Wide Bandgap Semiconductors: What Testing Challenges Must we Overcome?Follow article
Wide bandgap semiconductors (WBGs), silicon carbide (SiC) and gallium nitride (GaN) offer major benefits for electronics designers and manufacturers. The higher operating temperatures, frequencies and voltages that WBG semiconductors can withstand — along with potentially lower power loss compared to silicon semiconductors — make these devices a powerful alternative to semiconductors with smaller band gaps.
However, silicon remains the most popular material for semiconductor devices. This is in part due to challenges in testing the real-world capabilities of wide bandgap semiconductors. Sensitive testing equipment and careful attention to design for accurate results on WBG device behaviour are required.
Difficulties in characterizing WBGs make it harder to predict undesirable behaviour in real-world applications. This includes circuits that prevent problematic cross-talk and EMI issues associated with high-frequency switching in WBGs.
This interference and other unpredictable behaviours of wide bandgap semiconductors mean designers must overcome testing barriers. This needs to happen before the power electronics industry can pivot away from the use of silicon semiconductors.
Solving these challenges also may help designers better understand issues that may come with testing and characterizing ultrawide semiconductor bandgap materials. Gallium (III) trioxide could provide further performance improvements.
These are the key challenges designers face right now in testing new WBG semiconductor devices. They have been able to overcome some of these with the right equipment and testing circuit design, but more obstacles remain.
Key Challenges in WBG Testing
Devices based on wide bandgap materials are able to switch at much higher frequencies than silicon versions. They also tend to have much lower leakage. As a result, to properly characterize a WBG semiconductor, testing requires higher voltages and more sensitive measurement of currents.
While simpler types of semiconductor devices are easier to test, like diodes, they may still present challenges in circuit design testing. This means existing laboratory equipment sometimes can’t be used to characterize WBGs. Instead, the high switching frequency and low leakage require specialized, more sensitive equipment that semiconductor designers or testing facilities may not have on hand.
When designing and planning tests for a new circuit, designers should also consider how measurement may impact device performance. For example, measuring a signal will affect its operation.
Certain upgraded sensors may also need extra equipment to be properly used in WBG testing. High-precision, high-bandwidth current sensors are typically larger in size than less precise varieties. As a result, they may need special testing structures that will allow their use with minimal impact on circuit performance.
Before designers can even begin testing, they must consider how their current equipment may not be suitable for effective WBG tests and characterization. In most cases, these real-world tests can’t be side-stepped with digital modelling or simulations. The newness of WBGs also means that, when compared to silicon semiconductors, less accurate simulation models are all that’s available.
Simulation and Testing of Wide Bandgap Semiconductors
Difficulties in characterizing WBGs can also create problems during the manufacturing process. That could make these semiconductor devices less reliable in practice.
The high performance of WBGs often requires top precision in manufacturing. A 2020 Power Electronics UK position paper said that with GaN HEMTs, “the conduction path is in a very thin 30 nm sheet called a 2DEG (2-dimension electron gas). Any imperfection in this sheet will have a severe effect on the operation of the transistor.”
The quality of the WBG substrate material can also impact performance. Modern wide bandgap semiconductor manufacturing methods that involve careful, double-side lapping and polishing can help prevent some of these issues.
While WBG and silicon semiconductors may be measured in the same way, WBGs may also require different tests or testing details for proper characterization. They could require additional time spent in test design or resources put toward new testing equipment.
For example, the dynamic switching of both silicon and WBG semiconductors is conducted through double pulse testing. These semiconductors' unique properties mean the details need to be somewhat different for the test to be effective.
The newness of these devices also means that, while characterization sheets and other documentation of WBG behaviours exist, there is a significant variance in behaviour from device to device. This often requires special construction of characteristic circuits to properly understand how the WBG semiconductors will work in practice — meaning additional testing compared to a silicon semiconductor.
It also means that to know the “real” behaviour of a particular device, designers can’t rely on existing factsheets. More testing may be necessary for a circuit that uses WBGs compared to one that relies on more conventional silicon semiconductors.
Similarly, the rapid change in voltage or current can result in the production of significant electromagnetic interference (EMI) issues, which would make WBGs impractical. Advanced circuit control, the use of soft switching, updated layouts and gate drivers — as well as different construction techniques — can limit the impact of cross-talk and EMI. Implementing these effectively requires the correct characterization of WBG semiconductors.
How Better WBG Device Testing Can Change Power Electronics
Wide bandgap semiconductor devices offer major benefits in power electronics. These devices are already used in several applications, including LEDs and consumer smartphone chargers. Being able to fully harness their power could result in major improvements across the industry. This means better consumer electronics, electric vehicle battery packs and integration of renewable energy into the grid.
These potential applications are becoming especially important due to the growing need for fast-charging technology in advanced consumer electronics and for increasingly high-capacity electric vehicle battery packs. This demand will only increase as time goes by.
However, the adoption of WBGs will require designers to overcome several significant challenges in the testing and characterization of semiconductor devices. Highly sensitive testing equipment, improved test circuit design and other considerations will be necessary to properly characterize WBGs.