A transistor is a device composed of three layers of impurity semiconductors and has three electrodes, so it is also called a semiconductor triode., which can be used for detection, rectification, amplification, switching, voltage stabilization, signal modulation and many other functions. The low cost, flexibility and reliability of transistors make them a ubiquitous device. Transistor mechatronic circuits have become electromechanical equipment control devices to control machines. Compared with mechanical control systems, microcontrollers and computer programs are more convenient to control the system. So what are the types of transistors? Let's take a look:
1. Classification
1.1 Classified by function and purpose
Transistors can be divided into low noise amplifier transistors, medium and high-frequency amplifier transistors, low-frequency amplifier transistors, switching transistors, Darlington transistors, high back-voltage transistors, band resistance transistors, damped transistors, microwave transistors, phototransistors, and magnetic transistors and other types.
1.2 Classified by semiconductor material and polarity
Semiconductor materials used in transistors can be divided into silicon transistors and germanium transistors. According to the polarity of the transistor, it can be divided into germanium NPN transistor, germanium PNP transistor, silicon NPN transistor and silicon PNP transistor.
1.3 Classified by structure and manufacturing process
Transistors can be divided into diffusion transistors, alloy transistors and planar transistors according to their structure and manufacturing process.
1.4 Classification by current capacity
Transistors can be divided into low-power transistors, medium-power transistors and high-power transistors according to their current capacity.
1.5 Classification by operating frequency
Transistors can be divided into low-frequency transistors, high-frequency transistors and ultra-high-frequency transistors according to their operating frequency.
1.6 Classified by package structure
Transistors can be divided into gold sealed transistors, plastic sealed transistors, glass sealed transistors, surface mount (chip) transistors, and ceramic transistors according to their packaging structure. There are various package outlines.
2. Specific Types
2.1 Bipolar Junction Transistors
Bipolar Junction Transistor (BJT) is also called a semiconductor transistor. It is a device that combines two PN junctions through a certain process.
There are two combined structures of PNP and NPN, and three poles are drawn from the outside: collector, emitter and base. The collector is drawn from the collector region, the emitter is drawn from the emitter region, and the base is drawn from the base region (the base region is in the middle).
BJT has an amplifying effect, relying on its emitter current achieving the collector area through base area. In order to ensure this transmission process, on the one hand, internal conditions must be met, that is, the impurity concentration of the emitter area must be much greater than the impurity concentration of the base area, and the thickness of the base area must be small. Also, the external conditions must be met, that is, the emitter junction must be forward biased (apply forward voltage), and the collector junction must be reverse biased.
There are many types of BJTs.
According to frequency: high-frequency transistors and low-frequency transistors;
According to power: small, medium, and high-power transistors;
According to semiconductor materials: silicon transistors and germanium transistors, etc..
The amplifying circuit forms with BJTs are: common emitter, common base and common collector amplifying circuits.
2.2 Field Effect Transistor
Field-effect transistor is a transistor that uses the principle of field effect, abbreviated to FET. The field effect is to change the direction or size of the electric field applied perpendicular to the surface of the semiconductor to control the density or type of majority carriers in the semiconductor conductive layer (channel). It modulates the current in the channel by voltage, and its working current is transported by majority carriers in the semiconductor.
The transistor in which only one polar carrier participates in conduction is also called a unipolar transistor. Compared with bipolar transistors, field-effect transistors have high input impedance, low noise, high limit frequency, low power consumption, simple manufacturing process, and good temperature characteristics. They are widely used in various amplifying circuits, digital circuits and microwave circuits.
The metal-oxide-semiconductor field-effect transistor (MOSFET) is based on silicon material and the Schottky barrier gate field-effect transistor (MESFET) based on gallium arsenide material are the two most important field effect transistors, which are respectively the basic device of MOS large-scale integrated circuit and MES ultra-high-speed integrated circuit.
2.3 Insulated Gate Bipolar Transistor
Insulate-Gate Bipolar Transistor (IGBT) combines the advantages of the giant transistor(GTR) and power MOSFET, has good characteristics, and a wide range of applications. IGBTs also have three terminals, grid, collector and emitter.
IGBT is a bipolar device with a MOS structure, which is a power device with the high-speed performance of a power MOSFET and the bipolar low-resistance performance. The application range of IGBT is generally in the region where the withstand voltage is above 600V, the current is above 10A, and the frequency is above 1kHz. It is mostly used in industrial motors, civil small-capacity motors, converters (inverters), stroboscopes for cameras, induction heating rice cookers and other fields.
