An indium tin oxide target with a low tin oxide content and a preparation method thereof

Abstract

The present invention discloses an indium tin oxide target with a low tin oxide content and a preparation method thereof, belonging to the technical field of targets. The preparation method includes steps such as mixing, ball milling, forming, degreasing, sintering, etc. By reducing the content of tin oxide in the indium tin oxide target, the present invention can effectively avoid the appearance of second phases such as SnO2, In4Sn3O 12 in the indium tin oxide target with a low tin oxide content, thereby preventing the increase of phase boundary defects, and further enabling the obtained indium tin oxide target with a low tin oxide content to have a low resistivity and excellent conductivity. Moreover, by regulating the sintering temperature and sintering time, the present invention can still enable the indium tin oxide target with a low tin oxide content to have a high relative density, and the performance of the indium tin oxide target with a low tin oxide content can be effectively guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of target materials, and particularly relates to an indium tin oxide target with a low tin oxide content and a preparation method thereof. Background Art

[0002] Transparent conductive oxide films have both transparency and conductivity characteristics and are widely used in fields such as display panels, solar cells, sensors, microelectronic devices, and functional glass. Indium tin oxide (ITO) films are a highly representative type of transparent conductive oxide film, usually prepared by magnetron sputtering. High-quality ITO targets in China have long relied on imports. Although the domestic production speed has accelerated in recent years, problems such as relatively low density and an increase in defects after the size is enlarged still exist.

[0003] High-performance ITO targets are characterized by high purity, high density, low resistivity, and high tissue uniformity. Among them, the density index is the most important. How to prepare high-density ITO targets has always been the focus of research.

[0004] In recent years, with the continuous development of display panel technology, more and more display panel manufacturers have put forward varying degrees of requirements for indium tin oxide targets with a low tin oxide content (i.e., the mass percentage of tin oxide is less than 10 wt%). At the same time, there are relatively few relevant research reports on indium tin oxide targets with a low tin oxide content at home and abroad. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides an indium tin oxide target with a low tin oxide content and a preparation method thereof to obtain indium tin oxide targets of different types and characteristics.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is to provide a preparation method of an indium tin oxide target with a low tin oxide content, which is characterized by including the following steps:

[0007] S1: Mix indium oxide powder and tin oxide powder in a mass ratio of 93:7 to 97:3 to obtain a mixed material;

[0008] S2: Ball-mill the mixed material and then spray granulate it to obtain an ITO precursor;

[0009] S3: Mold the ITO precursor by combining die pressing and cold isostatic pressing to obtain a green ITO target;

[0010] S4: Degrease the green ITO target, and then heat the degreased green ITO target to a final temperature of 1505 - 1605 °C and keep it warm for sintering for 6 - 12 h to obtain the target.

[0011] On the basis of the above technical solutions, the present invention can be further improved as follows.

[0012] Further, the ball milling in S2 includes the following steps:

[0013] S21: Mix the mixture with the dispersant solution to obtain a slurry;

[0014] S22: Perform ball milling on the slurry, with the ball milling speed being 3000 - 5000 rpm and the ball milling time being 3 - 5 h;

[0015] S23: Add an adhesive to the ball - milled material and continue ball milling for 1 - 3 h.

[0016] Further, the solute of the dispersant solution is ammonium polyacrylate and the solvent is ultrapure water; the adhesive is polyvinyl alcohol.

[0017] Further, the pressure for die pressing in S3 is 60 MPa and the pressure - holding time is 1 - 3 min; the pressure for cold isostatic pressing is 250 MPa and the pressure - holding time is 8 - 12 min.

[0018] Further, the debinding process of the ITO target green body in S4 is: heat the ITO target green body to 550 - 650 °C in an air atmosphere and hold for 40 - 60 h.

[0019] Further, the heating rate of the ITO target green body is 0.5 - 1 °C / min.

[0020] Further, the heating and sintering of the debound ITO target green body are carried out in an oxygen atmosphere.

[0021] Further, the heating rate of the debound ITO target green body is 0.5 - 1 °C / min.

[0022] Further, the final heating temperature is 1585 °C and the holding and sintering time is 12 h.

