Ferroelectric thin film, electronic component using the same, and method for producing ferroelectric thin film

Abstract

The present invention aims to provide a ferroelectric thin film having much higher ferroelectricity than conventional ferroelectric thin films made of aluminum nitride doped with scandium and having practical stability, and an electronic device using the same. 1‑X M2 X A ferroelectric thin film and an electronic device using the same, wherein N represents, M1 represents Al or Ga, M2 represents at least one element selected from Mg, Sc and Nb, and x represents a range of 0 to 1.

Description

Technical Field

[0001] The present invention relates to a ferroelectric thin film, an electronic component using the same, and a method for producing the ferroelectric thin film. Background Art

[0002] Ferroelectric materials have long been known, such as barium titanate (BaTiO3), lead zirconate titanate (Pb(Zr,Ti)O3), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O3), and bismuth ferrite (BiFeO3). Ferroelectrics (ferroelectric thin films) are a type of dielectric material whose electric dipoles align even in the absence of an external electric field, and whose dipole orientation can change in response to an electric field. These ferroelectrics possess pyroelectric and piezoelectric properties in addition to ferroelectricity. Therefore, they are used in applications such as FeRAM (ferroelectric memory) that utilize ferroelectricity, as well as actuators that exploit the piezoelectric effect.

[0003] Among such ferroelectric materials, it has recently been reported that aluminum nitride doped with scandium has excellent ferroelectricity (see Non-Patent Document 1).

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-Patent Document 1: Simon Fichtner, Niklas Wolff, Fabian Lofink, Lorenz Kienle, and Bernhard Wagner, J. Appl. Phys. 125, 114103 (2019) Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, Non-Patent Document 1 describes that in aluminum nitride (Al 1-x Sc x In N), when the scandium concentration X is less than 0.22, dielectric breakdown occurs before the coercive electric field is reached.

[0009] Therefore, the concentration X of Sc is less than 0.22 of Al 1-x Sc x N has the problem of being unable to produce ferroelectric thin films.

[0010] In addition, by Al 1-x Sc x A ferroelectric thin film composed of N has the following problems: if the film thickness is not sufficient (for example, 600 nm or more), it does not exhibit sufficient ferroelectricity and does not have stability sufficient for practical use.

[0011] In view of the above circumstances, an object of the present invention is to provide a ferroelectric thin film having high ferroelectricity and stability sufficient for practical use, an electronic device using the same, and a method for producing the ferroelectric thin film.

[0012] Methods for solving problems

[0013] The inventors of the present invention have continued to conduct intensive research and development to address the above-mentioned problems, and as a result, have discovered the following revolutionary ferroelectric thin film, an electronic device using the same, and a method for producing the ferroelectric thin film.

[0014] A first embodiment of the present invention for solving the above-mentioned problems is a ferroelectric thin film characterized by having a chemical formula M1 1-X M2 X N represents that M1 is at least one element selected from aluminum (Al) and gallium (Ga), M2 is at least one element selected from magnesium (Mg), scandium (Sc), ytterbium (Yb) and niobium (Nb), and X is in the range of 0 to 1.

[0015] In this first aspect, a ferroelectric thin film having high ferroelectricity and high stability can be provided.

[0016] A second aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Al, M2 is Sc, and X is within a range of greater than 0 and not more than 0.219.

[0017] In this second embodiment, although the concentration is lower than the concentration of Sc which is considered to be impossible to produce, it is similar to the method of using Al2O3 as disclosed in Non-Patent Document 1. 1-X Sc X Compared with a ferroelectric thin film composed of N, a ferroelectric thin film having very high ferroelectricity and high stability can be provided.

[0018] A third aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Al, M2 is Sc, and X is within a range of 0.065 to 0.219.

[0019] In this third embodiment, although the concentration is lower than the concentration of Sc which is considered to be impossible to produce, it is similar to the method of using Al2O3 as disclosed in Non-Patent Document 1. 1-X Sc X Compared with a ferroelectric thin film composed of N, a ferroelectric thin film having very high ferroelectricity and high stability can be provided.

[0020] A fourth aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Al, M2 is Sc, and X is within a range of 0.16 to 0.219.

[0021] In this fourth embodiment, although the concentration is lower than the concentration of Sc which is considered to be impossible to produce, it is similar to the method of using Al as the catalyst disclosed in Non-Patent Document 1. 1-X Sc X Compared with a ferroelectric thin film composed of N, a ferroelectric thin film having very high ferroelectricity and high stability can be provided.

[0022] The fifth aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Al, M2 is Mg 1- Y Nb Y , X is within the range of 0 to 1, and Y is within the range of 0 to 1.

[0023] In this fifth aspect, a ferroelectric thin film can be provided at a lower cost and having higher ferroelectricity and higher stability.

[0024] A sixth aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Ga, M2 is Sc, and X is within a range of 0 to 1.

[0025] This sixth method can provide a ferroelectric thin film with higher ferroelectricity and greater stability. Furthermore, this method is highly compatible with existing gallium nitride semiconductors and their manufacturing processes, allowing the manufacturing process of this method to be easily incorporated into existing gallium nitride semiconductor manufacturing processes.

