Ferroelectric material and ferroelectric capacitor

Abstract

To provide a ferroelectric material with a base material of HfO2 with a stabilized polarization characteristic and a ferroelectric capacitor using the ferroelectric material.SOLUTION: A ferroelectric material according to the invention has a base material of HfO2 to which a first element that forms an ion with a valence of 3+ and a second element that forms an ion with a valence of 5+ are added such that an average valence is between 3.98+ and 4.02+. A ferroelectric capacitor according to the invention has a ferroelectric layer containing the ferroelectric material formed between an upper electrode and a lower electrode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a ferroelectric material and a ferroelectric capacitor that are suitable for use in semiconductor devices that are made of hafnium oxide (HfO2) as a base material and have a ferroelectric. [Background technology]

[0002] HfO2-based ferroelectrics have been attracting attention as a new ferroelectric material following existing perovskite-based ferroelectrics such as Pb(Zr,Ti)O3 (PZT) and SrBi2Ta2O9 (SBT). The ferroelectric properties of HfO2-based ferroelectrics were first reported in 2011, and HfO2 doped with Y, La, Al, Zr, etc. are known (see, for example, Non-Patent Document 1). The HfO2-based ferroelectrics are highly compatible with the manufacturing process of semiconductor devices, and have the property that their ferroelectricity does not deteriorate even when they are thinned. Therefore, they are expected to be applied to semiconductor devices that use ferroelectrics, such as ferroelectric-gate field-effect transistors (FeFETs) and ferroelectric random access memories (FeRAMs).

[0003] However, it has been reported that the HfO2-based ferroelectrics, unlike the perovskite-based ferroelectrics, are subject to degradation of polarization characteristics such as wake-up and polarization fatigue (see Non-Patent Document 2). The wake-up and polarization fatigue mean that the spontaneous polarization changes significantly with the progress of the rewriting process, resulting in unstable polarization characteristics. In other words, the current HfO2-based ferroelectrics have a problem in that they are unable to provide polarization characteristics similar to those of the perovskite-based ferroelectrics. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] TS Boscke, et. al., APL 99, 102903 (2011) [Non-patent document 2] AG Chernikova, et al., ACS Appl. Mater. Interfaces 10, 2701-2708 (2018) [Non-patent document 3] Hiroshi Funakubo et al., Applied Physics, Vol. 87, No. 12 (2018) [Non-patent document 4] Akira Toriumi, Applied Physics, Vol. 88, No. 9 (2019) [Non-patent document 5] M. Hoffman, et. al., JAP 118, 072006 (2015) Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to solve the above-mentioned problems in the prior art and to achieve the following object: That is, the present invention aims to provide a ferroelectric material having stabilized polarization characteristics while using HfO2 as a base material, and a ferroelectric capacitor using the ferroelectric material.

[0006] In order to solve the above problems, the present inventors have conducted extensive research and have obtained the following findings.

[0007] It has been reported that the ferroelectricity of the HfO2-based ferroelectrics is derived from the crystal structure of an orthorhombic crystal (space group: Pca21) that does not have centrosymmetrical symmetry (see Non-Patent Documents 3 and 4). It has also been reported that the orthorhombic crystal structure is stabilized when the number of oxygen vacancies in the crystal increases (see Non-Patent Document 5). In other words, it is believed that the presence of the oxygen vacancies plays an important role in stabilizing the orthorhombic crystal structure in the HfO2-based ferroelectrics.

[0008] On the other hand, the problems of wake-up and polarization fatigue are thought to be caused by changes in the arrangement of the oxygen vacancies in the crystal depending on the number of times the rewriting process is performed through the application of an electric field. In other words, the oxygen vacancies are thought to be the origin of the ferroelectricity in the HfO2-based ferroelectric material, but at the same time, they are also thought to present a dilemma by causing the problems of wake-up and polarization fatigue.

