Ferroelectric capacitor

Abstract

To provide a ferroelectric capacitor in which an increase in a coercive electric field and a deterioration in rewriting resistance are suppressed with a simple structure.SOLUTION: According to the present invention, a ferroelectric capacitor includes an upper electrode, a lower electrode, and a ferroelectric layer disposed between the upper electrode and the lower electrode in close contact with the electrodes, and at least either electrode of the upper electrode or the lower electrode is composed of a composite metal oxide electrode containing a composite metal oxide obtained by adding a second oxide in which oxygen dissociation energy is larger by 200 kJ / mol or more than a metal oxide in which oxygen dissociation energy is the largest in the first oxide when regarded as a metal oxide by at least one metal element to a first conductive oxide containing the one metal element selected from a group of In, Ga, Zn, Sn, Ru, Ir and Sr with a mole ratio smaller than the first oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a ferroelectric capacitor that exhibits excellent ferroelectric properties based on the selection of electrode materials. [Background technology]

[0002] The rapid development of advanced technologies such as AI and IoT has created a demand for the early realization of high-performance semiconductor devices capable of processing and storing vast amounts of data. As a key device to meet these demands, ferroelectric memory (FeRAM), which consists of a 1-transistor-1-capacitor (1T-1C) type and is a non-volatile memory capable of low power consumption and high-speed operation, has attracted attention since the report of HfO2-based ferroelectrics with Si, Al, Zr, etc., in 2011 (see Non-Patent Document 1).

[0003] The aforementioned HfO2-based ferroelectric material enables thin-film deposition (less than 10 nm), which was limited by existing perovskite materials such as Pb(Zr,Ti)O3(PZT) and SrBi2Ta2O9(SBT). Furthermore, it exhibits excellent compatibility with CMOS processes and, with advancements in atomic layer deposition (ALD) technology, can be homogeneously deposited on three-dimensional structures. Therefore, it is expected to enable the realization of ultra-high-density, high-performance ferroelectric non-volatile memory devices, which have been difficult to achieve until now.

[0004] The ferroelectric phase of the aforementioned HfO2-based ferroelectric material is thought to be a metastable, non-centrosymmetric orthorhombic phase (space group: Pca21) at room temperature and pressure, and exhibits polarization properties due to the movement of oxygen atoms within the unit cell. Therefore, it has been reported that the ferroelectricity of the aforementioned HfO2-based ferroelectric material is greatly influenced by the exchange of oxygen atoms with adjacent interface materials and the formation of interface layers (see Non-Patent Document 2).

[0005] To date, conductive materials such as metals and metal nitrides (such as W and TiN) with a large difference in thermal expansion coefficient compared to the HfO2-based ferroelectric have been used as electrode materials for the purpose of forming the orthorhombic phase, which is the ferroelectric phase of the HfO2-based ferroelectric (see Patent Document 1, Non-Patent Documents 3 and 4). However, when W or TiN is used as an electrode material, it is known that an interfacial layer is formed between the HfO2-based ferroelectric material and the electrode during the heat treatment process, and that oxygen moves from the HfO2-based ferroelectric material to the electrode side during heat treatment due to the scavenging effect of TiN, forming oxygen vacancies in the HfO2-based ferroelectric material film (see Non-Patent Literature 5). Furthermore, attempts have been made to form the HfO2-based ferroelectric material on Si for application in ferroelectric transistors, and it is known that an SiO2 interface layer can be easily formed at the interface between the HfO2-based ferroelectric layer and the Si layer (see Non-Patent Document 6). Thus, during process steps such as heat treatment and film deposition, and when voltage is applied for rewriting, defects such as oxygen vacancies and interfacial layers are easily formed between the electrode and the HfO2-based ferroelectric material. This leads to problems such as an increase in the coercive field and deterioration of rewriting endurance due to wake-up and polarization fatigue (see Non-Patent Literature 6).

[0006] To solve these problems, a ferroelectric capacitor has been proposed in which amorphous metal oxides, such as In-Ga-Zn-O oxide and In-Ga-Zn-Sn-O oxide, are inserted between the upper electrode and the HfO2-based ferroelectric material (see Non-Patent Documents 7 and 8). However, there is a problem in that it does not provide sufficient protection against the increase in coercive field strength and the deterioration of rewrite endurance.

[0007] Furthermore, a structure has been proposed in which a ferroelectric layer is sandwiched between non-ferroelectric metal oxides, with the aim of enabling the use of conductive electrode materials other than TiN, reducing the heat treatment process, and improving the performance of ferroelectric materials (see Patent Document 2). In this proposal, multiple layers of two or more different nonferroelectric metal oxides are stacked to form a composite laminate, and this composite laminate is placed between the ferroelectric layer and the capacitor electrode. Furthermore, the materials constituting each layer of the composite laminate are selected such that the overall conductivity of the composite laminate is lower than that of the capacitor electrode. However, the aforementioned composite laminate has a multilayer structure, making the manufacturing process complicated and difficult to produce, and it also has the problem of not being sufficiently effective against increased coercive field strength and deterioration of rewrite endurance. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2015-015334 [Patent Document 2] Japanese Patent Publication No. 2021-073747 [Non-patent literature]

[0009] [Non-Patent Document 1] TS Boscke et al., Appl. Phys. Lett. 99, 102903 (2011). [Non-Patent Document 2] M. Pesic et al., Adv. Funct. Mater. 26, 7486 (2016). [Non-Patent Document 3] SJ Kim et al., Appl. Phys. Lett. 111, 242901 (2017). [Non-Patent Document 4] G. Karbasian et al., Appl. Phys. Lett. 111, 022907 (2017). [Non-Patent Document 5] T. Ando, ​​Materials 5, 478 (2012). [Non-Patent Document 6] S. Oh et al., IEEE Electron Device Lett. 40(7), 1092 (2019). [Non-Patent Document 7] F. Mo et al., Appl. Phys. Express 13, 074005 (2020). [Non-Patent Document 8] J. Wu et al., VLSI Symposium on Technology, T16-2, June (2021). [Summary of the Invention] [Problem to be Solved by the Invention]

[0010] An object of the present invention is to solve the above-mentioned conventional problems and achieve the following object. Specifically, an object of the present invention is to provide a ferroelectric capacitor having a simple structure, in which an increase in coercive electric field and deterioration of rewritability resistance are suppressed. [Means for Solving the Problem]

