One-step SPS gradient sintering preparation process of long-strip-shaped AZO target material

Abstract

The invention discloses a one-step SPS (spark plasma sintering) gradient sintering preparation process of a long-strip-shaped AZO target material, and relates to the technical field of AZO target material preparation. A modular gradient mold is adopted, a spark plasma sintering (SPS) technology is combined, the grain size gradient in the length direction is formed by controlling the temperature difference between the two ends and the center of the mold, sintering parameter combination is optimized, and the AZO target material is prepared. And one-time sintering forming of the long-strip-shaped AZO target material is achieved. According to the long-strip-shaped AZO target material prepared through the method, the length can reach 1000-3000 mm, the density is larger than or equal to 97%, the dimensional tolerance is smaller than or equal to + / -0.03 mm, the binding fitting rate is larger than or equal to 99%, the sputtering uniformity error is smaller than or equal to 3%, the large-scale production requirement of new energy automobile glass is met, the yield is increased to 90% or above, and the production cost is remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of AZO target technology, specifically to a one-step SPS gradient sintering process for preparing elongated AZO targets. Background Technology

[0002] AZO (zinc aluminum oxide) sputtering targets are the core material for sputtering coatings on new energy vehicle glass, used to prepare transparent conductive films to ensure the heat insulation and electrical conductivity functions of automotive glass. With the development of the new energy vehicle industry, the demand for long strip-shaped AZO targets in continuous sputtering production lines for automotive glass is increasing, requiring target lengths of 1000-3000mm, while also meeting the requirements of high density, high dimensional accuracy, and excellent sputtering uniformity.

[0003] Currently, the preparation of elongated AZO targets mostly adopts a segmented sintering and splicing process, that is, short-sized target blanks are first prepared, and then spliced ​​into elongated targets through welding, bonding and other methods. This process has many drawbacks: First, the preparation efficiency is low, as the segmented sintering, splicing and subsequent processing steps are cumbersome and time-consuming; second, the yield is low, as gaps and insufficient bonding strength are prone to occur at the splicing joints, causing the target to easily detach and crack during splicing, with the current process yielding less than 80%; third, the splicing uniformity is poor, as the grain size of the segmented target is inconsistent, and there are abrupt changes in performance at the splicing joints, resulting in uneven thickness and resistivity of the spliced ​​glass film, affecting product quality.

[0004] Spark plasma sintering (SPS), as a novel rapid sintering technology, boasts advantages such as instantaneous high temperature, rapid heating rate, and short sintering time, and has been applied in the field of target material preparation. However, existing SPS sintering technologies are mostly designed for small-sized, irregularly shaped targets, lacking dedicated processes and molds suitable for long, strip-shaped targets. Due to the large length of long, strip-shaped targets, uneven temperature distribution is prone to occur during sintering, leading to inconsistent grain growth and further exacerbating the problem of poor sputtering uniformity. At the same time, existing SPS sintering parameters cannot simultaneously meet the density, dimensional accuracy, and grain gradient distribution requirements of long, strip-shaped targets, making it difficult to meet the large-scale production requirements of continuous sputtering for new energy vehicle glass.

[0005] Therefore, developing a preparation process that can achieve one-time sintering of long strip AZO targets while solving problems such as uneven temperature distribution, poor sputtering uniformity, and low yield has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a one-step SPS gradient sintering process for preparing elongated AZO targets, thereby solving the problems mentioned in the background section.

[0007] The present invention solves the technical problem by adopting the following technical solution: This invention provides a one-step SPS gradient sintering process for preparing elongated AZO targets, comprising the following steps: (1) Raw material pretreatment: Select AZO powder with a purity of ≥99.9%, put it in a drying oven, and dry it at 80-120℃ for 2-4 hours to remove the moisture in the powder; put the dried AZO powder into a grinding equipment for grinding, and then pass it through a 200-300 mesh sieve to obtain AZO raw material powder with uniform particle size and particle size fluctuation ≤0.5μm, to ensure the flowability of the raw material powder and facilitate uniform loading in the subsequent process.

[0008] (2) Mold assembly: A modular gradient mold is adopted. The mold is made of graphite, which has excellent thermal conductivity, high temperature resistance and lubricity, and is suitable for the SPS high-temperature sintering environment, while avoiding reaction with AZO raw materials. The mold is assembled by several splicing modules. The mold length can be adjusted by increasing or decreasing the number of splicing modules, which is suitable for the preparation of target materials of different lengths from 1000-3000mm, and has high flexibility.

