CN101670691A - Antiferroelectric film with adjustable working temperature zone and higher pyroelectric coefficient and preparation method thereof - Google Patents

Abstract

The invention discloses an antiferroelectric thin film with adjustable working temperature range and large pyroelectric coefficient, its preparation method and application. The antiferroelectric thin film (Pb, Nb)(Zr, Sn, Ti) _O3 as pyroelectric material according to the present invention is prepared by sol-gel method, and the solute of the precursor solution is lead acetate, lanthanum acetate La or Niobium ethoxide, tin acetate, zirconium isopropoxide and titanium isopropoxide, the solvent is glacial acetic acid, ethylene glycol ether, acetylacetone and water, the final concentration of the precursor solution is controlled between 0.2-0.4M, the substrate is LaNiO ₃ /Pt/Ti/SiO ₂ /Si and Pt/Ti/SiO ₂ /Si. The antiferroelectric thin film of the invention has high pyroelectric current and adjustable temperature, and can be used in infrared pyroelectric detectors, smart devices and systems.

Description

Antiferroelectric thin film with adjustable working temperature and large pyroelectric coefficient and its preparation

This application is a divisional application of a Chinese patent application with an application date of December 29, 2005, an application number of 200510112416.3, and an invention title of: antiferroelectric thin film as a pyroelectric material and its preparation method and application.

technical field

The invention belongs to the technical field of preparing an antiferroelectric thin film with adjustable working temperature range and large pyroelectric coefficient by chemical method, its preparation method and application.

Background technique

The antiferroelectric state (AFE) of antiferroelectric materials can be transformed into ferroelectric state (FE) by the action of temperature, electric field and pressure. Since there are abundant structural phases near the phase boundary where antiferroelectricity transforms into ferroelectricity, and external fields such as temperature, stress and electric field cause spontaneous polarization changes to produce phase transition effects, the region from antiferroelectricity to ferroelectricity The research has always focused on the two aspects of phase transition behavior and energy conversion using the field-induced phase transition effect.

In recent years, with the advancement of modern measurement technology and the development of material phase structure and microstructure characterization technology, it has become possible to accurately measure the relationship between the structure and performance of materials when they undergo phase transitions; and the electric field of antiferroelectrics, Temperature-induced phase transitions can be used to switch and adjust many functional effects such as piezoelectricity, pyroelectricity, and electrostrain. The research on such materials lays the foundation for the application of infrared pyroelectric detectors, smart devices and systems. In the middle and late 1990s, when studying the pyroelectric properties of antiferroelectric ceramic materials (Pb, La) (Zr, Sn, Ti) O ₃ (PLZST), it was found that between the ferroelectric state and the antiferroelectric state, the measured A very large pyroelectric current can be obtained, and its pyroelectric coefficient can reach 10 ^-6 C/cm ² ℃ ^-1 . As shown in the literature Yang Tongqing, Liu Peng, Xu Zhuo, Zhang Liangying _, YaoXi, Ferroelectrics, 230, (1999) 181-186, this value is the low-temperature ferroelectric phase FER(L ) and the high-temperature ferroelectric phase FER(H) phase transition is 10 times the pyroelectric coefficient; at the same time, the temperature range of the antiferroelectric-ferroelectric phase transition is very wide, so it is a kind of phase transition with great research and development prospects Pyroelectric material. Inducing a phase transition between the antiferroelectric and ferroelectric states will cause a pyroelectric current peak, which is the result of the joint action of the electric field and the temperature field. For general ferroelectric materials, the pyroelectric current I=(dPr/dT); but for antiferroelectric materials, the pyroelectric current is I=(dPr/dT)+Einduced(dε/dT)E, The second term is the pyroelectric current induced by the external DC electric field. Obviously, compared with general ferroelectric materials, antiferroelectric materials have relatively large pyroelectric current under the action of electric field. The temperature of the antiferroelectric-ferroelectric (AFE-FE) phase transition can be regulated by using an external bias voltage, thereby realizing an adjustable and reversible pyroelectric effect.