[0026] A seventh aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Al, M2 is Yb, and X is in the range of 0 to 1.

[0027] In this seventh aspect, a ferroelectric thin film having higher ferroelectricity and higher stability can be provided.

[0028] An eighth aspect of the present invention is the ferroelectric thin film according to the first aspect, wherein M1 is Ga and X is 0.

[0029] This eighth method can provide a ferroelectric thin film with higher ferroelectricity and greater stability. Furthermore, this method is highly compatible with existing gallium nitride semiconductors and their manufacturing processes, allowing the manufacturing process of this method to be easily incorporated into existing gallium nitride semiconductor manufacturing processes.

[0030] A ninth aspect of the present invention is the ferroelectric thin film according to any one of the first to eighth aspects, wherein u calculated by the following formula is within a range of 0.375 or more and less than 0.5.

[0031] [Number 1]

[0032]

[0033] (a represents the lattice constant of the a-axis in the crystal structure of the ferroelectric thin film, and c represents the lattice constant of the c-axis.)

[0034] In this ninth aspect, a ferroelectric thin film having a higher remanent polarization value (Pr) can be provided.

[0035] A tenth aspect of the present invention is the ferroelectric thin film according to any one of the first to ninth aspects, characterized in that the film thickness is within a range of 1 nm to 300 nm.

[0036] In the tenth aspect, a ferroelectric thin film can be provided which does not deteriorate in characteristics even with such a thin film thickness and has sufficient ferroelectricity and sufficiently high stability.

[0037] An eleventh aspect of the present invention is the ferroelectric thin film according to any one of the first to ninth aspects, characterized in that the film thickness is within a range of 1 nm to 200 nm.

[0038] In this eleventh aspect, a ferroelectric thin film can be provided which does not deteriorate in characteristics even with a thinner film thickness and has sufficient ferroelectricity and sufficiently high stability.

[0039] A twelfth aspect of the present invention is the ferroelectric thin film according to any one of the first to ninth aspects, characterized in that the film thickness is within a range of 1 nm to 100 nm.

[0040] In the twelfth aspect, it is possible to provide a ferroelectric thin film that does not deteriorate in characteristics even with a thinner film thickness and has sufficient ferroelectricity and sufficiently high stability.

[0041] A thirteenth aspect of the present invention is the ferroelectric thin film according to any one of the first to ninth aspects, characterized in that the film thickness is within a range of 20 nm to 80 nm.

[0042] The thirteenth aspect can provide a ferroelectric thin film that does not deteriorate in characteristics even with such a thin film thickness and has sufficient ferroelectricity and sufficiently high stability.

[0043] A fourteenth aspect of the present invention is a ferroelectric thin film characterized in that the ferroelectric thin film according to any one of the first to thirteenth aspects is provided on a low heat-resistant substrate.

[0044] Here, the low heat-resistant substrate is not particularly limited as long as it is a substrate with low heat resistance (a material with an upper temperature limit of 50°C to 700°C). Examples of the low heat-resistant substrate include soda-lime glass, organic substrates (polyethylene terephthalate (PET)), polyimide, and alkali-free glass.

[0045] In the fourteenth embodiment, the ferroelectric thin film of the present invention can be produced even when the substrate (base material) is heated to a low temperature (e.g., in the range of 20°C to 30°C) (or even when it is not heated). As a result, for example, flexible devices and display memories using the ferroelectric thin film of the present invention can be produced.

[0046] A fifteenth aspect of the present invention is an electronic device using the ferroelectric thin film according to any one of the first to fourteenth aspects.

[0047] Here, "electronic components" include ferroelectric non-volatile memories (including field effect ferroelectric non-volatile memories), resistance change non-volatile memories, piezoresistive transistors, energy storage elements, piezoelectric elements (piezoelectric elements), pyroelectric elements, piezoelectric sensors, and electrothermal effect elements. It should be noted that these electronic components, for example, Figure 1 The stacked structure shown in the figure is composed of a metal (conductor), a ferroelectric, a semiconductor, an insulator, and an antiferroelectric. As can be seen from the figure, these electronic components are constructed by forming a ferroelectric layer (F) on a metal (conductor) layer (M), a semiconductor layer (S), and an insulator layer (I).

[0048] In the fifteenth aspect, the ferroelectric thin film has very high ferroelectricity and high stability, and thus can provide an electronic device that is smaller and has higher performance than before.

[0049] The sixteenth embodiment of the present invention is a method for manufacturing a ferroelectric thin film, characterized in that it is a method for manufacturing a ferroelectric thin film using a sputtering method to manufacture the ferroelectric thin film described in any one of the first to fourteenth embodiments, the sputtering gas contains at least nitrogen, the molar concentration of nitrogen contained in the sputtering gas is in the range of 0.667 to 1.0, and the pressure of the sputtering gas is below 1 Pa.

[0050] Here, the "sputtering gas" refers to a gas used in a sputtering method, and examples thereof include inert gases such as nitrogen (N2) and argon (Ar).

