CN112259374A - BST-based multilayer dielectric enhanced film and preparation method thereof - Google Patents
BST-based multilayer dielectric enhanced film and preparation method thereof Download PDFInfo
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- 238000004528 spin coating Methods 0.000 claims abstract description 17
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- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 36
- 238000010438 heat treatment Methods 0.000 claims description 31
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- 238000001035 drying Methods 0.000 claims description 22
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- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 18
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- 150000004703 alkoxides Chemical class 0.000 claims description 10
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 claims description 10
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 10
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- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G4/00—Fixed capacitors; Processes of their manufacture
- H01G4/002—Details
- H01G4/005—Electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G4/00—Fixed capacitors; Processes of their manufacture
- H01G4/002—Details
- H01G4/005—Electrodes
- H01G4/008—Selection of materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G4/00—Fixed capacitors; Processes of their manufacture
- H01G4/002—Details
- H01G4/018—Dielectrics
- H01G4/06—Solid dielectrics
- H01G4/14—Organic dielectrics
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G4/00—Fixed capacitors; Processes of their manufacture
- H01G4/33—Thin- or thick-film capacitors
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Abstract
The invention discloses a BST-based multilayer dielectric enhancement film and a preparation method thereof. The structure is to use sol-gel spin coating to prepare a film, and multilayer heterostructure films with different period thicknesses are obtained through different sol concentrations and spin coating processes.
Description
Technical Field
The invention relates to the technical field of materials, in particular to a BST-based multilayer dielectric enhancement film and a preparation method thereof.
Background
It is desirable to increase the specific capacitance of thin film capacitors by reducing the dielectric layer thickness and by employing high dielectric constant dielectric materials. Developed countries such as the United states and Japan achieve great achievements in the research of thin film type integrated capacitor materials and device preparation technology and the device development, and a plurality of thin film type integrated capacitor products which are mature in process and protected by intellectual property rights are formed. Currently, with the introduction of large-scale integrated circuit technology and the multi-functional integration prospect beyond Moore's law, the integration of high-density and high-integration passive devices based on thin film integration technology, especially thin film type integrated capacitors with small size and high performance, is actively researched internationally. Nevertheless, there are many key problems to be solved in order to apply the existing high performance thin film dielectric material to the practical application of high performance, high integration thin film capacitor. For example, from the perspective of capacitor materials, the dielectric constant of the current films is not high enough, the specific capacitance value is different from the foreign level, the dielectric strength of the films is still low, and the fatigue resistance of the films cannot meet the requirements of practical application of capacitors.
In the case of high-density and high-integration electronic products, the size of the capacitor is required to be further reduced, the specific capacitance and the electrical property of the capacitor are improved, and under the condition of determining a material system, the specific capacitance is usually improved by reducing the thickness of the film, however, after the thickness of the ferroelectric film is reduced, the dielectric constant is reduced, the film has holes, the leakage current of the film is increased, the withstand voltage is reduced, and the surface smoothness and the temperature stability are deteriorated, so that the single-layer film capacitor cannot meet the application requirements, and a multi-layer film structure is a possible solution.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention provides a BST-based multilayer dielectric enhancement film and a preparation method thereof.
The invention adopts the following technical scheme:
a BST-based multilayer dielectric enhancement film comprises a substrate, wherein a sol-gel method is adopted to spin a multilayer heterogeneous film on the substrate, an Au electrode is deposited on the multilayer heterogeneous film by utilizing magnetron sputtering, and the multilayer heterogeneous film is formed by alternately stacking BST films and BTO films.
Preferably, the thickness of each of the plurality of heterogeneous thin films is equal.
Preferably, the substrate is Pt/Ti/SiO2/Si。
A preparation method of a BST-based multi-layer dielectric enhancement film comprises the following steps:
selecting a substrate, and carrying out ultrasonic cleaning and drying treatment on the substrate;
barium acetate, strontium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizing agent, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, and formamide is used as a drying agent to prepare BST precursor sol; similarly, barium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, and formamide is used as a drying agent to prepare BTO precursor sol;
spin coating, drying, thermal decomposition and pre-crystallization treatment are carried out on a substrate to obtain a pre-crystallization film to be required; repeating for multiple times to obtain a multilayer heterostructure film, and finally uniformly performing high-temperature annealing treatment;
one corner of the film is corroded by hydrofluoric acid, and then Au is magnetically sputtered on the film as a top electrode through a mask plate.
