CN1095455C - Manganese-doped barium titanate film material and preparation method thereof - Google Patents

Abstract

The invention relates to the field of materials. Substitution of Mn for BaTiO₃Part of Ti to provide a manganese-doped P-type barium titanate (BaMn)_xTi_1-xO₃) Blocks and films and methods of making. Wherein, the ratio of Ba to Ti to Mn is 1 to (1-x) to x; x is 0.005 to 0.5. When the value of x is smaller, the dielectric, ferroelectric and pyroelectric properties of the film are stronger; when the value of x is larger, the film has stronger conductivity and is a metallic oxide conductive film material. The doping concentration is changed, and the film has optical characteristics. The BaMn provided by the invention_xTi_1-xO₃The p-type material is a novel material with multiple performances and wide application, and the p-type characteristic of the material has important application in oxide electronics.

Description

Manganese-doped barium titanate thin film material and preparation method thereof

The present invention relates to the field of materials.

Barium titanate (BaTiO ₃ ) is a multifunctional material. He is a representative ferroelectric and has excellent piezoelectric, dielectric, photoelectric and nonlinear optical properties. It has a wide range of applications in memory, photodetection, photorefraction, etc. (eg Document 1: M. Sayer and K. Sreenivas, Science, 247 (1990) 1056; and Document 2: Gene H. Hearting, J. Vac. Sci. Technol. A, 9 (1991) 414). Some people use the method of doping in BaTiO ₃ to improve and change some characteristics of BaTiO ₃ . (such as document 3: Chinese patent, patent number: ZL 93104553.3). Document 3 is to prepare a single crystal material, and the doping concentration is only on the order of ppm. We have also applied for patents for niobium-doped n-type BaNb _x Ti _1-x O ₃ and indium-doped p-type BaIn _x Ti _1-x O ₃ materials, (document 4: Chinese patent, patent application number: 99108057.2, document 5: Chinese patent , patent application number: 99123796.x).

The invention provides another manganese-doped p-type barium titanate (BaMn _x Ti _1-x O ₃ ) bulk material, film and preparation thereof with various properties such as dielectric, ferroelectric, pyroelectric, conductive and optical nonlinear method. The present invention adopts a doping method in which part of Ti in _BaTiO3 is replaced by Mn, thereby providing P-type _{BaMnxTi1 -xO3 bulk} material and thin film. The present invention is accomplished through two steps of preparing body material and preparing thin film with body material.

The characteristics of BaMn _x Ti _1-x O ₃ films vary with the doping concentration of Mn. When the doping concentration is low, that is, the value of x is small, the dielectric, ferroelectric and pyroelectric properties of the film are strong. ; When the doping concentration is high, that is, when the value of x increases, the conductivity of the film is stronger. With the different doping concentration, the material also has different optical nonlinear properties. Therefore, x can be selected for stoichiometric proportioning according to the requirements of the characteristics. The value range of x is: 0.005-0.5.

The chemical raw materials for preparing blocks should be high-purity materials with a purity of more than 99.95%. Different materials can be selected for chemical formulation. These materials can be pure metals or their compounds. They are oxidized to oxides at high temperature or decomposed to oxides by heating. The chemical ratio of all metal atoms in the raw material is: Ba:Ti:Mn=1:(1-x):x. The solid phase composition is BaMn _x Ti _1-x O ₃ .

The recipe combination is:

BaCO ₃ +MnO+TiO ₂ (1)

BaO+Mn ₃ O ₄ +TiO ₂ (2)

BaO+MnO+TiO ₂ (3)

BaO+MnO ₂ +TiO ₂ (4)

BaCO ₃ +MnO ₂ +TiO ₂ (5)

BaCO ₃ +Mn+TiO ₂ (6)

BaCO ₃ +Mn ₃ O ₄ +Ti (7)

Eight combinations of BaO+Mn+Ti (8). After mixing, grinding and compacting, it can be sintered and reacted in air or oxygen or a mixed gas atmosphere containing oxygen to form BaMn _x Ti _1-x O ₃ .

The specific preparation methods of bulk and film are as follows:

1. Preparation of blocks

Blocks are prepared by sintering.