[0009] Now, let us assume that the stabilization of the orthorhombic crystal in the HfO2-based ferroelectric is brought about not by the oxygen vacancies themselves but by the crystal distortion caused by the oxygen vacancies. If this crystal distortion itself is the key to stabilizing the orthorhombic crystal, the orthorhombic crystal should be stabilized only by the crystal distortion, regardless of the oxygen vacancies.

[0010] Based on this assumption, the present inventors investigated the co-doping of two types of elements with different valences into the HfO2 base material in order to impart the crystal distortion not due to the oxygen vacancies. That is, the inventors considered that the two types of elements co-doped in the HfO2 matrix have different valences, which causes local inhomogeneity in the crystal, and gives rise to the crystal distortion not due to the oxygen vacancies. 4+ is equivalent to 4 + If the charge balance is maintained, some of the atoms of the two types of elements will be separated into Hf atoms (Hf 4+ ), the orthorhombic crystal structure of the HfO2 matrix is ​​maintained, and thus the stabilized orthorhombic crystal structure can be obtained without the presence of oxygen vacancies.

[0011] The present inventors' reasoning will be explained with reference to Figures 1 and 2. Figure 1 is an explanatory diagram that schematically shows the crystals in a conventional HfO2-based ferroelectric, and Figure 2 is an explanatory diagram that schematically shows the crystals in a new ferroelectric that the present inventors have devised. In conventional HfO2-based ferroelectrics, as shown in Figure 1, in the crystalline regions indicated by circles containing oxygen vacancies, the oxygen vacancies distort the surrounding lattice, resulting in the crystal distortion that does not exist in crystalline regions that do not contain oxygen vacancies. This stabilizes the orthorhombic crystals in the HfO2 base material, and the ferroelectricity resulting from the orthorhombic crystals is expressed. On the other hand, in the new ferroelectric material proposed by the present inventors, as shown in Figure 2, the crystal distortion due to the local charge imbalance occurs in the crystal region indicated by the ellipse containing the ions of the two types of co-doped elements, and the ferroelectricity is manifested due to the stabilized orthorhombic crystal structure, regardless of the oxygen vacancies. Here, the two types of co-doped elements have a valence of 3. + The type of element that forms ions of (A 3+ ) and valence 5 + The type of element that forms ions of (B 5+ ) In other words, by replacing some of the Hf atoms constituting the HfO2 base material with atoms of these two types of elements, the cubic crystal structure of the HfO2 base material is maintained while the crystal distortion is imparted based on the local inhomogeneity introduced into the crystal.

[0012] Based on this reasoning, the present inventors have actually found that the average valence of the HfO2 matrix is ​​4 + We fabricated a ferroelectric material in which the two types of elements with different valences were co-doped to achieve a polarization characteristic similar to that of the perovskite-based ferroelectric material. The experimental results support the above-mentioned hypothesis and suggest the existence of a new ferroelectric mechanism that can fundamentally resolve the problems of wake-up and polarization fatigue caused by oxygen vacancies. [Means for solving the problem]

