Among the most environmentally resistant of capacitors, glass capacitors are found in applications from aerospace to EVs.
This article is part of The engineer’s complete guide to capacitors. If you’re unsure of what type of capacitor is best for your circuit, read How to choose the right capacitor for any application.
What is a glass capacitor?
Glass capacitors use ultra-thin, high-purity glass as their dielectric. The glass dielectric is extremely stable, has negligible leakage and works well over a wide frequency range. One big advantage of glass capacitors is their ability to perform at high temperatures (up to a maximum of 200o C).
In nearly all aspects glass capacitors are the most environmentally resistant of capacitor types. Glass capacitors are also resistant to the effects of nuclear radiation.
How glass capacitors work
The capacitance range of glass capacitors is limited compared to other capacitor types, ranging from a few picofarads to a few nanofarads. However, large voltage values are available, and voltage does not affect the capacitance. Glass capacitors have a zero-voltage coefficient over an operating range from -75° C to 200° C. Glass capacitors are like multilayer ceramic chip (MLCC) capacitors in that they are manufactured in a stacked form.
Glass capacitor packaging is somewhat bulky compared to other technologies. However, they demonstrate very high stability such as no corrosion or degradation and no micro fractures. Glass capacitors demonstrate a zero-aging rate, high quality factor (Q) and large RF current capability. The dielectric absorption is very low, from 0.01% to 0.5%. Glass capacitors have a typical temperature coefficient of ±50 ppm/°C.
Applications of glass capacitors
Given the high temperature ability of glass capacitors, they serve many applications in the areas of aerospace, electric and hybrid electric vehicles, DC power transmission and pulsed-power systems.
Alternatives to glass capacitors
Mica capacitors are like glass capacitors in terms of capacitance values, voltage and temperature ratings. Mica capacitors have a high Q and perform well in RF applications. Axial leaded mica capacitors can have capacitance values as large as 3 µF and voltage ratings as large as 5 kV. While 200° C operation is possible for mica capacitors, 175° C is the usual limit.
The below table compares glass and mica capacitors.
|
Parameter |
Glass capacitor |
Mica (through-hole) |
Mica (SMD) |
|
Applications |
Coupling, decoupling, HF and timing circuits, tuning, pulse applications |
Coupling, decoupling, filtering, smoothing, HF applications, RC timing, transient suppression, tuning filters, oscillators |
Coupling, decoupling, filtering, smoothing, HF applications, RC timing, transient suppression, tuning filters, oscillators |
|
Capacitance |
0.5 pF to 10 nF |
1 pF to 100 nF |
1 pF to 10 nF |
|
Tolerance |
±0.25 pF to ±0.5 pF ±0.25% to ±20% |
±0.5 pF to ±1 pF ±0.1% to ±10% |
±0.25 pF to ±5 pF ±0.25% to ±5% |
|
Temperature range |
-55oC to 125oC (200oC) |
-55oC to 125oC |
-55oC to 125oC |
|
Temperature coefficient (ppm/oC) |
+140±25 |
0 to 70/-20 or 0 to ±100 or ±200 |
0 to 70/-20 or 0 to ±100 or ±200 |
|
Rated voltage (Vdc) |
50 to 500 |
50 to 5000 |
60 to 1000 |
|
tanδ, typical @1kHz, 25oC |
0.05 |
|
|
|
tanδ, typical @1MHz, 25oC |
0.06 |
0.06 |
0.06 |
|
Stability ΔC/C DC to 500 MHz |
0.5% |
0.5% |
2% |
|
Dielectric absorption |
0.01% |
0.5% to 0.8% |
0.5% to 0.8% |
|
Dielectric constant εr |
5 to 10 |
6 to 8 |
6 to 8 |
