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What are the common FETs?

back Date: 2021-12-03 17:19:02 Click:

The MOS field effect tube is a metal-oxide-semiconductor field effect tube, abbreviated as MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor), which belongs to the insulated gate type. Its main feature is that there is a silicon dioxide insulating layer between the metal gate and the channel, so it has a very high input resistance (up to 1015Ω). It is also divided into N-channel tube and P-channel tube. Usually, the substrate (substrate) and the source S are connected together. According to the different conduction mode, MOSFET is divided into enhancement type and depletion type. The so-called enhanced type refers to: when VGS=0, the tube is in an off state, and after adding the correct VGS, the majority of carriers are attracted to the gate, thereby "enhancing" the carriers in this area and forming a conductive channel . The depletion type means that a channel is formed when VGS=0, and when the correct VGS is added, the majority of carriers can flow out of the channel, thus "depleting" the carriers and turning the tube off.

Taking the N channel as an example, it is formed on a P-type silicon substrate with two source diffusion regions N+ and drain diffusion regions N+ with high doping concentration, and then the source S and the drain D are led out respectively. The source electrode and the substrate are connected internally, and the two always maintain the same potential. When the drain is connected to the positive pole of the power supply and the source is connected to the negative pole of the power supply and VGS=0, the channel current (that is, the drain current) ID=0. With the gradual increase of VGS, attracted by the positive voltage of the gate, negatively charged minority carriers are induced between the two diffusion regions, forming an N-type channel from the drain to the source. When VGS is greater than the tube When the turn-on voltage VTN (generally about +2V) is reached, the N-channel tube begins to conduct, forming a drain current ID.


VMOS field effect tube (VMOSFET) is abbreviated as VMOS tube or power field effect tube, and its full name is V-groove MOS field effect tube. It is a high-efficiency, power switching device newly developed after MOSFET. It not only inherits the high input impedance of the MOS field effect tube (≥108W), small drive current (about 0.1μA), but also has high withstand voltage (up to 1200V), large working current (1.5A~100A), and output Excellent characteristics such as high power (1~250W), good transconductance linearity, and fast switching speed. It is precisely because it combines the advantages of electron tubes and power transistors into one, it is being widely used in voltage amplifiers (voltage amplification up to thousands of times), power amplifiers, switching power supplies and inverters.

As we all know, the gate, source, and drain of a traditional MOS field effect transistor are on a chip whose gate, source, and drain are roughly on the same horizontal plane, and its working current basically flows in a horizontal direction. The VMOS tube is different, with two major structural features: first, the metal gate adopts a V-groove structure; second, it has vertical conductivity. Since the drain is drawn from the back of the chip, the ID does not flow horizontally along the chip, but starts from the heavily doped N+ region (source S), flows into the lightly doped N-drift region through the P channel, and finally reaches vertically downwards Drain Since the cross-sectional area is increased, large currents can be passed. Because there is a silicon dioxide insulating layer between the gate and the chip, it is still an insulated gate MOS field effect transistor.

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