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MOSFET Subthreshold Swing (S-Factor) & Leakage Calculator

Subthreshold swing dictates how sharply a MOSFET turns off, setting the fundamental physical limit on low-power supply voltage scaling.

Calculated Result
66.4 mV/decade

Subthreshold Swing (S)

Thermal Boltzmann Limit (m=1)

59.5 mV/dec (~60 mV at 300K)

Ideality Factor (m = 1 + Cdep/Cox)

1.116

Gate Oxide Capacitance (Cox)

1726567 pF/cm²

Calculation Breakdown

  1. Calculate gate dielectric capacitance Cox = ε_ox / toxCox = (3.9 * 8.854e-14) / (2e-7) = 1726567 pF/cm²
  2. Determine subthreshold swing S = (kT/q · ln10) · (1 + Cdep / Cox)S = 59.5 mV/dec * 1.116 = 66.4 mV/decade

Subthreshold Swing across Architecture

Interactive visualization based on your current inputs

mV/dec
0.0285583110Ideal Thermal LimitGAA / FinFETPlanar Bulk CMOSDegraded / Short-ChannelTransistor TypeSwing (mV/dec)

What Is the MOSFET Subthreshold Swing (S-Factor) & Leakage Calculator?

Subthreshold swing dictates how sharply a MOSFET turns off, setting the fundamental physical limit on low-power supply voltage scaling.

How Does the MOSFET Subthreshold Swing (S-Factor) & Leakage Calculator Work?

The calculation evaluates user-provided measurements using recognized domain equations, converts between measurement units, and adjusts for real-world efficiency factors.

MOSFET Subthreshold Swing (S-Factor) & Leakage Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

S = \left(\frac{k_B T}{q} \ln 10\right) \left(1 + \frac{C_{\text{dep}}}{C_{\text{ox}}}\right) \quad (\approx 60 \text{ mV/dec ideal at 300 K})

The Boltzmann thermal limit prevents standard room-temperature planar MOSFETs from switching faster than 60 mV per decade of drain current.

How to Use the MOSFET Subthreshold Swing (S-Factor) & Leakage Calculator

  1. Enter your primary measurements in the input fields above.
  2. Select your preferred units (e.g. metric or imperial) if applicable.
  3. Review or adjust operational assumptions such as field efficiency.
  4. Click Calculate to instantly generate the full results breakdown and visual chart.
  5. Use the Reset button at any time to clear the form and test a new scenario.

Step-by-Step Example Calculation

Modern 2nm Oxide High-k MOSFET

Input Values:

temperatureKelvin:300
gateOxideThicknessNm:2
depletionCapacitancePfPerCm2:200000

Understanding Your Result

Your calculated result represents the realistic operational capacity or baseline output under the specified conditions. Comparing theoretical and effective outputs reveals the direct impact of turns, overlap, and practical downtime.

Factors That Affect the Result

Field terrain, operator experience, equipment maintenance, overlap margin, and weather conditions can significantly influence real-world output.

When Should You Use This Calculator?

Use this calculator whenever you need quick, verified estimates for job planning, budgeting, equipment sizing, or project timelines.

Assumptions & Limitations

  • Uses SiO2 equivalent dielectric constant 3.9 for Cox calculation.

Frequently Asked Questions

Calculation Accuracy & Reference Note

This calculator implements verified, deterministic mathematical equations based on published standards. Results should be treated as professional engineering estimates; always verify critical operations with local equipment manuals and site inspections.

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