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The emergence of wide-bandgap (WBG) semiconductors, such as silicon carbide and gallium nitride, has revolutionized the landscape of power conversion. These materials boast superior properties over traditional silicon, enabling significant advancements in efficiency. This technological leap is instrumental in facilitating the widespread adoption of electrification.
To ensure the reliable and robust operation of WBG devices within next-generation power electronic systems, a critical reevaluation of current validation and testing practices is paramount. This may necessitate not only the adaptation of existing methodologies but potentially the development of entirely novel approaches.
In an interview with Power Electronics News, Jonathan Tucker, power market segment leader at Tektronix, will discuss the more appropriate testing methodologies for WBG power devices and how they can help to improve their performance.
Power trends
The acceleration of power efficiency demand can be attributed to the relevance of digitization and electrification in enhancing productivity and environmental responsibility, respectively. Access to energy and data is becoming more prevalent via alternative energy sources as opposed to fossil fuels, as a result of regional mandates and regulations driving the reduction of carbon emissions.
Public and private investments are being made in supply chains and novel semiconductor technologies to increase the efficiency of power modules, power transistors, power management integrated circuits and power conversion/inversion systems. Similarly, it is essential to decrease the size and weight of the power conversion apparatus, as well as improve its efficiency.
With the advent of WBG devices, engineers need to reassess their validation and testing methods. The testing procedures for power conversion devices and systems during design and manufacturing remain comparable to those used for earlier generations. However, the use of WBG materials necessitates additional rigor in the testing process.
According to Tucker, higher power density and higher power levels are probably the most important key factors driving power applications. SiC devices normally have a vertical structure, thus achieving higher-voltage and -current capabilities.
“The people I’ve talked to in the industry agree that changing the architecture of GaN devices from a lateral and planar kind to a vertical one, higher voltage levels and ultimately higher power densities, would be achieved,” Tucker said.
He added that SiC is mainly on the power density side, whereas GaN can operate at higher switching frequencies, reducing the power losses and the size of transformers and inductors.
“A big task is to ensure the long-term reliability of these WBG devices,” Tucker said. “Test and measurement companies play a big role in ensuring that they can run those tests properly and they can get the reliability they’re looking for.”
Currently, GaN and SiC are the preferred WBG semiconductors for fast charging, reducing conduction losses and enabling faster switching speeds. GaN technology reduces size while increasing power density, enhancing battery charge times in cellphones, hand tools and portable healthcare monitors. It is also increasingly used in electronic power supplies, RF power amplifiers, and EV infotainment and cockpit applications. Conversely, SiC technology excels in higher-power applications, such as power transmission, large-scale HVAC systems and industrial equipment, due to its suitability for handling higher power levels and efficiency in demanding environments.
However, ongoing research is exploring new WBG materials, such as aluminum nitride (AlN), gallium oxide (Ga2O3) and diamond. These novel materials possess the capacity to unleash enhanced power performance.
“As we get to ultra-wide-bandgap technologies like diamond, aluminum nitride and gallium oxide, testing instrumentation will need more bandwidth and probes capable of supporting that bandwidth as well,” Tucker said.
WBG device characterization
Gaining a comprehensive understanding of the electrical characteristics of SiC and GaN is crucial to establishing a compelling rationale for their utilization in developing power applications. To accomplish this, the process of characterizing the relationship between current and voltage (I-V) is carried out.
I-V characterization is a key technique for comprehending the current-voltage relationship of silicon, SiC and GaN, as well as their essential characteristics.
The Keithley portfolio of Tektronix offers a range of advanced instruments, including the 2400 Series Graphical Source Measure Units (SMUs; see Figure 1), the 4200A-SCS Parameter Analyzer and the 2600-PCT High-Power I-V Curve Tracer Systems. Several essential measurements for characterizing WBG devices, such as current versus voltage testing, breakdown voltage testing and leakage current testing, can be easily accessed through graphical user interfaces or application software like Keithley KickStart or ACS-Basic.
“As electronic devices and PCBs get smaller, it’s getting harder to make a good probe connection, especially in the presence of high voltages and high current ratings,” Tucker said. “People come to us because of our semiconductor testing systems that are used in wafer fabs, in the front end and in the back end of a semiconductor fab.”
Double-pulse testing
The double-pulse test (DPT) is the established procedure for quantifying switching parameters and assessing the dynamic characteristics of Si, SiC and GaN MOSFETs and IGBTs. DPT is employed to quantify the energy dissipation during the activation and deactivation of a device, as well as to determine the reverse-recovery characteristics.
As shown in Figure 2, the DPT is conducted by utilizing two WBG devices. The first device is referred to as the device under test (DUT), whereas the second device is usually of the same type as the DUT. Take note of the inductive load on the device connected to the “high” side. An inductor is employed to mimic circuit circumstances that may be present in a converter design.
The equipment utilized comprises a power supply or SMU for voltage supply, an arbitrary function generator for generating pulses that activate the gate of the MOSFET to initiate current conduction and an oscilloscope for measuring the resulting waveforms.
“Double-pulse testing provides many insights on how the device is performing, including rise times, fall times, energy on and energy off,” Tucker said. “However, what we’re hearing more and more about is people want to screen their devices more upstream, directly on the wafer.
“Keithley’s products can do a lot of quality control process monitoring like IV characterization directly on the wafer with a probing system, but when you start other tests like RDS(on), rise times and fall times, it becomes more challenging,” he added.
Validation of WBG devices
The capacity to examine power loss and enhance power supply efficiency has become crucial in power applications. Tektronix simplifies the process of doing switching loss measurements using the 5 and 6 Series B MSO oscilloscopes (Figure 3) and automated power analysis software.
Measuring floating differential quantities, such as high-side Vgs, is challenging or perhaps impossible due to the rapid switching on and off at high frequencies and the existence of large common-mode voltages, such as Vds. This is because oscilloscope probes lack the necessary ability to reject common-mode signals at high bandwidths.
The inadequate common-mode rejection results in the measurement being overwhelmed by the common-mode error rather than accurately capturing the differential signal. To address these problems, Tektronix IsoVu isolated probes can be used. By maintaining their performance regardless of common-mode voltage when used with GaN and SiC devices, they enable precise differential measurements to be made. Using IsoVu probes, one may accurately measure and validate conduction losses, deadtime losses and switching losses.
“If you look at the Tektronix portfolio, you can see we have a wide variety of scopes and probing technologies,” Tucker said. “The software is very important as well. We have a team that develops application-based software that can be installed right into the scope itself.
“Beyond the traditional characterization of WBG devices, validating the reliability of WBG devices and power modules requires high-voltage and higher-power capacities,” he added. “EA Elektro-Automatik, a German company specializing in high-efficiency power supplies, which was acquired recently, expands Tektronix’s High-Power Test and Measurement Solutions. The strength of the Tektronix, Keithley and EA portfolios enables the engineer to measure with confidence and bring their products to market faster. “
In a world where managing limited energy resources is crucial, WBG semiconductor technology like SiC and GaN is advancing clean, renewable energy. However, new challenges arise for engineers. Updated testing tools and techniques are essential to measure critical values and ensure the functionality of these important devices.
The post Addressing the Challenges of WBG Device Testing appeared first on Power Electronics News.
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