KR20130143395A - A COMPOSITION OF ZN AND TI-DOPED BiFeO3 THIN FILMS AND THEIR FABRICATION METHOD THEREOF - Google Patents

Abstract

The present invention relates to a composition for a BiFeO3 thin film with Zn and Ti and a fabrication method thereof. The composition for a BiFeO3 thin film with zinc and titanium enhances ferroelectric characteristics by increasing chemical stability through the excess addition of Bi ions in an A-site of the BiFeO3 and the substitution of a small amount of Zn ions and Ti ions in a B-site, improves ferroelectric characteristics and leakage current characteristics by reducing the generation of oxygen vacancies generated in the inner space of the thin film, improves the problems of the BFO thin film with a low residual polarization value and high conductivity by changing the deposition condition and addition of the Zn ions and Ti ions, and presents development possibility. [Reference numerals] (AA) Minimize the pressure of a chamber before deposition (Minimize impurities within the chamber);(BB) Fix the oxygen partial pressure of the chamber at 30 mTorr;(CC) Fix the temperature of a substrate at 530°C;(DD) Start deposition;(EE) Temperature drop after deposition;(FF) Deposited film

Description

A composition of Zn and Ti-doped BiFeO3 Thin Films and their fabrication method

The present invention improves the overall ferroelectric properties by increasing the chemical stability through the excessive addition of Bi ions in the A-site (Bi site) of BiFeO ₃ and the substitution of a small amount of Zn and Ti ions in the B-site (Fe site). Zn and Ti ions substituted in the B-site can reduce the formation of oxygen vacancies in the thin film, thereby improving the characteristics of ferroelectricity and leakage current, and changing the addition and deposition conditions of Zn and Ti ions. BiFeO ₃ with zinc and titanium can improve the problem of BFO thin films with low residual polarization value and high electrical conductivity and suggest potential development. It is a technique regarding the composition of a thin film and its manufacturing method.

In recent years, studies on ferroelectric materials have been actively carried out. This is because ferroelectric materials have not only ferroelectricity but also pyroelectric, piezoelectric, electro-optic and nonlinear optic properties. Because its application range is very large. By using these characteristics, ferroelectrics can be applied to nonvolatile memory devices, dynamic random access memories (DRAMs), infrared sensors, surface acoustic wave (SAW) filters, and second harmonic generators .

However, there is a need for new material development in the situation where the capacity is limited and application diversity is required, and the interest of the multi-rigid body, which has electric and magnetic characteristics at the same time, .

Such multiferroics refers to materials that exhibit two or more properties simultaneously, such as ferroelectric, ferromagnetic, and ferroelastic. In fact, it is a new generation multi-functional memory device with a new concept and its application possibility.

However, BiFeO ₃ is difficult to measure the material-specific ferroelectricity due to its high leakage current. This causes a high leakage current is Fe ^{3 +} ions in the B-site, with volatilization of Bi ^{3 +} ions in the A-site the manufacturing process is partially shifted to the Fe ^{2 +} ions coming to an imbalance of the space charge due to this Oxygen vacancies are formed. In addition, it has a magnetic structure of G-type anti-ferromagnetism, so that the effect of magnetic polarization is weak.

Therefore, it is possible to improve the overall ferroelectric properties by increasing the chemical stability through excessive addition of Bi ions of A-site of BiFeO ₃ and substitution of small amount of Zn and Ti ions in B-site, and Zn substituted in B-site. , Ti ions can reduce the formation of oxygen vacancies in the thin film to improve the ferroelectricity and leakage current characteristics, and the addition of Zn and Ti ions and the deposition conditions change the low residual polarization value and high electrical conductivity. BiFeO ₃ with zinc and titanium adds to the development of the BFO thin film and suggests potential for development. There is an urgent need for the development of the composition of the thin film and its manufacturing method.

Accordingly, the present invention has been conceived to solve the above problems, the overall ferroelectric properties by increasing the chemical stability through the excessive addition of Bi ions of the A-site of BiFeO ₃ and the substitution of a small amount of Zn, Ti ions in the B-site BiFeO ₃ with zinc and titanium It is an object of the present invention to provide a composition of a thin film and a method of manufacturing the same.

Another object of the present invention is a Zn, Ti ions BiFeO the addition of zinc and titanium, which can reduce the generation of oxygen vacancies to improve the characteristics of the ferroelectric thin film, and leakage current is generated inside the _{three-substituted} in the B-site It is to provide a composition of the thin film and a method of manufacturing the same.

