Reliability Testing of Wide Bandgap Semiconductor Devices

One of the more recent developments in power electronics are wide bandgap (WBG) semiconductor devices. According to the U.S. Department of Energy, WBG semiconductor devices will:

• Operate up to 300 degrees C
• Operate at voltage up to ten times the operating voltage of conventional semiconductors
• Eliminate up to 90% of the power losses in electricity transfer compared to current semiconductor technology

They also switch faster and have a higher frequency response than current semiconductor devices.

WBG semiconductor devices are made from silicon carbide (SiC) and gallium nitride (GaN) semiconductors. You can currently purchase SiC MOSFETS, BJTs, and Schottky diodes and GaN FETs and Schottky diodes. Applications for these devices include electric vehicles, power conversion for wind and solar energy systems, wireless charging, and even RF amplifiers.

 Reliability test challenges

Before you use these devices in your designs, you may want to test them to ensure that they will work reliably and meet spec. There are several JEDEC standards that specify reliability tests that you may wish to perform, including:

• JESD22-A108D “Temperature, Bias, and Operating Life,”
• JESD22-A110D “Highly Accelerated Temperature and Humidity Stress Test (HAST),”
• JESD236 “Reliability Qualification of Power Amplifier Modules.”

Reliability tests normally stress sample devices for hundreds or thousands of hours with bias voltages that are greater than or equal to their normal operating voltages at temperatures well beyond normal operating temperatures. Because WBG semiconductor devices are designed to operate at voltages and temperatures higher than conventional silicon devices, the test equipment that you currently use for this testing may not be up to the task. In addition, WBG devices exhibit failure mechanisms that are different from conventional silicon devices. Because of this, you will need larger sample sizes and longer stress durations to adequately characterize their reliability.

Another challenge for test engineers is measuring device parameters. WBG semiconductor devices have much lower leakage and on-resistance than conventional silicon devices. Operating voltages and currents are higher, too. For example, WBG devices typically switch currents that measure hundreds of amps in conduction mode, and remember that you may be testing many devices in parallel. That calls for some very high power sources.

Your test instrumentation must not only be able to measure these high voltages and currents, but also make those measurements with the required accuracy, resolution, and stability. In addition to performing tests at higher currents and voltages, WBG semiconductor devices switch faster and have higher bandwidth than current power electronics devices. This means that your test system must have higher bandwidth than systems used to test conventional power electronics and must make measurements faster.

Reliability test equipment suppliers/manufacturers

Since 2005, Axiom Test Equipment has been providing a variety of semiconductor test equipment for rent or sale. Additionally, we repair many brands and types of semiconductor test equipment. Major manufacturers we carry include:

• California Instruments power sources
• Chroma power sources and loads
• Keithley Instruments semiconductor characterization systems, source-measure units (SMUs) and switching systems
• Keysight (formerly Agilent) SMUs, semiconductor parametric analyzers, and switching systems
• Temperature chambers from Espec, Temptronic, Test Equity, Tenney, Thermonics, and Thermotron

References

1. Wide Bandgap Semiconductors, https://www.youtube.com/watch?v=V7w07-zYIJ4, January 15, 2014.
2. Optimizing Reliability Testing of Power Semiconductor Devices and Modules with Keithley SMU Instruments and Switch Systems, Keithley Instruments, Cleveland, OH. http://www.tek.com/sites/tek.com/files/media/document/resources/ReliabilityTesting_PwrSemi%20AppBrief.pdf