Stage I/2022

In this stage, preliminary technological parameters were obtained for the deposition by magnetron sputtering (MS) of HfO₂ and Ge_xSn_1-x films to create HfO₂/Ge_xSn_1-x neuronal-type synaptic structures. GeSn films were obtained by co-deposition in DC mode from separate Ge and Sn targets. GeSn nanocrystals (NC) and the crystallization of HfO2 layers are formed by RTA thermal treatments in a hydrogen atmosphere. After the thermal treatments of the GeSn layers, crystallization is initiated from 350 ^oC with a slight formation of β - Sn, and at 450 ^oC we obtain a clear separation of the two constituent phases, Ge, respectively β - Sn. In the case of the HfO₂/GeSn structure, the amorphous state is maintained up to 250 ^oC; above this temperature, the formation of GeSn NCs begins, which is very clearly evident at 450 ^oC, without the formation of the β-Sn phase. Above 450 ^oC, the crystallization of the HfO₂ layer begins, which at 550 ^oC shows a mixture of monoclinic and orthorhombic phases together with GeSn NCs. The absence of β-Sn phase formation up to temperatures above 500 ^oC in the case of HfO₂/GeSn structures compared to GeSn films can be explained by the appearance of stress at the interface of GeSn with HfO₂ during deposition. This stress can be due to the flow of atoms reaching the support and their energy (translated experimentally by the deposition rate and the power applied to the magnetron) and/or by the implantation of atomic hydrogen in the structure. Through XRR measurements, the density of 8.5 g/cm³ (ρHfO₂= 9.68 g/cm³-bulk) and the roughness of 0.7 nm for the HfO₂ layer and the density of 5.42g/cm³ (ρGe= 5.32 g/cm³-bulk, ρSn= 7.3 g/cm³-bulk) and the roughness of 1.2 nm for the GeSn layers. From the analysis of the Raman spectra obtained at various values of the incident laser power, the concentration of Sn in the GeSn NC was obtained between 6.3% and 8.2% Sn concentration in GeSn NCs. For the nanostructures treated by RTA at 250 ^oC, 550 ^oC and without thermal treatment, a residual polarization of ~1 μC/cm² was obtained, and the shape of the hysteresis curve shows the capacitive character combined with ohmic conduction caused by the formation of β - Sn.