[0009] The mold is divided into a high-temperature zone, a transition zone, and a low-temperature zone. The high-temperature zone corresponds to the central area of ​​the target material, the low-temperature zone corresponds to the two ends of the target material, and the transition zone connects the high-temperature and low-temperature zones to achieve a continuous temperature transition. The wall thickness difference between the high-temperature and low-temperature zones is 15-20mm. This wall thickness difference enables temperature gradient control—the greater the wall thickness, the slower the heat conduction rate and the higher the temperature of the area, and vice versa. The wall thickness of the transition zone changes linearly to ensure a continuous temperature transition from the high-temperature to the low-temperature zone, avoiding sudden temperature changes that could cause thermal stress on the target material. The various splicing modules are connected by positioning pins and sealing grooves with a positioning accuracy of ≤0.005mm to ensure the dimensional accuracy of the mold after assembly. High-temperature resistant sealing gaskets are installed in the sealing grooves to ensure the mold's sealing performance and prevent air from entering during sintering and affecting the quality of the target material.

[0010] (3) Loading and sealing: The AZO raw material powder obtained in step (1) is uniformly loaded into the molding cavity of the gradient mold assembled in step (2), and the raw material powder is compacted by vibration compaction to ensure that the raw material powder is filled evenly and has a consistent density, so as to avoid defects such as pores and uneven density in the target material after sintering; after compaction, the mold is sealed and placed in the designated position of the SPS sintering furnace to ensure that the mold is accurately positioned and has good contact with the electrodes of the sintering furnace.

[0011] (4) SPS gradient sintering: Start the SPS sintering furnace and use a combination of mechanical pumps and molecular pumps to evacuate the furnace to a vacuum level of ≤5×10. -3A vacuum environment can prevent the AZO raw material from oxidizing at high temperatures, while also reducing the residual gaseous impurities during sintering and improving the density of the target material. After the vacuum level is reached, an axial pressure of 30-40 MPa is applied to the mold. During the pressure application process, a uniform pressure is maintained, with the pressure application rate controlled at 2-5 MPa / min to avoid sudden pressure changes that could lead to uneven distribution of the raw material powder or damage to the mold.

[0012] The sintering power supply is started, and the temperature is increased at a rate of 50-80℃ / min. The temperature distribution is controlled by the difference in mold wall thickness, maintaining the temperature difference between the high-temperature and low-temperature zones of the mold at 50-80℃. The sintering temperature in the high-temperature zone is 1100-1200℃, while the sintering temperature in the low-temperature zone gradually changes to 1050-1150℃ with the wall thickness. Utilizing the instantaneous high-temperature characteristics of SPS technology, the AZO raw material powder quickly reaches the sintering temperature, shortening the sintering time. At the same time, through temperature gradient control, a continuous grain size gradient is formed along the length of the target material—the grain growth rate is faster in the high-temperature zone, with a grain size of 4-5μm, while the grain growth rate is slower in the low-temperature zone, with a grain size of 3-4μm. The grain size transition in the transition zone is continuous without abrupt changes. This grain size gradient can effectively compensate for the difference in sputtering rate between the two ends and the center during the sputtering of long strip targets, improving sputtering uniformity.

[0013] After reaching the preset sintering temperature, hold the temperature for 8-12 minutes. During the holding process, maintain a stable vacuum and pressure to ensure that the AZO particles are fully diffused and combined, thereby improving the density and structural stability of the target material. After the holding period, slowly cool the target material at a rate of 30-50℃ / min to avoid excessively rapid cooling that could cause thermal stress, cracks, deformation, or other defects.

[0014] (5) Cooling and demolding: After the temperature inside the SPS sintering furnace drops to room temperature, stop vacuuming, open the sintering furnace, take out the mold, disassemble the mold and demold to obtain a long strip of AZO target material. A special clamp is used during the demolding process to avoid damage to the target material surface.

[0015] (6) Post-processing: The rough target material is polished to remove the surface oxide layer, burrs and defects, so that the surface roughness of the target material is ≤0.8μm; after polishing, ultrasonic cleaning is used to remove surface impurities, and after drying, performance testing is carried out to screen out the finished strip-shaped AZO target material that meets the requirements.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves one-time sintering, improving preparation efficiency and yield: This invention uses a modular gradient mold combined with SPS technology to achieve one-time sintering of long strip AZO targets, completely replacing the traditional segmented sintering + splicing process, simplifying the preparation process and improving preparation efficiency by more than 50%; at the same time, it avoids problems such as gaps and insufficient bonding strength caused by splicing, increasing the yield from less than 80% to more than 90%, and significantly reducing production costs.

