CN115714035A - Flexible self-supporting ferroelectric film and preparation method thereof - Google Patents
Flexible self-supporting ferroelectric film and preparation method thereof Download PDFInfo
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- H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
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Abstract
The invention discloses a flexible self-supporting ferroelectric film and a preparation method thereof, wherein the flexible self-supporting ferroelectric film comprises a flexible substrate layer, an electrode layer and a functional layer, wherein the electrode layer is formed on the flexible substrate layer; the functional layer is formed on the electrode layer, and the functional layer is a multilayer structure film with ferroelectric property. The flexible self-supporting ferroelectric film adopting the technical scheme of the invention can keep a stable stress state and ferroelectric property.
Description
Technical Field
The invention relates to the technical field of flexible electronics, in particular to a flexible self-supporting ferroelectric film and a preparation method thereof.
Background
Flexible electronic products have gained wide attention due to their flexibility, multiple functions, adjustable properties, and low power consumption, as well as potential applications in wearable devices, implant systems, and brain-computer interfaces. The ferroelectric material has spontaneous polarization, can realize nonvolatile data storage, and can regulate and control the conductive state in multiple stages, so that the ferroelectric material has wide application prospect in the aspects of memories, memristors, capacitors and the like. Therefore, the flexibility of ferroelectric materials is an important approach to the development of flexible electronic devices.
In recent years, based on Sr 3 Al 2 O 6 The technology of obtaining flexible self-supporting functional films without substrate constraint by (SAO) water-soluble layers attracts great attention, and these films often have excellent mechanical flexibility after being dissolved in water, but the stress state of these flexible self-supporting functional films is often changed after the SAO is removed, so that the ferroelectric properties of the flexible self-supporting functional films are affected. At the same time, baTiO is used as ferroelectric material 3 (BTO) for example, leakage behavior often occurs, resulting in an impaired ferroelectric performance.
Disclosure of Invention
The invention mainly aims to provide a flexible self-supporting ferroelectric film, which aims to ensure that a certain stress exists in a functional layer while ensuring the epitaxial growth of a sample by inserting a flexible substrate layer and an electrode layer between a sacrificial layer and the functional layer, and can increase the breakdown field strength, stabilize the ferroelectric property and improve the storage density by arranging the functional layer into a multilayer structure film.
In order to achieve the above object, the present invention provides a flexible self-supporting ferroelectric thin film comprising:
a flexible substrate layer;
an electrode layer formed on the flexible substrate layer; and
and the functional layer is formed on the electrode layer and is a multilayer structure film with ferroelectric property.
In an alternative embodiment, the functional layer comprises alternately grown layers of ferroelectric material and SrTiO 3 (STO) layer.
In an alternative embodiment, the ferroelectric material layer is BaTiO 3 (BTO) material, the ferroelectric material layer and SrTiO 3 There is epitaxial growth between the (STO) layers.
In an alternative embodiment, the ferroelectric material layer has a thickness in a range of 15nm to 25nm, and the SrTiO layer 3 The thickness of the (STO) layer ranges from 2nm to 5nm.
In an alternative embodiment, the layer of ferroelectric material is SrTiO in the electrode layer and the functional layer 3 Between the (STO) layers of the substrate,the structure of the functional layer farthest from the electrode layer is a ferroelectric material layer.
In an optional embodiment, the flexible substrate layer is flexible SrTiO 3 (STO) material, the flexible SrTiO 3 The (STO) material has a crystal plane orientation of [ 001%]；
And/or the electrode layer is SrRuO 3 (SRO) material;
and/or epitaxial growth is carried out between the flexible substrate layer and the electrode layer.
In an optional embodiment, the thickness of the functional layer ranges from 200nm to 300nm;
and/or the thickness range of the flexible substrate layer is 80 nm-120 nm;
and/or the thickness range of the electrode layer is 40 nm-60 nm.
The invention also provides a preparation method of the flexible self-supporting ferroelectric film, which comprises the following steps:
providing a substrate, and pretreating the substrate;
sequentially growing a sacrificial layer, a flexible substrate layer, an electrode layer and a functional layer on the surface of the substrate from bottom to top, wherein the functional layer is a multilayer structure film with ferroelectric property;
and soaking the substrate-sacrificial layer-flexible substrate layer-electrode layer-functional layer film in a solvent to dissolve the sacrificial layer, thereby obtaining the flexible self-supporting ferroelectric film.
In an alternative embodiment, the substrate is made of SrTiO 3 、Nb-SrTiO 3 、LaAlO 3 、SrLaGaO 4 、SrLaAlO 4 、DyScO 3 、GdScO 3 、BaTiO 3 、LiNbO 3 One of MgO and PMN-PT;
and/or the material of the sacrificial layer is Sr 3 Al 2 O 6 、Ca 1.5 Sr 1.5 Al 2 O 6 、La 0.67 Sr 0.33 MnO 3 One of (1);
and/or the solvent is one of deionized water, potassium iodide and hydrochloric acid.
In an alternative embodiment, the substrate is SrTiO 3 (STO) substrate, said SrTiO 3 (STO) substrate having a crystal plane oriented to [001]]The sacrificial layer is Sr 3 Al 2 O 6 (SAO), the electrode layer is SrRuO 3 (SRO), the functional layer comprising BaTiO grown alternately 3 (BTO) layer and SrTiO 3 And (STO) layer to obtain STO/SAO/STO/SRO/(BTO/STO) n/BTO film, wherein n is a natural number more than 0.
In an alternative embodiment, a substrate is provided, and the step of pretreating the substrate is specifically as follows:
providing a substrate, soaking the substrate in acetone, and ultrasonically cleaning the substrate for 3-20 min at the temperature of 40-70 ℃;
then soaking the substrate in absolute ethyl alcohol, and ultrasonically cleaning for 1-6 min;
then soaking the substrate in deionized water, and ultrasonically cleaning for 1-6 min;
finally, the substrate was dried using nitrogen gas.
