MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a semiconductor device based on electric field effect to control current, widely used in modern electronic circuits, especially in switch and signal amplification scenarios, occupying a core position.
Structure and Composition
MOSFET consists of three main electrodes:
Source: The input terminal for charge carriers (electrons or holes).
Drain: The output terminal of charge carriers.
Gate: A switch that controls the conductive channel between the source and drain by applying voltage.
The core structure is an insulating layer (usually silicon dioxide) below the gate, which isolates the gate from the semiconductor substrate and forms a stacked structure of "metal oxide semiconductors". The substrate is divided into P-type or N-type semiconductors, corresponding to different conductivity types.
Working principle
MOSFETs regulate the conduction or turn off of conductive channels through small changes in gate voltage:
Enhancement Mode:
In the default state, there is no conductive channel between the source and drain (cut-off state).
When a forward voltage is applied to the gate, the electric field attracts carriers in the substrate to form a conductive channel, and current begins to flow.
Depletion Mode:
There is a conductive channel by default (conductive state).
Applying a reverse voltage can deplete the charge carriers in the channel, thereby blocking the current.
Type and Characteristics
Classified by conductivity type:
N-channel (NMOS): Electrons are carriers, with fast conduction speed, suitable for high-frequency applications.
P-channel (PMOS): Holes are charge carriers with strong anti-interference ability, often combined with NMOS to form complementary structures (CMOS).
Classified by working mode:
Enhanced (mainstream applications such as CPU and power management).
Exhaustive type (special scenarios, such as constant current sources).
Core advantages
High input impedance: The gate hardly draws current, and the driving power is extremely low.
Quick switch: suitable for high-frequency circuits such as 5G communication and switching power supplies.
Easy to integrate: Compatible with CMOS technology, it is the fundamental component of integrated circuits.
Typical applications
Power switch: Efficient energy conversion in mobile phone chargers and electric vehicle controllers.
Signal amplification: Low noise amplification in RF circuits and audio devices.
Digital logic: the core component unit of chips such as CPU and memory.
The invention of MOSFET has completely changed the design of electronic systems, and its low power consumption, high reliability, and miniaturization characteristics have become indispensable components in the modern digital age.