[0013] The present invention is based on the above findings, and the means for solving the above problems are as follows: <1> A part of the crystal lattice that makes up the HfO2 matrix has a valence of 3 +The first element that forms an ion of + and a second element forming an ion of the first element, and the average valence obtained by averaging the valences of the ions of the first element and the second element according to the composition ratio of the first element and the second element is 3.98 + ~4.02 + A ferroelectric material characterized by: <2> Average valence 4.0 + ~4.02 + The above-mentioned <1> The ferroelectric material according to claim 1. <3> The remanent polarization after the first rewrite due to the application of an electric field is Pr 1 The number of rewrites is 10 5 The remanent polarization is Pr 2 The number of rewrites is 10 10 The remanent polarization is Pr 3 When the above formula (1) and formula (2) are satisfied, <1> or <2> The ferroelectric material according to claim 1. 0.95≦Pr 1 / Pr 2 ≦1.05 (1) 0.95≦Pr 3 / Pr 2 ≦1.05 (2) <4> The first element is at least one selected from the group consisting of Y, La, Pr and Nd. <1> from <3> 10. The ferroelectric material according to any one of claims 1 to 9. <5> The second element is at least one selected from the group consisting of Nb and Ta. <1> from <4> 10. The ferroelectric material according to any one of claims 1 to 9. <6> The first element is Y and the second element is Nb. <1> from <5> 10. The ferroelectric material according to any one of claims 1 to 9. <7> The compound represented by the following chemical formula (1) <6> The ferroelectric material according to claim 1. Y x Nb x Hf 1-2x O2(1) In the chemical formula (1), x represents a numerical value of 0.02 to 0.10. <8> The aforementioned <1> from <7> 10. A ferroelectric capacitor comprising a ferroelectric layer containing the ferroelectric material according to any one of claims 1 to 9, disposed between an upper electrode and a lower electrode. <9> The ferroelectric layer has a thickness of less than 10 nm. <8> The ferroelectric capacitor according to claim 1. [Effects of the Invention]

[0014] According to the present invention, it is possible to solve the above-mentioned problems in the prior art, and to provide a ferroelectric having stabilized polarization characteristics while using HfO2 as a base material, and a ferroelectric capacitor using the ferroelectric. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an explanatory diagram schematically showing crystals in a conventional HfO2-based ferroelectric material. [Figure 2] FIG. 1 is an explanatory diagram schematically showing crystals in a new ferroelectric material devised by the present inventors. [Figure 3] 1 is an explanatory diagram showing a typical configuration example of a ferroelectric capacitor according to the present invention; [Figure 4] FIG. 2 is a diagram showing a hysteresis curve in the polarization (P)-electric field (E) characteristics of the ferroelectric capacitor according to Example 1, measured by the PUND method. [Figure 5] FIG. 2 is a diagram showing the endurance characteristics of the ferroelectric capacitor according to Example 1, measured by the PUND method. [Figure 6] FIG. 1 is a diagram showing the endurance characteristics of existing HfO2-based ferroelectrics (HZO, HZLO). [Figure 7] FIG. 1 is a diagram showing the endurance characteristics of existing perovskite ferroelectrics (PZT). [Figure 8] FIG. 10 is a diagram showing a hysteresis curve in the polarization (P)-electric field (E) characteristics of the ferroelectric capacitor according to Example 2. [Figure 9] FIG. 10 is a diagram showing the endurance characteristics of the ferroelectric capacitor according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] (ferroelectric) The ferroelectric material according to the present invention is a material in which a part of the crystal lattice constituting the HfO2 base material has a valence of 3. + The first element that forms an ion of + and a second element forming an ion of the first element, and the average valence obtained by averaging the valences of the ions of the first element and the second element according to the composition ratio of the first element and the second element is 3.98 + ~4.02 + It is characterized by being said to be.

[0017] Conventionally, Y has been used for the HfO2 base material. 3+ ,La 3+ ,Al 3+ ,Zr 3+ Ferroelectrics to which elements forming trivalent ions such as the above are added in the form of single elements have been reported. However, the Hf in the HfO2 matrix 4+ Part of Y 3+ ,La 3+ ,Al 3+ ,Zr 3+ When substituted with an element that forms a trivalent ion such as the above, oxygen vacancies are generated in the crystal to maintain the charge balance, and the polarization characteristics become unstable due to the oxygen vacancies. Therefore, by co-doping the first element and the second element into the HfO2 base material, the presence of the oxygen vacancies is reduced or eliminated.

[0018] The first element is not particularly limited as long as it is an element that forms trivalent cations in the HfO2 matrix, and examples thereof include elements such as Al, Sc, Y, La, Pr, Nd, and Sm. However, from the viewpoints of being available at relatively low cost and having a covalent bond radius close to that of Hf, Y, La, Pr, and Nd are preferred, Y and La are more preferred, and Y is particularly preferred. The first element may be used alone or in combination of two or more.