[0011] Means for solving the above problem are as follows. That is, <1> A ferroelectric capacitor comprising an upper electrode, a lower electrode, and a ferroelectric layer disposed between the upper electrode and the lower electrode in close contact with the electrodes, wherein at least one of the upper electrode and the lower electrode is a conductive first oxide containing at least one metal element selected from the group consisting of In, Ga, Zn, Sn, Ru, Ir and Sr, the composite metal oxide electrode is formed by including a composite metal oxide to which a second oxide is added at a smaller molar ratio than the first oxide, where the oxygen dissociation energy of the second oxide is 200 kJ / mol or more larger than that of the metal oxide having the largest oxygen dissociation energy among the first oxides when the first oxide is regarded as a metal oxide of one of the above metal elements, The composite metal oxide is in an amorphous structure. wherein the ferroelectric capacitor is characterized in that. <2> The ferroelectric capacitor according to <1>, wherein each of the upper electrode and the lower electrode is constituted by the composite metal oxide electrode. <3> In the composite metal oxide electrode layer, the contact electrode is formed on the surface opposite to the surface in contact with the ferroelectric layer. <1> or <2> A ferroelectric capacitor as described in any of the following. <4> The composite metal oxide is formed by adding 0.02 to 0.5 moles of a second oxide to 1 mole of a first oxide. <1> from <3> A ferroelectric capacitor as described in any of the following. <5> The composite metal oxide is formed by adding a second oxide containing at least one element selected from the group consisting of Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group consisting of Sn-O oxides, In-Sn-O oxides, Ga-Sn-O oxides, Zn-Sn-O oxides, In-Ga-Sn-O oxides, In-Zn-Sn-O oxides, Ga-Zn-Sn-O oxides, and In-Ga-Zn-Sn-O oxides. <1> from <3> A ferroelectric capacitor as described in any of the following. <6> The composite metal oxide is formed by adding a second oxide containing at least one element selected from the group of Er, Dy, Ni, V, Ge, Ti, W, Nb, Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group of In-O oxides, Ga-O oxides, Zn-O oxides, In-Ga-O oxides, In-Zn-O oxides, Ga-Zn-O oxides, and In-Ga-Zn-O oxides. <1> from <3> A ferroelectric capacitor as described in any of the following. <7> The composite metal oxide is formed by adding a second oxide containing at least one element selected from the group consisting of Ti, W, Nb, Zr, La, Si, Hf, Ta, and C to an In-O-based oxide. <6> A ferroelectric capacitor as described above. <8> The composite metal oxide includes an oxide selected from the group consisting of In-WO-based oxides and In-Si-O-based oxides. <7> A ferroelectric capacitor as described above. <9> The composite metal oxide is formed by adding a second oxide containing at least one element selected from the group of Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group of Ru-O oxides, Ir-O oxides, Sr-Ru-O oxides, and In-Sr-Ru-O oxides. <1> from <3> A ferroelectric capacitor as described in any of the following. <10> The composite metal oxide includes an In-Sr-Ru-Si-O system oxide. <9> A ferroelectric capacitor as described above. <11> The composite metal oxide electrode has a film thickness of 0.5 nm to 20 nm. <1> from <10> A ferroelectric capacitor as described in any of the following. <12> The composite metal oxide electrode has a film thickness of 0.5 nm to 2 nm. 3 >Ferroelectric capacitors as described above. <13> A ferroelectric capacitor comprising an upper electrode, a lower electrode, and a ferroelectric layer disposed in close contact with the upper and lower electrodes, wherein at least one of the upper and lower electrodes is a composite metal oxide electrode formed by adding a composite metal oxide to a conductive first oxide containing at least one metal element selected from the group In, Ga, Zn, Sn, Ru, Ir, and Sr, and a second oxide having an oxygen dissociation energy 200 kJ / mol or more greater than the metal oxide having the largest oxygen dissociation energy among the first oxides when viewed as a metal oxide with one of the metal elements, in a smaller molar ratio than the first oxide, wherein the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group Ru-O oxide, Ir-O oxide, Sr-Ru-O oxide, and In-Sr-Ru-O oxide. [Effects of the Invention]

[0012] According to the present invention, the aforementioned problems of the prior art can be solved, and a ferroelectric capacitor can be provided with a simple structure in which the increase in coercive field and the deterioration of rewrite endurance are suppressed. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional diagram of a ferroelectric capacitor according to the first embodiment of the present invention. [Figure 2] This diagram shows a list of oxygen dissociation energies for oxides. [Figure 3] This is a cross-sectional diagram of a ferroelectric capacitor according to a second embodiment of the present invention. [Figure 4] This is a perspective view showing one configuration of a ferroelectric capacitor according to an embodiment. [Figure 5] This figure shows the measurement results of the polarization-electric field characteristics of each ferroelectric capacitor according to Examples 1 and 2 and Comparative Example 1. [Figure 6]This figure shows the measurement results of the endurance characteristics (values ​​normalized by the maximum residual polarization value) of each ferroelectric capacitor related to Examples 1 and 2 and Comparative Example 1. [Figure 7] This is a perspective view showing another configuration of the ferroelectric capacitor according to the embodiment. [Figure 8] This is a perspective view showing yet another configuration of the ferroelectric capacitor according to the embodiment. [Figure 9] This figure shows the measurement results of the endurance characteristics (values ​​normalized by the number of dielectric breakdown rewrites for samples with only contact electrodes and no composite metal oxide electrodes) of each ferroelectric capacitor related to Examples 1, 2, 12, 13 and Comparative Example 1. [Modes for carrying out the invention]

[0014] [First Embodiment] First, a ferroelectric capacitor according to the first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a cross-sectional view of the ferroelectric capacitor according to the first embodiment of the present invention.

[0015] As shown in Figure 1, the ferroelectric capacitor 10 includes a lower contact electrode 12, a lower electrode 13, a ferroelectric layer 14, an upper electrode 15, and an upper contact electrode 16.

[0016] The lower electrode 13 and the upper electrode 15 are a pair of electrodes for applying a voltage to the ferroelectric layer 14. In the first embodiment, the lower electrode 13 and the upper electrode 15 are each composed of a composite metal oxide electrode, as described below. The composite metal oxide electrode is an electrode formed by including a composite metal oxide in which a second oxide is added to a first oxide.