[0017] 2. Optimize grain size gradient to solve the problem of poor sputtering uniformity: Through the wall thickness design of the modular gradient mold, the temperature gradient during SPS sintering is precisely controlled (temperature difference of 50-80℃ between the two ends and the center), so that the target material forms a continuous grain size gradient of 3-5μm along the length direction, which compensates for the sputtering rate difference between the two ends and the center during the sputtering of long strip target material, so that the sputtering uniformity error is ≤3%, which meets the quality requirements of continuous sputtering of new energy vehicle glass.

[0018] 3. Optimize sintering parameters to improve the overall performance of the target material: The optimized SPS sintering parameter combination of this invention (vacuum degree ≤ 5 × 10⁻⁶) -3 The combined effect of pressure (30-40 MPa, holding time 8-12 min) and gradient temperature control ensures that the target material has a density of ≥97%, a dimensional tolerance of ≤±0.03 mm, and a bonding rate of ≥99%, thus balancing the structural stability and dimensional accuracy of the target material and extending its service life.

[0019] 4. Modular design for mass production: The gradient mold adopts a modular splicing structure, and the length can be adjusted by adding or removing splicing modules to adapt to the preparation of target materials of different lengths from 1000-3000mm. It flexibly matches the diverse needs of the continuous splicing production line for new energy vehicle glass, and facilitates mass production and standardization. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 A one-step SPS gradient sintering process for preparing elongated AZO targets includes the following steps: (1) Raw material pretreatment: Select AZO powder with a purity of 99.9%, put it into a drying oven and dry it at 100℃ for 3h; put the dried AZO powder into a planetary ball mill for grinding, and then pass it through a 250-mesh sieve to obtain AZO raw material powder with a particle size fluctuation of ≤0.5μm.

[0022] (2) Mold assembly: A modular gradient mold made of graphite material is used to form a molding cavity with a length of 1000mm. The wall thickness of the high temperature zone of the mold is 35mm, the wall thickness of the low temperature zone is 15mm, the wall thickness difference is 20mm, and the wall thickness of the transition zone is linearly gradual. Each splicing module is connected by a positioning pin and a sealing groove with a positioning accuracy of 0.005mm. A graphite sealing gasket is set in the sealing groove.

[0023] (3) Loading and sealing: The AZO raw material powder is evenly loaded into the forming cavity of the mold, vibrated and compacted, and then the mold is sealed and placed in the SPS sintering furnace and positioned accurately.

[0024] (4) SPS gradient sintering: Start the SPS sintering furnace and evacuate to 3×10 -3 Apply an axial pressure of 35 MPa; heat at a rate of 60 °C / min, controlling the temperature in the high-temperature zone at 1150 °C and the temperature in the low-temperature zone at 1070 °C, with a temperature difference of 80 °C; after reaching the preset temperature, hold for 10 min, and then cool down at a rate of 40 °C / min.

[0025] (5) Cooling and demolding: After cooling to room temperature, disassemble the mold and demold to obtain a long strip of crude AZO target material.

[0026] (6) Post-processing: The surface of the target material is polished to a roughness of 0.6 μm, ultrasonically cleaned and dried, and its performance is tested.

[0027] Example 2 A one-step SPS gradient sintering process for preparing elongated AZO targets includes the following steps: (1) Raw material pretreatment: Select AZO powder with a purity of 99.9%, put it into a drying oven and dry it at 80℃ for 4 hours; put the dried AZO powder into a planetary ball mill for grinding, and then pass it through a 200-mesh sieve to obtain AZO raw material powder with a particle size fluctuation of ≤0.5μm.

[0028] (2) Mold assembly: A modular gradient mold made of graphite material is used to form a molding cavity with a length of 2000mm. The wall thickness of the high temperature zone of the mold is 30mm, the wall thickness of the low temperature zone is 12mm, the wall thickness difference is 18mm, and the wall thickness of the transition zone is linearly gradual. Each splicing module is connected by a positioning pin and a sealing groove with a positioning accuracy of 0.004mm. A graphite sealing gasket is set in the sealing groove.

[0029] (3) Loading and sealing: The AZO raw material powder is evenly loaded into the forming cavity of the mold, vibrated and compacted, and then the mold is sealed and placed in the SPS sintering furnace and positioned accurately.

