Not to be confused with Oxide Thickness (t_OX).

Equivalent Oxide Thickness (EOT), represented by teq or tOX, is the gate oxide thickness of the SiO₂ layer of a transistor that would be required to achieve similar capacitance density as the high-κ material used.

A gate dielectric with a dielectric constant that is substantially higher than that of SiO₂ will initially have a much smaller equivalent electrical thickness. This key feature allowed for the industry to continue on with Moore's Law. As the semiconductor industry began to experiment with transitioning from a SiO₂ gate oxide to a high-κ material, EOT can be used to quickly compare those materials using existing SiO₂-based models.

Equation

One can treat MOSFET behavior like two parallel plate capacitors,

Where is the relative dielectric constant of SiO₂ in our case. Therefore one calculate the equivalent oxide thickness as,

Note that the dielectric constant SiO₂ is 3.9

Where toxe is the equivalent oxide thickness, εhigh-κ is the dielectric constant of the high-κ material used, and tox is the physical oxide layer thickness.

Example

For example, consider Hafnium Dioxide (HfO₂) which has an (subject to variations in temperature). A layer of just 6.15 nm in thickness Hafnium Dioxide (HfO₂) would result in an equivalent SiO₂ oxide thickness of around 37.83nm. . This is indeed the material used by Intel following their transition to high-κ at the 45 nm process node.