Another object of the present invention is to change the addition of Zn, Ti ions and deposition conditions to improve the problem of BFO thin film with low residual polarization value and high electrical conductivity, as well as zinc and titanium which can suggest the possibility of development. Added BiFeO ₃ It is to provide a composition of the thin film and a method of manufacturing the same.

BiFeO ₃ added with zinc and titanium according to a preferred embodiment of the present invention for achieving the above object The thin film composition contains a composition represented by BiFeO ₃ as a main component, and is characterized in that Zn 1% or Ti 1% is substituted for Fe with 5% excess addition of Bi.

In addition, the manufacturing method of the composition of BiFeO ₃ thin film by the addition of zinc and titanium, according to a preferred embodiment of the present invention for achieving the abovementioned objects is _{Bi 1 .05 FeO 3 (BFO)} , _{Bi 1 .05 (Fe 0 .99 Zn} 0 .01) O 3 (BFZO), and _{Bi 1.05 (Fe 0.99 Ti 0.01)} O 3 (BFTO) Bi in order to produce the bulk of the ceramic target of the composition in the solid phase reaction method ₂ O ₃ , Fe ₂ O ₃ , ZnO, TiO ₂ Preparing a starting material of the powder; The prepared starting raw materials are mixed with ethanol and mixed to grind the powder by ball milling with a stabilized zirconia ball having a diameter of 10 mm for 6 hours, and after the milling, dried in an oven at 90 ° C., and dried powder. Preparing a powder for a ceramic target comprising a step of calcining at 700 ° C. for 2 hours; A polyvinyl alcohol (PVA) as a binder for molding is added to the powder for ceramic target and sieved by 150 sieves; and the sieved powder is uniaxially pressed and formed into a disk having a diameter of 1 inch and a thickness of 3 mm ≪ / RTI > The molded specimen is placed on an alumina plate and charged with powder having the same composition to prevent volatilization of Bi ions, and the target is placed in a box-type electric furnace and raised to a sintering temperature of 820 ° C. at a temperature rising rate of 5 ° C./min. Sintering and cooling, the process comprising: cooling to produce a target after holding for time; 300 nm of SiO ₂ was deposited on the Si (100) by thermal oxidation, 10 nm was coated by the sputtering method, and 150 nm was deposited by sputtering the Pt (111) / Ti / SiO ₂ /. Si (100) comprising the steps of: preparing a _{substrate, Bi 1 .05 FeO 3 (BFO} ), Bi 1 .05 (Fe 0 .99 Zn 0 .01) O 3 (BFZO), and Bi _{1 .05} (Fe _{0. 99 Ti 0 .01) O 3 (} BFTO) has a wavelength of 248 nm to a target on a substrate in the Kr: F excimer laser using oxygen partial pressure, substrate temperature, the cooling rate at 1.1 J / cm ² / shot energy density Preparing a substrate for thin film growth, including controlling and depositing thin film growth, and growing the thin film by pulse laser deposition; And a control unit.

In the present invention, in the step of preparing a powder for the ceramic target, in order to increase the homogeneity of the powder particles, and repeating the milling, drying, calcining process each two times, and then again milling, drying to obtain a final powder It features.

In the present invention, the cooling step, characterized in that it comprises the manufacture of the target through a rapid cooling process to avoid the impurity phase generated during the cooling.

BiFeO ₃ to which zinc and titanium are added according to the present invention The composition of the thin film and its manufacturing method have the following effects.

First, the present invention can improve the overall ferroelectric property by increasing the chemical stability through excessive addition of Bi ions at the A-site of BiFeO ₃ and substitution of a small amount of Zn and Ti ions at the B-site.

Second, the present invention can improve the characteristics of ferroelectricity and leakage current by reducing the formation of vacancies of oxygen generated in the thin film by Zn and Ti ions substituted in B-site.

Third, the present invention can improve the problem of the BFO thin film having low residual polarization value and high electric conductivity by changing the addition of Zn and Ti ions and the deposition conditions.

