sol-gel solution for PbSiO ₃ can be used as the sol-gel solution.

(6) The method for producing a ferroelectric film of this embodiment is a method for producing a PZT-based ferroelectric film, and when the stoichiometric composition of Pb as a constituent element on the A side is set to 1, it is used in the range of 0.9 to 1.2 The sol-gel solution containing Pb in the range is formed. the

(7) The method for producing a ferroelectric film according to this embodiment may include forming the PZT-based ferroelectric film on a metal film made of a platinum-based metal. the

(8) In the method for producing a ferroelectric film according to this embodiment, the platinum-based metal is at least one of Pt and Ir. the

(9) The ferroelectric memory according to the present embodiment includes a first electrode electrically connected to one of the source or drain electrodes of a CMOS transistor previously formed on a Si wafer, a ferroelectric film formed on the first electrode, The second electrode formed on the ferroelectric film, the capacitor formed by the first electrode, the ferroelectric film and the second electrode is selected by a CMOS transistor previously formed on the Si wafer, wherein, The ferroelectric film is composed of tetragonal PZT with a Ti ratio of 50% or more, 5 mol% to 40 mol% of the Ti composition is replaced by Nb, and it is composed of a ferroelectric film containing 1 mol% or more of Si and Ge. the

(10) The ferroelectric memory of this embodiment includes a first electrode formed in advance, a second electrode arranged in a direction intersecting the first electrode, and at least one electrode disposed between the first electrode and the second electrode. The ferroelectric film in the intersecting region, the capacitors composed of the first electrode, the ferroelectric film and the second electrode are arranged in a matrix, wherein the ferroelectric film is made of a Ti ratio of 50% or more Composed of tetragonal crystal PZT, 5 mol% to 40 mol% of the Ti composition is replaced by Nb, and it is composed of a ferroelectric film containing 1 mol% or more of Si and Ge. the

(11) The method for manufacturing a ferroelectric memory according to this embodiment includes: crystallizing a sol-gel solution for forming PbZrO ₃ as a first raw material solution after coating, and a sol-gel solution for forming PbTiO ₃ as a second raw material solution. solution, a sol-gel solution for forming _PbNbO3 as the third raw material solution, and a sol-gel solution for forming _PbSiO3 as the fourth raw material solution, the first, second and third raw material solutions are for forming ferroelectric The raw material solution for the layer, the fourth raw material solution is the raw material solution for forming the permanent dielectric layer having the catalytic effect indispensable for forming the first, second and third raw material solutions into the ferroelectric layer.

(12) The method for manufacturing a ferroelectric capacitor according to this embodiment includes: a step of forming a lower electrode on a predetermined substrate; The process of forming a ferroelectric film made of material; the process of forming an upper electrode on the ferroelectric film; the process of forming a protective film to cover the lower electrode, ferroelectric film and upper electrode; and at least forming the protective film Thereafter, a heat treatment step for crystallizing the PZTN composite oxide is performed. the

According to this embodiment, a PZTN composite oxide containing Pb, Zr, Ti, and Nb as constituent elements is used as a material of the ferroelectric film, and crystallization of this PZTN composite oxide is performed after forming a protective film. Therefore, even if the ferroelectric film is damaged by hydrogen generated during processing when the protective film is formed, the PZTN composite oxide can be crystallized while recovering the damage by subsequent heat treatment for crystallization. Therefore, the conventional process of forming a barrier film for protecting the ferroelectric film from the reduction reaction can be omitted, thereby improving productivity and reducing production cost. the

(13) In the method for manufacturing a ferroelectric capacitor according to this embodiment, the ferroelectric film is temporarily heat-treated in an oxidizing atmosphere during formation, and becomes amorphous before the heat treatment for crystallizing the PZTN composite oxide is performed. state. the

According to this aspect, before the ferroelectric film is crystallized, it becomes an amorphous state. Therefore, in the ferroelectric film of this form, deterioration of crystal quality due to grain boundary diffusion can be prevented by the amorphous state before forming the protective film. In addition, since the ferroelectric film in the amorphous state is temporarily heat-treated in an oxidizing atmosphere, oxygen is introduced into the film. Therefore, during heat treatment for crystallization, crystallization of the PZTN composite oxide can proceed regardless of the type of gas contained in the atmosphere. the

(14) In the method for manufacturing a ferroelectric capacitor according to this embodiment, the protective film is a silicon oxide film, which can be formed using trimethylsilane. the

According to this method, compared with tetraethylorthosilicate (TEOS) generally used for forming silicon oxide films, trimethylsilane (TMS) which generates less hydrogen during processing is used to form a protective film made of silicon oxide films. film, so the damage to the reduction reaction of the ferroelectric film can be reduced. the

(15) In the method for manufacturing a ferroelectric capacitor according to this embodiment, the heat treatment for crystallizing the PZTN composite oxide may be performed in a non-oxidizing atmosphere. the

According to this aspect, since the heat treatment for crystallization is performed in a non-oxidizing atmosphere, for example, even if peripheral components (such as metal wiring) other than capacitors are included in the device being processed, the peripheral components can be prevented from being damaged. Oxidative damage caused by high temperature heat treatment. the

(16) The ferroelectric capacitor of the present embodiment is formed using the method for manufacturing a ferroelectric capacitor described above. the

(17) In addition, the ferroelectric film and the ferroelectric capacitor of this embodiment can be applied to ferroelectric memories, piezoelectric elements, and semiconductor elements using them. the

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. the

1. Ferroelectric film, ferroelectric capacitor and manufacturing method thereof

FIG. 1 is a cross-sectional view schematically showing a ferroelectric capacitor 100 using a ferroelectric film 101 according to an embodiment of the present invention. the

As shown in FIG. 1 , a ferroelectric capacitor 100 is composed of a ferroelectric film 101 , a first electrode 102 and a second electrode 103 . the

The first electrode 102 and the second electrode 103 are composed of a single noble metal such as Pt, Ir, Ru, or a composite material mainly composed of the noble metal. When the ferroelectric element diffuses to the first electrode 102 and the second electrode 103, composition fluctuation (deviation) occurs at the interface between the electrode and the ferroelectric film 101, and the squareness of the hysteresis decreases. Therefore, the first electrode 102 and the second electrode 103 are required to The second electrode 103 has such a density that elements of the ferroelectric film do not diffuse. the

In order to improve the density of the first electrode 102 and the second electrode 103, for example, a method of sputtering a heavy gas into a film, a method of dispersing oxides such as Y and La in noble metal electrodes, etc. are used. the

The ferroelectric film 101 is formed using a PZT-based ferroelectric containing Pb, Zr, and Ti as constituent elements. In particular, in the present embodiment, the ferroelectric film 101 is characterized by using Pb(Zr, Ti, Nb)O ₃ (PZTN) doped with Nb on the Ti side.

Nb and Ti have roughly the same size (similar ionic radius and the same atomic radius.) and twice the weight of Ti. Even the interatomic impact caused by lattice vibration is difficult to escape atoms from the lattice. In addition, the atomic valence of Nb is stable at +5. Even if Pb escapes, Nb ⁵⁺ can be used to compensate for the escaped valence of Pb. In addition, even if Pb escapes during crystallization, Nb with a small size easily enters because O with a large size escapes.

