Effect of sintering temperature and time on composition, densification and electrical properties of InGaZnO4 ceramics

Effect of sintering temperature and time on composition, densification and electrical properties of InGaZnO4 ceramics

Materials Science in Semiconductor Processing 105 (2020) 104737 Contents lists available at ScienceDirect Materials Science in Semiconductor Process...

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Materials Science in Semiconductor Processing 105 (2020) 104737

Contents lists available at ScienceDirect

Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp

Effect of sintering temperature and time on composition, densification and electrical properties of InGaZnO4 ceramics

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Jiang-An Liu, Chen-Hui Li∗, Yang Zou, Jing-Jing Shan, Ru-Feng Gui, Yu-Sheng Shi State Key Laboratory of Material Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: InGaZnO4 Sintering Electrical properties Sputtering target

This paper studied the influence of sintering temperature on composition, density and electrical properties of InGaZnO4 ceramics synthesized by conventional solid-state reaction technique. Firstly, IGZO powders were prepared by mechanical ball milling of micron-scale In2O3, Ga2O3 and ZnO mixed powder and the effects of milling time, ball to powder weight ratio (BPR) and dispersant on the properties of mixed powders were investigated by XRD, SEM and laser diffraction particle size analyzer. Secondly, the green compacts formed by mixed powders were sintered at different temperatures (1100, 1200, 1300, 1400 °C) and time (0, 1, 3, 6 h), then the sintering behavior and electrical properties of the compacts were analyzed. The results showed that when the BPR was 10:1 and 2 wt % polyammonium acrylate was used as dispersant, the powder owed the best compression performance and the relative density of the green compact reached 67.14%. Owing to the decomposition of In2O3, obvious loss of mass phenomenon occurred during sintering process. When the compact was hold at 1400 °C for 150 min, the density of compact reached as high as 99.5%. The lowest resistivity of the compact reached 6.07 × 10−3 Ω cm when the compact was kept at 1400 °C for 3 h.

1. Introduction Transparent and conductive oxide film made of indium–gallium–zinc-oxide (IGZO) film have attracted more and more attention for their superior electron mobility, optical transparency and environmental/thermal stability compared to those of amorphous silicon thin films in the past years [1–10]. IGZO thin film are normally manufactured through magnetron sputtering process [2,11,12] and the composition purity and bulk density of the IGZO target have an important influence on the quality of obtained film. In practice, since the composition purity are determined by the raw material, the key point to the success manufacturing of high quality IGZO film is to obtain the IGZO target with high bulk density. Actually, a higher bulk density of the target not only contribute to a higher sputtering erosion resistance [13], but also can prevent the ion-eroded target surface being degraded by the conical protrusions [14]. In recent years, some studies have been devoted to a study of the preparation of high-density InGaZnO4 target. Lo [15] prepared the aqueous suspension containing nano-scale In2O3–Ga2O3–ZnO powder mixture via a hybrid process of chemical dispersion and mechanical grinding. After drying, pressing and sintering, they obtained the InGaZnO4 target with the relative density of 93%. Wu [16] ball milled the



IGZO ceramic slurry with a solid content of 25 vol %, then the slurry was spray-dried to prepare the IGZO powders. They prepared InGaZnO4 ceramic with the relative density of 99% by sintering the green compact at 1400 °C. Wu [17] and Liu [18] synthesized the nano-scale IGZO precipitate by multistep precipitation method, then they spraydried the obtained precipitate and calcined the precursor powders. After sintering process, they obtained the InGaZnO4 target with the relative density of 97.3% and 99.3% respectively. In those studies, it is apparent that the precipitation method and spray-drying process meant sophisticated equipment and low productivity, which greatly limit the application of IGZO ceramic. At the same time, since nano-scale powders show poor pressing performance, the relative density of pressed compact is inevitably small, which lead to the shown up of high shrinkage, warpage and even crack during the sintering process. New methods which can improve the bulk density of IGZO target more effectively are still needed. On the other hand, the previous studies [19–22] have demonstrated that the ZnO-based and Ga2O3-based ceramics will volatilize when the sintering temperature is beyond 1200 °C. When the compacts were heated to about 1400 °C, the densities of the targets decreased and its mechanism has not been studied yet. Therefore, the influence of sintering temperature and time on the composition of InGaZnO4 target needs to be studied.

