This article is a continuation of "Evolving Capacitors: Multilayer Ceramic Capacitors, Part 2—Technology (part 1/2)."
Consider Temperature and DC Voltage Characteristics
Along with their many advantages, multilayer ceramic capacitors have two major disadvantages.
First, they have poor temperature characteristics. Specifically, the electrostatic capacitance varies greatly with changes in temperature. The capacitance of an aluminum electrolytic capacitor varies by approximately ±15% within a temperature range of -55 to +125°C. In contrast, the capacitance of a multilayer ceramic capacitor varies greatly in a range of +30 to -80% depending on the model (e.g., Type F products). Therefore, if multilayer ceramic capacitors are to be used in electronic devices for the interior of cars or other locations where the temperature becomes very high, or electronic devices used in cold areas such as ski resorts, capacitors with little capacitance change such as Type B products should be selected when designing the electronic circuitry.
However, note that the disadvantage of poor temperature characteristics applies only to multilayer ceramic capacitors with a high dielectric constant (Class 2) that use barium titanate (BaTiO3) as the dielectric material. Class 1 multilayer ceramic capacitors that use titanium oxide (TiO2) have a small temperature coefficient of capacitance of ±60 ppm/°C at most in the temperature range of -55 to +125°C. However, a high-capacitance TiO2-based multilayer ceramic capacitor has not yet been commercialized because titanium oxide has a small relative dielectric constant.
Second, multilayer ceramic capacitors have DC voltage characteristics (DC bias characteristic). DC voltage characteristics refers to the phenomenon where the effective electrostatic capacitance decreases when DC voltage is applied to a multilayer ceramic capacitor (Fig. 3).
Multilayer ceramic capacitors have a characteristic where the effective electrostatic capacitance decreases when a DC voltage is applied. This is also known as the DC bias characteristic.
For example, when a 4 V DC voltage is applied to a multilayer ceramic capacitor with a rated voltage of 6.3 V and a capacitance of 100 μF, the capacitance is reduced by approximately 20% in the case of a Type B product, or approximately 80% in the case of a Type F product. This phenomenon does not occur in aluminum electrolytic and tantalum electrolytic capacitors.
Therefore, when selecting a multilayer ceramic capacitor, the DC voltage component of the signal line the capacitor is applied to should be measured in advance to determine the degree of reduction of the effective capacitance. (Refer to the separate article “JEITA Standardizes Notation in View of DC Bias Characteristic.”) However, semiconductor chips manufactured using advanced microfabrication technology have quite a low power supply. Recently, chips that operate at about 1.0 V are not uncommon, and as a result, the problem of DC voltage characteristics is not that significant in circuits driven at low voltages.
The problem related to DC voltage characteristics occurs only in Class 2 products. This is because the barium titanate used in products of this class is a ferroelectric material. Therefore, Class 1 products that use titanium oxide, which is a paraelectric material, are not affected by the problem.
* Indicated company and product names are the trademarks or the registered trademarks of each company.
* The content of this article listed in the February to March 2010 issue of "Tech On!" Nikkei Business Publications, Inc., was restructured.
* For more details on the Murata Manufacturing multilayer ceramic capacitors, please refer to the following: