MOSFET Threshold Voltage Calculator

Threshold Voltage in MOSFETs

The threshold voltage $V_T$ is the minimum gate voltage needed to form a conductive channel between source and drain. It depends on oxide capacitance, substrate doping, and surface potential.

Zero-Bias Threshold

$$V_{T0} = \frac{\sqrt{2\varepsilon_{\text{Si}}\, q\, N_A\, (2\phi_F)}}{C_0} - 2\phi_F$$

$\varepsilon_{\text{Si}}$ is silicon permittivity, $q$ is elementary charge, $N_A$ is acceptor doping concentration, $C_0$ is oxide capacitance per unit area, and $\phi_F$ is the surface potential for inversion.

Body Effect

When source and body are at different potentials:

$$V_T = V_{T0} + \gamma\left(\sqrt{2\phi_F + V_{sb}} - \sqrt{2\phi_F}\right)$$

where the body effect coefficient is:

$$\gamma = \frac{\sqrt{2\varepsilon_{\text{Si}}\, q\, N_A}}{C_0}$$

Related tools: MOSFET Calculator and Op-Amp Gain Calculator.

Frequently Asked Questions

What is a typical threshold voltage?

Enhancement-mode n-channel MOSFETs in 5 V logic often have VT between 0.7 V and 1.0 V, though exact values vary with process technology.

What is the body effect?

When the source is not tied to the substrate, a back-gate bias raises the threshold voltage. This is called the body effect and matters in analog switches and cascode circuits.

What units should I use for doping?

Enter substrate doping in cm⁻³ and oxide capacitance in F/cm². The calculator uses SI-compatible semiconductor constants internally.

What is surface potential?

Surface potential φF relates to the energy difference between bulk and surface at inversion. Typical values range from 0.2 V to 0.4 V for silicon.

Does higher doping increase VT?

Yes. Higher acceptor concentration makes inversion harder to achieve, which generally increases the threshold voltage.

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MOSFET Threshold Voltage Calculator

Threshold Voltage in MOSFETs

Zero-Bias Threshold

Body Effect

Frequently Asked Questions

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