Towards the implementation of diamond power devices in power converters and measurements of their switching losses

International audienceUltra wide bandgap (UWBG) materials such as monocrystalline diamond exhibit the best figure of merits for power semiconductor devices: the ultra-wide bandgap of 5.5eV translates into the highest electric field above 10MV/cm, which offers a thinner drift region with an associated higher doping level than with other Wide Bandgap (WBG) materials for the same breakdown voltage. Consequently, power semiconductor devices based on UWBG and diamond in particular have theoretically the lowest specific on state resistance, which leads to smaller active area and lower conduction and switching losses. Many different diamond power device architectures have been previously introduced, but the implementation of those in actual power converters was only reported in a limited number of communications [1-3]. Although the measurement of on state resistance is straight forward, the measurement of switching losses is challenging with the existing and future High Voltage (>600V) diamond power devices. First, diamond devices need to be packaged in order to be integrated in, at least, one power commutation cell (one transistor and one diode, or two transistors, with the same breakdown voltage). This packaging should also be compatible with a high junction temperature operation (above 150°C) to fully demonstrate the performances of diamond devices based on bulk conduction. Second, the active area of diamond devices can be relatively small compared to other available power devices. Consequently, the maximum switching speed of diamond power devices can be extremely fast, and the intrinsic parasitic capacitors much smaller than 1pF. Third, the total current rating of diamond power devices can be rather small (µA to mA), which makes it difficult to probe the fast large signal variation of low drain currents, also with high voltage swings. Finally, the required gate to source driving voltages of diamond power transistors can be different from their Silicon and WBG alternatives, with large gate to source voltage swing [5]. For all these reasons, a specific experimental approach must be developed to adapt the implementation of diamond power devices in power converters, and to be able to accurately extract the large signal switching behavior of those devices. In this work, we present the specific experimental characterization boards we designed and fabricated to achieve the fastest switching of diamond Schottky Barrier Diodes, and a flexible converter to extract switching losses of WBG and UWBG power transistors. The classical Double Pulse method is compared to the opposition method, where switching losses can be accurately measured without having to probe drain or source currents with fast dynamics. The converter is validated for high voltage inputs above 600V, load currents above 20A, switching frequencies above 100kHz, and flexible gate driver boards to adapt to specific gate voltages. Preliminary results on power switching with diamond MESFETs are also presented and discussed