JP6813844B2 - Tunnel junction element and non-volatile memory element - Google Patents

Description

The present invention relates to a tunnel junction element and a non-volatile memory element, and more particularly to a resistance change type having a barrier layer of an oxide ferroelectric substance.

In recent years, research and development of resistance-changing non-volatile memory devices using oxide ferroelectrics have been promoted.

The present inventors have already utilized that the height of the Schottky type barrier formed at the interface between a thick film (thickness 100 nm) of a conductive oxide ferroelectric substance and a metal depends on the ferroelectric polarization. We have proposed a non-volatile memory element (see Patent Document 1).

On the other hand, in a tunnel junction type device using an ultrathin oxide dielectric material for the barrier layer, a non-volatile memory device utilizing the fact that the tunnel barrier height depends on the ferroelectric polarization has been proposed (non-patent). Refer to Documents 1 and 2). For example, a tunnel junction device using Co for the upper electrode, BaTIO ₃ having a film thickness of 3 nm for the barrier layer, La _0.67 Sr _0.33 MnO _{3 for} the lower electrode, and NdGaO ₃ single crystal for the substrate has been reported.

The present inventors have a tunnel composed of an oxide ferroelectric substance (BiFeO ₃ ), a lower electrode (perovskite type manganese oxide (CCMO (Ca _0.96 Ce _0.04 MnO ₃ ))), and an upper electrode (metal cobalt). The joint structure is shown (see Non-Patent Document 3).

FIG. 7 schematically illustrates a tunnel junction element 10 of the prior art. The tunnel junction element 10 includes a substrate 2, a lower electrode 3 made of a metal oxide, a barrier layer 4 made of an oxide ferroelectric substance, an upper electrode 50 made of a metal such as Co, and a wiring laminated on the upper electrode. It is provided with a conductive layer 6 for use and the like.

In the device reported in Non-Patent Document 1, it is difficult to control the resistance state corresponding to the polarization of the strong dielectric. Therefore, the present inventors have a resistance change type having a tunnel junction that can be controlled constantly. We have developed a non-volatile memory device (see Patent Document 2). Patent Document 2 proposes a structure in which a monatomic film of an oxide of an alkaline earth metal, which is a normal dielectric oxide, is inserted between a barrier layer of an oxide ferroelectric substance and a metal electrode. For example, SrTiO ₃ substrate, La _0.6 Sr _0.4 MnO ₃ on the lower electrode, BaTiO ₃ to the barrier layer, BaO film monoatomic layer, Co in the upper electrode, layered structure using the Au conductive layer such as wiring is shown Has been done.

Further, the present inventors have proposed a structure in which a ferroelectric barrier layer is BaTiO ₃ and the terminal surface thereof is TiO ₂ or BaO in a resistance change type device having a tunnel junction (Non-Patent Documents). 4). For example, LSMO (eg, La _0.6 Sr _0.4 MnO ₃ ) or SrRuO _{3 is used} for the lower electrode, BaTiO ₃ (terminal surface is TiO ₂ or BaO) for the barrier layer, Co for the upper electrode, and Au for the conductive layer for wiring, etc. The laminated structure that was present is shown.

As a result of a prior literature search, the following patent documents were known.
Patent Document 3 discloses a capacitor structure in which a lower electrode and an upper electrode of a ferroelectric substance are formed of an iridium oxide layer. Note that Patent Document 3 is a non-volatile memory element that stores polarization charges in a ferroelectric capacitor structure and detects the sign and amount of the stored polarization charges by time integration of the current flowing through the circuit during polarization reversal. It is a technology related to FeRAM), not a technology of tunnel junction structure.

Japanese Unexamined Patent Publication No. 2013-008884 Japanese Unexamined Patent Publication No. 2016-0225258 JP-A-2007-194655

A. Chanthbouala, et al. Nature Nanotech. Vol 7, 101-104 (2012). S. Boyn et al. Appl. Phys. Lett. Vol 104, 052909 (2014). H. Yamada et al., ACS Nano, vol. 7, 5385-5390 (2013). H. Yamada et al., Advanced Functional Materials, vol 25, 2708-2714 (2015).

