CN103880414B - A kind of preparation method of cerium dopping barium strontium titanate - Google Patents
A kind of preparation method of cerium dopping barium strontium titanate Download PDFInfo
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- CN103880414B CN103880414B CN201410063515.6A CN201410063515A CN103880414B CN 103880414 B CN103880414 B CN 103880414B CN 201410063515 A CN201410063515 A CN 201410063515A CN 103880414 B CN103880414 B CN 103880414B
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Abstract
A preparation method for cerium dopping barium strontium titanate, belongs to technical field of function materials.Not to be better than the barium salt of acetic acid, strontium salt, cerium salt and butyl titanate for raw material, first prepare barium strontium precursor liquid, then add cerium salt and form barium strontium cerium precursor liquid, add PVP again and form PVP barium strontium cerium precursor liquid, add EGME and butyl titanate formation cerium dopping BST precursor liquid again, then add acetylacetone,2,4-pentanedione and use glacial acetic acid isochoric formation BST colloidal sol; Then adopt BST colloidal sol to obtain Multi-layer amorphous bst thin film through repeatedly even glue, drying, pyrolysis, pre-crystallization and cooling, obtain cerium dopping barium strontium titanate finally by Crystallizing treatment.The invention solves hydrolysis problem existing when high concentration cerium dopping (cerium dopping concentration is not less than 5% of titanium ion concentration) prepares barium strontium titanate, prepared cerium dopping bst thin film has lower leakage current density and dielectric loss, thus meets the microwave applications of cerium dopping bst thin film.
Description
Technical field
The invention belongs to technical field of function materials, relate to the preparation method of barium strontium titanate (BST) film, especially the preparation method of cerium dopping bst thin film.
Background technology
BST is with a wide range of applications in ferroelectric memory, pyroelectric detector and microwave-tuned device such as the fields such as phase shifter because of the dielectric property of its uniqueness, particularly, bst thin film, because of the non-linear relation display high tuning performance between dielectric constant and electric field, becomes the important candidate material of microwave-tuned device.
Cole etc. are at document 1 (Journal of applied physics, 2001,89, explicitly point out 6336-6340), realize the microwave applications of bst thin film, bst thin film must have low dielectric loss, high tuning rate, moderate dielectric constant less than normal, low leakage current density, fine and close ABO
3the comprehensive dielectric property that the film-Ji interface of perovskite microstructure, smooth flawless surface topography, good thermal stability etc. are excellent and architectural feature.But because of ferroelectric-para-electric phase transformation restriction, the comprehensive dielectric property of pure bst thin film are poor, and especially loss is very high, far can not meet microwave applications requirement.Doping assigns to improve structure by the one-tenth of alternative perovskite structure A position or B position, has the compound advantage of optimizing components and structure improvement, becomes a kind of effective way improving comprehensive dielectric property.
Document 2-Surface & coatings technology, 2012,206,4518-4524 research shows, cerium dopping makes that film is stratiform or class epitaxial growth, surface topography significantly improves, smooth densification, average crystal grain is about 30nm, surface roughness can be reduced to below 1 nanometer, thus tuning rate, dielectric constant and dielectric strength are significantly improved, thus cerium dopping is considered to be hopeful most to make bst thin film obtain excellent comprehensive dielectric property.But, up to the present, Ce doping biases toward the low concentration doping of about 1%, about the report of high-concentration dopant is little, because high-concentration dopant bst thin film is difficult to preparation, the hydrolysis problem of liquid processes as existed time prepared by sol-gel process (sol-gel) is especially used to be difficult to solve.
Ce doping content determines Ce
3+ion enters ABO
3perovskite structure replaces A position ion or B position ion.Ce
3+ionic radius is 0.103nm, is slightly less than Sr
2+(0.113nm) ionic radius, is less than Ba
2+(0.135nm) and be greater than Ti
4+(0.068nm) ionic radius, according to tolerance factor rule, two ionic radius are larger close to the probability of replacement, therefore when low concentration cerium dopping, Ce
3+the Sr of A position is preferentially replaced as donor doping
2+ion.Be good at due to cerium dopping and improve film growth behavior and pattern and crystal grain thinning, the former makes tuning rate increase substantially, the latter makes leakage current density and dielectric loss reduce, because crystal grain thinning can make, microstructure is fine and close, high resistance crystal boundary increases and extend along the charge carrier distance that crystal boundary conducts.But, when doping content is lower, due to Ce
3+ionic compartmentation Sr
2+ion, is difficult to dielectric constant is reduced, and is especially difficult to make dielectric loss be reduced to less than 1%, thus constrains the microwave applications of cerium dopping bst thin film.