In an optional embodiment, in the step of sequentially growing the sacrificial layer, the flexible substrate layer, the electrode layer and the functional layer on the surface of the substrate from bottom to top, a pulse laser deposition method is adopted.
In an optional embodiment, the deposition temperature of the sacrificial layer and the flexible substrate layer is 650-750 ℃, and the deposition oxygen pressure is 1 × 10 -6 Torr～5×10 -6 Torr。
In an optional embodiment, the deposition temperature of the electrode layer is 650-750 ℃, and the deposition oxygen pressure is 5 × 10 - 2 Torr～1×10 -1 Torr；
And/or the deposition temperature of the functional layer is 700-800 ℃, and the deposition oxygen pressure is 1 multiplied by 10 -3 Torr～1×10 -2 Torr。
In an alternative embodiment, the growth mode of the functional layer adopts an alternate growth mode of switching two targets, and the alternate growth is divided into 11 times.
In an optional embodiment, the energy range of laser in the pulse laser deposition process of any one of the sacrificial layer, the flexible substrate layer, the electrode layer and the functional layer is 280mJ to 380mJ, the frequency range is 8Hz to 10Hz, and the deposition time range is 10min to 90min.
In an optional embodiment, the step of soaking the substrate-sacrificial layer-flexible substrate layer-electrode layer-functional layer thin film in a solvent to dissolve the sacrificial layer to obtain the flexible self-supporting ferroelectric thin film specifically comprises:
mixing STO/SAO/STO/SRO/(BTO/STO) n Soaking the BTO film in deionized water for 30-60 min;
after the SAO sacrificial layer is completely dissolved, a Polydimethylsiloxane (PDMS) film is used for leading the STO/SRO/(BTO/STO) n BTO is fished out of water to obtain the flexible self-supporting ferroelectric film with stable ferroelectric property.
The technical scheme of the invention has the following beneficial technical effects:
1. the flexible substrate layer and the electrode layer are inserted between the sacrificial layer and the functional layer, so that the flexible self-supporting ferroelectric film can still maintain the inherent stress after being dissolved, and stable ferroelectric performance is obtained; the introduction of the flexible substrate layer can ensure that the crystal lattice of the flexible substrate layer is matched with the sacrificial layer, and the epitaxial growth is ensured; the electrode layer is added, so that the test of electrical properties can be facilitated.
2. The functional layer is provided with a multilayer structure film with ferroelectric property, so that the breakdown field intensity can be increased, and the functional layer has an important promotion effect on stabilizing the ferroelectric property, improving the storage density and further preparing the dielectric capacitor.
3. The flexible self-supporting ferroelectric film not only keeps excellent mechanical flexibility, but also can maintain stable room temperature ferroelectric performance in a self-supporting state, is beneficial to promoting the development of flexible ferroelectric materials, and further expands to various practical applications.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a lateral view of one embodiment of a flexible self-supporting ferroelectric thin film of the present invention;
FIG. 2 is a flow chart of one embodiment of a method for fabricating a flexible self-supporting ferroelectric thin film according to the present invention;
FIG. 3 is a flow chart of another embodiment of a method for making a flexible self-supporting ferroelectric thin film of the present invention;
FIG. 4 shows the STO/SAO/STO/SRO/(BTO/STO) before water-dissolving prepared according to one embodiment of the present invention 11 Comparative graphs of hysteresis loop (P-V) and switching current (I-V) curves of the/BTO film and the water-soluble flexible self-supporting ferroelectric film.
The reference numbers indicate:
| reference numerals | Name (R) | Reference numerals | Name(s) |
| 1 | Flexible self-supporting ferroelectric |
13 | |
| 111 | |
131 | |
| 113 | |
133 | SrTiO 3 (STO) layer |
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that all directional indicators (such as up, down, left, right, front, back \8230;) in the embodiments of the present invention are only used to explain the relative positional relationship between the components, the motion situation, etc. in a specific posture (as shown in the attached drawings), and if the specific posture is changed, the directional indicator is changed accordingly.
In addition, the descriptions related to "first", "second", etc. in the present invention are only for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise.
In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.
The invention provides a flexible self-supporting ferroelectric film and a preparation method thereof. The requirements of flexible wearable electronic devices can be better met through the self-supporting property of the flexible self-supporting ferroelectric film and less substrate constraint. According to the scheme, the flexible substrate layer and the electrode layer are added on the ferroelectric single crystal film, so that stress support is provided for a structure after the ferroelectric single crystal film is dissolved in water, the stress state and the ferroelectric property before the ferroelectric single crystal film is dissolved in water are kept, the ferroelectric film is set to be a multilayer structure film, the breakdown field intensity of the ferroelectric film is increased by adding other structure layers, the ferroelectric property is further stabilized, and the flexible self-supporting ferroelectric film with stable ferroelectric property is obtained.
Referring to fig. 1, in an embodiment of the present invention, a flexible self-supporting ferroelectric thin film 1 includes:
a flexible base layer 111;
an electrode layer 113, wherein the electrode layer 113 is formed on the flexible base layer 111; and
and a functional layer 13, wherein the functional layer 13 is formed on the electrode layer 113, and the functional layer 13 is a multilayer structure thin film having ferroelectric properties.
In this embodiment, the flexible substrate layer 111 is used to provide the necessary stress maintaining support function for the functional layer 13, and the material of the flexible substrate layer 111 is not limited herein, and may be a thin film structure material with stable performance, and has a relatively thin thickness and a certain flexibility, such as perovskite material, srTiO 3 (STO) or LaAlO 3 . The electrode layer 113 is formed on the flexible substrate layer 111 to provide a certain supporting function, but it is mainly used for detecting conductivity, so it has a certain conductivity, and the specific material is not limited, and may be conductive perovskite material, for example, srRuO 3 (SRO), etc., the functional layer 13 is a film layer which has a ferroelectric property and is added with other structural types in addition to the ferroelectric property, so as to maintain the stability of the ferroelectric property, and the type and the number of the other film layers in the multi-layer structure film are not limited herein.