Because the applied voltage of antiferroelectric ceramic bulk materials is relatively high, usually tens of kilovolts per centimeter, the application of antiferroelectric ceramics is limited. Therefore, the thin film of antiferroelectric ceramics is an important way to realize the application of such materials.

At present, the research on antiferroelectric thin films mainly focuses on: (1) the influence of chemical composition and synthesis conditions of materials on the microstructure and phase structure of thin films; Performance, influence of electric strain; such as literature Baomin Xu, Paul Moses, Neelesh G.Pai, and L.Eric Cross, Appl.Phys.Lett., 72, (1998) 593-395 and Baomin Xu, L.Eric Cross , Jonathan J. Bernstein, Thin Solid Films, 377, (2000) 712-718 et al. However, some critical phenomena in the phase transition of antiferroelectric thin films, especially the behavior of pyroelectricity, have not been deeply and systematically researched and developed.

At present, there are more studies on pyroelectric materials with phase transitions between ferroelectric-paraelectric and ferroelectric-ferroelectric, but less research on the pyroelectric effect of antiferroelectric-ferroelectric phase transitions, and they are all concentrated in Among antiferroelectric ceramic bulk materials, there is no report on the pyroelectric research of antiferroelectric thin films.

Contents of the invention

One of the objectives of the present invention is to provide an antiferroelectric thin film with adjustable working temperature range and large pyroelectric coefficient.

Another object of the present invention is to provide a preparation method of the above-mentioned antiferroelectric thin film.

Yet another object of the present invention is to demonstrate the use of such antiferroelectric thin films as described above.

Antiferroelectric thin film (Pb, La) (Zr, Sn, Ti) O ₃ or (Pb, Nb) (Zr, Sn, Ti) O ₃ as pyroelectric material of the present invention, which adopts sol-gel The solute of the precursor solution is lead acetate, lanthanum acetate La or niobium ethylate, tin acetate, zirconium isopropoxide and titanium isopropoxide, the solvent is glacial acetic acid, ethylene glycol ethyl ether, acetylacetone and water, the precursor solution The final concentration is controlled between 0.2-0.4M, and the substrates are LaNiO ₃ /Pt/Ti/SiO ₂ /Si and Pt/Ti/SiO ₂ /Si.

The antiferroelectric film (Pb, La) (Zr, Sn, Ti) O ₃ is specifically Pb _0.97 La _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 ) O ₃ and is close to the antiferroelectric and ferroelectric phase boundary but in the antiferroelectric The pyroelectric performance is better in the ferroelectric tetragonal phase region.

When the antiferroelectric thin film (Pb, Nb)(Zr, Sn, Ti)O ₃ is specifically Pb _0.99 Nb _0.02 (Zr _0.85 Sn _0.13 Ti _0.02 ) _0.98 O ₃ and is in the region of the antiferroelectric orthorhombic system Its pyroelectric performance is better.

The preparation method of the antiferroelectric thin film as pyroelectric material of the present invention is:

a. Preparation of precursor solution: the solute used is lead acetate, lanthanum acetate La or niobium ethoxide, tin acetate, zirconium isopropoxide and titanium isopropoxide, and the solvent is glacial acetic acid, ethylene glycol ether, acetylacetone and water, The final concentration of the precursor solution is controlled between 0.2-0.4M;

b. Preparation of the gel film: the gel film is prepared by a spin coating method compatible with the semiconductor process, and then heat-treated, and this process is repeated until a film of the required thickness is obtained, and then a layer of PbO gel is prepared on the surface. Adhesive film, finally heat treatment at 650-700 ℃.

For the (Pb, La)(Zr, Sn, Ti)O ₃ system, the specific steps to prepare the precursor solution are: first, lead acetate Pb(CH ₃ COO) ₂ ·3H ₂ O and lanthanum acetate La(CH ₃ COO) ₃ Weigh H ₂ O according to the stoichiometric ratio, add a certain amount of glacial acetic acid, heat to 110°C and reflux for 1 hour; after cooling to room temperature, add tin acetate Sn(CH ₃ COO) ₄ and continue reflux for 1 hour; after cooling to room temperature Add ethylene glycol ethyl ether, zirconium isopropoxide Zr(OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ respectively and heat to 110°C for reflux for 1 hour; after cooling to room temperature, add deionized water and Glacial acetic acid, so that the concentration of the synthesized precursor solution is 0.2-0.4M.

