Ceramic Capacitor - History


Since the beginning of the study of electricity, ceramics like porcelain have been used as insulators. It was obvious to use these ceramic materials, including mica, steatite and titanium dioxide (rutile), as dielectric for the first ceramic capacitors. The capacitors with paraelectric titanium dioxide as a dielectric had a linear temperature dependence of the capacitance for temperature compensation of resonant circuits and were produced in small quantities around 1926. But this dielectric had relatively low permittivity so that only smaller capacitance values could be realized.

After 1941, the ferroelectric ceramic material barium titanate, with a permittivity in the range of 1000, approximately 10 times higher than titanium dioxide, was also used. The higher permittivity resulted in much higher capacitance values, but this was coupled with some unstable electrical parameters. At that time, these ceramic capacitors replaced the commonly used mica capacitors for a lot of applications where stability was not so important. Smaller dimensions, as compared to the mica capacitors, cheaper production costs and independence from natural mica product accelerated the development of these new ceramic capacitors.

The fast-growing broadcasting technology after the Second World War brought a great deepening of knowledge in understanding the crystallography, phase transitions, and the chemical and mechanical optimization of the ceramic materials. Through the complex mixture of different basic materials, the electrical properties of ceramic capacitors can be precisely adjusted. To distinguish the electrical properties of ceramic capacitors, standardization created application classes. Class 1 capacitors with paraelectric dielectric includes capacitors with a defined temperature coefficient for temperature compensation of circuits requiring high frequency accuracy. Class 2 capacitors with ferroelectric dielectric have higher capacitance values and include ceramic capacitors for decoupling, buffering and filtering in power supplies.

The typical shape of the capacitors for radio applications at this time was the ceramic tubular condenser. This was a ceramic tube that was covered with tin or silver on both the inside and outside surface, and was provided with relatively long lead terminals forming, together with resistors and other components, a typical wired tangle of open circuit wiring.

The easy formability of the ceramic material facilitated the development of some special and quite large shapes of ceramic capacitors for high-voltage, high-frequency (RF) and power applications.

With the development of semiconductor technology in the 1950s, barrier layer capacitors, or class 3 capacitors, were developed using doped ferroelectric ceramics. Because the electrical parameters of these capacitors were exceedingly temperature dependent, they would be replaced some decades later by Y5V class 2 capacitors.

In addition to the typical early ceramic tubular capacitor, the more inexpensively produced ceramic disc capacitors were introduced into the industry in the 1950s and 1960s.

It was a U.S. company in the midst of the Apollo program, which was launched in 1961, that first came up with the idea of stacking multiple discs to a monolithic block. This “multi-layer ceramic capacitor” (MLCC) was invented to meet the need for a compact, high-capacitance capacitor. The production of these capacitors using the tape casting and ceramic-electrode cofiring processes meant a great challenge in precision and technology. MLCCs expanded the range of ceramic capacitor application to larger capacitance values in smaller cases. These ceramic chip capacitors were the driving force behind the conversion of the production of electronic devices from through-hole mounting to surface-mount technology in the 1980s.

At present (2012), more than 1012 MLCC are manufactured each year. They are the most produced capacitors ever. Along with ceramic chip capacitors, ceramic disc capacitors are often used as so called safety capacitors in EMI suppression applications. Besides these, large ceramic power capacitors for high voltage or high frequency transmitter applications are also to be found.

New developments in ceramic materials have been made with anti-ferroelectric ceramics. This material has a nonlinear antiferroelectric/ferroelectric phase change, which allows greatly increased energy storage with higher volumetric efficiency. They are used for energy storage (for example, in detonators).

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