[0017] The first oxide is a conductive oxide containing at least one metallic element selected from the group consisting of In, Ga, Zn, Sn, Ru, Ir, and Sr. There are no particular limitations on the specific first oxide, and it can be appropriately selected depending on the purpose. Examples include known oxides that are suitably used as conductive metal oxides, such as In-O oxides, Ga-O oxides, Zn-O oxides, Sn-O oxides, In-Ga-O oxides (IGO), In-Zn-O oxides (IZO), In-Sn-O oxides (ITO), Ga-Zn-O oxides (GZO), Ga-Sn-O oxides (GTO), Zn-Sn-O oxides (ZTO), In-Ga-Zn-O oxides (IGZO), In-Ga-Sn-O oxides (IGTO), In-Zn-Sn-O oxides (IZTO), Ga-Zn-Sn-O oxides (GZTO), In-Ga-Zn-Sn-O oxides (IGZTO), Ru-O oxides, Ir-O oxides, and Sr-Ru-O oxides. Furthermore, various oxides formed according to known formation methods (for example, In-Sr-Ru-O based oxides, etc.) can be mentioned. In this specification, "conductive" means 1 × 10 -4 This means having a resistivity of Ω·m or less. Furthermore, "system oxide" refers to an oxide that contains all the elements listed before this notation, but also means that the composition ratio of each element has a range that encompasses the stable composition as well as the entire range that can form this oxide.

[0018] Among the aforementioned first oxides, oxides containing In are preferred from the viewpoint of conductivity when viewed as an electrode material. In particular, while In2O3 alone readily crystallizes at low temperatures during film formation, the addition of the second oxide shifts the crystallization start temperature to a higher temperature, making it easier to maintain an amorphous structure. Maintaining this amorphous structure suppresses surface roughness compared to the case of crystallization, thereby reducing leakage current.

[0019] The second oxide is an oxide in which the oxygen dissociation energy is 200 kJ / mol or more greater than that of the metal oxide in the first oxide, when viewed as a metal oxide composed of a single metal element, compared to the metal oxide in the first oxide which has the largest oxygen dissociation energy. By adding the aforementioned second oxide with a large oxygen dissociation energy, it is possible to suppress the formation of defects such as interfacial layers and oxygen vacancies at the interface between the electrode and the ferroelectric layer, which cause an increase in the coercive field in conventional ferroelectric capacitors. Furthermore, it is also possible to suppress the formation of new defects such as oxygen vacancies caused by the movement of oxygen atoms during operation under voltage application. This effect of suppressing defect formation can be imparted by the second oxide, which has a higher oxygen dissociation energy than the first oxide. However, the greater the difference in oxygen dissociation energy of the first oxide between the first and second oxides, the more clearly this effect is manifested. Therefore, the composite metal oxide electrode is constructed with a sufficient difference.

[0020] The second oxide is added to the conductive first oxide in a smaller molar ratio than the first oxide. That is, in the composite metal oxide electrode comprising the first oxide and the second oxide, the conductivity of the first oxide is dominant, and conductivity is imparted to the composite metal oxide electrode. In particular, when the composite metal oxide is formed by adding the second oxide in a ratio of 0.5 moles or less to 1 mole of the first oxide, suitable conductivity can be obtained. On the other hand, if the composite metal oxide is formed by adding the second oxide in a ratio of less than 0.02 moles to 1 mole of the first oxide, the formation of defects such as oxygen vacancies may not be effectively suppressed. Therefore, it is particularly preferable that the composite metal oxide is formed by adding the second oxide in an amount of 0.02 to 0.5 moles to 1 mole of the first oxide.

[0021] The second oxide will be explained in more detail with reference to Figure 2. Figure 2 is a diagram showing a list of oxygen dissociation energies for oxides. The elements shown in Figure 2 are listed in order that the oxygen dissociation energy when they are oxides increases from Cd (236 kJ / mol) in the upper left to C (1,076 kJ / mol) in the lower right. The numbers to the right of each element indicate the magnitude of the oxygen dissociation energy (kJ / mol). The selection of the second oxide relative to the first oxide can be made by referring to Figure 2. For example, when In oxide, a monocrystalline oxide, is selected as the first oxide, the second oxide can be selected from Am oxide (553 kJ / mol) or later, whose oxygen dissociation energy is 200 kJ / mol or greater than that of In oxide (346 kJ / mol), as shown in Figure 2. Furthermore, when an In-Ga-Zn-O ternary oxide is selected as the first oxide, the oxygen dissociation energy can be determined according to Figure 2, when considering metal oxides (In oxide, Ga oxide, and Zn oxide) based on a single metal element (In, Ga, or Zn). Among these metal oxides, an oxide with an oxygen dissociation energy 200 kJ / mol or more greater than that of Ga oxide (374 kJ / mol) can be selected, starting with Os oxide (575 kJ / mol). For details on the oxygen dissociation energy of the aforementioned oxide, please refer to Reference 1 below. Reference 1: Y.-R. Luo, Comprehensive Handbook of Chemical Bond Energies, CRC Press (2007).

[0022] The second oxide can be selected from the first oxide as described above, but in particular, from the viewpoint of the conductivity of the resulting composite metal oxide electrode, the following oxides are preferred. That is, when the first oxide is selected from the group consisting of Sn-O oxides, In-Sn-O oxides, Ga-Sn-O oxides, Zn-Sn-O oxides, In-Ga-Sn-O oxides, In-Zn-Sn-O oxides, Ga-Zn-Sn-O oxides, and In-Ga-Zn-Sn-O oxides, the second oxide is preferably an oxide containing at least one element selected from the group consisting of Zr, Ce, La, Si, Hf, Ta, and C. Furthermore, when the first oxide is selected from the group consisting of In-O oxides, Ga-O oxides, Zn-O oxides, In-Ga-O oxides, In-Zn-O oxides, Ga-Zn-O oxides, and In-Ga-Zn-O oxides, the second oxide is preferably an oxide containing at least one element selected from the group consisting of Er, Dy, Ni, V, Ge, Ti, W, Nb, Zr, Ce, La, Si, Hf, Ta, and C. Among these, from the viewpoint of material handling and availability, it is particularly preferable to select an In-O oxide as the first oxide and an oxide containing at least one element selected from the group consisting of Ti, W, Nb, Zr, La, Si, Hf, Ta, and C as the second oxide. Furthermore, when the first oxide is selected from the group consisting of Ru-O oxides, Ir-O oxides, Sr-Ru-O oxides, and In-Sr-Ru-O oxides, the second oxide is preferably an oxide containing at least one element selected from the group consisting of Zr, Ce, La, Si, Hf, Ta, and C.

[0023] Furthermore, as described above, the composite metal oxide can take on various material configurations depending on the selection of the first oxide and the second oxide. However, for the reasons explained regarding the selection of the first and second oxides, it is particularly preferable that it contains either an In-WO-based oxide or an In-Si-O-based oxide, or that it contains an In-Sr-Ru-Si-O-based oxide. Furthermore, when both the lower electrode 13 and the upper electrode 15 are composed of the composite metal oxide electrodes, the composite metal oxide electrode constituting the lower electrode 13 and the composite metal oxide electrode constituting the upper electrode 15 may be formed from the same type of composite metal oxide, or from different types of composite metal oxides.

