CN104944951A - Preparation method of BMN ceramic target - Google Patents

Abstract

The invention discloses a preparation method of a BMN ceramic target, and belongs to the field of preparation of ceramic target. The preparation method comprises the following steps: step I, preparing BMN powder; step II, preparing green bodies; step III, sintering ceramic target to obtain needed ceramic target. The BMN ceramic target prepared by adopting the preparation method provided by the invention has the advantages of compact structure and excellent property, the prepared BMN ceramic target is compact in structure, less in air holes, regular in crystalline grains and 2-5 mum in sizes, the chemical formula of the component of ceramic target is Bi1.48MgNb1.5O6.97, the maximum value of the relative density is 97.03 wt%, the dielectric property is excellent, the dielectric constant below 1 MHz is 170.4, and the dielectric loss is 6.25*10-4.

Description

A kind of preparation method of BMN ceramic target material

technical field

The invention belongs to the field of preparation of ceramic targets, and in particular relates to a preparation method of BMN ceramic targets.

Background technique

The target is the sputtering source of the magnetron sputtering coating. The quality of the target plays a vital role in the performance of the film. Therefore, high-quality targets are the premise and basis for ensuring the quality of the film. A large number of studies have shown that the influence of the target The main factors of target material quality are: purity, density, structural orientation, grain size and distribution, size, shape, etc. Among them, the most important indicators to measure the quality of the target material are the relative density, purity, crystal orientation and microstructure of the target material. uniformity.

The sputtering process has high requirements on the density of the target material. If the target material structure is poor in density, when Ar+ with high energy density bombards the target material, it will cause the bulk material on the target surface to peel off, so that the film surface has More large particles. This will seriously affect the flatness of the film surface and eventually lead to the deterioration of film performance. In addition, the Ar+ bombardment with high energy density in the magnetron sputtering process will also cause the target to heat up. In order to better withstand the thermal stress inside the target, it is necessary to obtain a high-density and high-strength target.

The purity of the target is one of the main performance indicators of the target quality. The performance of the thin film is largely affected by the purity of the target material. The main pollution sources of sputter deposited films are impurities in the target and oxygen and water in the pores of the target. In practical applications, the use of the target has different requirements on the impurity content it contains.

BMN bottom electrode films have been prepared by radio frequency magnetron sputtering (RF sputtering), pulsed laser deposition (PLD), metal organic deposition (MOD), and chemical solution decomposition. However, to prepare high-quality BMN thin films by radio frequency magnetron sputtering and pulsed laser deposition, the premise is that high-quality BMN ceramic targets must be prepared.

Because the quality of the ceramic target will directly affect the chemical composition, compactness and crystallization of the film. Generally, the density of the target not only affects the deposition rate during sputtering, the density of sputtered film particles and discharge phenomena, but also affects the electrical and optical properties of the sputtered film. Therefore, how to obtain a BMN ceramic target with a uniform and dense structure is the key to obtaining a high-performance thin film material.

Contents of the invention

One of the purposes of the present invention is to overcome the problem of poor performance of BMN ceramic targets obtained in the prior art, and provide a method for preparing BMN ceramic targets. By applying this method, BMN ceramic targets with uniform and dense structure can be obtained.

In order to solve the above technical problems, the technical solution adopted is:

A method for preparing a BMN ceramic target, comprising the steps of:

Step 1: Preparation of BMN powder

Use Bi ₂ O ₃ , MgO and Nb ₂ O ₅ powders as starting materials, make the molar ratio 1.65:1:1.5, use absolute ethanol as the medium for ball milling for 6-10 hours, and place the materials in a constant temperature drying oven at 80-100°C dry;

Pre-fire the mixed material in air or oxygen atmosphere at a temperature of 700-900°C, keep it warm for 1-4 hours, and then naturally cool down to room temperature to obtain BMN powder;

Step 2: Preparation of green body

The BMN powder obtained in the first step is subjected to secondary ball milling for 6-10 hours, dried in a constant temperature drying oven at 80-100°C, then ground and sieved, and added with a binder to granulate;

The granulated powder is uniaxially pressed to form a BMN green body with a diameter of 65mm and a thickness of 6mm, and the pressure is 10MPa;

Step 3: Sintering of the target

The formed BMN ceramics are degummed at 500-700°C for 40-50 hours, and the heating time is 10-15 hours, and then sintered at 1000-1100°C in an oxygen atmosphere and kept for 2-10 hours to obtain the required target.