Choose one of the above 8 chemical formulas, and accurately weigh the various raw materials required according to the size of the required block and chemical ratio. There are three preparation methods:

1) Select the above chemical formula (2), (3) or (4), you can directly mix the weighed BaO, Mn ₃ O ₄ , TiO ₂ or BaO, MnO, TiO ₂ or BaO, MnO ₂ , TiO ₂ in Together, after oxidation treatment, repeated grinding, after the raw materials are fully mixed, put them into the abrasive tool of the required size and press them into shape, then put the pressed materials into a high-temperature furnace and heat them to 700°C~ Sinter at 1200°C for 12-40 hours. After the sintered material is taken out, it is crushed and ground—pressed and formed—(700°C~1200°C) and sintered for 12-40 hours. In order to obtain uniform high-quality blocks, the above process can be repeated 2-5 times. Finally, the ground and pressed material is sintered in a high-temperature furnace at 900°C to 1500°C for 20-50 hours to prepare a block. In order to prevent the fragmentation of the block, the rate of heating and cooling during sintering should not be too fast.

2) Select the above chemical formula (1), (5), (6) or (7), before mixing several raw materials, put the weighed carbonate compound into a crucible and other containers, and heat it at a high temperature of 600°C~1000°C Heat the furnace for 12-20 hours to decompose the salts. After the C is removed, use the chemical formula (2), (3) or (4) in 1) to prepare the blocks, and repeatedly mix several raw materials, Grinding, pressing, sintering, and finally preparing the desired block.

3) Using the conventional BaTiO ₃ crystal growth process, P-type BaMn _x Ti _1-x O ₃ crystals can also be grown directly.

The measured Hall coefficient proves that the prepared bulk material is P-type BaMn _x Ti _1-x O ₃ material.

2. Preparation of thin film

Thin films are prepared by radio frequency magnetron sputtering, DC magnetron sputtering, pulsed laser deposition, laser molecular beam epitaxy, molecular beam epitaxy and electron beam evaporation.

Most films are prepared from bulk materials. Different film-making technologies and methods have different requirements for bulk materials. Generally, there are three methods for preparing bulk films:

1) Preparation of composite blocks

Laser molecular beam epitaxy, pulsed laser deposition and magnetron sputtering and other film-making methods generally use composite targets, that is to say, try to mix and sinter all the elements contained in the film material according to the chemical composition ratio to prepare the thin film. composite blocks. The composite block can be prepared by any one of the above three methods for preparing the block.

2) Preparation of separated blocks

For film-making technologies such as electron beam evaporation, since it uses continuous heating and evaporation, it is easy to deviate the chemical composition of the film for compounds with different melting points. It is best to evaporate elements with different melting points separately. Therefore, the blocks need to be prepared into separate blocks according to different elements.

The preparation method of the separation block is the same as the preparation process of the composite target, but instead of mixing all the raw materials together, it is prepared into BaO, Mn ₃ O ₄ (or MnO or MnO ₂ or Mn) and TiO ₂ three separate targets.

3) Separation and preparation of semi-composite blocks

The c-oriented BaMn _x Ti _1-x O ₃ film consists of a BaO layer and a Mn _x Ti _1-x O ₂ layer to form a BaMn _x Ti _1-x O ₃ primitive cell layer. For the laser molecular beam epitaxy film formation technology that can precisely control the layered growth at the atomic scale, BaMn _x Ti _1-x O ₃ can be prepared by alternately growing BaO and Mn _x Ti _1-x O ₂ layers respectively. The preparation method of the block material is to prepare the block material into two blocks of a separated BaO and a composite Mn _x Ti _1-x O ₂ of Mn:Ti=x:(1-x).

The BaMn _x Ti _1-x O ₃ thin film can use SrTiO ₃ , BaTiO ₃ , LaAlO ₃ , ZrO ₂ and other single crystal materials with relatively matching lattice constants as the substrate. For single crystal materials with large mismatches, a buffer layer can also be added. transition.

For BaMn _x Ti _1-x O ₃ films, in addition to the decisive effect of the doping concentration on the properties of the film, the effect of oxygen vacancies is also obvious. Therefore, BaMn _x Ti _1-x O ₃ can be prepared by selecting the optimum growth rate and other process conditions under the conditions of the substrate temperature of 400~900°C and oxygen pressure of 70Pa~10 ^-5 Pa according to the conventional processes of various film making technologies. film. After the thin film is prepared, an annealing method can also be used to solve the oxygen deficiency problem of the thin film.

The manganese-doped barium titanate provided by the present invention has different characteristics with different manganese content. When the manganese content of the film is low, it has dielectric, ferroelectric and pyroelectric properties. , its conductivity is enhanced, and it becomes a metallic oxide conductive material. The films also have different optical properties depending on the manganese content. Therefore, BaMn _x Ti _1-x O ₃ is a new type of thin film material with multiple properties and wide applications. Especially its P-type characteristics will have important applications in oxide electronics.