[0024] Furthermore, while the composite metal oxide may be in a crystalline state, it is preferable to have an amorphous structure from the viewpoint of improving performance when constructing a device. With the amorphous structure, surface roughness can be suppressed compared to the case of crystallization, and leakage current can be reduced.

[0025] There are no particular restrictions on the thickness of the composite metal oxide electrode layer, and it can be appropriately selected depending on the purpose. However, from the viewpoint of being able to form a monomolecular film and obtaining a low resistance value that allows it to function as an electrode, a thickness of at least 0.5 nm is preferred, and from the viewpoint of high density when constructing a device, a thickness of at least 100 nm is preferred. Among these, from the above viewpoint, 0.5 nm to 20 nm is particularly preferred. Furthermore, when contact electrodes (lower contact electrode 12, upper contact electrode 16) are placed side by side with the composite metal oxide electrode, it is possible to make the electrode even thinner, and in this case, a thickness of 0.5 nm to 2 nm for the composite metal oxide electrode layer is particularly preferred. In this specification, the direction of "thickness" refers to the vertical direction as described in the notation for the lower electrode 13 and the upper electrode 15.

[0026] There are no particular limitations on the method for forming the composite metal oxide, and it can be appropriately selected depending on the purpose. For example, a known DC sputtering method using the first oxide and the second oxide as target materials can be used. Furthermore, the statement that "the composite metal oxide is formed by adding the second oxide to the first oxide" does not specify a method for forming the composite metal oxide, but rather means that the composition of the final composite metal oxide includes components of both the first oxide and the second oxide. For example, in one of several methods for forming the In-Sr-Ru-Si-O system oxide as a composite metal oxide, the In-Sr-Ru-Si-O system oxide is formed by a co-sputtering method using two target materials: a target material of SrRuO3 that can constitute the first oxide, and a target material of an In-Si-O system oxide that contains the SiO2 component, which is the second oxide, and the In2O3 component, which can constitute the first oxide, in its composition. This In-Sr-Ru-Si-O system oxide contains the In-Sr-Ru-O system oxide component as the first oxide and the SiO2 component as the second oxide in its composition, and corresponds to the composite metal oxide formed by adding the second oxide to the first oxide.

[0027] Referring again to Figure 1, the ferroelectric layer 14 is positioned between the upper electrode 15 and the lower electrode 13, in close contact with these electrodes. There are no particular restrictions on the material used to form the ferroelectric layer 14; it can be appropriately selected from known oxide ferroelectric materials depending on the purpose. In other words, from the viewpoint of obtaining high-performance devices, hafnium oxides (oxides obtained by doping HfO2 with different elements such as Si, Al, and Zr), hafnium oxide (HfO2), zirconium oxide (ZrO2), zirconium-hafnium oxide (Hf x Zr 1-x While high-performance ferroelectric materials such as O2 (where x is a value between 0 and 1) can be preferred, selecting a ferroelectric material composed of oxides such as perovskite materials like Pb(Zr,Ti)O3(PZT) or SrBi2Ta2O9(SBT) also provides the effect of suppressing defect formation such as oxygen vacancies by the second oxide, which has a large oxygen dissociation energy. Furthermore, the ferroelectric layer 14 is made of such ferroelectric metal oxides and AlO x or TiO x It may be composed of a composite laminated structure with non-ferroelectric metal oxides such as the above. The composite laminated structure can be appropriately selected from known ones.

[0028] There are no particular restrictions on the thickness of the ferroelectric layer 14, and it depends on the forming material, but from the viewpoint of increasing density when constructing the device, it is preferable that it be thin. When the high-performance ferroelectric material is selected, a thickness of about 0.5 nm to 100 nm is preferred, and when the perovskite-based material is selected, a thickness of about 10 nm to 100 nm is preferred based on its thinning limit.

[0029] There are no particular restrictions on the method for forming the ferroelectric layer 14, and it can be appropriately selected depending on the purpose. For example, known atomic layer deposition (ALD) methods can be used.

[0030] The lower contact electrode 12 and the upper contact electrode 16 are arranged to assist the electrode action of the lower electrode 13 and the upper electrode 15. In other words, these contact electrodes are formed on the surface opposite to the surface that is in close contact with the ferroelectric layer 14 of the lower electrode 13 and upper electrode 15 (both composed of the composite metal oxide electrodes), and assist the electrode action of the lower electrode 13 and upper electrode 15.

[0031] The materials used to form the lower contact electrode 12 and the upper contact electrode 16 are preferably materials having a lower resistivity than the composite metal oxide, and are known metal materials (e.g., Au or Ti), metal oxides (e.g., RuO x IrO x The materials can be appropriately selected from ) and metal nitrides (e.g., TiN). Furthermore, the lower contact electrode 12 and upper contact electrode 16 may be formed in a laminated structure of a material having a lower resistivity than the composite metal oxide. The lower contact electrode 12 and upper contact electrode 16 can be formed by known methods depending on the selected material. The thickness of the lower contact electrode 12 and upper contact electrode 16 is preferably about 2 nm to 100 nm. Furthermore, if the conductivity of the lower electrode 13 and the upper electrode 15 is sufficiently high for the purpose of the applied device, the lower contact electrode 12 and the upper contact electrode 16 are unnecessary. Therefore, the lower contact electrode 12 and the upper contact electrode 16 are arbitrary components, and a modified example is also provided in which the lower contact electrode 12 and the upper contact electrode 16 are removed from the ferroelectric capacitor 10.

[0032] [Second Embodiment] Next, a ferroelectric capacitor according to a second embodiment of the present invention will be described with reference to Figure 3. Figure 3 is a cross-sectional view of the ferroelectric capacitor according to a second embodiment of the present invention.

[0033] As shown in Figure 3, the ferroelectric capacitor 20 has a lower electrode 23, a ferroelectric layer 24, an upper electrode 25, and an upper contact electrode 26. The ferroelectric layer 24, upper electrode 25, and upper contact electrode 26 are configured in the same way as the ferroelectric layer 14, upper electrode 15, and upper contact electrode 16 in the ferroelectric capacitor 10. Furthermore, the lower electrode 23 is configured in the same way as the lower contact electrode 12 in the ferroelectric capacitor 10. In other words, in the ferroelectric capacitor 20, of the pair of lower electrodes 23 and upper electrodes 25, only the upper electrode 25 is composed of the composite metal oxide electrode. Even in such a ferroelectric capacitor 20, the formation of defects such as oxygen vacancies by the second oxide, which has a large oxygen dissociation energy contained in the composite metal oxide electrode, can be suppressed on the upper surface side of the ferroelectric layer 24. The upper contact electrode 26 is an arbitrary component, and a modified example is also provided in which the upper contact electrode 26 is removed from the ferroelectric capacitor 20. [Examples]

[0034] (Example 1; Composite metal oxide electrode with WO3 added to In2O3) To demonstrate the effects of the present invention, a ferroelectric capacitor according to the embodiment was manufactured with the configuration shown in Figure 4. Figure 4 is a perspective view showing one configuration of the ferroelectric capacitor according to the embodiment.

