Self-supporting thin film for maintaining initial state out-of-plane electric domain structure and preparation method of self-supporting thin film

Abstract

The invention discloses a self-supporting film for maintaining an initial state out-of-plane electric domain structure and a preparation method thereof, and belongs to the technical field of flexible electronics. The self-supporting thin film comprises a shielding buffer layer and a nano thin film layer containing an out-of-plane electric domain structure, and the self-supporting thin film is prepared by a pulse laser deposition technology. The self-supporting thin film designed by the invention has the capability of keeping an initial-state out-of-plane domain structure, shows excellent ferroelectricity and stable domain structure characteristics, and provides a stable electric domain structure solution for the development of the field of flexible electronic devices.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and in particular to a self-supporting film that maintains an initial out-of-plane electric domain structure and a preparation method thereof. Background Art

[0002] Free-standing films have excellent bending, stretching, and substrate compatibility properties, and have great application potential in information storage, intelligent sensing, biomedicine, energy, and other fields. For free-standing films with electric domain structures, their different electric domain configurations directly affect the realization of the functions of flexible electronic devices. For example, the out-of-plane single-domain structure has characteristics such as high polarization anisotropy and low crosstalk, which makes the film exhibit large saturation polarization and remanent polarization, while an increase in the proportion of in-plane domain structure will significantly reduce the macroscopic ferroelectricity of the film.

[0003] During the release and transfer process of self-supporting films with electric domain structures, a key problem is usually faced: as the nano-film layer containing the out-of-plane electric domain structure separates from the substrate, stress relaxation and surface charge redistribution will occur in the nano-film layer containing the out-of-plane electric domain structure, resulting in the inability to maintain the out-of-plane electric domains in the nano-film layer containing the out-of-plane electric domain structure and the transformation into an in-plane domain structure, which will have an adverse effect on the subsequent application of flexible electronic devices. Summary of the Invention

[0004] The present invention provides a self-supporting film which maintains an initial out-of-plane electric domain structure and a preparation method thereof, so as to solve the deficiencies in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A self-supporting film that maintains an initial out-of-plane electrical domain structure comprises a shielding buffer layer and a nanofilm layer containing the out-of-plane electrical domain structure. The shielding buffer layer exhibits nanostructure characteristics through a layer-island hybrid growth pattern, exhibits a charge shielding effect, and can maintain the initial out-of-plane electrical domain structure of the nanofilm layer.

[0007] Furthermore, the shielding buffer layer is made of any one of SrRuO3, LaNiO3, CaRuO3, and NdNiO3 materials.

[0008] Furthermore, the thickness of the shielding buffer layer is 50-100 nm.

[0009] Furthermore, the resistance value of the shielding buffer layer is 0.4-2.0 kΩ.

[0010] Furthermore, the nano-thin film layer containing the out-of-plane electric domain structure is PbZr 0.2 Ti 0.8Any of perovskite ferroelectric materials such as O3, BaTiO3, PbTiO3, etc.

[0011] Furthermore, the thickness of the nano-thin film layer containing the out-of-plane electric domain structure is 100 to 500 nm.

[0012] The present invention also provides a method for preparing a self-supporting film that maintains an initial out-of-plane electric domain structure, the preparation method comprising:

[0013] (1) Select a substrate and pre-treat it;

[0014] (2) growing a sacrificial layer, a shielding buffer layer, and a nano-thin film layer containing an out-of-plane electric domain structure on the surface of the substrate in order from bottom to top;

[0015] (3) Immersing the substrate-sacrificial layer-shielding buffer layer-nano film layer containing an out-of-plane electric domain structure in a solvent to dissolve the sacrificial layer, thereby obtaining a self-supporting film that maintains the initial out-of-plane electric domain structure.

[0016] Furthermore, the material of the above-mentioned substrate is one of SrTiO3, Nb-SrTiO3, LaAlO3, DyScO3, GdScO3, LiNbO3 and MgO.

[0017] Furthermore, the material of the sacrificial layer is Sr3Al2O6, Ca 1.5 Sr 1.5 Al2O6、La 0.67 Sr 0.33 One of MnO3.

