With the progress and development of society, the application of MOS tubes in the electronics industry has become more and more extensive. As a "silicon carbide expert" who can develop and produce silicon carbide SiC products, Saco Microelectronics SLKOR must come to popularize this knowledge.
MOS is short for MOSFET, and the full name is metal oxide field effect transistor. It is a semiconductor device that uses the electric field effect of the input loop to control the output loop current. The structure, principle, characteristics, symbol rules and package types of MOS tubes are roughly as follows.
1. The structure of MOS tube:
The structure of the MOS tube is on a P-type semiconductor silicon substrate with a lower doping concentration. Two N+ regions with a high doping concentration are fabricated by semiconductor photolithography and diffusion processes, and two electrodes are led out by metal aluminum as drains. Pole D and source S. Then the P-type semiconductor surface between the drain and the source is covered with a very thin silicon dioxide (SiO2) insulating film, and an aluminum electrode is installed on this insulating film as the gate G. This constitutes an N-channel (NPN type) enhanced MOS tube. Its grid and other electrodes are insulated.
In the same way as above, on an N-type semiconductor silicon substrate with a lower doping concentration, two P+ regions with a high doping concentration are fabricated by semiconductor photolithography and diffusion processes, and the same gate fabrication process described above is It is made into a P-channel (PNP type) enhanced MOS tube. Figure 1-1 shows (a) and (b) respectively the P-channel MOS pipeline structure diagram and representative symbols.
2. The working principle of MOS tube:
It can be seen from Figure 1-2-(a) that there are two back-to-back PN junctions between the drain D and source S of the enhanced MOS tube. When the gate-source voltage VGS=0, even if the drain-source voltage VDS is added, there is always a PN junction in the reverse bias state, and there is no conductive channel between the drain-source (no current flows), so the drain at this time Current ID=0. At this time, if a forward voltage is applied between the gate and the source, as shown in Figure 1-2-(b), that is, VGS>0, a gate will be generated in the SiO2 insulating layer between the gate and the silicon substrate The electric field directed to the P-type silicon substrate. Since the oxide layer is insulated, the voltage VGS applied to the gate cannot form a current. A capacitor is formed on both sides of the oxide layer. VGS is equivalent to charging the capacitor and forming a The electric field, as the VGS gradually rises, is attracted by the positive voltage of the gate, a large number of electrons are gathered on the other side of the capacitor and an N-type conductive channel from the drain to the source is formed. When the VGS is greater than the tube's When the turn-on voltage VT (generally about 2V) is turned on, the N-channel tube begins to conduct, forming a drain current ID. We call the gate-source voltage when the channel begins to form as the turn-on voltage, which is generally represented by VT. The magnitude of the control gate voltage VGS changes the strength of the electric field, and the goal of controlling the magnitude of the drain current ID can be achieved. This is also an important feature of the MOS tube using electric field to control the current, so it is also called a field effect tube.
3. Features of MOS tube:
It can be seen from the working principle of the above MOS tube that the gate G and the source S of the MOS tube are insulated. Due to the existence of the SiO2 insulating layer, there is equivalent to a capacitor between the gate G and the source S. , The voltage VGS generates an electric field, which leads to the generation of source-drain current. The gate voltage VGS at this time determines the magnitude of the drain current, and the magnitude of the drain current ID can be controlled by controlling the magnitude of the gate voltage VGS. This leads to the following conclusions:
1) MOS tube is a device that controls current by changing voltage, so it is a voltage device.
2) The input characteristic of MOS pipeline is capacitive, so the input impedance is extremely high.
4. Voltage polarity and symbol rules of MOS tube:
Figure 1-4-(a) is the symbol of the N-channel MOS transistor. In the figure, D is the drain, S is the source, and G is the gate. The arrow in the middle represents the substrate. MOS tube, the arrow outward indicates that it is a P-channel MOS tube.
Actually, in the process of MOS tube production, the substrate is connected to the source before leaving the factory, so in the rules of symbols, the arrow indicating the substrate must also be connected to the source to distinguish the drain from the source. Figure 1-4-(c) is the symbol of the P-channel MOS tube. The polarity of the applied voltage of the MOS tube is the same as that of our ordinary transistors. The N-channel is similar to the NPN transistor. The drain D is connected to the positive electrode, the source S is connected to the negative electrode, and the gate G is positive when the conductive channel is established, and the N channel is The MOS tube starts to work, as shown in Figure 1-4-(b). The same P-channel similar PNP transistor, the drain D is connected to the negative electrode, the source S is connected to the positive electrode, and the gate G is negative, the conductive channel is established, and the P-channel MOS transistor starts to work, as shown in Figure 1-4-(d) Shown.
N-channel MOS tube symbol Figure 1-4-(a)
N-channel MOS tube voltage polarity and substrate connection 1-4-(b)
(C)
(D)
P-channel MOS tube symbol Figure 1-4-(c)
P-channel MOS tube voltage polarity and substrate connection 1-4-(d)
5. The main package of MOS tube:
At present, conventional packages of TO-220, TO-3P, TO-247 and various modules are popular in the market. Special packages can be provided according to customer specific product requirements. We will organize the following for everyone based on the commonly used models and packages of Sacco SLKOR:
TO-3P
TO-220
TO-247
SOT-23
TO-252
SOT-227B
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