Capacitors

Capacitors

The capacitors are components incapable of controlling current by means of another electrical signal.its called passive devices.The Capacitors store and release electrical charge.  In other words, A capacitor is an electronic device that stores electric charge or electricity when voltage is applied and releases stored electric charge whenever required. capacitors are most widely used electronic components after resistors. 

The capacitor acts as a small battery that charges and discharges rapidly. Any object, which can store electric charge, is a capacitor. Capacitor is also sometimes referred as a condenser.

What is electric charge?

The electric charges is the basic property of particles such as electrons and protons. This electric charge causes them to experience an attractive or repulsive force when placed in an electromagnetic field.Electric charges are of two types-- positive and negative. 

Electrons have negative charge and protons have positive charge. Like gravitational energy present around the planets like Earth, electrical energy is present around the charged particles such as electrons and protons. However, he charged particles exert force only up to a small distance around them and beyond that they cannot exert force. The region up to which the charged particles exert force is called electric field. If we place any charged particle within this region, it will experience a force.

The electrical energy or electric charge present around the charged particle is represented by the electric lines of force. The direction of these electric lines of force is different for positive charge and negative charge. For positive charge, the electric lines of force begin from the center particle and flows away from it. For negative charge, the electric lines of force begins away from the charged particle and move towards its center.In electronics, hole is considered as the positive charge.

When the negative charged particle (electron) is placed within the electric field of positively charged particle (proton), it gets attracted. On the other hand, when the positively charged particle(proton) is placed within the electric field of another proton, it gets repelled. In other words, opposite electric charges attract each other and same electric charges repel each other.

Construction of a capacitor--
The basic construction of all capacitors is similar. The construction of capacitor is very simple. A capacitor is made of two electrically conductive plates placed close to each other, but they do not touch each other.  These conductive plates are normally made of material such as aluminum, brass, or copper.
The conductive plates of a capacitor is separated by a small distance. The empty space between these plates is filled with a non-conductive material or electric insulator or dielectric region. The non-conductive material or region between the two plates may be an air, vacuum, glass, liquid, or solid.

This non-conductive material is called dielectric.the two conductive plates of the capacitor are good conductors of electricity. Therefore, they can easily pass the electric current through them. The conductive plates of the capacitor also hold the electric charge. In capacitors, these plates are mainly used to hold or store the electric charge.

A dielectric material or medium is the poor conductor of electricity. they cannot pass electric current through them. In capacitors, the dielectric medium or material block the flow of charge carriers (especially electrons) between the conductive plates. As a result, the electric charges that try to move from one plate to another plate will be trapped with the plate because of the strong resistance from the dielectric.

If we place the conductive medium between these plates, the electric charges flow easily from one plate to another plate. However, electric current flow between the plates is not desirable. It indicates the failure of capacitor.

we know that electric current is the flow of charge carriers whereas electric force or electric field is the properly of electric charges. Dielectric material does not allow the flow of charge carriers, but they allow the electric force, electric charge, or electric field produced by the charged particles (electrons). As a result, when charge is build up on the two plates, a strong electric field is generated between the two plates.
                                    
They are used for filtering power supply lines, tuning resonant circuits, and for blocking DC voltages while passing AC signals, among numerous other uses

What is Capacitance?

The ability of a capacitor to store electric charge is called capacitance. capacitors with high capacitance will store large amount of electric charge whereas the capacitors with low capacitance will store small amount of electric charge.

The capacitance of a capacitor can be compared with the size of a water tank; the larger the water tank, the more water it can store, In the similar way, the larger the capacitance, the more electric charge or electricity it can store.
 The capacitance of a capacitor is mainly depends on the size of the plates facing each other, the spacing between two conductive plates, and the dielectric constant of the material between the plates.

