Multilayer ceramic capacitors (MLCCs) are today the most commonly used capacitors in electronic circuits. They stand out due to their compact design, low equivalent series resistance (ESR) and low equivalent series inductance (ESL). As a result of these properties and their low cost, they are frequently used in input and output filters of DC/DC converters. But they are also the preferred choice in many other designs: These capacitors can be found in almost every electronic device, from consumer electronics to industrial plants.
That said, the weaknesses of MLCCs are increasingly being exposed in complex applications:
- DC bias effect: The capacitance of these components varies with the applied DC voltage. In fact, it can lead to a capacitance drop of more than 70% compared to the data sheet specifications, meaning that the originally specified capacitance is often unavailable in real-world scenarios.
- Inverse piezoelectric effect: The application of a DC voltage to an MLCC may cause slight static deformation as a result of mechanical stress in the material. However, if high-frequency voltages are applied or certain operating conditions arise, it can lead to vibrations in conjunction with electromagnetic oscillations, which are perceived as an unpleasant screeching noise.
- Brittleness: Due to their brittle ceramic structure, MLCCs are susceptible to cracks, for example when bending the printed circuit board. These cracks have a tendency to spread under thermal or mechanical stress. This negatively impacts not only the capacitance but also the electrical parameters ESR (equivalent series resistance) and ESL (equivalent series inductance). Even the smallest of cracks can grow over time and significantly shorten the service life of the component.
- Large variations in capacitance with respect to frequency and temperature changes: Capacitance varies significantly depending on environmental factors and can impact system stability.
Polymer capacitors – stable capacitance, less faults
Thanks to their special design, conductive polymer capacitors are immune to many of the typical weaknesses of conventional MLCCs (Fig. 2). Instead of a ceramic dielectric, aluminum or tantalum with a thin oxide layer is used and combined with a solid electrolyte made of conductive polymer.
This type of design offers significant advantages: Compared to MLCCs, conductive polymer electrolytic capacitors exhibit considerably lower capacitance losses due to DC voltage bias and temperature fluctuations. The DC bias effect is negligible, as the effective capacitance remains stable even under load and circuits can be designed more precisely. Thanks to their high capacitance density, polymer capacitors enable a compact design combined with high effective capacitance. Far fewer components are often needed to ensure the same system performance. This reduces the required installation space and the overall costs – including packaging and assembly. Due to their actual design, polymer capacitors are less sensitive to mechanical and thermal stress. Their low susceptibility to crack formation and high resistance to thermal stress boost reliability.
Since piezoelectric effects do not occur, there is no noise or micro-vibrations – a crucial advantage, especially for sensitive applications. Polymer capacitors offer predictable, extensive operating periods without the aging effects typically associated with conventional electrolytic capacitors. The SMD design allows them to be integrated in a space-saving way and makes them particularly suitable for flat devices, such as sensor modules, display drivers or driver boards for power output stages. They enable automated assembly, reduce the space required on the printed circuit board and simplify the installation processes – especially for large production runs. Further, they have a low ESR across a wide frequency range. This helps smooth out ripple currents, making them the ideal choice for power management circuits.
Table 1: Comparison of properties of the various capacitor technologies
| Capacitance | Temperature behavior | DC bias | Voltage range | Size | ESR | Ripple | |
| Aluminum electrolytic cap. (SP-Cap) | o | + | ++ | o | + | ++ | ++ |
| Tantalum solid cap. (POSCAP) | + | ++ | ++ | o | ++ | ++ | ++ |
| Aluminum solid cap. (OS-CON) | ++ | ++ | ++ | + | o | ++ | ++ |
| Hybrid cap. | ++ | ++ | ++ | + | o | ++ | ++ |
| MLCC | x | o | x | ++ | ++ | ++ | ++ |
Legend: ++: very good, +: good, o: average, x: poor
Table 1 shows: Each type of capacitor has its strengths and weaknesses. To select suitable components, various factors like installation space, costs and aging behavior must be considered in addition to electrical parameters, such as ESR, capacitance and dielectric strength. Due to their high dielectric strength and reverse dielectric strength, MLCCs are ideal for applications with high voltage requirements and extremely low ESR.
Polymer capacitors show their strengths especially in applications with high current demands, space constraints and the need for stable capacitance under load. Their low ESR, high capacitance density and robust behavior under thermal and mechanical stress make them a reliable alternative – especially when multiple MLCCs can be replaced by a single polymer component.
Increase in efficiency for LED applications
In cutting-edge LED driver applications, e.g., in the automotive sector, developers have to come up with capacitors designed for high currents and compact sizes. A real-world example shows how the use of hybrid polymer capacitors can significantly reduce the number of components and the space required on the printed circuit board: Instead of four 10 µF/50 V MLCCs with a total of 23 µF and a footprint of 59 mm², a single 33 µF/50 V hybrid capacitor with just 53 mm² is sufficient. Besides effectively reducing the space needed by 10%, the hybrid capacitor features a low ESR of 40 mΩ, a high ripple current capacity of 1.1 Arms and a specified service life of 4,000 hours at 125 °C. The use of polymer technology enables stable light output, improved mechanical reliability and simplified installation processes.
Summary
MLCCs remain essential in many applications – especially where compact sizes and low ESR are needed. Nevertheless, their physical limitations make them vulnerable in critical applications. Conductive polymer capacitors offer a robust and capacitance-stable alternative in this case. They enable reliable, space-saving designs with high current carrying capacity and are, therefore, a valuable addition to pioneering electronics development.
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