FIG. 1 is a graph showing the relationship between the concentration of zinc and titanium added BiFeO ₃ Fig. 3 is a view showing a process of manufacturing a bulk ceramic target.
FIG. 2 illustrates XRD patterns of BFO, BFTO, and BFZO bulk ceramic targets in accordance with one embodiment of the present invention. FIG.
FIG. 3 is a graph showing the results of a comparison between BiFeO ₃ Fig.
FIG. 4 is a graph showing the relationship between the amount of zinc and titanium added BiFeO ₃ ≪ / RTI >
5 illustrates XRD patterns of BFO, BFTO, and BFZO thin films according to an embodiment of the present invention.
6 is a photograph showing the shape of a surface in BFO, BFZO, and BFTO thin films according to an embodiment of the present invention.
FIGS. 7 (a) to 7 (c) are diagrams showing ferroelectric hysteresis curves of BFO, BFZO, and BFTO thin film capacitors according to an embodiment of the present invention;
8 is a graph showing leakage currents of BFO, BFZO, and BFTO thin film capacitors according to an embodiment of the present invention.
9 is an XPS spectrum of BFO, BFZO, and BFTO thin films according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, when it is determined that a detailed description of related art or configuration may unnecessarily obscure the gist of the present invention, The description will be omitted, and the terms described below are defined in consideration of the function of the present invention, and this may vary depending on the intention or custom of the user, the operator, and the like. The definition of the present invention is BiFeO ₃ The composition of the thin film, and the manufacturing method thereof.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention in which BiFeO ₃ The composition of the thin film and the manufacturing method thereof will be described as follows.

FIG. 1 is a graph showing the relationship between the concentration of zinc and titanium added BiFeO ₃ A diagram illustrating a process of making a bulk ceramic target 2 is BiFeO ₃ by the addition of zinc and titanium, according to one embodiment of the present invention FIG. 3 is a graph showing the structure of a thin film of BiFeO ₃ Fig.

As shown in FIG. 1, first, as a process for preparing a starting material, Bi _{1 .05} FeO ₃ (BFO), Bi _1.05 (Fe _0.99 Zn _0.01 ) O ₃ (BFZO), and Bi _{1 .05} Fe _{0 .99} Ti _{0 .01} ) O ₃ (BFTO) A _{Bi 2 O 3 (99.99%)} , Fe 2 O 3 (99.99%), ZnO (99.99%), TiO 2 (99.9%) powder as a starting material to produce a bulk form of a ceramic target of the composition of the solid phase reaction method Respectively.

Secondly, as a process for producing a powder for a ceramic target, starting materials were mixed with ethanol, mixed and milled together with a stabilized zirconia ball having a diameter of 10 mm for 6 hours to mix and grind the powder. After milling, it was dried in an oven at 90 DEG C, and the dried powder was calcined at 700 DEG C for 2 hours. In order to increase the homogeneity of the powder particles, the milling, drying and calcination steps were repeated twice, and then milled and dried again to obtain a final powder.

Third, Poly Vinyl Alcohol (PVA) was added to the final powder as a binder for molding and 150 sieves were sieved. The sintered powders were fabricated by uniaxial pressing to form disks with a diameter of 1 inch and a thickness of 3 mm.

Fourthly, as a process of sintering and cooling, the prepared specimen was placed on an alumina plate and charged with powder of the same composition to prevent the volatilization of Bi ions. The target was placed in a box-type electric furnace, heated to a sintering temperature of 820 ° C at a heating rate of 5 ° C / min, held for 2 hours, and then subjected to a rapid cooling process to prepare a ceramic target to avoid impurities.

As a fifth step, a substrate is prepared for thin film growth and a thin film is grown by a pulse laser deposition method. First, as a substrate for preparing a thin film, Si (100) a thermal oxidation method to SiO ₂ to 300 nm of Pt (111) / Ti / SiO 2 / Si (100) of 150 nm deposited Pt (111) by sputtering process the substrate after the post-deposition Ti coated with approximately 10 nm sputtering method The substrate was cut into 1 cm × 1 cm and washed with acetone for 15 minutes using an ultrasonic cleaner to remove organic matter. The substrate was washed with distilled water and immediately dried with nitrogen gas as an inert gas. The substrate had a thermal conductivity In order to increase the adhesion between the substrate and the holder, the dried substrate was attached to the substrate using a high silver paste, and the substrate was dried in an oven at 90 ° C. for about 30 minutes.

As shown in FIG. 4, the thin film growth process by pulsed laser deposition is performed using Bi _{1 .05} FeO ₃ (BFO), Bi _{1 .05} (Fe _{0 .99} Zn _{0 .01} ) O ₃ (BFZO) And a Bi _{1 .05} (Fe _{0 .99} Ti _{0 .01} ) O ₃ (BFTO) target was deposited on the substrate at a energy density of 1.1 J / cm ² / shot using a Kr: F excimer laser having a wavelength of 248 nm And the deposition was performed by controlling the oxygen partial pressure of 30 mtorr, the substrate temperature of 530 ° C, and the cooling rate.

