CN106854748A - A kind of lead zirconate titanate/barium titanate ferroelectric superlattice material and preparation method thereof - Google Patents

Abstract

The invention provides a lead zirconate titanate/barium titanate ferroelectric superlattice material and a preparation method thereof. The composition of the material includes periodically grown lead zirconate titanate and barium titanate, and its periodic thickness is 5nm ~72nm. Compared with single-layer lead zirconate titanate and barium titanate ferroelectric films grown under the same preparation conditions, the advantages of the lead zirconate titanate/barium titanate ferroelectric superlattice of the present invention are: the leakage current is reduced by 2 to 3 orders of magnitude; While the dielectric loss is reduced by an order of magnitude, the dielectric constant is increased by nearly 100%; and the ferroelectric superlattice has a more symmetrical hysteresis loop. The preparation method of the material is to deposit periodically and alternately grown lead zirconate titanate and barium titanate on a 0.7% Nb-SrTiO ₃ (001) substrate with a buffer layer by pulsed laser deposition. By controlling different times of laser irradiation, precise Regulating the periodic thickness of the superlattice. As a high-performance ferroelectric material, the material has broad application prospects in integrated ferroelectric microelectronic devices such as sensors and memories.

Description

A kind of lead zirconate titanate/barium titanate ferroelectric superlattice material and preparation method thereof

technical field

The invention belongs to the fields of data storage materials, functional materials and intelligent materials, and in particular relates to a lead zirconate titanate/barium titanate ferroelectric superlattice material and a preparation method thereof.

Background technique

In the past two decades, with the development of thin film preparation technology and the continuous improvement of the miniaturization and multifunctional requirements of electronic products and their components, the preparation technology of ferroelectric thin films has also developed rapidly. The combination of ferroelectric thin film and semiconductor technology makes it have broad application prospects in the field of ferroelectric integrated microelectronics such as ferroelectric memory devices, crystal field effect transistors, and surface acoustic wave devices.

However, as the thickness of the ferroelectric film decreases, the electrical properties of the film will gradually weaken. Generally speaking, ferroelectric thin films have problems such as high leakage current, high dielectric loss and imprinting. These problems limit the application of ferroelectric thin films in microelectronic devices. It has been found that the preparation of ferroelectric superlattices can improve the electrical properties of ferroelectric thin films, so ferroelectric superlattice materials and their preparation have also received more and more attention, becoming one of the research hotspots in the field of ferroelectric materials. Although ferroelectric superlattice materials can improve some aspects of electrical properties compared with pure ferroelectric thin films, there are still some problems, such as the ferroelectric superlattice material has small ferroelectric polarization, leakage current and loss Higher, these do not meet people's requirements for high-performance integrated ferroelectric devices. At present, the selection of suitable parent materials is of great significance to obtain high-performance ferroelectric superlattices.

As important and industrially applied ferroelectric materials, lead zirconate titanate and barium titanate have the advantages of large ferroelectric remanent polarization, high dielectric constant, high Curie temperature and low coercivity, etc. Ferroelectric superlattice mother materials with promising industrial applications. In addition, lead zirconate titanate and barium titanate have similar physical and chemical properties, the same crystal structure, lattice matching and other advantages, and are suitable for growing high-quality ferroelectric superlattice.

To this end, we used two ferroelectric materials, lead zirconate titanate and barium titanate, to prepare lead zirconate titanate/barium titanate ferroelectric superlattice. By changing the thickness of the ferroelectric superlattice with different periods, the superlattice has the advantages of low leakage current, high dielectric constant, low dielectric loss and no imprint at room temperature. The development of lead zirconate titanate/barium titanate ferroelectric superlattice material and its preparation technology is compatible with microelectromechanical processing and integrated circuit technology, so it will have broad application prospects in microelectronic devices such as high-density storage and sensors.

Contents of the invention

The purpose of the present invention is to provide a kind of lead zirconate titanate/barium titanate ferroelectric superlattice material and preparation method thereof, the present invention adopts the pulsed laser deposition method to prepare superlattice material to have process simple, the periodic thickness of superlattice material Can be precisely controlled, crystal orientation epitaxy, has the advantages of low leakage current, high dielectric constant and low dielectric loss, and no imprint at room temperature, and has broad application prospects in the field of microelectronics such as integrated ferroelectric devices .

The invention provides a lead zirconate titanate/barium titanate ferroelectric superlattice material, the composition of the ferroelectric superlattice material is to meet the following requirements: Pb(Zr _0.52 Ti _0.48 )O ₃ and BaTiO ₃ periodic grow alternately. The periodic thickness is 5-72nm, the repetition times are 3-38 times, and the total film thickness is about 200-220nm.