[0051] In the sixteenth aspect, a ferroelectric thin film can be produced which does not cause dielectric breakdown even when a high electric field is applied and has a high residual polarization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] [ Figure 1 ] Figure 1 This is a conceptual side view showing an example of the stacked structure of the electronic component of the present invention.

[0053] [ Figure 2 ] Figure 2This is a schematic side view of the ferroelectric thin film according to the first embodiment.

[0054] [ Figure 3 ] Figure 3 This is a table showing the components, production methods, etc. of Examples 1 to 5 and Comparative Examples.

[0055] [ Figure 4 ] Figure 4 This is a graph showing the hysteresis curve of Example 1.

[0056] [ Figure 5 ] Figure 5 This is a graph showing the hysteresis curve of Example 2.

[0057] [ Figure 6 ] Figure 6 This is a graph showing the hysteresis curve of Example 3.

[0058] [ Figure 7 ] Figure 7 This is a graph showing the hysteresis curve of Example 4.

[0059] [ Figure 8 ] Figure 8 This is a graph showing the hysteresis curve of Example 5.

[0060] [ Figure 9 ] Figure 9 This is a graph showing the PUND measurement results of Examples 1 to 3 and 5 and Comparative Examples 6 and 7.

[0061] [ Figure 10 ] Figure 10 Graph showing the relationship between the Sc concentration X and the remanent polarization value (Pr) in Examples and Comparative Examples.

[0062] [ Figure 11 ] Figure 11 It is a graph showing the relationship between u and Pr.

[0063] [ Figure 12 ] Figure 12 This is a table showing the components and film thicknesses of Examples 6 to 8.

[0064] [ Figure 13 ] Figure 13 Graphs showing the hysteresis curve of Example 6 (upper section) and the relationship between electric field intensity and current (lower section).

[0065] [ Figure 14 ] Figure 14 Graphs showing the hysteresis curve of Example 7 (upper section) and the relationship between electric field intensity and current (lower section).

[0066] [ Figure 15 ] Figure 15Graphs showing the hysteresis curve of Example 8 (upper section) and the relationship between electric field intensity and current (lower section).

[0067] [ Figure 16 ] Figure 16 This is a schematic side view of the ferroelectric thin film according to the second embodiment.

[0068] [ Figure 17 ] Figure 17 This is a table showing the structures of Examples 9 to 13 and their thin films.

[0069] [ Figure 18 ] Figure 18 This is a graph showing the hysteresis curve of Example 9.

[0070] [ Figure 19 ] Figure 19 This is a graph showing the hysteresis curve of Example 10.

[0071] [ Figure 20 ] Figure 20 This is a graph showing the hysteresis curve of Example 11.

[0072] [ Figure 21 ] Figure 21 Graphs showing the hysteresis curve of Example 12 (upper section) and the relationship between electric field intensity and current (lower section).

[0073] [ Figure 22 ] Figure 22 Graphs showing the hysteresis curve of Example 13 (upper section) and the relationship between electric field intensity and current (lower section).

[0074] [ Figure 23 ] Figure 23 This is a table showing the structures of Examples 14 to 24 and their thin films.

[0075] [ Figure 24 ] Figure 24 Graphs showing the hysteresis curve of Example 14 (upper section) and the relationship between electric field intensity and current (lower section).

[0076] [ Figure 25 ] Figure 25 Graphs showing the hysteresis curve of Example 15 (upper section) and the relationship between electric field intensity and current (lower section).

[0077] [ Figure 26 ] Figure 26 Graphs showing the hysteresis curve of Example 16 (upper section) and the relationship between electric field intensity and current (lower section).

[0078] [ Figure 27 ] Figure 27Graphs showing the hysteresis curve of Example 17 (upper section) and the relationship between electric field intensity and current (lower section).

[0079] [ Figure 28 ] Figure 28 Graphs showing the hysteresis curve of Example 18 (upper section) and the relationship between electric field intensity and current (lower section).

[0080] [ Figure 29 ] Figure 29 Graphs showing the hysteresis curve of Example 19 (upper section) and the relationship between electric field intensity and current (lower section).

[0081] [ Figure 30 ] Figure 30 Graphs showing the hysteresis curve of Example 20 (upper section) and the relationship between electric field intensity and current (lower section).

[0082] [ Figure 31 ] Figure 31 Graphs showing the hysteresis curve of Example 21 (upper section) and the relationship between electric field intensity and current (lower section).

[0083] [ Figure 32 ] Figure 32 It is a graph showing the hysteresis curve of Example 22 (upper section) and the relationship between electric field intensity and current (lower section).

[0084] [ Figure 33 ] Figure 33 It is a graph showing the hysteresis curve of Example 23 (upper section) and the relationship between electric field intensity and current (lower section).

[0085] [ Figure 34 ] Figure 34 It is a graph showing the hysteresis curve of Example 24 (upper section) and the relationship between electric field intensity and current (lower section).

[0086] [ Figure 35 ] Figure 35 This is a table showing the structures of Examples 25 to 27.

[0087] [ Figure 36 ] Figure 36 This is a table showing the molar concentration of each gas contained in the sputtering gas used when preparing Examples 25 to 27.

