APPLICATION NOTES

Aluminum non-solid electrolytic capacitors (electrolytic capacitors) are used in many electronic devices as inexpensive, small-size, and large-capacitance devices.
However, electrolytic capacitors have higher resistance than other capacitors and their characteristics are sensitive to temperature. Especially in the low temperature range, the increase in the resistance and the decrease in the capacitance are remarkable, making the it not suitable for equipment used in low temperature.
In order to overcome this weakness, the development of electrolytes mainly affecting the electric characteristics has been extensively carried out. Now, electric characteristics of electrolytic capacitors have been improved, and longer life-time, lower resistance, smaller temperature dependence have been achieved, leading to considerable improvement of their performance. As a result, their adoption has been expanding in devices, such as in-vehicle, industrial, communication devices, and others requiring high reliability in a wide temperature range.
For in-vehicle equipment, the extension of functions has progressed in recent years mainly for safety systems such as advanced driving assistance system (ADAS) and for the full-scale introduction of automatic driving. In addition, as environ-mental regulations become severe, computerization of vehicles has been advancing. For this reason, the number of electronic control units (ECUs) mounted on in-vehicle devices has also increased significantly. Conventionally, in-vehicle ECUs are installed in a cabin space free from significant temperature variation and strong vibration. However, for the purpose of securing sufficient cabin space and reducing wire harnesses, installation in the engine room has become popular.
The temperature and vibration environment inside the engine room is more severe than inside the cabin. Therefore, the capacitors mounted on ECUs are required to have higher temperature and vibration resistance than before.
Moreover, demands for space saving, weight reduction, and power efficiency for in-vehicle devices increase the performance requirements, such as miniaturization, lower equivalent series resistance (ESR), and higher ripple current, which cannot be dealt with by conventional electrolytic capacitors.
In order to respond to these requirements, Rubycon Corporation has developed a high-performance hybrid capacitor based on the conventional conductive polymer aluminum solid electrolytic capacitor (conductive polymer capacitor) using its original hybrid technology, thus contributing to the high functionality of in-vehicle equipment.
This article introduces the technological trend of conductive polymer aluminum solid electrolytic capacitor (hybrid), which the company has developed up to now.

Development of Conductive Polymer Capacitor

Conductive polymer aluminum solid electrolytic capacitors use conductive polymers with excellent conductivity. They feature small temperature variation property and small resistance; can deal with high ripple current; and exhibit little aging of electric characteristics. Compared with an electrolytic solution, the conductive polymer has poor repairability of the dielectric fi lm. The upper limit of the rated voltage of the capacitors has been said to be 25V, making them less adaptable for in-vehicle ECUs.
The company elevated its development activities to solve these problems. As a result, Rubycon released in 2013 the PZA Series conductive polymer capacitors, which adopt an original polymer technology featuring high-purity PEDOT poly(3,4-ethylenedioxythiophene) and included a characteristic stabilizer and reaction inhibitor. The PZA Series features rated voltage up to 63V and maintains the characteristics of the conventional conductive polymer capacitor.
After that, the company has commercialized the surface-mounted PAV Series (105ºC product), which adopt the same polymer technology, and then the PZC and PCV Series (125ºC product), which guarantee high temperature operation, thus enhancing product variety.

Adoption of Original Hybrid Technology

The developed conductive polymer capacitors realize lower resistance, higher ripple current, and better temperature characteristics in comparison with the conventional electrolytic capacitor. However, its size is slightly larger and the electrostatic capacitance remains smaller as shown in Table 1. It incorporates a characteristic stabilizer with the function of repairing the dielectric film. In comparison with the electrolytic solution used in the electrolytic capacitor, however, the film's repair-ability remains small. Therefore, the product with the same rated voltage has to use an anode foil with a voltage resistance higher than the electrolytic capacitor. As a result, the conductive polymer capacitor has a capacitance smaller than the electrolytic capacitor.