Experimental study of threshold voltage shift for Si:HfO₂based ferroelectric field effect transistor

For a given three different Si doping concentrations at room and high temperatures, the threshold voltage shift (ΔV th) on silicon-doped hafnium-oxide-based ferroelectric field effect transistor (FeFET) is experimentally investigated. It turned out that charge trapping in the gate stack of FeFET (versus polarization switching in the gate stack of FeFET) adversely affects ΔV th. Charge trapping causes the positive ΔV th, while polarization switching causes the negative ΔV th. The dominance of polarization switching is predominantly determined by the total remnant polarization (2P r), which can be controlled by adjusting Si doping concentration in the hafnium-oxide layer. As the Si doping concentration increases from 2.5% to 3.6%, and 5.0%, 2P r decreases 19.8 μC cm-2 to 15.25 μC cm-2, and 12.5 μC cm-2, which leads to ΔVth of -0.8 V, -0.09 V, and +0.1 V, respectively, at room temperature. At high temperature, the effect of polarization switching is degraded due to the decreased P r, while the effect of charge trapping is very independent of temperature. For those three different Si doping concentrations (i.e. 2.5%, 3.6%, and 5.0%), at the high temperature, ΔV th of FeFET is -0.675 V, -0.075 V, and +0.15 V, respectively. This experimental work should provide an insight for designing FeFET for memory and logic applications.