[0088] [ Figure 37 ] Figure 37 This is a graph showing the relationship between the electric field intensity and the remanent polarization value (Pr) in the ferroelectric thin film produced using various sputtering gases.

[0089] [ Figure 38 ] Figure 38This is a graph showing the relationship between the electric field intensity and the leakage current density in the ferroelectric thin film produced using each sputtering gas. DETAILED DESCRIPTION

[0090] Hereinafter, embodiments of the ferroelectric thin film of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0091] (Implementation Method 1)

[0092] Figure 2 This is a schematic side view of the ferroelectric thin film of this embodiment. As shown in this figure, the ferroelectric thin film 10 is formed on a thin film composed of three layers stacked in order from bottom to top on a silicon substrate (Si substrate) 50: a silicon dioxide layer (SiO2 layer) 40, a titanium dioxide layer (TiO2 layer) 30, and a platinum (111) layer (Pt(111) layer) 20. Here, the Pt(111) layer refers to a platinum layer having a Miller index of (111).

[0093] The Si substrate 50 is not particularly limited, and a commercially available Si substrate can be used. Also, its thickness is not particularly limited.

[0094] The SiO 2 layer 40 is not particularly limited as long as it can be formed by sputtering, etc. The film thickness is not particularly limited as long as it is within the range of 10 nm to 2000 nm.

[0095] The TiO2 layer 30 is also not particularly limited as long as it can be formed by sputtering or the like. Its thickness is also not particularly limited as long as it is in the range of 2 nm to 100 nm. It should be noted that a tantalum layer, a tantalum oxide layer, a niobium layer, or a niobium oxide layer may be used in place of the TiO2 layer.

[0096] The Pt(111) layer 20 is not particularly limited as long as it can be formed by sputtering, etc. The film thickness is not particularly limited as long as it is within the range of 20 nm to 200 nm.

[0097] Furthermore, the ferroelectric thin film 10 formed on the upper portion of the Pt(111) layer 20 is composed of a chemical formula of Al 1-x Sc x The ferroelectric thin film 10 is composed of aluminum nitride doped with scandium (Sc), represented by N. Here, X represents the concentration of Sc, and the value of X in the ferroelectric thin film 10 is within the range of greater than 0 and not more than 0.219.

[0098] Although the ferroelectric thin film 10 has a lower concentration X than that of Sc which was previously considered impossible to produce, it is still different from the ferroelectric thin film 10 made of Al2O3 as disclosed in Non-Patent Document 1. 1-X Sc X Compared with the ferroelectric thin film composed of N, it has very high ferroelectricity and high stability.

[0099] The thickness of the ferroelectric thin film 10 is not particularly limited, but is preferably in the range of 1 nm to 300 nm. Even with such a thin film thickness, the ferroelectric thin film 10 has sufficient ferroelectricity and high stability.

[0100] Furthermore, the film thickness of the ferroelectric thin film 10 is more preferably in the range of 1 nm to 200 nm. Even with such a thin film thickness, the ferroelectric thin film 10 has sufficient ferroelectricity and sufficiently high stability.

[0101] Furthermore, the film thickness of the ferroelectric thin film 10 is more preferably in the range of 1 nm to 100 nm. Even with such a thin film thickness, the ferroelectric thin film 10 has sufficient ferroelectricity and sufficiently high stability.

[0102] The film thickness of the ferroelectric thin film 10 is particularly preferably in the range of 20 nm to 80 nm. Even with such a thin film thickness, the ferroelectric thin film 10 has sufficient ferroelectricity and sufficiently high stability.

[0103] Furthermore, electronic components using these ferroelectric thin films 10 have sufficient ferroelectricity and sufficiently high stability, and thus are smaller and more powerful than conventional electronic components.

[0104] Next, the manufacturing method (manufacturing method 1) of the ferroelectric thin film 10 of this embodiment is described. As described above, the ferroelectric thin film 10 is formed (film-formed) on a thin film composed of three layers, namely, a SiO2 layer 40, a TiO2 layer 30, and a Pt(111) layer 20, stacked in this order from bottom to top, on a Si substrate 50.

[0105] First, a SiO2 layer 40 is formed on a Si substrate 50. The film formation method of the SiO2 layer 40 is not particularly limited, and the SiO2 layer 40 can be formed using known techniques such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), MBE (molecular beam epitaxy), PLD (pulsed laser deposition), and oxidation (thermal oxidation, steam oxidation, etc.).

[0106] Next, a TiO2 layer 30 is formed on the formed SiO2 layer 40. The film formation method of the TiO2 layer 30 is not particularly limited, and the TiO2 layer 30 can be produced using known techniques such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), MBE (molecular beam epitaxy), PLD (pulsed laser deposition), and oxidation (thermal oxidation, water vapor oxidation, etc.).

[0107] Furthermore, a Pt(111) layer 20 is formed on the formed TiO2 layer 30. The film formation method of the Pt(111) layer 20 is not particularly limited, and it can be produced by known techniques such as sputtering, physical vapor deposition (PVD), and chemical vapor deposition (CVD).

