Trench MOSFET: Structure, Advantages, and Operation

Introduction

Trench MOSFETs are a breakthrough in power semiconductor technology, offering exceptional efficiency and a compact design. They are widely used in modern electronics for applications that demand high power density and switching speed. This guide explores the unique structure and technology of Trench MOSFETs, detailing their working principles, advantages, and significance in power electronics.

The trench gate MOSFET device has the lowest ON-state resistance among all variants of MOS devices. Hence, it is considered the most suitable power device for low to medium voltage power applications. The architecture is designed such that it conducts current vertically from one surface to the other. Due to this, the trench MOSFET achieves high drive capability.

It is realized by packing millions of trenches on a chip, deep enough to cross the oppositely doped “body” region below the top surface. Each trench houses a gate dielectric and a gate electrode to control the current conduction in its vicinity by virtue of the field effect.

Trench MOSFET Structure

Similar to any other MOSFET, a trench MOSFET cell contains the drain, gate, source, body, and channel regions but exhibits a vertical direction of current flow. All the cells are connected to work in parallel in order to reduce the value of $R_{ON}$.

Figure 1 depicts the basic device structure of a trench MOSFET.

Trench MOSFETs are mainly used for less than 200 voltage ratings due to their higher channel density and thus lower on-resistance.

Figure 1: Trench MOSFET structure

The amount of current a trench MOSFET conducts depends on the on-resistance of the MOSFET, which is expressed as follows:

$R_{DSON} = \frac{V_D}{I_D}$

For a trench MOSFET, $R_{DSON}$ consists of the following components, as depicted in Figure 2:

• $R_S$: source resistance
• $R_{CH}$: channel resistance
• $R_{ACC}$: resistance from the accumulation region
• $R_{EPI}$: resistance from the top layer of silicon (epitaxial silicon, also known as epi); epi controls the amount of blocking voltage the MOSFET can sustain.
• $R_{SUBS}$: resistance from the silicon substrate on which the epi is grown

_Figure 2: Trench MOSFET $R_{ON}$ components_

Trench MOSFET Working

Trench MOSFETs utilize a vertical structure where the gate electrode is embedded in a trench etched into the silicon substrate. This design allows the current to flow vertically through the device, reducing on-resistance and improving current-carrying capability. When a voltage is applied to the gate, it creates an electric field that controls the flow of electrons from the source to the drain, enabling efficient switching and amplification. This unique structure minimizes parasitic capacitance, enhancing switching speed and efficiency.

Advantages of Trench MOSFET

Following are some of the benefits of a trench gate MOSFET device:

1. Low On-Resistance: Enables efficient power handling with minimal energy loss.
2. High Switching Speed: Ideal for high-frequency applications such as DC-to-DC converters.
3. Compact Design: The vertical structure reduces the overall footprint, saving space in compact devices.
4. Enhanced Thermal Performance: Better heat dissipation ensures reliability in high-power applications.
5. Reduced Gate Charge: Low gate capacitance decreases power consumption in switching operations.

Trench MOSFETs are critical in modern power electronics, providing unmatched efficiency and compactness, making them indispensable in industries like automotive, consumer electronics, and renewable energy systems.

Conclusion

Trench MOSFETs have revolutionized the field of power electronics with their innovative structure and advanced technology. By providing high efficiency and compact designs, they are crucial in meeting the demands of modern electronic applications. Understanding their structure and technology not only enhances their utility but also paves the way for further innovation in power semiconductor devices.