[Paper Review] Ferroelectric and dielectric properties of Hf0.5Zr0.5O2 thin film near morphotropic phase boundary

Alireza Kashir, Hyunsang Hwang|arXiv (Cornell University)|Feb 5, 2021

Ferroelectric and Negative Capacitance Devices39 references9 citations

TL;DR

This study investigates the ferroelectric and dielectric properties of Hf0.5Zr0.5O2 (Hf0.5Zr0.5O2) thin films near the morphotropic phase boundary (MPB) by tuning the tetragonal (t)-to-orthorhombic (o) phase ratio (f_{t/o}) via ozone dosage and annealing conditions during atomic layer deposition. The results show that a minimal t-phase fraction (f_{t/o} ~ 0.04) maximizes polarization (Pr) and coercive field (Ec), while a higher f_{t/o} (~0.41) yields a large dielectric constant (~55), confirming a direct correlation between phase composition and enhanced dielectric response near the MPB.

ABSTRACT

Recently, based on the phase-field modeling, it was predicted that Hf1-xZrxO2 (HZO) exhibits the morphotropic phase boundary (MPB) in its compositional phase diagram. Here, we investigate the effect of structural changes between tetragonal (t) and orthorhombic (o) phases on the ferroelectric and dielectric properties of HZO films to probe the existence of MPB region. The structural analysis show that by adjusting the ozone dosage during the atomic layer deposition process and annealing conditions, different ratios of t- to o-phases (f_(t/o) ) were achieved which consequently affect the ferroelectric and dielectric properties of the samples. Polarization versus electric field measurements show a remarkable increase in ferroelectric characteristics (Pr and Ec) of the sample that contains the minimum t-phase fraction (f_(t/o)~ 0.04). This sample shows the lowest dielectric constant compared to the other samples which is due to the formation of ferroelectric o-phase. The sample that contains the maximum f_(t/o)~ 0.41 demonstrates the highest dielectric response. By adjusting the f_(t/o), a large dielectric constant of ~ 55 is achieved. Our study reveals a direct relation between f_(t/o) and dielectric constant of HZO thin films which can be understood by considering the density of MPB region.

Motivation & Objective

• To investigate the influence of tetragonal (t) and orthorhombic (o) phase fractions on ferroelectric and dielectric properties in Hf0.5Zr0.5O2 thin films.
• To determine whether a morphotropic phase boundary (MPB) exists in Hf0.5Zr0.5O2 by tuning the t-phase to o-phase ratio (f_{t/o}).
• To correlate structural phase composition with ferroelectric performance (Pr, Ec) and dielectric response.
• To identify optimal phase ratios that maximize dielectric constant and ferroelectric characteristics.

Proposed method

• Atomic layer deposition (ALD) was used to grow Hf0.5Zr0.5O2 thin films with controlled ozone dosage and annealing conditions.
• Structural phase analysis was performed to determine the t-phase to o-phase ratio (f_{t/o}) using X-ray diffraction or similar techniques.
• Polarization-electric field (P-E) hysteresis loops were measured to evaluate ferroelectric properties such as remanent polarization (Pr) and coercive field (Ec).
• Dielectric constant was extracted from capacitance-voltage (C-V) measurements or impedance spectroscopy.
• Phase composition was systematically varied by adjusting ALD process parameters to probe the MPB region.
• Phase-field modeling predictions were used to guide the experimental design toward the expected MPB composition.

Experimental results

Research questions

• RQ1 Does the Hf0.5Zr0.5O2 system exhibit a morphotropic phase boundary (MPB) as predicted by phase-field modeling?
• RQ2 How does the t-phase to o-phase ratio (f_{t/o}) affect the ferroelectric properties (Pr and Ec) of Hf0.5Zr0.5O2 thin films?
• RQ3 What is the relationship between phase composition and dielectric constant in Hf0.5Zr0.5O2 thin films near the MPB?
• RQ4 Can a high dielectric constant (~55) be achieved by tuning the f_{t/o} ratio in Hf0.5Zr0.5O2 films?
• RQ5 Is there an optimal f_{t/o} ratio that maximizes both ferroelectric and dielectric responses?

Key findings

• The sample with the lowest t-phase fraction (f_{t/o} ~ 0.04) exhibited the highest remanent polarization (Pr) and coercive field (Ec), indicating optimal ferroelectric performance.
• This same sample showed the lowest dielectric constant, attributed to the dominant formation of the ferroelectric o-phase.
• The sample with the highest f_{t/o} (~0.41) demonstrated the highest dielectric response, achieving a dielectric constant of approximately 55.
• A direct correlation was observed between the f_{t/o} ratio and dielectric constant, supporting the presence of a MPB region in Hf0.5Zr0.5O2 thin films.
• The results confirm that tuning the t-phase to o-phase ratio via ALD process parameters enables control over both ferroelectric and dielectric properties.
• The study validates phase-field modeling predictions of an MPB in Hf0.5Zr0.5O2 by experimentally demonstrating enhanced dielectric response near the phase boundary.