CN1276438A - Antimony-doped strontium titanate film and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of film materials. The present invention prepares a multifunctional antimony-doped strontium titanate (SrSb _x Ti _1-x O ₃ ) film by adopting an alternative method of doping antimony (Sb) in strontium titanate (SrTiO ₃ ) through two-part process of preparing a target material and preparing a thin film Materials, where Sr:Ti:Sb=1:(1—x):x. With the different antimony content, the film material has different characteristics. When the antimony content is low, its dielectric and pyroelectric properties are strong. When the antimony content is high, its conductivity is enhanced and it becomes a metallic oxide. Conductive film material. The thin film material of the invention can be used as an electrode and to prepare a photorefractive element or a photodetector.

Description

A kind of antimony-doped strontium titanate thin film and preparation method thereof

The invention belongs to the field of film materials.

Cubic strontium titanate (SrTiO ₃ ) crystals are used as infrared optical materials to make optical components such as special optical windows, prisms and infrared optical lenses. Since the advent of high-temperature superconductors, there has been a great deal of interest in thin films of oxides and superlattice materials. SrTiO ₃ crystals are widely used as substrates for preparing high-temperature superconducting and other oxide films. So far, the development of SrTiO ₃ crystals and thin films is still in progress, such as literature 1, Michio Naito, Hideki Yamamoto, Hisashi Sato, Physica C, 305 (1998), 233. Developed niobium (Nb) SrTiO ₃ doped with superconducting properties, such as literature 2, Arnold Leitner, Charles T.Rogers, John C. Price, David A. Rudman, David R. Herman, Appl. Phys. Lett., 72 (1998), 3065. Some people also use SrTiO ₃ materials to prepare dielectric and ferroelectric superlattices, such as literature 3, H. Tabata and T. Kawai, Appl. Phys. Lett., 70 (1997), 321.

The object of the present invention is to provide an antimony-doped strontium titanate (SrSb _x Ti _1-x O ₃ ) thin film material with multiple properties such as dielectric, pyroelectric, and conductive, and a preparation method thereof. The SrSb _x Ti _1-x O ₃ thin film provided by the present invention adopts a doping method in which a part of Ti is replaced by Sb, and is completed by two steps of preparing a target material and preparing a thin film.

The properties of SrSb _x Ti _1-x O ₃ films vary with the doping concentration of Sb. When the doping concentration is low, that is, the value of x is small, the dielectric and pyroelectric properties of the film are strong; when doping When the concentration is high, that is, when the value of x increases, the conductivity of the film is stronger. Therefore, the substitution method can be used to select x for stoichiometric ratio according to the requirements of the characteristics. The value range of x is: 0.005-0.5.

The chemical raw materials of the target are high-purity materials with a purity of more than 99.95%. These high-purity materials can be Sr, Sb, Ti pure metals or their compounds SrO, Sb ₂ O ₃ , 8b ₂ O ₅ , TiO ₂ , SrCO ₃ . They are oxidized to oxides at high temperature or their compounds are heated and decomposed into oxides. The solid phase composition of the product is SrSb _x Ti _1-x O ₃ . Its thin film can be made by laser molecular beam epitaxy, radio frequency sputtering, pulsed laser deposition, electron beam evaporation, molecular beam epitaxy and other methods. For example: a recipe combination could be:

SrCO ₃ +Sb ₂ O ₃ +TiO ₂ (1)

SrO+ _Sb2O3 + _TiO2 ( ₂ )

SrCO ₃ +Sb ₂ O ₅ +TiO ₂ (3)

SrCO ₃ +Sb+TiO ₂ (4)

SrCO ₃ +Sb ₂ O ₃ +Ti (5)

Various combinations such as SrO+Sb+Ti (6) can be sintered in air or oxygen or mixed gas atmosphere to form SrSb _x Ti _1-x O ₃ . All stoichiometric ratios are: Sr:Ti:Sb=1:(1-x):x.

The specific preparation method is as follows:

1. Preparation of target

Choose one of the above 6 chemical formulas, and accurately weigh the various raw materials required according to the size of the target material and chemical ratio. Different film-making technologies and methods have different requirements on the target material, so there are the following three target-making methods:

1) Preparation of composite target

Film-making methods such as laser molecular beam epitaxy, pulsed laser deposition and radio frequency sputtering 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 a composite target.

If the above chemical formula 2 or 6 is selected, the weighed SrO, Sb ₂ O ₃ , TiO ₂ or SrO, Sb, Ti can be mixed together for repeated grinding. After the raw materials are fully mixed, put the required target Press and form in a grinding tool of the same size, and then put the pressed and formed material into a high-temperature furnace, heat it to 700°C-1100°C and sinter for 12-36 hours. After the sintered material is taken out, it is crushed and ground, pressed into shape, and sintered at 700°C to 1100°C for 12-36 hours. In order to obtain uniform high-quality targets, the above process can be repeated 2-5 times. Finally, the pressed and formed material is sintered in a high-temperature furnace at 900° C. to 1300° C. for 20-50 hours to prepare a target.

