Total Ionizing Dose Effects on the Threshold Voltage of GaN Cascode Devices

GaN devices are nowadays attracting global attention due to their outstanding performance in high voltage, high frequency, and anti-radiation ability. Research on total ionizing dose and annealing effects on E-mode GaN Cascode devices has been carried out. The Cascode device consists of a low-voltage MOSFET and a high-voltage depletion-mode GaN MISHEMT. Cascode devices of both conventional processed MOSFET and radiation-hardened MOSFET devices are fabricated to observe the TID effects. Experiment results indicate that, for the Cascode device with conventional processed MOSFET, the V_TH shifts to negative values at 100 krad(Si). For the Cascode device with radiation-hardened MOSFET, the V_TH shifts by -0.5 V at 100 krad(Si), while shifts to negative values are 500 krad(Si). The annealing process, after the TID experiment, shows that it can release trapped charges and help V_TH recover. On one hand, the V_TH shift and recover trends are similar to those of a single MOSFET device, suggesting that the MOSFET is the vulnerable part in the Cascode which determines the anti-TID ability of the device. On the other hand, the V_TH shift amount of the Cascode device is much larger than that of a previously reported p-GaN HEMT device, indicating that GaN material shows a better anti-TID ability than Si.