[0023] The present invention also discloses an indium tin oxide target with a low tin oxide content, which is prepared by the above - mentioned preparation method.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. The electrical conductivity of the ITO target is one of its important physical properties. By reducing the content of tin oxide in the indium tin oxide target, the present invention can effectively avoid the appearance of second phases such as SnO 2 , In 4 Sn 3 O 12 and the like, thereby preventing the increase of phase - boundary defects, and further making the obtained ITO target have a lower resistivity and excellent electrical conductivity.

[0026] 2. By regulating the sintering temperature and sintering time, the present invention can enable the indium tin oxide target with a low tin oxide content to still have a high relative density, effectively ensuring the performance of the ITO target. Description of the Drawings

[0027] Figure 1 is the relative density of the indium tin oxide target with a low tin oxide content under different sintering temperature conditions;

[0028] Figure 2 is the fracture morphology of the indium tin oxide target with a low tin oxide content under different sintering temperature conditions;

[0029] Figure 3 is a schematic diagram of the measurement principle of the four-probe method;

[0030] Figure 4 is the metallographic structure of the indium tin oxide target with a low tin oxide content under different sintering temperature conditions;

[0031] Figure 5 is the relative density of the indium tin oxide target with a low tin oxide content under different sintering time conditions;

[0032] Figure 6 is the metallographic structure of the indium tin oxide target with a low tin oxide content under different sintering time conditions. Detailed Embodiments

[0033] The indium oxide powder and tin oxide powder used in the present invention are both from Guangxi Jinglian Optoelectronic Materials Co., Ltd.

[0034] The following detailed description of the specific embodiments of the present invention is made in conjunction with the examples.

[0035] Example 1: Preparation of an indium tin oxide target with a low tin oxide content

[0036] The indium tin oxide target with a low tin oxide content in the present invention is prepared through the following steps:

[0037] S1: Mix the indium oxide powder and tin oxide powder in a mass ratio of 93:7 to 97:3 to obtain a mixed material;

[0038] S2: Mix the mixed material, ultrapure water, and ammonium polyacrylate (CAS: 9003-03-6) according to a ratio of 10 g: 2 g: 15 mL to obtain a slurry; then ball-mill the slurry at 4000 rpm for 4 h; then add polyvinyl alcohol (CAS: 9002-89-5) accounting for 5% of the mass of the material to the ball-milled material and continue ball-milling for 1 h; subsequently, transfer the mixed slurry to a centrifugal spray granulator for spray granulation to obtain an ITO precursor;

[0039] S3: The ITO precursor is uniformly filled into a 300mm×200mm high-strength steel mold for compression molding, the molding pressure is 15MPa, and the pressure holding time is 1min; then, the indium tin oxide green body obtained by compression molding is placed in a vacuum bag for vacuum treatment, and the air must be extracted as much as possible during the vacuum treatment, and the packaging is repeated for 3 to 4 layers; the vacuum-packed indium tin oxide green body is placed in a cold isostatic press for cold isostatic pressing, the molding pressure is 250MPa, and the pressure holding time is 10min; and the ITO target green body is obtained;

[0040] S4: Load the indium tin oxide green body into a bell-shaped sintering furnace, heat the ITO target green body to 600°C at a heating rate of 0.5°C / min in an air atmosphere, and keep it warm for 40 hours to complete the degreasing of the ITO target green body; then immediately introduce pure oxygen into the bell-shaped sintering furnace, and heat the degreased ITO target green body to a final temperature of 1505-1605°C at a heating rate of 0.5°C / min, and keep it warm for 6-12 hours to obtain an indium tin oxide target with a low tin oxide content.

[0041] Example 2: Effect of sintering temperature on the performance of indium tin oxide target with low tin oxide content

[0042] In order to study the influence of sintering temperature on the main properties of indium tin oxide target with low tin oxide content, such as relative density, resistivity and grain size, and at the same time make the indium tin oxide target with low tin oxide content sintered in the middle and late stages as much as possible, the sintering temperature is selected in the range of 1505℃~1605℃, and a temperature point is selected at an interval of 20℃ as the sintering temperature test point. The specific process parameters are shown in Table 1.