[0019] The second element is not particularly limited as long as it is an element that forms pentavalent cations in the HfO2 matrix, and examples thereof include elements such as V, Nb, Ta, P, and Sb. However, Nb and Ta are preferred, with Nb being particularly preferred, from the viewpoints of being available at relatively low cost and having a covalent bond radius close to that of Hf. The second element may be used alone or in combination of two or more.

[0020] The average valence of Hf in the HfO2 matrix is 4+ ) and Hf(Hf 4+ ) to balance the charge between the first element and the second element substituted with 3.98 + ~4.02 + It is said that. That is, the average valence is 3.98 + If it is less than 4.02 + If it exceeds Hf(Hf 4+ ) and the charge balance is disrupted, and the desired ferroelectricity may not be obtained. Therefore, the average valence is 3.98 + ~4.02 + It would be good, but 4.0 + If the ratio is 4.0 or more, the generation of oxygen vacancies can be prevented from occurring in terms of charge balance. + ~4.02 + is preferred, 4.0 + is ideal.

[0021] 4.0 + In order to obtain the average valence of 3.98, the first element and the second element are co-doped in equimolar amounts to the HfO2 base material. + Over 4.0 + In order to obtain the average valence of less than 4.0, the amount of the first element added is slightly larger than that of the second element. + Exceeds 4.02 +In order to obtain the average valence below, the amount of the second element added may be slightly larger than that of the first element, and the first element and the second element may be co-doped.

[0022] The average valence is calculated by averaging the valences of the ions of the first element and the second element according to the composition ratio of the first element and the second element. For example, when a single element is used as the first element and a single element is used as the second element, and these two single elements are co-doped in equimolar amounts (1 / 2 each), the average valence can be determined as follows: 3 + ×1 / 2+5 + ×1 / 2=4 + In addition, when two elements are used as the first element and two elements are used as the second element, and these four elements are co-doped in equimolar amounts (1 / 4 each), the average valence is calculated as follows: 2 (3 + ×1 / 4)+2(5 + ×1 / 4)=4 + It is calculated as follows:

[0023] Although there are no particular limitations on the total content of the first element and the second element in the ferroelectric, when the content of Hf is 1-2x molar parts and the total amount of the added first element and the second element is 2x molar parts, x is preferably 0.02 to 0.10. That is, if x is less than 0.02, the total content of the first element and the second element will be insufficient, and the effect of these elements in imparting the crystal distortion to the ferroelectric may be insufficient, while if x exceeds 0.10, the total content of the first element and the second element will be excessive, and unintended physical properties may be produced in the ferroelectric.

[0024] For the reasons stated above, the best configuration of the ferroelectric is one containing a compound represented by the following chemical formula (1). Y x Nb x Hf 1-2x O2(1) In the chemical formula (1), x represents a numerical value of 0.02 to 0.10.

[0025] The contents and composition ratios of the first element and the second element in the ferroelectric can be measured by a known measurement method such as X-ray diffraction.

[0026] The method for producing the ferroelectric material is not particularly limited and can be appropriately selected depending on the purpose. For example, a method can be used in which the first element and the second element are co-doped into the HfO2 base material in accordance with the method of adding a single element (Y, La, Al, Zr, etc.) to the HfO2 base material in the conventional HfO2-based ferroelectric material. For example, a pulsed laser deposition (PLD) method or a sputtering method can be used, in which a mixed sintered body containing HfO2, the first element, and the second element in a predetermined composition ratio is used as a target material.

