Equivalent oxide thickness

An Equivalent oxide thickness is a distance, usually given in nanometers (nm), which indicates how thick a silicon oxide film would need to be to produce the same effect as the high-k 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 approached 5-10 nm, leakage became a problem and alternate materials were necessary to increase the thickness while retaining the switching speed. Materials having larger dielectric constants enable thicker films to be used for this purpose while retaining fast reaction of the transistor. For example, a high-k material with dielectric constant of 39 (compared to 3.9 for silicon oxide) can be made ten times thicker than silicon oxide which helps to reduce the leakage of electrons across the dielectric pad, while achieving the same capacitance. Commonly used high-k gate dielectrics include hafnium oxide and more recently aluminum oxide for Gate-all-around devices.