High Coercive Field Research Articles

Investigation of Optimum Deposition Conditions of Radio Frequency Reactive Magnetron Sputtering of Al0.7Sc0.3N Film with Thickness down to 20 nm

AbstractFerroelectric aluminum scandium nitride (Al0.7Sc0.3N) has attracted increasing interest due to its high remanent polarization (Pr, >100 µC cm−2) and coercive field (Ec, >5 MV cm−1). The four radio frequency reactive magnetron sputtering conditions (sputtering power, N2 flow ratio, pressure, and temperature) influence the ferroelectric and material properties of 45 nm‐thick Al0.7Sc0.3N deposited on the TiN/SiO2/Si substrate. Crystallinity is enhanced under the deposition conditions with higher adatom energy but deteriorates when the growth condition increases over the optimum. The well‐crystallized films have (002)‐preferred orientation with the in‐plane compressive stress imposed by the peening effect and thermal stress. The imposed compressive stress increases the c0/a0 value, where c0 and a0 mean the c‐ and a–axis lattice parameters, which eventually increases the Ec of the film. Pr increases with the c0/a0 value, but other factors also influence the change. The films with high oxygen concentration show the wake‐up properties due to the large percentage of domain walls and their depinning. Finally, ferroelectricity is confirmed with films down to a thickness of 20 nm. However, the thinnest film shows a higher Ec and lower Pr. These findings imply the presence of non‐ferroelectric interfacial layers, which induce the depolarization effect.

Critical Importance of Nonuniform Polarization and Fringe Field Effects for Scaled Ferroelectric FinFET Memory

The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) and high coercive field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> leads to a large MW is not always valid. For a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields.

Tuning piezoproperties of BiFeO3 ceramic by cobalt and titanium dual doping

Bismuth ferrite is a potentially interesting lead-free piezoelectric material for use in high-temperature applications due to its high Curie temperature. However, the high coercive field and high leakage currents of pure BiFeO3 (BFO) prevent reaching its theoretical performance level. The classic approach to tailoring piezoceramic properties to their desired use conditions is the use of doping. In this work, we produce bulk BFO piezoceramic by the conventional sintering method with single element doping with cobalt (0.125–3 at. %) or titanium (1–5 at. %) and dual doping (Co and Ti added simultaneously). Cobalt doping reduces the required field for poling and also increases the leakage currents. Titanium doping reduces the leakage currents but destroys the piezoelectric properties as the coercive field strength cannot be reached. However, when both elements are used simultaneously at their appropriate levels (0.25 at. % each), a piezoelectric ceramic material is obtained, requiring a low field for full poling (9 kV/mm) and showing excellent room temperature performance such as a d33 = 40 pC/N, a dielectric constant in the region of 100 and dielectric losses less than 1%.

Effect of Substrate-RF on Sub-200 nm Al0.7Sc0.3N Thin Films.

Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing.

High performance high-power textured Mn/Cu-doped PIN-PMN-PT ceramics

Piezoelectric ceramics with combinatory soft and hard characteristics are highly desired for high-power applications. However, it remains grand challenge to achieve simultaneous presence of hard (e.g. high coercive field, Ec; high mechanical quality factor, Qm) and soft (e.g. high piezoelectric constant, d; high electromechanical coupling factor, k) piezoelectric properties in piezoelectric ceramics since the mechanism controlling the hard behavior (pinned domain walls) will significantly reduce the soft behavior. Here, we address this grand challenge and demonstrate <001> textured MnO2 and CuO co-doped Pb(In1/2Nb1/2)O3- Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics exhibiting ultrahigh combined soft and hard piezoelectric properties (d33 = 713 pC N−1, k31 = 0.52, Qm≈950, Ec = 9.6 kV cm−1, tan δ = 0.45%). The outstanding electromechanical properties are explained by considering composition/phase selection, crystallographic anisotropy and defect engineering. Phase-field model in conjunction with high resolution electron microscopy and diffraction techniques is utilized to delineate the contributions arising from intrinsic piezoelectric response, domain dynamics, and local structural heterogeneity. These results will have significant impact in the development of high-power transducers and actuators.