[0030] (4) SPS gradient sintering: Start the SPS sintering furnace and evacuate to 5×10 -3Apply an axial pressure of 30 MPa; heat at a rate of 50 °C / min, controlling the temperature in the high-temperature zone to 1100 °C and the temperature in the low-temperature zone to 1050 °C, with a temperature difference of 50 °C; after reaching the preset temperature, hold for 12 min, and then cool down at a rate of 30 °C / min.

[0031] (5) Cooling and demolding: After cooling to room temperature, disassemble the mold and demold to obtain a long strip of crude AZO target material.

[0032] (6) Post-processing: The surface of the target material is polished to a roughness of 0.7 μm, ultrasonically cleaned and dried, and its performance is tested.

[0033] Example 3 A one-step SPS gradient sintering process for preparing elongated AZO targets includes the following steps: (1) Raw material pretreatment: Select AZO powder with a purity of 99.9%, put it into a drying oven and dry it at 120℃ for 2 hours; put the dried AZO powder into a planetary ball mill for grinding, and then pass it through a 300-mesh sieve to obtain AZO raw material powder with a particle size fluctuation of ≤0.5μm.

[0034] (2) Mold assembly: A modular gradient mold made of graphite material is used to form a molding cavity with a length of 3000mm. The wall thickness of the high temperature zone of the mold is 32mm, the wall thickness of the low temperature zone is 12mm, the wall thickness difference is 20mm, and the wall thickness of the transition zone is linearly gradual. Each splicing module is connected by a positioning pin and a sealing groove with a positioning accuracy of 0.005mm. A graphite sealing gasket is set in the sealing groove.

[0035] (3) Loading and sealing: The AZO raw material powder is evenly loaded into the forming cavity of the mold, vibrated and compacted, and then the mold is sealed and placed in the SPS sintering furnace and positioned accurately.

[0036] (4) SPS gradient sintering: Start the SPS sintering furnace and evacuate to 2×10 -3 Apply an axial pressure of 40 MPa; heat at a rate of 80 °C / min, controlling the temperature in the high-temperature zone to 1200 °C and the temperature in the low-temperature zone to 1120 °C, with a temperature difference of 80 °C; after reaching the preset temperature, hold for 8 minutes, and then cool down at a rate of 50 °C / min.

[0037] (5) Cooling and demolding: After cooling to room temperature, disassemble the mold and demold to obtain a long strip of crude AZO target material.

[0038] (6) Post-processing: The surface of the target material is polished to a roughness of 0.8 μm, ultrasonically cleaned and dried, and its performance is tested.

[0039] Comparative Example 1 A 1000mm long strip-shaped AZO target was prepared using a traditional process: AZO raw material powder was segmented and loaded into a common graphite mold, and then sintered using SPS (vacuum degree 5×10⁻⁶). -3 (Pa, pressure 35MPa, temperature 1150℃, heat preservation for 10min) to obtain 3 target blanks with a length of about 333mm; the 3 blanks are spliced ​​together by welding, and the finished product is obtained after grinding, cleaning and testing.

[0040] Comparative Example 2 A long strip AZO target with a length of 1000 mm was prepared using a common uniform wall thickness graphite mold (wall thickness 25 mm, no gradient design). The remaining steps were the same as in Example 1. There was no temperature gradient control during the sintering process, and the temperature difference between the high temperature zone and the low temperature zone was ≤10℃.

[0041] Comparative Example 3 Using the same modular gradient mold as in Example 1, a long strip-shaped AZO target with a length of 1000 mm was prepared, and the sintering parameters were adjusted to: vacuum degree 1×10 -2 Pa, pressure 25MPa, heat preservation time 5min, the remaining steps are the same as in Example 1.

[0042] Performance testing and data analysis The elongated AZO targets prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing. The test indicators included density, dimensional tolerance, bonding rate, grain size range, resistivity, bending strength, sputtering uniformity error, and yield. The test results are shown in the table below. 1. Density: The Archimedes displacement method was used for testing, in accordance with GB / T 5163-2022 "Determination of Density, Porosity and Open Porosity of Sintered Metallic Materials and Hard Alloys". First, the mass of the target material in air was weighed, then the mass of the target material completely immersed in distilled water was weighed. The actual density of the target material was calculated using the formula ρ = (m1 × ρwater) / (m1 - m2) (where m1 is the mass in air, m2 is the mass in water, and ρwater is the density of distilled water). This density was then compared with the theoretical density of AZO (5.61 g / cm³). 3 Compared to the previous method, the density was obtained by selecting 5 different detection points for each sample and taking the average value as the final result.