[0108] Then, a layer of chemical formula Al is formed on the formed Pt(111) layer 20. 1-x Sc x The ferroelectric thin film 10 represented by N. The ferroelectric thin film 10 can be produced by a general sputtering method, physical vapor deposition (PVD method), chemical vapor deposition (CVD method), MBE (molecular beam epitaxy method), PLD (pulsed laser deposition method), etc. Specifically, for example, in a nitrogen (N2) atmosphere or a mixed atmosphere of N2 and argon (Ar) (the gas pressure can be 1 Pa or less, preferably 0.267 Pa to 6.67 Pa), a target composed of Sc and a target composed of Al are simultaneously sputtered on the Pt (111) layer 20, thereby producing the ferroelectric thin film 10. It should be noted that as a target, an alloy containing Sc and Al in a specified ratio can also be used. In addition, a compound composed of Sc, Al, and N in a specified ratio, such as AlN, ScN, AlScN, etc., can also be used.

[0109] Alternatively, the ferroelectric thin film 10 of this embodiment may be directly formed (film-formed) on a Si substrate using a manufacturing method such as sputtering or vapor deposition, similarly to a general piezoelectric thin film, as described below (manufacturing method 2).

[0110] Specifically, for example, a target composed of Sc and a target composed of Al can be produced by simultaneously sputtering a target on a substrate (e.g., a silicon (Si) substrate) in an N2 atmosphere or a mixed atmosphere of N2 and Ar (the gas pressure is 1 Pa or less, preferably 0.10 Pa to 0.70 Pa). It should be noted that an alloy containing Sc and Al at a predetermined ratio can also be used as the target.

[0111] (Examples 1 to 5 and Comparative Examples 1 to 10)

[0112] In a sputtering apparatus, using the following sputtering target and the like, the above-described manufacturing method 1 was used to form a SiO2 layer having a thickness of 50 nm to 200 nm, a TiO2 layer having a thickness of 5 nm to 50 nm, a Pt(111) layer having a thickness of 50 nm to 200 nm, and a plurality of ferroelectric thin films having a thickness of 123 nm to 251 nm on an n-type Si substrate having a resistivity of 0.02 Ωcm. The concentration X of Sc contained in each ferroelectric thin film was different.

[0113] Sc sputtering target (concentration: 99.99%)

[0114] Al sputtering target (concentration: 99.999%)

[0115] Sputtering gas: N2 (purity: 99.99995% or more)

[0116] Substrate heating temperature: 400℃~500℃

[0117] Furthermore, a plurality of ferroelectric thin films with thicknesses of 290 nm to 460 nm were fabricated on an n-type Si substrate having a resistivity of 0.02 Ωcm using the above-described fabrication method 2. It should be noted that the concentration X of Sc contained in each ferroelectric thin film was different.

[0118] Sputtering equipment: BC3263 (manufactured by ULVAC)

[0119] Sc sputtering target (concentration: 99.99%)

[0120] Al sputtering target (concentration: 99.999%)

[0121] Sputtering gas: Mixed gas of N2 (purity: 99.99995% or more) and Ar (purity: 99.9999% or more) (mixing ratio 40:60)

[0122] Substrate heating temperature: 300℃~600℃

[0123] These film forming experiments were conducted under conditions where the pressure in the sputtering chamber was set to 10 -6 The high vacuum method was carried out after reducing the pressure with a vacuum pump to Pa or less. In order to prevent the incorporation of impurities such as oxygen, the target surface was cleaned after target installation and before each film formation experiment.

[0124] Then, a Pt electrode was placed on each ferroelectric thin film, and the FCE-1 / 1A (manufactured by Toyo Technology Co., Ltd.) was used to measure the Figure 3 The electric field-polarization characteristics of each ferroelectric thin film are shown.

[0125] The measurement results are as follows Figures 4 to 8 As shown in these figures, it can be seen that the ferroelectric thin films of Examples 1 to 5 each exhibit a clear hysteresis curve.

[0126] Furthermore, a negative electric field waveform was applied once to each ferroelectric thin film of Examples 1 to 3, 5, and Comparative Examples 6 and 7, and then a positive electric field waveform was applied twice and a negative electric field waveform was applied twice to measure the polarization reversal component using the so-called PUND (Positive-Up-Negative-Down) method.

[0127] The results are shown in Figure 9In the figure, the black circle represents Example 1, the hollow square represents Example 2, the hollow triangle represents Example 3, the hollow circle represents Example 5, the black inverted triangle represents Comparative Example 6, and the black square represents Comparative Example 7. As shown in the figure, it can be seen that the lower the Sc concentration, the higher the remanent polarization value (Pr).

[0128] Next, a graph showing the relationship between the concentration X of Sc and Pr in these ferroelectric thin films is shown in FIG. Figure 10 Here, the data indicated by black circles represent the data of the ferroelectric thin film produced by the production method 1 or 2, and the data indicated by black triangles are the values ​​described in Non-Patent Document 1.

[0129] As shown in the figure, it can be seen that the residual polarization value (Pr) of the ferroelectric film with a Sc concentration in the range of greater than 0.065 and less than 0.219 (Examples 1 to 5) is higher than that of the ferroelectric film with a Sc concentration in the range of 0.27 to 0.49 (Comparison Examples 1 to 8).