In addition, since the atomic valence of Nb still has a +4 valence, it can be sufficiently carried out instead of Ti ⁴⁺ . In addition, in fact, the co-combination of Nb is very strong, and it is considered difficult for Pb to escape (H. Miyazawa, E. Natori, S. Miyashita; Jpn. J. Appl. Phys. 39 (2000) 5679).

So far, doping Nb to PZT is mainly carried out in the rhombohedral region rich in Zr, but its amount is extremely small, being 0.2～0.025mol% (J.Am.Ceram.Soc, 84 (2001) 902; Phys.Rev . Let, 83 (1999) 1347) around. Thus, it is considered that the main reason why a large amount of Nb cannot be doped is that, for example, if 10 mol % of Nb is added, the crystallization temperature will rise to 800 degrees or more. the

Therefore, when forming the ferroelectric film 101, it is also preferable to add PbSiO ₃ silicate in a ratio of, for example, 1 to 5 mol%. Thereby, the crystallization energy of PZTN can be reduced. That is, when PZTN is used as the material of the ferroelectric film 101, the crystallization temperature of PZTN can be lowered by adding PbSiO ₃ silicate together with Nb.

Next, an example of a method of forming the PZTN ferroelectric film 101 applied to the ferroelectric capacitor 100 of this embodiment will be described. the

The PZTN ferroelectric film 101 can be obtained by preparing a mixed solution composed of first to third raw material solutions containing at least one of Pb, Zr, Ti, and Nb, and crystallizing oxides contained in these mixed solutions by heat treatment or the like. . the

As the first raw material solution, among the constituent metal elements of the PZTN ferroelectric phase, in order to form _PbZrO3 perovskite crystals based on Pb and Zr, the polycondensate is dissolved in a solvent such as n-butanol in an anhydrous state. The solution.

As the second raw material solution, among the constituent metal elements of the PZTN ferroelectric phase, in order to form PbTiO ₃ perovskite crystals based on Pb and Ti, a polycondensate is dissolved in a solvent such as n-butanol in an anhydrous state. solution.

As the third raw material solution, among the constituent metal elements of the PZTN ferroelectric phase, in order to form PbNbO ₃ perovskite crystals based on Pb and Nb, a polycondensate is dissolved in a solvent such as n-butanol in an anhydrous state. solution.

In the case of using the above-mentioned 1st, 2nd and 3rd raw material solutions to form, for example, the ferroelectric film 101 made of PbZr _0.2 Ti _0.8 Nb _0.2 O ₃ (PZTN), it can be (the first raw material solution): (the second raw material solution):(the third raw material solution)=2:6:2 ratio and mixed.

However, even if the mixed solution is directly crystallized, a high crystallization temperature is required to form the PZTN ferroelectric film 101 . That is, if Nb is mixed, the crystallization temperature will rise sharply, and since crystallization is impossible in the temperature range of 700 degrees or less that can be used as a device, Nb has not been used as a substitution element for Ti in the past at 5 mol % or more. Areas where additives have not been available so far. In addition, there is no example at all in the PZT tetragonal crystal containing more Ti than Zr. This can be known from references J. Am. Ceram. Soc, 84 (2001) 902 or Phys. Rev. Let, 83 (1999) 1347 and the like. the

Therefore, in this embodiment, for example, in order to form PbSiO ₃ crystals, in an anhydrous state, n- Solve the above-mentioned problems by dissolving the solution of the polycondensate in solvents such as butanol.

That is, by using the mixed solution of the above-mentioned first, second, third, and fourth solutions, it is possible to crystallize PZTN in a temperature range where the crystallization temperature of PZTN is 700 degrees or less and can be deviceized. the

Specifically, the ferroelectric film 101 is formed according to the flowchart shown in FIG. 2 . Perform a series of processes such as the mixed solution coating process (step ST11), ethanol removal process ~ drying heat treatment process ~ degreasing heat treatment process (step ST12, step ST13) for a desired number of times, and then perform firing by crystallization annealing (step ST14) to form Ferroelectric film 101. the

Examples of conditions in each step are shown below. the

First, a noble metal for electrodes such as Pt is covered on a Si substrate to form a film of a lower electrode (step ST10 ). Next, the mixed solution is applied by a coating method such as a spin coating method (step ST11 ). Specifically, the mixed solution was dropped onto the Pt-coated substrate. In order to make the dripped solution flow over the entire surface of the substrate, the substrate was rotated at about 500 rpm, and then the rotation speed was reduced to 50 rpm or less, and the substrate was rotated for about 10 seconds. The drying heat treatment step is performed at 150°C to 180°C (step ST13). The drying heat treatment is performed using a hot plate or the like in an air atmosphere. Similarly, in the degreasing heat treatment step, it is performed in an air atmosphere on a hot plate kept at 300°C to 350°C (step ST13). Firing for crystallization is performed in an oxygen atmosphere using rapid thermal annealing (RTA) or the like (step ST14 ). the

In addition, the film thickness after firing may be about 100 to 200 nm. Next, after the upper electrode is formed by sputtering or the like (step ST15), for the purpose of forming the interface between the second electrode and the ferroelectric thin film and improving the crystallinity of the ferroelectric thin film, as in the firing, the ferroelectric thin film is heated in an oxygen atmosphere. In this process, post-annealing is performed using RTA or the like (step ST16 ) to obtain the ferroelectric capacitor 100 . the

Next, the effect of using the PZTN ferroelectric film 101 on the hysteresis characteristics of the ferroelectric capacitor 100 will be considered. the

FIG. 3 is a diagram schematically showing a P (polarization)-V (voltage) hysteresis curve of the ferroelectric capacitor 100 . First, when the voltage +Vs is applied, it becomes the polarization amount P(+Vs), and then, when the voltage becomes 0, it becomes the polarization amount Pr. And, when the voltage is -1/3Vs, the polarization amount becomes P(~1/3Vs). Also, when the voltage is -Vs, the polarization amount becomes P(-Vs), and when the voltage becomes 0 again, the polarization amount becomes -Pr. In addition, when the voltage is +1/3Vs, the polarization amount becomes P(+1/3Vs), and when the voltage becomes +Vs again, the polarization amount returns to P(+Vs) again. the

In addition, the ferroelectric capacitor 100 also has the following characteristics in terms of hysteresis characteristics. First, after the voltage Vs is temporarily applied and becomes the polarization amount P(+Vs), a voltage of -1/3Vs is applied, and when the applied voltage becomes 0, the hysteresis loop traces the locus indicated by arrow A in Fig. 3 , the polarization has a stable value PO(0). Also, after temporarily applying a voltage of -Vs and changing the polarization amount to P(-Vs), a voltage of +1/3Vs is applied, and when the applied voltage becomes 0, the hysteresis loop traces that shown by arrow B in Fig. 3 trajectory, the polarization quantity has a stable value PO(1). If the difference between the polarization amount PO(0) and the polarization amount PO(1) is sufficiently large, the simple matrix type ferroelectric memory device can be operated by using the driving method disclosed in the aforementioned Japanese Patent Laid-Open No. 9-116107 or the like. . the

In addition, according to the ferroelectric capacitor 100 of the present embodiment, it is possible to lower the crystallization temperature, improve the squareness of hysteresis, and improve Pr. In addition, the improvement of the squareness of the hysteresis by the ferroelectric capacitor 100 has an effect on the disturbance that becomes important by driving the simple matrix type ferroelectric memory device.

