CN102775185A - Dielectric adjustable lead niobate thin film material - Google Patents

Abstract

The invention discloses a lead niobate thin film material with adjustable dielectric. Its chemical formula and molar content are: Pb _x Nb ₂ O _5+x where x=1.05-1.35. The preparation method is as follows: first prepare the citric acid aqueous solution of lead and niobium, then add ethylene glycol to the solution to obtain the precursor sol; then drop the precursor sol on the substrate, homogenize the gel, dry, heat treatment, and repeatedly prepare multiple sols. Layer thin film, and then heat treatment at 500~700°C for 0.5~2h to obtain dielectrically adjustable lead niobate dielectric thin film. The comprehensive performance of the present invention is better than that of BST film and BZN film which are the most widely studied at present. Its dielectric constant is 350~440, dielectric loss is 0.005~0.0007, and the tuning rate under 500kV/cm bias is 25%~30%. , the figure of merit ≥ 100; the method of the invention has the advantages of precisely controlling the chemical components of the film; the process of the invention is simple, the cost is low, and it has good application prospects.

Description

Lead niobate thin film material with tunable dielectric

technical field

The invention relates to electronic components, in particular to a lead niobate thin film used for microwave tuning components and a preparation method thereof.

Background technique

With the rapid development of microwave communication systems, people put forward higher requirements for microwave devices, especially microwave tuning devices. Microwave devices with fast response speed, small size, wide frequency band, high sensitivity, and low operating voltage are indispensable components of current and next-generation communication systems. These requirements have brought great challenges to current electronic materials and components.

Microwave dielectric tunable materials have broad application prospects in the field of microwave tunable components, such as phase shifters, resonators, and filters on phased array antennas. As far as the material system is concerned, perovskite-structured barium strontium titanate BST (Ba _x Sr _1-x TiO ₃ )-based materials and bismuth-based cubic pyrochlore-structured Bi _1.5 ZnNb _1.5 O ₇ (BZN) and Bi _1.5 MgNb _1.5 O ₇ (BMN) materials are two types of dielectrically tunable microwave dielectric materials that have been studied more at present. BST-based thin film materials are characterized by high dielectric tuning rate, but large dielectric loss, usually tgδ>0.01, and the reported minimum loss is 0.005. Microwave devices require dielectric materials with low dielectric loss, and the reduction of dielectric loss is conducive to reducing the insertion loss of the device. BZN and BMN materials with bismuth-based cubic pyrochlore structure also have dielectric tunability, and their dielectric loss is lower than that of BST. However, the bias voltage required to achieve a high tuning rate for this type of material is very high. For example, when the tuning rate of BZN film is 29.2%, a field strength of 1.2MV/cm is required, and when the tuning rate is 55%, it needs 2.4MV/cm field strength. Such a high operating electric field places extremely high requirements on the reliability of the device. Therefore, it has become an urgent need in the field of voltage-controlled microwave materials and devices to develop new material systems with low dielectric loss and high tuning rate at low field strength.

Contents of the invention

The object of the present invention is to provide a lead niobate thin film material with high tuning rate and low loss and adjustable dielectric and its preparation method.

The present invention is realized through the following technical solutions.

A lead niobate film material with adjustable dielectric, its chemical formula and molar content are: Pb _x Nb ₂ O _5+x where x=1.05-1.35.

The preparation method of the dielectrically adjustable lead niobate film material has the following steps:

(1) Preparation of citric acid aqueous solution of niobium

(a) Weigh _{Nb 2 O 5 according to the stoichiometric ratio of Pb x Nb 2 O 5+x where x=1.05～1.35, put Nb 2 O 5 into hydrofluoric acid , heat} in water bath until Nb ₂ O ₅ is completely dissolved ;

(b) adding ammoniacal liquor to generate niobic acid precipitation in above-mentioned solution;

(c) Wash the above precipitate by suction filtration, then add niobic acid into the aqueous solution of citric acid to obtain an aqueous solution of niobium citric acid, wherein the molar ratio of niobium ion to citric acid is 1:2~1:6.