Compared with pure lead zirconate titanate and barium titanate ferroelectric films, the leakage current of the ferroelectric superlattice material is reduced by 2 to 3 orders of magnitude; the dielectric constant increases by 100% (at 10kHz , the dielectric constant is 550-720), and the dielectric loss is less than 0.02; the ferroelectric superlattice has almost no imprinting problem, and the ferroelectric polarization curve becomes symmetrical.

The lead zirconate titanate/barium titanate ferroelectric superlattice material provided by the present invention is characterized in that the ferroelectric superlattice material has a (001) plane crystal orientation. Both the lead zirconate titanate and the barium titanate in the ferroelectric superlattice material grow in layers, and the thicknesses of the lead zirconate titanate and the barium titanate are equal in each cycle.

The present invention also provides a method for preparing the lead zirconate titanate/barium titanate ferroelectric superlattice material, which is characterized in that the specific steps are as follows:

(1) Place the lead zirconate titanate, barium titanate and lanthanum calcium manganese oxide targets in the deposition chamber of the pulsed laser deposition equipment, and use the pulsed laser deposition method to prepare the ferroelectric superlattice. Among them, lead zirconate titanate molar ratio Pb:Zr:Ti:O=1.1:0.52:0.48:3, barium titanate molar ratio Ba:Ti:O=1:1:3, lanthanum calcium manganese oxygen molar ratio La:Ca :Mn:O=0.7:0.3:1:3;

(2) Deposit lanthanum calcium manganese oxide and lead zirconate titanate buffer layer on 0.7% Nb-SrTiO ₃ substrate: use pulsed laser deposition method to deposit lanthanum with laser under the conditions of substrate temperature 750 ℃ and 40Pa deposition oxygen pressure The calcium manganese oxide target made the deposition thickness 4nm; then the temperature was lowered to 650°C, the oxygen pressure drop was 5Pa, and the lead zirconate titanate target was bombarded with laser to make the deposition thickness 5nm, and the lanthanum calcium manganese oxide and Lead zirconate titanate buffer layer;

(3) Change the deposition parameters, the deposition temperature is 650°C, the deposition oxygen pressure is 5Pa, and the barium titanate target and the lead zirconate titanate target are successively bombarded with laser to make the thickness equal to 5-72nm;

(4) By repeating step (3) for a number of times (preferably 3-38 times), it is ensured that the total thickness of the prepared superlattice is about 200-220 nm.

Wherein as preferred technical scheme:

In step (2), the 0.7% Nb-SrTiO ₃ substrate is cleaned with acetone and ethanol, and then heated to 750°C for 60 minutes; the laser energy is 0.5-1.2J/cm ² , and the distance between the target and the substrate is 4cm.

In step (3), when choosing to irradiate lead zirconate titanate and barium titanate targets with laser for different times, so that the thickness of lead zirconate titanate and barium titanate is 2.5nm, the periodic thickness of the superlattice is now 5nm, step (4) is repeated 38 times, and the total thickness of the obtained superlattice is about 200nm.

In step (3), when choosing to irradiate lead zirconate titanate and barium titanate targets with laser light for different times, so that the thickness of lead zirconate titanate and barium titanate is 5nm, the periodic thickness at this time is 10nm, step ( 4) The number of repetitions is 19 times, and the total thickness of the obtained superlattice is about 200 nm.

In step (3), when choosing to irradiate the lead zirconate titanate and the barium titanate target with the laser for different times, so that the thickness of the lead zirconate titanate and the barium titanate is 36nm, the periodic thickness at this time is 72nm, step ( 4) The number of repetitions is 3 times, and the total thickness of the obtained superlattice is about 220 nm.

In steps (3) and (4), when alternately growing barium titanate and lead zirconate titanate, it is ensured that the intermission time for each layer of film growth is 30 seconds.

In step (4), after film formation, the prepared ferroelectric superlattice material was annealed in situ under 5×10 ⁴ Pa high-purity oxygen for 30 minutes, and then cooled to room temperature at a rate of 2° C./min.

In order to test its electrical performance, vacuum sputtering technology can be used to plate gold electrodes on the surface of the ferroelectric superlattice, and the area of the gold electrodes is 0.1963mm ² .

Advantages of the present invention: the present invention adopts pulsed laser deposition method to prepare lead zirconate titanate/barium titanate ferroelectric superlattice material. The material has the advantages of layered growth, precise adjustable two-phase thickness, good crystal epitaxiality, simple preparation process, low leakage current, high dielectric constant, low dielectric loss, and symmetrical ferroelectric loops. The ferroelectric superlattice material has excellent dielectric and ferroelectric properties at room temperature, and will have broad application prospects in microelectronic devices such as high-performance micro memories and sensor tubes.