[0043] Table 1 Sintering temperature parameters of indium tin oxide target with low tin oxide content

[0044] Serial number Sintering temperature (°C) Sintering time (h) 1 1 505 8 2 1 525 8 3 1 545 8 4 1 565 8 5 1 585 8 6 1 605 8

[0045] 1. Effect of sintering temperature on relative density of indium tin oxide target with low tin oxide content

[0046] In the present invention, the density of the indium tin oxide target sample with low tin oxide content is measured and calculated based on the Toledo Mettler precision balance and the Archimedean principle. The specific operation process is as follows:

[0047] (1) First, the surface of the low-tin oxide content indium tin oxide target sample is ground and cleaned, and the actual weight is measured with a precision balance after the moisture is dried. The actual weight is recorded as m 1 , unit is g;

[0048] (2) The low tin oxide content indium tin oxide target sample is completely immersed in pure water, and its weight in pure water is measured with a precision balance. The weight in pure water is recorded as m2 , in g;

[0049] (3) Based on Archimedes' principle, calculate the true density of the indium tin oxide target sample with low tin oxide content according to the calculation formula (I);

[0050]

[0051] In the formula, ρ is the true density of the indium tin oxide target sample with low tin oxide content, in g / cm 3 ; ρ 纯水 is the density of pure water, and the density of pure water needs to be set according to the actual water temperature conditions, in g / cm 3 .

[0052] (4) Calculate the relative density of the indium tin oxide target sample with low tin oxide content according to formula (II);

[0053]

[0054] In the formula, ρ 相对 is the relative density of the indium tin oxide target sample with low tin oxide content, in g / cm 3 ; ρ 理论 is the theoretical density of the indium tin oxide target sample with low tin oxide content, in g / cm 3 .

[0055] Figure 1 is the relative density of the indium tin oxide target with low tin oxide content prepared under different sintering temperature conditions. It can be seen from the figure that the sintering temperature has a more obvious effect on the relative density of the indium tin oxide target with low tin oxide content. In the sintering temperature range of 1505 °C to 1605 °C, the relative density of the indium tin oxide target with low tin oxide content gradually increases with the increase of the sintering temperature; among them, when the mass ratio of the indium oxide powder and tin oxide powder used as raw materials is 93:7, the relative density of the obtained indium tin oxide target with low tin oxide content (7wt%-SnO 2 ) shows a trend of first monotonically increasing and then leveling off with the gradual increase of the sintering temperature. When the sintering temperature reaches 1585 °C, the relative density reaches 99.19%; when the mass ratio of the indium oxide powder and tin oxide powder used as raw materials is 97:3, the relative density of the obtained indium tin oxide target with low tin oxide content (3wt%-SnO 2 ) monotonically increases from 96.75% to 99.06% with the increase of the sintering temperature. In addition, the change degree of the relative density of the 3wt%-SnO 2 indium tin oxide target is more significant. From Figure 1 it can also be seen that in the sintering temperature range of 1505 °C to 1605 °C, at any sintering temperature condition, 7wt%-SnO2 The relative density of indium tin oxide target is always higher than that of 3wt%-SnO 2 the indium tin oxide target. It can be found that as the content of tin oxide decreases continuously, the relative density of the indium tin oxide target gradually decreases. This is because the single component In 2 O 3 is difficult to sinter. The less the content of tin oxide, the more difficult it is to achieve sintering densification of the target.

[0056] Figure 2 is the fresh fracture morphology of indium tin oxide target with low tin oxide content. Among them, (a), (c) and (e) are the fresh fracture morphologies of 7wt%-SnO 2 indium tin oxide target at the sintering temperatures of 1505°C, 1545°C and 1585°C respectively, and (b), (d) and (f) are the fresh fracture morphologies of 3wt%-SnO 2 indium tin oxide target at the sintering temperatures of 1505°C, 1545°C and 1585°C respectively. It can be seen from the fracture morphology of the target that as the sintering temperature gradually increases, the number of pores in the indium tin oxide target with low tin oxide content gradually decreases, and at the same time the size of the pores also gradually becomes smaller. Thus, it can be seen that as the sintering temperature continuously increases, the densification degree of the indium tin oxide target is gradually improved. In addition, from Figure 2 it can also be seen that cleavage steps are distributed on the fracture of the indium tin oxide target with low tin oxide content, and the fracture mode is mainly transgranular fracture.