Principle of electroneutrality shows, two ion combination valency changes are more little more easily to be replaced.Ce
3+the chemical valence of ion and Sr
2+, Ba
2+and Ti
4+ion all differs 1 valency, therefore, along with cerium dopping concentration increases, and Ce
3+ion will be transferred to the Ti of acceptor doping replacement B position gradually by donor doping
4+ion.According to defect equation, acceptor doping is more conducive to charge carrier in film to be reduced, thus reduces leakage current density and dielectric loss.Therefore, high concentration cerium dopping can replace A position and B position ion simultaneously, significantly reduces leakage current density and dielectric loss, improves the comprehensive dielectric property of bst thin film more significantly.
Sol-gel legal system for film have with low cost, film equality is high, stoichiometric proportion is accurate, easy and simple to handle, be easy to the advantages such as doping, become a kind of important means preparing bst thin film, and to prepare stable colloidal sol be sol-gel legal system for the prerequisite of film and key.
For conventional sol-gel legal system for cerium dopping BST colloidal sol, strong acid cerium salt is as cerous nitrate, cerium chloride or cerous sulfate because cost ratio cerous acetate is cheap often by as dopant or predecessor, but this inevitably exists hydrolysis problem.Strong acid cerium salt is insoluble in acetic acid and soluble in water, in cerium dopping BST colloidal sol preparation process, need in acetic acid solvent, add deionized water to be used widely as cosolvent, but the hydrolysis of cerium salt and butyl titanate must make colloidal sol contain the precipitation of hydroxide of cerium and titanium.Although can colloidal sol be obtained during low concentration doping, for no other reason than that the precipitation that deionized water is corresponding is on a small quantity fewer, almost be slightly soluble in acetic acid and not easily discover, but become in the process of gel at colloidal sol, the meeting crystallization because of the minimizing of acetic acid eventually of sl. sol. precipitation, gel is made to contain sediment, the structure of severe exacerbation bst thin film and dielectric property.A large amount of deionized water need be added during high concentration cerium dopping as cosolvent, intense hydrolysis occur and produces a large amount of precipitation, causing suspension-turbid liquid, can not get colloidal sol.Relevant hydrolysis formula is respectively Ce
3++ 3H
2o → Ce (OH)
3↓+3H
+and Ti (C
4h
9o)
4+ 4H
2o → Ti (OH)
4↓+4C
4h
9oH, wherein, Ti (C
4h
9o)
4for butyl titanate, C
4h
9oH is n-butanol.Therefore, high concentration cerium dopping BST colloidal sol is prepared with strong acid cerium salt as dopant infeasible.
The structure of bst thin film and dielectric property are except outside the Pass closely having with high-quality stable sol, and thin film preparation process is also most important, determines the growth behavior, surface topography, crystal structure, microstructure etc. of film, thus determines dielectric property.Pre-crystallization, as the important improvement step (refer to document 3: " a kind of preparation method of nano-crystalline BST film ", ZL2009102164077) of sol-gel legal system for film, is prepared high-quality bst thin film and has been played great function.
Summary of the invention
The invention provides a kind of preparation method of cerium dopping barium strontium titanate, hydrolysis problem existing when the method can avoid conventional high concentration cerium dopping (cerium dopping concentration is not less than 5% of titanium ion concentration) to prepare barium strontium titanate, prepared cerium dopping barium strontium titanate has lower leakage current density and dielectric loss, thus meets the microwave applications of cerium dopping bst thin film.