Description of drawings

Fig. 1 is the lead zirconate titanate/barium titanate ferroelectric superlattice X-ray diffraction pattern that the period thickness that the present invention makes is about 10nm;

Fig. 2 is the transmission electron microscope photo of the lead zirconate titanate/barium titanate ferroelectric superlattice that the periodic thickness that Fig. 2 makes is about 10nm;

Fig. 3 is the relationship figure of the lead titanate/barium titanate ferroelectric superlattice leakage current and the change of the applied electric field that the period thickness that the present invention makes is about 10nm zirconium;

Fig. 4 is the relationship diagram between the permittivity and frequency of the lead zirconate titanate/barium titanate ferroelectric superlattice ferroelectric superlattice that the period thickness that the present invention makes is about 10nm;

Fig. 5 is the relation figure of the lead zirconate titanate/barium titanate ferroelectric superlattice polarization intensity and the applied electric field that the period thickness that the present invention makes is about 10nm;

Fig. 6 is the X-ray diffraction pattern of lead zirconate titanate/barium titanate ferroelectric superlattice with periodic thicknesses of 5, 10 and 72nm prepared by the present invention.

detailed description

Example 1

(1) Microwave ultrasonically 0.7% Nb-SrTiO ₃ (001) substrate in acetone and alcohol for 20 minutes, then heat the substrate to 750°C in vacuum, keep it warm for 60 minutes and anneal;

(2) Deposit 4 nm of lanthanum calcium manganese oxide on a 0.7% Nb-SrTiO ₃ (001) substrate under the conditions of a deposition temperature of 750° C. and an oxygen pressure of 40 Pa by pulsed laser deposition; change the deposition temperature to 650° C. and oxygen pressure Under the condition of dropping to 5Pa, deposit 5nm lead zirconate titanate film on the lanthanum calcium manganese oxide;

(3) Under the conditions of maintaining the deposition temperature at 650°C and the oxygen pressure at 5 Pa, the laser bombarded the barium titanate target to make the deposition thickness 5nm. After 30 seconds, switched to the laser bombardment of the lead zirconate titanate target to make the deposition thickness 5nm. The periodic thickness of the superlattice material is 10nm;

(4) The process of (3) was repeated 19 times to obtain a lead zirconate titanate/barium titanate ferroelectric superlattice material with a total thickness of about 200 nm.

(5) In order to test the electrical properties, vacuum sputtering technology was used to plate gold electrodes on the surface of the superlattice, and the area of the gold electrodes was 0.1963mm ² .

The obtained material has a (001) crystal plane orientation (see Figure 1), the thickness of each layer of lead zirconate titanate and barium titanate in the superlattice is equal to about 5 nm, and the interface between the two phases is clear and smooth (see Figure 2). The ferroelectric superlattice has a leakage current density of less than 10 ³ mA/cm ² when the applied electric field is 500kV/cm (see Fig. 3), and at 10kHz, the dielectric constant and dielectric loss are 684 and 0.02 respectively (see Fig. 4) The ferroelectric saturation polarization, remanent polarization and coercive field of the superlattice are 41mC/cm ² , 17.1mC/cm ² and 230kV/cm respectively, and the bias field is less than 30kV/cm.

Example 2

(1) Microwave ultrasonically 0.7% Nb-SrTiO ₃ (001) substrate in acetone and alcohol for 20 minutes, then heat the substrate to 750°C in vacuum, keep it warm for 60 minutes and anneal;

(2) Deposit 4 nm of lanthanum calcium manganese oxide on a 0.7% Nb-SrTiO ₃ (001) substrate under the conditions of a deposition temperature of 750° C. and an oxygen pressure of 40 Pa by pulsed laser deposition; change the deposition temperature to 650° C. and oxygen pressure Under the condition of dropping to 5Pa, deposit 5nm lead zirconate titanate film on the lanthanum calcium manganese oxide;

(3) Under the conditions of maintaining a deposition temperature of 650°C and an oxygen pressure of 5Pa, the laser bombarded the barium titanate target to make the deposition thickness 2.5nm. After 30 seconds, switched to the laser bombardment of the lead zirconate titanate target to make the deposition thickness 2.5nm. , the periodic thickness of the superlattice material is 5nm;

(4) The process of (3) was repeated 38 times to obtain a lead zirconate titanate/barium titanate ferroelectric superlattice material with a total thickness of about 200 nm. The material has a (001) crystal plane orientation (see Figure 6). The dielectric constant of the superlattice with the periodic thickness is 10% lower than that of the periodic thickness of 10nm, and the polarization strength and coercive field are reduced by 50%, which is beneficial to increase the energy storage efficiency.