Conventional resistance-variable non-volatile memory (ReRAM) that utilizes the reversible and non-volatile switching phenomenon of junction resistance, which is expressed in a junction in which a metal oxide of an insulator or semiconductor is sandwiched between metal electrodes, is an oxygen defect due to an electric field. The movement of oxygen ions is the operating principle. As a result, the material deteriorates due to repeated switching, and there have been problems with repeated switching resistance and variations in resistance value for each switching. As a solution to this problem, resistance change memory using a conductive oxide ferroelectric substance, that is, ferroelectric electric polarization inversion, which is an electronic effect, is used to switch the element resistance (leakage current). A ferroelectric resistance change type non-volatile memory based on the principle of operation has been known (see Patent Document 1).

However, in the prior art strong dielectric resistance change type non-volatile memory using a material having a metal bond such as platinum or cobalt as the electrode material, when switching is repeated, the metal material of the electrode is oxidized and the band structure of the interface is formed. Therefore, there is a problem that it is not possible to secure a practical level of repeatability of switching and suppress fluctuations in resistance value due to repetition.

Patent Document 1 of the prior art shows that the Schottky-type resistance-changing non-volatile memory element having the structure described in the document can repeat the resistance-changing operation 1 million times. Further, Non-Patent Document 2 which is a tunnel junction type element shows a value of 4 million cycles. However, there is a problem that 1 million times or 4 million times is not sufficient as the resistance to the repetition of the resistance switching operation.

The present invention is intended to solve these problems, and provides an oxide ferroelectric thin film having high resistance to resistance switching operation due to voltage application and its repetition, and having a small variation in characteristics for each switching. It is an object of the present invention to provide a tunnel junction element used and a resistance change type non-volatile memory element using the tunnel junction element.

The present invention has the following features in order to achieve the above object.
(1) A tunnel junction element characterized by having a tunnel junction in which a barrier layer of an oxide ferroelectric substance is sandwiched between conductive metal oxide electrodes.
(2) Among the electrodes, when the electrode closer to the substrate is used as the first electrode and the electrode farther from the substrate is used as the second electrode, the second electrode is characterized by being an amorphous film. The tunnel junction element according to (1).
(3) The tunnel junction element according to (2), wherein the second electrode is a metal oxide of any one or more of ruthenium and iridium.
(4) The tunnel junction device according to (3), wherein the second electrode is a metal oxide of any one or more of ruthenium oxide and iridium oxide.
(5) The tunnel junction device according to (2), wherein the first electrode is a crystalline thin film, and the second electrode is an amorphous film of ruthenium oxide.
(6) The tunnel junction element according to any one of (2) to (5), wherein the first electrode is a crystalline thin film of a conductive perovskite-type metal oxide.
(7) The tunnel junction element according to any one of (1) to (6), wherein the oxide ferroelectric substance is a ferroelectric substance having a perovskite type structure.
(8) A resistance-changing non-volatile memory element including the tunnel junction element according to any one of (1) to (7).

The tunnel junction element of the present invention has high resistance to repeated voltage application and has a small variation in resistance value for each switching, so that stable resistance switching operation can be realized.

In the tunnel junction element of the present invention, by using a metal oxide electrode as the upper electrode, it was possible to secure a high degree of uniformity and stability of the interface band structure that strongly controls the amount of tunnel current. Stable resistance switching operation can be realized. In the case of a conventional tunnel junction element in which a metal electrode is used as the upper electrode, an unintended interface barrier layer (normal dielectric) is generated at the interface on the upper electrode side due to the progress of the oxidation reaction of the metal electrode due to repeated switching operations. It occurred in a part, and the junction resistance also changed significantly, the resistance switching operation became unstable, and its repeatability also deteriorated. On the other hand, in the tunnel junction element of the present invention, stable resistance switching operation can be realized without the generation of an unintended interface layer due to the conventional metal electrode. As described above, in the tunnel junction element of the present invention, since all the constituent materials constituting the tunnel junction are oxides, problems such as electrode deterioration (oxidation) due to repeated switching operations do not occur.

The non-volatile memory element provided with the tunnel junction element of the present invention is excellent in resistance switching operation due to voltage application and high resistance to repetition thereof, and can realize stable resistance switching repetition characteristics at a practical level as a memory element.