Stability has a dramatic effect. In a simple matrix ferroelectric memory device, since a voltage of ±1/3Vs is applied to cells that are not written or read, it is necessary that the polarization does not change at this voltage, that is, the disturbance characteristics are stable. In fact, the inventors of the present application found that in a general PZT, when 10 ⁸ 1/3Vs pulses were applied in the direction of reversing the polarization from a stable state of polarization, the amount of polarization decreased by about 80%, but it was confirmed that According to the ferroelectric capacitor 100 of the present embodiment, the decrease is 10% or less. Therefore, if the ferroelectric capacitor 100 of this embodiment is applied to a ferroelectric memory device, a simple matrix type memory can be put into practical use.

Next, detailed examples of this embodiment will be described. the

[Example 1]

In this example, the PZTN of the present invention is compared with conventional PZT. The film formation process all uses the above-mentioned Figure 2. the

Let Pb:Zr:Ti:Nb=1:0.2:0.6:0.2, 1:0.2:0.7:0.1 and 1:0.3:0.65:0.05. That is, the amount of Nb added is 5 to 20 mol% of the whole. Here, 0-1% of PbSiO ₃ is added.

4A to 4C show the surface structure of the film at this time. In addition, when the crystallinity of this film was measured by the X-ray diffraction method, it was as shown in FIGS. 5A to 5C . In the case of 0% (none) shown in FIG. 5A , even if the crystallization temperature was raised to 800° C., only the paradielectric pyrochlore (Pyrochlore) was obtained. In addition, in the case of 0.5% shown in FIG. 5B , PZT and pyrochlore are mixed. In addition, in the case of 1% shown in FIG. 5C, a PZT (111) single alignment film was obtained. In addition, the crystallinity is also the best that has not been obtained so far. the

Next, for the PZTN thin film added with 1% PbSiO ₃ , when the film thickness is set to 120 to 220 nm, as shown in FIGS. In addition, FIGS. 6A to 6C are electron micrographs showing the surface structure at a film thickness of 120 nm to 200 nm, and FIGS. 7A to 7C show the crystallinity of the PZTN thin film at a film thickness of 120 nm to 200 nm measured by the X-ray diffraction method. result. In addition, as shown in FIGS. 8A to 8C and FIGS. 9A to 9C , hysteresis characteristics with good squareness were obtained over the entire range of the film thickness from 120 nm to 200 nm. In addition, FIGS. 9A to 9C are enlarged views of the hysteresis curves in FIGS. 8A to 8C . In particular, as shown in FIGS. 9A to 9C , in the PZTN thin film of this example, it was confirmed that the hysteresis was sufficiently opened and saturated at a low voltage of 2 V or less.

In addition, as shown in FIG. 10A and FIG. 10B , the leakage characteristic is 5×10 ^-8 to 7×10 ^-9 A/cm when 2 V is applied (at saturation), regardless of the film composition or film thickness. ² , very good.

Next, when the fatigue properties and static impressions of the PbZr _0.2 Ti _0.6 Nb _0.2 O ₃ thin film were measured, they were very good as shown in FIGS. 11A and 11B . In particular, the fatigue characteristics shown in FIG. 11A are very good regardless of whether Pt is used for the upper and lower electrodes.

Furthermore, as shown in FIG. 12 , an attempt was made to form an ozone-TEOS-based SiO ₂ film 605 on a ferroelectric capacitor 600 in which a lower electrode 602 , a PZTN ferroelectric film 603 of this embodiment, and an upper electrode 604 were formed on a substrate 601 . It is known that when conventional PZT is formed into a _SiO2 film by ozone TEOS, hydrogen generated from TEOS passes through the upper Pt to reduce PZT, shows no hysteresis at all, and damages the PZT crystal.

However, as shown in FIG. 13, the PZTN ferroelectric film 603 of this embodiment hardly deteriorates and maintains good hysteresis. That is, it can be seen that the reduction resistance of the PZTN ferroelectric film 603 of this example is strong. In addition, in the tetragonal PZTN ferroelectric film 603 of the present invention, when Nb does not exceed 40 mol%, good hysteresis is obtained corresponding to the amount of Nb added. the

Next, the conventional PZT ferroelectric film was evaluated for comparison. As conventional PZT, Pb:Zr:Ti=1:0.2:0.8, 1:0.3:0.7, and 1:0.6:0.4 are respectively set. Its leakage characteristics are shown in Fig. 14. As the Ti content increases, the leakage characteristics deteriorate. In the case of Ti: 80%, when 2V is applied, it becomes 10 ^-5 A/cm ² , which is not suitable for memory applications. . Likewise, as shown in FIG. 15 , the fatigue properties deteriorate as the Ti content increases. In addition, after the impression, as shown in Fig. 16, it can be seen that basically no data was read.

As can be seen from the above examples, the PZTN ferroelectric film of the present example solves the problems of increased leakage current and deterioration of image characteristics, which were thought to be the essence of PZT in the past. The tetragonal crystal PZT used is used in memory applications. In addition, this material can also be applied to piezoelectric element applications where tetragonal PZT is not used for the same reason. the

[Example 2]

In this example, for the PZTN ferroelectric film, the amount of Nb added was changed to 0.5, 10, 20, 30, and 40 mol % to compare the ferroelectric properties. For all test pieces, 5 mol% _PbSiO3 silicate was added. Further, methyl succinate was added to the ferroelectric film-forming sol-gel solution constituting the film-forming raw material to set the pH to 6. The above-mentioned FIG. 2 was used for all the film formation processes.

17 to 19 show the measurement of the hysteresis characteristics of the PZTN ferroelectric film of this example. the

As shown in FIG. 17A , leakage hysteresis was obtained when the amount of Nb added was 0, but good hysteresis characteristics with high insulation were obtained when the amount of Nb added was 5 mol % as shown in FIG. 17B . the

In addition, as shown in FIG. 18A , substantially no change in the ferroelectric properties was seen until the Nb addition amount was 10 mol %. In the case where the amount of Nb added was 0, although there was leakage, no change was observed in the ferroelectric characteristics. In addition, as shown in FIG. 18B , when the amount of Nb added was 20 mol%, hysteresis characteristics with very good squareness were obtained. the

However, as shown in FIGS. 19A and 19B , when the amount of Nb added exceeds 20 mol %, the hysteresis characteristic changes greatly and deterioration is confirmed. the

Therefore, compare the X-ray diffraction patterns, as shown in FIG. 20 . When the Nb addition amount is 5 mol% (Zr/Ti/Nb=20/75/5), the (111) peak position does not change from that of the conventional PZT film without Nb addition, and increases to 20 as the Nb addition amount increases. Mole % (Zr/Ti/Nb=20/60/20), 40 mole % (Zr/Ti/Nb=20/40/40), (111) peak shifted to the low angle side. That is, it can be seen that the actual crystal becomes a rhombohedral crystal regardless of whether the composition of PZT is Ti-rich in a tetragonal crystal region. In addition, it can be seen that the ferroelectric properties change with the change of the crystal system. the

In addition, after adding 45 mol % of Nb, the hysteresis did not open, and the ferroelectric characteristics could not be confirmed (illustration omitted). the

In addition, it has been described that the PZTN film of the present invention has very high insulating properties, but the conditions for obtaining PZTN as an insulator here are shown in Fig. 21. the

That is, the PZTN film of the present invention has very high insulating properties, and Nb is added to the Ti side at a composition ratio equivalent to twice the amount of Pb defects. In addition, the perovskite crystal can be seen from the crystal structure of WO ₃ shown in FIG. 22 , even if the A-side ion deficiency is 100%, it is established, and the crystal system of WO ₃ is easy to change.

