http://www.cerac.com/pubs/proddata/ito.htm
ITO의 sheet resistance Rs 저항을 알면
Electric conductivity=1/(Rs*thickness of ITO)로 계산됨
ITO, TIN-DOPED INDIUM OXIDE
FOR OPTICAL COATING
Introduction
Indium oxide doped with tin oxide, ITO, is used to make transparent conductive coatings. Thin film layers can be deposited by electron-beam evaporation or sputtering. Roll or web coating on polymer substrates is done by magnetron or other techniques of sputtering.
Typical applications of ITO-coated substrates include touch panel contacts, electrodes for LCD and electrochromic displays, energy conserving architectural windows, defogging aircraft and automobile windows, heat-reflecting coatings to increase light bulb efficiency, gas sensors, antistatic window coatings, wear resistant layers on glass, etc.
--------------------------------------------------------------------------------
Film Properties
The optical and electronic properties of ITO films are highly dependent on the deposition parameters and the starting composition of evaporation material used. The deposited film layer must contain a high density of charge carriers for it to conduct. These carriers are free electron and oxygen vacancies, and an excessive population produces absorption. High conductivity (or low sheet resistance) is balanced against high transmission in the visible region. Sheet resistance can be less than 10 Ohms/sq. with a visible transmission of >80%. To obtain transmission near 90%, sheet resistance must be >100 Ohms/sq. ITO films behave as metals to long wavelength light because of the presence of a plasma wavelength above 1 ?m. At longer wavelengths, the film becomes reflecting, and the IR reflectance is related to the sheet resistance of the film; sheet resistance must be <30 Ohms/sq. to obtain IR reflectance >80%.
back to top
--------------------------------------------------------------------------------
Refractive Index
The refractive index for a film that is transparent in the visible region remains near 1.95 and is not strongly dependent on the deposition parameters. Index is generally of secondary concern for conducting applications. The extinction coefficient will vary with conductance.
back to top
--------------------------------------------------------------------------------
Material Behavior
The deposition parameters play interdependent roles in the optimization of film properties. Principal among the deposition parameters are partial pressure of oxygen, substrate temperature, rate of deposition and material composition. Some processes require post deposition baking at 300-500° C in air to oxidize residual fractionated metal component and improve conductivity. For sputter processes, a high energy plasma can be substituted for a high substrate temperature.
back to top
--------------------------------------------------------------------------------
Electron-Beam Deposition Parameters
Best results are obtained using reactive evaporation at a slow rate and relatively high pressure because the starting material is reduced (loses oxygen) during evaporation. Recommended preconditioning consists of slowly sweeping a low power electron beam to gradually and uniformly fuse the surfaces of the material and avoid hole drilling by the beam. Monitor the pressure and crucible to minimize outgassing and spitting while slowly increasing the power to just below evaporation temperature.
Evaporation Temperature ~600 ° C
Oxygen Partial Pressure Near 5 x 10-5 Torr. Range
Rate ~2 ?/sec.
Substrate Temperature Near 300° C.
Film thicknesses should be in the range 1000-2000 ? for high IR reflectivity, but there is little dependence of conductivity on thickness.
The specific geometry of the evaporation system can influence the results, so the parameters listed should be considered guidelines. Post baking in air might be required to adjust the transmission or to obtain minimum sheet resistance.
