Classification and characteristics of diodes
Semiconductor diodes mainly rely on PN junctions to work. The point contact type and Schottky type which are inseparable from the PN junction are also included in the range of general diodes. Including these two models, according to the characteristics of the PN structure, the crystal diodes are classified as follows:
1, point contact diode
The point contact type diode is formed by pressing a metal pin on a single wafer of germanium or silicon material and then performing an electric current method. Therefore, the PN junction has a small electrostatic capacitance and is suitable for use in a high frequency circuit. However, compared with the junction type, the point contact type diode has poor forward characteristics and reverse characteristics, and therefore cannot be used for large current and rectification. Because of its simple construction, it is cheap. It is a widely used type for general purposes such as detection, rectification, modulation, mixing and limiting of small signals.
2, key diode
The key diode is formed by fusing or silver filaments on a single wafer of germanium or silicon. Its characteristics are between the point contact diode and the alloy diode. Compared with the point contact type, although the PN junction capacitance of the key diode is slightly increased, the forward characteristic is particularly excellent. It is used for switching, and is sometimes used for detection and power rectification (not more than 50mA). In a key diode, a diode that fuses a gold wire is sometimes referred to as a gold bond type, and a diode that fuses a silver wire is sometimes referred to as a silver bond type.
3. Alloy diode
A PN junction is formed by a method of alloying a metal such as indium or aluminum on a single wafer of N-type germanium or silicon. The forward voltage drop is small, suitable for high current rectification. Since the PN junction is reversed with a large capacitance, it is not suitable for high frequency detection and high frequency rectification.
4, diffusion diode
In a high-temperature P-type impurity gas, a single wafer of N-type germanium or silicon is heated to make a portion of the surface of the single wafer P-type, and the PN junction is obtained by this method. Due to the small forward voltage drop of the PN junction, it is suitable for high current rectification. Recently, the mainstream of using large current rectifiers has been transferred from a silicon alloy type to a silicon diffusion type.
5, mesa type diode
Although the PN junction is fabricated in the same manner as the diffusion type, only the PN junction and its necessary portions are retained, and unnecessary portions are corroded with chemicals. The rest of the section is in the shape of a countertop, hence the name. The countertop type that was initially produced was made by using a diffusion method for semiconductor materials. Therefore, this type of mesa is called a diffusion mesa. For this type, it seems that there are few models for high current rectification, and there are many models for small current switches.
6, planar diode
On a semiconductor single wafer (mainly an N-type silicon single wafer), a P-type impurity is diffused, and a PN junction which is formed by selectively diffusing only a part of the N-type silicon single crystal wafer by the shielding action of the oxide film on the surface of the silicon wafer is diffused. Therefore, there is no need for the corrosive action of the drug for adjusting the PN junction area. The semiconductor surface is named because it is made flat. Further, since the surface of the PN bond is covered by the oxide film, it is recognized as a type having good stability and long life. Initially, the semiconductor material used was formed by an epitaxial method, and the planar type was also referred to as an epitaxial planar type. For planar diodes, it seems that there are few models for high current rectification, and there are many models for small current switches.
7, alloy diffusion diode
It is a type of alloy. Alloy materials are materials that are easily diffused. By making the difficult-to-manufacture material by subtly blending the impurities, it is possible to over-dif with the alloy to obtain an appropriate concentration distribution of the impurities in the already formed PN junction. This method is suitable for manufacturing high sensitivity varactor diodes.
8, epitaxial diode
A diode formed by fabricating a PN junction by a process of epitaxial length. Very high technology is required for manufacturing. Since it is possible to arbitrarily control the distribution of different concentrations of impurities, it is suitable for manufacturing a highly sensitive varactor.
9, Schottky diode
The basic principle is to block the reverse voltage with the already formed Schottky on the contact surface of the metal (for example, lead) and the semiconductor (N-type silicon wafer). There is a fundamental difference between the Schottky and PN junction rectification principles. Its pressure resistance is only about 40V. Its speciality is: the switching speed is very fast: the reverse recovery time trr is particularly short. Therefore, a switching diode and a low-voltage high-current rectifier diode can be fabricated.
Second, according to the purpose of classification
1. Detection diode
In principle, the modulation signal is taken from the input signal as a detection, and the magnitude of the rectified current (100 mA) is used as the boundary. The detection current is usually less than 100 mA.é”—Material point contact type, working frequency up to 400MHz, small forward voltage drop, small junction capacitance, high detection efficiency, good frequency characteristics, 2AP type. A diode for detection like a touch-type type can be used for circuits such as clipping, clipping, modulation, mixing, and switching, in addition to detection. There are also two diode assemblies with good characteristics for frequency modulation detection.