[0018] Furthermore, the solvent is one of deionized water, potassium iodide and hydrochloric acid.

[0019] Furthermore, the pre-treatment steps of the substrate are specifically as follows:

[0020] (1) Immerse the substrate in acetone and ultrasonically clean it at 50-80°C for 5-10 minutes;

[0021] (2) immersing the substrate in anhydrous ethanol and ultrasonically cleaning for 3 to 6 minutes;

[0022] (3) Then, immerse the substrate in deionized water and ultrasonically clean it for 3 to 6 minutes;

[0023] (4) Finally, the substrate is dried using nitrogen.

[0024] Furthermore, in the above steps, the sacrificial layer, the shielding buffer layer and the nano-thin film layer containing the out-of-plane electric domain structure are all deposited by a pulsed laser deposition method.

[0025] Furthermore, during the deposition of the sacrificial layer, the temperature was 700-800° C., the oxygen pressure was 100-140 mTorr, and the laser energy was 280-320 mJ. The sacrificial layer grew in a layered pattern on the substrate, with a dark green plume color and a convergent morphology.

[0026] Furthermore, during the deposition of the shielding buffer layer, the temperature was 600-700°C, the oxygen pressure was 60-100 mTorr, and the laser energy was 260-300 mJ. The shielding buffer layer grew in a layer-island hybrid growth mode on the sacrificial layer, with a light purple plume color and an elliptical shape.

[0027] Furthermore, when the above-mentioned nano-thin film layer containing the out-of-plane electric domain structure is deposited, the temperature is 550-650°C, the oxygen pressure is 80-120mTorr, and the laser energy is 270-310mJ. It has a layer-island mixed growth mode on the shielding buffer layer, and the plume color is bright yellow and the shape tends to be elliptical.

[0028] Furthermore, the steps of immersing the substrate-sacrificial layer-shielding buffer layer-nano film layer containing an out-of-plane electric domain structure in a solvent at a temperature of 5 to 25° C. to dissolve the sacrificial layer, thereby obtaining a self-supporting film retaining the initial out-of-plane electric domain structure are specifically as follows:

[0029] (1) Soak the film with the sacrificial layer in a solvent for 180 to 240 minutes;

[0030] (2) After the sacrificial layer is completely dissolved, the self-supporting film is removed from the solvent using a polyethylene terephthalate film to obtain a self-supporting film that maintains the initial out-of-plane electrical domain structure.

[0031] The technical solution of the present invention has the following beneficial effects:

[0032] 1. A shielding buffer layer is inserted between the sacrificial layer and the nanofilm layer containing an out-of-plane electrical domain structure. The growth pattern of the shielding buffer layer is controlled to give the film nanostructured features. The shielding buffer layer has a charge shielding effect, accumulating sufficient shielding charge at the interface with the nanofilm layer containing the out-of-plane electrical domain structure to compensate for the depolarization field of the film during the release and transfer process, thereby maintaining the initial out-of-plane electrical domain structure of the nanofilm layer. Simultaneously, a solvent with a temperature of 5 to 25°C reduces the dissolution rate of the sacrificial layer to control stress release.

[0033] 2. The self-supporting film that maintains the initial out-of-plane electric domain structure not only has excellent mechanical flexibility, but also can maintain stable room-temperature ferroelectric properties in the self-supporting state, which will help promote the development of flexible ferroelectric materials and further expand them to various practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0035] Figure 1 This is a schematic diagram of the structure of the self-supporting film of Example 1 before water dissolution;

[0036] Figure 2 X-ray diffraction patterns of the self-supporting film of Example 1 before and after water dissolution;

[0037] Figure 3 The vertical PFM (VPFM) and lateral PFM (LPFM) of the free-standing film of Example 1 before water dissolution;

[0038] Figure 4 The vertical PFM (VPFM) and lateral PFM (LPFM) of the self-supporting film after water dissolution in Example 1;

[0039] Figure 5 The vertical PFM (VPFM) and lateral PFM (LPFM) of the free-standing film of comparative example 1 before water dissolution;

