Hf(1-x)Z(x)O2 monolayers for nanosupercapacitors: a performance assessment study
Résumé
It’s been now more than a decade since the discovery of ferroelectricity in doped HfO2 thin films [1]. Among all other dopants, it has been shown that zirconium allows the lowest annealing temperature to crystallize orthorhombic phase, responsible for ferroelectricity, in polycrystalline Hf1-xZxO2 (HZO) monolayers [2]. Decreasing the annealing temperature allows to grow CMOS compatible monolayers. Additionally, a broader range of doping to crystallize the ferroelectric (FE) phase is observed for zirconium and at high doping, HZO layers can become antiferroelectric (AFE) [3]. The performance and properties of Metal/Insulator/Metal (MIM) capacitors will be presented, where the insulator is constituted by different HZO FE or AFE monolayers, depending on the processing conditions. A specific focus on AFE ZrO2 Energy Density Storage (ESD) in function of processing parameters (annealing temperature, monolayer thickness) will be presented. Our results show one of the highest, if not the highest, ESD ever reported so far of 125 mJ/cm3 for a ZrO2 monolayer of 10.3 nm. However, the efficiency and endurance of the MIM stack has also to be optimized and a wake-up effect is also observed for ZrO2 thin films, which is rarely observed for ZrO2 layers. A trade-off between these functional properties can be deduced from the study, to further optimize and reach the desired properties for a commercial supercapacitor. Nevertheless, the monolayer performance is extremely encouraging for attaining high energy storage density in multilayer stacks of HZO. 1] T. S. Böscke, J. Müller, D. Bräuhaus, U. Schröder, U. Böttger, Appl Phys Lett. 99, 102903 (2011). [2] J. Müller et al., Appl Phys Lett. 99, 112901 (2011). [3] Park, M. H., Lee, Y. H., Kim, H. J., Kim, Y. J., Moon, T., Kim, K. D., Müller, J., Kersch, A., Schroeder, U., Mikolajick, T., & Hwang, C. S., Advanced Materials, 27(11), 1811-1831 (2015).