It is a figure explaining the basic structure of embodiment of this invention. It is a figure explaining the characteristic evaluation of the tunnel junction element of 1st Embodiment of this invention. It is a figure explaining the characteristic evaluation of the tunnel junction element of 1st Embodiment of this invention. It is a figure explaining the characteristic evaluation of the tunnel junction element of this invention. (A), (b), and (c) are diagrams showing the measurement results of the repeatability of the switching operation in Example 1, Example 2, and Comparative Example, respectively. It is a figure which shows the current-voltage characteristic of the tunnel junction element of 1st Embodiment of this invention. It is a figure explaining the band structure and resistance switching operation of the tunnel junction element of this invention. (A) is the case of the first embodiment, and (b) is the case of the comparative example. It is a figure explaining the laminated structure of the conventional tunnel junction element.

Embodiments of the present invention will be described below.

The present inventor has arrived at the present invention by focusing on the upper electrode in the research process of advancing the technological development of a tunnel junction device using an oxide ferroelectric as a barrier layer. An embodiment of the present invention has a tunnel junction in which a barrier layer of an oxide ferroelectric substance is sandwiched between electrodes of a conductive metal oxide.

The basic structure of the tunnel junction element according to the embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the tunnel junction element 1 of the present embodiment includes a substrate 2, a first electrode 3 closer to the substrate (also referred to as a lower electrode 3), and a barrier layer 4 of an oxide strong dielectric. A second electrode 5 (also referred to as an upper electrode 5) farther from the substrate and a conductive layer 6 for wiring or the like laminated on the upper electrode are provided. The first electrode 3 and the second electrode 5 that sandwich the barrier layer 4 are metal oxides that form a tunnel junction with the tunnel barrier layer of the ultrathin film.

The material and film thickness of the barrier layer of the oxide ferroelectric substance of the tunnel junction element in the present embodiment are not particularly limited as long as the barrier layer can be tunnel-junctioned with the first and second electrodes. For example, a ferroelectric substance having a perovskite structure is preferable, and BaTIO ₃ , BiFeO ₃ , and PZT can be mentioned. It should be noted that the tunnel barrier layer cannot be formed by a ferroelectric substance such as Bi _1-x FeO ₃ which is made conductive by Bi deficiency used in the technique of Patent Document 1. A tunnel junction element is a junction composed of an electrode and a ferroelectric substance having high insulating properties and is not charge-doped. The film thickness of the ferroelectric barrier layer, which is an insulator, is the thinness of an ultrathin film (about 2 nm or more and 5 nm or less) capable of passing a tunnel current through a tunnel junction.

The upper electrode (second electrode) in the present embodiment is not particularly limited as long as it is a conductive metal oxide that forms a tunnel junction with the barrier layer of the oxide ferroelectric substance. For example, one or more metal oxides of ruthenium and iridium can be mentioned. More specifically, RuO ₂ , IrO ₂ , or a metal oxide composed of IrO ₂ and RuO ₂ can be mentioned.

The upper electrode (second electrode) in the present embodiment may be a crystal film or an amorphous film. It is desirable that the film of the upper electrode has high chemical and structural stability. Examples of the film of the upper electrode include an amorphous film of RuO ₂ , IrO ₂ , or a solid solution of IrO ₂ and RuO ₂ , and the film is not limited to this, and even an amorphous film exhibits high reproducibility and high conductivity. It should be.

In the lower electrode (first electrode) of the present embodiment, a barrier layer of an oxide ferroelectric substance can be epitaxially grown on the lower electrode (first electrode), and a conductive metal oxide forming a tunnel junction with the oxide ferroelectric substance. If so, there is no particular limitation. For example, when a perovskite-type epitaxial film such as BaTIO ₃ is used for the ferroelectric barrier layer above the lower electrode, the lower electrode (first electrode) has the same perovskite-type structure as BaTiO ₃ or the like. Metallic oxides with an electrical resistance of less than 10 mΩcm at room temperature, such as La _1-x Sr _x MnO ₃ (0.2 <x <0.5), SrRuO ₃ , LaNiO ₃ , La _1-x Sr _x CoO ₃ An epitaxial single crystal thin film or the like such as (0.3 <x <0.5) is desirable.

Since the materials listed as the electrode materials of the first or second electrodes have a deep work function (4.5 eV or more), any combination with the above-mentioned ferroelectric barrier layer material can be used for tunnel junction.

The element of the present embodiment reversibly changes the magnitude of the resistance value (leakage current) by applying a positive or negative pulse voltage to the element, like the conventional tunnel junction element provided with a ferroelectric barrier layer. It is something that can be done. In the device of the present embodiment, since the constituent materials are all oxides, problems peculiar to the metal film used in the prior art such as deterioration (oxidation) of the electrodes due to repeated switching operations do not occur. Therefore, a stable resistance switching operation can be realized, which is characterized by high resistance to repeated voltage application and small variation in resistance value for each switching.