[0035] The ferroelectric capacitor according to Example 1 was manufactured as follows. First, a TiN layer serving as a lower electrode 33 was formed to a thickness of 15 nm on a p-type Si substrate 31 subjected to buffered hydrofluoric acid (BHF) treatment by DC sputtering. Next, as a ferroelectric layer 34 on the lower electrode 33, Hf x Zr 1-x O₂ (HZO) (Hf / Zr=0.43:0.57) layer was formed to a thickness of 10 nm by atomic layer deposition (ALD). Next, an upper electrode 35 that is a composite metal oxide electrode was formed on the ferroelectric layer 34. Here, the upper electrode 35 was formed of an In-W-O based oxide (IWO) obtained by adding WO₃ (720 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more higher than that of In₂O₃ (346 kJ / mol), to In₂O₃. By adjusting the composition of the target material, an In-W-O based oxide electrode containing In₂O₃ and WO₃ at a ratio of 0.11 mol% of WO₃ per 1 mol% of In₂O₃ (In₂O₃:WO₃=1 mol%:0.11 mol%) was formed to a thickness of 10 nm by DC sputtering (DC power: 200 W, process gas flow rate: Ar 6 sccm / O₂ 6 sccm, substrate temperature: room temperature (23°C)). Next, rapid heat treatment was performed in air at 400°C for 1 minute. Next, a laminated electrode including a Ti layer (thickness: 10 nm) and an Au layer (thickness: 100 nm) serving as a contact electrode 36 was formed on the upper electrode 35 by resistive heating vapor deposition. Note that the upper electrode 35 and the contact electrode 36 were formed as an entirely columnar laminated body using a stencil mask. As described above, the ferroelectric capacitor 30 was manufactured as the ferroelectric capacitor according to Example 1.

[0036] (Example 2: Composite metal oxide electrode in which SiO₂ is added to In₂O₃) The upper electrode 35 was formed from an In-Si-O oxide (ISO) in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of In2O3 (346 kJ / mol), was added to In2O3. By adjusting the composition of the target material, an In-Si-O oxide electrode containing In2O3 and SiO2 at a ratio of 0.26 mol% per 1 mol% of In2O3 (In2O3:SiO2 = 1 mol%:0.26 mol%) was formed, and a ferroelectric capacitor according to Example 2 was manufactured in the same manner as in Example 1, except that the upper electrode 35 was formed from an In-Si-O oxide electrode containing In2O3 and SiO2 at a ratio of 0.26 mol% per 1 mol% of In2O3 (In2O3:SiO2 = 1 mol%:0.26 mol%) and deposited to a thickness of 10 nm using the DC sputtering method (DC power: 200 W, process gas flow rate: Ar 6 sccm / O2 6 sccm, substrate temperature: room temperature (23°C)).

[0037] (Comparative Example 1: Electrode in which Ga2O3 and ZnO are added to In2O3 (IGZO electrode)) A ferroelectric capacitor according to Comparative Example 1 was manufactured in the same manner as in Example 1, except that the upper electrode 35 was formed from an In-Ga-Zn-O oxide (IGZO), and an In-Ga-Zn-O oxide electrode containing equimolar amounts of In2O3, Ga2O3, and ZnO was formed by adjusting the composition of the target material, and a film thickness of 10 nm was deposited using the DC sputtering method (DC power: 100W, process gas flow rate: Ar 21.2 sccm / O 21.5 sccm, substrate temperature: room temperature (23℃)).

[0038] Figure 5 shows the measurement results of the polarization-electric field characteristics of each ferroelectric capacitor according to Examples 1 and 2 and Comparative Example 1.

[0039] As shown in Figure 5, a clear hysteresis loop due to ferroelectricity was observed in each ferroelectric capacitor according to Examples 1 and 2 and Comparative Example 1. On the other hand, the coercive field of the ferroelectric capacitor according to Example 1 (using In-WO oxide electrodes) was 1.30 MV / cm, and the coercive field of the ferroelectric capacitor according to Example 2 (using In-Si-O oxide electrodes) was 1.29 MV / cm, both of which were smaller than the coercive field of 1.59 MV / cm of the ferroelectric capacitor according to Comparative Example 1, which used In-Ga-Zn-O oxide electrodes with added Ga2O3 and ZnO having oxygen dissociation energies equivalent to or lower than those of In2O3. This is thought to be because the upper electrode 35 was constructed from a composite metal oxide electrode with a large oxygen dissociation energy, which suppressed the formation of defects such as interfacial layers and oxygen vacancies at the interface between the upper electrode 35 and the ferroelectric layer 34, causing an increase in the coelectric field.

[0040] Figure 6 shows the measurement results of the endurance characteristics (values ​​normalized by the maximum residual polarization value) of each ferroelectric capacitor related to Examples 1 and 2 and Comparative Example 1.

[0041] As shown in Figure 6, the ferroelectric capacitor according to Example 1 (using In-WO oxide electrodes) and the ferroelectric capacitor according to Example 2 (using In-Si-O oxide electrodes) showed smaller wake-up and polarization fatigue characteristics compared to the ferroelectric capacitor according to Comparative Example 1, which used In-Ga-Zn-O oxide electrodes with added Ga2O3 and ZnO having oxygen dissociation energies equivalent to or lower than those of In2O3.

[0042] Furthermore, as shown in Figure 6, the oxygen dissociation energy of the oxide added to In2O3 increases, and the number of rewritable cycles increases, reaching 4.0 × 10⁻¹⁰ in the ferroelectric capacitor (using In-Ga-Zn-O oxide electrodes) according to Comparative Example 1. 4 In the ferroelectric capacitor according to Example 1 (using In-WO oxide electrodes), 1.0 × 10 5 In the ferroelectric capacitor according to Example 2 (using In-Si-O oxide electrodes), 1.6 × 10 6 The number of rewrites allowed has reached [number].

[0043] The results shown in Figure 6 support the idea that by configuring the upper electrode 35 with a composite metal oxide electrode with a large oxygen dissociation energy, it is possible to suppress not only unintended defects such as interfacial layers and oxygen vacancies formed during the manufacturing process, but also the formation of defects such as oxygen vacancies caused by the movement of oxygen atoms during operation under voltage application. It is thought that this suppression effect is exerted depending on the magnitude of the oxygen dissociation energy.

