Formula Used
The calculator estimates resistivity first:
ρ = 1 / (q × µn × ND)
The effective n pillar area is:
Aeff = A × Wn / (Wn + Wp) × fill factor
The drift resistance is:
Rdrift = ρ × L / Aeff × temperature factor × crowding factor × mismatch penalty
The final resistance is:
Rtotal = Rdrift + Rchannel + Rcontact + Rsubstrate + Rpackage + Rspreading
Specific on resistance is:
Rsp,on = Rtotal × active area
How to Use This Calculator
Enter the active device area and drift height. Add n and p pillar widths. Enter donor and acceptor concentrations. Set electron mobility and cell fill factor. Add fixed resistance values from layout, package, or measured data. Press calculate. Review total resistance, drift share, charge balance, specific resistance, current, and power loss.
Example Data Table
| Case | Area mm² | Drift µm | ND cm⁻³ | Wn/Wp µm | Mobility | Use |
|---|---|---|---|---|---|---|
| Balanced low voltage | 18 | 30 | 8.0e15 | 3.0 / 3.0 | 1000 | Fast design check |
| Medium voltage | 25 | 45 | 6.0e15 | 3.2 / 3.2 | 950 | Default estimate |
| High voltage | 40 | 70 | 4.0e15 | 4.0 / 4.2 | 850 | Conservative study |
Understanding Superjunction Resistance
A superjunction device uses alternating n and p pillars in the drift region. This structure supports high voltage while keeping on resistance low. A normal drift region needs lighter doping as voltage rises. That raises resistance. A superjunction can use higher n pillar doping because the p pillar balances charge during blocking. The calculator estimates this behavior with geometry, mobility, doping, and temperature inputs.
Why Charge Balance Matters
Charge balance is central to the result. The n pillar charge comes from donor doping and n pillar width. The p pillar charge comes from acceptor doping and p pillar width. When those charges match, the electric field spreads more evenly. When they do not match, resistance and safety margin can suffer. The tool reports mismatch percentage and applies an optional penalty.
Main Resistance Parts
The drift part is usually the main term. It is calculated from resistivity, drift height, and the effective n pillar area. Contact, substrate, package, channel, and spreading terms can also be included. These values help compare silicon behavior with real measured resistance. The specific on resistance is also shown. It normalizes total resistance by active area.
Temperature and Mobility Effects
Resistance rises when mobility falls. Temperature can reduce carrier mobility and increase total resistance. The calculator uses a reference temperature and a temperature coefficient. This makes quick what if testing easier. Use measured mobility data when available. For early design studies, use typical values and add a design margin.
Practical Use
Enter active area, pillar dimensions, drift height, doping levels, and mobility. Add known fixed resistance values from layout or data sheets. Choose a correction factor if layout crowding or incomplete current sharing is expected. Press calculate to view drift resistance, total resistance, specific resistance, charge ratio, and estimated current at a selected voltage. Export results to keep design notes with simulations, lab tests, or spreadsheets.
Design Notes
This calculator is an engineering estimator. It does not replace TCAD, avalanche modeling, thermal simulation, or verified manufacturer data. Pillar shape, trench depth, lifetime control, edge termination, and process variation change the real value. Still, the method is useful for learning and fast comparison between candidate structures. Always validate final designs with reliable measured device data.
FAQs
What is superjunction resistance?
It is the on-state resistance created by the drift region and other series parts in a superjunction device. The calculator separates drift, contact, substrate, package, channel, and spreading resistance.
Why are n and p pillars used?
N and p pillars balance charge in the drift region. This allows higher doping while still supporting blocking voltage. Higher usable doping can reduce on resistance.
What does charge mismatch mean?
Charge mismatch compares donor charge in the n pillar with acceptor charge in the p pillar. A higher mismatch can reduce field balance and may increase design risk.
What is specific on resistance?
Specific on resistance is total resistance multiplied by active area. It helps compare different devices without area hiding the true resistance performance.
Should I include package resistance?
Yes, include it when comparing with measured device resistance. Leave it small or zero when studying only the silicon drift structure.
How does temperature affect the answer?
Higher temperature often lowers mobility and raises resistance. The temperature coefficient adjusts resistance from the reference condition to the selected operating condition.
Is the breakdown voltage exact?
No. It is a simple estimate from critical field and drift height. Real breakdown depends on termination, charge balance, pillar shape, process variation, and defects.
Can this replace simulation?
No. Use it for early calculations, teaching, and quick comparisons. Final semiconductor designs need verified data, measurements, and detailed device simulation.