Corresponding author. E-mail address: [email protected] (C.-H. Li).

https://doi.org/10.1016/j.mssp.2019.104737 Received 10 July 2019; Received in revised form 29 August 2019; Accepted 12 September 2019 1369-8001/ © 2019 Published by Elsevier Ltd.

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time reached 9 h, the InGaZnO4 single phase could not be obtained after the powders were calcined at 1300 °C. When the BPR was 5:1, 7:1 or 10:1 and the milling time was 9 h, the powder was the InGaZnO4 single phase after calcination at 1300 °C, showing that the mixed powder dispersed more indistinctly with the increase of BPR. As the ratio of raw powders to grinding ball decreased with the increase of BPR, collision area and collision probability between powders and the grinding balls increased. Thus, the coarse particles in raw powder were fully grinded, which made the particle size distribution of mixed powders more uniform and reduced uneven distribution of elements in the subsequent sintering process. As a result, sintered powders with single phase structure could be obtained. The comparison of sample 6 and sample 9 showed that the mixed powders were dispersed better and the reaction went on more complete with the help of ammonium polyacrylate, when the BPR was 10:1 and the ball milling time was 6 h, the InGaZnO4 single phase could be obtained after calcination. At the same time, the particle size of the powder gradually decreased with the increase of the BPR and milling time. However, the D50 of sample 11 showed that when the milling time reached 12 h, the particle size was larger than that of sample 10, which might be attributed to the reason that the excessive energy leaded to agglomeration of particles with the increase of milling time. Fig. 1 showed the microstructure and size distribution of the sample 4, 5, 7, 9, 10 and 11. Fig. 1a and b showed that there were still coarse particles (> 20 μm) in the sample 4 and 5, the size distribution in Fig. 1a and b confirmed the results. Fig. 1c and d indicated that with the BPR increased to 7:1 and 10:1, the particle sizes of the milled powders were further reduced to sub-micron level. The SEM images of Fig. 1e and f showed the coarse particles of the mixed powders nearly disappeared and the size become more uniform in sample 10 and 11, which corresponding to the particle size distribution curves shown in Fig. 1e and f. The SEM images of Fig. 1f showed that the agglomeration of the powder becomes obvious, which coincided with the phenomenon that the particle size increased with the milling time increased to 12 h in Table 1. Table 2 showed the relative density of green compacts formed by cold isostatic pressing at 280 MPa. The results showed that from sample 4 to sample 11, the density of the green compacts increased with the particle size decreasing. When the particle size was submicronlevel (sample 5, 7, 9, 10 and 11), the relative density of the green compacts were 62.04%, 64.85%, 64.58% 67.74% and 65.43%, which was far higher than that of the green compact by using nanometer powders as raw materials [16,18]. This reason could be explained by the grain composition and close packing theory illustrated in Fig. 2. Because the sub-micron grade particles have a wider particle size distribution range, the fine particle could be enriched in the space of coarse particles to improve the compaction density of the compacts; while the particle size distribution of the nanoparticles was more concentrated and the stacking pores between the particles were not easy to be eliminated, thus the density of the green densities of the above samples were higher than that of green compacts prepared by

In the present paper, the IGZO powders were prepared with using the In2O3, Ga2O3 and ZnO micro-particles as the raw materials by different ball milling process. The high-density and low shrinkage rate InGaZnO4 ceramic targets were fabricated by pressureless sintering. The effect of sintering temperature and holding time on composition, density and electrical properties of InGaZnO4 ceramics were studied in detail. Furthermore, the best sintering process of high-density InGaZnO4 ceramic targets was proposed according to the above results. 2. Experimental section 2.1. Preparation of IGZO powders and targets Commercial available In2O3 (CG 99.999%), Ga2O3 (CG 99.999%) and ZnO (CG 99.999%, Wuhan Xintaige Material Co., LTD., Hubei, China) raw powders were mixed with the molar ratio In2O3: Ga2O3: ZnO = 1:1:2. The In2O3, Ga2O3, and ZnO powders were added into anhydrous ethanol with 2 wt % dispersant of polyacrylic acid ammonia mixed solution, and then the powder slurry was ball milled for different ball to powder ratio (BPR) (3:1, 5:1, 7:1, 10:1) and time (3, 6, 9 h). Then the obtained powder slurry was washed with anhydrous ethanol, followed by calcination at 600 °C for 2 h. The green compacts were formed by the Cold Isostatic Pressing at 280 MPa, and the obtained green compacts were sintered at 1100 °C, 1200 °C, 1300 °C and 1400 °C for 0, 1, 3, 6 h. 2.2. Characterization The phase composition of the sintered powders and compacts were analyzed by x-ray diffraction (Panalytical B.V., Holland) within the CuKa radiation (λ = 1.5418 Å). The element composition of the compacts was characterized by X-ray fluorescence diffraction (Idax Co., Ltd., America). The morphology of the compacts was analyzed by scanning electron microscopy (FEI 200, Holland Sirion) and Electron probe microanalyzer (EPMA-8050G, Shimadzu, Japan). The size distribution of the powder was analyzed by particle size analyzer (Mastersizer 2000, Dandong Baite Instrument Co., Ltd., China). Thermal behavior of the InGaZnO4 ceramic targets was analyzed by Thermogravimetry and differential scanning calorimetry (TG-DSC, STA449F3, Credit company, Germany). The sintering shrinkage of sintered compacts was measured by high temperature optical dilatometer. The density of InGaZnO4 target was measured based on the Archimedes' principle. The resistivities of the compacts were tested using the source-meter equipped with four-probe resistor (2000, Keithely Instruments Inc., Cleveland, OH) at room temperature. 3. Results and discussion 3.1. Characterization of milled powders and green compacts Table 1 showed that when the BPR was 3:1, even if the ball milling Table 1 The sintered powders of different ball milling process. Sample