[0027] In the ferroelectric material having the above-described structure, the oxygen vacancies that cause instability in the polarization characteristics are reduced or eliminated. As a result, the ferroelectric can be given the following polarization characteristics, which are similar to those of the perovskite-based ferroelectric. That is, the remanent polarization after the first rewrite due to the application of an electric field is Pr 1 The number of rewrites is 10 5 The remanent polarization is Pr 2 The number of rewrites is 10 10 The remanent polarization is Pr 3 When the above formula is satisfied, the polarization characteristics satisfy the following formulas (1) and (2). 0.95≦Pr 1 / Pr 2 ≦1.05 (1) 0.95≦Pr 3 / Pr 2 ≦1.05 (2)

[0028] The polarization characteristic expressed by the formula (1) is related to the wake-up, and the polarization characteristic expressed by the formula (2) is related to the polarization fatigue. In the conventional HfO2-based ferroelectrics, the wake-up and polarization fatigue are easily caused due to the presence of the oxygen vacancies, and it has not been possible to obtain polarization characteristics that simultaneously satisfy the formulas (1) and (2). The number of rewrite operations is counted as one cycle of the hysteresis loop in the polarization (P)-electric field (E) characteristics of the ferroelectric material based on the application of a periodic electric field.

[0029] (ferroelectric capacitor) The ferroelectric capacitor according to the present invention is configured by disposing a ferroelectric layer containing the ferroelectric material of the present invention between an upper electrode and a lower electrode. A typical example of the configuration of the ferroelectric capacitor will be described with reference to FIG.

[0030] As shown in FIG. 3, the ferroelectric capacitor 10 is configured by arranging a ferroelectric layer 1 and an upper electrode 3 in this order on a lower electrode 2. The lower electrode 2 and the upper electrode 3 may be formed from known metal materials (e.g., Au or Ti), metal oxides (e.g., RuO x and IrO x ), metal nitrides (for example, TiN), and the like.

[0031] The thickness of the ferroelectric layer 1 is not particularly limited and may be appropriately selected depending on the purpose, but from the viewpoint of producing a highly dense semiconductor device, it is preferably 10 nm or less. The ferroelectric layer 1 formed including the ferroelectric of the present invention differs from the perovskite-based ferroelectric in that the ferroelectricity is derived from the crystalline structure of the orthorhombic system (space group: Pca21) in the HfO2 base material. Therefore, it is possible to thin the layer (to 10 nm or less), which was previously the limit for the perovskite-based materials, and this has important technical significance in manufacturing the semiconductor device. The lower limit of the thickness is about 3 nm.

[0032] The ferroelectric capacitor 10 is an example of a configuration in which a ferroelectric layer 1 is disposed between a lower electrode 2 and an upper electrode 3 in close contact with these electrodes, but this example is merely illustrative, and the ferroelectric capacitor may be given any modified form based on the configuration of a known ferroelectric capacitor. For example, based on previous research results by the present applicant (see WO2023 / 238523), a ferroelectric capacitor 10 shown in Fig. 3 may be configured by using the lower electrode 2 and the upper electrode 3 as contact electrodes, and disposing a composite metal oxide electrode between the lower electrode 2 and the ferroelectric layer 1 and / or between the upper electrode 3 and the ferroelectric layer 1, the composite metal oxide being formed by adding a second oxide having an oxygen dissociation energy 200 kJ / mol or more higher than that of the first oxide, the second oxide being the largest among the first oxides when considered as a metal oxide of one of the metal elements, at a molar ratio lower than that of the first oxide, based on a conductive first oxide containing at least one metal element selected from the group consisting of In, Ga, Zn, Sn, Ru, Ir, and Sr. Furthermore, a known intermediate layer, such as a conductive buffer layer, may be disposed between the lower electrode 2 and / or the upper electrode 3 and the ferroelectric layer 1. [Example]

[0033] Example 1 The ferroelectric capacitor according to Example 1 was manufactured as follows.