Further, the ball milling time in the first step is 8h, ZrO ₂ balls are used as the grinding body, and the mass ratio of ZrO ₂ balls, Bi ₂ O ₃ , MgO and Nb ₂ O ₅ powders to the total weight of absolute ethanol is 1:2 : 1; in the pre-calcination, heat preservation at 750° C., 800° C., 850° C. and 900° C. for 2 hours and calcining respectively. The preferred pre-firing temperature is 850°C.

Further, in the first step, an oxygen atmosphere is used to replace air, the temperature is raised at a rate of 5°C/min, and O ₂ is filled at 500-600°C, kept at 750-900°C and cooled with the furnace, and stopped at 500-600°C Fill with O ₂ .

Further, the secondary ball milling in the step 2 is 8 hours, and the sieve is 120 meshes; the binder is 5wt% polyvinyl alcohol solution, and the mass ratio of the polyvinyl alcohol solution to the calcined powder is about The ratio is 1:10; the resting time of the granulated powder in the step 2 is 24 hours, the green body molding holding time is 5 minutes, and the isostatic pressure is placed under 300 MPa for 5 minutes.

Further, the debinding temperature in step 3 is 600°C, the heating time is 12h, and the holding time is 36h; the sintering in step 3 is to raise the BMN green body from room temperature to 100°C for 10 minutes, Then it rises from 100°C to a sintering temperature of 1000-1100°C with a heating rate of 5°C/min. The preferred sintering temperature is 1050°C.

The effect of the present invention is: the BMN ceramic target prepared by the method of the present invention has the advantages of compact structure and excellent performance; The composition chemical formula of the material is Bi _1.48 MgNb _1.5 O _6.97 , its relative density reaches the maximum value of 97.03wt%, and its dielectric properties are excellent, the dielectric constant at 1MHz is 170.4, and the dielectric loss is 6.25×10 ^-4 .

Description of drawings

Fig. 1 is the XRD spectrum of the BMN calcined powder synthesized at different temperatures in the present invention, (a) 750°C, (b) 800°C, (c) 850°C, (d) 900°C;

Fig. 2 is the SEM secondary electron image of the BMN calcined powder synthesized at 850°C in the present invention;

Fig. 3 is the SEM secondary electron image of the BMN calcined powder synthesized at 900°C in the present invention;

Fig. 4 is the SEM secondary electron image of the BMN powder of the present invention after being calcined at 850°C and ball-milled for 12 hours;

Figure 5 is the XRD patterns of BMN ceramics at different sintering temperatures of the present invention, (a) 1010°C, (b) 1030°C, (c) 1050°C, (d) 1070°C, (e) 1090°C;

Figure 6 prepares BMN ceramic cation molar ratios under different sintering temperatures;

Figure 7 is the SEM secondary electron image of the BMN ceramic section sintered at different sintering temperatures for 2 hours; (a) 1010°C, (b) 1030°C, (c) 1050°C, (d) 1070°C, (e) 1090°C ;

Fig. 8 is the variation curve of relative density and linear shrinkage of BMN ceramic sample with sintering temperature;

Figure 9 is the frequency characteristic curves of BMN ceramics at different sintering temperatures, (a) 1kHz-1MHz, (b) 1MHz;

Figure 10 is the influence of different heat preservation measured by XRF on the composition change of BMN ceramics;

Figure 11 is the secondary electron image of the cross section of BMN ceramics prepared under different holding time conditions, (a) 2h, (b) 4h, (c) 6h, (d) 8h, (e) 10h;

Fig. 12 is the variation curve of relative density and linear shrinkage of BMN ceramic samples with sintering holding time;

Figure 13 is the frequency characteristic curves of BMN ceramics prepared under different holding time conditions at 1050°C, (a) 1kHz-1MHz, (b) 1MHz.