BPR

Milling time (h)

Dispersant

1 2 3 4 5 6 7 8 9 10 11

3:1 3:1 3:1 5:1 7:1 7:1 10:1 10:1 10:1 10:1 10:1

3 6 9 9 9 6 9 3 6 9 12

Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous Anhydrous

ethanol ethanol ethanol ethanol ethanol ethanol ethanol ethanol ethanol ethanol ethanol

2

and and and and

Ammonium Ammonium Ammonium Ammonium

polyacrylate polyacrylate polyacrylate polyacrylate

D50 (μm)

calcination at 1300 °C

2.211 1.876 1.325 1.303 0.977 0.914 0.876 0.998 0.916 0.784 0.815

Heterozygous Heterozygous Heterozygous InGaZnO4 InGaZnO4 Heterozygous InGaZnO4 Heterozygous InGaZnO4 InGaZnO4 InGaZnO4

phase phase phase

phase phase

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Fig. 1. SEM images and the particle size distribution of different powder samples in Table 1: (a) sample 4, (b) sample 5, (c) sample 7, (d) sample 9, (e) sample 10, (f) sample 11.

at different temperatures and holding time. Fig. 3a showed the relative densities of compacts when sintered at 1100, 1200, 1300, 1400 °C for 0, 1, 3, 6 h respectively. The results showed that when the compacts were hold at 1100 °C and 1200 °C, the densities of the compacts increased slowly with the increase of sintering temperature and holding time, the maximum relative densities of the compacts reached 87.13% and 94.79% with the holding time increased to 6 h respectively. When the compacts were hold at 1300 °C and 1400 °C for 3 h, the relative densities of the compacts reached the maximum of 99.22% and 99.26% respectively, then the relative densities of the compacts slightly decreased to 98.85% and 97.25% with the holding time increased to 6 h. Fig. 3b showed the weight losses of the compacts when sintered at 1100, 1200, 1300, 1400 °C for 0, 1, 3, 6 h respectively. When the sintering temperature was 1100 °C, the weight loss of the compact was only 1.62% even the holding time reached 6 h. However, the mass

Table 2 The relative density of green compacts formed by different powder samples. Sample

Relative Density (%)

Sample

Relative Density (%)

4 5 7

61.57 62.04 64.85

9 10 11

64.58 67.14 65.43

nanometer powders. As the density of sample 10 was highest, the followed research chose sample 10 as the raw material of the green compact. 3.2. Sintering behavior and weight loss of InGaZnO4 compacts Fig. 3 showed the sintering behavior of the compacts when sintered 3

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Fig. 2. Schematic diagram of grain gradation for different powders: (a) submicron-level powders and (b) nanometer powders.

