On the Imprint Mechanism of Thin-Film Hf₀.₅Zr₀.₅O₂ Ferroelectrics

Imprint is a well-known phenomenon in metal–ferroelectric–metal (MFM) capacitors, yet the causal mechanisms are still unclear. The currently prevailing theory is that it is caused by variation, over the imprinting time, of internal electric fields that are due to charge displacement and incomplete polarization charge screening due to thin nonpolarizable layers at the interface between the polarizable ferroelectric (FE) phase and the electrodes. In the present work, by studying both imprint and its reversal in thin-film Hf0.5Zr0.5O2 (HZO) capacitors, we find that the dominant mechanism in imprinting and deimprinting is the variation of the activation electric field, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{a}$ </tex-math></inline-formula>, of nucleation of reversed polarity seeds in the individual domains of the film, postulated by the nucleation-limited FE switching theory. The displacement of any significant magnitude of charge does not appear to be involved in the FE imprint/deimprint phenomena, at least in thin-film HZO. The varying <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E} _{a}$ </tex-math></inline-formula> is likely a manifestation of seed inhibition, and it captures well the macroscopic phenomenology of imprint, but the detailed microscopic physical mechanism behind it is still unclear.