[0057] II. Influence of Sintering Temperature on Resistivity of Indium Tin Oxide Target with Low Tin Oxide Content

[0058] In the present invention, the resistivity of the indium tin oxide target with low tin oxide content is measured by using an ST2258C type digital four-probe tester, and the measurement principle is as Figure 3 shown. The specific measurement principle is as follows: metal probes 1, 2, 3, and 4 at the same straight-line position are pressed on the sample with a certain pressure, and a constant-current power supply is used to pass current I through probes 1 and 4, then a potential difference V will be generated between probes 2 and 3, and the resistivity of the sample can be calculated by formula (III);

[0059]

[0060] In the formula, ρ r is the resistivity of the indium tin oxide target sample with low tin oxide content, and the unit is Ω·cm; C is the probe coefficient, which is a constant related to the probe geometry, and the unit is cm; V 23 is the potential difference between probes 2 and 3, and the unit is V; I is the current passing through between probes 1 and 4, and the unit is A.

[0061] In the present invention, when measuring the resistivity of an indium tin oxide target sample with a low tin oxide content, the following operation process shall be followed: First, grind the surface of the indium tin oxide target with a low tin oxide content; then, select several points in a fixed area of the indium tin oxide target sample with a low tin oxide content for resistivity measurement (in the present invention, 30 points are taken); finally, take the arithmetic mean of all resistivities as the resistivity of the target sample.

[0062] The resistivities of indium tin oxide targets with low tin oxide content under different sintering temperature conditions are shown in Table 2.

[0063] Table 2 Resistivities of indium tin oxide targets with low tin oxide content under different sintering temperature conditions

[0064]

[0065] As can be seen from Table 2, the resistivity of the indium tin oxide target with a low tin oxide content is significantly affected by the sintering temperature. In the range of sintering temperature from 1505 °C to 1605 °C, as the sintering temperature continuously increases, the resistivity of the indium tin oxide target with a low tin oxide content shows a trend of first decreasing and then increasing. Among them, when the sintering temperature is 1585 °C, the resistivity of the 7wt%-SnO 2 indium tin oxide target reaches a minimum value of 1.512×10 -4 Ω·cm; similarly, when the sintering temperature is 1585 °C, the resistivity of the 3wt%-SnO 2 indium tin oxide target reaches a minimum value of 1.329×10 -4 Ω·cm. In addition, it can also be seen from Table 2 that in the sintering temperature range of 1505 °C to 1605 °C, under any sintering temperature condition, the resistivity of the 7wt%-SnO 2 indium tin oxide target is higher than that of the 3wt%-SnO 2 indium tin oxide target. With a tin doping rate 4 percentage points higher, other phases may precipitate, such as SnO 2 , and another second phase In 4 Sn 3 O 12 . The appearance of the second phase causes an increase in phase boundary defects, resulting in a decrease in the mobility of carriers, so the resistivity increases. It can be seen from this that the resistivity corresponding to the indium tin oxide target with a lower tin oxide content is relatively low.

[0066] III. Influence of Sintering Temperature on Grain Size of Indium Tin Oxide Targets with Low Tin Oxide Content

[0067] In the present invention, the metallographic sample preparation of indium tin oxide target with low tin oxide content is carried out according to the conventional metallographic sample preparation method. The specific operation process is as follows: Use a cutting tool to cut and sample at a specific position of the indium tin oxide target sample with low tin oxide content, and then complete the metallographic sample preparation through steps such as grinding, polishing, etching, and rinsing in sequence; among them, when grinding, the indium tin oxide target sample with low tin oxide content should be ground through sandpapers of 800 mesh, 1500 mesh, and 2500 mesh in sequence, and then polished. The metallographic sample preparation is etched by acid etching, and the etching solution used is aqua regia, that is, concentrated nitric acid (HNO 3 ), and concentrated hydrochloric acid (HCl) are mixed and configured according to a volume ratio of 1:3, and the etching time is 20 min. In the present invention, the grain microstructure morphology of the indium tin oxide target metallographic sample preparation is observed by means of an optical microscope (OM), and finally, using Nano Measurer 1.2 software, a number of (100 in number are selected in the present invention) grains are selected for statistical analysis to obtain the grain size of the indium tin oxide target sample.

