Breakdown Electric Field (V/cm) of Materials
The breakdown electric field (dielectric strength) is the maximum electric field a material can withstand before it becomes conductive.
It is measured in V/cm or MV/cm.
Gases
- Air (dry, at STP): ~3 × 10⁴ V/cm
- SF₆ (sulfur hexafluoride): ~9 × 10⁴ V/cm
Liquids
- Transformer oil: ~1 × 10⁵ V/cm
- Distilled water: ~6 × 10⁴ – 7 × 10⁴ V/cm
Solid Insulators
- Glass: ~1 × 10⁶ – 3 × 10⁶ V/cm
- Mica: ~1 × 10⁶ – 2 × 10⁶ V/cm
- Porcelain: ~1 × 10⁵ – 2 × 10⁵ V/cm
- Rubber: ~1 × 10⁵ – 5 × 10⁵ V/cm
- Polyethylene: ~5 × 10⁵ – 1 × 10⁶ V/cm
- Teflon (PTFE): ~6 × 10⁵ – 1 × 10⁶ V/cm
Semiconductors
- Silicon (Si): ~3 × 10⁵ V/cm
- Germanium (Ge): ~1 × 10⁵ V/cm
- Gallium arsenide (GaAs): ~4 × 10⁵ V/cm
- Silicon carbide (SiC): ~2 × 10⁶ – 4 × 10⁶ V/cm
- Gallium nitride (GaN): ~3 × 10⁶ V/cm
Vacuum
- Not a fixed value; depends on electrode shape and spacing
- Typical practical breakdown: ~10⁵ – 10⁶ V/cm
Summary
- Breakdown field depends on temperature, purity, thickness, surface defects, and frequency.
- Thin films often have higher breakdown strength than bulk materials.
- Real-world values may vary from ideal laboratory values.