Annealing temperature dependence of crystalline structure and magnetic properties in nano-powder strontium-substituted cobalt ferrite

Strontium-substituted cobalt ferrite nanoparticles were synthesised via the co-precipitation method. Thermogravimetric analysis (TGA) showed that the relative reduction of the mass was supported by the available strontium cations. X-ray diffraction analyses clarified that single-phase nanoparticles were obtained and indicated that the strontium cations substituted metal cations in the cobalt ferrite nanoparticle system. The crystallite size increased on increasing the annealing temperature. By contrast, the crystalline stress decreased on increasing the annealing temperature. Furthermore, the saturated magnetisation decreased with an increased annealing temperature. Finally, the annealing temperature dependence of the coercive field is shown in this paper and the highest coercive field, HC, of 2.76 kOe is obtained for Sr0.1Co0.9Fe2O4 nanoparticles with an annealing temperature of 1000 °C. Here, the Sr2+ cations facilitate the high value of the anisotropic magnetic realisation for the whole annealing temperature treatment.

Electrochemical Deposition of Fe–Co–Ni Samples with Different Co Contents and Characterization of Their Microstructural and Magnetic Properties

In this study, to explore the effect of Co contents on the electroplated Fe–Co–Ni samples, three different Fe–Co33–Ni62, Fe–Co43–Ni53, and Fe–Co61–Ni36 samples were electrochemically grown from Plating Solutions (PSs) containing different amounts of Co ions on indium tin oxide substrates. Compositional analysis showed that an increase in the Co ion concentration in the PS gives rise to an increment in the weight fraction of Co in the sample. In all samples, the co–deposition characteristic was described as anomalous. The samples exhibited a predominant reflection from the (111) plane of the face–centered cubic structure. However, the Fe–Co61–Ni36 sample also had a weak reflection from the (100) plane of the hexagonal close–packed structure of Co. An enhancement in the Co contents caused a strong decrement in the crystallinity, resulting in a decrease in the size of the crystallites. The Fe–Co33–Ni62 sample exhibited a more compact surface structure comprising only cauliflower–like agglomerates, while the Fe–Co43–Ni53 and Fe–Co61–Ni36 samples had a surface structure consisting of both pyramidal particles and cauliflower–like agglomerates. The results also revealed that different Co contents play an important role in the surface roughness parameters. From the magnetic analysis of the samples, it was understood that the Fe–Co61–Ni36 sample has a higher coercive field and magnetic squareness ratio than the Fe–Co43–Ni53 and Fe–Co33–Ni62 samples. The differences observed in the magnetic characteristics of the samples were attributed to the changes revealed in their phase structure and surface roughness parameters. The obtained results are the basis for the fabrication of future magnetic devices.

Growth of large size near-stoichiometric lithium niobate single crystals with low coercive field for manufacturing high quality periodically poled lithium niobate

Periodically poled lithium niobate is an important component in mid-infrared lasers due to its perfect nonlinear optical property. However, fabrication of high-power laser based on periodically poled lithium niobate is still a great challenge, because lithium niobate crystal wafer with large thickness for large clear aperture periodically poled lithium niobate is hard to be completely poled due to the high coercive field of commercial congruent lithium niobate (LiNbO3). In this work, we have successfully grown 3-inch near-stoichiometric LiNbO3 by efficiently regulation of temperature gradient with the aid of thermal field simulation. Characteristics on the as-grown large size near-stoichiometric LiNbO3 proved that the [Li]/[Nb] of crystal is around 1:1, and the crystal possesses a typical single domain with high optical homogeneity. Compared with congruent and Mg-doped LiNbO3, the near-stoichiometric LiNbO3 crystal has better piezoelectric performance. The forward and backward coercive fields of the near-stoichiometric LiNbO3 crystal were 2.90 kV/mm and 2.43 kV/mm, respectively, which were approximately 8 times lower than that for CLN (21 kV/mm). The periodically polarization experiments proved that only 1.36 kV can realize the complete polarization for a 1 mm thick near-stoichiometric LiNbO3 wafer. The mass-productive near-stoichiometric LiNbO3 crystals grown in this work will have great applications in high-power mid-infrared solid-state laser.