[0043] 2. Dimensional tolerance: High-precision vernier calipers (accuracy 0.001mm) combined with a coordinate measuring machine (measurement accuracy ≤0.002mm) are used for inspection. Ten inspection points are evenly selected along the length of the target material, and five inspection points are selected in the width and thickness directions. The dimensions of each point are measured and compared with the design dimensions. The dimensional deviation is calculated, and the maximum deviation value is taken as the dimensional tolerance of the target material.

[0044] 3. Bonding and Adhesion Rate: Ultrasonic flaw detector (frequency 2.5-5MHz) is used for testing, in accordance with GB / T 11344-2013 "Ultrasonic Testing Methods and Acceptance Grades for Non-destructive Testing of Welds". The bonding surface of the target material is scanned, and bonding defects (such as gaps and unbonded areas) are judged by ultrasonic reflection signals. The ratio of the bonding area to the total area of ​​the bonding surface is calculated to obtain the bonding and adhesion rate. The scanning range covers the entire bonding surface of the target material to avoid missing defect areas.

[0045] 4. Grain size range: Metallographic analysis was used for testing. The target material was first cut into samples along its length. After grinding, polishing, and etching (using 5% nitric acid alcohol solution), the grain morphology was observed using a metallographic microscope (1000x magnification). Six typical regions were selected, including the target center, transition zone, and both ends. Three metallographic images were taken for each region. Image-Pro Plus image analysis software was used to measure the grain size and statistically analyze the grain size distribution range to ensure coverage of the entire gradient distribution range.

[0046] 5. Sputtering Uniformity Error: The target material was installed on a continuous sputtering production line for new energy vehicle glass to simulate actual sputtering conditions (sputtering power 1500W, sputtering pressure 0.3Pa, sputtering distance 80mm) and sputtering coating was completed on the same substrate. A film thickness measuring instrument (measurement accuracy ≤0.1nm) was used to uniformly select 15 detection points along the film length direction to measure the film thickness at each point. The average film thickness was calculated, and the sputtering uniformity error was calculated using the formula δ=(|d_max-d_avg|) / d_avg×100% (where d_max is the maximum film thickness and d_avg is the average film thickness). The average value of three parallel tests was taken as the final result.

[0047] 6. Yield: The total number of targets prepared in each group of tests is counted. The qualified standards are "density ≥ 97%, dimensional tolerance ≤ ±0.03 mm, bonding rate ≥ 99%, and sputtering uniformity error ≤ 3%". The ratio of qualified targets to the total number is calculated to obtain the yield. At least 10 samples are prepared for each group of tests to ensure that the statistical results are representative. 7. Resistivity: A four-probe tester was used, and the test was performed according to GB / T 1551-2023 "Test Method for Resistivity and Hall Coefficient of Semiconductor Single Crystals". Eight test points were evenly selected along the length of the target material, and the resistivity was measured at room temperature. The average value was taken as the final result. The test accuracy was ≤1×10⁻⁶. -4 Ω·cm.

[0048] 8. Bending strength: The three-point bending test was adopted and performed in accordance with GB / T 6569-2022 "Test Method for Bending Strength of Fine Ceramics". A standard sample (3mm×4mm×40mm in size) was prepared from the defect-free area in the middle of the target material, with a span of 30mm and a loading rate of 0.5mm / min. Each sample was tested 3 times and the average value was taken as the final bending strength.

[0049]

[0050] The elongated AZO targets prepared in Examples 1-3 of this invention exhibit superior performance indicators compared to Comparative Examples 1-3. Compared to Comparative Example 1, the target density of the embodiments of this invention is increased by more than 2%, dimensional tolerance is reduced, bonding rate is increased by more than 4%, sputtering uniformity error is reduced by more than 50%, yield is increased by more than 12%, resistivity is reduced by more than 45%, and bending strength is increased by more than 21%. This completely solves many defects of traditional splicing processes, resulting in a significant improvement in overall performance. Compared to Comparative Example 2, the embodiments of this invention achieve temperature gradient and grain size gradient control through gradient molds, reducing sputtering uniformity error by more than 40%, resistivity by more than 19.5%, and bending strength by more than 7%. Although the differences in density and bonding rate are not significant, the sputtering uniformity is significantly optimized, meeting the core requirements for sputtering of new energy vehicle glass. Compared with Comparative Example 3, the density of the present invention is increased by more than 3%, the dimensional tolerance is more accurate, the bonding rate is increased by more than 3%, the yield is increased by more than 8%, the resistivity is reduced by more than 32.7%, and the bending strength is increased by more than 13.9%. This shows that the optimized combination of SPS sintering parameters (vacuum degree, pressure, and holding time) and the gradient mold work together to achieve the optimal comprehensive performance of the target material.