In order to observe the structure and crystallinity of the ceramic target and the thin film, it was measured using an X-ray diffractometer (Minflex II, Rigaku), and a field emission scanning electron microscope Electron Microscope (FESEM, Tescan, MIRA II LMH) was used to measure the average grain size, surface and cross-sectional states and thickness of the thin films. X- ray photoelectron spectroscopy XPS) was used to irradiate BiFeO ₃ with X-rays to determine the kinetic energy of photoelectrons The binding energy was determined and the coexistence ratio of Fe ^{3 +} and Fe ^{2 +} according to the transition metal added to the Fe-site was analyzed.

In order to measure the ferroelectric hysteresis curves of the BFO thin films, a ferroelectric property measuring device (Home Made) was used and measured with a 10 kHz triangular wave at room temperature. In order to measure the leakage current density, a Semiconductor parameter analyzer HP 4145b)

Figure 2 shows the results of XRD patterns of BFO, BFTO, and BFZO bulk ceramic targets according to one embodiment of the present invention.

XRD analysis shows that the polycrystalline bulk ceramic target is well suited to the perovskite structure. All diffraction patterns were found to maintain the BFO phase well (JCPDS Card no. 86-1518). All bulk ceramics were found to have a secondary phase, Fe-rich and Bi-rich phases. In BFZO bulk ceramics, the least secondary phase was found, whereas in BFTO, more secondary phases were found than in other bulk ceramics. This is closely related to the crystallization temperature, and BFO bulk ceramics doped with Ti ⁴⁺ ions show a similar tendency.

FIG. 5 shows XRD results of BFO, BFTO, and BFZO thin films according to an embodiment of the present invention.

As a result, it seems that it does not affect Zn or Ti crystal structure. This is probably because the Ti ion or Zn ion has a radius of ions similar to that of Fe ion. The volume (area) of the volumes arranged in (100), (110), and (111) is expected as shown in Figure 2,

(1)

(One)

F _fast , LP _hkl is Lorentz's polarization factor, MP _hkl is a complex factor, A _hkl absorption factor, V , And the volume of the V _c unit cell. Here, we have considered only " V " because the other factors are constants (the constants in the same material are considered the same). The BFO calculated in (Bi _{1 .05} FeO ₃₎ thin-film 100, 110, and 111, and the amount of the sort volumes each of 0.3%, 3.7%, and _{96.0%, BFZO (Bi 1 .05} (Fe _{0. 99} Zn _{0 .01} ) O ₃ ) were 0.4%, 9.0% and 90.6%, respectively. In the case of BFTO (Bi _{1 .05} (Fe _{0 .99} Ti _{0 .01} ) O ₃ ) thin film, there was no (111) reflection. As a result, the BFO and BFZO thin films were aligned in the <111> direction. Since the spontaneous polarization direction of the BFO thin film is the [111] direction, it is expected that the BFO and BFZO thin films have excellent spontaneous polarization.

FIG. 6 shows the surface shapes of BFO, BFZO, and BFTO thin films according to an embodiment of the present invention.

It was observed that BFO and BFZO films had considerably similar size and average particle size. BFTO thin films show non-particle growth (shape of particles with different sizes and big difference in size). As a result of SEM observation, it was observed that BFO, BFZO and BFTO thin films were grown at 400 nm, 570 nm and 420 nm, respectively.

7 (a), 7 (b), and 7 (c) show the ferroelectric hysteresis curves of BFO, BFZO, and BFTO thin film capacitors according to an embodiment of the present invention.

The ferroelectric hysteresis curve was measured at a frequency of 10 kHz. The residual polarization (2 P _r ) and the coercive field (2 E _c ) values of BFO, BFZO and BFTO thin film capacitors were 100 μC / cm ² and 678 kV / cm, 107 μC / cm ² and 540 kV / And 100 μC / cm ² and 720 kV / cm, respectively. In the ferroelectric hysteresis curve of the P ( E ) loop of the BFTO thin film capacitor, imprint effects were found in the negative direction. Developing bias in this one direction is such as electrons are to be tied to the defect sites, the problem of the interface between the oxygen vacancies or the thin film and the electrode, or a mixture of Fe ions (Fe ^{2 +} and Fe ^{3 +} state) and / or Bi vacancy There is a reason. In contrast, the development of excellent ferroelectric hysteresis curves was observed in the BFZO thin film capacitors compared in the same electric field.