the sintering process, the crystal structure of InGaZnO4 compact had been destroyed when the compact was hold at 1400 °C for 6 h while the perfect crystal structure of InGaZnO4 compact could be maintained when the compact was hold at 1300 °C even the holding time reached 6 h. Previous studies [23–25] attributed the weight losses of ZnO-based ceramics to the evaporation of ZnO for low steam pressure of ZnO when the ceramics were sintered beyond 1400 °C. Fig. 4a indicated that the weight loss of ZnO powder was higher than that of In2O3, and Ga2O3 when the sintering temperature was beyond 1400 °C. The weight loss of ZnO, In2O3 and Ga2O3 powder were 6.8%, 3.9% and 4.6% respectively when sintered at 1450 °C. However, the XRD pattern of Fig. 4c indicated the yellow precipitate in Fig. 4b was mainly composed of In2O3 and part of ZnO. The results revealed that although the volatilization of In2O3, Ga2O3 and ZnO powders occurred simultaneously and the order

losses of the compacts increased to 2.70% and 3.52% when the compacts were hold 1300 °C and 1400 °C for 6 h respectively. Fig. 3c and d showed the X-ray diffraction patterns of compacts when sintered at 1300 °C and 1400 °C for 1, 3 and 6 h. The results indicated that the XRD pattern of the compact coincided with the standard spectral line of InGaZnO4 (JCPDS card No. 38–1104) even if the compact was hold at 1300 °C for 6 h, showing that the phases composition of the compacts were InGaZnO4 single phases. The intensity of the peaks increased with the holding time increased from 1 h to 6 h, showing that the crystallization of the compact was enhanced. However, the X - ray diffraction pattern of the compact appeared many impure peaks when the compact was hold at 1400 °C for 6 h, showing that the crystallization of the compact had been destroyed. This phenomenon might attribute to the excessive mass loss of the compact. The above results showed that the densification and mass loss of the compacts simultaneously occurred in

Fig. 3. Sintering behavior of the compacts when sintered at different temperatures and holding time (a) the relative densities of the compacts versus sintering temperatures and holding time, (b) the weight losses of the compact versus sintering temperatures and holding time, X-ray diffraction patterns of the compacts sintered at (c)1300 °C and (d) 1400 °C for different time. 4

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Fig. 4. (a) The TGA curves of the In2O3, Ga2O3 and ZnO powders used in this study, (b) the precipitate of the compact sample after sintering at 1400 °C, (c) X - ray diffraction pattern of the precipitate.

of volatilization rates were ZnO > Ga2O3 > In2O3 during the sintering process, the volatile was mainly composed of In2O3 and part of the ZnO. Fig. 5a–h showed the XRF patterns of the compacts when sintered at 1300 °C and 1400 °C for 0, 1, 3, 6 h; Fig. 5i–k showed mass fraction of elements for different holding time. The results showed that when the compacts were sintered at 1300 °C, the mass fraction of In element slowly decreased from 38.67% to 37.24%, while the mass fraction of Ga increased significantly from 33.46% to 39.92% and the mass fraction of Zn kept basically unchanged with the holding time increased from 0 h to 6 h. When the compacts were sintered at 1400 °C from 0 h to 6 h, the mass fraction of In in compacts decreased from 38.28% to 34.64%, while the mass fraction of Ga increased from 34.12% to 43.83% and the mass fraction of Zn slightly decreased from 38.28% to 34.64%. The results showed that the main cause of mass loss during sintering process was the volatilization of In element, the increased content of Ga element might be due to the loss of In element. Fig. 5a showed that the atomic content of In, Ga and Zn were 27.09%, 34.30% and 38.61% respectively when the compact was sintered at 1300 °C, indicating that the composition of the compact had deviated from the stoichiometric ratio of InGaZnO4. This reason could be explained by Fig. 6. Fig. 6 indicated that the main phase compositions of compact were In2O3, Ga2O3, and ZnO at 700 °C, showing that there was no chemical reaction in the compact at this time. When the sintering temperature reached 800 °C, the compact began to appear ZnGa2O4. The phases of the compacts were In2O3 and ZnGa2O4 when the sintering temperature was 900 °C and the phase of InGaZnO4 began to form at 1000 °C. When the sintering temperature reached 1100 °C, the phase of the whole compact was transformed into InGaZnO4 single phase. Therefore, it could be deduced that the reaction process of compacts could be expressed in the following equations:

Ga2 O3 + ZnO

ZnGa2 O4 + In2 O3 + ZnO

1100 °C → InGaZnO4

When the compacts were sintered, Ga2O3 reacted with ZnO to form ZnGa2O4 at about 800 °C, then the formed ZnGa2O4 reacted with In2O3 and the residual ZnO to form InGaZnO4 when the compacts were sintered at 1100 °C. The main phase compositions of the compacts were ZnGa2O4, In2O3 and ZnO when the compact was heated from 800 °C to 1100 °C. In previous studies, De Wit [26] and Nicolas [27] studied the sublimation of In2O3 and found the rapid vaporization of In2O3 when the temperature T > 1200 °C with a dissociative type as follows:

