Ceramic Capacitors: Structure, Types, Applications and Development

Ⅰ. The structure of ceramic capacitors

Ceramic capacitors are mainly composed of the following parts:

1. Casing

In order to protect the capacitor from the external environment, ceramic capacitors usually have a case or package. This can be made of plastic, ceramic or other materials.

2. Dielectric Layer

This is the core part of ceramic capacitors. Ceramic material is usually an insulating material, such as aluminum oxide (Al2O3), titanium dioxide (TiO2), etc. The thickness and material of this layer determine the electrical properties of the capacitor, especially the capacitance value.

3. Terminals

Capacitors usually have two leads or terminals for connection into a circuit. These leads are connected to the electrode layers of the capacitor by soldering, printing or other means.

4. Electrode Layers

Both sides of the ceramic material layer are coated with metal electrodes, usually silver, copper, nickel and other metals with good conductivity. Together with the ceramic layers, these electrodes form the positive and negative plates of the capacitor.

Ⅱ. The classification of ceramic capacitors

According to different designs, materials and uses, ceramic capacitors can be divided into the following types. These different types of capacitors have different electrical properties and temperature characteristics, and are suitable for different circuits and application scenarios.

1. High-frequency ceramic capacitors (Class I ceramic capacitors)

Class I ceramic capacitors were formerly known as high-frequency ceramic capacitors. Due to its non-ferroelectric formula (dielectric constant less than 150) with TiO2 as the main component, it has the most stable performance; or by adding a small amount of other (ferroelectric) oxides, such as CaTiO3 or SrTiO3, to form an "extended" temperature Compensating ceramics, which can display approximately linear temperature coefficients, increase the dielectric constant to 500. These two dielectrics have low loss, high insulation resistance and good temperature characteristics. It is especially suitable for oscillators, resonant circuits, coupling capacitors in high-frequency circuits and other circuits with small loss and stable capacitance, or for temperature compensation.

Class I ceramic capacitors have the following characteristics:

① No aging: Since the material used in the manufacturing process is a parapotential material, it will not undergo a severe aging process.

② Linear temperature coefficient: Its capacitance changes linearly with temperature.

③ No power loss: Compared with class II capacitors, the electrical loss of class I capacitors is much lower.

④ Use in high-Q filters: In view of the above characteristics, such capacitors are often used in applications such as resonant circuits, PLLs, and oscillators.

⑤ No voltage dependence: its capacitance does not depend on the applied voltage.

⑥ High stability and accuracy: According to the EIA RS-1988 standard, they will use 3-digit symbols to indicate the dielectric used.

According to the standards of the American Electrotechnical Institute (EIA), the ceramic media of C0G or NP0 and CC series (temperature coefficient 0±30PPM/℃) are very stable, with a very low temperature coefficient and no aging phenomenon. Dissipation factor is independent of voltage, frequency, temperature and time. The dielectric coefficient can reach 400, and the dielectric strength is relatively high. The dielectric is well suited for high frequencies (especially high frequency power oscillations for industrial high frequency induction heating, high frequency wireless transmission and other applications of high frequency power capacitors), ultra high frequencies and timing and oscillations with critical capacitance and stability requirements The working environment of the circuit. The only disadvantage of this type of dielectric capacitor is that the capacitance cannot be very large (due to the relatively small permittivity). Typically, 1206 surface mount C0G dielectric capacitors range in capacitance from 0.5PF to 0.01μF.

2. Low-frequency ceramic capacitors (Class II ceramic capacitors)

Class II ceramic capacitors are also called low frequency ceramic capacitors. It refers to a capacitor with a ferroelectric ceramic as a medium, so it is also called a ferroelectric ceramic capacitor. Its capacitance varies nonlinearly with temperature, and its loss is large. It is commonly used in electronic equipment for bypassing, coupling, or other circuits that require less loss and capacitance stability. Class II ceramic capacitors are divided into stable grades and usable grades. X5R and X7R belong to the stable grade of Class II ceramics, while Y5V and Z5U belong to the usable grade.