[0044] (Example 3; Composite metal oxide electrode with SiO2 added to an In-Sn-O-based oxide) The upper electrode 35 is formed from an In-Sn-Si-O oxide (ITO) to which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of SnO2 (528 kJ / mol), is added. In a co-sputtering method using In-Sn-O and SiO2 targets containing 0.20 mol% SnO2 per 1 mol% In2O3, sputtering with the In-Sn-O target is performed using the DC method, and sputtering with the SiO2 target is performed. Sputtering was performed using an RF method, and by changing the ratio of each sputtering power, an In-Sn-Si-O oxide electrode containing In2O3, SnO2, and SiO2 was deposited with a thickness of 10 nm, with a ratio of 0.24 mol% of SiO2 per 1 mol% of In2O3 (In2O3:SnO2:SiO2 = 1 mol%:0.20 mol%:0.24 mol%). The ferroelectric capacitor according to Example 3 was manufactured in the same manner as in Example 1, except that this In-Sn-Si-O oxide electrode was used as the upper electrode 35.

[0045] (Example 4; Composite metal oxide electrode with SiO2 added to SnO2) The upper electrode 35 was formed from a Sn-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of SnO2 (528 kJ / mol), was added to SnO2. In a co-sputtering method using SnO2 and SiO2 targets, sputtering with the SnO2 target was performed using the DC method, and sputtering with the SiO2 target was performed using the RF method. By changing the ratio of the respective sputtering powers, a Sn-Si-O oxide electrode containing SnO2 and SiO2 at a ratio of 0.20 mol% of SiO2 per 1 mol% of SnO2 (SnO2:SiO2 = 1 mol%:0.20 mol%) was deposited with a thickness of 10 nm, and this Sn-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 4 was manufactured in the same manner as in Example 1.

[0046] (Example 5; Composite metal oxide electrode with WO3 added to In-Ga-Zn-O system oxide) The upper electrode 35 is formed from an In-Ga-Zn-WO oxide (IGZO) to which WO3 (720 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of GaO (374 kJ / mol), is added. In a co-sputtering method using In-Ga-Zn-O and WO3 targets containing equimolar amounts of In2O3, Ga2O3, and ZnO, sputtering with the In-Ga-Zn-O target is performed using the DC method, and sputtering with the WO3 target is performed using the RF method. The ferroelectric capacitor according to Example 5 was manufactured in the same manner as in Example 1, except that the method was used and the ratio of each sputtering power was changed to deposit an In-Ga-Zn-WO system oxide electrode with a thickness of 10 nm containing In2O3, Ga2O3, ZnO, and WO3 in a ratio of 0.24 mol% of WO3 per 1 mol% of In2O3, Ga2O3, and ZnO (In2O3:Ga2O3:ZnO:WO3 = 1 mol%:1 mol%:1 mol%:0.24 mol%), and this In-Ga-Zn-WO system oxide electrode was used as the upper electrode 35.

[0047] (Example 6; Composite metal oxide electrode with SiO2 added to Ga2O3) The upper electrode 35 was formed from a Ga-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of Ga2O3 (374 kJ / mol), was added to Ga2O3. In a co-sputtering method using Ga2O3 and SiO2 targets, sputtering with the Ga2O3 target was performed using the DC method, and sputtering with the SiO2 target was performed using the RF method. By changing the ratio of the respective sputtering powers, a Ga-Si-O oxide electrode containing Ga2O3 and SiO2 at a ratio of 0.11 mol% of SiO2 per 1 mol% of Ga2O3 (Ga2O3:SiO2 = 1 mol%:0.11 mol%) was deposited with a thickness of 10 nm, and this Ga-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 6 was manufactured in the same manner as in Example 1.

[0048] (Example 7; Composite metal oxide electrode with SiO2 added to ZnO) The upper electrode 35 was formed from a Zn-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of ZnO (250 kJ / mol), was added to ZnO. In a co-sputtering method using ZnO and SiO2 targets, sputtering with the ZnO target was performed using the DC method, and sputtering with the SiO2 target was performed using the RF method. By changing the ratio of the respective sputtering powers, a Zn-Si-O oxide electrode containing ZnO and SiO2 at a ratio of 0.12 mol% of SiO2 per 1 mol% of ZnO (ZnO:SiO2 = 1 mol%:0.12 mol%) was deposited with a thickness of 10 nm, and this Zn-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 7 was manufactured in the same manner as in Example 1.

[0049] (Example 8; Composite metal oxide electrode with SiO2 added to RuO2) The upper electrode 35 was formed from a Ru-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of RuO2 (528 kJ / mol), was added to RuO2. In an RF co-sputtering method using RuO2 and SiO2 targets, the ratio of the respective sputtering powers was changed to deposit a Ru-Si-O oxide electrode with a thickness of 10 nm containing RuO2 and SiO2 at a ratio of 0.28 mol% of SiO2 per 1 mol% of RuO2 (RuO2:SiO2 = 1 mol%:0.28 mol%), and this Ru-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 8 was manufactured in the same manner as in Example 1.

[0050] (Example 9; Composite metal oxide electrode with SiO2 added to IrO2) The upper electrode 35 was formed from an Ir-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of IrO2 (414 kJ / mol), was added to IrO2. In an RF co-sputtering method using IrO2 and SiO2 targets, the ratio of the respective sputtering powers was changed to deposit an Ir-Si-O oxide electrode with a thickness of 10 nm containing IrO2 and SiO2 at a ratio of 0.23 mol% of SiO2 per 1 mol% of IrO2 (IrO2:SiO2 = 1 mol%:0.23 mol%), and this Ir-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 9 was manufactured in the same manner as in Example 1.

[0051] (Example 10; Composite metal oxide electrode with SiO2 added to SrRuO3) The upper electrode 35 was formed from a Sr-Ru-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of RuO2 (528 kJ / mol), was added to SrRuO3. In an RF co-sputtering method using SrRuO3 and SiO2 targets, the ratio of the respective sputtering powers was changed to deposit a Sr-Ru-Si-O oxide electrode with a thickness of 10 nm containing SrRuO3 and SiO2 at a ratio of 0.16 mol% of SiO2 per 1 mol% of SrRuO3 (SrRuO3:SiO2 = 1 mol%:0.16 mol%), and this Sr-Ru-Si-O oxide electrode was used as the upper electrode 35. Except for this, the ferroelectric capacitor according to Example 10 was manufactured in the same manner as in Example 1.

