DMOS vs VMOS vs LDMOS | Difference between DMOS, VMOS, LDMOS

This page compares DMOS vs VMOS vs LDMOS and mentions difference between DMOS, VMOS and LDMOS. It mentions DMOS structure, VMOS structure and LDMOS structure.

DMOS basics | DMOS structure

DMOS structure

DMOS stands for Double-Diffused MOS. The device is widely used in switching applications requiring high voltage and high frequency behavior. The other applications of DMOS are Inkjet printheads, automobile control electronics, power supplies etc.

The figure-1 depicts DMOS structure. Following are the properties of DMOS device.
• The DMOS device uses a double diffusion process.
• The p-region and the n+ source regions are diffused through common window. This is defined by edge of the gate.
• The p-region is being diffused deeper compare to n+ source.
• The surface channel length is defined as the lateral diffusion distance between the p-substrate and the n+ source.
• The breakdown voltage and on-resistance are two important parameters of DMOS device.
• Due to high voltage and high frequency characteristics it is similar to BJT.
• The very high breakdown voltage is achieved due to lightly doped drift region between Drain and channel regions.
• The n-drift region thickness should be as thin as possible in order to achieve lower drain resistance.

VMOS basics | VMOS structure

VMOS structure

VMOS stands for Vertical Metal Oxide Silicon. The device has V-shaped gate region. The devices are used for applications requiring medium powers such as power amplifiers and switching.

The figure-2 depicts VMOS structure. Following are the properties of VMOS device.
• It consists of shaped groove.
•  Due to source at top and drain at bottom, the current flows vertically rather than horizontally.
• V shaped gate makes cross-sectional area of source to drain path larger. Hence lower ON resistance of the device can be achieved which allows much higher power.
• The gate consists of metallised area over the V groove which controls current flow in P-region.
• VMOS structure is more complex compare to traditional FET device. This makes it more expensive.

LDMOS basics | LDMOS structure

LDMOS structure

LDMOS is asymmetric power MOSFET device. It is designed for applications requiring lower on-resistance and higher blocking voltage.

In LDMOS channel current is being controlled by vertical electric field (E). This E-field is induced by gate and lateral field which exists between S (Source) and D (Drain). In LDMOS device, channel is determined by three parameters viz. gate length, drain diffusion and source diffusion.

The device is fabricated using diffusion and ion implantation processes. Initially p-type region is constructed. Later shallow p+ and n+ regions are being formed. The source and drain contact regions are created from n+ regions. The p+-region contacts with the p-type body. This is shorted to source part. This will eliminate body effect. The figure-3 depicts LDMOS structure.
Refer Advantages and disadvantages of LDMOS>> for more information.

MOSFET and BJT related links

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Depletion MOSFET vs Enhancement MOSFET➤
MOSFET Fabrication Technology➤
MOSFET vs BJT-Difference between MOSFET and BJT➤
Application Note-MOSFET as switch and amplifier➤
Difference between NMOS vs PMOS➤

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