Technical solution of the present invention is as follows:
A preparation method for cerium dopping barium strontium titanate, comprises the following steps:
Step 1: be not better than the barium salt of acetic acid, strontium salt, cerium salt and butyl titanate for raw material with acidity, first take barium salt, strontium salt and butyl titanate, wherein 0≤x≤1 respectively by the mol ratio of Ba:Sr:Ti=(1-x): x:1; Then barium salt and the hot glacial acetic acid of strontium salt are formed barium strontium precursor liquid; Then in barium strontium precursor liquid, add the cerium salt being equivalent to 5% ~ 20% titanium atom molal quantity, stir and form barium strontium cerium precursor liquid; Adding at barium strontium cerium precursor liquid the mean molecule quantity being equivalent to 0.6% ~ 0.8% titanium atom molal quantity is again the polyvinylpyrrolidone of 30000, stirs and forms PVP barium strontium cerium precursor liquid; Finally in PVP barium strontium cerium precursor liquid, add EGME, add butyl titanate after stirring, continue to stir and form cerium dopping BST precursor liquid, wherein the consumption of EGME is that the butyl titanate of one of every percentage mole adopts 40 ~ 50 milliliters.
Step 2: the ratio adding 40 ~ 50 milliliters in the butyl titanate of one of every percentage mole in the cerium dopping BST precursor liquid that step 1 is prepared adds acetylacetone,2,4-pentanedione, then adopt glacial acetic acid constant volume, under stirring continuously, be finally mixed with the BST colloidal sol that cerium dopping concentration is 5% ~ 20%, molar concentration is 0.25 mol/L.
Step 3: the BST colloidal sol adopting step 2 to prepare drops on substrate, obtains ground floor amorphous bst thin film respectively after even glue, drying, pyrolysis, pre-crystallization and thermal treatment and cooling processing.
Step 4: repeat step 3, until obtain the amorphous bst thin film of the required number of plies.
Step 5: carry out Crystallizing treatment to step 4 gained amorphous bst thin film, Crystallizing treatment temperature is 650 DEG C, and the Crystallizing treatment time is not less than 60 minutes, after Crystallizing treatment, cooling obtains final cerium dopping barium strontium titanate naturally.
It should be noted that:
1, described in step 1, the acid barium salt not being better than acetic acid is barium acetate or brium carbonate, and the strontium salt that described acidity is not better than acetic acid is strontium acetate or strontium carbonate, and the cerium salt that described acidity is not better than acetic acid is cerous acetate or cerous carbonate.
2, in step 1 and step 2 relevant precursor liquid and colloidal sol be prepared in the acid condition of 80 DEG C under carry out, deionized water isohydric solvent can not be added, with precaution of hydrolysis.
3, during the even glue of step 3, first with the rotating speed whirl coating 5 seconds of 3500 ~ 4000 revs/min, then with the rotating speed whirl coating 30 seconds of 4500 ~ 5000 revs/min; When step 3 is dry, baking temperature is 110 DEG C, and drying time is 5 minutes; During step 3 pyrolysis, pyrolysis temperature is 350 DEG C, and pyrolysis time is 10 minutes; During the pre-crystallization and thermal treatment of step 3, pre-crystallization temperature is 600 ~ 650 DEG C, and pre-crystallization time is 10 minutes.
The preparation method of cerium dopping barium strontium titanate provided by the invention, solve hydrolysis problem existing when conventional high concentration cerium dopping (cerium dopping concentration is not less than 5% of titanium ion concentration) prepares barium strontium titanate, prepared cerium dopping barium strontium titanate has lower leakage current density and dielectric loss (lower than 0.72%), thus meet the microwave applications of cerium dopping bst thin film, especially frequency applications.
Accompanying drawing explanation
Fig. 1 is schematic flow sheet of the present invention.
Fig. 2 doping content is on the impact of the electric capacity that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz.
Fig. 3 doping content is on the impact of the dielectric constant that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz.
Fig. 4 doping content is on the impact of the tuning rate that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz.
Fig. 5 doping content is on the impact of the dielectric loss that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz.
Fig. 6 doping content is on the impact of the FOM that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz.
Embodiment
Below in conjunction with example, the present invention is specifically described, but embodiments of the present invention are not limited thereto.