[0052] (Example 11; Composite metal oxide electrode with In-Si-O oxide added to SrRuO3) The upper electrode 35 is formed from an In-Sr-Ru-Si-O oxide containing an In-Si-O oxide in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of RuO2 (528 kJ / mol), is added to SrRuO3. In a co-sputtering method using a SrRuO3 target and an In-Si-O oxide target containing In2O3 and SiO2 at a ratio of 0.26 mol% per 1 mol% of In2O3 (In2O3:SiO2=1 mol%:0.26 mol%) through composition adjustment, sputtering by the SrRuO3 target is performed using the RF method. The process was carried out using a DC sputtering method with an In-Si-O oxide target, and by changing the ratio of the respective sputtering powers, an In-Sr-Ru-Si-O oxide electrode containing SrRuO3, In2O3, and SiO2 in a ratio of 0.88 mol% and 0.23 mol% of SiO2 per 1 mol% of SrRuO3 (SrRuO3:In2O3:SiO2 = 1 mol%:0.88 mol%:0.23 mol%) was deposited with a thickness of 10 nm. The ferroelectric capacitor according to Example 11 was manufactured in the same manner as in Example 1, except that this In-Sr-Ru-Si-O oxide electrode was used as the upper electrode 35.

[0053] In each of the ferroelectric capacitors according to Examples 3 to 11, good ferroelectricity and endurance characteristics were obtained, similar to the ferroelectric capacitors according to Examples 1 and 2, and superior to the ferroelectric capacitor according to Comparative Example 1. These results mean that even if the constituent materials of the composite metal oxide electrode are changed, if the second oxide, which has a larger oxygen dissociation energy than the first oxide, is added, a ferroelectric capacitor with excellent ferroelectricity and endurance characteristics can be obtained.

[0054] (Example 12: Composite metal oxide electrode applied to the lower electrode) Furthermore, a ferroelectric capacitor according to another embodiment was manufactured with the configuration shown in Figure 7. Figure 7 is a perspective view showing another configuration of the ferroelectric capacitor according to the embodiment. Unlike the ferroelectric capacitor 30 shown in Figure 4, the ferroelectric capacitor 40 shown in Figure 7 has a lower electrode 43 made of the composite metal oxide electrode, and the upper electrode consists only of an upper electrode 45 formed in the same way as the upper contact electrode 36.

[0055] The ferroelectric capacitor according to Example 12 was manufactured as follows. First, a TiN layer to serve as a contact electrode 42 was deposited on a p-type Si substrate 41 treated with buffered hydrofluoric acid (BHF) to a thickness of 15 nm using DC sputtering. Next, a lower electrode 43, which is a composite metal oxide electrode, was formed on the contact electrode 42. Here, the lower electrode 43 was formed from an In-Si-O oxide (ISO) in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of In2O3 (346 kJ / mol), was added to In2O3. By adjusting the composition of the target material, an In-Si-O oxide electrode containing In2O3 and SiO2 at a ratio of 0.26 mol% of SiO2 per 1 mol% of In2O3 (In2O3:SiO2 = 1 mol%:0.26 mol%) was formed, and a film with a thickness of 10 nm was deposited by DC sputtering (DC power: 200 W, process gas flow rate: Ar 6 sccm / O2 6 sccm, substrate temperature: room temperature (23°C)). Next, Hf as a ferroelectric layer 44 is placed on the lower electrode 43. x Zr 1-x A 10 nm thick O2(HZO) (Hf / Zr=0.43:0.57) layer was deposited using atomic layer deposition (ALD). Next, it was rapidly heated at 400°C for 1 minute in air. Next, a multilayer electrode consisting of a Ti layer (10 nm thick) and an Au layer (100 nm thick) was deposited on the ferroelectric layer 44 as the upper electrode 45 by resistance heating deposition. Based on the above, a ferroelectric capacitor 40 was manufactured as the ferroelectric capacitor according to Example 12.

[0056] (Example 13: Composite metal oxide electrode applied to both the upper and lower electrodes) Furthermore, a ferroelectric capacitor according to yet another embodiment was manufactured with the configuration shown in Figure 8. Figure 8 is a perspective view showing yet another configuration of the ferroelectric capacitor according to the embodiment. Unlike the ferroelectric capacitors 30 and 40 shown in Figures 4 and 7, the ferroelectric capacitor 50 shown in Figure 8 has both the upper electrode 55 and the lower electrode 53 composed of the composite metal oxide electrodes.

[0057] The ferroelectric capacitor according to Example 13 was manufactured as follows. First, a TiN layer to serve as a contact electrode 52 was deposited on a buffered hydrofluoric acid (BHF) treated p-type Si substrate 51 with a thickness of 15 nm using DC sputtering. Next, a lower electrode 53, which is a composite metal oxide electrode, was formed on the contact electrode 52. Here, the lower electrode 53 was formed from an In-Si-O oxide (ISO) in which SiO2 (799 kJ / mol), whose oxygen dissociation energy is 200 kJ / mol or more greater than that of In2O3 (346 kJ / mol), was added to In2O3. By adjusting the composition of the target material, an In-Si-O oxide electrode containing In2O3 and SiO2 at a ratio of 0.26 mol% of SiO2 per 1 mol% of In2O3 (In2O3:SiO2 = 1 mol%:0.26 mol%) was formed, and a film with a thickness of 10 nm was deposited by DC sputtering (DC power: 200 W, process gas flow rate: Ar 6 sccm / O2 6 sccm, substrate temperature: room temperature (23°C)). Next, Hf as a ferroelectric layer 54 is placed on the lower electrode 53. x Zr 1-x A 10 nm thick O2(HZO) (Hf / Zr=0.43:0.57) layer was deposited using atomic layer deposition (ALD). Next, using the same formation method as for the lower electrode 53, a layer of the upper electrode 55, which is the composite metal oxide electrode, was formed on the ferroelectric layer 54 with a thickness of 10 nm. This layer is an In-Si-O based oxide electrode containing In2O3 and SiO2 at a ratio of 0.26 mol% of SiO2 per 1 mol% of In2O3 (In2O3:SiO2 = 1 mol%:0.26 mol%). Next, it was rapidly heated at 400°C for 1 minute in air. Next, a multilayer electrode consisting of a Ti layer (10 nm thick) and an Au layer (100 nm thick) was deposited on the upper electrode 55 as a contact electrode 56 by resistance heating deposition. Based on the above, a ferroelectric capacitor 50 was manufactured as the ferroelectric capacitor according to Example 13.

[0058] Figure 9 shows the measurement results of the endurance characteristics (values ​​normalized by the number of dielectric breakdown rewrites in samples with only contact electrodes and no composite metal oxide electrodes) of each ferroelectric capacitor related to Examples 1, 2, 12, 13 and Comparative Example 1.