Detailed ways

Below in conjunction with embodiment further illustrate the present invention, but not limit the scope of the present invention.

Preparation of Example 1 BMN Ceramic Target

1. Raw materials

The raw material is bismuth trioxide with a purity of 99.0wt% purchased from Wenzhou Chemical Materials Factory, magnesium oxide with a purity of 97.0wt% purchased from Shanghai Zhenxin Reagent Factory, and niobium pentoxide with a purity of 99.5wt% purchased from Sinopharm Chemicals Reagent Co., also includes distilled water and absolute ethanol.

2. Preparation of BMN ceramic target

Step 1: Preparation of BMN powder

According to the chemical formula Bi _1.5 Mg _1.0 Nb _1.5 O ₇ , the mass of raw materials such as Bi ₂ O ₃ , MgO, Nb ₂ O ₅ after pretreatment was calculated. Considering the volatilization _{of Bi2O3} during the sintering process, Bi was weighed in excess of 10wt%. After batching, put the weighed raw materials into a ball mill tank for mixing, use absolute ethanol as a dispersant, and perform ball milling with a mass ratio of balls, material, and ethanol at 1:2:1, and the ball milling time is 8 hours. The main purpose is to mix the raw materials evenly and refine the powder. After ball milling, the powder is dried, ground, and passed through a 120-mesh sieve. Pre-burn at 750°C, 800°C, 850°C and 900°C for 2 hours. During pre-calcination, the powder should be compacted as much as possible to reduce the volatilization of Bi during the calcination process.

Step 2: Preparation of green body

The pre-burned powder is subjected to secondary ball milling, and the ball milling time is 8 hours. The purpose of secondary ball milling is mainly to refine the crystallized powder and improve the reactivity of subsequent sintering. After ball milling, it is dried, ground, passed through a 120-mesh sieve, and added with a binder for granulation. The adhesive uses 5wt% polyvinyl alcohol (PVA) solution as the adhesive for granulation, and the mass ratio of the PVA solution to the calcined powder is about 1:10.

The granulated powder was left to stand for 24 hours and then compressed into tablets. The pressure used in the tablet press is 10MPa, the holding time is 5min, and then the pressure is released slowly, and then isostatically pressed at 300MPa for 5min to make it more compact, so as to obtain off-white BMN with a smooth surface and no cracks Green target for sputtering.

Step 3: Sintering of the target

The sintering process adopted by the method of the present invention is normal pressure sintering. Since the binder polyvinyl alcohol is added to the target green body, the polyvinyl alcohol is easily decomposed by heat in a high-temperature environment. In order to reduce the rapid discharge of the binder during the sintering process, resulting in a large number of pores inside the target and uneven distribution of internal stress, it is necessary to perform high-temperature debinding treatment on the green target body before sintering. Due to the large size of the ceramic target, the shrinkage stress during the debinding process is likely to cause cracks in the target, so the heating rate of the debinding should be as slow as possible. In the method of the present invention, the degumming temperature is 600° C., the temperature is raised for 12 hours, and the temperature is kept for 36 hours.

The sintering of the BMN ceramic target in the method of the present invention adopts buried firing. First, the green body is raised from room temperature to 100°C for 10 minutes, and then raised from 100°C to the sintering temperature of 1000-1100°C, with a heating rate of 5°C/min. Insulate at the sintering temperature for 2 to 10 hours, and then naturally cool to room temperature with the furnace to obtain a ceramic target with a dense structure.

The surface of the sintered ceramic target is polished so that its two surfaces are smooth and parallel. The smooth and flat surface can closely fit the target device table in the sputtering instrument, which is conducive to the cooling of the target during the sputtering process, and prevents the high temperature of the target induced by ion bombardment, which will cause stress to cause the target to crack.