(First Embodiment)
This embodiment will be described below with reference to FIGS. 1 to 6. As shown in FIG. 1, the tunnel bonding element of the present embodiment has a tunnel bonding structure in which an ultra-thin film of an oxide ferroelectric substance is used as the barrier layer 4, and the two electrodes sandwiching the barrier layer 4 are formed by the lower electrode 3. It is an epitaxial (single crystal) perovskite type oxide thin film, and the upper electrode 5 is a crystalline or amorphous conductive oxide thin film.

In the element of the present embodiment, an epitaxial thin film of a perovskite-type oxide such as La _1-x Sr _x MnO ₃ (0.2 <x <0.5) is deposited as three layers of the lower electrode, and the epitaxial thin film is deposited on the perovskite type oxide. An epitaxial thin film of a perovskite-type oxide such as BaTiO ₃ having a thickness of 2 to 5 nm is deposited as a ferroelectric tunnel barrier layer, and a crystalline or amorphous metal oxide such as ruthenium oxide is deposited as an upper electrode layer. It is a deposit of thin films. Tunnel junction device, since it is formed on the substrate, as an example, SrTiO ₃ as the substrate 2, La _0.7 Sr _0.3 MnO ₃ as a lower electrode, BaTiO ₃ as a barrier layer 4, RuO ₂ as an upper electrode, the upper electrode A laminated structure formed in the order of stacking Au is provided as a conductive layer for wiring or the like.

In order to evaluate the characteristics of the element of this embodiment, Example 1, Example 2, Comparative Example and Example 3 will be described.

[Example 1]
A single crystal substrate having a perovskite structure ((001) oriented SrTiO ₃ ) was prepared. A thin film of a conductive perovskite-structured oxide (La _0.7 Sr _0.3 MnO ₃ ) was deposited on the substrate to a thickness of 30 nm by a pulse laser deposition method under the conditions of a substrate temperature of 750 ° C. and an oxygen pressure of 1 mTorr. .. Subsequently, BaTIO ₃ (hereinafter, also referred to as BTO) to be a ferroelectric barrier layer was formed to a thickness of 4 nm on the substrate under the production conditions of a substrate temperature of 630 ° C. and an oxygen pressure of 35 mTorr. Further, after cooling the substrate temperature to room temperature, an amorphous thin film of RuO ₂ to be an upper electrode was formed to a thickness of 10 nm under the production conditions of an oxygen pressure of 40 mTorr to prepare a sample.
Next, the produced sample is processed into a fine element shape so that the memory characteristics such as resistance switching operation can be evaluated. First, a photoresist pattern having a size of 3 μm × 3 μm is produced by photolithography, and the RuO ₂ thin film not covered with the resist is completely removed by argon ion milling, and the upper electrode of the tunnel junction is miniaturized. Subsequently, a SiO ₂ thin film is deposited to a thickness of 250 nm by a sputtering method, and then the photoresist is removed by lift-off. As a result, the finely processed tunnel junction becomes a form surrounded by a SiO ₂ thin film. Next, in order to evaluate the electrical characteristics and memory characteristics of the tunnel junction, a wiring layer to the upper electrode and the lower electrode is prepared. The SiO ₂ thin film is an interlayer insulating film for preventing a short circuit between the two. The wiring layers of the upper electrode and the lower electrode are prepared by preparing an inverted resist pattern by photolithography, depositing an Au thin film to a thickness of 400 nm, and then lifting off.

[Example 2]
Example 2 was produced in the same manner as in Example 1 except that the upper electrode was made of a crystalline film of RuO ₂ .

[Comparison example]
A comparative example was produced in the same manner as in Example 1 except that the upper electrode was formed of a Co metal film.

