Indium tin oxide (ITO) is an important raw material for the preparation of ITO conductive glass. Transparent ITO conductive film can be formed on glass by sputtering ITO target. Its performance is the key factor to determine the quality, production efficiency and yield of conductive glass. The composition, phase structure and density are the important indexes of ITO target performance. The composition of ITO sputtering target is In2O3 + SnO2, and the component ratio of indium oxide to tin oxide is usually 90:10 (mass ratio). In the production process of ITO target, the chemical oxygen content and impurity content must be strictly controlled to ensure the purity of the target.
ITO target preparation process
Forming technology of ITO target
The results show that the green billets with uniform composition and high density play an important role in the densification and resistivity of the target after low temperature thermal debinding and sintering. At present, the commonly used methods in target forming are cold isostatic pressing, grouting formation, explosive compaction, gel casting and so on.
Sintering process of ITO target
After forming process, the ITO blank is only semi-finished product, which needs further sintering to obtain ITO target.
The sintering technology of ITO target mainly includes the following: atmospheric pressure sintering, hot pressing, hip, microwave sintering, spark plasma sintering, etc.
Also known as atmosphere sintering method, it refers to the method of producing high density target material by pre pressing and sintering under certain atmosphere and temperature. Due to the strict control of atmosphere and temperature, the grain growth is avoided and the uniformity of grain distribution is improved.
Characteristic:This method has the advantages of low production cost, high target density and large size target preparation. However, the atmospheric pressure sintering process is usually sintered by adding sintering additives, which are difficult to remove completely, and the target is easy to fracture in the sintering process. Therefore, this method puts forward higher technical requirements for its production process. Japanese enterprises take the mature atmospheric pressure sintering method as the main technology, and the target materials produced have high performance.
Hot isostatic pressing (HIP)
The principle is that the powder material is put into the container with high temperature and high pressure in the atmosphere of high pressure argon, and the powder forms a target with very high density under the action of uniform pressure.
Characteristic:The hot isostatic pressing (hip) method has the advantages of high sintering density (almost close to the theoretical sintering density of 7.15g/cm3), the required mould is not easy to be reduced, the required sintering temperature is low, and the large-scale target can be made. However, the equipment required by this method is expensive, the production efficiency is low and the cost is high.
Hot pressing method
Usually, ITO powder material is filled into the mold, uniaxial compression, and blowholes are discharged in the temperature range of 1000 ~ 1600 ℃ to improve the sintering density of the green body.
Characteristic: Hot pressing usually needs heating and pressing at the same time, so the energy applied to the powder material is relatively large, which obviously shortens the sintering time. The forming pressure of hot pressing is small. At the same time, the loss of hot pressing die is large, which is mostly used in low-end market.
The principle is that microwave energy is applied to the powder material, and the material absorbs electromagnetic energy and generates heat by coupling vibration to heat the material for sintering.
Characteristic: The difference between microwave sintering method and traditional method is that the heat is generated by internal heating elements, and then transferred to the sample by radiation, rather than the external energy directly acting on the powder material. This method has the advantages of low activation energy level, high sintering rate, low sintering temperature and strong dispersion. At the same time, it is dangerous to sinter the target in pure oxygen atmosphere.
Spark plasma sintering
The principle is to apply a certain intensity of pulse current to the powder, which makes the powder discharge between particles and produce plasma, so the powder material is heated and sintered.
Characteristic: High density materials can be prepared by spark plasma sintering in a short time, which has the characteristics of low temperature and high efficiency. Because the sintering temperature has a great influence on the method, when the temperature is higher than 1000 ℃, the densification process is hindered due to the violent decomposition of In2O3; moreover, the targets prepared at different temperatures have partial oxygen loss.