The characterization of embodiment 2BMN ceramic target

(1) Phase structure analysis

X-ray diffraction (XRD) is an important means of material phase identification. Through XRD, the pre-sintered synthesis product can be analyzed, and the phase structure of the sintered target can be identified. In this experiment, an X-ray diffractometer (ARL X'TRA, Thermo Electron Co., Switzerland) was used for phase identification of BMN ceramic targets. The X-ray source adopts Cu target Kа line, the wavelength λ=0.15406nm, the main working parameters of the instrument are: the accelerating voltage is 40kV, the working current is 35mA, the scanning speed is 5/m, and the scanning angle range is 10°～60°.

(2) Shape analysis

The ceramic samples were cut off and polished, and then etched for 30 minutes under the condition of 100 °C lower than the sintering temperature, and then gold-plated with a JFC-1600 ion sputtering device, and the secondary electron image (SEI, Secondary Electron Image) mode to observe the morphology and structure of ceramic samples. Through the characterization of the sample cross section by SEM, the grain size of the sample, the state of the pores, and the bonding state between the grains can be directly observed.

(3) Component analysis

The elemental composition of the target was analyzed by X-ray fluorescence spectrometer (XRF, ARL 9900XRF, Thermo Scientific, Switzerland).

(4) Measurement of density

Based on Archimedes' principle, the volume density ρ of ceramic samples was measured by the drainage method, and the accuracy of the electronic balance used was 0.001g. The calculation formula is:

$\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; cm</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>$

In the formula, m ₀ is the mass of the dried sample in the air (unit: g); m ₁ is the mass of the sample in the air after fully absorbing water (unit: g); m ₂ is the mass of the sample in water after fully absorbing water The mass (unit g), ρ ₀ is the density of water (unit: g/cm ³ ).

The measurement process is as follows: first clean the prepared ceramic sample, put it in an oven to dry, and measure the mass of the sample in the air, which is recorded as m ₀ . Heat the sample in boiling distilled water for 30 minutes to fully absorb water, take it out and cool it to measure the wet weight of the sample, which is recorded as m ₁ . Put the sample in the fine copper mesh, immerse it in water together, hang it on the balance and weigh it, record it as m ₂₁ ; take out the sample and weigh the weight of the copper mesh, record it as m ₂₂ . The suspended weight of the sample in water is then. Calculate the bulk density ρ of the sample according to the formula.

(5) Test of line shrinkage

The dimensional change of the ceramic green body after sintering into a ceramic block can directly reflect the densification degree of the ceramic sample. The shrinkage of ceramic samples is characterized by linear shrinkage (S), and the calculation formula is:

$\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; \%</span>}$

In the above formula, D is the diameter of the ceramic sample after sintering (in cm); D ₀ is the diameter of the green body before sintering (in cm).

(6) Dielectric performance test

At room temperature, capacitance C (nF) and dielectric loss tanδ were measured using a precision impedance analyzer (Agilent 4294A, America). Use the following formula to calculate the relative permittivity of the sample:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 14.4</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}$

In the formula, h is the thickness of the ceramic sample (in mm), and D is the diameter of the electrode on the surface of the ceramic sample (in mm).

Example 3 BMN ceramic target pre-firing optimization

The pre-firing temperature is a crucial step in the preparation of ceramic samples. The main crystal phase of the required product is generated through pre-firing, which is beneficial to the molding and sintering of ceramic samples. The mixed raw materials were calcined at 750°C, 800°C, 850°C and 900°C, and kept for 2 hours to synthesize BMN calcined powder.

Figure 1 is the XRD pattern of the calcined powder at different temperatures. Diffraction peaks of Nb ₂ O ₅ precalcined at 750°C. In the BMN powder pre-calcined at 800℃, the diffraction peaks of the raw materials are all eliminated, but the intermediate product BiNdO ₄ exists in it. After the pre-calcination temperature increased to 850℃, the intermediate products disappeared, and the synthesized BMN powder showed a single cubic pyrochlore structure. As the calcining temperature continued to increase, the XRD diffraction peaks of the BMN calcined powder gradually became sharper, and the crystallinity of the powder gradually increased. Although high pre-calcination temperature is conducive to the growth of crystals, the powder will cause serious agglomeration, and sometimes it is not easy to crush. And too high temperature will reduce the activity of the powder, which will cause the firing temperature to rise and the firing range to shrink. Therefore, it should not be too high when selecting the pre-burning temperature.

