Multilayer ceramic capacitors and tantalum capacitors are among the most popular capacitor technologies applicable in a wide variety of electronics applications. While both capacitor technologies perform more or less similar essential functions, they have plenty of differences in terms of materials, performance under different conditions and construction techniques.
It is important to understand their inherent characteristics to comprehend the potential impact of choosing one capacitor technology over the other.
These capacitors are made from a metal called tantalum and are capable of achieving high capacitance values by combining various factors such as:
- An incredibly thin dielectric thickness
- Tantalum pentoxide
- A huge plate area
Positively charged dielectric plates made by pressing and sintering tantalum powder into a pellet are a vital component in these capacitors. These pellets are very porous, hence allowing the surface area of individual particles to make up the area of one equivalent capacitor plate cumulatively.
Additionally, the dielectric layer of tantalum pentoxide is typically made at around 17 Å per volt, while ensuring its thickness remains equal to the voltage applied. The result is a super thin dielectric layer that is attributable to the high capacitance values.
Tantalum Capacitor Styles
Most surface-mount applications use one of two tantalum capacitor styles. Each of these styles uses a manganese dioxide-based cathode due to its incredible self-healing characteristics. The molded tantalum capacitor style is a more conventional configuration that involves embedding tantalum wire into the pellet to achieve a positive connection in the circuit.
The microchip-style configuration is smaller, more modern, and quite popular in applications with little board spaces and high component densities. Manufacturers make this tantalum capacitor style by pressing and sintering tantalum powder onto the surface of a tantalum wafer. High-precision sewing operations define individual anodes.
Both the microchip and molded tantalum capacitor styles use similar basic elements. They have proven their suitability for high-reliability applications through years of manufacturing and testing.
Unlike their tantalum counterparts, ceramic capacitors have significantly thicker layers and a smaller overall plate area. However, they compensate for these shortcomings by integrating dielectric materials with significantly higher dielectric constants.
Barium titanate and titanium dioxide are among the most common dielectric materials used in manufacturing ceramic capacitors. Each of these materials has its own category of capacitors.
Class I Ceramic Capacitors
This category of ceramic capacitors provides the best capacitance stability relative to temperature, applied voltage and frequency. These ceramic capacitors consist of paraelectric materials like titanium dioxide, modified using additives such as niobium, zirconium and zinc to achieve stellar linear capacitance characteristics synonymous with tantalum.
Paraelectric materials like titanium have low permittivity. Therefore, these capacitors are the least volumetric efficient among ceramic capacitors. Consequently, their capacitance values are often very low.
Class II Ceramic Capacitors
This class of ceramic capacitors uses ferroelectric dielectric components like barium titanate, modified by additives such as aluminum oxide, aluminum silicate and magnesium silicate. These components have a greater permittivity compared to class I capacitors; hence they are capable of achieving higher volumetric efficiency despite exhibiting lower stability and accuracy.
In addition, this class of ceramic capacitors exhibits nonlinear capacitance values that largely depend on the applied voltage and operating temperatures, not to mention their relatively drastic aging over time. This combination of factors can significantly affect their performance.
Tantalum versus Ceramic Capacitors
Decades of testing have revealed how a typical tantalum capacitor consistently showcases linear capacitance change relative to operating temperature. For instance, the average capacitance change at -67°F is -5% compared to an over 8% capacitance change at 257°F.
Among ceramic capacitors, class II capacitors have the greatest non-linear capacitance response relative to temperature change. However, these capacitors can achieve desirable linear responses to temperature in applications that feature narrow ranges of operating temperatures, e.g., in implantable medical devices. Manufacturers have to take account of the average temperature responses when designing these circuits.
Besides providing a linear performance relative to temperature, a tantalum capacitor does not exhibit capacitance instability relative to the applied voltage. A class II ceramic capacitor, on the other hand, is likely to show capacitance change as the applied voltage fluctuates. This is attributable to the shrinking permittivity of its dielectric materials in response to increasing the applied voltage.
The change in capacitance demonstrated by ceramic capacitors is relatively linear, hence easy to take into consideration during circuit design. However, it is worth mentioning that some dielectrics with higher permittivity can lose upwards of 70% of their capacitance if operated close to or at their rated voltages.
Aging refers to the loss of capacitance over time. Ceramic capacitors display a gradual loss of capacitance over time, meaning that they have a relatively short shelf life. Their short lifespan is attributable to the degeneration of its polarized domains in the ferro electric dielectrics, which reduces permittivity throughout their operation.
Essentially, the capacitance of a ceramic capacitor reduces as its components age. A tantalum capacitor, on the other hand, has no wear-out mechanisms and does not display similar aging tendencies.
Insulation resistance abbreviated as IR is the resistance measured in ohms across a capacitor’s dielectric. As capacitance values – and consequently, the area of the dielectric – increase, the insulation resistance reduces. Therefore, the product of capacitance and insulation resistance is expressed in either Ohm Farads or megaohms.
On the other hand, if you divide the rated voltage of a capacitor by insulation resistance (according to Ohm’s Law), you get the leakage current. While ceramic capacitors are often specified by insulation resistance, their tantalum counterparts are usually specified by DCL, i.e., Direct Current Leakage. DCL and IR are equivalent, and converting from one unit to the other is possible through Ohm’s Law.
DC leakage current occurs when dielectric insulation is not perfect, hence causing a capacitor to discharge. A ceramic capacitor is better than a tantalum capacitor in this regard since its DC leakage current is significantly less.
Unlike ceramic capacitors that are non-polarized, tantalum capacitors are essentially a subset of electrolytic capacitors, meaning that they are polarized. Mounting a polarized capacitor incorrectly or subjecting it to pulses of high reversed polarity exposes it to more risk of damage or explosion compared to a non-polarized capacitor.
Tantalum and ceramic capacitors each have their fair share of advantages that enable the production of highly reliable and efficient electronics across a diverse range of industries. Nevertheless, these capacitors differ in terms of materials, performance and composition, hence making the choice of one capacitor over the other dependent on the specific requirements and considerations of an application.