Example 3

(1) Microsonicate 0.7% Nb-SrTiO ₃ (001) substrate in acetone and alcohol for 20 minutes, then heat the substrate to 750°C in vacuum, keep it warm for 60 minutes and anneal;

(2) Deposit 4 nm of lanthanum calcium manganese oxide on a 0.7% Nb-SrTiO ₃ (001) substrate under the conditions of a deposition temperature of 750° C. and an oxygen pressure of 40 Pa by pulsed laser deposition; change the deposition temperature to 650° C. and oxygen pressure Under the condition of dropping to 5Pa, deposit 5nm lead zirconate titanate film on the lanthanum calcium manganese oxide;

(3) Under the conditions of maintaining the deposition temperature of 650°C and the oxygen pressure of 5Pa, the laser bombarded the barium titanate target to make the deposition thickness 36nm. After 30 seconds, switched to the laser bombardment of the lead zirconate titanate target to make the deposition thickness 36nm. The periodic thickness of the superlattice material is 72nm;

(4) The process of (3) was repeated three times to obtain a lead zirconate titanate/barium titanate ferroelectric superlattice material with a total thickness of about 220 nm. The material has a (001) crystal plane orientation (see FIG. 6 ), and the dielectric constant of the superlattice with this periodic thickness is reduced by 10% relative to the periodic thickness of 10 nm. The polarization strength and coercive field are basically unchanged.

Comparative example 1

(1) Put the 0.7% Nb-SrTiO ₃ (001) substrate in acetone and alcohol for 20 minutes for microwave ultrasonication, then heat the 0.7% Nb-SrTiO ₃ (001) substrate to 750°C for 30 minutes in vacuum annealing;

(2) Deposit lanthanum calcium manganese oxide 4nm on a 0.7% Nb-SrTiO ₃ (001) substrate by pulsed laser deposition at a deposition temperature of 750°C and an oxygen pressure of 40Pa;

(3) Under the conditions of changing the deposition temperature to 650° C. and the oxygen pressure down to 5 Pa, deposit 120 nm of lead zirconate titanate on lanthanum calcium manganese oxide;

(4) In order to test the electrical properties, a gold electrode was plated on the surface of the lead zirconate titanate film by vacuum sputtering technology, and the area of the gold electrode was 0.1963mm ² .

The prepared lead zirconate titanate film has a leakage current density higher than 10 ⁵ mA/cm ² when the applied electric field is 500kV/cm (see Figure 3). At 10kHz, the dielectric constant and dielectric loss are 290 and 0.28 respectively (See FIG. 4 ), the bias field of the lead zirconate titanate film is less than 185kV/cm. The thin film material has a (001) crystal plane orientation (see Figure 1). In contrast, the lead zirconate titanate/barium titanate ferroelectric superlattice with a periodic thickness of 5nm, 10nm and 72nm reduces the leakage current by 2-3 orders of magnitude, the dielectric constant increases by more than 100%, and the dielectric loss is greatly reduced , and the bias of the ferroelectric loop is greatly reduced.

Comparative example 2

(1) Put the 0.7% Nb-SrTiO ₃ (001) substrate in acetone and alcohol for 20 minutes for microwave ultrasonication, then heat the 0.7% Nb-SrTiO ₃ (001) substrate to 750°C for 30 minutes in vacuum annealing;

(2) Deposit lanthanum calcium manganese oxide 4nm on a 0.7% Nb-SrTiO ₃ (001) substrate by pulsed laser deposition at a deposition temperature of 750°C and an oxygen pressure of 40Pa;

(3) Under the condition that the deposition temperature is changed to 650° C. and the oxygen pressure is reduced to 5 Pa, 200 nm of barium titanate is deposited on the lanthanum calcium manganese oxide;

(4) In order to test the electrical performance, a gold electrode was plated on the surface of the barium titanate film by vacuum sputtering technology, and the area of the gold electrode was 0.1963mm ² .

The prepared barium titanate film has a leakage current density higher than 10 ⁵ mA/cm ² when the applied electric field is 500kV/cm (see Figure 3), and at 10kHz, the dielectric constant and dielectric loss are 400 and 0.10 ( See Figure 4), the bias field of the barium titanate film is less than 90kV/cm. The thin film material has a (001) crystal plane orientation (see Figure 1). In contrast, the lead zirconate titanate/barium titanate ferroelectric superlattice with periodic thicknesses of 5nm, 10nm and 72nm reduces the leakage current by 2-3 orders of magnitude, the dielectric constant increases and the dielectric loss is greatly reduced, and the polarization The strength is increased and the bias is greatly reduced.