High Coercive Field in Tbfe/Fe/Tbfe Exchange-Coupledsystem with Mixed Magnetic Anisotropy

High Coercive Field in Tbfe/Fe/Tbfe Exchange-Coupledsystem with Mixed Magnetic Anisotropy

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State.

The paper presents results of investigation of Fe65.3–100Zr34.7–0N7.5–0 films prepared by dc magnetron deposition on glass substrates and subsequent 1-hour annealing at temperatures of 300–600 °C. The influence of the chemical and phase compositions and structure of the films, which were studied by TEM, SEM, XRD, and GDOES, on their mechanical properties determined by nanoindentation and static magnetic properties measured by VSM method is analyzed. The studied films exhibit the hardness within a range of 14–21 GPa, low elastic modulus (the value can reach 156 Gpa), and an elastic recovery of 55–83%. It was shown that the films are strong ferromagnets with the high saturation induction Bs (up to 2.1 T) and low coercive field Hc (as low as 40 A/m). The correlations between the magnetic and mechanical properties, on one hand, and the chemical composition of the films, their phase, and structural states as well, on the other hand, are discussed.

Growth, Structure, and characterization of new High-TC Piezo-/Ferroelectric Bi(Zn2/3Ta1/3)O3-PbTiO3 single crystals

In this work, new bismuth-based complex perovskite piezo-/ferroelectric single crystals of the (1-x)PbTiO3-xBi(Zn2/3Ta1/3)O3 solid solution have been successfully grown by the high temperature solution method (HTSG). The crystal structure was found to be tetragonal at room temperature by means of structural analysis by X-ray diffraction and domain examination by polarized light microscopy (PLM). High Curie temperature (TC = 470 °C) was determined by dielectric measurements and PLM observations. Band-like domain structures were observed in the (001)-oriented single crystal with a width of 100–200 µm. Good piezoelectric performance (d33 = 251 pC/N) and high coercive field (EC = 30 kV/cm) were found by the piezoelectric and ferroelectric characterizations. Detailed crystal structural refinement was performed to establish the structure–property relationship in this system. Comparative studies of current bismuth-based complex perovskite solid solution single crystals point to the advantages of the Bi(Zn2/3Ta1/3)O3-PbTiO3 single crystals in terms of high TC, good piezoelectric performance, and high coercive field. These advantages make this piezo-crystal system a favourable candidate for potential high-temperature and high-power electromechanical applications.

Wake‐Up in Al1−xBxN Ferroelectric Films

AbstractThe polarization wake‐up process is demonstrated here for ferroelectric switching in epitaxial Al0.93B0.07N films on W coated c‐axis oriented Al2O3 (sapphire) substrates. During the wake‐up process, the remanent polarization grows from ≈0 to &gt;100 µC cm−2. As it does so, both the reversible and irreversible Rayleigh coefficients rise substantially, suggesting that the concentration of mobile interfaces that separate regions of opposite dipole orientation is increasing. The irreversible Rayleigh coefficient is very small (≈3.5 × 10−4 cm kV−1), four to five orders of magnitude below those of perovskite ferroelectric films such as PbZr0.52Ti0.48O3. These small values are consistent with the high coercive fields observed in the nitride ferroelectrics. The temperature dependence of the Rayleigh coefficients suggests that the interface motion is thermally activated. On increasing frequency, the Rayleigh coefficients drop, suggesting time‐dependent pinning processes also occur in this family of materials. With information from anisotropic etching experiments upon field‐cycling, a self‐consistent model that describes a polar domain microstructure evolution process during wake‐up is proposed.

The High Coercivity Field in Chemically Bonded WSe2/MoSe2 Powder.

