Improved Performance of MoS₂ Negative-Capacitance Field-Effect Transistors With Hf_1–xLa_xO_yN_z as Gate Dielectric by Optimizing La Content and Anneal Temperature Plus NH₃-Plasma Treatment

A negative-capacitance field-effect transistor (NCFET) is fabricated by co-sputtering lanthanum (La)-doped hafnium-based oxynitride (HfLaON) as ferroelectric gate dielectric and using MoS2 as the channel. The ferroelectricity of the HfLaON thin films is verified through microanalyses on the thin film and electrical characterization. Effects of La content and anneal temperature on the ferroelectricity of the thin films and electrical properties of MoS2 NCFETs are investigated. It is found that a low subthreshold swing (SS = 44.5 mV/dec) and small hysteresis (94.4 mV) can be achieved when the La content and anneal temperature are 10% and 800 °C respectively, due to the formation of more orthorhombic phases and thus enhanced ferroelectricity. Further, a remote NH3-plasma treatment is used to improve the quality of the HfLaON thin film and electrical properties of the devices, which results in a lower SS (38.2 mV/dec), a smaller hysteresis (54.7 mV), and a higher ON/ OFF current ratio (1.57 $\times \,\,10^{{6}}$ ) than that of the device without NH3-plasma treatment. The involved mechanisms lie in the fact the N incorporation into the thin film could improve the qualities of the thin film and its interfaces by passivating oxygen vacancies and dangling bonds, and reducing its surface roughness, which enhances the ferroelectricity of the thin films and thus negative-capacitance (NC) effect of NCFETs.