박민혁 교수

The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, l

The effects of annealing temperature (Tanneal) and film thickness (tf) on the crystal structure and ferroelectric properties of Hf0.5Zr0.5O2 films were examined. The Hf0.5Zr0.5O2 films consist of tetragonal, orthorhombic, and monoclinic phases. The orthorhombic phase content, which is responsible for the ferroelectricity in this material, is almost independent of Tanneal, but decreases with increasing tf. In contrast, increasing Tanneal and tf monotonically increases (decreases) the amount of mo

To elucidate the origin of the formation of the ferroelectric phase in Hf0.5Zr0.5O2 films, the effects of film strain and crystallographic orientation on the properties were examined. Using a (111)-textured Pt bottom electrode, Hf0.5Zr0.5O2 films with a (111)-preferred texture inappropriate for transforming their phase from non-ferroelectric tetragonal to ferroelectric orthorhombic phase were deposited. In contrast, randomly oriented Hf0.5Zr0.5O2 films, grown on the TiN electrode, showed feasibl

The unexpected ferroelectric properties of nanoscale hafnia-zirconia are considered to be promising for a wealth of applications including ferroelectric memory, field effect transistors, and energy-related applications. However, the reason why the unexpected ferroelectric Pca2₁ phase can be stabilized has not been clearly understood although numerous extensive theoretical and experimental results have been reported recently. The ferroelectric orthorhombic phase is not a stable phase u

The promising energy storage properties of new lead-free antiferroelectric HfxZr1-xO2 (x = 0.1–0.4) films with high energy storage density are reported. The energy storage density of the Hf0.3Zr0.7O2 capacitor does not decrease with the increase in temperature up to 175 °C, and it decreases by only ≈4.5% after field cycling 109 times.

Quantitative phase analysis is first performed on doped Hafnia films to elucidate the structural origin of unexpected ferroelectricity.

In this study, the changes in the structural and electrical properties of ferroelectric Hf1-xZrxO2 films with various Zr contents (0.26-0.70) were systematically examined during electric field cycling, resulting in a "wake-up" effect. To quantify the degree of wake-up effect, a "variable" polarization as the difference between remanent and saturation polarization was suggested as a new parameter, which could be calculated by excluding the linear dielectric contribution from the total electric di

Hf_1-xZr_xO₂ (x ∼ 0.5-0.7) has been the leading candidate of ferroelectric materials with a fluorite crystal structure showing highly promising compatibility with complementary metal oxide semiconductor devices. Despite the notable improvement in device performance and processing techniques, the origin of its ferroelectric crystalline phase (space group: Pca2₁) formation has not been clearly elucidated. Several recent experimental and theoretical studies

Abstract Ferroelectricity in fluorite structure oxides such as HfO 2 and ZrO 2 has been intensively studied since the first report on it in 2011. The ferroelectricity in this material system is induced by the formation of a non‐centrosymmetric orthorhombic phase, which is not thermodynamically stable under the normal thin‐film processing conditions. Therefore, the thermodynamic and kinetic origins of the formation of the ferroelectric phase have yet to be clearly elucidated. Here, the previously

The effects of forming gas annealing (FGA) on the ferroelectric properties of Hf0.5Zr0.5O2 (HZO) films were examined. Although the H-incorporation during FGA degrades the ferroelectric properties of Hf0.5Zr0.5O2 films, the degree of degradation was much lower compared with other ferroelectrics, such as Pb(Zr,Ti)O3. Pt worked as a catalyst for H-incorporation, and maximum 2Pr loss of ∼40% occurred. However, the insertion of a ∼20-nm-thick TiN layer between Pt and Hf0.5Zr0.5O2 decreased the degrad

The effects of film thickness and wake-up field cycling on the ferroelectricity in Hf0.5Zr0.5O2 films thinner than 8 nm were carefully examined. The Hf0.5Zr0.5O2 films became more antiferroelectric-like with decreasing film thickness in pristine state, whereas all the Hf0.5Zr0.5O2 films showed ferroelectric characteristics after wake-up process. The decrease in the coercive field with decreasing film thickness could be understood based on the depolarization correction. From the temperature-depen

Over the last few decades, the research on ferroelectric memories has been limited due to their dimensional scalability and incompatibility with complementary metal-oxide-semiconductor (CMOS) technology. The discovery of ferroelectricity in fluorite-structured oxides revived interest in the research on ferroelectric memories, by inducing nanoscale nonvolatility in state-of-the-art gate insulators by minute doping and thermal treatment. The potential of this approach has been demonstrated by the

Hf0.5Zr0.5O2 films could show excellent ferroelectricity with a large remanent polarization (Pr, > 16 μC/cm2) on TiN and Ir electrodes, but their Pr decreased with the increasing thickness and monoclinic phase portion. The critical thickness for the degradation of the ferroelectricity of Hf0.5Zr0.5O2 films was smaller on the Ir electrode than the TiN electrode. This was due to the formation of larger grains, favorable for the formation of the monoclinic phase, on the Ir electrode than on the TiN