[0130] That is, it is found that the aluminum nitride (Al 1- x Sc x N) has a higher remanent polarization value (Pr) than aluminum nitride in which the concentration X of added Sc is in the range of 0.27 to 0.49.

[0131] Furthermore, regarding Figure 3 A portion of each ferroelectric thin film is shown in FIG. 1 , and a graph showing the relationship between u and Pr is shown in FIG. Figure 11 Here, u refers to the ratio of the lattice constant in the polarization direction to the average distance between nitrogen atoms and metal atoms such as Al. For example, in the case of a wurtzite crystal structure, u can generally be calculated using the following formula.

[0132] [Number 2]

[0133]

[0134] In this formula, a represents the lattice constant of the a-axis, and c represents the lattice constant of the c-axis. It should be noted that u, which is related to the distance of the electric dipole, is considered to strongly affect ferroelectric properties such as polarization value.

[0135] As can be seen from the graph, a ferroelectric thin film having u in the range of 0.375 or more and less than 0.5 has a high remanent polarization value (Pr) as described above.

[0136] It should be noted that, regardless of the crystal structure, as long as the ferroelectric film has u in the range of 0.375 or more and less than 0.5, it has a high residual polarization value, but if it is a ferroelectric film with u in the range of 0.382 or more and less than 0.5, it reliably has a high Pr, so it is more preferred. In addition, if it is a ferroelectric film with u in the range of 0.383 or more and less than 0.396, it more reliably has a high Pr, so it is further preferred. Furthermore, if it is a ferroelectric film with u in the range of 0.383 or more and less than 0.387, it further reliably has a high Pr, so it is particularly preferred. These relationships are established in all ferroelectric films included in the present invention.

[0137] (Examples 6 to 8)

[0138] In order to confirm that the ferroelectric thin film of this embodiment has sufficient ferroelectricity even with a small film thickness, a ferroelectric thin film with a smaller film thickness was produced using the above-mentioned manufacturing method 2. Pt electrodes were provided on each of these ferroelectric thin films, and FCE-1 / 1A (manufactured by Toyo Technology Co., Ltd.) was used to conduct the Figure 12 For each of the ferroelectric thin films shown, hysteresis curves and current versus electric field intensity were measured.

[0139] Regarding the results, Figures 13 to 15 The upper part of the graph shows the hysteresis curves of each ferroelectric film. Figures 13 to 15 The lower part of is a graph showing the relationship between the current and the electric field strength. As can be seen from these graphs, the ferroelectric thin films of Examples 6 to 8 each have ferroelectricity.

[0140] (Implementation Method 2)

[0141] In the first embodiment, a relatively high temperature process is used to produce the ferroelectric thin film, but the manufacturing method of the present invention is not limited thereto. For example, even if the substrate (base material) heating temperature in the above-mentioned manufacturing method is set to a low temperature (e.g., in the range of 20°C to 30°C) (or even if no heating is performed), the ferroelectric thin film of the present invention can be produced.

[0142] Therefore, the ferroelectric thin film of the present invention can also be formed (film-formed) on a low-heat-resistant substrate, which is a substrate with low heat resistance. As a result, the ferroelectric thin film of the present invention can also be used in electronic components with low heat resistance. Here, examples of low-heat-resistant substrates include soda-lime glass, organic substrates (polyethylene terephthalate (PET)), polyimide, and alkali-free glass.

[0143] (Examples 9 to 13)

[0144] The following sputtering targets are used in the sputtering device, such as Figure 16As shown, an ITO (Indium Tin Oxide) layer 30A with a thickness of 50nm to 200nm, a Pt (111) layer 20A with a thickness of 50nm to 200nm, and multiple ferroelectric thin films 10A with a thickness of 138nm to 145nm are fabricated on each substrate 40A.

[0145] Sc sputtering target (concentration: 99.99%)

[0146] Al sputtering target (concentration: 99.999%)

[0147] Sputtering gas: N2 (purity: 99.99995% or more)

[0148] Substrate heating temperature: 20℃~30℃

[0149] These film forming experiments were conducted in the same manner as in the above-mentioned Examples and Comparative Examples, with the pressure in the sputtering chamber being set to 10 -6 The high vacuum method was carried out after reducing the pressure with a vacuum pump to Pa or less. In order to prevent the incorporation of impurities such as oxygen, the target surface was cleaned after target installation and before each film formation experiment.

[0150] Then, a Pt electrode was placed on each ferroelectric thin film, and FCE-1 / 1A (manufactured by Toyo Technology Co., Ltd.) was used to Figure 17 The electric field strength is applied to each ferroelectric film shown in the figure. The measurement results are shown in the figure. Figures 18 to 22 As shown in these figures, each ferroelectric thin film exhibits a clear hysteresis curve. Therefore, it can be seen that each ferroelectric thin film has ferroelectricity.