Through the analysis of the morphology of the BMN pre-fired powder, it was found that the BMN powder particles pre-fired at 850°C were well dispersed in SEM, as shown in Figure 2; while the BMN powder pre-fired at 900°C showed serious agglomeration, As shown in Figure 3, the sintering activity decreases. Therefore, the experiment determined that 850°C is the pre-firing temperature of BMN porcelain.

Since the pre-sintering process is accompanied by the process of grain growth, the BMN powder particles after pre-sintering are relatively large, which is not conducive to the sintering of the target. This is because the particle size directly affects the reaction rate. The smaller the particle size, the larger the specific surface area of the reaction system, and the corresponding increase in the reaction interface and diffusion interface, so the reaction rate is higher. Figure 4 is the SEM image of the pre-fired ceramic material at 850°C after 12 hours of secondary ball milling. The particle size of the BMN powder after ball milling is uniform, and its average particle size is less than 1 μm.

Example 4 Determination of BMN target sintering system

The determination of the sintering system includes determining the firing temperature, heating and cooling speed, holding time and sintering atmosphere during the sintering process. Generally, under the best sintering conditions, ceramics can reach the maximum bulk density, and can also achieve the best electrical properties. The basis for determining the sintering system mainly includes: phase diagram, differential thermal analysis, bulk density and firing shrinkage curve. Among them, bulk density is an important means to measure the density and crystallization status of ceramics. The firing temperature and holding time are different, and the bulk density of ceramics is also different.

1. Determination of sintering temperature

Select the BMN ceramic material synthesized under the condition of pre-fired at 850°C and heat preservation for 2 hours. , insulation 2h for sintering. The effect of sintering temperature on the structure and properties of BMN ceramics was studied by X-ray diffractometer (XRD), scanning electron microscope (SEM), precision impedance analyzer, etc., so as to determine the optimal sintering temperature.

2. The effect of sintering temperature on the phase structure of BMN ceramics

It can be seen from Figure 5 that the BMN ceramics at each sintering temperature exhibited an obvious cubic pyrochlore structure, and no other second-phase diffraction peaks appeared, indicating that the BMN ceramic samples were all single-phase structures with good crystallization, and the temperature range of 1010 ° C to 1090 ° C Inside, the sintering temperature has no significant effect on the structure and phase composition of BMN targets.

(1). Effect of sintering temperature on BMN ceramic composition

In the experiment, the influence of different sintering temperatures on the composition of BMN ceramics was studied by XRF composition analysis, and the rules are shown in Figure 6. The dotted lines in the figure represent the Bi/Mg ratio and (Bi+Nb)/Mg ratio under stoichiometric conditions, respectively. With the increase of sintering temperature, a small amount of Bi ₂ O ₃ volatilizes gradually. The excess of Bi ₂ O ₃ was 10wt% in the initial batching, and about 5.4wt% of Bi was missing after the BMN ceramics were sintered at 1050°C for 2 hours. The calculated chemical formula of the composition was Bi _1.56 MgNb _1.5 O _7.09 .