[0040] Figure 6 These are the vertical PFM (VPFM) and lateral PFM (LPFM) of the self-supporting film of comparative example 1 after water dissolution. DETAILED DESCRIPTION

[0041] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0042] Example 1

[0043] The present invention provides a self-supporting film that maintains an initial out-of-plane electric domain structure and a preparation method thereof, comprising the following steps:

[0044] a. Select a

[001] SrTiO3 (STO) substrate and pretreat it, specifically comprising the following steps: (1) Immerse the

[001] STO substrate in acetone and ultrasonically clean it at 60°C for 10 minutes; (2) Then immerse the

[001] STO substrate in anhydrous ethanol and ultrasonically clean it for 5 minutes; (3) Then immerse the

[001] STO substrate in deionized water and ultrasonically clean it for 5 minutes; (4) Finally, dry the

[001] STO substrate with nitrogen.

[0045] b. Pulsed laser deposition was used to deposit 50 nm thick Sr3Al2O6 (SAO), 50 nm thick SrRuO3 (SRO), 400 nm thick PbZr 0.2 Ti 0.8 O3(PZT) film, and finally PZT / SRO / SAO / STO film was prepared, such as Figure 1 shown.

[0046] c. The PZT / SRO / SAO / STO sample prepared in the above steps was immersed in deionized water at 15°C for 240 min. After the SAO water-soluble layer was completely dissolved, the PZT / SRO film was removed from the water using a polyethylene terephthalate film to obtain a self-supporting PZT / SRO film that maintained the initial out-of-plane electrical domain structure.

[0047] Figure 2 The X-ray diffraction patterns of the free-standing PZT / SRO film in Example 1 before and after water dissolution show that the PZT layer in the PZT / SRO / SAO / STO film prepared in this invention grows along the (001) direction, without any significant impurities or structural phases. Furthermore, after hydrolysis, the SAO layer is completely removed, while the suspended PZT layer remains single crystalline.

[0048] Figure 3 Figure 2 is the DART-PFM result of the PZT / SRO / SAO / STO film in Example 1 before water dissolution. It can be seen that the film has a regular out-of-plane a / c multi-domain structure, where the bright area represents the out-of-plane c domain distribution, and the dark stripes correspond to the two main in-plane ferroelastic domain distribution directions

[100] and

[010] .

[0049] Figure 4 The DART-PFM results for the free-standing PZT / SRO film in Example 1 show that the free-standing PZT / SRO film prepared by the present invention maintains the regular out-of-plane domain structure prior to water dissolution. During the release and transfer process of the free-standing PZT / SRO film, the charge shielding effect of the shielding buffer layer and the synergistic effect of stress relaxation maintain the initial domain structure in the nanofilm layer, providing an effective method for improving the stability of the out-of-plane domain structure in free-standing films.

[0050] Example 2

[0051] The present invention provides a self-supporting film that maintains an initial out-of-plane electric domain structure and a preparation method thereof, comprising the following steps:

[0052] a. Select a

[001] SrTiO3 (STO) substrate and pretreat it, specifically comprising the following steps: (1) Immerse the

[001] STO substrate in acetone and ultrasonically clean it at 60°C for 10 minutes; (2) Then immerse the

[001] STO substrate in anhydrous ethanol and ultrasonically clean it for 5 minutes; (3) Then immerse the

[001] STO substrate in deionized water and ultrasonically clean it for 5 minutes; (4) Finally, dry the

[001] STO substrate with nitrogen.

[0053] b. Pulsed laser deposition was used to deposit 50 nm thick Sr3Al2O6 (SAO), 50 nm thick SrRuO3 (SRO), and 400 nm thick BaTiO3 (BTO) films on the pretreated

[001] STO substrate, and finally a BTO / SRO / SAO / STO film was prepared.

[0054] c. The BTO / SRO / SAO / STO sample prepared in the above steps was immersed in deionized water at 15°C for 240 min. After the water-soluble SAO layer was completely dissolved, the BTO / SRO film was removed from the water using a polyethylene terephthalate film to obtain a self-supporting BTO / SRO film that maintained the initial out-of-plane electrical domain structure.

