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The impact of N on HfAlON dielectrics has been extensively studied in devices with TaN metal and poly-Si gate electrodes. A similar trend of the N effects was observed in both TaN and poly-Si devices in terms of equivalent oxide thickness, gate leakage current, threshold voltage (V th), transconductance, and subthreshold swing. However, compared to the HfAlON with TaN metal gate, a severe V th instability induced by charge trapping was generally observed in the poly-Si/HfAlON devices. In addition, the incorporation of N in the HfAlON films was found to play an opposite role in the V th instability between the TaN and poly-Si devices: In the TaN metal gate devices, the charge-trapping-induced V th instability in the HfAlON was slightly degraded by increasing the N concentration, whereas the V th instability was remarkably improved by increasing the N concentration in the poly-Si gate devices. The degradation of the V th instability observed in the TaN metal gate devices is believed to be due to the increase in preexisting bulk traps that is caused by incorporating N into the gate dielectric. The significant improvement on the V th instability in the devices with poly-Si gate could be mainly attributed to the remarkable suppression of electron trapping at oxygen vacancies by adding N into the high-K gate dielectric.