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How much do you know about Schottky diodes?

Source:Dongguan Hoen Semiconductor Co.,Ltd. Popularity:58 Time:2020-07-02 23:45:04
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The 21st century is an era of Internet informatization, and this era has achieved many great technologies. Electronic components such as Schottky diodes may seem insignificant, but their role in these technological achievements cannot be underestimated. Many scientific and technological achievements are inseparable from these small semiconductor electronic components. How much do you know about it?
  
The inventor of Schottky diode is Dr. Schottky (Schottky), the name of this element is also named after Dr. Schottky, Schottky barrier diode (Schottky Barrier Diode, abbreviated as SBD) is referred to as SBD. It is not made using the principle of P-type semiconductor and N-type semiconductor contact to form a PN junction, but is made using the principle of metal-semiconductor junction formed by the contact of metal and semiconductor. Therefore, SBD is also called metal-semiconductor (contact) diode or surface barrier diode, it is a kind of hot carrier diode.
  
  Principle
  
  Schottky diode is a metal-semiconductor device made of precious metal (gold, silver, aluminum, platinum, etc.) A as the positive electrode and N-type semiconductor B as the negative electrode. The barrier formed on the contact surface of the two has rectifying characteristics. Because there are a large number of electrons in the N-type semiconductor, there are only a few free electrons in the precious metal, so the electrons diffuse from the high concentration B to the low concentration A. Obviously, there are no holes in metal A, so there is no hole diffusion from A to B. As electrons continue to diffuse from B to A, the electron concentration on the surface of B gradually decreases, and the surface electrical neutrality is destroyed, so a potential barrier is formed, and the direction of the electric field is B→A. However, under the action of this electric field, the electrons in A will also drift from A→B, thus weakening the electric field formed by the diffusion motion. When a space charge region with a certain width is established, the electron drift motion caused by the electric field and the electron diffusion motion caused by different concentrations reach a relative balance, and a Schottky barrier is formed.
  
   The internal circuit structure of a typical Schottky rectifier is based on an N-type semiconductor, and an N-epitaxial layer using arsenic as a dopant is formed on it. The anode uses molybdenum or aluminum and other materials to make the barrier layer. Use silicon dioxide (SiO2) to eliminate the electric field in the edge area and improve the pressure resistance of the tube. The N-type substrate has a very small on-state resistance, and its doping concentration is 100% higher than that of the H-layer. An N+ cathode layer is formed under the substrate, and its function is to reduce the contact resistance of the cathode. By adjusting the structural parameters, a Schottky barrier is formed between the N-type substrate and the anode metal, as shown in the figure. When a forward bias is applied to both ends of the Schottky barrier (the anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode of the power supply), the Schottky barrier layer becomes narrower and its internal resistance becomes smaller; otherwise, if When a reverse bias is applied across the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.
  
In summary, the structural principle of Schottky rectifiers is very different from PN junction rectifiers. Usually PN junction rectifiers are called junction rectifiers, and metal-semiconductor rectifiers are called Schottky rectifiers. Aluminum-silicon Schottky diodes manufactured using silicon planar technology have also been introduced, which not only saves precious metals, greatly reduces costs, but also improves the consistency of parameters.
  
   Disadvantages
  
The biggest disadvantage of Schottky diodes is their low reverse bias voltage and large reverse leakage current. Like Schottky diodes that use silicon and metals as their materials, their reverse bias voltages have the highest rated withstand voltage. To 50V, and the reverse leakage current value is a positive temperature characteristic, it is easy to increase rapidly as the temperature rises, and practical design needs to pay attention to the hidden worry of thermal runaway. In order to avoid the above problems, the reverse bias of Schottky diodes in actual use will be much smaller than their rated values. However, the technology of Schottky diodes has also been improved, and its reverse bias voltage can be rated up to 200V.
  
The main advantages of    include two aspects:
  
   1. Because the height of the Schottky barrier is lower than the height of the PN junction barrier, its forward conduction threshold voltage and forward voltage drop are lower than the PN junction diode (about 0.2V lower).
  
   2. Since SBD is a majority carrier conductive device, there are no minority carrier lifetime and reverse recovery problems. The reverse recovery time of SBD is only the charging and discharging time of Schottky barrier capacitor, which is completely different from the reverse recovery time of PN junction diode. Since the reverse recovery charge of SBD is very small, the switching speed is very fast, and the switching loss is particularly small, which is especially suitable for high frequency applications. However, since the reverse barrier of the SBD is thin and breakdown easily occurs on its surface, the reverse breakdown voltage is relatively low. Since SBD is more susceptible to thermal breakdown than PN junction diodes, the reverse leakage current is larger than PN junction diodes.
  
Schottky diodes have many applications in the semiconductor industry. The use of Schottky diodes has been on the market for decades. Its development and products have continuously enhanced its characteristics and the possibility of multiple applications. It has also been expanded. In addition to the previous solar panels and cars, it is now also used in battery chargers for smartphones, laptops, and tablets.

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