The capacitance of a capacitor is directly proportional to the size of conductive plates and inversely proportional to the distance between two plates in other words, the capacitor with large conductive plates stores large amount of electric charge whereas the capacitor with small conductive plates stores small amount of electric electric charge. and we can say the capacitor with large separation distance between the plates has low capacitance (low charge storage) whereas the capacitor with small separation distance between the plates has high capacitance( high charge storage)

Measurement of  a capacitance--- the capacitance of a capacitor is measured in farad. It is represented by a symbol F. Farad is named after the English physicist Michael Faraday. A 1 farad capacitor charged with 1 coulomb of electric charge has a potential difference or voltage of 1 Volt between it s plates. One farad is very large amount of capacitance. Hence, in most cases we use very small unit of capacitance. The most common sub units of capacitance we use today are micro farad (µF) 
Nano farad nF, Picofarad (pF) and Femofarad (fF)

1 Micro farad= 10-6 farads 
1 Nano farad =10-9 farads
1 Pico farad = 10-12 farads
1 Femo farad -10-15 farads

There are many types of capacitor like Integrated capacitors - In integrated circuits, nano-scale capacitors can be formed by appropriate patterns of materialization on an isolating substrate. They may be packaged in multiple capacitor arrays with no other semi conductive parts as discrete components

1.  MIS capacitor. -- A MIS capacitor is a capacitor formed from a layer of metal, a layer of insulating material and a layer of semiconductor material. It gets its name from the initials of he metal - insulator- semiconductor structure. As with the MOS field-effect transistor structure, for historical reasons, this layer is also often referred to  as a MOS capacitor, but  this specifically refers to an oxide insulator material.The production method depends on materials used (it is even possible that polymers can be used as the insulator). The example of a MOS capacitor based on silicon and silicon dioxide. On the semiconductor substrate, a thin layer of oxide(silicon dioxide) is applied (by, for example, thermal oxidation, or chemical vapour deposition) and then coated with a metal                                                                                                      
2. Trench capacitor.-- New technologies and new device concepts are necessary to meet the demands. In this work, a trench capacitor developed for RF applications is presented for the first time. This so- called SilCap (silicon capacitor) device features very high capacitance density, extreme low-voltage dependence, excellent temperature stability, good RF performance and a high breakthrough voltage. First, the device function and the technological concept are introduced.The concept is realized without implementing cost-intensive high-k materials. This trench capacitor is integrated in the front end of line of a passive integration technology. The achieved specific capacitance density is compared to a standard planar capacitor.. Performance of the SilCap in terms of quality factor and breakthrough voltage is shown. Finally, reliability data of this Trench capacitor are presented with special focus on extrinsic and dielectric lifetime.

 Fixed capacitors-- As we know capacitor is an electronic device that stores electric charge. when voltage is applied to the capacitor, it stores electric charge. This charge storage may be fixed or variable depends upon the type of capacitor. The fixed capacitors is a type of capacitor which provides fixed amount of capacitance( capacitance means ability to store electric charge) in other words, fixed capacitor is a type of capacitor that stores fixed amount of electric charge which is not adjustable.
   
Ceramic capacitor-- the ceramic capacitor are used when large charge storage and small physical size is required. They are mostly used capacitors in the electronic circuits. In ceramic capacitor, ceramic material is used as dielectric and conductive metals are used as electrodes. Ceramic material is chosen as dielectric because of its great ability to allow electrostatic repulsion and attraction. Ceramic dielectric is poor conductor of electricity. therefore, it does electric current between two electrodes. However, ceramic dielectric electric field between two electrodes.

1. Film capacitor
2. Electrolytic capacitor
3. Aluminum electrolytic capacitor
4. Tantalum electrolytic capacitor
5. Niobium electrolytic capacitor
6. Polymer capacitor OS-CON

Super capacitor (Electric double-layer-capacitor) -- super capacitors can store large amount of electric charge compared to the electrolytic and all other types of conventional capacitors. Super capacitors are also known as ultra capacitors or electric double layer capacitors. Super capacitor consists of two electrodes, separator and electrolyte. The electrolyte is the mixture of negative ions and positive ions dissolved in water. The two electrodes of the super capacitor are separated by a separator.

1. Nano ionic super capacitor
2. Lithium-iron capacitor

Variable capacitor-- it is a adjustable capacitance

1. Tuning capacitor- Variable capacitor for tuning a radio, oscillator, or tuned circuit.
2. Trim capacitor-- small variable capacitor for seldom or rare adjustments of LC-Circuit
3. Vacuum variable capacitor

Capacitors for special applications

1. Power capacitor 
2. Safety capacitor
3. Filter capacitor
4. Light-emitting capacitor
5. Motor capacitor
6. Photo flash capacitor

Capacitor network(array)
Varicap diode - AC capacitance varies according to the DC voltage applied