Subthreshold Leakage Calculator

Analyze weak inversion current with practical semiconductor inputs. Compare trends across bias, size, and temperature. Build faster intuition for leakage sensitive circuit design decisions.

Calculator Form

Use the responsive input grid below. Large screens show three columns, medium screens show two, and mobile screens show one.

The model uses voltage magnitudes for the current estimate.
Use the off-state or near-threshold gate bias.
Enter threshold magnitude for the selected device.
This affects the drain correction term in weak inversion.
Typical room temperature is near 300 K.
Common values often fall between 1.1 and 1.8.
Reference current at |Vgs| = |Vth| and reference geometry.
Larger width generally raises leakage current.
Shorter length generally increases leakage sensitivity.
Reference geometry used with Iref.
Keep reference geometry consistent with your Iref value.
Used to estimate leaked charge and leakage energy.
Reset Form

Example Data Table

These sample scenarios show how temperature and gate bias can shift leakage under the current geometry and model settings.

Condition Temperature (K) Vgs (V) Vth (V) n Leakage (nA)
Cool standby 275 0 0.45 1.45 0.001643
Room standby 300 0 0.45 1.45 0.004892
Warm standby 325 0 0.45 1.45 0.012319
Mild bias shift 300 0.1 0.45 1.45 0.070485
Near threshold 300 0.37 0.45 1.45 94.674763

Formula Used

This calculator uses a practical weak inversion approximation for engineering estimates, not a full compact process model.

I_sub = I_ref × ((W/L) / (W_ref/L_ref)) × exp((|Vgs| - |Vth|) / (n × V_T)) × (1 - exp(-|Vds| / V_T))
V_T = (k / q) × T ≈ 8.617333262145 × 10^-5 × T
SS = n × V_T × ln(10) × 1000   mV/dec
P_leak = I_sub × |Vds|
Q_leak = I_sub × time
E_leak = P_leak × time

Meaning of the Terms

  • Iref is the reference drain current at threshold and reference geometry.
  • W/L scaling adjusts the current for your chosen transistor size.
  • n captures how strongly the channel responds in weak inversion.
  • VT is the thermal voltage, which rises with temperature.
  • Drain correction keeps the current finite when Vds is small.

Effect of Temperature on Subthreshold Leakage of MOSFET

Higher temperature usually increases subthreshold leakage. Thermal voltage rises with temperature, carrier activity increases, and threshold voltage often drops with heat. Those combined effects can make standby current grow sharply, which matters in low-power chips, always-on blocks, and battery-driven systems.

How to Use This Calculator

  1. Select nMOS or pMOS.
  2. Enter the relevant bias voltages for your operating point.
  3. Provide the device threshold voltage magnitude.
  4. Set the temperature in kelvin.
  5. Enter the subthreshold factor n from measurement or literature.
  6. Enter the reference current and its reference geometry.
  7. Set your actual transistor width and length.
  8. Enter the observation time to estimate leaked charge and energy.
  9. Press Calculate Leakage.
  10. Review the result cards, Plotly graph, and example table.
  11. Use the export buttons to save CSV or PDF summaries.

Frequently Asked Questions

1) What is subthreshold leakage in a MOSFET?

Subthreshold leakage is the drain current that flows when a MOSFET is nominally off, with gate voltage below threshold. It comes from diffusion in weak inversion and becomes important in scaled, low-power, and always-on designs.

2) What is the effect of temperature on subthreshold leakage of MOSFET?

Higher temperature usually increases subthreshold leakage. Thermal voltage rises, carrier transport changes, and threshold voltage often shifts downward. The net result is often much larger off-state current, especially in short-channel and low-threshold devices.

3) Why does threshold voltage strongly affect leakage?

Leakage depends exponentially on the difference between gate voltage and threshold voltage. A small threshold reduction can therefore create a large current increase. That is why process spread, body bias, and temperature shifts matter so much.

4) What does the subthreshold factor n represent?

The factor n describes how effectively the gate controls channel charge in weak inversion. Lower values mean sharper switching and better slope. Higher values mean more current is needed for each decade change in drain current.

5) Why are width and length included?

Leakage roughly scales with transistor geometry. Wider devices leak more because they provide a larger conduction path. Shorter devices can show higher leakage sensitivity because electrostatic control is weaker in many practical technologies.

6) Is this calculator accurate for every fabrication process?

No. It is a useful engineering estimator. Real silicon depends on process node, DIBL, body effect, mobility degradation, short-channel behavior, and compact-model details. For signoff work, use foundry models and circuit simulation.

7) Why does Vds appear in the equation?

At very low drain voltage, the off-current is reduced because the drain has less ability to collect carriers across the channel. The drain correction term models that effect and approaches one when Vds becomes sufficiently large.

8) When should engineers worry most about subthreshold leakage?

It matters most in standby modes, battery systems, IoT nodes, memory arrays, sleep transistors, and always-on control logic. It also becomes critical when chips run hot, use low threshold devices, or contain massive transistor counts.

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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.