Embodiment 1: take cerous acetate as 6 layers of Ba that dopant prepares that cerium dopping concentration is 1%
0.6sr
0.4tiO
3film
Step 1: take barium acetate, strontium acetate and butyl titanate 0.012,0.008 and 0.02 mole respectively than 0.6:0.4:1 by the atomic molar of Ba, Sr and Ti; Barium acetate and strontium acetate are added in the beaker of Sheng 250 ~ 300 milliliters of hot glacial acetic acids and form barium strontium precursor liquid; Add the cerous acetate of 1%Ti atomic molar number, stir after 25 ~ 30 minutes and form barium strontium cerium precursor liquid; The PVP adding 0.6%Ti atomic molar number again stirs after 20 ~ 30 minutes and forms PVP barium strontium cerium precursor liquid.
Step 2: add 80 ~ 100 milliliters of EGMEs and add butyl titanate after stirring 15 ~ 20 minutes in PVP barium strontium cerium precursor liquid, stirring and form cerium dopping BST precursor liquid after 25 ~ 30 minutes.
Step 3: add 80 ~ 100 milliliters of acetylacetone,2,4-pentanediones in cerium dopping BST precursor liquid, stirs the BST colloidal sol that obtained even, transparent, stable cerium dopping concentration after 5 ~ 6 hours is 1%, molar concentration is 0.25 mol/L.
Step 4: the colloidal sol of preparation is dropped in Si/SiO
2on/Ti/Pt substrate, after even glue, drying, pyrolysis, pre-crystallization and cooling, obtain ground floor film respectively, on ground floor film, repeat these 5 steps subsequently obtain second layer film, so repeat 6 times to obtain 6 layers of noncrystal membrane;
Step 5: this noncrystal membrane is heated to 650 DEG C in Muffle furnace and naturally cools to room temperature after being incubated 60 minutes and obtain the crystallization bst thin film that cerium dopping concentration is 1%.
Illustrate:
In step 1 ~ 3, relevant colloidal sol preparation is all carried out under about 80 DEG C of constant temperature acid conditions.
Even glue in step 4 carries out on CKF-411 type purification sol evenning machine, first with 3500 ~ 4000 revs/min of whirl coatings 5 seconds, again with 4500 ~ 5000 revs/min of whirl coatings 30 seconds, insulation 5 minutes, 10 minutes and 10 minutes after dry, pyrolysis and pre-crystallization are heated to 110 DEG C, 350 DEG C and 600 DEG C ~ 650 DEG C respectively.
If prepare the film of other number of plies, only the step of 5 in step 4 need be repeated corresponding number of times.
Embodiment 2: take cerous acetate as 6 layers of Ba that dopant prepares that cerium dopping concentration is 20%
0.6sr
0.4tiO
3film
Implementation step is as follows:
Substantially identical with " step of embodiment 1 ", just " 1% " in step 1, step 3 and step 5 is replaced with " 20% ".
In like manner, the cerium dopping Ba of other doping content as " 0% " is prepared
0.6sr
0.4tiO
3film and pure Ba
0.6sr
0.4tiO
3film, only need leave out " adding the cerous acetate of 1%Ti atomic molar number, stirring after 25 ~ 30 minutes and form barium strontium cerium precursor liquid " in rapid 1, relevant in step " cerium ", " cerium dopping " and " cerium dopping concentration is 1% " etc. is left out simultaneously.
Embodiment 1 and embodiment 2 show, take cerous acetate as dopant, cerium dopping concentration be 0% ~ 20% BST colloidal sol and film all can successfully prepare.
Embodiment 3: take cerous carbonate as 6 layers of Ba that dopant prepares that cerium dopping concentration is 1%
0.6sr
0.4tiO
3film
Implementation step is as follows:
Substantially identical with " step of embodiment 1 ", just relevant " cerous acetate " in step 1 is replaced with " cerous carbonate ".
Embodiment 4: take cerous carbonate as 6 layers of Ba that dopant prepares that cerium dopping concentration is 20%
0.6sr
0.4tiO
3film
Implementation step is as follows:
Substantially identical with " step of embodiment 3 ", just " 1% " in step 1, step 3 and step 5 is replaced with " 20% ".