(2). Effect of sintering temperature on the morphology of BMN ceramics

The microscopic appearance of ceramic samples can reflect whether the density of ceramics is good. Ceramic samples with uniform grain growth, less pores, and appropriate grain size have relatively high density; on the contrary, ceramic samples with more pores have lower density. Figure 7 is the SEM secondary electron image of the cross-section of BMN ceramics sintered at different sintering temperatures for 2 hours. With the increase of sintering temperature, the grain size of BMN ceramics increases gradually. When the sintering temperature is 1010 °C, the grain size of BMN ceramics is small, about 3-4 μm, and there are more pores in the sample, and the structure is looser. When the sintering temperature was increased to 1030°C, more pores could still be observed in the sample. When the sintering temperature reaches 1050 °C, the grain size is about 5 μm, the number of pores is significantly reduced, and the grains of BMN ceramic samples are relatively regular and the grain boundaries are clear. As the sintering temperature further increased, the grains of the BMN ceramic sample began to grow rapidly. When the sintering temperature reached 1090 °C, large closed pores were observed in the ceramic sample. This is because, in the middle and late stages of sintering, the isolated pores will Diffusion to the grain boundary and exclusion, that is to say, the material on the grain boundary continues to diffuse and fill the pores, so that the densification continues; but in the later stage of sintering, the grain grows rapidly, and the discharge rate of the pores will be lower than the migration of the grain boundary These unexcluded pores will break away from the grain boundaries and be wrapped inside the grains, and the high temperature will cause the air pressure in the pores to increase, forming closed large pores. At this time, further shrinkage and exclusion of pores will not be realized.

(3). Effect of sintering temperature on linear shrinkage and relative density of BMN ceramics

Linear shrinkage and relative density are the easiest means to measure the density of ceramics. In general, ceramics with large linear shrinkage and high relative density have correspondingly high density. Through theoretical calculation, the theoretical density of BMN ceramics is 7.149g/cm ³ , and the ratio of the volume density to the theoretical density is the relative density of BMN ceramics. Fig. 8 is the curve of relative density and linear shrinkage of BMN ceramic samples with sintering temperature. It can be seen that the change trend of the relative density of the sample is consistent with the change trend of its linear shrinkage rate. As the sintering temperature increases, the kinetic energy of thermal vibration of the particles in the solid structure increases, and its reaction ability and diffusion ability are enhanced, so the rate of material migration and diffusion is accelerated, and the gas in the green body is further removed, so that the volume of the ceramic sample Gradually shrink and increase in density. When the sintering temperature reaches 1050°C, its relative density reaches the maximum value of 89.65 wt%, and the linear shrinkage rate at this time is 14.54%. However, with the further increase of the sintering temperature, the shrinkage rate of the ceramic reaches saturation, but the relative density of the target decreases due to the volatilization _{of Bi2O3} .

(4). Effect of sintering temperature on the dielectric properties of BMN ceramics

The frequency characteristic curves of BMN ceramics at different sintering temperatures are shown in Figure 9. It can be seen from Figure 9a that in the frequency range of 1KHz-1MHz, with the increase of the test frequency, the dielectric constant of the BMN ceramics prepared at each sintering temperature hardly changes, and the frequency stability is better. In the frequency range of 1kHz-10kHz, the dielectric loss decreases rapidly with the increase of frequency. Although the dielectric loss is still decreasing with the increase of frequency after 10kHz, the decreasing trend is not great. , and the size of its dielectric loss has been reduced to 10 ^-4 orders of magnitude, indicating that BMN ceramics are high-frequency stable ceramics. Fig. 9b is the variation curve of the dielectric constant and dielectric loss of BMN ceramics with sintering temperature at 1 MHz. As the sintering temperature increases, the dielectric constant of BMN ceramics first increases and then decreases. When the sintering temperature rises to 1050 °C, the dielectric constant reaches a maximum value of 166.5, which is related to the increase in the density of BMN ceramics. At the same time, it can be seen that the variation trend of the dielectric loss of BMN ceramics is completely opposite to that of the dielectric constant. When the sintering temperature is 1050℃, the dielectric loss of BMN ceramics is the smallest, which is 7.23×10 ^-4 . This is because as the sintering temperature increases, the grain size of BMN ceramics gradually increases, but when the sintering temperature exceeds 1050 °C, the grains of BMN ceramics grow abnormally, the grain size varies greatly, and over-burning occurs , resulting in the deterioration of the dielectric properties of BMN ceramics.

In summary, the sintering temperature ranges from 1010°C to 1050°C. As the sintering temperature increases, the relative density and grain size of BMN ceramics increase, which effectively improves the dielectric properties of the ceramics. However, too high sintering temperature will also lead to uneven grain growth of BMN ceramics, and closed pores inside the grains, which will deteriorate the dielectric properties of BMN ceramics. Finally, 1050℃ was selected as the optimum sintering temperature of BMN ceramics.