[0034] First, a conductive Nb:SrTiO3 (001) substrate (Shinkosha, Nb (0.05 wt%):SrTiO3, step substrate) was prepared, and a pulsed laser deposition (PLD) device (Vacuum Products Co., Ltd.) was used to deposit a conductive buffer layer on the substrate. 0.7 Sr 0.3 The MnO3 (LSMO) layer was formed to a thickness of 30 nm. 0.7 Sr 0.3The LSMO layer was formed using a target material with a composition ratio of MnO3 in an oxygen atmosphere under a deposition pressure of 150 mTorr at a substrate temperature of 600°C, a laser intensity of 6.0 J, a pulse laser frequency of 5 Hz, and 15,000 shots. The LSMO layer has a perovskite crystal structure and was epitaxially grown with the crystal plane of the substrate oriented.

[0035] Next, using the PLD device, a new ferroelectric material, Y, was deposited on the LSMO layer. 0.06 Nb 0.06 Hf 0.88 The O2 layer (YNHO layer) was formed to a thickness of 8.9 nm. 0.06 Nb 0.06 Hf 0.88 The YNHO layer was formed using a target material with a composition ratio of O2 in an oxygen atmosphere under a deposition pressure of 75 mTorr at a substrate temperature of 750°C, a laser intensity of 6.0 J, a pulse laser frequency of 5 Hz, and 6,000 shots. This YNHO layer was epitaxially grown with the crystal plane of the LSMO layer oriented.

[0036] Next, a laminated electrode consisting of a 10 nm thick Pt layer and a 100 nm thick Au layer was formed on the YNHO layer using an electron beam vacuum deposition apparatus (manufactured by Eiko Engineering Co., Ltd.) and then microfabrication was performed on the laminated electrode to form the electrode shape. In this manner, the ferroelectric capacitor according to Example 1 was manufactured.

[0037] Fig. 4 shows a hysteresis curve of the polarization (P)-electric field (E) characteristics of the ferroelectric capacitor according to Example 1, measured by the PUND (positive-up negative-down) method. Fig. 5 shows the endurance characteristics of the ferroelectric capacitor according to Example 1, measured by the PUND method. The measurement by the PUND method was carried out by applying a periodic electric field of 2V 1kHz to the YNHO layer having a thickness of 8.9nm. 10 It was carried out as a series of sessions. Furthermore, the hysteresis curve shown in FIG. 4 has a special shape, but this is the shape seen when measurements are performed using the PUND method, as shown in the following references 1 and 2, and does not cast any doubt on the measurement results. Reference 1: X. Li, et al., Appl. Phys. Lett. 110, 042901 (2017) Reference 2: R. Nishino, et al., Sci. Rep. 10, 10864 (2020)

[0038] For comparison, Fig. 6 shows the endurance characteristics of existing HfO2-based ferroelectrics (HZO, HZLO). This data is published in Non-Patent Document 2. Fig. 7 shows the endurance characteristics of existing perovskite-based ferroelectrics (PZT). This data is published in Reference Document 3 below. Reference 3:MD Nguyen, et al., ACS Appl. Mater. Interfaces 8, 31120-31127 (2016)

[0039] As shown in Fig. 4, a polarization (P)-electric field (E) hysteresis curve showing ferroelectricity is observed in the ferroelectric capacitor according to Example 1. The hysteresis curve also changes after 10 rewrites. 10 The hysteresis curve is plotted so as to trace the first rewrite cycle, and the shape of the hysteresis curve remains unchanged from the first rewrite cycle to the second rewrite cycle. In other words, the ferroelectric capacitor according to Example 1 has extremely stable polarization characteristics.

