Understanding and Tuning Mobile Interfaces in Ferroelectric Hf _0.5 Zr _0.5 O ₂ Thin Films in Relation to Microstructure

ABSTRACT We investigate the field‐ and frequency‐dependent dielectric response in ferroelectric (HZO) thin films at subswitching conditions by impedance spectroscopy. Two different capacitor stacks were fabricated and tested on ‐type doped Si/Mo substrates and Mo top contacts, both had a 7‐nm‐thick HZO layer grown by atomic layer deposition (ALD) with either (HZO #1) or (HZO #2) as oxidizing agents. Impedance spectra from 100 Hz to 1 MHz were collected at different excitation field amplitudes on the ferroelectric HZO capacitors in pre‐poled and non‐saturated polarization conditions. Impedance spectra were fit with an equivalent‐circuit model incorporating a domain wall pinning element, to account for mobile interfaces (either domain walls and/or interphase boundaries) to the dielectric response. Using a Rayleigh analysis, we determine a stronger pinning of mobile interface segments in HZO #2 as compared to HZO #1. Only HZO #2 exhibits partial switching behavior for field amplitudes exceeding 0.7 MV/cm , together with a higher coercive field and dislocation density, which is beneficial for neuromorphic computing applications. Our results demonstrate the high tunability of HZO films for different ferroelectric devices and describe a systematic method to optimize HZO films for their specific target application.