Influence of chemical composition and mechanical strain on the ferroelectricity of freestanding Hf1-xZrxO2 membranes

Abstract

Freestanding Hf_1-xZr_xO₂ (HZO) membranes have received considerable attention for their potential in flexible electronics applications. The relaxation of substrate clamping usually results in the emergence of non-ferroelectric phases, which leads to a reduction in remanent polarization (P_r). In this study, by optimizing the chemical composition and appropriately increasing the Zr content (x), the ferroelectric properties are significantly enhanced, with a 10-nm-thick HZO membrane achieving a 2P_r of approximately 59 μC/cm². Furthermore, in situ morphological, structural and electrical measurements under uniaxial tensile strains are conducted on freestanding HZO membranes by using a custom-built stretching stage. At a strain as low as 0.05%, the ferroelectricity is slightly diminished, indicating a small degree of strain-induced phase transformations, although the external mechanical strain is largely mitigated by the formation of cracks. The mechanical damages to the membranes can gradually increase with cyclic strains (0.05%), eventually leading to complete membrane failure after just a few cycles. This suggests that the HZO membranes exhibit poor durability under mechanical stretching, even at such a low strain level (0.05%). Therefore, further research is required to improve the stretching stability of freestanding HZO membranes.