MOSFET Threshold Voltage Calculator
Calculate the threshold voltage of a MOSFET using oxide capacitance, doping concentration, and surface potential. Free online semiconductor calculator with body-effect charts and detailed parameter breakdowns.
About This Calculator
The MOSFET Threshold Voltage Calculator computes the minimum gate voltage required to create a conducting channel in a metal-oxide-semiconductor field-effect transistor. This parameter is fundamental to understanding and designing CMOS integrated circuits, power electronics, and semiconductor devices. Students, engineers, and researchers in microelectronics and VLSI design use this calculator to analyze how fabrication parameters affect device behavior.
The zero-bias threshold voltage is calculated using the formula VT0 = √(2·εSi·q·NA·2φF) / C0 − 2φF, where εSi is the silicon permittivity (11.68 × ε0), q is the elementary charge, NA is the substrate doping concentration, φF is the surface potential, and C0 is the gate oxide capacitance per unit area. The body effect is modeled by VT = VT0 + γ(√(2φF + Vsb) − √(2φF)), where γ = √(2·εSi·q·NA) / C0 is the body-effect coefficient and Vsb is the source-body voltage.
The calculator supports all common MOSFET configurations including enhancement-mode and depletion-mode n-channel and p-channel devices. The interactive body-effect chart visualizes how the threshold voltage shifts as the source-body voltage increases, helping engineers understand the trade-offs in analog and mixed-signal circuit design.
Regional Notes
The threshold voltage is a material and fabrication parameter that does not depend on currency or regional standards. The calculator uses SI units and semiconductor physics constants that are universal across all regions (India, United States, United Kingdom, and worldwide).
Frequently Asked Questions
What is the threshold voltage of a MOSFET?
The threshold voltage (VT) of a MOSFET is the minimum gate-to-source voltage required to create a conducting channel between the source and drain terminals. Below this voltage, the MOSFET remains in cut-off mode with negligible current flow.
How is MOSFET threshold voltage calculated?
The zero-bias threshold voltage VT0 is calculated using VT0 = √(2·ε_Si·q·N_A·2φ_F) / C₀ − 2φ_F, where ε_Si is the permittivity of silicon, q is the elementary charge, N_A is the substrate doping concentration, φ_F is the surface potential, and C₀ is the oxide capacitance per unit area.
What is the body effect in a MOSFET?
The body effect describes how the threshold voltage increases when a voltage is applied between the source and the substrate (body). The threshold voltage with body effect is VT = VT0 + γ(√(2φ_F + V_sb) − √(2φ_F)), where γ is the body-effect coefficient and V_sb is the source-body voltage.
What is a typical threshold voltage for an n-type MOSFET?
Typical threshold voltage values for enhancement-mode n-type MOSFETs range from 0.7 V to 1 V for 5 V logic devices. Depletion-mode MOSFETs can have negative threshold voltages. The exact value depends on fabrication parameters such as oxide thickness, doping concentration, and gate material.
What is the difference between VT0 and VT?
VT0 is the zero-bias threshold voltage measured with the source and body at the same potential. VT includes the body-effect correction when a source-body voltage V_sb is present. When V_sb = 0, VT equals VT0. As V_sb increases, VT rises above VT0 due to the body effect.
What is the body-effect coefficient gamma?
The body-effect coefficient γ = √(2·ε_Si·q·N_A) / C₀ determines how strongly the threshold voltage shifts with source-body voltage. It depends on the doping concentration and oxide capacitance. Higher doping or thinner oxide reduces the body effect.
How does oxide capacitance affect threshold voltage?
A higher oxide capacitance per unit area (C₀) reduces the threshold voltage magnitude. Thinner gate oxides increase C₀, which is why advanced CMOS technologies with sub-2nm oxides have lower threshold voltages. This relationship is critical for low-power semiconductor design.
What is surface potential and why does it matter?
Surface potential (φ_F) is the potential difference between the semiconductor surface and the bulk. For inversion to occur, the surface potential must reach approximately 2φ_F. It is given by φ_F = (kT/q)·ln(N_A/n_i), where k is Boltzmann's constant, T is temperature, and n_i is the intrinsic carrier concentration of silicon.