[0059] As shown in Figure 9, it was confirmed that the oxygen dissociation energy of the oxide added to In2O3 increases, as does the normalized dielectric breakdown rewrite cycle. This is consistent with the results shown in Figure 6 regarding the number of rewriteable cycles before normalization.

[0060] Furthermore, as shown in Figure 9, when an In-Si-O-based oxide (ISO) was used as the composite metal oxide electrode, the ferroelectric capacitor according to Example 12, in which the composite metal oxide electrode was applied only to the lower electrode 43, showed a greater number of rewrite cycles compared to the ferroelectric capacitor according to Example 2, in which the composite metal oxide electrode was applied only to the upper electrode 35. This is because, in the ferroelectric capacitor according to Example 2, which was manufactured by performing a rapid heating treatment at 400°C for 1 minute after the formation of the upper electrode 35 (composite metal oxide electrode), and the ferroelectric capacitor according to Example 12, which was manufactured by performing a rapid heating treatment at 400°C for 1 minute before the formation of the upper electrode 45, the ferroelectric layer 34 and the ferroelectric layer 44 are affected by different thermal expansions during the rapid heating treatment due to themselves and the surrounding layers, resulting in the same Hf x Zr 1-x Even though it is an O2(HZO) layer, the ferroelectric layer 44 in Example 12 is thought to have yielded a more stable ferroelectric phase, which is likely the reason for this difference.

[0061] Furthermore, as shown in Figure 9, the ferroelectric capacitor 50 according to Example 13 has a higher number of rewrite cycles than the ferroelectric capacitor 30 with only the upper electrode 35 in Example 2 and the ferroelectric capacitor 40 with only the lower electrode 43 in Example 12, and among the ferroelectric capacitors according to Examples 1 to 12, it has the best ferroelectricity and endurance characteristics. In other words, in the ferroelectric capacitor according to Example 13, since both the upper electrode 55 and the lower electrode 53 are composed of the composite metal oxide electrodes, it is considered that defects such as oxygen vacancies and the formation of unintended interface layers can be suppressed at the two interfaces: between the ferroelectric layer 54 and the upper electrode 55, and between the ferroelectric layer 54 and the lower electrode 53. [Explanation of Symbols]

[0062] 10, 20, 30, 40, 50 Ferroelectric Capacitors 12, 22, 32, 42, 52 Lower contact electrodes 13,43,53 Lower electrode (composite metal oxide electrode) 14, 24, 34, 44, 54 ferroelectric layers 15,25,35,55 Upper electrode (composite metal oxide electrode) 16, 26, 36, 56 Upper contact electrodes 23,33 Lower electrode 31, 41, 51 circuit boards 45 Upper electrode

Claims

1. It has an upper electrode, a lower electrode, and a ferroelectric layer disposed between the upper electrode and the lower electrode in close contact with these electrodes, At least one of the upper electrode and the lower electrode is a composite metal oxide electrode formed by adding a composite metal oxide to a conductive first oxide containing at least one metal element selected from the group In, Ga, Zn, Sn, Ru, Ir, and Sr, wherein the second oxide has an oxygen dissociation energy that is 200 kJ / mol or more greater than the first oxide, when viewed as a metal oxide composed of one of the metal elements, compared to the metal oxide in the first oxide which has the largest oxygen dissociation energy among the first oxides, in a molar ratio smaller than that of the first oxide. A ferroelectric capacitor characterized in that the composite metal oxide has an amorphous structure.

2. The ferroelectric capacitor according to claim 1, wherein the upper electrode and the lower electrode are each composed of a composite metal oxide electrode.

3. A ferroelectric capacitor according to claim 1 or 2, wherein a contact electrode is formed on the surface of the composite metal oxide electrode layer opposite to the surface in contact with the ferroelectric layer.

4. A ferroelectric capacitor according to claim 1 or 2, wherein the composite metal oxide is formed by adding 0.02 to 0.5 moles of a second oxide to 1 mole of a first oxide.

5. A ferroelectric capacitor according to claim 1 or 2, wherein the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group consisting of Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group consisting of Sn-O oxides, In-Sn-O oxides, Ga-Sn-O oxides, Zn-Sn-O oxides, In-Ga-Sn-O oxides, In-Zn-Sn-O oxides, Ga-Zn-Sn-O oxides, and In-Ga-Zn-Sn-O oxides.

6. A ferroelectric capacitor according to claim 1 or 2, wherein the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group of Er, Dy, Ni, V, Ge, Ti, W, Nb, Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group of In-O oxides, Ga-O oxides, Zn-O oxides, In-Ga-O oxides, In-Zn-O oxides, Ga-Zn-O oxides, and In-Ga-Zn-O oxides.

7. The ferroelectric capacitor according to claim 6, wherein the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group consisting of Ti, W, Nb, Zr, La, Si, Hf, Ta, and C to an In-O based oxide.

8. The ferroelectric capacitor according to claim 7, wherein the composite metal oxide includes an oxide selected from the group consisting of In-W-O oxides and In-Si-O oxides.

9. A ferroelectric capacitor according to claim 1 or 2, wherein the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group of Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group of Ru-O oxides, Ir-O oxides, Sr-Ru-O oxides, and In-Sr-Ru-O oxides.

10. The ferroelectric capacitor according to claim 9, wherein the composite metal oxide includes an In-Sr-Ru-Si-O system oxide.

11. The ferroelectric capacitor according to claim 1 or 2, wherein the film thickness of the composite metal oxide electrode is 0.5 nm to 20 nm.

12. The ferroelectric capacitor according to claim 3, wherein the film thickness of the composite metal oxide electrode is 0.5 nm to 2 nm.

13. The device comprises an upper electrode, a lower electrode, and a ferroelectric layer disposed between the upper electrode and the lower electrode in close contact with these electrodes, At least one of the upper electrode and the lower electrode is a composite metal oxide electrode formed by adding a composite metal oxide to a conductive first oxide containing at least one metal element selected from the group In, Ga, Zn, Sn, Ru, Ir, and Sr, wherein the second oxide has an oxygen dissociation energy that is 200 kJ / mol or more greater than the first oxide, when viewed as a metal oxide composed of one of the metal elements, compared to the metal oxide in the first oxide which has the largest oxygen dissociation energy among the first oxides, in a molar ratio smaller than that of the first oxide. A ferroelectric capacitor characterized in that the composite metal oxide is formed by adding a second oxide containing at least one element selected from the group of Zr, Ce, La, Si, Hf, Ta, and C to a first oxide selected from the group of Ru-O oxides, Ir-O oxides, Sr-Ru-O oxides, and In-Sr-Ru-O oxides.

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