We studied the magnetic properties of WSe/MoSe powder. The coercivity field reaches 2600 Oe at 5 K, 4233 Oe at 100 K and 1300 Oe at 300 K. These are the highest values reported for two-dimensional transition metal dichalcogenides. This study is different from the widely reported vacancy and zigzag structure-induced ferromagnetism studies. Importantly, a Raman peak red shift was observed, and that supports the chemical bonding at the interface between WSe and MoSe. The large coercivity field originates from the chemical bonding-induced structural distortion at the interface between WSe and MoSe.

Effect of Yb doping on the structural and magnetic properties of cobalt ferrite nanoparticles

The low coercivity of spinel ferrites is a significant barrier limiting their use in high-density magnetic recording applications. The large magnitude of the magnetocrystalline anisotropy of the rare earth group elements can lead to a high coercivity field by doping the magnetic ferrites with these elements. In this research, using the hydrothermal method, Fe+3 in cobalt ferrite was substituted with Yb+3 to make CoFe2-xYbxO4 with x = 0, 0.025, 0.05, 0.075, and 0.1. By analyzing the X-ray diffraction analysis and confirming the spinel structure, the crystallite sizes were obtained in the range of 31 nm to 45 nm. The lattice parameter was estimated to be in the range of 8.30 nm to 8.36 nm. The FTIR analysis of the nanoparticles showed the ν1 absorption band in the range 584 Cm−1 to 594 Cm−1. The Raman spectroscopy analysis showed that CoFe2-xYbxO4 nanoparticles have a mixed spinel structure. Hysteresis loops at room temperature and 10 K obtained by the vibrating sample magnetometer (VSM) indicate that the coercivity field (HC) increases significantly from 0.55 to 1.05 KOe and 9.48 to 12.00 KOe, respectively, by increasing Yb doping from x = 0 to x = 0.1.

Impact of Thickness and Poling Condition on Dielectric and Piezoelectric Properties of Pb(In0.5Nb0.5)O3–PbTiO3 Ferroelectric Crystals

The alternating current poling (ACP) method has received many attentions for the improvement of the piezoelectricity of ferroelectric crystals through domain engineering with low cost and high efficiency. However, the effects of ACP and sample thickness have never been reported in ferroelectric crystals with high coercive field. Herein, the piezoelectric and dielectric properties of [001]c‐oriented Pb(In0.5Nb0.5)O3–PbTiO3 ferroelectric single crystals with different thicknesses are investigated using ACP. The highest piezoelectric coefficient d 33 (1720 pC N−1) and free permittivity ε T 33/ε 0 (3690) are obtained for ACP samples with the thickness of 2 mm. The domain structure is significantly affected by the thickness and poling method. The 2 mm ACP samples have the more regular domain structure and smaller domain width compared with others. In addition, the decrease in coercive field is beneficial to the enhancement of the piezoelectric performance.

Ferroelectricity in CMOS-Compatible Hafnium Oxides: Reviving the ferroelectric field-effect transistor technology

A Ferroelectric Field-Effect Transistor (FEFET) is a promising candidate for next-generation memory devices because it offers numerous advantages, such as its high speed, low energy profile, and nondestructive readout process. FEFETs merge logic and memory functionality in a single device, allowing efficient data transfer and a high packing density, which could make them vital for use in future in-memory computing architectures. Although issues related to the integration of perovskite materials in the state-of-the art semiconductor industry limited their commercial success, the discovery of ferroelectricity in CMOS-compatible doped hafnium oxides led to a re-emergence of FEFETs in advanced microelectronics. The demonstration of ferroelectricity in doped hafnia at extremely thin film thicknesses plus its low permittivity, high coercive field (Ec), environment-friendly composition, and excellent CMOS compatibility are expected to unleash the promise of FEFETs, and significant progress has been made in this regard.