The technical scheme of the invention has the following beneficial technical effects:
1. the flexible substrate layer 111 and the electrode layer 113 are inserted between the sacrificial layer and the functional layer 13, so that the flexible self-supporting ferroelectric film 1 can still maintain the inherent stress after being dissolved, and stable ferroelectric performance is obtained; the introduction of the flexible substrate layer 111 can ensure that the crystal lattice of the flexible substrate layer is matched with the sacrificial layer, and the epitaxial growth is ensured; the addition of the electrode layer 113 may facilitate the testing of electrical properties.
2. The functional layer 13 is a multi-layer structure film with ferroelectric properties, which can increase the breakdown field strength, and thus has an important promoting effect on stabilizing the ferroelectric properties, increasing the storage density, and further preparing the dielectric capacitor.
3. The flexible self-supporting ferroelectric film 1 not only maintains excellent mechanical flexibility, but also can maintain stable room temperature ferroelectric performance in a self-supporting state, is beneficial to promoting the development of flexible ferroelectric materials, and further expands to various practical applications.
In an alternative embodiment, the functional layer 13 comprises a layer 131 of ferroelectric material and a layer 133 of SrTiO3 (STO) grown alternately.
SrTiO 3 The (STO) material layer has good physical and mechanical properties, and has the advantages of high dielectric constant, low dielectric loss, good thermal stability and the like. Therefore, in this embodiment, a SrTiO3 (STO) layer 133 is added to the functional layer 13, and the material layer can increase the breakdown field strength of the ferroelectric material layer 131, thereby improving the energy storage density and the energy storage efficiency. Here, the ferroelectric material layer 131 and SrTiO 3 (STO) are provided with at least two layers, and the two layers alternately grow in sequence, so that the stability and uniformity of ferroelectric properties are ensured.
In an alternative embodiment, the ferroelectric material layer 131 is BaTiO 3 (BTO) material, epitaxially grown between the ferroelectric material layer 131 and the SrTiO3 (STO) layer 133.
In this embodiment, the ferroelectric material layer 131 is BaTiO 3 (BTO), the material film has better physical and chemical stability, good photocatalysis, photoelectric response and dielectric property, is widely applied to optoelectronic devices, such as ceramic capacitors and the like, and can enable the use performance of the devices to be more stable. Here, baTiO 3 (BTO) andSrTiO 3 epitaxial growth is carried out between the (STO), so that the (STO) and the (STO) both keep better self characteristics, and the method is simple and convenient.
In other embodiments, the ferroelectric material may be potassium dihydrogen phosphate (KH 2PO 4) or the like.
In an alternative embodiment, the ferroelectric material layer 131 has a thickness ranging from 15nm to 25nm, and the SrTiO3 (STO) layer 133 has a thickness ranging from 2nm to 5nm.
In this embodiment, the thickness of the ferroelectric material layer 131 is not too large, which may affect the overall flexibility, and certainly, the thickness is not too small, which may affect the ferroelectric performance, so the thickness is set to be in the range of 15nm to 25nm, for example, 15nm, 17nm, 20nm, 23nm, 25nm, and the like, which has good ferroelectric performance and flexibility. Similarly, the thickness of the SrTiO3 (STO) layer 133 should not be too large, which affects the overall flexibility by increasing the thickness of the material, but certainly not too small, otherwise, the breakdown field strength cannot be increased, so the thickness is set to be in the range of 2nm to 5nm, for example, 2nm, 3nm, 4nm or 5nm, which ensures that the ferroelectric material layer 131 has better breakdown field strength and stable ferroelectric performance.
In an alternative embodiment, the ferroelectric material layer 131 is located between the electrode layer 113 and the SrTiO3 (STO) layer 133 of the functional layer 13, and the structure of the functional layer 13 farthest from the electrode layer 113 is the ferroelectric material layer 131.
In this embodiment, the ferroelectric material layer 131 is adjacent to the electrode layers 113, and the structure of the functional layer 13 farthest from the flexible substrate layer 111 is also the ferroelectric material layer 131, so that the periphery of the functional layer 13 is all the ferroelectric material layer 131, and the ferroelectric performance is good. And the electrode layer 113 is positioned between the functional layer 13 and the flexible substrate layer 111, so that the conductivity is good, and the detection is convenient. The flexible substrate layer 111 is in direct contact with the sacrificial layer, so that growth and molding are easier.
In an alternative embodiment, the flexible substrate layer 111 is flexible SrTiO 3 (STO) material, the flexible SrTiO 3 The (STO) material has a crystal plane orientation of [ 001%]；
And/or, the electrode layer 113 is SrRuO 3 (SRO) material;
and/or, epitaxial growth is performed between the flexible substrate layer 111 and the electrode layer 113.
In this embodiment, the flexible substrate layer 111 is selected to be SrTiO 3 (STO) material and having a crystal plane orientation selected to be [001]]Therefore, the sacrificial layer with the same crystal face orientation can be obtained, and then the sacrificial layer is easy to dissolve in water and remove, and the preparation is convenient. And flexible SrTiO 3 The (STO) material facilitates the growth of the sacrificial layer of the SAO material, thereby improving the preparation efficiency and the preparation quality.
On the basis of the above structure, the selective electrode layer 113 is SrRuO 3 The (SRO) material has better conductivity, and is the only substance in the 4d transition metal oxide which has ferromagnetism and metal conductivity. Meanwhile, the flexible self-supporting ferroelectric film has higher vertical remanent magnetization, higher conductivity and better chemical stability, and can remarkably improve the ferroelectric property and the conductivity of the flexible self-supporting ferroelectric film 1. And has a good lattice matching relationship with the ferroelectric material layer 131 of the functional layer 13, which facilitates the growth of the ferroelectric material layer 131. When the materials are arranged or not arranged, an epitaxial growth mode is adopted between the flexible substrate layer 111 and the electrode layer 113, so that the growth can be facilitated, and the preparation process is simpler.
In an alternative embodiment, the thickness of the functional layer 13 ranges from 200nm to 300nm;
and/or the thickness range of the flexible substrate layer 111 is 80 nm-120 nm;
and/or the thickness range of the electrode layer 113 is 40nm to 60nm.