3. Determination of holding time

(1). Effect of holding time on BMN ceramic components

After determining the sintering temperature, sinter at 1050°C and hold for 2h, 4h, 6h, 8h and 10h respectively to investigate the effect of holding time on BMN ceramics. Figure 10 shows the effect of different heat preservation on the composition change of BMN ceramics measured by XRF. The dotted lines in the figure represent the Bi/Mg ratio and (Bi+Nb)/Mg ratio under stoichiometric conditions, respectively. With the extension of the holding time, a small amount of Bi ₂ O ₃ volatilized. The chemical formula of BMN ceramics after sintering at 1050℃ for 6h is Bi _1.48 MgNb _1.5 O _6.97 . Compared with the initial batch Bi _1.65 MgNb _1.5 O _7.225 , Bi is about 10.3wt% missing.

(2). The effect of holding time on the grain morphology of BMN ceramics

Figure 11 is the secondary electron image of the cross section of BMN ceramics prepared under different holding time conditions. When the holding time is 2-4h, there are still obvious pores in the BMN ceramics, and the density of the ceramics is not high. The BMN ceramic samples prepared under the holding time of 6-10h have a dense structure, less pores, regular grains, and an equidiameter polygon. The grain boundaries are clear. At the same time, with the extension of the holding time, the grains of BMN ceramics grow gradually. The heat preservation process in the sintering process is mainly the process of grain boundary movement. If the heat preservation process is too long, the grains will grow abnormally. The grain size of BMN ceramics sintered at 1050℃ for 6h is about 2-5μm. When the holding time is extended to 10h, the grain size of BMN ceramics increases abnormally to 10-12μm. It can be considered that the holding time is too long; As the size of the particles increases, the size difference is gradually obvious, and the size distribution is uneven. When used for sputtering targets, it will not be conducive to the uniformity of the film thickness, and will lead to a decrease in the sputtering rate. Therefore, considering comprehensively, it is considered that the sintering system at 1050 °C for 6 h is more in line with the preparation requirements of BMN ceramic targets for grain size.

(3). Effect of holding time on linear shrinkage and relative density of BMN ceramics

Fig. 12 is the curve of relative density and linear shrinkage of BMN ceramic samples with sintering holding time. The change trend of the relative density of the sample is consistent with the change trend of its linear shrinkage rate. With the extension of the holding time, the relative density and linear shrinkage of BMN ceramics gradually increase, and tend to be saturated when the holding time is 6h, and the relative density reaches the maximum value of 97.03wt%, and the linear shrinkage is 14.68%.

(4). The influence of holding time on the dielectric properties of BMN ceramics

The frequency characteristic curves of BMN ceramics prepared under different holding time conditions at 1050°C are shown in Figure 13. It can be seen from Figure 13a that in the frequency range of 1kHz-1MHz, as the test frequency increases, the dielectric constant of the BMN ceramics prepared under various holding time conditions does not change with frequency, and the frequency stability is good. In the frequency range of 1kHz-10kHz, the dielectric loss decreases rapidly with the increase of frequency. After 10kHz, although the dielectric loss is still decreasing with the increase of frequency, the decreasing trend is already very strong. Small, and its dielectric loss is on the order of 10 ^-4 , indicating that BMN ceramics are high-frequency stable ceramics. Fig. 13b is the variation curve of the dielectric constant and dielectric loss of BMN ceramics with the holding time at 1 MHz. With the extension of the holding time, the dielectric constant of BMN ceramics increases first and then decreases. When the holding time is 6h, the dielectric constant reaches a maximum value of 170.4, which is consistent with the change of the density of BMN ceramics with the holding time. . At the same time, it can be seen that the change trend of the dielectric loss of BMN ceramics is completely opposite to the change trend of its dielectric constant. When the holding time is 6h, the dielectric loss of BMN ceramics is the smallest, which is 6.25×10 ^-4 .