If the above chemical formula 1, 3, 4 or 5 is selected, before mixing several raw materials, put the weighed carbonate compound into a crucible and other containers, and heat it in a high-temperature furnace at 600°C to 1000°C for 12-20 hours to remove C treatment, it can be distinguished whether C is removed according to the weight of raw materials. After the C is removed, repeat the above-mentioned target making process with chemical formula 2 or 6, and finally prepare a composite target.

2) Preparation of separation targets

For some 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 target material needs to be prepared as a separate target material according to different elements.

The preparation method of the separation target is the same as the preparation process of the composite target. It does not mix all the raw materials together, but prepares them into SrO, Sb ₂ O ₃ (or Sb ₂ O ₅ ) and TiO ₂ according to the elements. block separation target.

3) Preparation of separation and composite targets

The c-oriented SrSb _x Ti _1-x O ₃ film consists of a SrO layer and a Sb _x Ti _1-x O ₂ layer to form a SrSb _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, SrSb _x Ti 1-x O ₃ can be prepared by alternately growing SrO and Sb _x Ti _{1 -x} O ₂ layers respectively. Therefore, two targets, one SrO and one Sb _x Ti _1-x O ₂ , can be prepared according to the method described in 1).

2. Preparation of thin film

For the preparation of SrSb _x Ti _1-x O ₃ thin film, SrTiO ₃ , BaTiO ₃ , LaAlO ₃ , ZrO ₂ and other single crystal materials with relatively matched lattice constants can be used as substrates, and a buffer layer can be added for transition to those with large mismatch. It is prepared by different film-making methods and technologies such as laser molecular beam epitaxy, pulsed laser deposition, radio frequency sputtering, electron beam evaporation and molecular beam epitaxy. For SrSb _x Ti _1-x O ₃ films, in addition to the decisive effect of the doping concentration on the film properties, the effect of oxygen vacancies is also obvious. Therefore, SrSb _x Ti _1-x O 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. ₃ Thin films can also be grown alternately with other materials to prepare multi-layer film materials.

The SrSb _x Ti _1-x O ₃ thin film prepared by the invention has good electrical conductivity, strong infrared light absorption and pyroelectric properties are observed, and it is expected to have properties such as photorefraction, ferroelectricity and superconductivity. The thin film can be used as an electrode of electronic and functional devices, and can also be used to prepare photorefractive elements or photodetectors.

The present invention will be further described below in conjunction with embodiment:

Example 1:

Select chemical formula 2, select x=0.2, and prepare a target material with a thickness of Ф30 mm and a thickness of about 4 mm. Sintering was carried out in an air atmosphere at a temperature of 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 SrSb _0.2 Ti _0.8 O ₃ target.

SrTiO ₃ (001) of 10mm×10mm×0.5mm was selected as the substrate, and SrSb _0.2 Ti _0.8 O ₃ with a film thickness of 5000 Å was prepared by laser molecular beam epitaxy at a substrate temperature of 620°C and an oxygen pressure of 1×10 ^-4 Pa. film.

High-energy electron diffraction and X-ray diffraction prove that the prepared SrSb _0.2 Ti _0.8 O ₃ film 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 ^-4 Ω·cm, and the n-type carrier concentration is 10 ²¹ cm ^-3 . Properties such as pyroelectricity have been observed, and properties such as ferroelectricity and superconductivity are expected.

Example 2:

According to Example 1, the chemical formula 1 was selected, and x=0.005 was selected to prepare the target material. Before the raw materials were mixed, SrCO ₃ was first decarbonized in an oxygen atmosphere at a temperature of 850°C for 20 hours. A SrSb _0.005 Ti _0.995 O ₃ film with a film thickness of 2000 Å was prepared.

Example 3:

According to Example 1, a SrSb _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:

According to Example 1, a 3000 Å SrSb _0.2 Ti _0.8 O ₃ film was prepared by radio frequency sputtering at a substrate temperature of 650° C. and a mixed pressure of Ar and O ₂ at 15 Pa.

Example 5:

According to Example 1, the chemical formula 3 is selected, and x=0.5 is selected to prepare the target material. Before the raw materials were mixed, the _SrCO3 was decarbonized at 1000 °C for 10 h. Prepare a SrSb _0.5 Ti _0.5 O ₃ target with a thickness of Φ50 mm and a thickness of 5 mm. Choose LaAlO ₃ of Ф40mm×0.5mm as the substrate, and prepare a SrSb _0.5 Ti _0.5 O ₃ thin film with a film thickness of 2000 Å.

Embodiment 6:

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

Embodiment 7:

Select chemical formula 4 to prepare three separate targets of SrO, SbO and TiO ₂ . The _SrCO3 was sintered at a temperature of 900 °C for 20 h to remove C. Then select a sintering temperature of 1000°C respectively, crushing and grinding-pressing molding-sintering twice, and finally sintering at a temperature of 1300°C for 36 hours to make three separate targets of SrO, Sb ₂ O ₃ and TiO ₂ material.

