Search

Ferroelectric thin films based on HfO2 have garnered increasing attention worldwide, primarily due to their remarkable compatibility with silicon and scalability, in contrast to traditional perovskite-structured ferroelectric materials. Nonetheless, significant challenges remain in their widespread commercial utilization, particularly concerning their notable wake-up effect and limited endurance. To address these challenges, we propose a novel strategy involving the inhomogeneous distribution of Hf/Zr elements within thin films and explore its effects on the ferroelectricity and endurance of Hf0.5Zr0.5O2 thin films. Through techniques such as grazing incidence X-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy, we investigated the structural characteristics and domain switching behaviors of these materials. The experimental results indicate that the inhomogeneous distribution of Hf/Zr contributes to improving the frequency stability and endurance while maintaining a large remnant polarization in Hf0.5Zr0.5O2 ferroelectric thin films. By adjusting the distribution of Zr/Hf within the Hf0.5Zr0.5O2 thin films, significant enhancements in the remnant polarization (2Pr > 35 μC/cm2) and endurance (> 109) along with a reduced coercive voltage can be achieved. Additionally, the fabricated ferroelectric thin films also exhibit high dielectric tunability (≥ 26%) under a low operating voltage of 2.5 V, whether in the wake-up state or not. This study offers a promising approach to optimize both the ferroelectricity and endurance of HfO2-based thin films.

Hf0.5Zr0.5O2 (HZO) ferroelectric thin films have gained significant attention for the development of next-generation ferroelectric memories by complementary-metal-oxide semiconductor (CMOS) back-end-of-line (BEOL) processing, due to their relatively low crystallization temperature. However, it remains challenging to achieve excellent ferroelectric properties with post deposition annealing (PDA) process at a BEOL compatible temperature. Along these lines, in this work, it is demonstrated that the ferroelectricity of 15 nm thick HZO thin film prepared by PDA process at 400 °C can be improved to varying degrees, via depositing 2 nm thick dielectric layers of Al2O3, HfO2, or ZrO2 at either the bottom or the top of the film. Notably, the HZO thin film with the top-Al2O3 layer exhibits remarkable ferroelectric properties, which are independent of the thickness of HZO. The 6 nm thick HZO thin film shows a total remanent polarization (2Pr) of 31 μC/cm2 under an operating voltage of 2.5 V. These results represent a significant advancement in the fabrication of high-performance, BEOL compatible ferroelectric memories, as compared to previously reported state-of-the-art works.

Abstract The metastable polar orthorhombic phase is believed to be the origin of the ferroelectricity of hafnia-based films. The adjustment of stain, oxygen vacancies and dopant during film deposition and the wake-up electric cycling are common strategies to induce the ferroelectricity in hafnia. However, none of them could independently render the ferroelectric phase to be the most stable phase from the theoretical calculation results. The exact external conditions to stabilize orthorhombic phase still remain elusive. In this paper, we investigate the effects of the type, distribution, concentration, and charge state characteristics of oxygen vacancies and the uniaxial strain on the crystal’ energy, dielectric constant and spontaneous polarization (P s ); In addition, the impact of the applied electric field parallel to the P s on the crystal’ energy is explored by first-principles calculations. It is challenging to independently stabilize the ferroelectric phase of hafnia-based films by a single component owing to the rather strict conditions. Surprisingly, the ferroelectricity can be easily obtained when simultaneously considering the effects of oxygen vacancies, uniaxial strain, and applied electric fields, suggesting the extremely important mechanical-electrical-chemical coupling effects. This work provides an explanation for the typical wake-up phenomenon in hafnia and a guidance for film applications.

HfO2-based ferroelectric field-effect transistors (FeFETs) are regarded as one of the most promising non-volatile memory technologies in the future. However, the charge trapping phenomenon during the program/erase operation is still a challenge. In this work, we comprehensively investigate the behaviors of semiconductor/insulator interface charge trapping in HfO2-based FeFETs. Through analyzing the effects of the spatial distribution of interface traps and the polarization switching speed, the coupling effects of semiconductor/insulator interface charge trapping and polarization switching are recognized. We also find that the band tail state traps have much less influence on the electrical characteristics of the FeFETs than the deep level state traps. Through engineering the devices with band tail state traps with concentrations as small as possible, the influences of charge trapping could be effectively suppressed. Moreover, the gate voltage (VG) scanning rate has a significant influence on the interface charge trapping process due to the time dependent change of ferroelectric polarization. The largest memory window could be obtained by carefully choosing the VG scanning rate of the FeFETs based on the polarization switching speed. This work represents a key step for realizing highly reliable HfO2-based FeFETs.