[0068] Figure 4 The metallographic structure and grain size statistics of the indium tin oxide target with low tin oxide content prepared under different sintering temperature conditions are shown. Among them, (a)-(f) are the metallographic structure and grain size statistics of 7wt%-SnO 2 indium tin oxide target, and (g)-(l) are the metallographic structure and grain size statistics of 3wt%-SnO 2 indium tin oxide target. It can be seen from the figure that in the sintering temperature range of 1505°C to 1605°C, the grains of the indium tin oxide target with low tin oxide content are relatively regular and are basically closely combined between grains; when the sintering temperature gradually increases from 1505°C to 1605°C, the average grain size of the indium tin oxide target with low tin oxide content gradually increases with the increase of the sintering temperature. Among them, the average grain size of 7wt%-SnO 2 indium tin oxide target monotonically increases from 5.64 μm to 14.49 μm. Similarly, the average grain size of 3wt%-SnO 2 indium tin oxide target monotonically increases from 4.03 μm to 8.24 μm. The growth of grains is actually the displacement behavior of grain boundaries. When the temperature is higher, the grain boundary displacement is faster and the grain size becomes larger and larger. It can also be seen from Figure 4 that in the range of sintering temperature of 1505°C to 1605°C, under the same sintering temperature condition, the average grain size of 7wt%-SnO 2 indium tin oxide target is larger than that of 3wt%-SnO 2 indium tin oxide target. It can be seen from this that under the same sintering temperature condition, with the decrease of the tin oxide content, the average grain size of the indium tin oxide target shows a trend of first increasing and then decreasing.

[0069] Example 3: Influence of Sintering Time on the Properties of Indium Tin Oxide Targets with Low Tin Oxide Content

[0070] To study the influence of sintering time on the main properties such as relative density, resistivity, and grain size of indium tin oxide targets with low tin oxide content, the indium tin oxide targets with low tin oxide content were sintered using the sintering process parameters shown in Table 3.

[0071] Table 3 Sintering Time Parameters of Indium Tin Oxide Targets with Low Tin Oxide Content

[0072] Serial number Sintering temperature (°C) Sintering time (h) 1 1 585 6 2 1 585 8 3 1 585 12

[0073] I. Influence of Sintering Time on the Relative Density of Indium Tin Oxide Targets with Low Tin Oxide Content

[0074] Figure 5 The relative density of indium tin oxide targets with low tin oxide content under different sintering time conditions. From Figure 5 It can be seen that under the condition of the same sintering temperature of 1585 °C, the influence of sintering time on the relative density of indium tin oxide targets with low tin oxide content is more obvious. In the range of sintering time from 6 h to 12 h, as the sintering time prolongs, the relative density of the 7wt%-SnO 2 indium tin oxide target increases from 99.08% to 99.19% and then tends to be stable. Similarly, the relative density of the 3wt%-SnO 2 indium tin oxide target increases from 98.91% to 99.01% and then tends to be stable. Thus, it can be seen that by prolonging the sintering time, the relative density of indium tin oxide targets with low tin oxide content does not increase to a large extent, which also shows that when the tin oxide content is lower, it is more difficult to achieve high density for the target.

[0075] II. Influence of Sintering Time on the Resistivity of Indium Tin Oxide Targets with Low Tin Oxide Content

[0076] The resistivity of indium tin oxide targets with low tin oxide content under different sintering time conditions is shown in Table 4. It can be seen from the table that the resistivity of indium tin oxide targets with low tin oxide content is significantly affected by the sintering time. Under the condition of the same sintering temperature of 1585 °C, in the range of sintering time from 6 h to 12 h, as the sintering time gradually prolongs, the resistivity of indium tin oxide targets with low tin oxide content shows a trend of first decreasing and then increasing. When the sintering time is 8 h, the resistivity of the 7wt%-SnO 2 indium tin oxide target reaches the minimum value of 1.512×10 -4 Ω·cm. Similarly, when the sintering time is 8 h, the resistivity of the 3wt%-SnO 2 indium tin oxide target reaches the minimum value of 1.329×10-4 Ω·cm. In addition, it can also be seen from the table that within the sintering time range of 6h to 12h, under any sintering time condition, the resistivity of the indium tin oxide target with 7wt%-SnO 2 is higher than that of the indium tin oxide target with 3wt%-SnO 2 . It can be found that the indium tin oxide target with a lower tin oxide content has a relatively lower resistivity.