Class II stable ceramic dielectric materials, such as X7R and X5R of the American Electrotechnical Association (EIA) standard and CT series of the Chinese standard (the temperature coefficient is ±15.0%). The dielectric coefficient of this medium changes greatly with temperature, so it is not suitable for occasions with high temperature coefficient requirements such as timing and oscillation. However, because their dielectric coefficient can be very large (up to 1200), the capacitance can be made relatively large, which is suitable for coupling, bypass and filtering that require high working environment temperature (X7R: -55~+125°C). Usually, the capacitance of 1206 SMD package can reach 10μF or higher.

Class II usable grade ceramic dielectric materials, such as Z5U and Y5V of the American Electrotechnical Association (EIA) standard and low-grade product models of the Chinese standard CT series (the temperature coefficient is +22% of Z5U, -56% and +22% of Y5V , -82%). The dielectric coefficient of this medium varies greatly with temperature, so it is not suitable for occasions that require high temperature coefficients such as timing and oscillation. However, due to its large dielectric coefficient (up to 1000~12000), the capacitance can be made relatively large. This applies to coupling, bypass and filtering for general operating ambient temperature requirements (-25~+85°C). Usually, 1206 surface mounted Z5U and Y5V dielectric capacitors can even reach 100μF. In a sense, it is a strong contender to replace tantalum electrolytic capacitors.

3. High voltage ceramic capacitor

The ceramic materials of high voltage ceramic capacitors are barium titanate base and strontium titanate base. Barium titanate-based ceramic materials have the advantages of high dielectric coefficient and good AC withstand voltage characteristics, but they also have the disadvantages that the capacitance change rate increases with the increase of medium temperature and the insulation resistance decreases. The temperature of the strontium titanate crystal is -250°C, and it has a cubic perovskite structure at room temperature.

It is paraelectric and has no spontaneous polarization. Under high pressure, the dielectric constant of strontium titanate ceramic material does not change much. The dielectric loss tangent (tgδ) and capacitance change rate are very small, and it is a high-voltage capacitor medium.

4. Semiconductor ceramic capacitors

Semiconductor ceramic capacitors are divided into grain boundary layer ceramic capacitors and surface ceramic capacitors, which usually have the characteristics of large capacity, small size and wide operating temperature range. It is suitable for filtering, bypassing, coupling and other circuits. Semiconductor ceramic capacitor is a kind of miniaturized capacitor, that is, the capacitor obtains as large a capacity as possible in as small a volume as possible. This is also one of the trends in the development of capacitors.

For discrete capacitor components, there are two basic approaches to miniaturization:

① Make the dielectric constant of the dielectric material as high as possible;

② Make the thickness of the dielectric layer as thin as possible.

Among ceramic materials, ferroelectric ceramics have a high dielectric constant and are usually used to prepare ceramic capacitors. Common ferroelectric ceramics are mostly of perovskite structure, such as barium titanate ceramics and its solid solution, and there are also tungsten bronze, bismuth-containing layered compounds and pyrochlore structures. However, when using ferroelectric ceramics to make ordinary ferroelectric ceramic capacitors, it is difficult to make the ceramic dielectric very thin. First of all, due to the low strength of ferroelectric ceramics, it is easy to break when it is thin, and it is difficult to carry out actual production operations. Secondly, when the ceramic medium is very thin, it is easy to cause various structural defects, and the production process is very difficult.