The gases discharged from the new generation of lean-burn combustors usually have hot streaks (HS) and swirls. The thermal performance of rotor thermal barrier coatings (TBCs) exhibits significant non-constant behavior due to inlet non-uniformity and blade row interaction. To investigate the non-constant thermal insulation performance of the blade TBCs, non-constant numerical simulations were carried out for the first stage vane and blade of the High-pressure turbine of the GE-E3 engine. The normalized temperature results for the HS and the combination of HS and swirl cases were compared with the uniform inlet case to investigate the effect of inlet non-uniformity on the surface temperature and thermal insulation effect of the blade TBCs. The results show that a credible investigation of rotor TBCs should consider the unsteady blade row interaction. HS causes high-temperature hot spots on the surface of the TBCs and redistributes them with the change in the direction of the swirl. HS and swirl significantly reduce the turbine blade cooling effectiveness and thermal insulation effectiveness of TBCs. The lowest overall cooling performance of the blades was observed during the 1/4 T stator period. The added swirl reduces the insulation effectiveness's fluctuation value by reducing positive swirl (PSW) by 52.6 % and negative swirl (NSW) by 57.8 %. Therefore, applications and designs of TBCs should consider the effects of HS and swirl.

The leaf epidermis is sealed by a lipid-rich cuticle to prevent water loss and interspersed with stomatal pores to allow gas exchange. Here the authors provide evidence that two barley proteins, HvYDA1 and HvBRX-Solo, regulate both processes linking epidermal patterning with cuticular properties in a cereal crop.

Multilevel ferroelectric field−effect transistors (FeFETs) integrated with HfO2−based ferroelectric thin films demonstrate tremendous potential in high−speed massive data storage and neuromorphic computing applications. However, few works have focused on the stability of the multiple memory states in the HfO2−based FeFETs. Here we firstly report the write/read disturb effects on the multiple memory states in the Hf0.5Zr0.5O2 (HZO)−based FeFETs. The multiple memory states in HZO−based FeFETs do not show obvious degradation with the write and read disturb cycles. Moreover, the retention characteristics of the intermediate memory states in HZO−based FeFETs with unsaturated ferroelectric polarizations are better than that of the memory state with saturated ferroelectric polarization. Through the deep analysis of the operation principle of in HZO−based FeFETs, we speculate that the better retention properties of intermediate memory states are determined by the less ferroelectric polarization degradation and the weaker ferroelectric polarization shielding. The experimental and theoretical evidences confirm that the long−term stability of the intermediate memory states in HZO−based FeFETs are as robust as that of the saturated memory state, laying a solid foundation for their practical applications.

HfO2-based ferroelectrics have evoked considerable interest owing to the complementary metal–oxide semiconductor compatibility and robust ferroelectricity down to a few unit cells. However, the unique wake-up effect of HfO2-based ferroelectric films severely restricts the improvement of their performance. In particular, the domain structure is an important characteristic of ferroelectric materials, which still has not been well understood in HfO2-based ferroelectrics. In this work, a Hf0.5Zr0.5O2 ferroelectric thin film is grown on a typical Si substrate buffered with TiN electrode. The 90° domains of the Pca21 ferroelectric phase with head-to-tail and tail-to-tail structures can be observed by Cs-corrected scanning transmission electron microscope under their pristine condition. After waking up, the 180° domain is displayed in the ferroelectric phase. The remarkable differences in domain walls for 90° and 180° domains are characterized by qualitatively mapping the polarization distributions at the atomic scale. The domain wall changes from the [Formula: see text] of the Hf0.5Zr0.5O2 film to the [001] of the Hf0.5Zr0.5O2 film. This result provides fundamental information for understanding the domain structure of HfO2-based ferroelectrics.