[0151] (Other embodiments)

[0152] In the above embodiment, aluminum nitride (AlN) doped with Sc is used as the ferroelectric thin film. 1-x Sc x N) is used as an example, but the present invention is not limited thereto. As the ferroelectric thin film of the present invention, for example, Al 1-X (Mg 1-Y Nb Y ) X N (0≤X≤1, 0≤Y≤1). Such a ferroelectric thin film is cheaper and has high ferroelectricity and high stability.

[0153] It should be noted that X is preferably in the range of 0.01 to 0.7, and Y is preferably in the range of 0 to 1. In addition, X is more preferably in the range of greater than 0.01 to 0.7, and Y is further preferably in the range of greater than 0 to less than 1.0. 1-X (Mg 1-YNb Y ) X N) is cheaper, has higher ferroelectricity and higher stability. Moreover, X is more preferably in the range of 0.57 to 0.63, and Y is more preferably in the range of 0.365 to 0.532. 1-X (Mg 1-Y Nb Y ) X N) has further higher ferroelectricity and further higher stability.

[0154] In addition, Al 1-X Yb X N (0≤X≤1). Such a ferroelectric thin film is cheaper and has high ferroelectricity and high stability.

[0155] It should be noted that X is preferably in the range of greater than 0 and less than 1, and more preferably in the range of greater than 0.01 and less than 0.8. 1-X Yb X N) is cheaper, has higher ferroelectricity and higher stability. Moreover, X is further preferably in the range of 0.25 or more and 0.282 or less. 1-X Yb X N) has further higher ferroelectricity and further higher stability.

[0156] In addition, examples of the ferroelectric thin film of the present invention include Ga 1-X Sc X N (0≤X≤1). Such a ferroelectric thin film has high ferroelectricity and high stability.

[0157] It should be noted that X is preferably in the range of 0 or more and less than 1, more preferably in the range of greater than 0 and less than 1, further preferably in the range of 0 or more and 0.50 or less, and particularly preferably in the range of greater than 0 and 0.50 or less. 1-X Sc X N) has higher ferroelectricity and higher stability. Moreover, X is more preferably in the range of 0 or more and 0.41 or less, and particularly preferably in the range of greater than 0 and 0.41 or less. 1-X Sc X N) has further higher ferroelectricity and further higher stability.

[0158] Furthermore, as an example of the ferroelectric thin film of the present invention, GaN can be cited. Such a ferroelectric thin film has high ferroelectricity and high stability.

[0159] It should be noted that the above-mentioned ferroelectric thin film can be actually produced using the same production method as that in the first embodiment.

[0160] (Examples 14 to 24)

[0161] Using the above film forming method, a film is formed on a substrate (Si, Hf, Ti) Figure 23 Here, "layer stacking order" means the layer stacking order of each film on the substrate, indicating that the layer on the left is stacked in order from the layer on the right. For example, "Al 0.37 Mg 0.4 Nb 0.23 N / Si" means that Al film is formed on Si substrate. 0.37 Mg 0.4 Nb 0.23 N layer. In addition, "ferroelectric layer thickness" means the film thickness of each corresponding layer.

[0162] Then, similarly to the above embodiment, Pt electrodes were provided on each ferroelectric thin film, and FCE-1 / 1A (manufactured by Toyo Technology Co., Ltd.) was used to Figure 23 The electric field strength of each ferroelectric film is shown in FIG. Figures 24 to 34 As shown in these figures, each ferroelectric thin film exhibits a clear hysteresis curve. Therefore, it can be seen that each ferroelectric thin film has ferroelectricity.

[0163] In the above-described embodiment, the type and pressure of the sputtering gas used in the sputtering method are not particularly limited. However, if the molar concentration of nitrogen contained in the sputtering gas is within the range of 0.667 to 1.0 and the pressure of the sputtering gas is 1 Pa or less, a ferroelectric thin film having a higher remanent polarization value (Pr) can be provided. It should be noted that the gas other than nitrogen contained in the sputtering gas is not particularly limited as long as it is an inert gas.

[0164] (Examples 25 to 27)

[0165] The sputtering device uses the following sputtering target, etc., and uses the above-mentioned manufacturing method 1 to produce three SiO2 layers with a thickness of 50nm to 200nm, a TiO2 layer with a thickness of 5nm to 50nm, and a Pt(111) layer with a thickness of 50nm to 200nm on an n-type Si substrate with a resistivity of 0.02Ωcm. Figure 35 The ferroelectric film (Al 1-x Sc x N). Wherein, when forming the film, as Figure 36 As shown, only the molar concentration of nitrogen and the molar concentration of argon contained in the sputtering gas were changed.

[0166] Sc sputtering target (concentration: 99.99%)

[0167] Al sputtering target (concentration: 99.999%)

[0168] Gas used for sputtering: N2 (purity: 99.99995% or higher), Ar (purity: 99.9999% or higher)

[0169] Sputtering gas pressure: 0.667Pa

[0170] The electric field-polarization characteristics of each ferroelectric thin film obtained were measured. The results are shown in Figure 37 In the figure, the black dot mark represents Example 25, the hollow diamond mark represents Example 26, and the black inverted triangle mark represents Example 27. As shown in the figure, it can be seen that the higher the molar concentration of nitrogen contained in the sputtering gas, the higher the remanent polarization value (Pr) shows.

