Ultra-Thin HZO Films for Low-Voltage Ferroelectric Memories: FINC Activation, BEoL Compatibility, and Reliability

We systematically investigate the crystallization onset and ferroelectric (FE) properties of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{H f}_{0.5} \mathbf{Z r}_{0.5} \mathbf{O}_{2} (\mathbf{H Z O})$</tex> thin films with thicknesses between 4 nm and 12 nm. Grazingincidence X-ray diffraction (GIXRD) reveals that films <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\geq 7 \text{nm}$</tex> crystallize below 400 °C, while thinner films require higher annealing temperatures, limiting their compatibility with back-end-of-line (BEoL) integration. However, field-induced crystallization (FINC) enables FE switching in 5 nm-thick films, even in the absence of a clearly detectable crystalline diffraction lines, highlighting its potential to push thickness scaling beyond the conventional limits. In contrast, 4 nm films remain non-FE, suggesting that the presence of crystalline nuclei is a prerequisite for FINC activation. Films <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\geq 6 \text{nm}$</tex> exhibit characteristic wake-up behavior and robust ferroelectricity after low-field cycling. Temperature-dependent measurements confirm stable switching up to 200 °C for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5-7 \text{nm}$</tex> films, whereas thicker films suffer from increased leakage at elevated temperatures. These findings delineate an optimal thickness window for reliable FE performance, enabling ultra-thin, BEoL-compatible memory applications.