For the (Pb, Nb)(Zr, Sn, Ti)O ₃ system, the preparation of the precursor solution: first weigh the lead acetate Pb(CH ₃ COO) ₂ 3H ₂ O according to the stoichiometric ratio, and add a certain amount of glacial acetic acid , heated to 110°C and refluxed _for 1 hour; after cooling to room temperature, adding tin acetate Sn ₍ CH ₃ COO) ₄ and continuing to reflux for ₁ hour; , zirconium isopropoxide Zr(OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ were heated to 110°C and refluxed for 1 hour; after cooling to room temperature, deionized water and glacial acetic acid were added to make the synthesized The concentration of the precursor solution is 0.2-0.4M.

The specific process of step b is: using a spin coating method compatible with the semiconductor process to prepare a gel film, and then performing heat treatment at 450-550 ° C for 3-7 minutes, repeating this process until a film with a desired thickness is obtained, and then A layer of PbO gel film is prepared on the surface, and finally heat treated at 650-700° C. for 30-60 minutes.

The PLZST and PNZST antiferroelectric thin films as pyroelectric materials described in the present invention can realize the adjustment of their phase transition temperature under the action of an external bias voltage. For PLZST antiferroelectric film, with the increase of applied bias voltage, the pyroelectric switching temperature increases; for PNZST antiferroelectric film, with the increase of applied bias voltage, the pyroelectric switching temperature decreases. Therefore, the switching temperature range of the pyroelectric coefficient can be adjusted by changing the applied bias voltage, and then the working temperature of the infrared pyroelectric detector can be adjusted to make it more intelligent. And because this kind of antiferroelectric film has a large pyroelectric coefficient at its phase transition point, the sensitivity of the infrared pyroelectric detector can be improved.

The PLZST and PNZST antiferroelectric thin films as pyroelectric materials of the present invention are prepared by a chemical sol-gel method, and the production process is simple; the prepared antiferroelectric thin film has a large pyroelectric release at its phase transition point electric coefficient, and the phase transition temperature is adjustable under the action of an external bias voltage, and has broad market prospects in the application of infrared pyroelectric detectors.

Description of drawings

Figure 1 shows the pyroelectric current, pyroelectric coefficient and temperature of (Pb, Nb)(Zr, Sn, Ti)O ₃ antiferroelectric thin film prepared on LaNiO ₃ /Pt/Ti/SiO ₂ /Si substrate , Applied bias voltage diagram.

Figure 2 shows the pyroelectric current, pyroelectric coefficient and temperature of (Pb, La)(Zr, Sn, Ti)O ₃ antiferroelectric thin film prepared on LaNiO ₃ /Pt/Ti/SiO ₂ /Si substrate , Applied bias voltage diagram.

Detailed ways

Below in conjunction with example to be described in further detail, should be understood that the example given below is only in order to illustrate the present invention, does not comprise all content of the present invention:

Example 1

For the (Pb, Nb)(Zr, Sn, Ti)O ₃ system, select Pb _0.99 Nb _0.02 (Zr _0.85 Sn _0.13 Ti _0.02 ) _0.98 O ₃ (PNZST) to be in the region of the antiferroelectric orthorhombic system.

The chemical raw materials used are lead acetate Pb(CH ₃ COO) ₂ ·3H ₂ O, niobium ethoxide Nb(OC ₂ H ₅ ) ₅ , tin acetate Sn(CH ₃ COO) ₄ , zirconium isopropoxide Zr(OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ , the solvent is glacial acetic acid, ethylene glycol ether and deionized water. First, weigh lead acetate Pb(CH ₃ COO) ₂ 3H ₂ O according to the stoichiometric ratio, add a certain amount of glacial acetic acid, the molar ratio of Pb to glacial acetic acid is 1:10, heat to 110°C and reflux for 1 hour; cool to After room temperature, add tin acetate Sn(CH ₃ COO) ₄ and continue to reflux for 1 hour; after cooling to room temperature, add ethylene glycol ethyl ether, niobium ethoxide Nb(OC ₂ H ₅ ) ₅ , zirconium isopropoxide Zr(OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ , the molar ratio of (Zr+Ti+Nb) to ethylene glycol ether is 1:10, and heated to 110°C for reflux for 1 hour; after cooling to room temperature, add Deionized water and glacial acetic acid, the molar ratio of (Zr+Ti+Nb) to water is 1:12, and glacial acetic acid is added to make the concentration of the precursor solution 0.3M.

