The difference between mos transistor and bipolar junction transistor

MOS transistor and bipolar transistor (BJT) are two common transistor devices that have significant differences in operating principles, structures, and functions. This article will compare and analyze them. If you are interested in the content to be covered, please continue reading the following content, hoping it can be helpful to you.

There are three areas for constructing BJT: emitter, base, and collector. The emitting and collecting regions are N-type or P-type semiconductors, while the base region is another type of semiconductor device doped from one side to the other, forming a PNP or NPN structure.

MOS transistors are divided into N-channel and P-channel types, and their basic structure is based on a four layer composite structure: substrate, insulator, gate, and source/drain. The substrate is a high-purity semiconductor chip, and the insulation layer is generally silicon dioxide or silicon nitride. A gate is a layer of conductive material attached to an insulating layer, such as metal or polycrystalline silicon. The source/leakage electrode is the area generated by P or N type semiconductors, connected to the substrate.

The working principle of BJT is based on the injection of a small number of carriers into the amplified base region, which controls the current flow rate. When the positive voltage in the base region is applied to a certain extent, the carriers in the base region inject into the collector region, resulting in an amplification of the current.

The working principle of MOS transistor is to form an electric field between the gate and drain, which can control the number of electrons in the source/drain, and then manipulate the flow of current. There is a thin oxide insulation layer (also known as gate oxide layer) in the MOS pipeline. When a certain voltage is applied to the gate, the semiconductor under the insulation layer will generate reverse bias. This will lead to the formation of bandable bends in the semiconductor, creating conductive channels between the source and drain electrodes, thereby controlling the flow of current.

BJT and MOS transistors have different performance characteristics compared to each other. The BJT control circuit is simple and stable, suitable for amplifying signals and high-precision amplification, with a large linear gain range. But its main drawbacks are low input impedance, high noise, voltage saturation, etc.

MOS transistors are suitable for controlling size signals, high currents, and high-frequency signals. Its input impedance is high, noise is low, and power consumption is low, making it suitable for high-power and high-frequency devices. However, its main drawbacks are grid capacitors, frame loss, impact, and other issues, which require additional static voltage control.

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