Therefore, in the case of PZTN, by adding Nb, the amount of Pb defects is actively controlled and the crystal system is controlled. the

This shows that the PZTN film of this embodiment is also very effective in application to piezoelectric elements. In general, when PZT is applied to a piezoelectric element, a rhombohedral domain having a Zr-rich composition is used. In this case, Zr-rich PZT is called soft PZT. This, as the text indicates, means crystalline soft. For example, although soft PZT is used in ink ejection nozzles of inkjet printers, it cannot be extruded by applying ink pressure because it is too soft for ink with too high viscosity. the

On the other hand, Ti-rich tetragonal crystal PZT is called hard PZT, which means firm and brittle. However, in the PZTN film of the present invention, it is possible to artificially change the crystal system to a rhombohedral crystal while being hard. Among them, the crystal system can be changed arbitrarily by the amount of Nb added, and since the specific permittivity of the Ti-rich PZT-based ferroelectric film is small, the device can be driven at low voltage. the

Thus, for example, hard PZT, which has not been used until now, can be used in ink ejection nozzles of inkjet printers. In addition, since Nb softens PZT, it is moderately hard and can provide PZT that is not brittle. the

Finally, as described above, in this embodiment, not only Nb is added, but silicate may be added at the same time as Nb, thereby lowering the crystallization temperature. the

[Example 3]

In this embodiment, for example, Pt or Ir used as an electrode material of a ferroelectric capacitor constituting a memory cell portion of a ferroelectric memory, or a piezoelectric actuator constituting an ink ejection nozzle portion of an inkjet printer, etc. The effectiveness of using a PZTN film was investigated from the viewpoint of lattice matching properties when a PZTN film is formed on a metal film composed of a platinum-based metal. When a PZT-based ferroelectric film is applied to a device, the platinum-based metal serves as an underlying film that determines the crystal orientation of the ferroelectric film and is also useful as an electrode material. However, the fatigue properties of the ferroelectric film pose a problem for device applications because the lattice matching properties of both are insufficient. the

Therefore, the inventors of the present application developed a technique for improving the lattice mismatch between the PZT-based ferroelectric film and the platinum-based metal thin film by including Nb in the constituent elements of the PZT-based ferroelectric film. 23A to 23C show the film-forming process of the PZT-based ferroelectric film at this time. the

First, as shown in FIG. 23A , a predetermined substrate 11 is prepared. As the substrate 11, a substrate in which a TiOx layer was formed on an SOI substrate was used. In addition, as the substrate 11 , an appropriate substrate can be selected from substrates made of known materials and used. the

Afterwards, as shown in FIG. 23B, on the substrate 11, for example, a sputtering method is used to form a metal film (first electrode) 102 made of PT. After that, as shown in FIG. 23C, a PZTN film is formed on the metal film 102, as the ferroelectric film 101. As a material for forming the PZTN film, for example, a sol-gel solution can be used. More specifically, a solution in which a sol-gel solution for PbNbO ₃ was further added to a solution in which a sol-gel solution for PbZrO ₃ , a sol-gel solution for PbTiO _{3 , and a sol-gel solution for PbNbO 3 was} mixed was used. In addition, since the PZTN film contains Nb as a constituent element, its crystallization temperature is high. Therefore, in order to lower the crystallization temperature, it is preferable to use a solution in which a sol-gel solution for PbSiO ₃ is further added. In this embodiment, the above-mentioned sol-gel solution is coated on the Pt metal film 102 by a spin coating method, and after a predetermined heat treatment is performed, crystallization is performed. The flow of the film forming process is the same as that shown in FIG. 2 .

In this example, for the PZTN film in which the amount of Nb added was in the range of 0 mol % to 30 mol %, the lattice constant of the crystal was measured by the X-ray diffraction method as shown in FIGS. 24A and 24B . From FIGS. 24A and 24B , it can be seen that the larger the amount of Nb added, the closer the lattice constant on the a-axis (or b-axis) is to the lattice constant on the c-axis. In addition, V(abc) in FIG. 24A is an index obtained by changing the volume of lattice constants (a, b, c). In addition, V/V ₀ in FIG. 24A is the ratio of V(abc) of the PZTN crystal to the exponent V ₀ of the volume conversion index V 0 of the lattice constant of the PZT crystal to which Nb is not added. In this way, it can also be confirmed from the columns of V(abc) or V/V ₀ that the crystal lattice of PZTN crystals becomes smaller as the amount of Nb added increases.

In addition, Fig. 25 shows the calculation of the lattice mismatch rate with the lattice constant (a, b, c+3.96) of the Pt metal film from the lattice constant of the PZTN film formed after adding Nb in this way. The added amount (mol %) is a graph plotted on the horizontal axis. According to FIG. 25, the effect of adding Nb to the PZT-based ferroelectric film is not only the effect of improving the ferroelectric characteristics in the above-mentioned examples, but also the effect of the lattice constant close to that of platinum-based metal crystals such as Pt. In particular, it was confirmed that this effect is remarkably exhibited in the range where the amount of Nb added is 5 mol or more. the

Therefore, if the method of the present invention is used, the lattice mismatch between the metal film as the electrode material and the ferroelectric film is reduced. For example, when the addition amount of Nb is 30 mol%, it is confirmed that the lattice mismatch ratio is improved to 2% or so. It is considered that in the crystal structure of PZTN, the Nb atom replacing the Ti atom on the B side and the O atom have a strong bond with both ionic bonding and shared bonding, and this bonding force acts in the direction of compressing the crystal lattice. , the lattice constant changes to a smaller direction. the

In addition, platinum-based metals such as Pt are chemically stable substances, and are suitable for electrode materials of ferroelectric memories or piezoelectric actuators. According to the method of this embodiment, even if a PZTN film is directly formed on the Pt metal film, it can also be used on the Pt metal film. The interface properties are improved while relieving the lattice mismatch more than before. Therefore, the method of this embodiment can reduce the fatigue characteristics of the PZT ferroelectric film, and is also suitable for the application of components such as ferroelectric memories or piezoelectric actuators. the

(reference example)

In this example, a PbZr _0.4 Ti _0.6 O ₃ ferroelectric film is produced.

In the conventional method, a solution containing excessively about 20% of Pb is used for the purpose of suppressing volatilization of Pb and lowering the crystallization temperature. However, it is not known how excessive Pb is in the obtained thin film, but it should be suppressed with the minimum excess amount of Pb. the

Therefore, sol-gel solutions (solvent: n-butanol) for forming PbZr _0.4 Ti _0.6 O ₃ with a concentration of 10% by weight with an excess of Pb of 0.5, 10, 15, and 20% (solvent: n-butanol) were used, and 1 mol% of 10% by weight was added. % concentration of PbSiO ₃ formation sol-gel solution ( _solvent : n-butanol), each step _ST20 ~ step _ST25 shown in FIG. The surface structure at this time is shown in FIGS. 27A to 27C , and the XRD patterns are shown in FIGS. 28A to 28C .