(2) Weigh lead nitrate according to the stoichiometric ratio of Pb _x Nb ₂ O _5+x where x=1.05～1.35, add it into deionized water, stir until fully dissolved, and obtain an aqueous solution of lead nitrate.

(3) Add the citric acid solution of niobium prepared in step (1) into the liquid prepared in step (2), and stir evenly to obtain an aqueous solution of citric acid of lead and niobium.

(4) Add ethylene glycol to the citric acid aqueous solution of lead and niobium prepared in step (3), heat and stir to obtain a precursor sol, and the molar ratio of citric acid to ethylene glycol is 1:1~1:4.

(5) Drop the precursor sol prepared in step (4) on the substrate, and use a desktop homogenizer to evenly coat the sol on the substrate, and then dry it on a hot plate;

(6) heat-treating the dried film in step (5) at 500-700°C;

(7) Repeat steps (5) and (6) to prepare multilayer films;

(8) heat-treat the prepared multilayer film at 500-700° C. for 0.5-2 hours to obtain a lead niobate dielectric film with adjustable dielectric.

The substrate in the step (5) is an ITO glass substrate or a Si substrate covered with electrodes.

The Pb _x Nb ₂ O _5+x (x=1.05～1.35) lead niobate dielectric adjustable thin film disclosed by the present invention has high tuning rate and low dielectric loss, its dielectric constant is 350~440, and the dielectric loss is 0.005～0.0007, the tuning rate under 500kV/cm bias is 25%～30%, the figure of merit ≥ 100, the overall performance is better than the most widely studied BST film and BZN film at present; the method provided by the invention has the ability to precisely control the film chemical The advantages of the components; the preparation process of the present invention is simple, low in cost and has good application prospects.

Detailed ways

The present invention will be further described by specific examples below, and the raw materials used in the present invention are commercially available analytically pure raw materials.

The preparation method of the dielectrically adjustable lead niobate film material of the present invention has the following steps:

(1) Preparation of citric acid aqueous solution of niobium

(a) Weigh _{Nb 2 O 5 according to the stoichiometric ratio of Pb x Nb 2 O 5+x where x=1.05～1.35, put Nb 2 O 5 into hydrofluoric acid , heat} in water bath until Nb ₂ O ₅ is completely dissolved ;

(b) adding ammoniacal liquor to generate niobic acid precipitation in above-mentioned solution;

(c) Wash the above precipitate by suction filtration, then add niobic acid into the aqueous solution of citric acid to obtain an aqueous solution of niobium citric acid, wherein the molar ratio of niobium ion to citric acid is 1:2~1:6.

(2) Weigh lead nitrate according to the stoichiometric ratio of Pb _x Nb ₂ O _5+x where x=1.05～1.35, add it into deionized water, stir until fully dissolved, and obtain an aqueous solution of lead nitrate.

(3) Add the citric acid solution of niobium prepared in step (1) into the liquid prepared in step (2), and stir evenly to obtain an aqueous solution of citric acid of lead and niobium.

(4) Add ethylene glycol to the citric acid aqueous solution of lead and niobium prepared in step (3), heat and stir to obtain a precursor sol, and the molar ratio of citric acid to ethylene glycol is 1:1~1:4.

(5) Drop the precursor sol configured in step (4) on the substrate, and use a desktop homogenizer to evenly coat the sol on the substrate, and then dry it on a hot plate; the substrate is ITO Glass substrate or Si substrate covered with electrodes;

(6) heat-treating the dried film in step (5) at 500-700°C;

(7) Repeat steps (5) and (6) to prepare multilayer films;

(8) heat-treat the prepared multilayer film at 500-700° C. for 0.5-2 hours to obtain a lead niobate dielectric film with adjustable dielectric. The raw material consumption relation of specific embodiment of the present invention is shown in Table 1.