In this embodiment, the main structure of the flexible self-supporting ferroelectric thin film 1 is the functional layer 13, so the thickness range is thicker than that of other two layers, and certainly, the thickness of the functional layer 13 is not too large, which affects the flexibility; the thickness is not too small, which affects the ferroelectric property and energy storage efficiency. Therefore, the functional layer 13 is set to have a thickness ranging from 200nm to 300nm, for example, 200nm, 230nm, 250nm, 270nm or 300nm, so as to ensure good ferroelectric properties and flexibility. Here, the ferroelectric material layer 131 and SrTiO may be formed according to the above 3 (STO) is provided in such a manner that the number of layers is set to satisfy the thickness of the entire functional layer 13And (4) requiring.
In addition to the above structure, the thickness range of the flexible base layer 111 is not excessively large, and is set to 80nm to 120nm, for example, 80nm, 90nm, 100nm, or 120nm, so that it has a certain stress supporting effect and good flexibility. In addition, the thickness of the electrode layer 113 is set to be in a range of 40nm to 60nm, for example, 40nm, 45nm, 50nm, 55nm, 60nm, or the like, so that the flexibility of the entire device is not affected while good conductivity is ensured.
Referring to fig. 2, the present invention further provides a method for preparing a flexible self-supporting ferroelectric thin film, the method comprising:
step S1: providing a substrate and pretreating the substrate;
step S2: sequentially growing a sacrificial layer, a flexible substrate layer, an electrode layer and a functional layer on the surface of the substrate from bottom to top, wherein the functional layer is a multilayer structure film with ferroelectric property;
and step S3: and soaking the substrate-sacrificial layer-flexible substrate layer-electrode layer-functional layer film in a solvent to dissolve the sacrificial layer, thereby obtaining the flexible self-supporting ferroelectric film.
In the embodiment, the substrate is a foundation for deposition growth of each film layer, and the substrate can be made of perovskite materials or perovskite-like materials, so that the substrate has good stability. In an alternative embodiment, the substrate is made of SrTiO 3 、Nb-SrTiO 3 、LaAlO 3 、SrLaGaO 4 、SrLaAlO 4 、DyScO 3 、GdScO 3 、BaTiO 3 、LiNbO 3 MgO and PMN-PT. In the step S1, the surface of the substrate needs to be kept clean and meet the preset temperature requirement because the surface of the substrate needs to be subjected to film growth, and other films need to be pretreated when grown to meet the growth requirement. The pretreatment includes, but is not limited to, cleaning and activation.
In step S2, a sacrificial layer, a flexible substrate layer, an electrode layer, and a functional layer are sequentially grown on the substrate, where the deposition manner is not limited, and may be, for example, pulsed laser deposition or magnetron sputtering.
In step S3, the prepared film is placed in a solvent, and the sacrificial layer is dissolved and removed, thereby obtaining a desired film from which the substrate and the sacrificial layer are removed. The sacrificial layer may be a water-soluble or other solvent-soluble material, and the solvent may be water or other solvent. Optionally, the material of the sacrificial layer is Sr 3 Al 2 O 6 、Ca 1.5 Sr 1.5 Al 2 O 6 、La 0.67 Sr 0.33 MnO 3 Can be selected as desired. Correspondingly, the solvent is one of deionized water, potassium iodide and hydrochloric acid, and is selected by matching with the sacrificial layer.
The technical scheme of the invention has the following beneficial technical effects:
1. the flexible substrate layer and the electrode layer are inserted between the sacrificial layer and the functional layer, so that the flexible self-supporting ferroelectric film can still maintain inherent stress after being dissolved, and stable ferroelectric performance is obtained; the introduction of the flexible substrate layer can ensure that the crystal lattice of the flexible substrate layer is matched with the sacrificial layer, and the epitaxial growth is ensured; the electrode layer is added, so that the test of electrical properties can be facilitated.
2. The functional layer is provided with a multilayer structure film with ferroelectric property, so that the breakdown field intensity can be increased, and the functional layer has an important promotion effect on stabilizing the ferroelectric property, improving the storage density and further preparing the dielectric capacitor.
3. The flexible self-supporting ferroelectric film not only keeps excellent mechanical flexibility, but also can maintain stable room-temperature ferroelectric performance in a self-supporting state, is beneficial to promoting the development of flexible ferroelectric materials, and is further expanded to various practical applications.
4. The flexible self-supporting ferroelectric film can be prepared by dissolving the flexible sacrificial layer, and the process does not damage the structure of the film, so that the process is simple and convenient.
In an alternative embodiment, the substrate is SrTiO 3 (STO) substrate, said SrTiO 3 (STO) substrate having a crystal plane oriented to [001]]The sacrificial layer is Sr 3 Al 2 O 6 (SAO), the electrode layer is SrRuO 3 (SRO), the functional layer comprising alternately grownBaTiO 3 (BTO) layer and SrTiO 3 And (STO) layer to obtain a STO/SAO/STO/SRO/(BTO/STO) n/BTO film, wherein n is a natural number more than 0.
Because the water solubility of the sacrificial layer is determined by the material and the crystal face orientation of the substrate, the material of the substrate and the material of the sacrificial layer can be selected cooperatively, that is, the lattice constant of the substrate is selected to be matched with the lattice constant of the sacrificial layer, in this embodiment, the crystal face orientation is selected to be [001]]The STO substrate of (1) can obtain better single crystal SAO layer, thereby epitaxially growing Sr 3 Al 2 O 6 The (SAO) has excellent water solubility, can be removed only by using deionized water, has simple process, can not remain on the surface of the STO layer after being dissolved in water, and can not damage an electrode layer and a functional layer. Understandably, sr 3 Al 2 O 6 The lattice constant of (SAO) is well matched to the 4 STO substrate lattice constant, thereby ensuring that SAO can be epitaxially grown, resulting in a smooth surface, while ensuring that functional films grown thereon can be epitaxially grown.