Preferably, the thickness of each layer is 40-160 nm.
Preferably, the concentration of the precursor sol of BST and the concentration of the precursor sol of BTO are 0.2-0.3 mol/L.
Preferably, the pH value of a precursor solution of BST and BTO is controlled to be 3-4 by adjusting the content of acetic acid; formamide is added as a drying agent according to the molar mass ratio of 1:20, so that the volatilization and decomposition of organic matters are more moderate.
Preferably, the drying temperature is 120 ℃, and the drying time is 15 min; firstly, at a low temperature rising rate: heating from room temperature to 350 deg.C at 1.5 deg.C/min, and maintaining for 5 min; then at a high temperature rise rate: heating to the pre-crystallization temperature of 600 ℃ at the temperature of 4 ℃/min, preserving the heat for 10min, and annealing to obtain a single layer of film.
Preferably, the top electrode has a diameter of 0.5mm and a thickness of 100 nm.
Preferably, the multilayer heterogeneous thin film is subjected to one-step high-temperature annealing treatment, the annealing temperature is 700 ℃, the heat preservation time is 30min, and the multilayer heterogeneous thin film is taken out after being cooled to the room temperature.
The invention has the beneficial effects that:
1) compared with a homogeneous film, the heterogeneous film forms space charge accumulation at a heterogeneous interface due to the Maxwell-Wagner effect, space charge polarization is generated, and the polarizability of the whole film system is improved, so that the dielectric enhancement is shown as the whole.
2) The film forming quality of the film is obviously improved by adding formamide, the occurrence of holes and cracks is reduced, and the surface of the film is smoother.
Drawings
FIGS. 1(a) -1 (d) are schematic structural diagrams of BST-based multi-layer dielectric enhancement films of examples 1, 2, 3 and 4, respectively;
FIG. 2 is a schematic representation of a multilayer heterostructure of the present invention, i.e., at Pt/Ti/SiO2A BST/BTO multilayer heterogeneous thin film prepared on a Si substrate;
FIGS. 3 and 4 are flow charts of the preparation of BST and BTO sols;
FIGS. 5(a) -5 (d) are SEM photographs of surface features with total thickness of about 480nm and periodic thicknesses of 40nm, 80nm, 120nm and 160nm, respectively;
FIGS. 6(a) and 6(b) are graphs of dielectric constant, dielectric loss and leakage current for total thickness of about 480nm and periodic thicknesses of 40nm, 80nm, 120nm and 160nm, respectively.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples.
Examples
As shown in FIG. 2, a BST-based multilayer dielectric enhancement film comprises a substrate, wherein the substrate can be Pt/Ti/SiO2the/Si material, i.e. prepared on a Si substrate 6 with Pt as bottom electrode 3, SiO2As barrier layer 5, Ti as bottom electrode and SiO2And a transition layer 4 therebetween. Then adopting a sol-gel method toSpin-coating a multilayer heterogeneous film 2 on a substrate, depositing an Au electrode 1 on the multilayer heterogeneous film by utilizing magnetron sputtering, wherein the multilayer heterogeneous film is a multilayer BST/BTO film, the multilayer heterogeneous film is prepared by spin-coating on the substrate by adopting a sol-gel method, firstly, the BST film is prepared, then, the BTO film is prepared on the BST film, the BST film and the BTO film are alternately arranged, and the Au electrode is deposited on the multilayer heterogeneous film by utilizing magnetron sputtering; wherein, the thickness relation of each layer of the BST/BTO heterostructure is as follows: 1:1.
According to the invention, the BST and BTO sol is prepared by a sol-gel method, the BST/BTO heterogeneous multilayer film is prepared by a spin coating method, and the cycle thickness of the film can be regulated and controlled by selecting different concentrations and spin coating rotating speeds.
A preparation method of a BST-based multi-layer dielectric enhancement film comprises the following steps:
step 1: selecting Pt/Ti/SiO2The substrate is subjected to ultrasonic cleaning by using deionized water-alcohol-acetone-alcohol-deionized water and drying treatment.