Table 1

№ Pb(NO ₃ ) (g) Nb ₂ O ₅ (g) Citric acid (grams) Ethylene glycol (ml) Example 1 10.433 7.974 64.29 18.60 Example 2 10.632 7.974 23.06 10.01 Example 3 10.930 7.974 55.56 64.29 Example 4 11.228 7.974 26.77 15.49 Example 5 11.625 7.974 47.48 43.95 Example 6 11.923 7.974 39.42 29.65 Example 7 12.221 7.974 69.17 34.02 Example 8 12.619 7.974 55.42 57.71 Example 9 12.917 7.974 46.26 37.47 Example 10 13.414 7.974 34.65 19.04

The invention uses a dielectric performance testing system to test and calculate the dielectric constant, dielectric loss and tuning rate of the film.

Detection equipment and detection method of the present invention are as follows:

Use the Agilent4285A LCR tester connected to the probe station to measure the capacitance C and dielectric loss tanδ of the film capacitor (the test frequency is 1MHz), and calculate the dielectric constant ε by the following formula:

$\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 14.4</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them, C is the capacitance of the film capacitor, the unit is pF; d is the film thickness, the unit is cm; D is the dielectric diameter of the film capacitor, the unit is cm.

The tuning ratio η is calculated by the following formula:

$\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$

Among them, ε ₀ is the dielectric constant of the film when there is no external bias; ε _E is the dielectric constant of the film when the bias field strength E is applied.

The figure of merit FOM is calculated by the following formula:

FOM=η/tanδ

The test results of the dielectric properties of the above embodiments are shown in Table 2. The test frequency of the dielectric properties is 1 MHz, and the applied bias field strength is 500 kV/cm.

Table 2

№ ε ₀ tanδ η FOM Example 1 378 0.002 25% 125 Example 2 350 0.002 28% 140 Example 3 382 0.001 26% 260 Example 4 410 0.0007 27% 386 Example 5 425 0.003 30% 100

Example 6 433 0.0007 29% 414 Example 7 440 0.0009 30% 333 Example 8 420 0.0007 30% 429 Example 9 400 0.002 28% 140 Example 10 392 0.001 27% 270

The present invention is not limited to the above-described embodiments, and changes in many details are possible without departing from the scope and spirit of the present invention.

Claims (2)

1. A lead niobate film material with adjustable dielectric, its chemical formula and molar content are: Pb _x Nb ₂ O _5+x where x=1.05-1.35. The preparation method of the dielectrically adjustable lead niobate film material has the following steps: (1) Preparation of citric acid aqueous solution of niobium (a) Weigh _{Nb 2 O 5 according to the stoichiometric ratio of Pb x Nb 2 O 5+x where x=1.05～1.35, put Nb 2 O 5 into hydrofluoric acid , heat} in water bath until Nb ₂ O ₅ is completely dissolved ; (b) adding ammoniacal liquor to generate niobic acid precipitation in above-mentioned solution; (c) Wash the above precipitate by suction filtration, then add niobic acid into the aqueous solution of citric acid to obtain an aqueous solution of niobium citric acid, wherein the molar ratio of niobium ion to citric acid is 1:2~1:6. (2) Weigh lead nitrate according to the stoichiometric ratio of Pb _x Nb ₂ O _5+x where x=1.05～1.35, add it into deionized water, stir until fully dissolved, and obtain an aqueous solution of lead nitrate. (3) Add the citric acid solution of niobium prepared in step (1) into the liquid prepared in step (2), and stir evenly to obtain an aqueous solution of citric acid of lead and niobium. (4) Add ethylene glycol to the citric acid aqueous solution of lead and niobium prepared in step (3), heat and stir to obtain a precursor sol, and the molar ratio of citric acid to ethylene glycol is 1:1~1:4. (5) Drop the precursor sol prepared in step (4) on the substrate, and use a desktop homogenizer to evenly coat the sol on the substrate, and then dry it on a hot plate; (6) heat-treating the dried film in step (5) at 500-700°C; (7) Repeat steps (5) and (6) to prepare multilayer films; (8) heat-treat the prepared multilayer film at 500-700° C. for 0.5-2 hours to obtain a lead niobate dielectric film with adjustable dielectric. 2. The dielectrically adjustable lead niobate thin film material according to claim 1, wherein the substrate in the step (5) is an ITO glass substrate or a Si substrate covered with electrodes.