The STO/SRO layer is inserted between the SAO and the functional layer, so that the functional layer for protecting the BTO can still maintain the inherent stress after being dissolved, and the stable ferroelectric property is obtained. The addition of SROs can facilitate the testing of electrical properties. Meanwhile, the BTO and the STO alternately grow in the functional layer, so that the breakdown field intensity can be increased, and the BTO and the STO alternately grow in the functional layer, thereby having an important promotion effect on stabilizing the ferroelectric property, improving the storage density and further preparing the dielectric capacitor.
Here, the thickness ranges of the film layers can refer to the ranges in the above embodiments, and are not described herein again.
In an optional embodiment, providing a substrate, and the step S1 of performing pretreatment on the substrate specifically includes:
step S11: providing a substrate, soaking the substrate in acetone, and ultrasonically cleaning the substrate for 3 to 20min at the temperature of between 40 and 70 ℃;
step S12: then soaking the substrate in absolute ethyl alcohol, and ultrasonically cleaning for 1-6 min;
step S13: then soaking the substrate in deionized water, and ultrasonically cleaning for 1-6 min;
step S14: finally, the substrate was dried using nitrogen gas.
In this embodiment, the purpose of pretreating the substrate is to remove impurities, dirt, and various kinds of grease on the substrate. Soaking in acetone solution, and ultrasonic cleaning in an ultrasonic instrument at 40-70 deg.C (e.g. 50 deg.C, 60 deg.C) for 3-20 min (e.g. 5min, 10min, 15 min) to remove organic impurities. Then taking out the substrate, soaking the substrate in absolute ethyl alcohol, and continuing to perform ultrasonic cleaning in an ultrasonic instrument for 1-6 min, for example, 2min, 3min, 5min and the like. Finally, continuing ultrasonic cleaning for 1-6 min by using deionized water to remove the chemical reagent. After cleaning, the sample was taken out, blown dry with nitrogen and dried for use. Of course, in other embodiments, wiping or other mechanical means may be used for the treatment.
In an optional embodiment, in the step of sequentially growing the sacrificial layer, the flexible substrate layer, the electrode layer and the functional layer on the surface of the substrate from bottom to top, a pulse laser deposition method is adopted.
In the embodiment, the pulsed laser deposition method is used for depositing the layers, so that a multi-component film with a desired stoichiometric ratio is easier to obtain, namely, the multi-component film has good composition preservation performance, and meanwhile, the method has the advantages of high deposition rate, short test period, low requirement on substrate temperature, and uniform prepared film, so that the quality of the flexible self-supporting ferroelectric film is improved.
In an optional embodiment, the deposition temperature of the sacrificial layer and the flexible substrate layer is 650-750 ℃, and the deposition oxygen pressure is 1 × 10 -6 Torr～5×10 -6 Torr。
In an optional embodiment, the deposition temperature of the electrode layer is 650-750 ℃, and the deposition oxygen pressure is 5 × 10 - 2 Torr～1×10 -1 Torr；
And/or the deposition temperature of the functional layer is 700-800 ℃, and the deposition oxygen pressure is 1 multiplied by 10 -3 Torr～1×10 -2 Torr。
According to the material characteristics, the deposition sacrificial layer and the flexible substrate layer can be set on the basis of ensuring better deposition effectThe deposition temperature ranges are 650 ℃ to 750 ℃, for example, 650 ℃, 670 ℃,700 ℃, 720 ℃, 750 ℃ and the like. And the oxygen pressure range of the deposition of the two is 1 x 10 -6 Torr～5×10 -6 Torr, e.g. 1X 10 -6 Torr、2×10 -6 Torr、3×10 -6 Torr and the like.
Meanwhile, the deposition temperature of the electrode layer is 650 ℃ to 750 ℃, for example, 650 ℃, 670 ℃,700 ℃, 720 ℃, 750 ℃ and the like. The oxygen pressure range of the deposition is 5 x 10 -2 Torr～1×10 -1 Torr, e.g. 5X 10 -2 Torr、7×10 -2 Torr、9×10 - 2 Torr and the like.
The deposition temperature of the functional layer is 700 ℃ to 800 ℃, for example, 700 ℃, 750 ℃, 770 ℃, 790 ℃ and the like, and the deposition oxygen pressure is 1 × 10 -3 Torr～1×10 -2 Torr, e.g. 2X 10 -3 Torr、4×10 -3 Torr、6×10 -3 Torr、8×10 -3 Torr and the like.
In an optional embodiment, the energy range of the laser in the pulse laser deposition process of any one of the sacrificial layer, the flexible substrate layer, the electrode layer and the functional layer is 280mJ to 380mJ, the frequency range is 8Hz to 10Hz, and the deposition time range is 10min to 90min.
Here, when each of the sacrificial layer, the flexible substrate layer, the electrode layer, and the functional layer is deposited, the energy range of the laser is set to be 280mJ to 380mJ during the pulsed laser deposition, and the range may take values of 280mJ, 300mJ, 320mJ, 350mJ, 380mJ, and the like. The frequency range of the laser is set to be 8Hz to 10Hz, such as 8Hz, 9Hz, 10Hz, etc., and the deposition time range is set to be 10min to 90min, such as 20min, 30min, 40min, 70min, etc.
The invention optimizes the deposition temperature, dynamic oxygen partial pressure, laser energy, laser pulse frequency, deposition time and the like of the SAO water-soluble layer, the STO, the SRO and the BTO-STO prepared by the pulse laser method, and prepares the SAO sacrificial layer, the STO, the SRO and the BTO-STO film which grow in a preferred orientation, have smooth surfaces and excellent water solubility.
In an optional embodiment, the growth mode of the functional layer is an alternate growth mode of switching between two targets, and the alternate growth is divided into 11 times.
In this embodiment, to achieve an alternating layer of BTO-STO, BTO and STO targets are placed on adjacent targets, and the structure for deposition is placed in the growth chamber and controlled to be within a suitable distance from both targets. And bombarding the BTO target by a laser for a plurality of times, then rapidly transferring to the STO target to bombard the BTO target for a plurality of times, and repeating the steps to obtain the BTO-STO film layer which alternately grows, wherein the number of times of alternate growth can be set as 11 times.