[0040] As can be clearly seen in FIG. 5, the ferroelectric capacitor according to Example 1 has a rewrite count of 1 to 10. 10 There is no significant change in the remanent polarization Pr up to the time of the test, and the following polarization characteristics are confirmed. That is, the remanent polarization after the first rewrite due to the application of an electric field is Pr 1 The number of rewrites is 10 5 The remanent polarization is Pr2 The number of rewrites is 10 10 The remanent polarization is Pr 3 When the above formula is satisfied, the polarization characteristics satisfy the following formulas (1) and (2). 0.95≦Pr 1 / Pr 2 ≦1.05 (1) 0.95≦Pr 3 / Pr 2 ≦1.05 (2)

[0041] On the other hand, in existing HfO2-based ferroelectrics, as shown in the example of "HZLO" in Figure 6, a phenomenon called wake-up has been observed, in which the initial spontaneous polarization increases with the number of rewrites (electric field applications), making it difficult or impossible to obtain the polarization characteristic described in (1). Furthermore, as shown in Figure 6, in existing HfO2-based ferroelectrics, a phenomenon known as polarization fatigue has been observed, in which, after a certain number of rewrite cycles, the spontaneous polarization decreases as the number of rewrite cycles (electric field application) increases, making it impossible to obtain the polarization characteristics described in (2) above.

[0042] In FIG. 6, the region where spontaneous polarization corresponding to the number of rewrites is not shown is the region where the ferroelectricity has disappeared or dielectric breakdown has occurred due to the polarization fatigue. 10 It is now difficult to achieve rewrite endurance for multiple times. That is, in existing HfO2-based ferroelectrics, the oxygen vacancies are considered to be the origin of ferroelectricity, but the positions of these oxygen vacancies in the crystal are thought to change depending on the number of rewrites (electric field applications). Therefore, unstable polarization characteristics such as the wake-up and polarization fatigue are exhibited, and ultimately, 10 After about 1000 rewrites or less, the ferroelectricity is lost or dielectric breakdown occurs.

[0043] Rather, as is clear from a comparison between FIG. 5 (the ferroelectric capacitor according to Example 1) and FIG. 7 (the existing perovskite-based ferroelectric), the ferroelectric capacitor according to Example 1 exhibits polarization characteristics similar to those of the existing perovskite-based ferroelectrics that are free from the problems of wake-up and polarization fatigue. This result strongly supports the idea that the ferroelectric phase (the orthorhombic crystal) of the HfO2-based ferroelectric can be stabilized even without the oxygen vacancies, and at the same time suggests that the presence of the oxygen vacancies is the cause of the deterioration of the ferroelectricity. In addition, the endurance characteristics (maximum number of rewrites: 10 10 The measurement time is 10 10 The results were obtained by stopping the measurement after 10 rewrites. 10 This does not deny the ferroelectricity of the ferroelectric capacitor according to Example 1 that has been rewritten more than times.

[0044] Example 2 The ferroelectricity and polarization characteristics of the ferroelectric capacitor according to Example 1 are believed to be due to the introduction of the crystal distortion resulting from local non-uniformity of charge into the HfO2 crystal by co-doping the first element (Y) and the second element (Nb). On the other hand, in the ferroelectric capacitor according to Example 1, the YNHO layer is formed as an epitaxial thin film that is subjected to stress from the substrate, and therefore, it cannot be completely denied that the origin of the crystal distortion is due to the stress effect from the substrate. Therefore, a ferroelectric capacitor according to Example 2 was manufactured in which the YNHO layer was formed as a polycrystalline thin film, and its ferroelectricity and polarization characteristics were examined.

[0045] The ferroelectric capacitor according to Example 2 was manufactured as follows.

[0046] First, a conductive, highly doped n-type Si(111) substrate (Miyoshi Co., Ltd., 2 inches, N-type, resistance 0.004 Ωcm or less) was prepared, and a TaN layer was formed on the substrate as a lower electrode to a thickness of 10 nm using a sputtering apparatus (ULVAC, Inc., model: BC4967).

[0047] Next, using the sputtering device, a polycrystalline thin film of Y was deposited on the lower electrode. 0.06 Nb 0.06 Hf 0.88 The O2 layer (YNHO layer) was formed to a thickness of 10 nm. 0.06 Nb 0.06 Hf 0.88 The YNHO layer was formed using a target material having a composition ratio of O2 as a raw material in an Ar atmosphere under a deposition pressure of 1.1 mTorr, a substrate temperature of room temperature, and an RF output of 50 W.

