Manually characterizing wafer- and package-part level devices for electrical performance requires learning new techniques, equipment, and probing infrastructure for low level measurement (e.g. pA of leakage current measurement in the presence of high breakdown voltage). Source current up to 100A and voltage up to 3000V, as well as optimize the often complex and time-consuming set-up changes between ON-state, OFF-state, and capacitance measurements with Keithley power device test solutions.

Typical ON-state measurement setup.

Floating differential measurements (such as high-side Vgs) are difficult or impossible to make due to high frequency (fast turn on and turn offs), and the presence of high common mode voltages (such as Vds) because oscilloscope probes do not have sufficient common mode rejection at high bandwidth. The poor common mode rejection leads to the measurement being dominated by the common mode error instead of the actual differential signal. Tektronix has the only solution offering an isolated probe (IsoVu) that does not de-rate with frequency at the operating requirements of GaN and SiC devices, allowing you to make accurate differential measurements. This allows you to precisely calculate and prove conduction losses, dead time losses, switching losses. Additionally, if you are not using an integrated gate driver, the ability to make floating differential measurements allows you to precisely measure and control dead-time for turn-on and turn-off of your device. You can also now avoid overestimation of high-frequency emissions from power converters due to the transient voltage (dv/dt) and current generated during hard switching.

One more thing to watch out for is the impact of probe capacitance at higher switching frequencies. Too much probe capacitance results in the rising edge of the being rounded off in the measurement, leading to important high frequency switching characteristics being lost. Also, adding the probe to the very sensitive floating gate signals can lead to damaging the device due to transient signals caused capacitance charge. The low capacitance of the IsoVu probe also minimizes probe capacitance issues at the gate and risk of damage to the device due to transient signals.

With the IsoVu probe, the high-side gate voltage waveform can be accurately captured to evaluate and optimize switching performance and reliability without degrading dV/dt.