The MOS field effect transistor is a metal-oxide-semiconductor field effect transistor, abbreviated as MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor, that is, a field-effect transistor of a metal-oxide-semiconductor), which belongs to the insulated gate type. There is a silicon dioxide insulating layer between the metal gate and the channel, so it has a 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; 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 Tao. The depletion type means that when VGS=0, a channel is formed, 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 made on a P-type silicon substrate with two source diffusion regions N+ and drain diffusion regions N+ with a high doping concentration, and then the source S and the drain D are led out respectively. The source and the substrate are connected internally, and the two always maintain the same potential. The direction of the potential is from the outside to the inside, which means from the P-type material (substrate) to the N-type channel. 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 (usually about +2V) is reached, the N-channel tube begins to conduct, forming a drain current ID.

MOS field effect tube is more "squeaky". This is because its input resistance is very high, and the capacitance between the gate and the source is very small, it is very easy to be charged by the external electromagnetic field or electrostatic induction, and a small amount of charge can form a very high voltage on the capacitance between the electrodes (U =Q/C), damage the tube. Therefore, when leaving the factory, the pins are twisted together, or installed in metal foil, so that the G pole and the S pole are at the same potential to prevent the accumulation of static charge. When the tube is not in use, all leads should be short-circuited. Be extra careful when measuring, and take corresponding anti-static measures.