Embodiment 3 and 4 shows, the cerium salt being weaker than acetic acid with acidity, if cerous carbonate is for dopant, and is that dopant is the same with cerous acetate, all successfully can prepare BST colloidal sol and film that cerium dopping concentration is 0% ~ 20%.
Embodiment 5: take cerous nitrate as dopant and be 6 layers of Ba that cosolvent prepares that cerium dopping concentration is 1% with deionized water
0.6sr
0.4tiO
3film
Implementation step is as follows:
Substantially identical with " step of embodiment 1 ", just " 250 ~ 300 milliliters of hot glacial acetic acids " in step 1 is replaced with " 5 ~ 10 ml deionized water and 250 ~ 300 milliliters of hot glacial acetic acids " and " cerous acetate " in step 1 is replaced with " cerous nitrate ".
Embodiment 6: take cerous nitrate as dopant and be 6 layers of Ba that cosolvent prepares that cerium dopping concentration is 4% with deionized water
0.6sr
0.4tiO
3film
Implementation step is as follows:
Substantially identical with " step of embodiment 5 ", just " 5 ~ 10 ml deionized water " in step 1 is replaced with " 20 ~ 40 ml deionized water " and " 1% " in step 1 is replaced with " 4% ".
Embodiment 5 and 6 shows, the cerium salt of acetic acid is better than if cerous nitrate is for dopant with acidity, be insoluble to weak acid due to strong acid salt and cerous nitrate is insoluble to acetic acid, a certain amount of deionized water hydrotropy cerous nitrate must be added, but generate Ce (OH) along with hydrolysis
3with Ti (OH)
4precipitation.Result shows, when cerium dopping concentration not higher than 4% time, the precipitation of generation can be slightly soluble in acetic acid, can obtain colloidal sol and film.But, when doping content higher than 4% time, the precipitation of generation is apparent, can not obtain colloidal sol and film, as shown in the result of embodiment 7.
Embodiment 7: take cerous nitrate as dopant and be the Ba that cosolvent prepares that cerium dopping concentration is 5% with deionized water
0.6sr
0.4tiO
3colloidal sol
Implementation step is as follows:
Substantially identical with " step of embodiment 5 ", just " 5 ~ 10 ml deionized water " in step 1 is replaced with " 25 ~ 50 ml deionized water " and " 1% " in step 1 is replaced with " 5% ".
As the analysis of embodiment 5 and 6, produce a large amount of precipitation in precursor liquid, colloidal sol and film can not be obtained.Other doping content being greater than 4% can not obtain colloidal sol and film.
In like manner, with the result that cerous chloride replacement cerous acetate also has because of strong hydrolysis and replaces cerous acetate similar with cerous nitrate.
Other examples of implementation are not tired to be stated.
The structure of above-described embodiment and dielectric property are characterized and are tested, is summarized as follows:
1. architectural feature
Architectural feature mainly characterizes with regard to film thickness, phase structure, growth behavior, grain size, surface topography, roughness etc., specific as follows:
The first, embodiment 1 and embodiment 2 take cerous acetate as cerium dopping concentration prepared by dopant is the bst thin film of 0% ~ 20%
JEOL JSF-7500F type ESEM (SEM) shows, the average thickness of 6 layer films of preparation is about 700nm.Being 0% i.e. pure bst thin film with doping content, thickness 760nm compares, doping film is obviously thinning, increase to 20% from 1% with doping content, thickness reduces to 630nm by 710nm, and analysis below shows that this is slack-off to the speed of growth of film, crystal grains fine, density increase relevant.
SXAM800 type X-ray diffraction (XRD) shows, film is main along the growth of (110) crystal face, and crystallization is thorough, shows typical ABO
3perovskite structure.To compare with pure bst thin film, the crystallization that doped BST membrane display strengthens and the average crystal grain size of reduction, and along with the increase of doping content, lattice constant in reducing → increase → reduce change, show the Ce adulterated
3+ion is introduced into ABO
3the A position of perovskite structure replaces Sr
2+ion, then enter B position replacement Ti
4+ion, then enter A position replacement Ba
2+ion, and the result that tolerance factor rule is analyzed is consistent.