[0171] Next, a Pt electrode was placed on each ferroelectric thin film, and a DC electric field strength was applied to each ferroelectric thin film using FCE-1 / 1A (manufactured by Toyo Technology Co., Ltd.), and the leakage current density flowing therethrough was measured. The results are shown in FIG. Figure 38 . As can be seen from the figure, Example 27 produces dielectric breakdown when an electric field strength of 2.20MV / cm is applied, and it is impossible to apply a higher electric field to measure the leakage current density. On the other hand, in Example 26, if an electric field strength higher than 2.75MV / cm is applied, the leakage current density shows a sharply large value, but no dielectric breakdown occurs. Similarly, compared with Example 26, Example 25 shows a lower leakage current density and no dielectric breakdown occurs. Here, based on the results of Example 25 and Example 26, it is believed that the ferroelectric thin film produced using a sputtering gas with a nitrogen molar concentration in the range of 0.667 to 1.0 will not cause dielectric breakdown even if an electric field strength of more than 2.20MV / cm is applied. It should be noted that as long as the pressure of the sputtering gas is below 1Pa, the same ferroelectric thin film as them can be obtained.

[0172] This shows that by using a sputtering gas with a nitrogen molar concentration in the range of 0.667 to 1.0 and a sputtering gas pressure of 1 Pa or less, dielectric breakdown does not occur even when a high electric field strength is applied, and a ferroelectric thin film with a high remanent polarization value can be produced.

[0173] It should be noted that by using a sputtering gas that meets this condition, it is believed that even in all ferroelectric thin films described in this specification, dielectric breakdown will not occur even when a high electric field strength is applied, and a ferroelectric thin film with a high residual polarization value can be produced.

[0174] Explanation of symbols

[0175] 10, 10A: ferroelectric thin film,

[0176] 20, 20A: Pt(111) layer,

[0177] 30: TiO2 layer,

[0178] 30A: ITO layer,

[0179] 40: SiO2 layer,

[0180] 40A: Substrate,

[0181] 50: Si substrate.

Claims

1. A ferroelectric thin film, characterized in that From the chemical formula M1 1-X M2 X A ferroelectric thin film having ferroelectricity and showing reversible positive and negative polarization reversal represented by N, M1 is at least one element selected from Al and Ga, M2 is at least one element selected from Mg, Sc, Yb and Nb, and x is in the range of 0 to 1. The crystal structure is wurtzite type. The film thickness is in the range of 1 nm to 200 nm.

2. A ferroelectric thin film, characterized in that From the chemical formula M1 1-X M2 X A ferroelectric thin film having ferroelectricity and showing reversible positive and negative polarization reversal represented by N, M1 is at least one element selected from Al and Ga, M2 is at least one element selected from Mg, Sc, Yb and Nb, and x is in the range of 0 to 1. The crystal structure is wurtzite type. The film thickness is in the range of 1nm to 300nm. The ferroelectric thin film is produced by sputtering, and the pressure of the sputtering gas is 1 Pa or less.

3. The ferroelectric thin film according to claim 2, wherein The sputtering gas contains at least nitrogen, and the molar concentration of the nitrogen contained in the sputtering gas is within a range of 0.667 to 1.

0.

4. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Al, M2 is Sc, and x is within the range of greater than 0 and 0.219 or less.

5. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Al, M2 is Sc, and X is in the range of 0.065 to 0.

219.

6. The ferroelectric thin film according to any one of claims 1 to 3, characterized in that M1 is Al, M2 is Sc, and X is in the range of 0.16 to 0.

219.

7. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Al, M2 is Mg 1-Y Nb Y , X is within the range of 0 to 1, and Y is within the range of 0 to 1.

8. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Ga, M2 is Sc, and X is in the range of 0 or more and 1 or less.

9. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Al, M2 is Yb, and X is in the range of 0 or more and 1 or less.

10. The ferroelectric thin film according to any one of claims 1 to 3, wherein M1 is Ga and X is 0.

11. The ferroelectric thin film according to any one of claims 1 to 3, wherein u calculated by the following formula is within the range of 0.375 or more and less than 0.5, In this formula, a represents the lattice constant of the a-axis in the crystal structure of the ferroelectric thin film, and c represents the lattice constant of the c-axis.

12. The ferroelectric thin film according to any one of claims 1 to 3, wherein The film thickness is in the range of 1 nm to 100 nm.

13. The ferroelectric thin film according to any one of claims 1 to 3, wherein The film thickness is in the range of 20 nm to 80 nm.

14. A ferroelectric thin film, characterized in that: The ferroelectric thin film according to any one of claims 1 to 3 is provided on a low heat-resistant substrate. 15 . An electronic device using the ferroelectric thin film according to claim 1 .

16. A method for manufacturing a ferroelectric thin film, characterized in that: The ferroelectric thin film according to claim 1 is manufactured by sputtering. The sputtering gas contains at least nitrogen, and the molar concentration of the nitrogen contained in the sputtering gas is in the range of 0.667 to 1.

0. The pressure of the sputtering gas is 1 Pa or less.

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