Put three separate targets into the electron beam evaporation epitaxy chamber, choose 30mm×30mm× _1mmZrO2 as ^the substrate, and evaporate the three targets with three electron beams respectively. Under the condition of ℃, adjust the energy of the three electron beams to prepare SrSb _x Ti _1-x O ₃ films with different doping concentrations.

Embodiment 8:

Made according to Example 1, sintering SrO and Sb:Ti=3:7 Sb ₂ O ₃ +TiO ₂ targets, using the real-time monitoring of the reflective high-energy electron diffractometer, and using laser molecular beam epitaxy to alternately grow SrO in a layered manner. and Sb _0.3 Ti _0.7 O ₂ to prepare SrSb _0.3 Ti _0.7 O ₃ film.

Embodiment 9:

Select chemical formula 6, only sinter a TiO ₂ target with a thickness of Ф20mm and 3mm, put the TiO ₂ target into a molecular beam epitaxy chamber equipped with electron beam evaporation, and then put SrO and Sb into two beam sources of molecular beam epitaxy respectively SrSb _x Ti _1-x O ₃ thin films with different doping concentrations were prepared by molecular beam epitaxy in a furnace.

Example 10:

Prepare according to embodiment 7, select chemical formula 5 for use.

Claims (8)

1, a kind of Sb-doped strontium titanate film is characterized in that: its molecular formula is SrSb _xTi _1-xO ₃,

Wherein the span of x is: 0.005-0.5, and its stoicheiometry is:

Sr∶Ti∶Sb＝1∶(1-x)∶x。

2, a kind of method for preparing claim 1 is characterized in that: may further comprise the steps:

1) preparation composite target material: it is high-purity material more than 99.95% that the chemical feedstocks of target is chosen purity, and they are Sr, Sb, Ti pure metal or their compound S rO, Sb ₂O ₃, Sb ₂O ₅, TiO ₂, SrCO ₃Select a kind of chemical formulation, size according to required target size, press stoicheiometry Sr: Ti: Sb=1: (1-x): the x good required various raw materials of accurate weighing respectively, all raw materials that weigh up are mixed, grind repeatedly, behind the thorough mixing, put into the grinding tool pressure of desired size and form type, the material of pressure being formed type is put into High Temperature Furnaces Heating Apparatus then, in oxygen atmosphere, heat to 700 ℃～1100 ℃, sintering 12-36 hour, after the material that sintering is intact takes out, crushing is ground again, pressure is formed type, and this process can repeat 2-5 time, and last material of again pressure being formed type is placed in 900 ℃～1300 ℃ the High Temperature Furnaces Heating Apparatus sintering 20-50 hour and is prepared into target;

If contain carbonate compound in the raw material of selecting for use, then before several raw materials mix, earlier the carbonate compound that weighs up is put into containers such as crucible, taking off C in 12-20 hour 600 ℃～1000 ℃ High Temperature Furnaces Heating Apparatus heating handles, after treating that C purifies, repeat above-mentioned system target process again, be prepared into composite target material at last;

2) preparation film: preparation SrSb _xTi _1-xO ₃Film can be selected SrTiO for use ₃, BaTiO ₃, LaAlO ₃, ZrO ₂Do substrate etc. the monocrystal material that lattice parameter is comparatively mated, also can the add buffer layer bigger for mismatch carries out transition, adopts the film-forming method and the technology preparation of laser molecular beam epitaxy, presses the common process of masking technique, base reservoir temperature is 400～900 ℃, keeps oxygen and presses 70Pa～10 ^-5Pa selects processing condition such as optimum growh speed, prepares SrSb _xTi _1-xO ₃Film.

3, by the described method for preparing claim 1 of claim 2, it is characterized in that:

Composition of raw materials combination can for:

SrCO ₃+Sb ₂O ₃+TiO ₂ (1)

SrO+Sb ₂O ₃+TiO ₂ (2)

SrCO ₃+Sb ₂O ₅+TiO ₂ (3)

SrCO ₃+Sb+TiO ₂ (4)

SrCO ₃+Sb ₂O ₃+Ti (5)

SrO+Sb+Ti (6)

4,, it is characterized in that by the described method for preparing claim 1 of claim 2: its step 1) also can prepared composition from target: technology is identical with the preparation composite target material, still is prepared into SrO, Sb respectively ₂O ₃(or Sb ₂O ₅) and TiO ₂Three are separated target.

5,, it is characterized in that by the described method for preparing claim 1 of claim 2: its step 1) also can prepared composition from composite target material: the preparation of technology and composite target material is identical, still is prepared into SrO and Sb respectively _xTi _1-xO ₂Two targets.

6, by the described method for preparing claim 1 of claim 2, it is characterized in that: its step 2) also can adopt the film-forming method and the technology preparation of pulsed laser deposition, radio-frequency sputtering, electron beam evaporation and molecular beam epitaxy.

7, by the described method for preparing claim 1 of claim 2, it is characterized in that: the system target atmosphere of its step 1) also can be selected air or mixed gas.

8,, it is characterized in that by the described method for preparing claim 1 of claim 2: its step 2) also can with other material alternating growth, be prepared into the assembly of thin films material.