A Novel Evaluation Method of the Effect of Space Charge in Insulating Materials to IGBTs Blocking Voltage

We propose a novel evaluation method for the effect of space charge in passivation materials to blocking voltage of high voltage power devices like IGBT and diode devices. In the method, an electrode called Guard Probe (GP) is placed above the edge termination area of high voltage power chip. Dependence of the collector current on collector-emitter voltage (
$\mathbf{I}_{\text{ce}}-\mathbf{V}_{\text{ce}}$
curve) is measured repeatedly with increasing the voltage applied to the GP electrode step-by-step. The GP electrode simulates the space charges which are the major cause of long-term instability of high voltage devices. The GP voltage when an indication of avalanche breakdown, that is a sudden increase of
$\mathbf{I}_{\text{ce}}$
, appeared in
$\mathbf{I}_{\text{ce}}-\mathbf{V}_{\text{ce}}$
curve just below the rated voltage, is defined as “the GP voltage at avalanche breakdown”. A good correlation between the GP voltage at avalanche breakdown and long-term instability of
$\mathbf{I}_{\text{ce}}$
was observed for several IGBT and diode devices with different edge termination structures and passivation materials. Therefore, the GP voltage at avalanche breakdown can be used as an index of ruggedness of high voltage power devices against external electric field perturbation by space charges in passivation and encapsulation materials.