Referring to fig. 3, in an alternative embodiment, the step S3 of soaking the substrate-sacrificial layer-flexible base layer-electrode layer-functional layer thin film in a solvent to dissolve the sacrificial layer so as to obtain the flexible self-supporting ferroelectric thin film specifically includes:
step S31: mixing STO/SAO/STO/SRO/(BTO/STO) n Soaking the BTO film in deionized water for 30-60 min;
step S32: after the SAO sacrificial layer is completely dissolved, a Polydimethylsiloxane (PDMS) film is used for leading STO/SRO/(BTO/STO) n the/BTO is fished out from the water to obtain the flexible self-supporting ferroelectric film with stable ferroelectric property.
When the water-soluble sacrificial layer material SAO is used, the prepared film is soaked in deionized water, the method is simpler and more convenient, is environment-friendly, and does not damage STO/SRO/(BTO/STO) n Structure of BTO film. After the sacrificial layer is dissolved, STO/SRO/(BTO/STO) is put through PDMS n The BTO is fished out of water, and the PDMS has better chemical stability and superior extensibility, so that the integrity of a film structure can be ensured, and the subsequent deformation experiments such as bending, hitting and stretching are facilitated. Of course, in other embodiments, other flexible materials may be selected to take out the film, such as cloth-based adhesive tape, polyimide, etc.
The flexible self-supporting BTO film prepared by the invention not only keeps excellent mechanical flexibility, but also can maintain stable room temperature ferroelectric property in a self-supporting state, is beneficial to promoting the development of flexible ferroelectric materials, and further expands to various practical applications.
The following specific preparation examples are given as an illustration, and are not to be construed as limiting.
Example one
Flexible self-supporting BaTiO with stable ferroelectric property 3 The preparation method of the film comprises the following steps:
step S1: selecting an STO [001] substrate and pretreating the substrate, wherein the method specifically comprises the following steps:
step S11: soaking STO 001 substrate in acetone, and ultrasonic cleaning at 60 deg.C for 10min;
step S12: then soaking STO 001 substrate in absolute ethyl alcohol, ultrasonic cleaning for 5min;
step S13: then immersing STO 001 substrate in deionized water, ultrasonic cleaning for 5min;
step S14: finally, the STO 001 substrate was dried with nitrogen.
Step S2: a. application of pulsed laser deposition method to pretreated STO [001]]Selecting Sr on the substrate 3 Al 2 O 6 (SAO) deposition of a target material at a deposition temperature of 700 ℃ and a dynamic oxygen partial pressure of 3X 10 -6 And Torr, the laser energy and frequency are respectively 300mJ and 10Hz, and the deposition time is 20min, so that the SAO water-soluble layer is prepared.
b. And after the preparation is finished, keeping the temperature, the oxygen pressure, the laser energy and the frequency unchanged, switching a target position to an STO target material, and depositing on the STO/SAO for 10min to prepare an STO/SAO/STO sample.
c. Subsequently, the oxygen pressure was increased to 8X 10 with the temperature being kept constant -2 And (3) Torr, after the oxygen pressure is stabilized, selecting an SRO target material for deposition, keeping the laser energy at 370mJ, the frequency at 10Hz and the deposition time at 10min in the deposition process, and preparing the STO/SAO/STO/SRO sample.
d. After the growth of SRO is finished, the temperature is raised to 780 ℃, and the oxygen pressure is reduced to 5 multiplied by 10 -3 Torr, after the temperature and oxygen pressure are stable, adopting a double-target switching mode, respectively selecting BTO and STO targets to alternately grow, wherein the laser energy and frequency are respectively 330mJ and 10Hz in the growth process, the single growth time of BTO is 2.5min, the single growth time of STO is 2.5min, and the single growth time of STO is prolongedIs 0.5min, the times of alternate growth are 11 times, and the STO/SAO/STO/SRO/(BTO-STO) is finally prepared 11 A film.
e. Then STO/SAO/STO/SRO/(BTO-STO) is obtained 11 After the film is formed, a layer of BTO film is covered on the film by using the same growth parameters as the step d to obtain the final STO/SAO/STO/SRO/(BTO-STO) 11 A BTO film.
And step S3: STO/SAO/STO/SRO/(BTO-STO) prepared by the steps 11 Soaking the BTO sample in deionized water for 30min, and dissolving the SAO water-soluble layer completely, and then treating STO/SRO/(BTO/STO) with Polydimethylsiloxane (PDMS) 11 The BTO is fished out of the water, and the flexible self-supporting BTO film with stable ferroelectric property is obtained.
Bending experiments are carried out on the formed flexible self-supporting BTO film, and the results show that the flexible self-supporting BaTiO transferred to PDMS 3 The film is capable of maintaining integrity and excellent flexibility in a bent state.
Referring to FIG. 4, the flexible self-supporting BaTiO can be seen by P-V 3 The film has the characteristics of the ferroelectric hysteresis loop of a typical ferroelectric material before and after water dissolution, and is not obviously different, so that the stress state of the film before water dissolution is kept; the I-V curve also shows the same leakage current characteristics, confirming that the flexible self-supporting BaTiO 3 The film has stable ferroelectric properties.
Example two
Flexible self-supporting BaTiO with stable ferroelectric property 3 The preparation method of the film comprises the following steps:
step S1: selecting an STO [001] substrate and pretreating the substrate, wherein the method specifically comprises the following steps:
step S11: soaking STO 001 substrate in acetone, and ultrasonic cleaning at 60 deg.C for 10min;
step S12: then soaking STO 001 substrate in absolute ethyl alcohol, ultrasonic cleaning for 5min;
step S13: then soaking STO 001 substrate in deionized water, ultrasonic cleaning for 5min;
step S14: finally, the STO 001 substrate was dried with nitrogen.