The above-mentioned examples and comparative examples are only to illustrate the technical conception and characteristics of the present invention, and its purpose is to allow those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. A lead zirconate titanate/barium titanate ferroelectric superlattice material, characterized in that: the ferroelectric superlattice material comprises Pb(Zr _0.52 Ti _0.48 )O ₃ and BaTiO ₃ periodically alternately grown. 2. The lead zirconate titanate/barium titanate ferroelectric superlattice material according to claim 1, characterized in that the ferroelectric superlattice material has a (001) plane orientation. 3. according to the described lead zirconate titanate/barium titanate ferroelectric superlattice material of claim 1, it is characterized in that: the periodic thickness of lead zirconate titanate and barium titanate in this ferroelectric superlattice material is 5～ 72nm, the number of repetitions is 3 to 38 times. 4. according to the described lead zirconate titanate/barium titanate ferroelectric superlattice material of claim 1, it is characterized in that: lead zirconate titanate and barium titanate in this ferroelectric superlattice material all present layered growth , the thicknesses of lead zirconate titanate and barium titanate are equal in each cycle. 5. according to the described lead zirconate titanate/barium titanate ferroelectric superlattice material of claim 1, it is characterized in that: this ferroelectric superlattice material compares with single-layer lead zirconate titanate and barium iron titanate film , the leakage current is reduced by 2 to 3 orders of magnitude, the dielectric constant is increased by 100%, the dielectric loss is lower than 0.02, and the ferroelectric polarization curve is symmetrical. 6. a preparation method of lead zirconate titanate/barium titanate ferroelectric superlattice material described in claim 1, is characterized in that, concrete steps are as follows: (1) Place lead zirconate titanate, barium titanate and lanthanum calcium manganese oxide targets in the deposition chamber of pulsed laser deposition equipment, wherein the molar ratio of lead zirconate titanate Pb:Zr:Ti:O=1.1:0.52: 0.48:3, barium titanate molar ratio Ba:Ti:O=1:1:3, lanthanum calcium manganese oxygen molar ratio La:Ca:Mn:O=0.7:0.3:1:3; (2) Deposition of lanthanum calcium manganese oxide and lead zirconate titanate buffer layer on 0.7% Nb-SrTiO ₃ substrate: use pulsed laser deposition method to bombard lanthanum calcium manganese with laser under the condition of substrate temperature of 750 ℃ and oxygen pressure of 40Pa The oxygen target makes the deposition thickness 4nm; then the temperature is lowered to 650°C, the oxygen pressure drop is 5Pa, and the lead zirconate titanate target is bombarded with a laser to make the deposition thickness 5nm, and lanthanum calcium manganese oxide and zirconium titanium are sequentially deposited on the substrate Lead acid buffer layer; (3) Keep the temperature of the deposition system at 650°C and the oxygen pressure at 5Pa, and bombard the barium titanate target and the lead zirconate titanate target with laser successively, so that the thicknesses of barium titanate and lead zirconate titanate are equal, and the periodic thickness is 5nm～72nm; (4) By repeating the process of step (3), ensure that the total thickness of the prepared superlattice is 200-220 nm. 7. According to the preparation method of lead zirconate titanate/barium titanate ferroelectric superlattice material according to claim 6, it is characterized in that: in step (2), the laser energy is 0.5～1.2J/cm ² , and the target material and The distance between the substrates was 4 cm. 8. according to the preparation method of the described lead zirconate titanate/barium titanate ferroelectric superlattice material of claim 6, it is characterized in that: in step (2), described 0.7%Nb-SrTiO ₃ substrates use acetone and ethanol After washing, the temperature was raised to 750° C. for 60 minutes. 9. according to the preparation method of lead zirconate titanate/barium titanate ferroelectric superlattice material described in claim 6, it is characterized in that: in step (3) and (4), in alternate growth barium titanate and zirconate titanate When using lead, ensure that the interval between each layer of film growth is 30 seconds. 10. according to the preparation method of the described lead zirconate titanate/barium titanate ferroelectric superlattice material of claim 6, it is characterized in that: in step (4), after film forming finishes, the ferroelectric superlattice material that prepares In-situ annealing was performed under 5×10 ⁴ Pa high-purity oxygen for 30 minutes, and then cooled to room temperature at a rate of 2°C/min.