Indium Tin Oxide ( ITO ), is a transparent semiconductor which can be coated onto optical filter materials. ITO benefits over metal depositions because it is more transparent and less reflective, for a given impedance level. A good ITO coating will have optical transmission levels of greater than 75 %.
The ITO coating can be sputtered onto glass or plastic and has good chemical and mechanical durability. It will also not oxidize when exposed to air.
The oxygen content of the coating is adjusted to a compromise point, giving good optical transparency and low impedance, normally between 10 – 40 Ohms / square for shielding.
The shielding effect of thin film coatings is due to reflection of the electromagnetic wave. This means that the coatings are only effective when the wave impedance is greater than the coating impedance. This in turn means that the coatings have no effect in the magnetic, or H – Field, and are not suitable for all applications. There can also be some optical limitations to ITO coated windows and these should be fully discussed before selection is made.
Performance of an ITO window will depend on its impedance and the field impedance, but generally will produce between 80 and 120 dB attenuation in the E – Field, and around 20 dB for Plane waves.