Step S2: a. application of pulsed laser deposition method to pretreated STO [001]]Selecting Sr on the substrate 3 Al 2 O 6 Depositing (SAO) target material at 700 deg.C and dynamic oxygen partial pressure of 3 × 10 -6 And Torr, the laser energy and the laser frequency are respectively 300mJ and 10Hz, and the deposition time is 20min, so that the SAO water-soluble layer is prepared.
b. And after the preparation is finished, keeping the temperature, the oxygen pressure, the laser energy and the frequency unchanged, switching the target position to the STO target material, depositing on the STO/SAO for 10min, and preparing to obtain the STO/SAO/STO sample.
c. Subsequently, the oxygen pressure was increased to 8X 10 while keeping the temperature constant -2 And (4) Torr, after the oxygen pressure is stabilized, selecting an SRO target for deposition, keeping laser energy at 370mJ, frequency at 10Hz and deposition time at 10min in the deposition process, and preparing an STO/SAO/STO/SRO sample.
d. After the growth of SRO is finished, the temperature is raised to 780 ℃, and the oxygen pressure is reduced to 5 multiplied by 10 -3 Torr, after the temperature and oxygen pressure are stable, adopting a mode of double-target switching, respectively selecting BTO and STO targets to alternately grow, wherein the laser energy and frequency are respectively 330mJ and 10Hz in the growth process, the single growth time of BTO is 5min, the single growth time of STO is 1min, and the alternate growth times are 5 times, and finally preparing the STO/SAO/STO/SRO/(BTO-STO) 5 A film.
e. Then STO/SAO/STO/SRO/(BTO-STO) is obtained 5 After the film is formed, a layer of BTO film is covered on the film by using the same growth parameters as the step d to obtain the final STO/SAO/STO/SRO/(BTO-STO) 5 A BTO film.
And step S3: STO/SAO/STO/SRO/(BTO-STO) prepared by the steps 5 Soaking the BTO sample in deionized water for 30min, and dissolving the SAO water-soluble layer completely, and then treating STO/SRO/(BTO/STO) with Polydimethylsiloxane (PDMS) 5 The BTO is fished out of the water, and the flexible self-supporting BTO film with stable ferroelectric property is obtained.
EXAMPLE III
Flexible self-supporting BaTiO with stable ferroelectric property 3 Method for producing thin filmThe method comprises the following steps:
step S1: selecting an STO [001] substrate and pretreating the substrate, wherein the method specifically comprises the following steps:
step S11: soaking STO 001 substrate in acetone, and ultrasonic cleaning at 60 deg.C for 10min;
step S12: then soaking STO 001 substrate in absolute ethyl alcohol, ultrasonic cleaning for 5min;
step S13: then soaking STO 001 substrate in deionized water, ultrasonic cleaning for 5min;
step S14: finally, the STO 001 substrate was dried with nitrogen.
Step S2: a. application of pulsed laser deposition method to pretreated STO [001]]Selecting Sr on the substrate 3 Al 2 O 6 (SAO) deposition of a target material at a deposition temperature of 700 ℃ and a dynamic oxygen partial pressure of 3X 10 -6 And Torr, the laser energy and the laser frequency are respectively 300mJ and 10Hz, and the deposition time is 20min, so that the SAO water-soluble layer is prepared.
b. And after the preparation is finished, keeping the temperature, the oxygen pressure, the laser energy and the frequency unchanged, switching the target position to the STO target material, depositing on the STO/SAO for 10min, and preparing to obtain the STO/SAO/STO sample.
c. Subsequently, the oxygen pressure was increased to 8X 10 while keeping the temperature constant -2 And (4) Torr, after the oxygen pressure is stabilized, selecting an SRO target for deposition, keeping laser energy at 370mJ, frequency at 10Hz and deposition time at 10min in the deposition process, and preparing an STO/SAO/STO/SRO sample.
d. After the growth of SRO is finished, the temperature is raised to 780 ℃, and the oxygen pressure is reduced to 5 multiplied by 10 -3 Torr, after the temperature and oxygen pressure are stable, adopting a mode of double-target switching, respectively selecting BTO and STO targets to alternately grow, wherein the laser energy and frequency are respectively 330mJ and 10Hz in the growth process, the single growth time of BTO is 1.25min, the single growth time of STO is 0.25min, the alternate growth times are 23 times, and finally preparing the STO/SAO/STO/SRO/(BTO-STO) 23 A film.
e. Then STO/SAO/STO/SRO/(BTO-STO) is obtained 23 After the film is formed, the film is covered by the growth parameters the same as those in the step 5Covering with a BTO film to obtain the final STO/SAO/STO/SRO/(BTO-STO) 23 A BTO film.
And step S3: STO/SAO/STO/SRO/(BTO-STO) prepared by the steps 23 Soaking the BTO sample in deionized water for 30min, and dissolving the SAO water-soluble layer completely, and then treating STO/SRO/(BTO/STO) with Polydimethylsiloxane (PDMS) 23 The BTO is fished out of the water, and the flexible self-supporting BTO film with stable ferroelectric property is obtained.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (17)
1. A flexible self-supporting ferroelectric thin film, comprising:
a flexible base layer;
an electrode layer formed on the flexible substrate layer; and
and the functional layer is formed on the electrode layer and is a multilayer structure film with ferroelectric property.
2. The flexible self-supporting ferroelectric thin film of claim 1, wherein the functional layer comprises alternating layers of ferroelectric material and SrTiO 3 (STO) layer.
3. The flexible self-supporting ferroelectric thin film of claim 2, wherein the layer of ferroelectric material is BaTiO 3 (BTO) material, the ferroelectric material layer and SrTiO 3 Epitaxial growth occurs between the (STO) layers.
4. The flexible self-supporting ferroelectric thin film of claim 3, wherein the ferroelectric material layer has a thickness in the range of 15nm to 25nm, and the SrTiO is 3 The thickness of the (STO) layer ranges from 2nm to 5nm.
5. The flexible self-supporting ferroelectric thin film of claim 3, wherein the layer of ferroelectric material is located between the SrTiO of the electrode layer and the functional layer 3 The structure of the functional layer furthest from the electrode layer between the (STO) layers is a ferroelectric material layer.