The substrates used are LaNiO ₃ /Pt/Ti/SiO ₂ /Si(100) and Pt/Ti/SiO ₂ /Si, and the thicknesses of LaNiO ₃ , Pt, Ti, SiO ₂ and Si flakes are 150nm, 150nm, 50nm, 150nm and 3500nm.

The above precursor solution with a molar concentration of 0.3M was taken, and a thin film was prepared by spin coating at a spin speed of 3000 rpm for 15 seconds. The gel film was directly placed in a tube furnace at 500°C for 5 minutes, then cooled to room temperature after being taken out, and the next layer of gel film was applied, and the thickness of the film obtained after 15 cycles was 820nm.

Weigh a certain amount of lead acetate Pb(CH ₃ COO) ₂ 3H ₂ O, add glacial acetic acid, heat to 110°C until completely dissolved, add ethylene glycol and reflux at 110°C for 2 hours, the mixture of glacial acetic acid and ethylene glycol The volume ratio is 4:1, and the molar concentration of the solution is 0.8M, cooled to room temperature to synthesize a 0.8M PbO precursor solution. Then, a PbO gel film was prepared on the surface of the 820nm film prepared in the previous step by using a PbO precursor solution with a concentration of 0.8M.

Finally, the film was heat-treated at 700°C for 30 minutes. Then, the upper electrode is sputtered on its upper surface by DC sputtering method, with a diameter of 0.5mm and a thickness of about 100nm. Then, the upper electrode is sputtered on its upper surface by DC sputtering method, with a diameter of 0.5mm and a thickness of about 100nm.

Figure 1 shows the pyroelectric current, pyroelectric coefficient and temperature of Pb _0.99 Nb _0.02 (Zr _0.85 Sn _0.13 Ti _0.02 ) _0.98 O ₃ antiferroelectric thin films prepared on LaNiO ₃ /Pt/Ti/SiO ₂ /Si substrates , Applied bias voltage relationship.

Example 2

For the (Pb, La)(Zr, Sn, Ti)O ₃ system, choose Pb _0.97 La _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 )O ₃ (PLZST) close to the antiferroelectric and ferroelectric phase boundary but in the antiferroelectric Quartet area.

The chemical raw materials used are lead acetate Pb(CH ₃ COO) ₂ ·3H ₂ O, lanthanum acetate La(CH ₃ COO) ₃ ·H ₂ O, tin acetate Sn(CH ₃ COO) ₄ , zirconium isopropoxide Zr( OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ , the solvent is glacial acetic acid, ethylene glycol ether and deionized water.

First, weigh lead acetate Pb(CH ₃ COO) ₂ ·3H ₂ O and lanthanum acetate La(CH ₃ COO) ₃ ·H ₂ O according to stoichiometric ratio, add a certain amount of glacial acetic acid, (Pb+La) and glacial acetic acid The molar ratio is 1:10, heated to 110°C and refluxed for 1 hour; after cooling to room temperature, tin acetate Sn(CH ₃ COO) ₄ was added and continued to reflux for 1 hour; after cooling to room temperature, ethylene glycol ethyl ether and isopropanol were added Zirconium Zr(OC ₃ H ₇ ) ₄ and titanium isopropoxide Ti(OC ₃ H ₇ ) ₄ , the molar ratio of (Zr+Ti) to ethylene glycol ether is 1:10, and heated to 110°C for 1 hour under reflux; After cooling to room temperature, deionized water and glacial acetic acid were added, the molar ratio of (Zr+Ti) to water was 1:12, and glacial acetic acid was added to make the concentration of the precursor solution 0.3M.