In2 O3 (gas ) → InO (gas ) + O2 (gas ) indicating that the mass loss of IGZO target during sintering process was mainly caused by volatilization of In2O3. 3.3. Optimal sintering process for InGaZnO4 ceramics Fig. 7a showed the in-situ measurement images of the compact when sintered at 1300 °C for 0 h, 10 min, 1 h and 3 h respectively; Fig. 7b showed the weight loss of the compacts when sintered at 1300 °C and 1400 °C from 0 h to 6 h. The sintering process of compacts could be regarded as equal volume shrinkage and the diameter of the compacts could be measured from the images (the measurement accuracy is 0.001 mm). The measurement method and the accuracy had been proved in our previous research [18,19]. Combining with mass loss data of the compacts sintered from 0 to 6 h in Fig. 7b, the density of the compact in any time during the sintering process could be obtained. In this experiment, both In-situ measurement and the weight loss data were recorded every 10 min. Fig. 7c showed the calculated densities of the compacts when sintered at 1300 °C and 1400 °C from 0 h to 6 h. It could be seen from the figure that the density of compact fluctuated irregularly with the increase of holding time. The highest densities of compacts were obtained at 1300 °C for 220 min and 1400 °C for

800 °C → ZnGa2 O4

5

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Fig. 5. XRF patterns of the compacts sintered at different time and temperature: 1300 °C for (a) 0 h, (b) 1 h, (c) 3 h, (d) 6 h; 1400 °C for (e) 0 h, (f) 1 h, (g) 3 h, (h) 6 h. The mass fraction of the relative content of elements sintered at (i) 1300 °C and (k) 1400 °C for 0, 1, 3, 6 h.

identical with the peak line of InGaZnO4, which showed that no phase transformation occurred in the compact at this time. Fig. 8c showed that the microstructure of the grains was lamellar in shape, the lamellae in the same grain were arranged in parallel while the parallel arrangement of the lamellae in adjacent grains was inconsistent. At the same time, the target was very compact and there were almost no pores. The EPMA mapping of the compact in Fig. 8d–f showed that the In and Ga elements of the compound were distributed uniformly, while there were some uneven spots on the surface for Zn element. It might be due to the evaporation of ZnO, the Zn content in diffusible channels decreased. As Zn element distribution was uniform on most of the areas, confirming that all the constituent elements were fully incorporated to give rise to the single phase of InGaZnO4.

3.4. Electrical properties Fig. 9 showed the resistivities of compacts when sintered at 1100 °C, 1200 °C, 1300 °C and 1400 °C for 0, 1, 3, 6 h. When the sintering temperature was 1100 °C, the resistivities of the compacts gradually decreased from 10.37 × 10−3 Ω cm to 9.74 × 10−3 Ω cm with the holding time increasing from 0 h to 6 h. When the compacts were hold at 1200 °C for 0 h and 1 h, the resistivities of the compacts were 9.85 × 10−3 Ω cm and 9.61 × 10−3 Ω cm respectively; however, when the holding time increased to 3 h and 6 h, the resistivities of the compacts sharply decreased to 7.22 × 10−3 Ω cm and 7.01 × 10−3 Ω cm.

Fig. 6. XRD pattern of compacts sintered from 700 °C to 1100 °C.

150 min, the maximum theoretical densities were 99.45% and 99.50% respectively. Fig. 8a showed the image of the compact when sintered at 1400 °C for 2.5 h. Fig. 8b showed that the XRD spectrum of the target was 6

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Fig. 7. (a) In-situ measurement images of the compacts when sintered at 1300 °C for (1) 0 h, (2)10 min, (3) 1 h and (4) 3 h, (b) weight loss and (c) calculated density of the compacts when hold at 1300 °C and 1400 °C for 6 h.

compact increased sharply to 7.55 × 10−3 Ω cm with the holding time increased to 6 h. Fig. 10 showed the fracture morphology of compacts sintered at 1100 °C, 1200 °C, 1300 °C and 1400 °C for 0, 1, 3, 6 h. Previous studies have shown that interconnected pores significantly increased the resistivity of ceramic target [21,28], the increase of density could not