[0077] Table 4 Resistivity of indium tin oxide targets with low tin oxide content under different sintering time conditions

[0078]

[0079] III. Influence of Sintering Time on Grain Size of Indium Tin Oxide Targets with Low Tin Oxide Content

[0080] Figure 6 shows the metallographic structure and grain size statistics of the indium tin oxide targets with low tin oxide content prepared under different sintering time conditions. Among them, (a)-(c) show the metallographic structure and grain size statistics of the indium tin oxide target with 7wt%-SnO 2 , and (d)-(f) are the metallographic structure and grain size statistics of the indium tin oxide target with 3wt%-SnO 2 . It can be seen that within the sintering time range of 6h to 12h, the average grain size of the indium tin oxide targets with low tin oxide content gradually increases with the extension of the sintering time. Among them, the average grain size of the indium tin oxide target with 7wt%-SnO Figure 6 monotonically increases from 7.84μm to 14.29μm. Similarly, the average grain size of the indium tin oxide target with 3wt%-SnO 2 gradually increases from 6.02μm to 7.75μm. Grain growth is actually the displacement behavior of grain boundaries. With the extension of the sintering time, the target has more sufficient time for grain boundary displacement during sintering, and the grains grow. It can also be seen from Figure 6 that under the same sintering time condition, the average grain size of the indium tin oxide target with 7wt%-SnO 2 is larger than that of the indium tin oxide target with 3wt%-SnO 2 . It can be found that under the same sintering time condition, with the decrease of the tin oxide content, the average grain size of the indium tin oxide target also shows a trend of first increasing and then decreasing. 2

[0081] Although the specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, it should not be construed as a limitation on the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative efforts still fall within the scope of protection of this patent.

Claims

1. A method for preparing an indium tin oxide target with a low tin oxide content, characterized in that: The following steps are involved: S1: mixing indium oxide powder and tin oxide powder in a mass ratio of 93:7 to 97:3 to obtain a mixture; S2: ball milling the mixture and then spray granulating it to obtain an ITO precursor; S3: The ITO precursor is molded by molding combined with cold isostatic pressing to obtain an ITO target green body; the molding pressure is 60MPa, and the holding time is 1-3min; the cold isostatic pressing pressure is 250MPa, and the holding time is 8-12min; S4: Degreasing the ITO target green body, then heating the degreased ITO target green body to a final temperature of 1505~1605°C, and sintering at this temperature for 6~12h; the degreasing process of the ITO target green body is as follows: heating the ITO target green body to 550~650°C at a heating rate of 0.5~1°C / min in an air atmosphere, and keeping it at this temperature for 40~60h.

2. The preparation method according to claim 1, characterized in that: The ball milling in S2 includes the following steps: S21: mixing the mixed material with the dispersant solution to obtain a slurry; S22: ball milling the slurry, the ball milling speed is 3000-5000 rpm, and the ball milling time is 3-5 hours; S23: Add adhesive to the milled material and continue milling for 1 to 3 hours.

3. The preparation method according to claim 2, characterized in that: The solute of the dispersant solution is ammonium polyacrylate, the solvent is ultrapure water; and the adhesive is polyvinyl alcohol.

4. The preparation method according to claim 1, characterized in that: The heating and sintering of the degreased ITO target green body are carried out in an oxygen atmosphere.

5. The preparation method according to claim 1 or 4, characterized in that: The heating rate of the degreased ITO target green body is 0.5~1℃ / min.

6. The preparation method according to claim 1, characterized in that: The final temperature of the heating is 1585℃, and the sintering time is 12h.

7. An indium tin oxide target with a low tin oxide content obtained by the preparation method according to any one of claims 1 to 6.

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