[0055] The sample of Example 2 was tested according to the testing method of Example 1. The results showed that the effect of the sample of Example 2 was basically the same as that of Example 1.

[0056] Example 3

[0057] The present invention provides a self-supporting film that maintains an initial out-of-plane electric domain structure and a preparation method thereof, comprising the following steps:

[0058] a. Select a

[001] SrTiO3 (STO) substrate and pretreat it, specifically comprising the following steps: (1) Immerse the

[001] STO substrate in acetone and ultrasonically clean it at 60°C for 10 minutes; (2) Then immerse the

[001] STO substrate in anhydrous ethanol and ultrasonically clean it for 5 minutes; (3) Then immerse the

[001] STO substrate in deionized water and ultrasonically clean it for 5 minutes; (4) Finally, dry the

[001] STO substrate with nitrogen.

[0059] b. Pulsed laser deposition was used to deposit 50 nm thick Sr3Al2O6 (SAO), 80 nm thick SrRuO3 (SRO), 400 nm thick PbZr 0.2 Ti 0.8 O3(PZT) film, and finally PZT / SRO / SAO / STO film was prepared.

[0060] c. The PZT / SRO / SAO / STO sample prepared in the above steps was immersed in deionized water at 15°C for 240 min. After the SAO water-soluble layer was completely dissolved, the PZT / SRO film was removed from the water using a polyethylene terephthalate film to obtain a self-supporting PZT / SRO film that maintained the initial out-of-plane electrical domain structure.

[0061] The sample of Example 3 was tested according to the testing method of Example 1. The results showed that the effect of the sample of Example 3 was basically the same as that of Example 1.

[0062] Comparative Example 1

[0063] The difference between this comparative example and the embodiment is that there is no shielding buffer layer.

[0064] The self-supporting film of the comparative example and the preparation method thereof comprise the following steps:

[0065] a. Select a

[001] STO substrate and pretreat it, specifically including the following steps: (1) immerse the

[001] STO substrate in acetone and ultrasonically clean it at 60°C for 10 minutes; (2) immerse the

[001] STO substrate in anhydrous ethanol and ultrasonically clean it for 5 minutes; (3) then immerse the

[001] STO substrate in deionized water and ultrasonically clean it for 5 minutes; (4) finally dry the

[001] STO substrate with nitrogen.

[0066] b. Pulsed laser deposition was used to sequentially deposit 50 nm thick SAO and 400 nm thick PZT films on the pretreated

[001] STO substrate to obtain a PZT / SAO / STO film.

[0067] c. The PZT / SAO / STO sample prepared in the above steps was immersed in deionized water at 15° C. for 240 min. After the SAO water-soluble layer was completely dissolved, the PZT film was removed from the water using a polyethylene terephthalate film to obtain a self-supporting PZT film.

[0068] Figure 5This is the DART-PFM result of the PZT / SAO / STO film in Comparative Example 1 before water dissolution. It can be seen that the film has the same out-of-plane a / c multi-domain structure as the PZT / SRO / SAO / STO film before water dissolution.

[0069] Figure 6 The DART-PFM results for the free-standing PZT film in Comparative Example 1 show a significant change in the domain structure of the free-standing PZT film prepared in the present invention: the domain structure transforms from the initial out-of-plane a / c multi-domain structure to an in-plane domain structure. During the water dissolution process, the free-standing PZT film cannot maintain the initial out-of-plane domain structure in the nanofilm layer due to the lack of the charge shielding and buffering effect of the shielding buffer layer.

[0070] The disclosed embodiments are described to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A self-supporting film that maintains an initial out-of-plane electric domain structure, characterized in that: The self-supporting film maintaining the initial out-of-plane electric domain structure comprises a shielding buffer layer and a nano-film layer containing the out-of-plane electric domain structure: The shielding buffer layer exhibits nanostructure characteristics through a layer-island hybrid growth mode, has a charge shielding effect, and can maintain the initial out-of-plane electric domain structure of the nano-thin film layer.

