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BaSiCs of SiC Series: Comparing SiC MOSFETs to Si MOSFETs

In this installment BaSiCs of SiC blog series, we will compare SiC to Si MOSFETs, starting with a quick review of MOSFETs.

MOSFETs are the basic building block of modern electronics and considered one of the most important inventions of the last century. However, there have been improvements on MOSFETs, including moving from Si (Silicon) to SiC (Silicon Carbide) — which has significantly improved their performance. But what is a MOSFET, anyway?

Basics of MOSFET

A MOSFET (Metal Oxide Semiconductor Field-Effect Transistor) is a field-effect transistor, which means that it controls current flow by using an electric field. The MOSFET usually has three terminals: gate, drain, and source. The current that is conducted between the drain and the source is controlled via a voltage applied to the gate. Compared to other types of transistors, MOSFETs have a higher power density, which is a definite advantage. In addition, compared to BJTs (Bipolar Junction Transistors), MOSFETs require a minimal amount of input current in order to control the load current.

Quick History of MOSFETs

Invented in 1959 by Mohamed M. Atalla and Dawon Kahng at Bell Labs, the presence of MOSFETs in modern electronics is ubiquitous and it is widely considered the most important invention in the field of electronics. They quickly proved indispensable to computers, the digital revolution, the information revolution, and the silicon age.

One of the keys to the development of MOSFETs was an innovative approach to surface passivation, the primary hurdle to building a working MOSFET, using thermal oxidation. The insulator on the MOSFET was silicon dioxide, while the conductor was crystalline silicon.

Silicon has long been the semiconductor material of choice for MOSFET. However, a major shift has been taking place after Cree created the first SiC MOSFET. Silicon carbide has proven to be a game-changer in MOSFET technology, providing a variety of advantages.

Advantages of SiC over Si

SiC has quite a list of advantages over Si when used in semiconductor technology, including:

  • A higher critical breakdown field, which means a voltage rating can be maintained while still reducing the thickness of the device
  • A wider bandgap, leading to lower leakage current at relatively high temperatures
  • A higher thermal conductivity, which supports a higher current density
  • An overall reduction in energy losses

Using SiC in place of Si in MOSFETs also results in:

  • Reduced switching losses, which impact losses that occur when the MOSFET is transitioning from blocking to conducting (and vice versa)
  • Higher switching frequencies, which means smaller peripheral components (e.g., filters, inductors, capacitors, transformers) can be used
  • Increased critical breakdown strength, about 10x what is achievable with Si
  • Higher temperature operation, which means simplified cooling mechanisms (e.g., heat sinks)

SiC versus Si: SiC Wins

When compared to their Si counterparts, SiC MOSFETs offer better overall performance, higher efficiency, higher switching frequencies, and more compact components. More and more engineers are turning to SiC MOSFETs and taking advantage of the superior properties that they offer. Will you be one of them?

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