The mosfet threshold voltage calculator works out body effect constant (γ), threshold voltage (vt0) and surface potential (ϕf) from aq, are, capacitance of the insulator (c₀), charge (q), d1, doping of the substrate (na), relative permittivity (ɛr), fara, intrinsic concentration (ni), leng, temperature (t) and source-body voltage (vsb). Enter what you have and the relationship is applied straight away, so you get the answer without working through the algebra yourself.
What Is the MOSFET Threshold Voltage Calculator?
This mosfet threshold voltage calculator is for the kind of problem where you know the physical quantities but not the number you need. It turns aq, are, capacitance of the insulator (c₀), charge (q), d1, doping of the substrate (na), relative permittivity (ɛr), fara, intrinsic concentration (ni), leng, temperature (t) and source-body voltage (vsb) into body effect constant (γ), threshold voltage (vt0) and surface potential (ϕf).
Physics calculations go wrong in predictable ways, usually through mixing units or dropping a digit. Work through the result one step at a time and check that the figures are the size you would expect at each stage.
How the MOSFET Threshold Voltage Physics Works
The relationship is applied step by step, and each step is a standard piece of physics rather than a single opaque formula. That means you can check the intermediate values against what the theory predicts, which is usually faster than checking only the final answer.
Keep every value in the same unit system throughout the calculation. Mixing metres and feet part way through is the single most common reason a correct formula gives a wrong answer.
Units, Assumptions and the Limits of the Model
The calculation assumes ideal conditions: no air resistance, no heat loss, and dimensions that do not change while you work. Those assumptions are reasonable for most classroom and engineering estimates, and unreasonable for anything more precise.
Where a value is a rate, it has to be quoted for the same period as everything else. A per-hour figure cannot be combined with a per-day figure without converting one of them first.
A Worked Example
Working through an example, with aq set to 10, are set to 5, capacitance of the insulator (c₀) set to 2, the calculator returns permittivity (ɛ) of 0, and k of 0, and body effect constant (γ) of 0.0047. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out body effect constant (γ)?
Enter aq, are, capacitance of the insulator (c₀), charge (q), d1, doping of the substrate (na), relative permittivity (ɛr), fara, intrinsic concentration (ni), leng, temperature (t) and source-body voltage (vsb). The calculator then works through the relationship and reports body effect constant (γ), threshold voltage (vt0) and surface potential (ϕf).
What does the mosfet threshold voltage actually calculate?
It takes aq, are, capacitance of the insulator (c₀), charge (q), d1, doping of the substrate (na), relative permittivity (ɛr), fara, intrinsic concentration (ni), leng, temperature (t) and source-body voltage (vsb) and converts them into body effect constant (γ), threshold voltage (vt0) and surface potential (ϕf) using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter aq?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.