Equivalent oxide thickness


An equivalent oxide thickness is a distance, usually given in nanometers, which indicates how thick a silicon oxide film would need to be to produce the same effect as the high-κ material being used.
The term is often used when describing field effect transistors, which rely on an electrically insulating pad of material between a gate and a doped semiconducting region. Device performance has typically been improved by reducing the thickness of a silicon oxide insulating pad. As the thickness of the insulating pad approached 5–10 nm, current leakage became a problem and alternate materials were necessary to increase the equivalent oxide thickness while retaining the switching speed. Materials having larger dielectric constants enable thinner films to be used for this purpose while retaining fast transistor switching. For example, a high-κ material with dielectric constant of 39 has an equivalent oxide thickness ten times that of a similar film of silicon oxide, helping to reduce the leakage of electrons across the dielectric pad, while achieving the same capacitance and high performance. Commonly used high-κ gate dielectrics include hafnium oxide and more recently aluminum oxide for gate-all-around devices.
The EOT definition is useful to quickly compare different dielectric materials to the industry standard silicon oxide dielectric, as: