Effect of capping layer on the ferroelectricity of hafnium oxide

•The effect of AlOxcapping layer on HfO2MFM devices wereinvestigated.•Ferroelectric polarization can be significantly improved by AlOxcapping.•Nitrogen plasma treatment on AlOxcan alleviate stress-induced defect traps.•AlOxlayer with nitrogen incorporation further improve electrical stress resistance. 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.