From the above examples, it can be seen that the BMN ceramic target prepared by the method of the present invention has the advantages of compact structure and excellent performance. The composition chemical formula of the material is Bi _1.48 MgNb _1.5 O _6.97 , its relative density reaches the maximum value of 97.03wt%, and its dielectric properties are excellent, the dielectric constant at 1MHz is 170.4, and the dielectric loss is 6.25×10 ^-4 .

Although some embodiments of the present invention have been given herein, those skilled in the art should understand that the embodiments herein can be changed without departing from the spirit of the present invention. The above-mentioned embodiments are only exemplary, and the embodiments herein should not be used as limitations on the scope of rights of the present invention.

Claims (8)

1. a preparation method for BMN ceramic target, is characterized in that, has following steps:

Step one: the preparation of BMN powder

With Bi ₂o ₃, MgO and Nb ₂o ₅powder is starting raw material, and mol ratio is 1.65:1:1.5, take dehydrated alcohol as medium ball milling 6 ~ 10h, and material is dry in 80 ~ 100 DEG C of thermostatic drying chambers;

By the material pre-burning in air or oxygen atmosphere mixed, temperature is 700 ~ 900 DEG C, insulation 1 ~ 4h, and then Temperature fall is to room temperature, obtains BMN powder;

Step 2: the preparation of green compact

The BMN powder that described step one is obtained carries out secondary ball milling 6 ~ 10h, and dry in 80 ~ 100 DEG C of thermostatic drying chambers, rear grinding is also sieved, and adds tackiness agent granulation;

By powder single shaft compression moulding good for granulation, making diameter is the thick BMN green compact for 6mm of 65mm, and pressure is 10MPa;

Step 3: the sintering of target

Come unstuck at 500 ~ 700 DEG C of insulation 40 ~ 50h by shaping BMN pottery, the heating-up time is 10 ~ 15h, afterwards 1000 ~ 1100 DEG C of sintering in oxygen atmosphere, and insulation 2 ~ 10h, obtains required target.

2. the preparation method of a kind of BMN ceramic target as claimed in claim 1, is characterized in that, the Ball-milling Time in described step one is 8h, ZrO ₂ball as grinding element, ZrO ₂ball, Bi ₂o ₃, MgO and Nb ₂o ₅the mass ratio of powder gross weight and dehydrated alcohol is 1:2:1;

In described pre-burning, at 750 DEG C, 800 DEG C, 850 DEG C and 900 DEG C, be incubated pre-burning in 2 hours respectively.

3. the preparation method of a kind of BMN ceramic target as claimed in claim 1, is characterized in that, adopt oxygen atmosphere to substitute air in described step one, with the ramp of 5 DEG C/min, starts to be filled with O at 500 ~ 600 DEG C ₂, furnace cooling after 750 ~ 900 DEG C of insulations, is filled with O 500 ~ 600 DEG C of stoppings ₂.

4. the preparation method of a kind of BMN ceramic target as claimed in claim 1, it is characterized in that, the secondary ball milling in described step 2 is 8h, and sieve 120 orders.

5. the preparation method of a kind of BMN ceramic target as claimed in claim 1, is characterized in that, the tackiness agent in described step 2 is 5wt% polyvinyl alcohol solution, and described polyvinyl alcohol solution and the mass ratio of preburning powdered material are about 1:10.

6. the preparation method of a kind of BMN ceramic target as claimed in claim 1, is characterized in that, the powder time of repose that granulation is good in described step 2 is 24h, and the green compact shaping dwell time is 5min, leaves standstill 5min at the inferior static pressure of 300MPa.

7. the preparation method of a kind of BMN ceramic target as claimed in claim 1, is characterized in that, the dump temperature in described step 3 is 600 DEG C, and the heating-up time is 12h, and soaking time is 36h.

8. the preparation method of a kind of BMN ceramic target as claimed in claim 1, it is characterized in that, sintering process in described step 3 for by described BMN green compact from room temperature rise to 100 DEG C insulation 10min, after rise to sintering temperature 1000 ~ 1100 DEG C from 100 DEG C, temperature rise rate is 5 DEG C/min.