Example 1:

Select the chemical formula (2), select x=0.2, and prepare a composite block with a thickness of Φ30mm and a thickness of about 4mm. In an air atmosphere, sinter at a temperature of 600-900°C for 15 hours. Co-crushing and grinding-pressing molding-sintering for 3 times, and finally sintering at a temperature of 1200°C for 48 hours. Made of BaMn _0.2 Ti _0.8 O ₃ bulk material.

Choose this block as the target, choose 10mm×10mm×0.5mm SrTiO ₃ as the substrate, and use laser molecular beam epitaxy at the substrate temperature of 620°C and the oxygen pressure of 1×10 ^-4 Pa to prepare BaMn _0.2 with a film thickness of 5000 Å. Ti _0.8 O ₃ film.

High-energy electron diffraction and X-ray diffraction prove that the P-type BaMn _x Ti _1-x O ₃ film we prepared is a c-oriented single crystal film with a very good epitaxial single crystal phase. The resistivity of the film measured by the standard four-probe method is 10 ^-5 Ω·cm, and the P-type carrier concentration is 10 ²² cm ^-3 . And observed pyroelectric characteristics.

Example 2:

According to Example 1, the chemical formula (1) was selected, and x=0.005 was selected to prepare a composite block. Before the raw materials were mixed, the _BaCO3 was decarbonized for 20 hours under an oxygen atmosphere and a temperature of 850° C. to prepare a block.

The bulk material was selected as a target to prepare a BaMn _0.005 Ti _0.995 O ₃ thin film with a film thickness of 2000 Å.

Example 3:

Manufactured according to Example 1, the chemical formula (3) was selected, and a BaMn _0.2 Ti _0.8 O ₃ thin film with a film thickness of 4000 Å was prepared by pulsed laser deposition at a substrate temperature of 700° C. and an oxygen pressure of 20 Pa.

Example 4:

Manufactured according to Example 1, select chemical formula (4), and use magnetron sputtering method, under the condition of substrate temperature 650 ℃, Ar and O ₂ mixed pressure 15Pa conditions, prepare the BaMn _0.2 Ti _0.8 O ₃ film of 3000 Å.

Example 5:

Made according to Example 1, select the chemical formula (5), select x=0.5, and prepare the composite block. The _BaCO3 was decarburized at 1000°C for 10 hours before the raw materials were mixed. A bulk of BaMn _0.5 Ti _0.5 O ₃ with a thickness of Φ50 mm and a thickness of 5 mm was prepared.

The block material was selected as the target, and LaAlO ₃ of Φ40mm×0.5mm was selected as the substrate to prepare a BaMn _0.5 Ti _0.5 O ₃ thin film with a film thickness of 2000 Å.

Embodiment 6:

Make according to embodiment 1, grow the BaMn _0.2 Ti _0.8 O ₃ thin film of 2000 Å on the SrTiO ₃ substrate of 20mm × 20mm × 0.5mm first, then grow the BaTiO ₃ thin film of 4000 Å on the BaMn _0.2 Ti _0.8 O ₃ thin film, finally Then grow a 2000 Å BaMn _0.2 Ti _0.8 O ₃ film on the BaTiO ₃ film. Two layers of BaMn _0.2 Ti _0.8 O ₃ thin films above and below the BaTiO ₃ thin film are used as electrodes.

Embodiment 7:

The chemical formula (4) is selected to prepare three separate targets of BaO, Mn ₃ O ₄ and TiO ₂ . _BaCO3 was sintered at a temperature of 900 °C for 20 hours to remove C. Then select a sintering temperature of 1000°C, crush and grind the three materials together—pressing and molding—sintering twice, and finally sintering at 1300°C for 36 hours to produce BaO, Mn ₃ O ₄ and Three separate blocks of _TiO2 .

Select the three separated blocks, use the three separated blocks as targets, put them into the electron beam evaporation epitaxy chamber, choose _ZrO2 of 30mm×30mm×1mm as the substrate, and evaporate the three blocks with three electron beams respectively. Under the conditions of oxygen pressure 5×10 ^-4 Pa and substrate temperature 580°C, the energy of three electron beams was adjusted to prepare BaMn _x Ti _1-x O ₃ thin films with different doping concentrations.

Embodiment 8:

Manufactured according to Example 1, two blocks of separated BaO and Mn:Ti=3:7 composite Mn ₃ O ₄ +TiO ₂ were sintered.

The two blocks were selected as targets, and BaMn _0.3 Ti 0.7 O ₃ films were prepared by layer-controlled alternate growth of _BaO and Mn _0.3 Ti _0.7 O ₂ by laser molecular beam epitaxy under the real-time monitoring of a reflective high-energy electron diffractometer.