[0048] Next, a TaN layer was formed as an upper electrode on the YNHO layer using the sputtering apparatus to a thickness of 10 nm, and the lower and upper electrodes were subjected to microfabrication to form the electrode shapes. In this way, the ferroelectric capacitor according to Example 2 was manufactured.

[0049] Similar to the measurements on the ferroelectric capacitor according to Example 1, the polarization (P)-electric field (E) characteristics and endurance characteristics of the ferroelectric capacitor according to Example 2 were measured by the PUND method. Fig. 8 shows a hysteresis curve in the polarization (P)-electric field (E) characteristics of the ferroelectric capacitor according to Example 2. Fig. 9 shows the endurance characteristics of the ferroelectric capacitor according to Example 2. The measurement by the PUND method was carried out by applying a periodic electric field of 5 V and 1 kHz to the YNHO layer having a thickness of 10 nm. 10 It was carried out as a series of sessions.

[0050] As shown in FIGS. 8 and 9, the ferroelectric capacitor according to Example 2 also provided measurement results similar to those of the ferroelectric capacitor according to Example 1 (see FIGS. 4 and 5). That is, even when the YNHO layer is formed as a polycrystalline thin film, the wake-up and polarization fatigue are not observed, and the polarization characteristics (1) and (2) are obtained. 10 Even after repeated rewriting (electric field application), the remanent polarization Pr remains almost unchanged, and polarization characteristics similar to those of existing perovskite-type ferroelectrics are obtained. This result strongly supports the idea that the crystal distortion that contributes to the ferroelectricity of the ferroelectric capacitor according to Example 1 is not an extrinsic property caused by the stress effect from the substrate, but an intrinsic property of the substance itself (HfO2 co-doped with the first element (Y) and the second element (Nb)). [Explanation of symbols]

[0051] 1 Ferroelectric layer 2 Lower electrode 3 Upper electrode 10 Ferroelectric capacitor

Claims

1. HfO ２ A part of the crystal lattice that makes up the base material has a valence of 3 ＋ The first element that forms an ion of ＋ is substituted with a second element to form an ion of The average valence obtained by averaging the valences of the ions of the first element and the second element according to the composition ratio of the first element and the second element is 3.

98. ＋ ~4.02 ＋ A ferroelectric material characterized by:

2. Average valence is 4.0 ＋ ~4.02 ＋ 2. The ferroelectric material according to claim 1 ,

3. The remanent polarization after the first rewrite due to the application of an electric field is Pr １ The number of rewrites is 10 ５ The remanent polarization is expressed as Pr ２ The number of rewrites is 10 １０ The remanent polarization is Pr ３ 3. The ferroelectric material according to claim 1, which satisfies the following formulas (1) and (2): 0.95≦Pr １ / Pr ２ ≦1.05 (1) 0.95≦Pr ３ / Pr ２ ≦1.05 (2)

4. 3. The ferroelectric according to claim 1, wherein the first element is at least one element selected from the group consisting of Y, La, Pr, and Nd.

5. 3. The ferroelectric material according to claim 1, wherein the second element is at least one element selected from the group consisting of Nb and Ta.

6. 3. The ferroelectric material according to claim 1, wherein the first element is Y and the second element is Nb.

7. 7. The ferroelectric according to claim 6, comprising a compound represented by the following chemical formula (1): Y ｘ Nb ｘ Hf １－２ｘ O ２ (1) In the chemical formula (1), x represents a value of 0.02 to 0.

10.

8. 3. A ferroelectric capacitor comprising a ferroelectric layer containing the ferroelectric material according to claim 1, and disposed between an upper electrode and a lower electrode.

9. 9. The ferroelectric capacitor of claim 8, wherein the thickness of the ferroelectric layer is less than 10 nm.

Images