When the compacts were sintered at 1300 °C from 0 h to 3 h, the resistivity of the compacts decreased from 7.13 × 10−3 Ω cm to 6.22 × 10−3 Ω cm, then the resistivity of the compact increased slightly to 6.36 × 10−3 Ω cm when the holding time was 6 h. When the compacts were sintered at 1400 °C for 3 h, the resistivities of the compacts reached the minimum of 6.07 × 10−3 Ω cm, then the resistivity of the

Fig. 8. The image of the compact sintered at 1400 °C for 150 min: (a) sintered pellet, (b) XRD pattern, (c) the SEM surface morphology (BSE model) and the EPMA mapping of (d) In, (e) Ga and (f) Zn element. 7

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the pores of the compacts changed from interconnected pore to isolated pore and the resistivity of compacts sharply decreased. When the sintering temperature was 1300 °C, the resistivity of the compact decreased slightly as the holding time increased from 1 h to 3 h. The resistivity of the compact slightly increased when the compact was sintered at 1300 °C for 6 h, and this phenomenon might be due to the increase of voids in the compact with the increase of element volatilization, the appearance of submicron pores in the grain of Fig. 10l could verify the purpose. It might ascribe the appearance of submicron pores to agglomeration of powders and inhomogeneous shrinkage of different area in the compact during sintering process. With the rapid growth of grains and grain boundaries, the voids were transferred into grains. In the heat preservation process, submicron pore remained in IGZO grain since N2 existed in the pore was had to be eliminated. When the compacts were sintered at 1400 °C, the resistivity reached the minimum with the holding time increased to 3 h, the reason could be explained by Figs. 10n and fig10o that the grain size of the compact increased significantly when the compact was hold for 3 h, the intergranular area in the compact decreased and the reflection effect of electrons decreased, thus the resistivity of the compact obviously decreased. When the time was added to 6 h, the crystal structure of the compact had been destroyed due to excessive element volatilization, resulting in a sharp increase in the electrical resistivity of the compact.

Fig. 9. Resistivities of compacts sintered at temperatures different and holding time.

obviously decrease the resistivities of ceramic targets after interconnected pores transformed into isolated ones. As could be seen from the picture, when the sintering temperature was 1100 °C, although the density of the compact increased from 70.17% to 87.13% with the holding time increased from 0 h to 6 h, the pores in the compact were mainly interconnected, so the resistivities of the compacts were high and the change of the resistivities was small. When the sintering temperature was 1200 °C and the holding time increased from 1 h to 3 h,

4. Conclusions In this study, the effect of sintering temperature and time on composition, densification and electrical properties of InGaZnO4 targets was investigated in detail, Sub-micron level IGZO powders with different

Fig. 10. Macro-morphology of the compacts sintered at different time and temperature: 1100 °C for (a) 0 h, (b) 1 h, (c) 3 h, (d) 6 h; 1200 °C for (e) 0 h, (f) 1 h, (g) 3 h, (h) 6 h; 1300 °C for (i) 0 h, (j) 1 h, (k) 3 h, (l) 6 h; 1400 °C for (m) 0 h, (n) 1 h, (o) 3 h, (p) 6 h. 8

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BPR and time by ball milling method were prepared. The powders were compacted and subsequently sintered at 1100, 1200 1300 and 1400 °C for 0, 1, 3, 6 h respectively. The results showed that the density of green compact reached as high as 67.14%. The reaction process of the compact in sintering process was that Ga2O3 reacted with ZnO to form ZnGa2O4 at about 800 °C and then ZnGa2O4 reacted with In2O3 and residual ZnO to form InGaZnO4 at 1100 °C. Thermodynamic analysis showed that although ZnO powder had a stronger volatilization than In2O3, the volatile of compacts was mainly In2O3 rather than ZnO. When the compact was sintered at 1400 °C for 150 min, the relative density of the target reached the maximum of 99.50%. After the compact was sintered at 1200 °C for 3 h, the pores in compact changed from interconnected pores to isolated pores, which greatly reduced the resistivity of the compact. When the compact was sintered at 1400 °C for 3 h, the resistivity of the compact reached the minimum of 6.07 × 10−3 Ω cm.

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Acknowledgments

[16]

Thanks for the fund support of the National Natural Science Foundation of China (Grant no. 51372093), China Postdoctoral Science Foundation funded project (2019M652635), the Special Funding for Postdoctoral Scientific Research of Hubei Province (0106110094) and the test support of the Analysis and Testing Center of Huazhong University of Science and Technology.

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