Power MOSFET in Relation to DMOS

Technological innovations have made it possible to integrate more digital circuits in a smaller area. This is largely due to the evolution of transistors.

This article explains what a MOSFET is for beginners in relation to DMOS.

What is a Power MOSFET?

Metal-oxide-semiconductor field-effect transistors (MOSFETs) are one of the most commonly used types of transistors. A MOSFET basically consists of three terminals, called the gate, drain, and source. When a voltage is applied to the gate, which is the terminal used for voltage control, current flow between the drain and source is increased. Compared to bipolar transistors, which were commonly used in the past, MOSFETs can more easily achieve high-speed switching with less power. They also have high temperature stability.

MOSFETs work mainly as switching elements in electronic circuits and are widely used in memory, CPU, and motherboards.

MOSFETs developed to handle high currents are called power MOSFETs. They are used in circuits that require large current, such as switching power supplies and DC-DC converters. Power MOSFETs use DMOS as the basic circuit structure.

What is DMOS?

A double-diffused metal-oxide semiconductor (DMOS) is a circuit structure used in power MOSFETs. DMOS has two types of configuration, namely vertical (VDMOS) and lateral (LDMOS), depending on the direction of current flow.

In both structures, when a voltage is applied to the gate, a channel forms between the source and drain, allowing current to flow. However, the structure of the transistor substrate differs between the two configurations as follows. For LDMOS, the N and P regions are placed laterally, with the source and drain positioned across the gate at the top of the substrate. For VDMOS, the N and P regions are placed vertically, with the source at the top of the substrate and the drain at the bottom of the substrate.

LDMOS is difficult to integrate because the current flows laterally, whereas VDMOS is easy to integrate because the current flows vertically. VDMOS can achieve a lower on-resistance under low-voltage conditions. LDMOS can achieve the same or better on-resistance than that of VDMOS under high-voltage conditions.

Summary

We have now briefly introduced power MOSFETs and DMOS. Power MOSFETs are used in circuits that require large amounts of power and DMOS is employed as their typical circuit configuration.

DMOS is classified into vertical and lateral types according to the direction of current flow. In addition to MOSFETs, other types of transistors exist, such as bipolar transistors and IGBT. It is important to determine which type is best suited for your application based on its characteristics.