2, rectifier diode
In principle, the DC output from the input AC is rectified. Taking the magnitude of the rectified current (100 mA) as the boundary, the output current is usually greater than 100 mA. Face junction type, the operating frequency is less than KHz, the highest reverse voltage is from 25 volts to 3000 volts A to X total 22 files. The classification is as follows: 1 silicon semiconductor rectifier diode 2CZ type, 2 silicon bridge rectifier QL type, 3 2CLG type used for TV high voltage silicon reactor working frequency nearly 100KHz.
3. Limiting diode
Most diodes can be used as limiting. There are also special limiting diodes like the protection meter and the high frequency Zener. In order to make these diodes have a particularly strong effect of limiting the sharp amplitude, diodes made of silicon material are usually used. There are also components sold: a number of necessary rectifier diodes are connected in series to form a single unit, depending on the voltage limit.
4, modulation diode
Usually referred to as a diode dedicated to ring modulation. It is a combination of four diodes with positive forward characteristics. Even though other varactors have modulation purposes, they are usually used directly as frequency modulation.
5, mixing diode
When the diode mixing method is used, Schottky type and point contact type diodes are often used in the frequency range of 500 to 10,000 Hz.
6, amplifying diode
Amplification with diodes generally approximates the amplification of negative-resistance devices such as tunnel diodes and body-effect diodes, as well as parametric amplification with varactors. Therefore, the diode for amplification generally refers to a tunnel diode, a body effect diode, and a varactor diode.
7, switching diode
There are logic operations used at low currents (10 mA) and magnetic core excitation switching diodes used at hundreds of milliamps. Low-current switching diodes are typically diode-type and key-type diodes, as well as silicon-diffused, mesa-type and planar diodes that can operate at high temperatures. The specialty of switching diodes is the fast switching speed. The Schottky diode has an extremely short switching time and is therefore an ideal switching diode. 2AK type point contact is used for medium speed switch circuit; 2CK type plane contact is used for high speed switch circuit; used for circuit of switching, limiting, clamping or detecting; Schottky (SBD) silicon high current switch, forward voltage drop Small, fast and efficient.
8, varactor diode
Small power diodes for automatic frequency control (AFC) and tuning are called varactors. There are many other names in Japanese manufacturers. The electrostatic capacitance of the PN junction is changed by applying a reverse voltage. Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation, and tuning. Usually, although a diffusion diode using silicon is used, a specially fabricated diode such as an alloy diffusion type, an epitaxial type, or a double diffusion type can be used because these diodes have a particularly large rate of change in electrostatic capacitance with respect to voltage. The junction capacitance changes with the reverse voltage VR, instead of the variable capacitor, it is used as a tuning loop, an oscillating circuit, a phase-locked loop, and is commonly used for channel switching and tuning circuits of television tuner, mostly made of silicon material.
9, frequency doubled diode
For frequency multiplication of diodes, there is a frequency multiplication by varactors and a frequency multiplication by a step (ie, jerk) diode. The varactor diode for frequency multiplication is called a varactor. Although the varactor works the same as the varactor diode for automatic frequency control, the structure of the reactor can withstand high power. The step diode, which is also called a step recovery diode, has a short reverse recovery time trr when switching from on to off, and therefore its characteristic is that the transition time that rapidly becomes off is significantly short. If a sine wave is applied to the step diode, since the tt (transition time) is short, the output waveform is suddenly pinched off, so that many high-frequency harmonics can be generated.
10, Zener diode
It is a product that replaces the regulated electronic diode. It is made into a diffusion type or an alloy type of silicon. It is a diode whose reverse breakdown characteristic curve changes rapidly. Made as a control voltage and standard voltage. The terminal voltage (also known as Zener voltage) when the diode is working is from about 3V to 150V, and can be divided into many grades every 10%. In terms of power, there are also products ranging from 200mW to more than 100W. Working in the reverse breakdown state, made of silicon material, the dynamic resistance RZ is small, generally 2CW type; the two complementary diodes are reversely connected in series to reduce the temperature coefficient is 2DW type.
11, PIN type diode (PIN Diode)
This is a crystal diode in which a layer of intrinsic semiconductor (or a semiconductor having a low concentration of impurities) is sandwiched between the P region and the N region. The I in the PIN is an English abbreviation of the meaning of "intrinsic". When its operating frequency exceeds 100MHz, due to the storage effect of minority carriers and the transit time effect in the "intrinsic" layer, its diode loses rectification and becomes an impedance element, and its impedance value varies with the bias voltage. And change. In the case of zero bias or DC reverse bias, the impedance of the "intrinsic" region is very high; when the DC is forward biased, the "intrinsic" region is presented due to the carrier being injected into the "intrinsic" region. Low impedance state. Therefore, the PIN diode can be used as a variable impedance element. It is often used in high frequency switching (ie microwave switching), phase shifting, modulation, limiting and other circuits.