(1) Boundarglayer ceramic capacitor

The boundarglayer ceramic capacitor forms an insulating layer along the grain boundary of the semiconductorized ceramic body, and then burns electrodes on both sides of the ceramic chip, thus forming multiple series and parallel capacitor networks. We usually coat appropriate metal oxides (such as CuO or Cu2O, MnO2, Bi2O3, Tl2O3, etc.) on the surface of BaTiO3 semiconductor ceramics with relatively well-developed grains. At an appropriate temperature, it is heat-treated under oxidizing conditions, and the coated oxide will form a low eutectic solution phase with BaTiO3, rapidly diffuse and penetrate into the interior of the ceramic along the open pores and grain boundaries, and form a thin layer on the grain boundaries Solid solution insulating layer. The resistivity of this thin solid solution insulating layer is very high (up to 1012-1013Ω·cm). Although the interior of the ceramic grains is still a semiconductor, the entire ceramic body behaves as an insulator medium with a high apparent dielectric constant. The capacitors prepared with this kind of porcelain are called boundarglayer ceramic capacitors, or BL capacitors for short.

(2) Surface type ceramic capacitors

Surface type semiconducting ceramic capacitor means that the body of the ceramic chip has been semiconducted, and then the surface is re-oxidized to form a very thin dielectric layer, and then the electrodes are fired on both sides of the ceramic chip to form a capacitor. Usually, a very thin insulating layer formed on the surface of semiconductor ceramics such as BaTiO3 is used as the dielectric layer, and the semiconductor ceramic itself can be regarded as a series circuit of the dielectric. The thickness of the insulating surface layer of surface layer ceramic capacitors fluctuates between 0.01 and 100 μm depending on the formation method. This not only utilizes the high dielectric constant of ferroelectric ceramics, but also effectively reduces the thickness of the dielectric layer. This is an effective scheme for preparing microminiature ceramic capacitors.

5. In-line ceramic capacitor

In-line ceramic capacitors are often used in high-stable oscillation circuits, bypass capacitors and pad capacitors for their good stability, good insulation, and high-voltage resistance.

6. AC ceramic capacitor

AC ceramic capacitors are also called safety ceramic capacitors. Y capacitors are used in coupling, DC blocking, filtering and bypass circuits in high-frequency circuits to suppress EMI conduction interference, remove common-mode interference and high-frequency interference above 1M.

7. Multilayer Ceramic Capacitor (MLCC)

It is the most widely used category of chip components. It stacks the internal electrode material and the ceramic body alternately and in parallel in multiple layers, and co-fires them as a whole, also known as chip monolithic capacitor. It has the characteristics of small size, high specific volume and high precision. It can be mounted on printed circuit board (PCB) and hybrid integrated circuit (HIC) substrates, which effectively reduces the volume and weight of electronic information terminal products (especially portable products) and improves product reliability. This also complies with the development direction of the IT industry for miniaturization, light weight, high performance and multi-function.

The country's 2010 long-term goal outline clearly stated that new components such as surface mount components should be the focus of the development of the electronics industry. It not only has simple encapsulation and good sealing performance, but also can effectively isolate the electrodes of the opposite sex. MLCC can store charge, block DC, filter, combine, distinguish different frequencies and tune the circuit in electronic circuits. In high-frequency switching power supply, computer network power supply and mobile communication equipment, it can partially replace organic film capacitors and electrolytic capacitors, greatly improving the filtering performance and anti-interference performance of high-frequency switching power supply.

Ⅲ. Applications of ceramic capacitors

High-voltage ceramic capacitors used in high-power and high-voltage fields are required to have the characteristics of small size, high withstand voltage and good frequency characteristics. With the advancement of materials, electrodes and manufacturing technology, the development of high-voltage ceramic capacitors has made great progress and has been widely used. High-voltage ceramic capacitors have become one of the indispensable components of high-power and high-voltage electronic products. High-voltage ceramic capacitors are mainly used in power equipment for power transmission and distribution systems and equipment that handles pulse energy. It is applied as follows:

1. Industry

The industrial capacitor market mainly includes system communication equipment, industrial control equipment, medical electronic equipment, automotive electronics, precision instrumentation, oil exploration equipment, etc. Industrial equipment is developing towards the trend of mechatronics and intelligence. The continuous improvement of the informatization ratio of application electronic control, data analysis, and interface display will provide a relatively broad market prospect for industrial high-reliability MLCC products.