6. The flexible self-supporting ferroelectric thin film of any one of claims 1 to 5, wherein the flexible substrate layer is flexible SrTiO 3 (STO) material, the flexible SrTiO 3 (STO) Material has a crystal plane oriented as [001]]；
And/or the electrode layer is SrRuO 3 (SRO) material;
and/or epitaxial growth is carried out between the flexible substrate layer and the electrode layer.
7. The flexible self-supporting ferroelectric thin film of any one of claims 1 to 5, wherein the functional layer has a thickness in the range of 200nm to 300nm;
and/or the thickness range of the flexible substrate layer is 80 nm-120 nm;
and/or the thickness range of the electrode layer is 40 nm-60 nm.
8. A method of preparing a flexible self-supporting ferroelectric thin film as in any one of claims 1 to 7, comprising:
providing a substrate, and pretreating the substrate;
sequentially growing a sacrificial layer, a flexible substrate layer, an electrode layer and a functional layer on the surface of the substrate from bottom to top, wherein the functional layer is a multilayer structure film with ferroelectric property;
and soaking the substrate-sacrificial layer-flexible substrate layer-electrode layer-functional layer film in a solvent to dissolve the sacrificial layer, thereby obtaining the flexible self-supporting ferroelectric film.
9. The flexible self-supporting ferroelectric thin film of claim 8The preparation method of the film is characterized in that the material of the substrate is SrTiO 3 、Nb-SrTiO 3 、LaAlO 3 、SrLaGaO 4 、SrLaAlO 4 、DyScO 3 、GdScO 3 、BaTiO 3 、LiNbO 3 One of MgO and PMN-PT;
and/or the material of the sacrificial layer is Sr 3 Al 2 O 6 、Ca 1.5 Sr 1.5 Al 2 O 6 、La 0.67 Sr 0.33 MnO 3 One of (1);
and/or the solvent is one of deionized water, potassium iodide and hydrochloric acid.
10. The method of claim 8, wherein the substrate is SrTiO 3 (STO) substrate, said SrTiO 3 (STO) substrate having a crystal plane oriented to [001]]The sacrificial layer is Sr 3 Al 2 O 6 (SAO), the electrode layer is SrRuO 3 (SRO), the functional layer comprising BaTiO grown alternately 3 (BTO) layer and SrTiO 3 And (STO) layer to obtain STO/SAO/STO/SRO/(BTO/STO) n/BTO film, wherein n is a natural number more than 0.
11. The method of claim 8, wherein the step of providing a substrate and pre-treating the substrate comprises:
providing a substrate, soaking the substrate in acetone, and ultrasonically cleaning the substrate for 3 to 20min at the temperature of between 40 and 70 ℃;
then soaking the substrate in absolute ethyl alcohol, and ultrasonically cleaning for 1-6 min;
then soaking the substrate in deionized water, and ultrasonically cleaning for 1-6 min;
finally, the substrate was dried using nitrogen.
12. The method for preparing a flexible self-supporting ferroelectric thin film as claimed in any one of claims 8 to 11, wherein a pulsed laser deposition method is employed in the step of growing the sacrificial layer, the flexible base layer, the electrode layer and the functional layer on the surface of the substrate in this order from bottom to top.
13. The method for preparing a flexible self-supporting ferroelectric thin film as claimed in claim 12, wherein the sacrificial layer and the flexible base layer are deposited at a temperature of 650 ℃ to 750 ℃ and a deposition oxygen pressure of 1 x 10 -6 Torr～5×10 -6 Torr。
14. The method for preparing a flexible self-supporting ferroelectric thin film as claimed in claim 13, wherein the deposition temperature of said electrode layer is 650 ℃ to 750 ℃ and the deposition oxygen pressure is 5 x 10 -2 Torr～1×10 -1 Torr；
And/or the deposition temperature of the functional layer is 700-800 ℃, and the deposition oxygen pressure is 1 multiplied by 10 -3 Torr～1×10 - 2 Torr。
15. The method for preparing a flexible self-supporting ferroelectric thin film as claimed in claim 12, wherein the functional layer is grown by an alternate growth method with dual-target switching, and the alternate growth is divided into 11 times.
16. The method of claim 12, wherein the energy range of the laser in the pulsed laser deposition process for any of the sacrificial layer, the flexible substrate layer, the electrode layer and the functional layer is 280mJ to 380mJ, the frequency range is 8Hz to 10Hz, and the deposition time range is 10min to 90min.
17. The method for preparing a flexible self-supporting ferroelectric thin film according to claim 10, wherein the step of immersing the substrate-sacrificial layer-flexible base layer-electrode layer-functional layer thin film in a solvent to dissolve the sacrificial layer to obtain the flexible self-supporting ferroelectric thin film comprises:
mixing STO/SAO/STO/SRO/(BTO/STO) n Soaking the BTO film in deionized water for 30-60 min;
after the SAO sacrificial layer is completely dissolved, a Polydimethylsiloxane (PDMS) film is used for leading the STO/SRO/(BTO/STO) n BTO is fished out of water to obtain the flexible self-supporting ferroelectric film with stable ferroelectric property.
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| WO2024109847A1 (en) * | 2022-11-24 | 2024-05-30 | 深圳先进技术研究院 | Flexible self-supporting ferroelectric film and preparation method therefor |
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| WO2024109847A1 (en) * | 2022-11-24 | 2024-05-30 | 深圳先进技术研究院 | Flexible self-supporting ferroelectric film and preparation method therefor |
| CN117328139A (en) * | 2023-09-14 | 2024-01-02 | 西安交通大学 | Flexible transparent potassium-sodium niobate-based leadless ferroelectric single crystal film and preparation method thereof |
| CN117328139B (en) * | 2023-09-14 | 2024-05-10 | 西安交通大学 | Flexible transparent potassium-sodium niobate-based leadless ferroelectric single crystal film and preparation method thereof |
| CN117604461A (en) * | 2023-11-29 | 2024-02-27 | 成光新材料科技(无锡)有限公司 | Preparation method of epitaxial pleated film |
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