Conventionally, an excess of about 20% of Pb was required, but an excess of 5% of Pb showed that crystallization proceeded sufficiently. This represents only 1 mol% _PbSiO3 catalyst, in order to lower the crystallization temperature of PZT, the excess Pb basically disappears. Hereafter, 5% Pb-excess solutions were all used as PZT, PbTiO ₃ , and PbZrTiO ₃ forming solutions.

Next, a sol-gel solution for forming PbZrO ₃ at a concentration of 10% by weight (solvent: n-butanol) and a sol-gel solution for forming PbTiO ₃ at a concentration of 10% by weight (solvent: n-butanol) mixed at a ratio of 4:6 (solvent: n-butanol) solution, add 1 mol% 10% by weight concentration of PbSiO ₃ forming a sol-gel solution (solvent: n-butanol) mixed solution, according to the flow chart in Figure 2, to produce 200nm ~ PbZr _0.4 Ti _0.6 O ₃ ferroelectric film. The hysteresis characteristic at this time is as shown in Fig. 29A and Fig. 29B, and the squareness is good. However, it turns out that it leaks at the same time.

In addition, for comparison, in the conventional method, using the flow chart of FIG. 26 , using a sol-gel solution (solvent: n-butanol) for forming PbZr _0.4 Ti _0.6 O ₃ at a concentration of 10% by weight, adding 1 A mixed solution of a sol-gel solution (solvent: n-butanol) is used to form a PbSiO ₃ with a concentration of 10% by weight by mole %, and a 200nm-PbZr _0.4 Ti _0.6 O ₃ ferroelectric film is produced. At this time, the hysteresis characteristic is as shown in Fig. 30, and good hysteresis is not provided.

Therefore, after degassing analysis was performed using each ferroelectric film, as shown in FIGS. 31A and 31B . the

As shown in FIG. 31A , the outgassing associated with H or C was always confirmed for the conventional ferroelectric film fabricated using the PZT sol-gel solution with respect to the temperature rise from room temperature to 1000°C. the

On the other hand, as shown in FIG. 31B , when a sol-gel solution (solvent: n-butanol) for forming PbZrO ₃ at a concentration of 10 wt % and a concentration of PbTiO ₃ for forming 10 wt % were mixed at a ratio of 4:6, When using the ferroelectric film of the present invention as a solution of a sol-gel solution (solvent: n-butanol), it was found that there was substantially no outgassing before decomposition.

This _is considered to be achieved by using a sol-gel solution for forming PbZrO ₃ at a concentration of 10% by weight (solvent: n-butanol) and a sol-gel solution for forming PbTiO at a concentration of 10% by weight (solvent : n-butanol) solution, first use the 10% by weight concentration _of PbTiO in the mixed solution to form a sol-gel solution (solvent: n-butanol), and PbTiO ₃ crystallizes on Pt, which becomes the crystallization initial nucleus , Moreover, eliminating the lattice mismatch between Pt and PZT, PZT is easy to crystallize. Also, it is considered that by using a mixed solution, PbTiO ₃ and PZT are continuously formed at a good interface, which is associated with good squareness of hysteresis.

2. Manufacturing method of ferroelectric capacitor

32A to 32C are cross-sectional views schematically showing an example of the manufacturing process of the ferroelectric capacitor according to the embodiment of the present invention. the

(1) First, as shown in FIG. 32A , the lower electrode 102 , the ferroelectric film 101 , and the upper electrode 103 are sequentially stacked on a predetermined substrate 110 . the

As the substrate 110 , for example, a substrate suitable for use in ferroelectric capacitors, such as a semiconductor substrate and a resin substrate, can be used without any particular limitation. the

As the lower electrode 102 and the upper electrode 103 , for example, electrodes composed of a single noble metal such as Pt, Ir, and Ru, or a composite material mainly composed of the noble metal can be used. In addition, the lower electrode 102 and the upper electrode 103 can be formed using, for example, a known film-forming method such as a sputtering method or a deposition method. In addition, when the constituent elements of the ferroelectric diffuse to the lower electrode 102 and the upper electrode 103, compositional fluctuations will occur at the interface between the electrode and the ferroelectric film 101, and the squareness of the hysteresis will decrease. Therefore, it is desirable that the lower electrode 102 and the upper electrode 103 Density with no diffusion of the constituent elements of the ferroelectric. Therefore, in order to improve the densification of the lower electrode 102 and the upper electrode 103, a method of sputtering a heavy gas into a film, or a method of dispersing oxides such as Y and La in noble metal electrodes, etc. can be used. the

The ferroelectric film 101 is a so-called PZTN composite oxide containing Pb, Zr, Ti, and Nb as constituent elements. In addition, the ferroelectric film 101 can be formed by applying a sol-gel solution containing Pb, Zr, Ti, and Nb on the lower electrode 102, for example, using a spin coating method or the like. As such a sol-gel solution, a solution obtained by mixing the first sol-gel solution, the second sol-gel solution, and the third sol-gel solution can be used, wherein the first sol-gel solution is to form a Pb- and Zr-based A solution in which PbZrO ₃ perovskite is crystallized and the condensation polymer is dissolved in a solvent such as n-butanol in an anhydrous state. The second sol-gel solution is to form PbTiO based on Pb and Ti among the constituent metal elements of the PZTN ferroelectric phase. _3. A solution in which perovskite crystals are dissolved in a solvent such as n-butanol in an anhydrous state. The 3rd sol-gel solution is to form PbNbO ₃ based on Pb and Nb among the constituent metal elements of the PZTN ferroelectric phase. A solution in which perovskite is crystallized and the polycondensate is dissolved in a solvent such as n-butanol in an anhydrous state. In addition, when forming the ferroelectric film 101, in order to lower the crystallization temperature of the PZTN composite oxide, a sol-gel solution containing silicate or germanate may be added. Specifically, a fourth sol-gel solution may be added to the above-mentioned mixed sol-gel solution at, for example, 1 mol% or more and less than ₅ mol%. A solution in which the polycondensate is dissolved in a solvent such as n-butanol in a state. By mixing such a fourth sol-gel solution, it is possible to crystallize in a temperature range where the crystallization temperature of the PZTN composite oxide whose crystallization temperature is increased by containing Nb as a constituent element is 700 degrees or less and can be deviceized.