Step 2: as shown in fig. 3 and 4, barium acetate, strontium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent to prepare BST sol, the pH value of a precursor solution of BST is controlled to be 3-4, and the ratio of the solution to formamide is 1: 20; similarly, barium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent to prepare BTO precursor sol, the pH value of BTO precursor solution is controlled to be 3-4, and the ratio of the solution to the formamide is 1: 20.
And step 3: in Pt/Ti/SiO2Coating on a Si substrate at low rotation speed and high rotation speed, drying on a heating table at 120 ℃ for 15min, and heating at a low heating rate: heating from room temperature to 350 deg.C at 1.5 deg.C/min, and maintaining for 5 min; then at a high temperature rise rate: heating to the pre-crystallization temperature of 600 ℃ at the temperature of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the single-layer film. The first film may be a BST film or a BTO film.
And 4, step 4: and (3) repeating the step (3), when the last layer of thin film is spin-coated, carrying out one-step high-temperature annealing treatment on the multiple layers of heterogeneous thin films, wherein the annealing temperature is 600-750 ℃, the heat preservation time is 30min, and cooling to room temperature and then taking out.
And 5: one corner of the film is corroded by hydrofluoric acid, and then Au is magnetically sputtered on the film through a mask plate to serve as a top electrode, wherein the diameter of the Au top electrode is 0.5mm, and the thickness of the Au top electrode is 100 nm.
The structure is characterized in that a sol-gel spin coating film is used for preparing the film, a multi-layer heterostructure film with different period thicknesses is obtained through different sol concentrations and a spin coating process, and a Maxwell series capacitor is formed by a Maxwell-Wagner effect between heterogeneous transition layers and an insulated ferroelectric film layer, so that dielectric enhancement is realized. The invention improves the problem of dielectric property reduction caused by further reducing the thickness of the film, and enables the dielectric constant of the material to be increased sharply.
Comparative example 1
Eight BST homogeneous films with a total thickness of about 480nm were prepared, including:
barium acetate, strontium acetate and tetrabutyl titanate are used as metal alkoxide precursor raw materials, the molar ratio is 0.6:0.4:1, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent, BST sol with the concentration of 0.2mol/L is prepared at 80 ℃, the pH value of BST precursor solution is controlled to be 3-4, the ratio of the solution to the formamide is 1:20, and after 5 hours of magnetic stirring, the BST sol is aged for 24 hours.
Pt/Ti/SiO after cleaning and drying2BST sol is coated on a Si substrate in a spin mode, the low speed is firstly 1500r/min for 10s, and then the substrate is rotated at the high speed of 8000r/min for 40 s. Drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and holding for 5 min. And then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the single-layer film. Repeating the process eight times to obtain eight layers of BST thin films, and finally performing one-time annealing treatment at 700 ℃ to obtain the homogeneous BST thin film.
Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by magnetron sputtering.
Comparative example 2
Preparing eight layers of BTO homogeneous film with the total thickness of 480nm, specifically comprising:
barium acetate and tetrabutyl titanate are used as metal alkoxide precursor raw materials, the molar ratio is 1:1, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent, BTO sol with the concentration of 0.2mol/L is prepared at 80 ℃, the pH value of BTO precursor solution is controlled to be 3-4, the ratio of the solution to the formamide is 1:20, and after 5 hours of magnetic stirring, the BTO precursor solution is aged for 24 hours.
Pt/Ti/SiO after cleaning and drying2Coating BTO sol on a Si substrate in a spin mode, firstly rotating at a low speed of 1500r/min for 10s, and then rotating at a high speed of 8000r/min for 40 s; drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and maintaining for 5 min; and then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, cooling to the room temperature to obtain a single-layer film, repeating the process for eight times to obtain eight layers of BTO films, and finally performing annealing treatment at the temperature of 700 ℃ once to obtain the homogeneous BTO film.
Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by magnetron sputtering.
Example 1
As shown in fig. 1(a) and fig. 5(a), eight BST/BTO heterogeneous thin films with a total thickness of about 480nm were prepared, which specifically included:
BST Sol is the Sol of comparative example 1, BaTiO3The sol was the sol of comparative example 2
Pt/Ti/SiO after cleaning and drying2Spin-coating BST sol on a Si substrate, firstly rotating at a low speed of 1500r/min for 10s, and then rotating at a high speed of 8000r/min for 40 s; drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and maintaining for 5 min; and then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the BST single-layer film.
