In this work, we investigate the effect of a capping layer of aluminum oxide (AlOx) on dopant-free hafnium-oxide (HfO2) ferroelectric layer. According to our experimental results, the AlOx-capped HfO2 ferroelectric capacitor exhibits the significant improvement on ferroelectric polarization strength and also presents a comparable electrical stress resistance in comparison with control HfO2 ferroelectric capacitor with a very weak ferroelectric hysteresis. An additional nitrogen treatment on AlOx capping layer effectively alleviate the stress-induced generation of defect traps near the interface of tantalum nitride (TaN) electrode under negative-bias voltage stress. Therefore, the performance improvement can be ascribed to the introduction of AlOx capping layer and well-controlled nitrogen plasma treatment to improve interface traps and stabilize the ferroelectric phase transformation during high-temperature annealing process.
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