As automotive and industrial electronic modules move closer to heat sources, demand is increasing for MLCC dielectrics rated for operation up to +150°C.
There are several ceramic capacitor dielectrics families in regular use today: ultra-stable Class I types such as P90 (porcelain), NP0/C0G and U2J, alongside higher-capacitance Class II types such as X7R, X5R and Y5V.
With increasing use of electronic modules in under-the-hood applications in the automotive industry, X8* type ceramic dielectrics are also becoming more and more popular.
X8G, X8L and X8R are high-temperature ceramic dielectric designations for components intended to operate from -55°C to +150°C. In the Class II EIA code system, the first character defines the low-temperature limit, the second character the upper-temperature limit and the third character the allowed capacitance variation over that range. However, X8G is commonly used by manufacturers as a high-temperature Class I dielectric designation, while X8L and X8R are Class II characteristics.
Important note: X8R specifies a capacitance variation of ±15% from -55°C to +150°C. X8L allows a wider variation of +15% / -40% over the same coded temperature range. X8G is a stable Class I dielectric with a temperature coefficient commonly specified as 0 ±30 ppm/°C, but the exact manufacturer specification should always be checked.
| Dielectric | Dielectric class | Operating temperature range | Capacitance behaviour versus temperature | DC-bias and ageing sensitivity | Typical use |
|---|---|---|---|---|---|
| X8G | Class I | -55°C to +150°C | Typically 0 ±30 ppm/°C; check the individual manufacturer specification | Very low DC-bias effect; negligible ageing | High-temperature precision, timing, resonant and filtering circuits |
| X8L | Class II | -55°C to +150°C | +15% / -40% over the coded temperature range; commonly ±15% to +125°C, then +15% / -40% to +150°C | Present; verify with the part-specific datasheet | High-temperature applications where higher capacitance density is needed and wider temperature variation is acceptable |
| X8R | Class II | -55°C to +150°C | ±15% over the coded temperature range, measured without applied DC voltage | Can be significant; verify effective capacitance at applied DC voltage | High-temperature decoupling, bypass and bulk-capacitance functions |
Why the difference matters in practice
X8G is a Class I dielectric, so it offers the best capacitance stability with temperature and also very low sensitivity to DC bias and ageing. The trade-off is its lower permittivity, which usually means lower achievable capacitance and lower CV in a given package size.
X8L and X8R are Class II dielectrics, so they are generally more attractive when higher capacitance density is needed at up to +150°C. However, designers should remember that effective capacitance in real circuits can be reduced by DC bias, ageing and operating conditions, especially for X8R parts with high nominal capacitance in small case sizes.
How to choose between X8G, X8L and X8R
- Choose X8G when high-temperature capacitance stability, low loss and negligible DC-bias dependence are more important than maximum capacitance density. Typical applications include precision analogue, timing, resonant and filtering circuits.
- Choose X8R when a predictable ±15% temperature characteristic through +150°C is required for decoupling, bypassing or bulk-capacitance functions. Check the manufacturer’s DC-bias curves to determine effective in-circuit capacitance.
- Choose X8L only when its wider temperature characteristic of +15% / -40% is acceptable and the selected supplier offers the required capacitance, voltage rating, qualification and reliability level.
Important caveats for design engineers
- The X8* code alone does not confirm automotive qualification. AEC-Q200 compliance, reliability grade, termination type and manufacturer-specific derating guidance must still be checked separately.
- Two capacitors with the same X8R marking may behave quite differently under DC bias depending on capacitance value, rated voltage, case size and supplier technology.
- Availability of X8G parts is typically narrower than X8L or X8R, especially at higher capacitance values.
Availability and qualification
X8R and X8L MLCCs are offered by several major manufacturers for high-temperature applications. X8G is less widely available and is generally limited to lower capacitance values than Class II alternatives. The dielectric code alone does not establish automotive qualification: verify AEC-Q200 status, voltage rating, reliability grade, termination system and manufacturer-specific derating guidance for the exact part number.
Dielectric designation is therefore a starting point for capacitor selection, not a complete prediction of in-circuit performance. Confirm final component selection using the manufacturer datasheet, temperature characteristic, DC-bias curve, ageing data and application-specific derating requirements.
featured image credit: Knowles