Average crystal grain size D is tried to achieve by Scherrer formula D=0.9 λ/(Bcos θ), and wherein λ is the wavelength 0.15405nm of X-ray, the halfwidth that diffraction maximum that B and θ is respectively (110) is corresponding and the angle of diffraction.The average crystal grain size of pure bst thin film is 42nm, and the remarkable refinement of the average crystal grain of doping film, along with doping content reduces to 21nm to 20% by 33nm from 1% increasing.
SPI4000 type atomic force microscope (AFM) shows, pure bst thin film is layer growth, and fast growth and uneven, crystal boundary fuzzy, crystal grain gap are obviously, mean roughness is greater than 4nm.And doping film all in class epitaxial growth, poor growth is even, crystal boundary is obvious, little, the smooth densification in crystal grain gap, flawless, be less than 1nm without shrinkage cavity, mean roughness, and to improve along with the increase of doping content.
In addition, phase structure and surface topography increase along with the film number of plies and improve.
The second, embodiment 3 and embodiment 4 take cerous carbonate as cerium dopping concentration prepared by dopant is the bst thin film of 1% ~ 20%
About phase structure and close corresponding with embodiment 1 and embodiment 2 of surface topography, and the structure of the bst thin film prepared for dopant with other cerium salt that acidity is not better than acetic acid is all close with pattern, tiredly states.
3rd, embodiment 5 and embodiment 6 take cerous nitrate as cerium dopping concentration prepared by dopant is the bst thin film of 1% ~ 4%
About phase structure and surface topography are than the variation of embodiment 1 and embodiment 2 correspondence, there are oxide and dephasign to occur, are deteriorated along with the increase of doping content.
4th, embodiment 7 take cerous nitrate as the colloidal sol of cerium dopping concentration >=5% prepared by dopant
Due to intense hydrolysis, colloidal sol and film can not be obtained.
2. dielectric property
Mainly test with regard to capacitance-voltage characteristics, I-E characteristic, dielectric frequency characteristics, dielectric temperature characteristic etc.Test voltage is-40V ~ 40V, test frequency is 1kHz ~ 1MHz, probe temperature is-50 DEG C ~ 50 DEG C.Capacitance-voltage characteristics HP4284A LCR instrument test, I-E characteristic HP4155B semiconductor analysis instrument is tested.Concrete outcome is as follows:
The first, embodiment 1 and embodiment 2 take cerous acetate as cerium dopping concentration prepared by dopant is the bst thin film of 0% ~ 20%
(1) I-E characteristic shows, leakage current density is non-linear increase along with the increase of absolute value of voltage, and pure bst thin film is in the maximum leakage current density 5.4 × 10 of 40V
-5a/cm
2, and the leakage current density of doping film is hundred times of reductions, along with doping content is increased to 20% from 1%, leakage current density is from 5.2 × 10
-7a/cm
2be reduced to 1.3 × 10
-8a/cm
2.
(2) in whole doping scope, dielectric frequency characteristics and temperature characterisitic are all very stable.
(3) capacitance-voltage characteristics and correlated performance excellence, specific as follows:
As shown in Figure 2, electric capacity C is nonlinear change with voltage V, and curve is close to along transverse axis symmetrical, the corresponding maximum C of 0V
0, the corresponding minimum value C of ± 40V
± 40.
As shown in Figure 3, DIELECTRIC CONSTANT ε and electric capacity C are similar change.ε is obtained by formula C=ε S/ (4 π kd), and wherein, k is electrostatic force constant, and d is film thickness.
As shown in Figure 4, tuning rate Tunability=(C
0-C
40)/C
0× 100%, with the increase of voltage, be contrary change with electric capacity, the corresponding maximum of ± 40V.
Dielectric loss Dielectric loss and electric capacity are similar change, the corresponding maximum of 0V, as shown in Figure 5.
FOM FOM shown in Fig. 6 is the ratio of the maximum loss of tuning rate and 0V, is similar change with change in voltage and tuning rate, the corresponding maximum of ± 40V.
