1、 Basic properties of ITO thin film
The microstructure of ITO (In2O3: SnO2=9:1) shows that after doping Sn into In2O3, Sn can replace In in the In2O3 lattice and exist in the form of SnO2. This is because In in In2O3 is trivalent, which contributes one electron to the conduction band when forming SnO2. At the same time, oxygen holes are generated in a certain oxygen deficient state, resulting in a carrier concentration of 1020 to 1021cm-3 and a mobility of 10 to 30cm2/vs. This mechanism provides low film resistivity on the order of 10-4 Ω· cm, so ITO films have semiconductor conductivity. ITO is a wide bandgap thin film material with a bandgap of 3.5-4.3 eV.
The excitation absorption threshold for the bandgap generated in the ultraviolet region is 3.75eV, which is equivalent to a wavelength of 330nm. Therefore, the light transmittance of ITO thin films in the ultraviolet region is extremely low. At the same time, reflection occurs in the near-infrared region due to the plasma vibration phenomenon of charge carriers, so the light transmittance of ITO film in the near-infrared region is also very low. However, the transmittance of ITO film in the visible region is very good. Due to the specific physical and chemical properties of the material itself, ITO film has good conductivity and high light transmittance in the visible region.
2、 Several factors affecting the conductivity of ITO thin films
The surface resistance (R), film thickness (d), and resistivity (ρ) of ITO thin films are interrelated, and the calculation formula for these three is: R=ρ/d。 From the formula, it can be seen that in order to obtain ITO thin films with different surface resistances (R), it is actually necessary to obtain different film thicknesses and resistivity.
Generally speaking, it is relatively easy to obtain different film thicknesses when preparing ITO thin films. The desired film thickness can be obtained by adjusting the deposition rate and time during film deposition, and precise film thickness and uniformity control can be achieved through corresponding process methods and means.
The magnitude of the resistivity (ρ) of ITO film is the key to the preparation process of ITO film, and resistivity (ρ) is also an important indicator for measuring the performance of ITO film. The formula ρ=m/ne2T provides several main factors that affect the resistivity (ρ) of thin films, where n and T represent carrier concentration and carrier mobility, respectively. As n and T increase, the resistivity (ρ) of the film decreases, and vice versa. The carrier concentration (n) is related to the composition of the ITO film material, that is, the tin content and oxygen content that make up the ITO film itself. In order to obtain a higher carrier concentration (n), it can be achieved by adjusting the tin content and oxygen content of the ITO deposition material; The carrier mobility (T) is related to the crystalline state, crystal structure, and defect density of the ITO film. In order to obtain a higher carrier mobility (T), factors such as deposition temperature, sputtering voltage, and film formation conditions during film deposition can be reasonably adjusted.
So from the perspective of the preparation process of ITO film, the resistivity of ITO film is not only related to the composition of ITO film material (including tin content and oxygen content), but also to the process conditions during the preparation of ITO film (including substrate temperature during deposition, sputtering voltage, etc.). There is a large amount of scientific literature and experimental analysis on the relationship between the resistivity of ITO films and the content of Sn and O2 elements in ITO materials, as well as the substrate temperature and other process conditions during ITO film preparation.
Conductive principle of ITO conductive film
ITO conductive film is an indium tin oxide film, mainly composed of 90% In2O3 and 10% SnO2. Its crystal structure is cubic iron manganese ore structure, which is a semiconductor material with a wide bandgap that can directly transition. The main component of ITO conductive film, In2O3, does not form an ideal chemical ratio structure during the formation process. The crystal structure lacks oxygen atoms, resulting in excess free electrons. Therefore, ITO film has a certain degree of conductivity.
How to improve the conductivity of ITO conductive film
If you want to improve the conductivity of ITO film, you can use high priced cations such as Sn doped in the In2O3 lattice to replace the position of In ^ 3. This will increase the concentration of free conductive electrons, thereby enhancing the conductivity of indium oxide and improving the conductivity of ITO film. It should be noted that in the ITO film layer, Sn usually exists in the form of Sn ^ 2 or Sn ^ 4. Since In is trivalent in In2O3, the presence of Sn ^ 4 creates an electron conduction band, while the presence of Sn ^ 2 reduces the electron density in the conduction band.
en 
