Model subthreshold swing with flexible physics inputs. See thermal limits, body factors, and slope trends. Create reports, review examples, and visualize performance clearly today.
Use one method at a time. Capacitance inputs only need consistent units because the ratio determines the body factor.
The chart compares the ideal thermal limit with the currently selected body-factor trend.
Definition
S = dVG / d(log10ID)
Weak-inversion equation
S = n × ln(10) × kT / q
Body-factor relation
n = 1 + Cdep / Cox
Measured sweep formS = ΔVg / log10(I2/I1)
Where S is the subthreshold slope in volts per decade, n is the body factor, k is the Boltzmann constant, T is absolute temperature, and q is the electron charge.
For an ideal conventional MOSFET at 300 K, the lower thermal limit is near 60 mV/dec. Higher depletion effects or non-ideal electrostatics increase the slope.
| Temperature (K) | Cdep | Cox | n | Ideal S (mV/dec) | Actual S (mV/dec) |
|---|---|---|---|---|---|
| 300 | 0.20 | 1.00 | 1.20 | 59.53 | 71.44 |
| 325 | 0.15 | 1.00 | 1.15 | 64.49 | 74.16 |
| 350 | 0.10 | 1.00 | 1.10 | 69.45 | 76.39 |
It measures how much gate voltage is needed to change drain current by one decade in weak inversion. Lower values mean sharper switching and usually better low-voltage behavior.
At about 300 K, a conventional MOSFET has an ideal thermal lower limit near 60 mV/dec. This comes from Boltzmann carrier statistics in the subthreshold region.
They set the body factor n. A larger depletion contribution makes n bigger, which directly raises the subthreshold slope and weakens switching sharpness.
They only need consistent units because the capacitance method uses the ratio Cdep/Cox. Per-area units are common, but any matching units work.
Subthreshold slope scales roughly linearly with absolute temperature in the ideal model. Higher temperature increases the thermal voltage and usually increases the slope.
Use it when you already have two current points and the gate-voltage difference between them. It extracts slope directly from measured transfer data.
It is intended for conventional weak-inversion style analysis. Exotic devices that beat the thermal limit need different physical models and extraction methods.
CSV files help with spreadsheets and lab logs. PDF files help with reports, sharing, and documenting assumptions, trends, and final extracted values.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.