In addition, it is preferable that ferroelectric film 101 temporarily heat-treats this coating film at a temperature (for example, 400 degrees or less) at which the PZTN composite oxide does not crystallize in an oxidizing atmosphere, so that the PZTN composite oxide becomes amorphous. Therefore, since the ferroelectric film 101 is in an amorphous state, grain boundaries do not exist, and the steps described later can be advanced while preventing diffusion of constituent elements. In addition, performing this temporary heat treatment in an oxidizing atmosphere also serves to introduce into the ferroelectric film 101 an oxygen component required to crystallize the PZTN composite oxide after formation of the protective film described later. the

(2) Next, as shown in FIG. 32B, the lower electrode 102, the ferroelectric film 101, and the upper electrode 103 are etched, processed into a desired shape, and a protective film 104 made of a SiO ₂ (silicon oxide) film is formed to cover the Lower electrode, ferroelectric film and upper electrode. The protective film 104 at this time can be formed by a CVD method using trimethylsilane (TMS). Trimethylsilane (TMS) generates less hydrogen in the CVD process than tetraethylorthosilicate (TEOS) generally used for silicon oxide film formation. Therefore, if trimethylsilane (TMS) is used, the process damage caused by the reduction reaction of the ferroelectric film 101 can be reduced. In addition, because the formation process of the protective film 104 using trimethylsilane (TMS) can be carried out at a low temperature (room temperature to 350 degrees) compared with the formation process using TEOS (the formation temperature is 400 degrees or higher), so in (1) process In the case where the ferroelectric film 101 is formed in an amorphous state, crystallization of the PZTN composite oxide due to heat generated during the formation process of the protective film 104 can be prevented, and the amorphous state can be maintained.

(3) Next, as shown in FIG. 32C, a heat treatment is performed to crystallize the PZTN composite oxide constituting the ferroelectric film 101 to obtain a ferroelectric capacitor having the PZTN ferroelectric crystal film 101a. In this heat treatment, the PZTN composite oxide can be crystallized not only in an oxygen atmosphere but also in a non-oxidizing gas atmosphere such as Ar or N ₂ or in the air.

Here, when applying the production method of this embodiment to form a SiO ₂ protective film using TMS on a ferroelectric capacitor composed of a PZTN ferroelectric film and a Pt upper electrode, it was measured that after the formation of such a SiO ₂ protective film, The results of capacitive hysteresis characteristics in the case of crystallizing the PZTN ferroelectric after heat treatment in an oxygen atmosphere and in the air are shown in FIGS. 33A and 33B . FIG. 33A shows the case where the heat treatment is performed in an oxygen atmosphere, and FIG. 33B shows the case where the heat treatment is performed in the air. According to FIG. 33A and FIG. 33B , when the heat treatment is performed in either the oxygen atmosphere or the air atmosphere, hysteresis characteristics with good squareness can be obtained even though no hydrogen-resistant barrier film is formed. This is because when the ferroelectric film 101 is formed, a preliminary heat treatment is performed in an oxidizing atmosphere, so oxygen necessary for crystallization is introduced into the film in advance. That is, in the manufacturing method of this embodiment, the crystallization of the ferroelectric can be performed independently of the atmosphere of the heat treatment. And, in the case where the heat treatment for crystallization is carried out in a non-oxidizing gas atmosphere, in the case of applying to the manufacturing method of the ferroelectric memory described later, etc., damage to peripheral components (such as metal wiring) other than capacitors can be prevented. Oxidative damage caused by high temperature heat treatment. In addition, since the heat treatment for crystallization of the PZTN composite oxide in this process is less dependent on the gas species in the atmosphere, it is also possible to form a metal structure for connecting the upper electrode 103 to the outside in the protective film 104 . The contact hole of the line is carried out after that.

In addition, a SiO ₂ protective film using TMS is formed on a ferroelectric capacitor composed of a Pt lower electrode, a PZTN ferroelectric film, and a Pt upper electrode to which the manufacturing method of this embodiment is applied, and after the SiO ₂ protective film is formed, For the crystallized PZTN ferroelectric, the hysteresis characteristics were measured when the _SiO2 protective film was formed at room temperature, 125 degrees, and 200 degrees, and as a comparative example, the crystallized PZTN ferroelectric film was not formed with a _SiO2 protective film. Figure 34 shows the hysteresis characteristics and the measurement of the change in the value of the remanent polarization 2Pr. According to FIG. 34 , even when the SiO ₂ protective film was formed at any temperature of room temperature, 125°C, or 200°C, there was no change in the residual polarization 2Pr, and it was confirmed that the value was not inferior to that obtained when the SiO ₂ protective film was formed. That is, in the manufacturing method of the present embodiment, even if the ferroelectric film 101 is damaged by hydrogen generated during the process when the protective film 104 is formed, it is possible to recover after heat treatment for crystallization of the PZTN composite oxide. At the same time as this damage, the PZTN composite oxide is crystallized, so the formation process of the barrier film that was necessary to protect the ferroelectric film 101 from the reduction reaction can be omitted, and the productivity can be improved and the production cost can be reduced.

3. Ferroelectric memory

35A and 35B are diagrams showing the configuration of a simple matrix ferroelectric memory device 300 according to an embodiment of the present invention. Fig. 35A is a plan view, and Fig. 35B is a cross-sectional view along line A-A of Fig. 35A. As shown in FIGS. 35A and 35B , the ferroelectric memory device 300 has a predetermined number of word lines 301 to 303 and a predetermined number of bit lines 304 to 306 formed on a substrate 308 . Between the word lines 301 to 303 and the bit lines 304 to 306, the ferroelectric film 307 made of PZTN described in the above embodiment is inserted to form a ferroelectric film capacitor. the

In the ferroelectric memory device 300 in which the memory cells constituted by this simple matrix are arranged, a peripheral drive circuit, a readout amplifier circuit, etc. (not shown in the figure) (referred to as a peripheral circuit) are used to perform pairing formed on the word line 301. Writing and reading of the ferroelectric capacitors in the crossing regions of 303 and bit lines 304-306. The peripheral circuit is formed on a substrate other than the memory cell array by MOS, and connected to the word lines 301-303 and bit lines 304-306, or the peripheral circuit can be integrated by using a single crystal silicon substrate as the substrate 308. On the same substrate as the memory cell array. the

36 is a cross-sectional view showing an example of a ferroelectric memory device 300 in which a memory cell array and peripheral circuits are commonly integrated on the same substrate in this embodiment. the

In FIG. 36, a MOS transistor 402 is formed on a single crystal silicon substrate 401, and this transistor formation region constitutes a peripheral circuit portion. The MOS transistor 402 is composed of a single crystal silicon substrate 401 , a source/drain region 405 , a gate insulating film 403 and a gate electrode 404 . the

In addition, the ferroelectric memory device 300 has an oxide film 406 for element isolation, a first interlayer insulating film 407 , a first wiring layer 408 , and a second interlayer insulating film 409 . the

In addition, the ferroelectric memory device 300 has a memory cell array composed of ferroelectric capacitors 420, and the ferroelectric memory 420 has a lower electrode (first electrode or second electrode) 410 constituting a word line or a bit line, including a ferroelectric phase It consists of a ferroelectric film 411 in a paraelectric phase, and an upper electrode (second electrode or first electrode) 412 formed on the ferroelectric film 411 and constituting a bit line or a word line. the

Furthermore, the ferroelectric memory device 300 has a third interlayer insulating film 413 on the ferroelectric capacitor 420 , and the memory cell array and peripheral circuits are connected by a second wiring layer 414 . In the ferroelectric memory device 300 , a protective film 415 is formed on the third interlayer insulating film 413 and the second wiring layer 414 . the

According to the ferroelectric memory device 300 having the above configuration, the memory cell array and the peripheral circuit unit can be integrated on the same substrate. In addition, the ferroelectric memory device 300 shown in FIG. 36 has a structure in which a memory cell array is formed on the peripheral circuit portion, but it may also be configured such that the memory cell array is not disposed on the peripheral circuit portion, and the memory cell array and the peripheral circuit portion are in planar contact. . the