Thermal barrier coatings (TBCs) are inevitably subject to corrosion caused by molten calcium-magnesium-alumino-silicate (CMAS), which leads to severe degradation in the properties of the coatings. In this study, a novel device for evaluating the wetting performance of molten CMAS was developed, which solved the challenging problem of measuring the contact angle of CMAS on TBCs at high temperatures. The wetting and spreading behaviour of CMAS under various conditions was studied, and the effect of various factors such as temperature, surface roughness, and the coating preparation process on the wetting behaviour was systematically analysed using this new method. The results demonstrate that the spreading distance can decrease and the contact angle can increase on rough surfaces, and the contact angle is proportional to the square of the roughness at the stable stage. The wettability is also determined by the viscosity, which in turn is governed by the temperature and the reactive production of CMAS and the coatings.

Abstract The HfO2-based ferroelectric field effect transistor (FeFET) with a metal/ferroelectric/insulator/semiconductor (MFIS) gate stack is currently being considered as a possible candidate for high-density and fast write speed non-volatile memory. Although the retention performance of the HfO2-based FeFET with a MFIS gate stack could satisfy the requirements for practical applications, its memory window (MW) and reliability with respect to endurance should be further improved. This work investigates the advantage of employing ZrO2 seed layers on the MW, retention, and endurance of the Hf0.5Zr0.5O2 (HZO)-based FeFETs with MFIS gate stacks, by using fast voltage pulse measurements. It is found that the HZO-based FeFET with a ZrO2 seed layer shows a larger initial and 10-year extrapolated MW, as well as improved endurance performance compared with the HZO-based FeFET without the ZrO2 seed layer. The results indicate that employing of a direct crystalline high-k/Si gate stack would further improve the MW and reliability of the HfO2-based FeFETs.

The multilevel memory performances of ferroelectric field effect transistor (FeFET) with Hf0.5Zr0.5O2 (HZO) ferroelectric thin film are investigated. First, similar retention characteristics are observed for intermediate and saturated polarization states of HZO ferroelectric thin film, which enables memories for multi-bit data storage. And then, 2-bit/cell operation of HZO-based FeFET is demonstrated utilizing two NAND architecture compatible write schemes of varying program pulse amplitude and width. Low cycle-to-cycle variability, long retention to extrapolation of 10 years at 85°C, and endurance of 500 cycles are achieved for the both schemes. Moreover, the mechanism for multilevel memory operations of the FeFET is illustrated based on the polarization switching dynamics of HZO ferroelectric thin film.

Two-dimensional electron gases that form in some complex oxide heterostructures may have useful functional behavior due to the interaction of the parent materials. Here the authors show that PZT/STO interfaces can host a spin-polarized electron gas, even though the bulk materials are nonmagnetic.

We experimentally demonstrate that hysteresis of negative capacitance (NC) Ge pFETs is reduced through modulating the ferroelectric properties in HfZrOx (HZO) by changing the post annealing temperature. As annealing temperature varies from 350 °C to 450 °C, HZO exhibits a significant increasing in the ratio of remnant polarization Pr to coercive field Ec, which results in the improvement of the magnitude of ferroelectric NC CFE, therefore contributing to the reduction of hysteresis of the ferroelectric NC Ge transistors. It is also reported that the NC Ge transistor annealed at 450 °C has a small hysteresis of 0.10 V, and achieves the improved SS and IDS compared to control device without HZO.

Volcanic ash (VA) corrosion is a critical factor accelerating the failure of thermal barrier coatings (TBCs). The service life of the TBCs corroded by molten VA is controlled by its penetration depth. Here theoretical model as well as experimental testing is carried out to systematically investigate the factors influencing the penetration depth of VA. The results demonstrate that the most significant factor is the temperature, followed by the infiltration time and VA amount, while both exhibit more obvious effect than the surface roughness of TBCs. Furthermore, a theoretical approach to inhibit the penetration of VA is also proposed based on Cassie model. Keywords: Thermal barrier coatings, Volcanic ash, Modeling, Infiltration

Using scanning transmission electron microscopy, we report direct observation of oxygen vacancy ordering induced atomic displacements of the cation sub-lattice in yttria-stabilized zirconia (YSZ). We find that the cation lattice adopts a zigzag configuration along the [100] direction with alternately narrow and wide lattice spacings equivalent of 0.85 and 1.15 times of the (200) inter-planar distance of the cubic YSZ. Using atomistic simulations, we show that the cation displacements are induced by the alternate presence of oxygen vacancies at the (1/4, 1/4, 1/4) and (1/4, 3/4, 1/4) sites of the unit cells in the [001] direction. The results demonstrate that significant enrichment of yttrium atoms can occur within individual YSZ grains in addition to the typical surface or grain boundary segregation of dopant atoms.