<Evaluation of electrical characteristics of tunnel junction and resistance change type memory characteristics>
A pulse voltage was applied between the upper and lower electrodes of the miniaturized element through the wiring layer for evaluation. Specifically, a positive voltage of + 3V (or + 2V) is applied to the upper electrode for 10 μs. Due to this pulse voltage, the direction of polarization of BaTiO _{3 in} the tunnel junction becomes stable downward (direction of the lower electrode). Moreover, since the ferroelectricity is non-volatile, the polarization direction is memorized even when the pulse voltage application is canceled. Then, a low voltage of −0.2 V is applied and the current passing through the junction is measured. The value obtained by multiplying the reciprocal of the measured current value by -0.2 V is evaluated as "bonding resistance when the polarization is downward". Next, a negative voltage pulse of -3V (or -2V) is applied for 10 μs. As a result, the polarization of BaTiO ₃ is reversed in the upward direction (direction of RuO ₂ ). After applying the pulse voltage, a voltage of −0.2 V is applied in the same manner as described above, the current value is measured, and the junction resistance when the polarization is upward is evaluated. When the applied pulse voltage is positive (polarization is downward), the junction resistance is low, and when it is negative (polarization is upward), it is increased. Therefore, they are defined as a low resistance state (LRS) and a high resistance state (HRS), respectively. The above operation was repeated to evaluate the repeatability of the resistance change memory characteristics.

FIG. 2 shows the measurement results of the repeatability of the switching operation. The horizontal axis of FIG. 2 is the number of repetitions, and the vertical axis is the resistance value. (A) is a measurement result when Vp = ± 3V, and (b) is a measurement result when Vp = ± 2V. The resistance values of HRS and LRS are shown by black and white squares in the figure, respectively.
As shown in FIG. 2A, in the element of the first embodiment of the present embodiment, the resistance value is almost constant even if the resistance switching operation by applying a pulse voltage having a size of ± 3 V and a width of 10 μs is repeated 10 million times. It can be seen that almost no variation occurs and the switching ratio (about 7, the read voltage is −0.2 V) is maintained at a substantially constant level.
As shown in FIG. 2B, when the applied pulse is reduced to ± 2V, the switching ratio is reduced to about 3, but the switching operation with small characteristic variation can be repeated for 1 billion cycles.

FIG. 3 shows the results of variations in characteristics (resistance values) in the resistance switching operation. The horizontal axis of FIG. 3 is the resistance value characteristic, and the vertical axis is the Cumulative Probability (%). It can be seen that the variation is extremely small in both the low resistance state (LRS) and the high resistance state (HRS) because the distribution curve is a straight line standing substantially vertically. The distribution width of the resistance value in each resistance state is particularly small within the initial hundreds of thousands of cycles, and the standard deviation is about 2% in the low resistance state and about 3% in the high resistance state.

4A, 4B, and 4C are the measurement results of the repeatability of the switching operation in Example 1, Example 2, and Comparative Example, respectively. In the comparative example, it can be seen that when the same pulse voltage is applied to the tunnel junction type element using the metal cobalt film as the upper electrode, the resistance value varies from about 100 cycles (see FIG. 4C). ).

Regarding the repeatability of the conventional tunnel junction type element, the value of 4 million cycles described in Non-Patent Document 2 has been published as the highest value of the prior art, but the distribution of the resistance value at this time. The width is about the same as the magnitude of the resistance value, and the characteristic variation is very large. Compared with this, it can be seen that the variation of Examples 1 and 2 is extremely small.

<Current-voltage characteristics>
FIG. 5 shows the current-voltage characteristics measured by sweeping the voltage of the upper electrode of RuO ₂ (in the case of polycrystalline and amorphous) in the order of 0V → + 3V → -3V → 0V. Non-linear current-voltage characteristics peculiar to tunnel junctions have been observed. In the case of amorphous and polycrystalline, the characteristics do not match when the voltage is increased from -3V and when the voltage is decreased from + 3V, and hysteresis is observed. It corresponds to the memory characteristic that the polarization direction is written with a pulse voltage of several V and the resistance value read out as the current value at a minute voltage changes depending on the polarity of the pulse.

