Core concept
LDMOS is an abbreviation for laterally diffused metal oxide semiconductor.It is a semiconductor technology designed for radio frequency power applications and manufactured on a silicon substrate.
In simple terms, you can understand it as a kind of transistor that can "do heavy work", especially good at working under high-frequency and high-power conditions.
1. What is it?Basic principles and structural characteristics
LDMOS is a kind of MOSFET, but its structure has been specially optimized to achieve high breakdown voltage and high frequency performance.
The "horizontal diffusion" in its name reveals the key：
Transverse: Current flows horizontally inside the transistor (from source to drain, parallel to the surface of the silicon wafer).This is different from another current flow direction called a "vertical" device.
Diffusion: In the manufacturing process, a specific doped region (especially the P-body region) is formed through a process step called "diffusion".This diffusion process creates a precise concentration gradient, which is the key to achieving high performance.
Core structural characteristics of LDMOS：
Drift zone: There is a lightly doped "drift zone" between the drain and the channel.This area is the essence of LDMOS's success：
Function: Withstand high voltage.When the transistor is turned off, most of the voltage drops in this area to prevent the device from being broken down.
Benefits: It allows LDMOS to work at a higher power supply voltage, thereby outputting greater power.
Silicon oxide isolation: Early LDMOS usually used local oxidation isolation technology to reduce parasitic capacitance.
Asymmetric structure: The source, gate, and drain of LDMOS are not geometrically symmetrical.This is one of the main differences between it and the standard symmetrical MOSFET.
2. Main advantages
The reason why LDMOS has dominated the field of RF power for decades is due to its series of outstanding advantages：
High power output: it can handle high voltages and currents, and output tens of watts to several kilowatts of radio frequency power.
High gain: At a given frequency, it can provide high signal amplification capability.
Good linearity: this is one of its most critical advantages.Good linearity means that the signal distortion is small, which is essential for modern complex modulation formats (such as OFDM used in 4G/5G) to ensure the quality and efficiency of data transmission.
High durability: can withstand harsh load conditions (such as load mismatch), such as when the antenna is damaged, it is not easy to burn down.
Cost-effectiveness: Based on mature silicon process manufacturing, the cost is much lower than other high-frequency and high-power technologies (such as GaAs or GaN-on-SiC).
Single power supply: usually only one positive power supply voltage is required to work, simplifying the circuit design.
3. Main application areas
LDMOS is the main force of many infrastructure applications：
Mobile communication base stations: This is the largest and most important market for LDMOS.
Macro base station power amplifier: It is widely used in 2G, 3G, and 4G networks, especially in the 1.8GHz to 2.2GHz frequency band.
5G Massive MIMO active antenna unit: Although facing GaN competition in the high frequency band, LDMOS is still a competitive choice in the Sub-6GHz band such as 3.5GHz.
Broadcast transmitter：
The power amplifier stage of FM radio and television broadcasting.
Industrial, scientific and medical frequency bands：
It is used as a power source for plasma generation, radio frequency heating, medical microwave ablation and other equipment.
Avionics and Public safety：
Used in radar, radio communication and other systems.