2. Consumer market

The consumer market includes general consumer products and high-end consumer products. The former includes electronic products such as laptops, televisions, telephones, ordinary mobile phones, and ordinary digital cameras; the latter includes professional recording equipment, professional video equipment, high-end smart phones and other high-end electronic products. Compared with the demand for military and industrial MLCC products, the market demand for consumer products is the largest.

From a global perspective, Japanese manufacturers have a clear lead. Among the top ten MLCC manufacturers in the world, Japanese manufacturers account for more than 40% of the global market sales. The main reason is that Japanese manufacturers lead manufacturers in other countries and regions in cutting-edge high-capacity products and ceramic powder technology. Compared with well-known foreign manufacturers, domestic manufacturers of ceramic capacitors are mostly small and medium-sized enterprises, and most of their products are at the low-to-medium level.

3. Military industry

As a basic electronic component, military MLCC is more and more widely used in military electronic equipment such as aviation, aerospace, military mobile communication equipment, pocket military computers, weapon warhead control and military signal monitoring, radar, artillery fuze, ships, and weapon systems. widely. With the acceleration of digitization and informatization of national defense equipment and the strong demand for localization in the military industry market, the market prospect of military high-reliability MLCC is very broad. In 2009, the market size of China's military MLCC products was 750 million yuan. By 2013, it had grown to 1.44 billion yuan, an increase of nearly double. It is expected that it will still be able to maintain a stable and high growth rate in the future.

Ⅳ. The advantages and disadvantages of ceramic capacitors

1. Advantages

(1) Its physical structure is very compact.

(2) It is reasonably priced and can handle voltages up to 100 volts.

(3) Due to its non-polarization characteristics, it is very suitable for the application of AC signals.

(4) It can improve signal interference suppression, such as radio frequency suppression and electromagnetic interference suppression.

2. Disadvantages

(1) Its capacitance is less than one microfarad.

(2) Because it can easily affect the dielectric in it, it cannot withstand high voltage.

Ⅴ. The development of ceramic capacitors

In recent years, thanks to the development of my country's information industry, digital electronic products have been updated faster and faster. The production and sales of consumer electronic products, mainly flat-panel TVs (LCD and PDP), notebook computers, and digital cameras, continue to grow, driving the growth of the capacitor industry and increasing the market size. At present, my country has become the world's largest capacitor market, accounting for more than 70% of the global market. Capacitor is one of the three major electronic passive components and an indispensable basic component in electronic circuits, accounting for about 40% of all electronic components and 66% of output value. The scale growth rate of China's capacitor industry continues to be higher than the global scale growth rate. The rapid growth of the Chinese market has become the main driving force for the growth of the global capacitor industry.

China's research and production of ceramic capacitors began in the mid-1980s. Through the introduction and absorption of foreign advanced technology, our country has accumulated a certain amount of research and production capacity, and has become a major producer of ceramic capacitors in the world. With the continuous development of my country's ceramic capacitors, the market scale will also continue to expand. Judging from the current domestic competition pattern, most of the well-known foreign ceramic capacitor manufacturers have production bases in my country. Relying on their technology and scale advantages, they occupy a large share of China's civilian ceramic capacitor market, and some high-end products are even in a monopoly position.

In the future, with the rapid development of the downstream application industry of China's ceramic capacitors, the demand for ceramic capacitors will further increase, and the application range of products will continue to expand. At the same time, downstream products are showing a trend of miniaturization, which promotes the development of upstream ceramic capacitors in the direction of miniaturization, ultra-thinning, large capacity, and solid state. However, at present, our country's high-end ceramic capacitors and some raw materials still need to be imported in large quantities, and the localization process is imminent. With the continuous development of production technology of domestic manufacturers, the process of localization of ceramic capacitors in our country will be accelerated.