<Explanation of resistance switching operation by band structure>
FIG. 6 is a diagram illustrating a resistance switching operation due to the band structure. (A) is the band structure in the case of the present embodiment (LSMO / BTO / RuO ₂ laminated structure), and (b) is the band structure in the case of the comparative example (LSMO / BTO / Co laminated structure). is there. The correlation between ferroelectricity and junction resistance in the resistance-variable memory characteristics observed in a tunnel junction having a ferroelectric barrier layer is explained by the asymmetry of the interface band structure as shown in FIG. 6A. It is known that the ferroelectricity is reduced at the epitaxial LSMO / BaTiO ₃ interface, and the interface layer functions as a normal dielectric barrier layer. As a result, a large gradient of the potential distribution is generated at the interface between the ferroelectric barrier layer that retains the polarization charge and the upper and lower electrodes that shield the charge on the lower electrode side. When the polarization direction of the ferroelectric barrier layer is reversed, the sign of the charge is reversed, so that the potential gradient also changes (see the right side of FIG. 6A). This change in the potential distribution changes the height of the barrier for electron conduction, that is, the junction resistance. In this way, a resistance state depending on the polarization direction is developed. When a metal electrode is used as the upper electrode as in the comparative example, the unintended formation of the interface barrier layer (normal dielectric) is caused by the progress of the oxidation reaction of the electrode due to the repetition of the switching operation, which is part of the interface on the upper electrode side. Can occur in. As a result, the potential distribution is considered to change as shown in FIG. 6 (b). Along with this, the height of the barrier of electron and electrical conduction and the junction resistance also change significantly, so that the resistance switching operation becomes unstable and its repeatability also deteriorates. Such a problem does not occur if a stable conductive metal oxide is used for the electrode.

For example, when a polycrystalline RuO ₂ film deposited under the conditions of about 300 ° C. and 40 mTorr is used for the upper electrode, the instability of the resistance value as in the case of using the metal film does not occur. However, in the case of polycrystalline, the resistance switching ratio itself is smaller and the magnitude of hysteresis of the current-voltage characteristic is smaller than in the case of amorphous (see FIGS. 4 (b) and 5). This is because in polycrystalline films, crystal films with various crystal orientations and their domain boundaries are mixed, so the interface state is not uniform, and parts that form different potential distributions are mixed, resulting in resistance. It is considered that the switching ratio is reduced. Therefore, an amorphous film is more preferable than a crystalline film. A structure having structural uniformity such as an amorphous film has the effect of making the interface band structure uniform and more prominently expressing the resistance switching operation.

Therefore, an amorphous film of an oxide such as ruthenium oxide is excellent in structural uniformity, chemical stability, and conductivity, and is therefore most suitable as an upper electrode of a resistance-changing non-volatile memory element. On the other hand, the polycrystalline oxide ruthenium film has excellent voltage application resistance, but the resistance switching ratio (hysteresis of current-voltage characteristics) is small due to poor structural uniformity.

[Example 3]
A laminated structure SrRuO ₃ / BaTIO ₃ / amorphous RuO ₂ made of materials different from those of Examples 1 and ₂ was prepared to prepare a tunnel junction element. The resistance switching phenomenon was also observed in the tunnel junction element of Example 3. Also in this example, RuO ₂ used as the upper electrode showed greater resistance switching when it was amorphous than when it was polycrystalline. The upper electrode is more preferably an amorphous conductive oxide than a polycrystalline.

The examples shown in the above-described embodiments and the like are described for easy understanding of the invention, and are not limited to this embodiment.

Since the tunnel junction element of the present invention is a resistance-changing non-volatile memory element and has excellent memory characteristics such as repeatability, it can be widely applied to a memory device and is industrially useful.

1 Tunnel junction element of the present invention 2 Substrate 3 Lower electrode (first electrode)
4 Oxide ferroelectric barrier layer 5, 50 Upper electrode (second electrode)
6 Conductive layer for wiring, etc. 10 Conventional tunnel junction element h Barrier height

Claims (6)

From the substrate side, the first electrode made of a conductive metal oxide and
A barrier layer of an oxide ferroelectric substance formed on the first electrode and in contact with the first electrode,
A second electrode formed on the barrier layer and made of an amorphous film of one or more of conductive ruthenium and iridium in contact with the barrier layer is provided.
A tunnel junction element in which a laminate of the first electrode, the barrier layer, and the second electrode has a tunnel junction. It said second electrode is any one or more metal oxides of ruthenium oxide and iridium oxide of claim 1, wherein the tunnel junction device. The first is the electrodes a crystalline thin film, wherein the second electrode is an amorphous film of ruthenium oxide, according to claim 1 wherein the tunnel junction device. The tunnel junction element according to any one of claims 1 to 3 , wherein the first electrode is a crystalline thin film of a conductive perovskite-type metal oxide. It said oxide ferroelectric is a ferroelectric having a perovskite structure, a tunnel junction device according to any one of claims 1-4. A resistance-changing non-volatile memory element including the tunnel junction element according to any one of claims 1 to 5 .

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