As is known, the ITO sputtering target is a black-gray ceramic semiconductor formed by a series of production processes after indium oxide and tin oxide powder are mixed in a certain proportion, and then sintered in a high temperature atmosphere (1600 degrees, oxygen sintering). The ITO film was subjected to magnetron sputtering to oxidize the ITO target onto a glass substrate or a flexible organic film by using an ITO target as a raw material. The ITO film has electrical conductivity and light transmittance, and the thickness is generally 30 nm to 200 nm. At present, there are four main molding methods for ITO targets:
Spraying method uses high-pressure gas (N2, H2, mixed gas or air) to carry powder particles through a zoom tube to produce a supersonic two-phase flow, impacting the substrate in a completely solid state, and depositing on the surface of the bonded back plate by the good plasticity. The coating is thickened layer by layer to obtain a ceramic target.
Cold Isostatic Pressing (CIP)
The cold isostatic pressing method puts the pre-formed prime embryo into a rubber sheath and immerses it under a high-pressure liquid, so that it is subjected to pressure of the same nature in all directions, and the density of the prime embryo is enhanced. Cold isostatic pressing is only to obtain the prime embryo with the highest density, so that the sintering densification of the prime embryo is easier. Since the cold isostatic pressing does not have the sintering ability of hot isostatic pressing, the independent sintering process is required to burn the prime embryo.
Cold isostatic pressing can produce large-sized targets, making itself the most preferred molding method by most companies at present. Various molding studies have shown that cold isostatic pressing can produce high quality prime embryos that meet the requirements of ceramic targets. However, limited by the size of the chamber, when cold isostatic pressing produces super-sized embryos, the equipment investment is very expensive, and there is a deformation problem when the prime embryo is thin and the size is large. At the same time, while producing different sizes of prime embryos, it is necessary to prepare pre-pressing molds of different specifications, and the mold cost is high.
Hot Isostatic Pressing(HIP)
The hot isostatic pressing method removes the air inside the sleeve before puts the powder or the pre-compressed plain embryo into the wrap, and then welds and seals them in a vacuum environment. It is then put into a high-pressure container, making the powder at high temperature and equal pressure in all directions, to sinter. Molding and sintering are carried out simultaneously.
In the development of ITO targets, the early use of hot isostatic pressing technology made it difficult to obtain materials of high-density and large-size. The target prepared by the hot isostatic pressing method is small in size, low in density, high in oxygen loss rate, and the equipment required for the method is expensive and high in cost. These shortcomings make the hot isostatic pressing method no longer have a competitive advantage in the preparation of ITO ceramic targets, and its subsequent research and industrialization are gradually ignored by the industry. But it is still suitable for ceramic targets that require oxygen-free vacuum preparation.
Wet Molding Method
In the wet molding method, the oxide powder is prepared into a slurry, and then a specific shape of the prime embryo is realized by self-solidification, stream water or pressure. After drying, a high density of prime embryos is obtained. Wet molding method can not only realizes the function of cold isostatic pressing, but also compensates for the shortcomings of cold isostatic pressing. The wet forming of ceramic targets includes grouting, colloidal molding and direct solidification.