GaN Power Electronics and Reliability

Modern ultra-fast-transition transistors made from silicon carbide (SiC) and gallium nitride (GaN) would bring 10-fold reductions in power losses in power electronics. The chief concern about these devices is however their reliability. As a result, we are developing technologies to allow the measurement of junction temperature during operation, and to automatically determine the health of power devices without interrupting their operation.

Junction temperature sensor for GaN FETs

A number of temperature indicators (aka temperature-sensitive electrical parameters TSEPs) have been demonstrated in the literature. For example, when the GaN FET is turned on, the current would ideally jump instantaneously to the full load current.

 

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‌However, the hotter a GaN devices gets, the slower this transition becomes.  Here, we use a magnetic field probe (Infinity Sensor) to measure the rate of change of current (di/dt) at turn-on to determine the temperature inside a GaN device.  This is done by detecting the peak output signal of the sensor and looking up the corresponding device temperature.

  

‌The final value of the current (i.e. the load current) also needs to be measured, as it too affects switching speed: the current slew rate increases with load current.

References

J. Wang, M. H. Hedayati, D. Liu, S. E. Adami, H. C. P. Dymond, J. J. O. Dalton, and B. H. Stark, “Infinity Sensor: Temperature Sensing in GaN Power Devices using Peak di/dt”, IEEE Energy Conversion Congress and Exposition (ECCE), 2018.