12. Avalanche Diode
It is a transistor that can generate high frequency oscillations under the action of an applied voltage. The working principle of generating high-frequency oscillation is flawed: the carrier is injected into the crystal by avalanche breakdown. Since the carrier takes a certain time to pass the wafer, the current lags behind the voltage, and a delay time occurs. The more time, then, the negative resistance effect occurs in the relationship between current and voltage, resulting in high frequency oscillation. It is often used in oscillating circuits in the microwave field.
13. Jiangsui Diode (Tunnel Diode)
It is a crystal diode with a tunneling current as the main current component. The base materials are gallium arsenide and antimony. The N-type region of its P-type region is highly doped (i.e., highly concentrated). The tunneling current is produced by the quantum mechanical effects of these degenerate semiconductors. Tunneling has three conditions: 1 Fermi level is in the conduction band and full band; 2 space charge layer width must be very narrow (below 0.01 microns); holes in degenerate semiconductor P-type and N-type regions There is the possibility of overlapping with electrons at the same energy level. The Jiangsaki diode is a two-terminal active device. The main parameters are peak-to-valley current ratio (IP/PV), where the subscript "P" stands for "peak" and the subscript "V" stands for "valley". The Jiangsaki diode can be used in low-noise high-frequency amplifiers and high-frequency oscillators (which operate at frequencies up to the millimeter band) and can also be used in high-speed switching circuits.
14, fast shutdown (step recovery) diode (Step Recovary Diode)
It is also a diode with a PN junction. Its structural characteristics are: there is a steep impurity distribution area at the boundary of the PN junction, thereby forming a "self-service electric field". Since the PN junction is under forward bias, it conducts with minority carriers and has a charge storage effect near the PN junction, so that its reverse current needs to undergo a "storage time" before it can be reduced to a minimum (reverse Saturation current value). The "self-service electric field" of the step recovery diode shortens the storage time, allows the reverse current to be quickly turned off, and produces rich harmonic components. A comb spectrum generation circuit can be designed using these harmonic components. Fast turn-off (step recovery) diodes are used in pulse and higher harmonic circuits.
15. Schottky Barrier Diode
It is a "metal-semiconductor junction" diode with Schottky characteristics. Its forward starting voltage is lower. In addition to the material, the metal layer may also be made of gold, molybdenum, nickel, titanium or the like. Its semiconductor material uses silicon or gallium arsenide, mostly N-type semiconductors. This device is electrically conductive by majority carriers, so its reverse saturation current is much larger than that of a minority carrier-conducting PN junction. Since the minority carrier in the Schottky diode has a very small memory effect, its frequency response is only limited by the RC time constant. Therefore, it is an ideal device for high frequency and fast switching. It operates at frequencies up to 100 GHz. Also, MIS (Metal-Insulator-Semiconductor) Schottky diodes can be used to fabricate solar cells or light-emitting diodes.
16, damper diode
It has high reverse working voltage and peak current, low forward voltage drop, high frequency high voltage rectifier diode, used in TV line scanning circuit for damping and boost rectifier.
17. Transient voltage suppression diode
TVP tube, which provides fast overvoltage protection for the circuit, divided into bipolar and unipolar, classified by peak power (500W-5000W) and voltage (8.2V~200V).
18, double base diode (single junction transistor)
Two bases, one emitter three-terminal negative resistance device, are used for the relaxation oscillation circuit, and the timing voltage readout circuit has the advantages of easy frequency adjustment and good temperature stability.
19. Light-emitting diode
Made of gallium phosphide or phosphorous arsenide material, it is small in size and positively drives light. Low working voltage, small working current, uniform illumination, long life, red, yellow and green monochromatic light.
Third, according to the characteristics of classification
Point contact diodes are classified as follows according to the forward and reverse characteristics.
1. Generally use point contact diodes
Such diodes, as the title says, are commonly used in detection and rectification circuits and are intermediate products where the forward and reverse characteristics are neither particularly good nor particularly bad. Such as: SD34, SD46, 1N34A, etc. fall into this category.
2, high reverse withstand voltage point contact diode
It is a product with a maximum peak reverse voltage and a maximum DC reverse voltage. Used for detection and rectification of high voltage circuits. This type of diode generally has poor forward characteristics or is generally inferior. Among the point contact type germanium diodes, there are SD38, 1N38A, OA81 and the like. This tantalum material diode is limited in withstand voltage. Silicon alloys and diffusion types are required when higher.
3, high reverse resistance point contact diode
The forward voltage characteristics are the same as those of a general diode. Although the withstand voltage in the reverse direction is particularly high, the reverse current is small, so the characteristic is that the reverse resistance is high. For circuits with high input resistance and high resistance load resistance circuits, SD54, 1N54A, etc. are suitable for such high-reverse-resistance diodes.
4, high conduction point contact diode
It is the opposite of the high reverse resistance type. Its reverse characteristic, although poor, makes the forward resistance small enough. For high-conductivity point contact diodes, there are SD56, 1N56A, and so on. For high conductivity key diodes, better characteristics can be obtained. Such diodes have higher rectification efficiency when the load resistance is particularly low.
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