Schottky knowledge introduction introduction topic
How Schottky diodes work
1. Structural principle
The Schottky diode is a multi-genus semiconductor device in which noble metal (gold, silver, aluminum, platinum, etc.) A is a positive electrode, and N-type B is a negative electrode, and a barrier formed on the contact surface thereof has a rectifying property. Since there are a large number of N-type semiconductors and only a very small amount of free electrons in the noble metal, the electrons diffuse from the high concentration B to the low concentration A. Obviously, there is no hole in the metal A, and there is no diffusion movement of holes from A to B. As the electrons continue to diffuse from B to A, the surface of the electron concentration on the B surface gradually decreases in the light industrial sector, and the surface electrical neutrality is destroyed, thus forming a barrier with an electric field direction of B→A. However, under the action of the electric field, the electrons in A also produce a drift motion from A→B, thereby weakening the electricity formed by the diffusion motion. When the space charge region of a certain width is established, the electrons caused by the electric field The electron diffusion movement caused by the drift motion and the concentration is relatively balanced, and a Schottky barrier is formed.
The internal structure of a typical Schottky rectifier is shown in Figure 1. It is based on an N-type semiconductor on which an N- epitaxial layer using arsenic as a dopant is formed. The anode (barrier layer) metal is molybdenum. Dioxide (SiO2) is used to eliminate the electric field in the edge region and increase the withstand voltage of the tube. The N-type substrate has a small on-state with a doping concentration 100% higher than that of the H-layer. An N+ cathode layer is formed under the substrate to reduce the contact resistance of the cathode. By adjusting the structural parameters, a suitable Schottky barrier can be formed between the substrate and the anode metal. When a positive bias voltage E is applied, the positive and negative electrodes of the metal A and the N-type substrate B are respectively connected. The width Wo is narrowed. When the negative bias -E is applied, the barrier width increases.
In summary, the structural principle of the Schottky rectifier is very different from that of the PN junction rectifier. The PN junction rectifier is usually called a junction rectifier, and the metal-semiconductor rectifier is called a Schottky rectifier. In recent years, aluminum-silicon Schottky diodes fabricated using a silicon planar process have also been introduced, which not only saves precious metals, significantly reduces costs, but also improves parameter consistency.
The Schottky rectifier uses only one kind of carrier (electron) to transport the charge, and there is no excess of minority carriers on the outside of the barrier. Therefore, there is no charge storage problem (Qrr→0), which makes the switching characteristics visible. improve. Its reverse recovery time can be shortened to less than 10ns. However, its reverse withstand voltage is low, generally not exceeding 100V when going. Therefore, it is suitable to work under high current conditions. With its low dropout characteristics, the efficiency of low voltage, high current rectification (or freewheeling) circuits can be improved.
2. Performance comparison
Table 1 lists the performance comparisons of Schottky diodes for ultra-fast, fast recovery diodes, silicon high-frequency, and silicon high-speed switching diodes. It can be seen from the table that although the trr of the silicon high-speed switching diode is extremely low, the average rectified current is small and cannot be used for large current rectification.
How Schottky diodes work
1. Structural principle
The Schottky diode is a multi-genus semiconductor device in which noble metal (gold, silver, aluminum, platinum, etc.) A is a positive electrode, and N-type B is a negative electrode, and a barrier formed on the contact surface thereof has a rectifying property. Since there are a large number of N-type semiconductors and only a very small amount of free electrons in the noble metal, the electrons diffuse from the high concentration B to the low concentration A. Obviously, there is no hole in the metal A, and there is no diffusion movement of holes from A to B. As the electrons continue to diffuse from B to A, the surface of the electron concentration on the B surface gradually decreases in the light industrial sector, and the surface electrical neutrality is destroyed, thus forming a barrier with an electric field direction of B→A. However, under the action of the electric field, the electrons in A also produce a drift motion from A→B, thereby weakening the electricity formed by the diffusion motion. When the space charge region of a certain width is established, the electrons caused by the electric field The electron diffusion movement caused by the drift motion and the concentration is relatively balanced, and a Schottky barrier is formed.
The internal structure of a typical Schottky rectifier is shown in Figure 1. It is based on an N-type semiconductor on which an N- epitaxial layer using arsenic as a dopant is formed. The anode (barrier layer) metal is molybdenum. Dioxide (SiO2) is used to eliminate the electric field in the edge region and increase the withstand voltage of the tube. The N-type substrate has a small on-state with a doping concentration 100% higher than that of the H-layer. An N+ cathode layer is formed under the substrate to reduce the contact resistance of the cathode. By adjusting the structural parameters, a suitable Schottky barrier can be formed between the substrate and the anode metal. When a positive bias voltage E is applied, the positive and negative electrodes of the metal A and the N-type substrate B are respectively connected. The width Wo is narrowed. When the negative bias -E is applied, the barrier width increases.
In summary, the structural principle of the Schottky rectifier is very different from that of the PN junction rectifier. The PN junction rectifier is usually called a junction rectifier, and the metal-semiconductor rectifier is called a Schottky rectifier. In recent years, aluminum-silicon Schottky diodes fabricated using a silicon planar process have also been introduced, which not only saves precious metals, significantly reduces costs, but also improves parameter consistency.
The Schottky rectifier uses only one kind of carrier (electron) to transport the charge, and there is no excess of minority carriers on the outside of the barrier. Therefore, there is no charge storage problem (Qrr→0), which makes the switching characteristics visible. improve. Its reverse recovery time can be shortened to less than 10ns. However, its reverse withstand voltage is low, generally not exceeding 100V when going. Therefore, it is suitable to work under high current conditions. With its low dropout characteristics, the efficiency of low voltage, high current rectification (or freewheeling) circuits can be improved.
2. Performance comparison
Table 1 lists the performance comparisons of Schottky diodes for ultra-fast, fast recovery diodes, silicon high-frequency, and silicon high-speed switching diodes. It can be seen from the table that although the trr of the silicon high-speed switching diode is extremely low, the average rectified current is small and cannot be used for large current rectification.
Shenzhen Ever-smart Sensor Technology Co., LTD , https://www.fluhandy.com