Since the ferroelectric capacitor 420 used in this embodiment is composed of the PZTN of the above-mentioned embodiment, the squareness of hysteresis is very good and has stable disturbance characteristics. In addition, since the ferroelectric capacitor 420 has less damage to other elements such as peripheral circuits due to lower processing temperature, and has less processing damage (especially hydrogen reduction), deterioration of hysteresis due to damage can be suppressed. Therefore, by using such a ferroelectric capacitor 420, the simple matrix ferroelectric memory device 300 can be put into practical use. the

In addition, FIG. 37A shows a configuration diagram of a 1T1C type ferroelectric memory device 500 as a modified example. FIG. 37B is an equivalent circuit diagram of the ferroelectric memory device 500 . the

As shown in FIG. 37A, a ferroelectric memory device 500 is a capacitor 504 (1C) composed of a lower electrode 501, an upper electrode 502 connected to a plate line, and a ferroelectric film 503 to which the PZTN ferroelectric of this embodiment is applied. A memory element having a structure similar to a DRAM, composed of a switching transistor element 507 (1T) connected to a data line 505 with one of source/drain electrodes connected to a word line and having a gate electrode 506 connected to a word line. The 1T1C type memory can be written and read at a high speed of 100 ns or less, and since the written data is not easily lost, it is expected to replace the SRAM or the like. the

4. Manufacturing method of ferroelectric memory

Next, a case where the manufacturing method described in the column "2. Manufacturing method of a ferroelectric capacitor" is applied to a manufacturing method of a ferroelectric memory will be described. the

38A to 38C are cross-sectional views schematically showing an example of the manufacturing process of the ferroelectric memory according to the embodiment of the present invention. the

In this embodiment, first, as shown in FIG. 38A , lower electrode 102 , PZTN ferroelectric film 101 , and upper electrode 103 of ferroelectric capacitor 100 are sequentially formed on base 110 . At this time, the PZTN ferroelectric film 101 becomes amorphous after being temporarily heat-treated in an oxidizing atmosphere. In addition, as the base 100, for example, as shown in FIG. 38A, a base in which a transistor 116 for cell selection is formed on a semiconductor base 111 can be used. The transistor 116 may have a source/drain 113 , a gate oxide film 114 , and a gate electrode 115 . Also, on one source/drain 113 of the transistor 116, a plug electrode 117 made of tungsten or the like is formed, and a stacked structure capable of being connected to the lower electrode 102 of the ferroelectric capacitor 100 can be employed. In addition, in the base body 110, the transistor 116 is isolated for each cell by the element isolation region 112 between cells, and an interlayer insulating film 118 made of, for example, an oxide film may be provided above the transistor 116. the

Next, in the manufacturing process of this embodiment, as shown in FIG. 38B , ferroelectric capacitor 110 is patterned into a desired size and shape. Afterwards, use trimethylsilane (TMS) to form a protective film 104 made of _SiO to cover the ferroelectric capacitor 100, and after forming a contact hole 105 for external connection therein, heat treatment is performed to crystallize the PZTN ferroelectric material to form a PZTN ferroelectric film 101a. When crystallizing the PZTN ferroelectric, heat treatment for crystallization can be performed in a non-oxidizing atmosphere. Accordingly, it is possible to prevent oxidation damage caused by high-temperature heat treatment to peripheral components other than ferroelectric capacitor 100 (for example, metal wiring) and the like.

Finally, as shown in FIG. 38C , a contact hole for connecting the transistor 116 to the dining portion is formed in the SiO ₂ protective film 104 , and metal wiring layers 191 and 192 are formed to obtain a ferroelectric memory. According to the manufacturing process of this embodiment, it is possible to omit the formation process of the barrier film for protecting the ferroelectric film 101 from the reduction reaction, which was necessary in the past, so that the productivity can be improved and the production cost can be reduced. In addition, since the ferroelectric capacitor 100 having good square hysteresis characteristics can be formed even if such barrier film forming process is omitted, a ferroelectric memory with good characteristics can be obtained.

In addition, the manufacturing process of a so-called 1T1C type ferroelectric memory has been described above, but the method of manufacturing a ferroelectric capacitor according to this embodiment can also be applied to a so-called 2T2C type or a simple matrix type (cross-point type) using various cell systems. In the manufacturing process of ferroelectric memory. the

5. Piezoelectric element and inkjet recording head

Next, the ink jet type recording head in the embodiment of the present invention will be described in detail. the

In the ink jet type recording head, a vibrating plate constitutes a part of a pressure generating chamber communicating with a nozzle opening from which ink droplets are ejected, and the vibrating plate is deformed by a piezoelectric element to pressurize the ink in the pressure generating chamber to thereby The nozzle opening ejects ink droplets, and the inkjet recording head using the piezoelectric actuator in the longitudinal vibration mode that expands and contracts in the axial direction of the piezoelectric element, and the inkjet recording head using the piezoelectric actuator in the bending vibration mode, etc. two kinds. the

In addition, as an inkjet type recording head using an actuator in a bending vibration mode, for example, it is known to form a uniform piezoelectric layer on the entire surface of the vibrating plate by a film-forming technique, and to form the piezoelectric layer by photolithography. It is divided into shapes corresponding to the pressure generating chambers, and piezoelectric elements are formed independently for each pressure generating chamber. the

39 is a schematic exploded perspective view showing an ink jet recording head according to an embodiment of the present invention. FIGS. 40A and 40B are a plan view and an AA' sectional view of FIG. schematic diagram. As shown in the figure, the channel-forming substrate 10 is composed of a plane-oriented (110) single-crystal silicon substrate in this embodiment, and on one of its planes is formed a silicon dioxide layer with a thickness of 1mm formed by thermal oxidation in advance. Elastic membrane 50 of ~2 microns. In the flow path forming substrate 10, a plurality of pressure generating chambers 12 are arranged side by side along the width direction thereof. In addition, in the region of the pressure generating chamber 12 of the flow path forming substrate 10 in the lengthwise outer direction, a communication portion 13 is formed, which communicates with each pressure generating chamber 12 via an ink supply path 14 provided for each pressure generating chamber 12. with. In addition, the communicating portion 13 communicates with the reservoir portion 32 of the sealing substrate 30 described later, and constitutes a part of the reservoir 800 forming a common ink chamber for the pressure generating chambers 12 . The ink supply path 14 is formed narrower than the pressure generating chamber 12 , and keeps constant the flow path resistance of the ink flowing from the communication portion 13 into the pressure generating chamber 12 . the

In addition, on the opening surface side of the flow path forming substrate 10, the nozzle opening 21 penetrating and communicating with the end portion on the side opposite to the ink supply path 14 of each pressure generating chamber 12 is fixed via an adhesive, a heat-melt film, or the like. The nozzle plate 20. the

