Experimental Investigation of Variations in Polycrystalline Hf0.5Zr0.5O2 (HZO)-based MFIM

TL;DR

This study experimentally investigates device-to-device variations in Hf0.5Zr0.5O2-based ferroelectric capacitors, revealing how variations depend on voltage and thickness, and validating findings with phase-field simulations.

Contribution

It provides the first experimental validation of simulation-predicted polarization variation mechanisms in HZO-based devices, linking variations to domain nucleation and polycrystallinity.

Findings

PR variation peaks near coercive voltage (VC)

PR variations are influenced by charge traps and domain switching

Scaling down TFE reduces variation non-monotonicity

Abstract

Device-to-device variations in ferroelectric (FE) hafnium oxide (HfO2)-based devices pose a crucial challenge that limits the otherwise promising capabilities of this technology. Although previous simulation-based studies have identified polarization (P) domain nucleation and polycrystallinity as key contributors to variations in HfO2, experimental validation remains limited. Here, we experimentally investigate variations in remanent polarization (PR) of Hf0.5Zr0.5O2 (HZO)-based metal-ferroelectric-insulator-metal (MFIM) capacitors across different set voltages (VSET) and FE thicknesses (TFE). Our measurements reveal a non-monotonic behavior of the standard deviation of PR with VSET peaking around coercive voltage (VC), which is consistent with previous simulation-based predictions. In the low- and high-VSET regions, PR variations are primarily dictated by saturation polarization (PS) variations, mainly originating from charge trap effects at the interface between the FE-dielectric (DE) layer and the polycrystallinity of FE. On the other hand, in the mid-VSET region peak, the PR variations are attributed to the VC variation, which comes from a combined effect of multi-domain (MD) P switching and polycrystallinity. Notably, sharp P switching associated with domain nucleation amplifies the variations, resulting in a peak of PR variations in this VSET range. Further, we observe that as HZO thickness (TFE) is scaled, the non-monotonicity in variations with VSET is reduced, primarily due to reduced domain nucleation and smaller grain sizes. We experimentally establish a strong correlation of PR with PS in the low- and high-VSET regions and with VC in the mid-VSET region across various TFE. Finally, our experimental findings are corroborated with simulations using a 3D phase-field model.