What Defines a WBG Semiconductor?
Physicists define the bandgap of a material as the difference in energy between the highest occupied state of the valence band (the band of electron orbits from which electrons jump when excited by the application of energy) and the lowest unoccupied state of the conduction band (the band to which those electrons can jump). The band gap dictates the energy required for electrons to move from the valence band to the conduction band.
Legacy silicon, which has been the primary material for semiconductors since the 1950s, has a bandgap of 1.1 eV. The latest wide bandgap (WBG) semiconductors are those based on new and emerging materials that have bandgaps typically in the region of two to three times that of silicon.
What are the Benefits of WBG Semiconductors?
Silicon has been dominant for many years but is reaching its performance limits in a growing number of existing and emerging applications. Because WBG semiconductors can withstand higher electric fields they can sustain higher voltages. They can also operate at higher switching frequencies. The latter not only supports improved performance but also minimizes filtering requirements and allows the use of smaller external components (faster switching means energy is delivered in smaller packets and, therefore, less energy needs to be stored in the circuit’s passive and inductive devices).
When compared to legacy silicon these factors translate into a number of benefits including smaller, faster, more efficient and more reliable operation. Higher voltage capabilities open up opportunities in higher power designs while dramatically improved efficiencies enable the same performance in smaller form factors or allow improved performance in the same form factor. Efficiency also has an impact on weight and, ultimately, the carbon emissions associated with the operation of the target application.
Many devices based on WBG technologies also offer the benefit that they can operate at higher maximum temperatures than their legacy silicon counterparts.
What WBG Materials are Used for Semiconductors?
A number of materials including boron nitride, silicon dioxide and even diamond are all defined as WBG materials.
GaN and SiC are the two most prevalent WBG technologies in use today
However, the most prevalent WBG semiconductors today are those based on gallium nitride (GaN) and silicon carbide (SiC). The bandgaps of these materials are around three times greater than that of silicon, at 3.2 eV and 3.4 eV respectively.
What are the Differences Between GaN and SiC?
While GaN and SiC are compound semiconductors with similar bandgaps and both can support higher voltages and higher frequencies, there are a number of differences between the two technologies that impact how they work and where they are used.
Application design parameters for Si, GaN and SiC
The key differentiator between GaN and SiC is speed in terms of electron mobility – how quickly electrons can move through the semiconductor material. At 2,000 cm2/Vs, GaN’s electron mobility is 30% faster than that of silicon and 300% faster than SiC, which makes it much more suitable for high-performance, high-frequency applications. With GaN, a very, very small percentage of the chip is actually consumed by the gate electrode. This ensures very low capacitance meaning it is very easy to get high frequencies. In fact, GaN semiconductors are widely used in RF devices that switch in the gigahertz range. Silicon carbide, on the other hand, has a lot of gate area, requires a very much higher gate charge to switch and is, therefore, slower.
GaN’s wide band gap allows power applications with voltages between 100 V and 600 V to use smaller, more efficient chips, reducing costs and carbon emissions. SiC, with higher thermal conductivity and lower frequency operation is more suited for the highest power applications such as rail traction and wind turbines that require slower switching speeds and large heat dissipation.
GaN structure supports monolithic integration
One other factor is the potential for integration, which depends on the current flow within the WBG semiconductor material. SiC is a ‘vertical’ device that is optimized for high power only, while Navitas’ GaN, for example, has a ‘lateral’ structure. The latter makes monolithic (‘same chip’) integration possible, enabling GaN power ICs to integrate power FETs with drive, logic, protection, sensing and control in a single chip.
WBG Semiconductor Applications
The following diagram illustrates the existing and potential applications for GaN and SiC in power applications.
GaN – The Second Revolution
In 1977, two major events changed the lives of many engineers: the movie “Star Wars” was released, and there was a revolution in power electronics. Since then we have had many Star Wars movies, many more new engineers and a new performance revolution, with wide bandgap materials, enhanced high-frequency magnetics, new controllers, enabled topologies and device integration.
What is the Potential for WBG Semiconductors?
The potential market for WBG semiconductors is already significant and growing rapidly as companies look to replace legacy silicon in existing applications and to harness the power of GaN and SiC in new and emerging designs where silicon cannot compete. At Navitas we believe there is a $13 billion electrification opportunity for GaN by 2026.