The substrates used are LaNiO ₃ /Pt/Ti/SiO ₂ /Si(100) and Pt/Ti/SiO ₂ /Si, and the thicknesses of LaNiO ₃ , Pt, Ti, SiO ₂ and Si flakes are 150nm, 150nm, 50nm, 150nm and 3500nm.

The above precursor solution with a molar concentration of 0.3M was taken, and a thin film was prepared by spin coating at a spin speed of 3000 rpm for 15 seconds. Put the gel film directly into a tube furnace at 500°C for 5 minutes, take it out, cool it to room temperature, and coat the next layer of gel film. The thickness of the film obtained by repeating 15 times is 810nm, and then coat it on the surface A PbO gel film was prepared by using a PbO precursor solution with a concentration of 0.8M, and finally the film was heat-treated at 700°C for 30 minutes. Then, the upper electrode is sputtered on its upper surface by DC sputtering method, with a diameter of 0.5mm and a thickness of about 100nm. Then, the upper electrode is sputtered on its upper surface by DC sputtering method, with a diameter of 0.5mm and a thickness of about 100nm.

Figure 2 shows the pyroelectric current, pyroelectric coefficient and temperature of Pb _0.97 La _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 )O ₃ antiferroelectric thin films prepared on LaNiO ₃ /Pt/Ti/SiO ₂ /Si substrates, Applied bias voltage relationship.

The concentration of the precursor solution used and the number of coating layers are related to the total thickness of the final film, that is, the greater the molar concentration, the greater the thickness; the more layers, the greater the thickness. For the ferroelectric thin film, its thickness is generally 600-800nm.

Claims (4)

1. An antiferroelectric thin film with adjustable working temperature range and large pyroelectric coefficient, comprising: antiferroelectric thin film Pb _0.97 Nb _0.02 (Zr _0.75 8n _0.16 Ti _0.09 )O ₃ and covered in antiferroelectric thin film Pb _0.97 Nb _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 )O ₃ surface PbO gel film; the antiferroelectric thin film Pb _0.97 Nb _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 )O ₃ was prepared by sol-gel method, the precursor solution The solute is lead acetate, lanthanum acetate, tin acetate, zirconium isopropoxide and titanium isopropoxide, the solvent is glacial acetic acid, ethylene glycol ether and water, the final concentration of the precursor solution is controlled between 0.2-0.4M, and the substrate is LaNiO ₃ /Pt/Ti/SiO ₂ /Si, the antiferroelectric thin film Pb _0.97 Nb _0.02 (Zr _0.75 Sn _0.16 Ti _0.09 )O ₃ is close to the boundary between antiferroelectric and ferroelectric but in the region of antiferroelectric tetragonal phase. 2. An antiferroelectric thin film with adjustable working temperature range and high pyroelectric coefficient as claimed in claim 1, characterized in that: the antiferroelectric thin film is Pb _0.97 Nb _0.02 (Zr _0.73 8n _0.16 Ti _0.09 )O ₃ has a thickness of 600-800 nm. 3. The preparation method of any antiferroelectric thin film with adjustable working temperature zone and large pyroelectric coefficient as claimed in claims 1-2, the method comprises the following two steps: a. Preparation of precursor solution: the solutes used are lead acetate, lanthanum acetate, tin acetate, zirconium isopropoxide and titanium isopropoxide, the solvent is glacial acetic acid, ethylene glycol ether and water, and the final concentration of the precursor solution is controlled Between 0.2-0.4M; b. Preparation of adhesive film: Prepare gel film by spin coating method compatible with semiconductor technology, then heat treatment at 450-550°C for 3-7 minutes, repeat this process until a film of required thickness is obtained, and then A layer of PbO gel film is prepared on the surface, and finally heat treated at 650-700° C. for 30-60 minutes. 4. The antiferroelectric thin film with adjustable working temperature range and high pyroelectric coefficient as claimed in claim 1 is used as the pyroelectric film of the infrared pyroelectric detector.

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