As the devices (i.e. DUT1~4) were not failed, more
stringent stress was further used to investigate the device failure
mechanism. The DUT5 was stressed at V GS=6 V,V DD=70 V with a larger SC pulse duration ofT SC=20 μs. DUT5 failed within the16th SC cycle with the SC waveform as shown in
Fig. 7. It can be seen that the SC current I Dexhibits an abrupt increase at 20.5 μs. The failed device behaves as the
typical electrical shorting behavior between the drain and gate
terminal. The failed device is then decapsulated and drain electrode
burnout was
observed
in Fig. 8 (a). Since the SC current before the device failure is 17.4 A
that is even lower than that as shown in Fig. 2 (b), the device failure
is prone to be induced by the substantially high SC energy and its
accumulation effect during the repetitive SC events (e.g. the1st ~15thSC cycles) prior to eventual device failure.
We compare the SC energy (E SC) of a single SC
pulse of DUT-1~5 as illustrated in Fig. 8 (b). It is
worth noticing that E SC increases with the
enhanced SC stress. Besides, the E SC of DUT1-4
are much lower compared with DUT-5 attributes to the longerT SC. More importantly, the much higher SC energy
can cause a higher local temperature close to the drain electrode
[3], [4]. The local temperature fluctuates between on-state and
off-state in the repetitive SC cycles, generating cyclic mechanical
stress of thermal expansion and contraction phases. Together with the
repetitive SC events, the mechanical stress leads to accumulative
degradation at drain electrodes during the 1stto 15th SC cycles. After that, in the16th SC cycle, the accumulative degradation
exceeds to a critical level and leads to fatigue failure and then the
subsequent gate-to-drain short circuit with abrupt increase in SCI D as observed in Fig. 7(c). Consequently, the
substantially high current results in the catastrophic thermal burned up
of the two drain electrodes as shown in Fig. 8 (a).
Conclusion: The SC capability and device failure mechanism of the
100 V p-GaN gate HEMTs were investigated by the repetitive SC stress. In
the repetitive SC stress with 150 SC cycles atV GS=6 V,V DD=40~70 V andT SC=10 μs, the device exhibits strong repetitive
SC capability without device failure. However, significant positive
shift in V th stems from electron trapping in the
p-GaN/AlGaN gate stack is observed prior to the device failure.
Accordingly, the electron-filled traps in turn to result in a suppressed
gate leakage and off-state drain leakage current in the device after SC
stress. By further enhancing the SC stress condition with a larger SC
duration of 20 μs, the device can withstand ~15 cycles
at V GS=6 V and V DD=70 V.
The resultant significantly higher SC energy leads to thermal fatigue
crack formation at the drain electrode due to the local temperature
fluctuations, which results in the consequent thermal burnout.