Tetravalent doping in hafnium-zirconium oxides to lower polarization switching voltage

Effects of tetravalent doping (Si, Ge, Ti, Ce) are investigated in hafnium-zirconium oxide (HZO). Density functional theory is employed to demonstrate: 1) relative stability change, 2) polarization switching energy barrier, and 3) electronic structures in doped HZO. Si and Ge induce large local bond distortions and have more significant effects on stabilizing the tetragonal phase and lowering the polarization switching voltage than Ti and Ce. They also do not introduce any midgap states rendering great promise for memory applications.