The Typical dielectric performance number comparative result of several Vital Voltage point is as shown in table 1:
Table 1 doping content is on the impact of the dielectric property that the bst thin film taking cerous acetate as dopant is tested under room temperature and 100kHz, wherein, electric capacity, dielectric constant and dielectric loss are the maximum under 0V bias voltage respectively, and tuning rate and FOM are the maximum under 40V respectively.
Table 1
| Doping content | Electric capacity (pF) | Dielectric constant | Tuning rate (%) | Dielectric loss (%) | FOM |
| 0% | 340 | 2361 | 70.9 | 4.23 | 16.9 |
| 1% | 361 | 2587 | 73.3 | 1.81 | 40.5 |
| 5% | 416 | 2892 | 80.1 | 1.64 | 48.9 |
| 9% | 243 | 1711 | 65.4 | 1.14 | 57.3 |
| 14% | 65 | 379 | 48.2 | 0.92 | 52.4 |
| 20% | 19 | 130 | 31.3 | 0.72 | 43.5 |
The dielectric constant of pure bst thin film is close to 2400, and tuning rate about 71%, but dielectric loss is greater than 4%, FOM is less than 17.The obvious improvement of the pure bst thin film of report in this Performance Ratio document 2, this mainly gives the credit to pre-crystallization temperature and is raised to 600 DEG C ~ 650 DEG C by 550 DEG C.Note: the FOM FOM in document 2 is obtained divided by the loss of this electric field by the tuning rate of corresponding electric field, but not obtains divided by the maximum loss of 0 electric field.
Doping content is the dielectric constant about 2600 of the bst thin film of 1%, and tuning rate is greater than 73%, dielectric loss about 1.8%, FOM is greater than 40, obviously, all significantly improve than the properties of the Ce-BST film of report in document 2, also mainly give the credit to the rising of pre-crystallization temperature.And these comprehensive dielectric property significantly improve than unadulterated.
Along with doping content is increased to 5%, dielectric constant and tuning rate are increased to about 2900 and be greater than 80% respectively, and dielectric loss is reduced to about 1.6%, and FOM is increased to more than 48;
Along with doping content is increased to 9%, dielectric constant, tuning rate and dielectric loss are reduced to about 1700,65% and 1.1% respectively, and FOM is increased to more than 57;
Along with doping content is increased to 14%, dielectric constant, tuning rate, dielectric loss and FOM are reduced to about 380,48%, 0.9% and 52 respectively;
Along with doping content is increased to 20%, dielectric constant, tuning rate, dielectric loss and FOM are reduced to about 130,31%, 0.7% and 43 respectively.
Obviously, be that bst thin film prepared by dopant shows following superior dielectric performance with cerous acetate:
1. dielectric strength or compressive resistance high, in the scope of-40V ~ 40V, film is all not breakdown;
2. the rising of pre-crystallization temperature is conducive to the improvement of every dielectric property;
3. cerium dopping can significantly improve comprehensive dielectric property, and when 1% ~ 20% scope doping, FOM is all greater than 40, and when 5% ~ 14% scope doping, FOM is all greater than 48.
4. during low concentration doping, dielectric constant and tuning rate are preponderated, and can meet the application of microwave Low Medium Frequency;
5. during high-concentration dopant, comprehensive dielectric property are preponderated, and can meet microwave high-frequency application.
The second, embodiment 3 and embodiment 4 take cerous carbonate as cerium dopping concentration prepared by dopant is the bst thin film of 1% ~ 20%
About dielectric property and embodiment 1 corresponding with embodiment 2 similar and close, tiredly to state.The dielectric property of the bst thin film that other cerium salt not being better than acetic acid with acidity is prepared for dopant are also close therewith.
3rd, embodiment 5 and embodiment 6 take cerous nitrate as cerium dopping concentration prepared by dopant is the bst thin film of 1% ~ 4%
About dielectric property are than the making moderate progress of pure bst thin film of embodiment 1 and embodiment 2 correspondence, but than the obvious variation of doping film, and be deteriorated further along with the increase of doping content.