2. The self-supporting film maintaining the initial out-of-plane electric domain structure according to claim 1, characterized in that: The shielding buffer layer is any one of SrRuO3, LaNiO3, CaRuO3, and NdNiO3 materials; The thickness of the shielding buffer layer is 50 to 100 nm; The resistance value of the shielding buffer layer is 0.4-2.0 kΩ.

3. The self-supporting film maintaining the initial out-of-plane electric domain structure according to claim 1, characterized in that: The nano film layer containing the out-of-plane electric domain structure is PbZr 0.2 Ti 0.8 Any one of perovskite ferroelectric materials such as O3, BaTiO3, PbTiO3; The thickness of the nano film layer containing the out-of-plane electric domain structure is 100-500 nm.

4. The method for preparing a self-supporting film having an out-of-plane electric domain structure according to any one of claims 1 to 3, wherein: The preparation method comprises: Select a substrate and pre-treat it; A sacrificial layer, a shielding buffer layer, and a nano-thin film layer containing an out-of-plane electric domain structure are sequentially grown on the surface of the substrate from bottom to top; The substrate-sacrificial layer-shielding buffer layer-nano film layer containing an out-of-plane electric domain structure is immersed in a solvent to dissolve the sacrificial layer, thereby obtaining a self-supporting film that maintains the initial out-of-plane electric domain structure.

5. The method for preparing a self-supporting film maintaining an initial out-of-plane electric domain structure according to claim 4, characterized in that: The material of the substrate is one of SrTiO3, Nb-SrTiO3, LaAlO3, DyScO3, GdScO3, LiNbO3 and MgO; The material of the sacrificial layer is Sr3Al2O6, Ca 1.5 Sr 1.5 Al2O6、La 0.67 Sr 0.33 One of MnO3; The solvent is one of deionized water, potassium iodide and hydrochloric acid.

6. The method for preparing a self-supporting film maintaining an initial out-of-plane electric domain structure according to claim 4, characterized in that: The steps of pre-treating the substrate are specifically as follows: Select a substrate, immerse it in acetone, and ultrasonically clean it at 50-80°C for 5-10 minutes; Then, the substrate is immersed in anhydrous ethanol and ultrasonically cleaned for 3 to 6 minutes; Then, the substrate is immersed in deionized water and ultrasonically cleaned for 3 to 6 minutes; Finally, the substrate was dried using nitrogen.

7. The method for preparing a self-supporting film maintaining an initial out-of-plane electric domain structure according to claim 4, characterized in that: In the steps, the sacrificial layer, the shielding buffer layer and the nano-thin film layer containing the out-of-plane electric domain structure are all deposited by a pulsed laser method.

8. The method for preparing a self-supporting film maintaining an initial out-of-plane electric domain structure according to claim 4, characterized in that: The growth parameters of the sacrificial layer include: temperature of 700-800°C, oxygen pressure of 100-140mTorr, laser energy of 280-320mJ, and a layered growth mode on the substrate with a dark green plume color and convergent morphology. The growth parameters of the shielding buffer layer include: temperature of 600-700°C, oxygen pressure of 60-100mTorr, laser energy of 260-300mJ, and a layer-island hybrid growth mode on the sacrificial layer. The feather color is light purple and the shape tends to be elliptical. The growth parameters of the nano-thin film layer containing the out-of-plane electric domain structure include: temperature of 550-650°C, oxygen pressure of 80-120mTorr, laser energy of 270-310mJ, and a layer-island mixed growth mode on the shielding buffer layer. The plume color is bright yellow and the shape tends to be elliptical.

9. The method for preparing a self-supporting film maintaining an initial out-of-plane electric domain structure according to claim 4, characterized in that: The steps of immersing the substrate-sacrificial layer-shielding buffer layer-nano film layer containing an out-of-plane electric domain structure in a solvent at a temperature of 5 to 25° C. to dissolve the sacrificial layer, thereby obtaining a self-supporting film retaining the initial out-of-plane electric domain structure are specifically as follows: Soak the film with the sacrificial layer in the solvent for 180 to 240 minutes; After the sacrificial layer is completely dissolved, the self-supporting film is fished out of the solvent using a polyethylene terephthalate film to obtain a self-supporting film that maintains the initial out-of-plane electric domain structure.

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