Embodiment 9:

Select the chemical formula (8), sinter only a Φ20mm thick 3mm TiO ₂ block, put the TiO ₂ block into the molecular beam epitaxy chamber equipped with electron beam evaporation, and then put BaO and Mn into two molecular beam epitaxy chambers respectively. Beam source furnace, BaMn _x Ti _1-x O ₃ films with different doping concentrations prepared by molecular beam epitaxy.

Example 10:

Select chemical formula (7) for use, prepare according to embodiment 7.

Example 11:

The BaMn _0.01 Ti _0.99 O ₃ crystal was grown by conventional BaTiO ₃ crystal growth process.

Claims (8)

1. A manganese-doped barium titanate thin film material, characterized in that: its molecular formula BaMn _x Ti _1-x O ₃ , wherein the value range of x is: 0.005-0.5, and its molar ratio is: Ba:Ti:Mn =1:(1-x):x. 2. A method for preparing the manganese-doped barium titanate thin film material according to claim 1, characterized in that: comprising the following steps: 1) Preparation of blocks: The chemical raw materials are high-purity materials with a purity of more than 99.95%, which are Ba, Mn, Ti pure metals or their compounds BaO, BaCO ₃ , Mn ₃ O ₄ , MnO ₂ , MnO, TiO ₂ , according to the required bulk size According to the molar ratio of Ba:Ti:Mn=1:(1-x):x, the various raw materials needed are accurately weighed respectively; all the raw materials that have been weighed are mixed together, repeatedly ground, and after being fully mixed, Put it into a grinding tool of the required size and press it into shape, then put the pressed material into a high-temperature furnace, heat it to 700°C~1200°C in an oxygen atmosphere, and sinter it for 12-40 hours; put the sintered After the material is taken out, it is crushed and ground, pressed and formed, and sintered. This process can be repeated 2-5 times; the pressed and formed material is sintered in a high-temperature furnace at 900°C~1500°C for 20-50 hours to prepare blocks; If the raw materials contain carbonic acid compounds, put the weighed carbonic acid compounds into crucibles and other containers before mixing several raw materials, and heat them in a high-temperature furnace at 600°C~1000°C for 12-20 hours. After the C is removed, repeat The above process of preparing blocks is finally prepared into blocks; 2) Preparation of film: SrTiO ₃ , BaTiO ₃ , LaAlO ₃ or ZrO ₂ single crystal materials are selected as the substrate, and a buffer layer can also be added for transition to single crystal materials with large mismatch. The conventional process of the technology, the substrate temperature is 400~900℃, the oxygen pressure is maintained at 70Pa~10 ^-5 Pa, and the optimal growth rate is selected to prepare the BaMn _x Ti _1-x O ₃ film. 3. The method for preparing the manganese-doped barium titanate thin film material according to claim 2, characterized in that: The combination of raw material formula can be: BaCO ₃ +MnO+TiO ₂ (1) BaO+Mn ₃ O ₄ +TiO ₂ (2) BaO+MnO+TiO ₂ (3) BaO+MnO ₂ +TiO ₂ (4) BaCO ₃ +MnO ₂ +TiO ₂ (5) BaCO ₃ +Mn+TiO ₂ (6) BaCO ₃ +Mn ₃ O ₄ +Ti (7) BaO+Mn+Ti (8) 4, by the preparation method of manganese-doped barium titanate film material as claimed in claim 2, it is characterized in that: its step 1) also can be prepared into separate block material, and technique is identical with preparing composite block material, but prepares respectively into BaO, Three separate blocks of MnO (or MnO ₂ or Mn ₃ O ₄ ) and TiO ₂ . 5. The method for preparing manganese-doped barium titanate thin film material according to claim 2, characterized in that: its step 1) can also be prepared as a separate and semi-composite block: the process is the same as the preparation of the composite block, but respectively Prepared as isolated BaO and semi-composite Mn _x Ti _1-x O ₂ two bulk materials. 6. The preparation method of manganese-doped barium titanate thin film material according to claim 2, characterized in that: its step 2) can also adopt pulsed laser deposition, radio frequency sputtering, magnetron sputtering, electron beam evaporation or molecular Film-making methods and techniques of beam epitaxy to prepare thin films. 7. The method for preparing manganese-doped barium titanate thin film material according to claim 2, characterized in that the atmosphere of the block material preparation in step 1) can also be air or a mixed gas containing oxygen. 8. The method for preparing manganese-doped barium titanate thin film material according to claim 2, characterized in that: in the step 2), it can also grow alternately with other materials to prepare a multilayer film structure or a superlattice material.