In a word, the cerium salt not being better than acetic acid with acidity successfully can prepare uniform and stable BST colloidal sol and film for dopant.Due to the rising of pre-crystallization temperature, structure and the dielectric property of film are significantly improved.Compare with pure bst thin film, doping film structure and dielectric property are significantly improved, and during low concentration doping, tuning rate is preponderated, and rise to more than 80%, can meet the application of microwave Low Medium Frequency; During high-concentration dopant, comprehensive dielectric property are preponderated, and especially dielectric loss can be reduced to less than 0.72%, can meet microwave applications, and especially high-frequency microwave application, can also meet the application of pyroelectricity, ferroelectric memory device.
Claims (7)
1. a preparation method for cerium dopping barium strontium titanate, comprises the following steps:
Step 1: be not better than the barium salt of acetic acid, strontium salt, cerium salt and butyl titanate for raw material with acidity, first take barium salt, strontium salt and butyl titanate, wherein 0≤x≤1 respectively by the mol ratio of Ba:Sr:Ti=(1-x): x:1; Then barium salt and the hot glacial acetic acid of strontium salt are formed barium strontium precursor liquid; Then in barium strontium precursor liquid, add the cerium salt being equivalent to 5% ~ 20% titanium atom molal quantity, stir and form barium strontium cerium precursor liquid; Adding at barium strontium cerium precursor liquid the mean molecule quantity being equivalent to 0.6% ~ 0.8% titanium atom molal quantity is again the polyvinylpyrrolidone of 30000, stirs and forms PVP barium strontium cerium precursor liquid; Finally in PVP barium strontium cerium precursor liquid, add EGME, add butyl titanate after stirring, continue to stir and form cerium dopping BST precursor liquid, wherein the consumption of EGME is that the butyl titanate of one of every percentage mole adopts 40 ~ 50 milliliters;
Step 2: the ratio adding 40 ~ 50 milliliters in the butyl titanate of one of every percentage mole in the cerium dopping BST precursor liquid that step 1 is prepared adds acetylacetone,2,4-pentanedione, then adopt glacial acetic acid constant volume, under stirring continuously, be finally mixed with the BST colloidal sol that cerium dopping concentration is 5% ~ 20%, molar concentration is 0.25 mol/L;
Step 3: the BST colloidal sol adopting step 2 to prepare drops on substrate, obtains ground floor amorphous bst thin film respectively after even glue, drying, pyrolysis, pre-crystallization and thermal treatment and cooling processing;
Step 4: repeat step 3, until obtain the amorphous bst thin film of the required number of plies;
Step 5: carry out Crystallizing treatment to step 4 gained amorphous bst thin film, Crystallizing treatment temperature is 650 DEG C, and the Crystallizing treatment time is not less than 60 minutes, after Crystallizing treatment, cooling obtains final cerium dopping barium strontium titanate naturally.
2. the preparation method of cerium dopping barium strontium titanate according to claim 1, it is characterized in that, described in step 1, the acid barium salt not being better than acetic acid is barium acetate or brium carbonate, the strontium salt that described acidity is not better than acetic acid is strontium acetate or strontium carbonate, and the cerium salt that described acidity is not better than acetic acid is cerous acetate or cerous carbonate.
3. the preparation method of cerium dopping barium strontium titanate according to claim 1, is characterized in that, in step 1 and step 2 relevant precursor liquid and colloidal sol be prepared in the acid condition of 80 DEG C under carry out.
4. the preparation method of cerium dopping barium strontium titanate according to claim 1, is characterized in that, during the even glue of step 3, first with the rotating speed whirl coating 5 seconds of 3500 ~ 4000 revs/min, then with the rotating speed whirl coating 30 seconds of 4500 ~ 5000 revs/min.
5. the preparation method of cerium dopping barium strontium titanate according to claim 1, is characterized in that, when step 3 is dry, baking temperature is 110 DEG C, and drying time is 5 minutes.
6. the preparation method of cerium dopping barium strontium titanate according to claim 1, is characterized in that, during step 3 pyrolysis, pyrolysis temperature is 350 DEG C, and pyrolysis time is 10 minutes.
7. the preparation method of cerium dopping barium strontium titanate according to claim 1, is characterized in that, during the pre-crystallization and thermal treatment of step 3, pre-crystallization temperature is 600 ~ 650 DEG C, and pre-crystallization time is 10 minutes.
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