Evaporation Materials Indium/Tin Oxide (ITO) Granule, ITO Tablets, Optical Coating Use ITO 99.99%

Evaporation Materials Indium/Tin Oxide (ITO) Granule, ITO Tablets, Optical Coating Use ITO 99.99%

90wt%In2O3+10wt%SnO2

Transparent conducting films (TCO) thin films, especially indium tin oxide (ITO) films, are widely used in solar cells, flat panel displays, gas sensors, thermal shielding, because of their high conductivity and high visible light transmittance, It has been widely used in optoelectronic devices such as indium tin oxide. ITO films can form antireflective coatings alone or with other materials.

At present, a variety of processes can be used to prepare ITO films, such as spray pyrolysis, sol-gel, chemical vapor deposition, vacuum evaporation, pulsed laser deposition, magnetron sputtering, etc. magnetron sputtering has been widely applied in industrial production for its excellent performance. With the continuous development of display technology, the demand for visible light transmittance is higher and higher. This has greatly promoted the study of visible light transmittance of ITO films. How to further improve the visible light transmittance of ITO films has become a hot research topic under the condition of ensuring high conductivity

Ito has high visible light transmittance (90%), low resistivity (10-4 ~ 10-3 Ω· cm), good wear resistance and stable chemical properties. Therefore, the proportion of Ito in TCO film is the highest.

In general, ITO is body centered cubic ferromanganese structure, which is based on the doping of In2O3 crystal structure. The in atom in In2O3 is six coordinated and the O atom is four coordinated. The intrinsic vacancy (oxygen vacancy) and Sn4 + substitution for in site contribute a lot of free electrons in the In2O3 crystal structure. Therefore, ITO is an n-type semiconductor with a carrier concentration of about 1021 / cm3, which is heavily doped.

The conductive mechanism of indium tin oxide mainly involves two factors: intrinsic defect and impurity defect. In the In2O3 lattice, the six top corners of the cube are occupied by oxygen atoms, leaving two oxygen vacancies, which makes the two oxygen ions near the vacancy and far from the vacancy not equivalent. In the reduction atmosphere, some oxygen ions in In2O3 generate oxygen (or combine with reducing agent to form other substances) to precipitate, leaving an oxygen vacancy, and the excess electrons form stoichiometric in3 + 2-x (in3 + · 2e) xo2-3-x in In2O3

In2O3→ In3+2-x(In3+·2e)xO2-3-x+ x/2 O2

When a certain proportion of tin is added into In2O3, the high valence tin ion (Sn4 +) occupies the indium (in3 +) site and generates an electron. Finally, the structure of in3 + 2-x (Sn4 + · E) xo3 is formed. The doping reaction formula is as follows:

In2O3+x Sn4+→In3+2-x(Sn4+·e)xO3+ x In3+

In ITO films deposited at low temperature, the electrons provided by oxygen vacancy play an important role in their good conductivity; in ITO films deposited at high temperature or annealed, electrons generated by substitution of Sn4 + for in3 + become the main source of carriers.

As a direct band gap semiconductor material, the band gap of ITO is generally in the range of 3.5 ~ 4.3 ev. The band gap of undoped In2O3 is 3.75 EV, and the effective mass of electrons in the conduction band is MC ≈ 0.35m0, where M0 is the mass of free electron. Due to the doping of Sn, n-type impurity level will be formed at the bottom of conduction band. With the increase of Sn, the Fermi level EF also moves upward. When it moves to the bottom of the conduction band, the carrier concentration is defined as the critical value NC. The value of NC can be obtained by mottv's criterion

nc1/3a0*≈0.25

Where A0 * is the effective Bohr radius, which is about 1.3nm, so the critical concentration is 7.1 × 1018 / cm3. The carrier concentration of ITO film is generally above 1021 / cm3, which is heavily doped and higher than the critical concentration. Due to the Burstein moss effect, the optical bandwidth of ITO films increases, and the actual absorption limit wavelength shifts blue. The increment of band gap can be expressed as follows:

ΔEgBM(n)= h/2{1/mc*+1/mv*}(3π2n)2/3

On the contrary, the electron wave functions of impurity atoms overlap, and the single impurity energy level expands to form the energy band, which is connected with the bottom of the conduction band to form a new degenerate conduction band, which results in the tail extending into the forbidden band and narrowing the band gap. In addition, there are some other factors, such as the multi-body effect, the decrease of exciton binding strength and the change of crystal self energy. But usually the Burstein moss effect is dominant.

The applications of Ito in various fields focus on its excellent properties of transparency and conductivity. The optical properties of ITO films are mainly affected by two factors: optical band gap width and plasma oscillation frequency. The former determines the spectral absorption range, and the latter determines the spectral reflection range and intensity. In general, ITO has high absorptivity in short wave region, high reflectivity in long wavelength range and highest transmittance in visible light range. Taking 100 nm ITO as an example, the average transmittance of 400-900 nm wavelength range is as high as 92.8%

The properties of ITO films are mainly determined by the preparation process, and heat treatment is often used as an auxiliary means of optimization. In order to obtain ITO films with good conductivity, high transmittance and smooth surface morphology, it is necessary to select appropriate deposition methods and optimize process parameters. The common coating methods include electron beam evaporation and magnetron sputtering.

The main principle of electron beam evaporation: in high vacuum environment, the high-energy electrons emitted by the electron gun bombard the surface of ITO target under the action of electric field and magnetic field, so that the kinetic energy is converted into heat energy. The target material is heated up and becomes molten or evaporated directly, and the ITO film is deposited on the substrate surface.

Magnetron sputtering belongs to the category of glow discharge. The film particles come from the cathode sputtering effect of argon ion on cathode ITO target in glow discharge. The target atoms are sputtered by argon ion and deposited on the surface of substrate to form ITO film.

The upstream industrial chain of ITO is the manufacturing technology of raw material targets, which aims to obtain uniform and high density green bodies. Improving the forming technology is the key step to improve the quality of ITO target products. ITO target forming technology is generally divided into dry method and wet method. In essence, dry forming is a die pressing forming method, which is easy to realize automatic production. Moreover, under the action of pressure, the batch has a high density, which usually does not need to be dried. The dry forming process of ITO target mainly includes cold isostatic pressing forming, stamping forming, die pressing forming and explosive forming. Wet forming is a process that uses solution, solid-liquid mixture, gas-liquid mixture and other raw materials to prepare target material. The wet process needs drying treatment, with large deformation and shrinkage, more pores and lower compactness. However, it can produce large size and complex shape targets. Through reasonable sintering process, ITO targets with high stability, high uniformity and high density can be obtained. The wet process of ITO target is mainly extrusion forming, gel casting and grouting forming.

The downstream industry of ITO is mainly the conductive glass technology in the flat panel display industry, that is, on the basis of sodium calcium based or silicon boron based glass substrate, a layer of indium tin oxide film is coated. In the flat panel display industry, it is used in the field of touch screen and LCD panel. Tp-ito conductive glass is applied in touch screen field, while lcd-ito conductive glass is applied in LCD panel field. The main difference between the two is that before ITO coating, lcd-ito conductive glass will be coated with a layer of silica barrier layer to prevent sodium ions from diffusing into the liquid crystal inside the cell.

Compared with other transparent conductive film materials, ITO has some disadvantages in many aspects. For example, ZnO film has the advantages of low cost, non-toxic and pollution-free. However, due to the relatively late start of the research on ZnO, the overall photoelectric performance is worse than that of ITO film, so the ITO film based on indium oxide is still the most widely used in industrial production.