MOSFET SiO₂ Oxide Thickness Calculator
Compute the equivalent SiO₂ gate oxide thickness from capacitance per unit area using εox = 3.9·ε0.
Description
Calculate equivalent SiO₂ gate oxide thickness in nanometers from oxide capacitance per unit area in fF/µm².
Gate oxide capacitance per area can be converted to an equivalent silicon-dioxide thickness with the ideal parallel-plate relation. The result is physical thickness only when the dielectric is SiO₂ with relative permittivity 3.9; for another dielectric it is an SiO₂-equivalent value.
When to use MOSFET SiO₂ Oxide Thickness Calculator
- Infer ideal SiO₂ thickness from measured or specified Cox
- Convert between common fF/µm² and nanometer process-design units
- Cross-check the inverse gate-oxide capacitance calculation
How the calculation works
The calculation rearranges Cox = εox/tox and uses εox = 3.9·ε0. The conversion 1 fF/µm² = 10⁻⁷ F/cm² is applied before solving for thickness.1
tox = εox / Cox, where εox = 3.9·ε0 Interpreting the result
Higher capacitance per area corresponds to a thinner equivalent oxide. Interface traps, depletion, and quantum capacitance can make an electrical extraction differ from physical thickness.
Assumptions and limitations
- The ideal parallel-plate model assumes a uniform dielectric and ignores fringing and parasitic capacitance.
- For high-k stacks, the output is equivalent oxide thickness unless the permittivity is changed outside this tool.
- Use oxide capacitance per area, not the total capacitance of a finite gate.
References
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EE105 Lecture 7: MOSFET — University of California, Berkeley