Preparing a second layer of BTO film on the BST film in the same spin coating and heat treatment modes, overlapping to form 8 layers of BST/BTO heterogeneous films, and finally unifying 700 ℃ annealing treatment to obtain the heterogeneous BST film. Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by utilizing magnetron sputtering.
Example 2
As shown in FIG. 1(b) and FIG. 5(b), a 6-layer BST/BTO heterogeneous thin film with a total thickness of about 480nm is prepared, which specifically includes:
Ba0.6Sr0.4TiO3sols and BTO sols were the sols in example 1.
Pt/Ti/SiO after cleaning and drying2Spin-coating BST sol on a Si substrate, firstly rotating at a low speed of 1200r/min for 10s, and then rotating at a high speed of 4000r/min for 30 s; drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and maintaining for 5 min; and then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the BST single-layer film.
Preparing a second layer of BTO film on the BST film in the same spin coating and heat treatment modes, overlapping to form 6 layers of BST/BTO heterogeneous films, and finally performing one-time 700 ℃ annealing treatment to obtain the heterogeneous BST film.
Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by utilizing magnetron sputtering.
Example 3
As shown in FIG. 1(c) and FIG. 5(c), 4 BST/BTO heterogeneous thin films having a total thickness of about 480nm were prepared, which specifically included:
barium acetate, strontium acetate and tetrabutyl titanate are used as metal alkoxide precursor raw materials, the molar ratio is 1:1, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent, BTO sol with the concentration of 0.3mol/L is prepared at 80 ℃, the pH value of BTO precursor solution is controlled to be 3-4, the ratio of the solution to the formamide is 1:20, and after 5 hours of magnetic stirring, the BTO precursor solution is aged for 24 hours.
Barium acetate and tetrabutyl titanate are used as metal alkoxide precursor raw materials, the molar ratio is 1:1, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, formamide is used as a drying agent, BTO sol with the concentration of 0.3mol/L is prepared at 80 ℃, the pH value of BTO precursor solution is controlled to be 3-4, the ratio of the solution to the formamide is 1:20, and after 5 hours of magnetic stirring, the BTO precursor solution is aged for 24 hours.
Pt/Ti/SiO after cleaning and drying2Spin-coating BST sol on a Si substrate, firstly rotating at a low speed of 1000r/min for 10s, and then rotating at a high speed of 3000r/min for 30 s; drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and maintaining for 5 min; and then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the BST single-layer film.
Preparing a second layer of BTO film on the BST film in the same spin coating and heat treatment modes, overlapping to form 4 layers of BST/BTO heterogeneous films, and finally performing one-time 700 ℃ annealing treatment to obtain the heterogeneous BST film.
Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by utilizing magnetron sputtering.
Example 4
As shown in FIG. 1(d) and FIG. 5(d), 3 BST/BTO heterogeneous thin films with a total thickness of about 480nm were prepared, which specifically included:
BST sol and BTO sol were the same as in example 3.
Pt/Ti/SiO after cleaning and drying2Spin-coating BST sol on a Si substrate, firstly rotating at a low speed of 800r/min for 10s, and then rotating at a high speed of 2000r/min for 30 s; drying on a heating table for 15min, heating at 1.5 deg.C/min from room temperature to 350 deg.C, and maintaining for 5 min; and then heating to the pre-crystallization temperature of 600 ℃ at the speed of 4 ℃/min, preserving the heat for 10min, and cooling to the room temperature to obtain the BST single-layer film.
Preparing a second layer of BTO film on the BST film in the same spin coating and heat treatment modes, overlapping to form 3 layers of BST/BTO heterogeneous films, and finally performing one-time 700 ℃ annealing treatment to obtain the heterogeneous BST film.
Diluting according to the volume ratio of hydrofluoric acid to water of 1:20, corroding one corner of the film to expose the Pt electrode, and sputtering an Au round electrode with the diameter of 0.5mm and the thickness of about 100nm on the upper surface of the film by utilizing magnetron sputtering.