Structure and properties of Bi(Zn½Ti½)O3‐modified Pb(Zr,Ti)O3 piezo‐/ferroelectric ceramics around the ternary morphotropic phase boundary

AbstractTo develop high‐performance piezo‐/ferroelectric materials, Bi(Zn½Ti½)O3–PbZrO3–PbTiO3 (BZT–PZ–PT) ternary solid solution with compositions around the morphotropic phase boundary (MPB) is synthesized by solid‐state reaction. The crystal structure and electric properties are investigated systematically by X‐ray powder diffraction (XRD), dielectric spectroscopy, and ferroelectric and piezoelectric measurements. On the basis of the results of the XRD, dielectric and ferroelectric measurements, the pseudo‐binary phase diagram of the yBi(Zn½Ti½)O3–(1 − y)[(1 − x)PbZrO3–xPbTiO3] system has been constructed for three series, namely, y = 0.05, 0.10, and 0.15. It is found that the introduction of BZT into the PZT system makes the paraelectric to ferroelectric phase transition more diffuse, brings the MPB to a lower PT content, and enlarges the MPB region. The best properties with an improved dielectric constant ε' = 1248, and a large remnant polarization Pr = 33 μC/cm2, as well as a relatively high TC = 286°C, and a high coercive field Ec = 23 kV/cm was achieved in the y = 0.15 series with MPB composition x = 0.425, making it a promising material for high‐power piezoelectric applications.

High magnetic coercive field in Ca‐Al‐Cr substituted strontium hexaferrite

The structural and magnetic properties of Sr0.67Ca0.33Fe9Al3−xCrxO19 submicrometric powders with substitution levels ranging from x = 0 up to x = 3, prepared by sol-gel synthesis method, have been investigated. The powders were characterized by high resolution synchrotron X-ray diffraction, scanning electron microscopy, powder neutron diffraction and MPMS-SQUID magnetometer. The structural analysis shows that upon Ca-substitution of SrFe12O19 at the Sr site and Al–Cr at the Fe sites, the magnetoplumbite structure is preserved, even for large levels of substitutions. The X-ray powder diffraction peak broadening and Williamson-Hall plots analyses indicate an increase of crystallites size and relaxation of the microstrain with increasing amounts of Chromium. The magnetic hysteresis loops reveal high coercivity fields at room temperature, with the highest value of HC = 1125 kA/m (1.41 T) obtained for Sr0.67Ca0.33Fe9Al2.5Cr0.5O19 powder interesting to develop free-Rare Earth high coercivity magnets. The saturation magnetization and remanence values increase monotonically with increasing Cr content while the switching field decreases. The structural Rietveld refinement of combined X-ray/neutron diffraction data shows the affinity of Al3+ and Cr3+ cations to migrate mainly towards (2a) Fe-Oh2 and (12k) Fe-Oh3 sites and only minor amounts is found on the (4f1) Fe-Oh1 octahedral sites. The structural observations corroborate the magnetic properties, demonstrating a correlation between the structure and magnetic properties in Ca–Al–Cr substituted strontium hexaferrite. The role of the particle size to maximize the coercivity properties is discussed.

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb25Fe61Co14 thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb25Fe61Co14 films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.

Effects of growth behavior on magnetic property of LaBaCo2O6−δ epitaxial films on MgO substrates

LaBaCo2O6−δ (LBCO) films were grown on MgO substrates by a pulsed laser deposition method in O2 atmosphere of 2 × 10−4 and 2 Pa. The LBCO films are epitaxial, but actually consist of 90°-oriented ordered LaBaCo2O6 grains in O-annealed samples. Paramagnetic to ferromagnetic transition occurs at ~200 K and the coercive fields at 10 K are as high as 8.8 and 7.2 kOe for the O-annealed low- and high-oxygen LBCO films, respectively. The high coercive fields are attributed to the co-existed 90°-oriented grains, which play a role in locking magnetic spins. A magnetization model of ferromagnetic nanoclusters is established and applied to the discussion of irreversibility in temperature-dependent magnetization curves and the fitting of magnetization loops at different temperatures, revealing that oxygen vacancies may have impacts on the magnetization of LBCO films. In addition, the electric transport properties were studied and linked to the growth behavior of LBCO films.