According to the different packages, IGBTs are roughly divided into two types. One is a three-terminal monolithic package type sealed by molded resin, which has formed a series from TO-3P to small surface mount. The other is a module type in which IGBTs and FWD (Flee Wheel Diode) are packaged in pairs (2 or 6 groups), which are mainly used in the industry. The types of modules have various shapes and packaging methods according to different uses, all of which have been serialized.
2.4 Static induction transistor
SIT (Static Induction Transistor) was born in 1970 and is actually a junction field-effect transistor. It has high input impedance, high output power, good switching characteristics, good thermal stability and strong radiation resistance.
SIT adopts multi-unit integration technology in structural design, so it can be made into high-voltage and high-power devices. It can not only work in the on-off state as a high-power current switch, but also as a power amplifier for high-power medium frequency transmitters, long-wave radios, transponders, high-frequency induction heating devices, and radars. At present, SIT products have reached a voltage of 1500V, a current of 300A, power dissipation of 3kW, and a cut-off frequency of 30-50MHz.
However, the SIT is turned on when no signal is applied to the gate, and it is turned off when the gate is negatively biased. This is called a normal conduction device and is not convenient to use. In addition, the on-state resistance of SIT is large, which makes the on-state loss also large, so SIT has not been widely used in most power electronic equipment.
2.5 Single Electron Transistor
A transistor that can record signals with one or a small number of electrons. With the development of semiconductor etching technology and technology, the integration of large-scale integrated circuits is getting higher and higher. Take dynamic random access memory (DRAM) as an example, its integration level is growing at a rate of almost four times every two years. It is expected that single-electron transistors will be the ultimate goal.
At present, the general memory contains 200,000 electrons in each storage element, while the single-electron transistor only contains one or a small number of electrons in each storage element. Therefore, it will greatly reduce power consumption and improve the integration of integrated circuits. In 1989, J.H. F. Scott-Thomas and his team discovered the Coulomb obstruction in experiments. On the two-dimensional electron gas formed by the modulated-doped heterojunction interface, a metal electrode with a small area is made, so that a quantum dot is formed in the two-dimensional electron gas, which can only hold a small number of electrons with a very small capacitance of 10-15 farads.
When a voltage is applied, if the change in the voltage causes the charges in the quantum dot to change by less than an electron, no current will flow through until the voltage increases to cause an electron to change. Therefore, the current-voltage relationship is not in the usual linear relationship, but a stepped shape.
For the first time in history, this experiment realized the manual control of the movement of an electron, which provided an experimental basis for manufacturing single-electron transistors. In order to increase the operating temperature of single-electron transistors, the size of quantum dots must be less than 10 nanometers.
Currently, laboratories around the world are thinking of various ways to solve this problem. Some laboratories claim that they have produced single-electron transistors that work at room temperature, and they have observed stepped current-voltage curves formed by electron transport, but they are still far from practical.
2.6 Giant Transistor
A giant Transistor is a kind of bipolar junction transistor that can withstand high voltage and large current, so it is sometimes called Power BJT.
It has high voltage resistance, large current, good switching characteristics. But the driving circuit is complex, and the driving power is large. The working principle of GTR and ordinary bipolar junction transistors is the same.
2.7 Phototransistor
A phototransistor is a photoelectric device composed of three-terminal devices such as bipolar transistors or field-effect transistors. Light is absorbed in the active area of this type of device to generate photo-generated carriers, which generate photocurrent gain through the internal electrical amplifying mechanism.
The phototransistor works with three terminals, so it is easy to realize electric control or electric synchronization. The material used for phototransistors is usually gallium arsenide (GaAs).
It is mainly divided into bipolar phototransistors, field-effect phototransistors and related devices. Bipolar phototransistors usually have high gain, but not too fast. For GaAs-GaAlAs phototransistors, the amplification factor can be greater than 1000, and the response time is greater than nanoseconds, which is often used for photodetectors and can also be used for optical amplification.
The field-effect phototransistor has a fast response speed (about 50 picoseconds), but the disadvantage is that the photosensitive area is small and the gain is small (the amplification factor can be greater than 10), and it is often used as an extremely high-speed photodetector. Besides, there are many other planar optoelectronic devices, all of which have fast speed (response time of tens of picoseconds) and are suitable for integration. Such devices are expected to be used in optoelectronic integration.
The above is an example of the classification and types of transistors. The advancement of transistor manufacturing and production technology has reduced the cost of computers and make computers become more popular, speeding up the pace of informationization of human society, and saving a lot of manpower and material resources. Many of today's production activities are completed indirectly by humans through various tools. It can be said that the development and progress of transistors have accelerated the progress of human civilization.
For more interesting details about the transistors, try to read this:
What are Transistors and How do They Work?