[0051] In summary, the preparation process of this invention, through modular gradient mold design and SPS gradient sintering parameter optimization, achieves one-time sintering of elongated AZO targets, taking into account preparation efficiency, yield, and overall performance. It is suitable for the large-scale requirements of continuous sputtering production lines for new energy vehicle glass and has significant industrial application value.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0053] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A one-step SPS gradient sintering process for preparing elongated AZO targets, characterized in that, Includes the following steps: (1) Raw material pretreatment: The AZO powder is dried, ground, and sieved to obtain AZO raw material powder with uniform particle size; (2) Mold assembly: A modular gradient mold is adopted. The mold includes a high temperature zone, a transition zone and a low temperature zone. The wall thickness difference between the high temperature zone and the low temperature zone is 15-20mm. It is assembled and formed by modular splicing structure. The mold is suitable for forming long strip target materials with a length of 1000-3000mm. (3) Loading and sealing: The AZO raw material powder obtained in step (1) is evenly loaded into the gradient mold assembled in step (2), compacted, sealed and placed in the SPS sintering furnace to ensure good sealing inside the furnace; (4) SPS gradient sintering; (5) Cooling and demolding: After sintering, the SPS sintering furnace is slowly cooled down. After cooling to room temperature, the material is demolded to obtain a long strip of crude AZO target material. (6) Post-processing: The rough target material is polished, cleaned and inspected to remove surface impurities and defects, and the finished long strip AZO target material is obtained.

2. The preparation process according to claim 1, characterized in that, In step (1), the purity of the AZO powder is ≥99.9%, the drying temperature is 80-120℃, the drying time is 2-4h, and after grinding, it passes through a 200-300 mesh sieve. The particle size fluctuation of the raw material powder is ≤0.5μm.

3. The preparation process according to claim 1, characterized in that, In step (2), the modular gradient mold is made of graphite. The high temperature zone corresponds to the central area of ​​the target material, the low temperature zone corresponds to the two ends of the target material, the transition zone connects the high temperature zone and the low temperature zone, the wall thickness gradually changes from the high temperature zone to the low temperature zone, and the modular splicing is sealed with a sealing groove with a sealing accuracy of ≤0.01mm.

4. The preparation process according to claim 1, characterized in that, During SPS gradient sintering, the SPS sintering furnace is started and evacuated to a vacuum level ≤ 5 × 10⁻⁶. -3 Apply axial pressure of 30-40 MPa, control the temperature difference between the high-temperature zone and the low-temperature zone of the mold to be 50-80℃, heat to the sintering temperature and hold for 8-12 minutes to form a grain size gradient along the length of the target material, with a grain size range of 3-5 μm.

5. The preparation process according to claim 4, characterized in that, In step (4), the sintering temperature is controlled as follows: the sintering temperature in the high-temperature zone is 1100-1200℃, and the sintering temperature in the low-temperature zone gradually changes to 1050-1150℃ with the wall thickness. The heating rate is 50-80℃ / min, and the cooling rate is 30-50℃ / min, so as to avoid thermal stress cracks in the target material.

6. The preparation process according to claim 4, characterized in that, In step (4), the grain size gradient gradually changes from the center to both ends along the length of the target material. The grain size at the center is 4-5 μm, and the grain size at both ends is 3-4 μm. The grain size in the transition zone is continuously transitioned without abrupt changes.

7. A modular gradient mold for use in any of the preparation processes described in claims 1-6, characterized in that, It includes several splicing modules, which are combined to form a molding cavity adapted to a long strip target material. The mold is divided into a high-temperature zone, a transition zone, and a low-temperature zone. The wall thickness of the high-temperature zone is greater than that of the low-temperature zone, with a wall thickness difference of 15-20mm. The wall thickness of the transition zone changes linearly. The splicing modules are connected by positioning pins and sealing grooves, with a positioning accuracy of ≤0.005mm. A high-temperature resistant sealing gasket is set in the sealing groove.

8. The modular gradient mold according to claim 7, characterized in that, The forming cavity of the mold has a rectangular cross-section, which is suitable for forming long strip AZO targets. The length of the mold can be adjusted by increasing or decreasing the number of splicing modules, and it is suitable for preparing targets of different lengths from 1000 to 3000 mm.

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