ito film            PVD Coating February 24            ITO is a kind of N-type oxide semiconductor-indium tin oxide. ITO thin films, i.e. transparent conductive indium tin oxide semiconductor films, usually have two performance indicators: resistivity and transmittance.            Development            The real research work on ITO thin films was at the end of the 19th century, when very thin metal films were obtained on photoconductive materials. The research on transparent conductive materials should be applied to deicing window glass of aircraft during World War II. In 1950, In2O3, the second transparent semiconductor oxide, was first prepared. Especially after tin was doped in In2O3, this material has been widely used in transparent conductive films and has broad application prospects.            Basic performance            First, the basic properties of ITO thin films ITO (In2O3:SnO 2=9:1) micro-structure, Sn element can replace the in element in In2O3 lattice and exist in the form of SnO 2, because the in element in In2O3 is trivalent, when SnO 2 is formed, it will contribute an electron to the conductive band, at the same time, oxygen holes will be generated under a certain oxygen-deficient state, forming carrier concentration of 1020-1021 cm-3 and 10-21 cm-3. Mobility to 30 cm2/vs.            This mechanism provides low film resistivity in the order of 10-4_.cm, so ITO thin films have semiconductor conductivity. ITO is a wide band thin film material with a bandgap of 3.5-4.3ev. The threshold of excitation and absorption of forbidden band in the ultraviolet region is 3.75 ev, which is equivalent to 330 nm wavelength. Therefore, the optical penetration of ITO films in the ultraviolet region is very low. At the same time, the near infrared region reflects because of the carrier plasma vibration, so the transmittance of ITO thin films in the near infrared region is very low, but the transmittance of ITO thin films in the visible region is very good. Because of the specific physical and chemical properties of the material itself, ITO thin films have good conductivity and high transmittance in the visible region.            2. Several factors affecting the conductivity of ITO films are interrelated among the surface resistance (R), film thickness (d) and resistivity (p). The formula for calculating these three factors is R=p/d. It can be seen from the formula that in order to obtain ITO films with different surface resistance (R), it is actually necessary to obtain different film thickness and resistivity.            Generally speaking, it is easy to get different thickness of ITO film. The thickness of ITO film can be obtained by adjusting the deposition rate and time. The thickness and uniformity of ITO film can be controlled accurately by the corresponding process and means.            The resistivity (p) of ITO thin films is the key to the preparation of ITO thin films. Resistivity (p) is also an important index to measure the performance of ITO thin films. Formula p=m/ne2T gives several main factors affecting film resistivity (p). N and T represent carrier concentration and carrier mobility respectively. When N and T are larger, the resistivity (p) of the film is smaller, and vice versa. The carrier concentration (n) is related to the composition of ITO film materials, i.e. the tin content and oxygen content of ITO film itself. In order to obtain a higher carrier concentration (n), the tin content and oxygen content of ITO deposited materials can be adjusted; while the carrier mobility (T) is related to the crystalline state, crystal structure and defect density of ITO film, in order to obtain a higher carrier concentration (n). Higher carrier mobility (T) can reasonably adjust the deposition temperature, sputtering voltage and film forming conditions.            Therefore, the resistivity of ITO thin films is not only related to the composition of ITO thin films (including tin and oxygen content), but also to the process conditions (including substrate temperature and sputtering voltage) of ITO thin films. A large number of scientific and technological literatures and experiments have analyzed the relationship between the resistivity of ITO films and the Sn and O2 contents in ITO materials, as well as the substrate temperature during the preparation of ITO films.            3. Technology and Method of ITO Thin Films Prepared by Low Sputtering Voltage            1. ITO thin films prepared by low voltage sputtering contain oxygen element. In the process of magnetron sputtering, a large number of negative oxygen ions will be produced. Under the action of electric field, negative oxygen ions will bombard the surface of ITO thin films deposited with a certain particle energy, resulting in structural defects in the crystalline structure and crystal state of ITO thin films. The higher the sputtering voltage is, the greater the energy of oxygen anion bombarding the surface of the film is. The more likely this structural defect will be caused, and the more serious the crystal structural defect will be, which will lead to the increase of the resistivity of ITO films. Generally speaking, the sputtering voltage of magnetron sputtering deposition of ITO films is about - 400V. If a certain process is used, the sputtering voltage will be reduced to - 200V. Following, the resistivity of ITO films deposited will be reduced by more than 50%, which not only improves the quality of ITO films, but also reduces the cost of production.            2. Two effective ways to reduce the sputtering voltage of ITO thin films prepared by DC magnetron sputtering are the influence of magnetic field intensity on the sputtering voltage. When the magnetic field intensity is 300 G, the sputtering voltage is about - 350 v; but when the magnetic field intensity is increased to 1000 G, the sputtering voltage drops to - 250 v. Generally speaking, the higher the magnetic field intensity is, the lower the sputtering voltage is. But when the magnetic field intensity is more than 1000G, the influence of magnetic field intensity on the sputtering voltage is not obvious. Therefore, in order to reduce the sputtering voltage of ITO thin films, the magnetic field intensity of sputtering cathode can be reasonably enhanced. EFFECT OF RF+DC POWER ON SPUTTERING VOLTAGE FOR EFFECTIVE REDUCTION OF MAGNETRON SPUTTERING ELECTRICITY