FIG. 8 shows leakage currents of BFO, BFZO, and BFTO thin film capacitors according to an embodiment of the present invention.

The leakage current of BFZO thin films is about 2.8 × 10 ^-4 A / cm ² , which is 20-30 times larger than that of other thin films. It has been observed that there is an improvement in the value of the current.

9 shows XPS spectra of BFO, BFZO and BFTO thin films according to an embodiment of the present invention.

The binding energy of 3/2 1/2 spin-orbitals of Fe ^{3 +} ions is reported to be 709.6 eV and 722.3 Ev. The peak positions were represented by Gaussian profiles. The percentages of Fe ^{2 +} in BFO, BFZO, and BFTO thin films were calculated as 38%, 31%, and 35%, respectively. As a result of XPS, the presence of Fe in all the BFO thin films was confirmed (Fe ^{3 + -} Fe ^{2 +} ). BFO, BFTO and BFZO thin films showed low Fe ^{2 +} ion concentration. As a result, it was confirmed that acceptor Zn ions suppress oxygen vacancy and show low leakage current.

The above-mentioned zinc and titanium-added BiFeO ₃ Applications of thin film materials are very diverse, including nonvolatile memory devices, dynamic random access memory (DRAM), infrared sensors, surface acoustic wave (SAW) filters, and second harmonic generators Do.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. It is not.

Claims (4)

BiFeO ₃ with Zinc and Titanium The composition of the thin films, and containing as a main component a composition represented by Bi _{1 .05} FeO _3, the addition of zinc and titanium, characterized in that the Zn or Ti 1% 1% with respect to the Bi-substituted at the same time as 5% over-impregnated with Fe One BiFeO ₃ Thin film composition. BiFeO ₃ with Zinc and Titanium In the method for producing a thin film composition,
_{Bi 1 .05 FeO 3 (BFO)} , Bi 1 .05 (Fe 0 .99 Zn 0 .01) O 3 (BFZO) or _{Bi 1 .05 (Fe 0 .99 Ti} 0 .01) O 3 (BFTO) Bi ₂ O ₃ , Fe ₂ O ₃ , ZnO, TiO ₂ Preparing a starting material of the powder;
Mixing and mixing the prepared starting raw materials with ethanol, mixing and milling the powders by ball milling for 6 hours with a stabilized zirconia ball having a diameter of 10 mm,
Preparing a powder for a ceramic target, which comprises drying the oven at 90 ° C. after the milling and calcining the dried powder at 700 ° C. for 2 hours;
A polyvinyl alcohol (PVA) as a binder for molding is added to the powder for ceramic target and sieved by 150 sieves; and the sieved powder is uniaxially pressed and formed into a disk having a diameter of 1 inch and a thickness of 3 mm &Lt; / RTI &gt;
The molded specimen is placed on an alumina plate and charged with powder having the same composition to prevent volatilization of Bi ions, and the target is placed in a box-type electric furnace and raised to a sintering temperature of 820 ° C. at a temperature rising rate of 5 ° C./min. Sintering and cooling, the process comprising: cooling to produce a target after holding for time;
300 nm of SiO ₂ was deposited on the Si (100) by thermal oxidation, 10 nm was coated by the sputtering method, and 150 nm was deposited by sputtering the Pt (111) / Ti / SiO ₂ /. Si (100) comprising the steps of: preparing a _{substrate, Bi 1 .05 (Fe 0 .99} Zn 0 .01) O 3 or _{Bi 1 .05 (Fe 0 .99 Ti} 0 .01) O 248 nm for ₃ target on the substrate The substrate is prepared for thin film growth including thin film growth by depositing by controlling oxygen partial pressure, substrate temperature and cooling rate at 1.1 J / cm ² / shot energy density using Kr: F excimer laser having a wavelength of Growing a thin film by pulsed laser deposition; Method for producing a composition of BiFeO ₃ thin film with zinc and titanium added, comprising a. 3. The method of claim 2,
In the step of preparing the powder for the ceramic target, zinc and titanium, characterized in that to obtain a final powder by repeating the milling, drying, calcination process twice to increase the homogeneity of the powder particles, and then again milling, drying Added BiFeO ₃ Method for producing a thin film composition. 3. The method of claim 2,
In the cooling step, BiFeO ₃ added with zinc and titanium, comprising preparing a target through a rapid cooling process to avoid an impurity phase generated during the cooling. Method for producing a thin film composition.

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