On the other hand, on the opposite side of the opening surface of the flow path forming substrate 10, as described above, an elastic film 50 having a thickness of about 1.0 microns is formed, and on this elastic film 50, a film having a thickness of about 0.4 microns is formed. insulator film 55 . Further, on this insulator film 55, a lower electrode film 60 having a thickness of approximately 0.2 micrometers, a piezoelectric layer 70 having a thickness of approximately 1.0 micrometers, and an upper electrode film 80 having a thickness of approximately 0.05 micrometers are stacked by a process described later. , to constitute the piezoelectric element 700. Here, the piezoelectric element 700 refers to a portion including the lower electrode film 60 , the piezoelectric layer 70 , and the upper electrode film 80 . Usually, one of the electrodes of the piezoelectric element 700 is used as a common electrode, and the other electrode and the piezoelectric layer 70 are patterned for each pressure generating chamber 12 . In addition, here, a portion constituted by one of the patterned electrodes and the piezoelectric layer 70 and subjected to piezoelectric deformation by applying a voltage to both electrodes is referred to as a piezoelectric active portion. In this embodiment, the lower electrode film 60 is used as a common electrode of the piezoelectric element 700, and the upper electrode film 80 is used as an individual electrode of the piezoelectric element 700. It doesn't matter. In either case, the piezoelectric active portion may be formed for each piezoelectric generating chamber. Here, the piezoelectric element 700 and the vibrating plate that is displaced by driving the piezoelectric element 700 are collectively referred to as a piezoelectric actuator. In addition, the piezoelectric layer 70 is independently provided for each pressure generating chamber 12, and is composed of a multilayer ferroelectric film 71 (71a to 71f) as shown in FIG. 40 . the

The inkjet recording head constitutes a part of a recording head unit having an ink flow path communicating with an ink cartridge or the like, and is mounted on an inkjet recording apparatus. FIG. 42 is a schematic diagram showing an example of the ink jet recording device. As shown in FIG. 42, recording head units 1A and 1B having ink jet type recording heads are detachably provided with chucks 2A and 2B constituting ink supply units, and carriages 3 loading the recording head units 1A and 1B are axially moved. It is freely movably installed on the bracket shaft 5 mounted on the device main body 4 . The recording head units 1A and 1B eject, for example, a black ink composition and a color ink composition, respectively. In addition, the carriage 3 carrying the recording head units 1A and 1B is moved along the carriage shaft 5 by transmitting the driving force of the driving motor 6 to the carriage 3 through a plurality of gears and a timing belt 7 not shown. On the other hand, a platen 8 is provided along the carriage shaft 5 on the apparatus main body 4 , and a recording sheet S as a recording medium such as paper fed by a paper feed roller (not shown) is conveyed on the platen 8 . the

In addition, an inkjet type recording head that ejects ink is described as an example of a liquid ejection head, but the present invention may also be a liquid ejection head using a piezoelectric element and a liquid ejection device as a whole. Examples of liquid ejection heads include recording heads used in image recording devices such as printers, color material ejection heads used in the manufacture of color filters such as liquid crystal displays, and electrodes used in electrode formation such as organic EL displays and FEDs (surface emission displays). Material injection head, bio-organic matter injection head used in biochip manufacturing, etc. the

In the piezoelectric element of this embodiment, since the PZTN film of the above-mentioned embodiment is used for the piezoelectric layer, the following effects are obtained. the

(1) The piezoelectric constant is increased by increasing the shared bonding property in the piezoelectric layer. the

(2) Since PbO defects in the piezoelectric layer can be suppressed, the generation of heterogeneous phases in the interface between the piezoelectric layer and the electrode is suppressed, an electric field is easily applied, and the efficiency as a piezoelectric element is improved. the

(3) Since the leakage current of the piezoelectric layer is suppressed, the piezoelectric layer can be thinned. the

In addition, since the liquid ejection head and the liquid ejection device according to the present embodiment use the piezoelectric element including the above-mentioned piezoelectric layer, the following effects can be obtained particularly. the

(4) Since the deterioration of the fatigue of the piezoelectric layer can be reduced, the temporal change of the displacement amount of the piezoelectric layer can be suppressed and the reliability can be improved. the

The best embodiments of the present invention have been described above, but the present invention is not limited thereto and can be implemented in various embodiments within the scope of the spirit of the invention. the

For example, on the ferroelectric film 101, even if Ta, W, V, and Mo are added as additives instead of Nb to PZT, the same effect can be obtained. In addition, even if Mn is used as an additive, it can have the same effect as Nb. In addition, based on the same consideration, in order to prevent Pb from escaping, it is also considered to replace Pb with an element with a valence of +3 or more. As a substitute, there are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy , Ho, Er, Tm, Yb and Lu and other lanthanides. In addition, germanate (Ge) may be used instead of silicate (Si) as an additive for promoting crystallization. FIG. 43A shows hysteresis characteristics when 10 mol% of Ta is used instead of Nb as an additive to PZT. FIG. 43B shows hysteresis characteristics when 10 mol% of W is used instead of Nb as an additive to PZT. It can be seen that the same effect as that of adding Nb can be obtained also in the case of using Ta. In addition, it was found that the use of W has the same effect as that of adding Nb in terms of obtaining hysteresis characteristics with good insulation. the

Claims (17)

1. strong dielectric film is by AB _1-XNb _XO ₃General formula represent, wherein,

At least contain Pb as the A element,

Constitute by more than at least a among Zr, Ti, V, W, Hf and the Ta as the B element,

0.1≤x≤0.4。

2. strong dielectric film according to claim 1, wherein,

0.1≤x≤0.3。

3. strong dielectric film according to claim 1, wherein,

0.1≤x≤0.2。

4. strong dielectric film according to claim 1, wherein,

0.2≤x≤0.3。

5. strong dielectric film according to claim 1, wherein,

0.2≤x≤0.4。

6. strong dielectric film according to claim 1, wherein,

0.3≤x≤0.4。

7. according to each the described strong dielectric film in the claim 1～6, wherein,

Described strong dielectric film be Ti ratio of components Zr form many and Ti formed in 2.5 moles of 40 moles of PZT class strong dielectric films that are replaced as Nb below the % more than the %, comprise the Si more than 0.5 mole of %.

8. strong dielectric film according to claim 7, wherein,

Described Si is more than 0.5 mole of %, less than 5 moles of %.

9. according to each the described strong dielectric film in the claim 1～6, wherein,

Described strong dielectric film be Ti ratio of components Zr form many and Ti formed in 2.5 moles of 40 moles of PZT class strong dielectric films that are replaced as Nb below the % more than the %, comprise Si and Ge more than 0.5 mole of %.

10. the manufacture method of strong dielectric film according to claim 9, wherein,

Described Si and Ge are more than 0.5 mole of %, less than 5 moles of %.

11. according to each the described strong dielectric film in the claim 1～6, wherein,

Described strong dielectric film is that Ti ratio of components Zr forms many and with 2.5 moles of 40 moles of PZT class strong dielectric films that are replaced as Nb below the % more than the % in the Ti composition, has at least a crystal structure of tetragonal system and rhombohedral system.

12. a ferroelectric memory device uses each described strong dielectric film in the claim 1～11.

13. a semiconductor element uses each described strong dielectric film in the claim 1～11.

14. a piezoelectric element uses each described strong dielectric film in the claim 1～11.

15. a piezoelectric-actuator uses the described piezoelectric element of claim 14.

16. a jet head liquid uses the described piezoelectric-actuator of claim 15.

17. a printer uses the described jet head liquid of claim 16.

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