As shown in fig. 5(a) -5 (d), as the cycle thickness decreases, the number of interfaces increases, and the grains tend to become larger, which also contributes to further polarization enhancement.
As shown in fig. 6 and fig. 6(b), it is obvious that the dielectric constant of the thin film system is higher as the cycle thickness is reduced and the number of interfaces is increased, but the loss is also simultaneously increased, table 1 shows the dielectric loss of the multilayer thin films prepared in comparative example 1, comparative example 2 and examples 1 to 4 under the test frequency of 100kHz, and when the cycle thickness reaches 60nm, the dielectric constant is 4 times that of pure BST and twice that of pure BTO, and the enhancement effect is obvious. Although the multilayer heterogeneous thin film stack can be dielectric-enhanced by multiple times, the loss and the improvement of leakage current are inevitably brought about by the problems such as defects brought by the interface.
TABLE 1 dielectric constant and dielectric loss of multilayer heterogeneous thin film with 480nm total thickness and different period thickness
According to Maxwell theory, the invention successfully utilizes the sol-gel method to prepare the multilayer heterogeneous film with the period thickness of about 60nm, the dielectric constant of the multilayer heterogeneous film is greatly increased and reaches 1083.98 under the test frequency of 100 kHz. The problem of dielectric constant reduction of the ferroelectric film when the thickness is reduced is solved.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. The BST-based multilayer dielectric enhancement film is characterized by comprising a substrate, wherein a sol-gel method is adopted to spin-coat a multilayer heterogeneous film on the substrate, an Au electrode is deposited on the multilayer heterogeneous film by utilizing magnetron sputtering, and the multilayer heterogeneous film is formed by alternately stacking BST films and BTO films.
2. The BST-based multilayer dielectric enhancement film of claim 1, wherein each of the plurality of heterogeneous layers has an equal thickness.
3. The BST-based multilayer dielectric enhancement film of claim 1, wherein the substrate is Pt/Ti/SiO2/Si。
4. A method of preparing a BST based multi-layer dielectric enhancement film as claimed in any one of claims 1 to 3, comprising the steps of:
selecting a substrate, and carrying out ultrasonic cleaning and drying treatment on the substrate;
barium acetate, strontium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizing agent, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, and formamide is used as a drying agent to prepare BST precursor sol; similarly, barium acetate and tetrabutyl titanate are used as metal alkoxide, acetic acid is used as a stabilizer, ethylene glycol monomethyl ether is used as a solvent, acetylacetone is used as a chelating agent, and formamide is used as a drying agent to prepare BTO precursor sol;
spin coating, drying, thermal decomposition and pre-crystallization treatment are carried out on a substrate to obtain a pre-crystallization film to be required; repeating for multiple times to obtain a multilayer heterostructure thin film, and finally performing high-temperature annealing treatment;
one corner of the film is corroded by hydrofluoric acid, and then Au is magnetically sputtered on the film as a top electrode through a mask plate.
5. The method according to claim 4, wherein the thickness of each layer is 40 to 160 nm.
6. The preparation method according to claim 4, wherein the concentration of the precursor sol of BST and the concentration of the precursor sol of BTO are 0.2-0.3 mol/L.
7. The preparation method according to claim 4, wherein the pH value of the precursor solution of BST and BTO is controlled to be 3-4 by adjusting the content of acetic acid; formamide is added as a drying agent according to the molar mass ratio of 1:20, so that the volatilization and decomposition of organic matters are more moderate.
8. The method according to claim 4, wherein the drying temperature is 120 ℃ and the drying time is 15 min; firstly, at a low temperature rising rate: heating from room temperature to 350 deg.C at 1.5 deg.C/min, and maintaining for 5 min; then at a high temperature rise rate: heating to the pre-crystallization temperature of 600 ℃ at the temperature of 4 ℃/min, preserving the heat for 10min, and annealing to obtain a single layer of film.
9. The method of claim 4, wherein the top electrode has a diameter of 0.5mm and a thickness of 100 nm.
10. The preparation method according to claim 4, characterized in that the multilayer heterogeneous thin film is subjected to one-step high temperature annealing treatment at 700 ℃ for 30min, and is taken out after being cooled to room temperature.
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