Sapphire is an insulator, and even with the addition of various dopants, it is difficult to make it conductive. For this reason, it is often used as a material that takes advantage of its insulating properties.
On the other hand, sapphire is also a promising material for microwave applications because of its extremely low dielectric loss factor (ε・tan δ) and chemical stability.
| Sapphire | MgO | Silica glass | ||
|---|---|---|---|---|
| Temperature | Room Temperature | |||
| Frequency | 13GHz | 30GHz | 14~16GHz | 10GHz |
|
Relative permittivity εr |
9.4 （⊥c) | 9.41 （//c) |
9.85 |
3.81 |
|
Dielectric loss tan δ |
1.6×10-5 （⊥c) | 3×10-5 （//c) | 0.78×10-6 | 1.7×10-4 |
| Chemical stability | Chemically stable and can be used at temperatures above 1000°C |
Tidal solubility, requires humidity control |
Devitrification appears due to high temperature and impurities |
|
