The ferroelectric negative capacitance (NC) draws a great deal of attention for low‐power negative capacitance field‐effect transistors (NCFET) and NC capacitors. The fabrication of steep‐slope FET ...(subthreshold swing < 60mVdec−1) is reported, followed by modeling approaches. While the device fabrication favors a ferroelectric gate structure without interlayer metal, many NCFET models adopt interlayer metal between the ferroelectric layer and metal–insulator–semiconductor structure. The metal interlayer averages out spatial variation in the ferroelectric polarization, enabling a compact charge‐based relation between the layers. In addition, the approach assumes that the NC effect emerges from the ferroelectric layer regardless of the metal interlayer, which is not necessarily probable. This work reinvestigates the possible NC effect in ferroelectric–dielectric capacitors connected by a metal interlayer. The experiment confirms that the NC effect in the metal–ferroelectric–dielectric–metal structure does not appear in the metal–ferroelectric–metal–dielectric–metal structure. These results are inconsistent with the multidomain‐1D Landau–Ginzburg‐Devonshire model. In contrast, the suppression of the NC effect in the structure is fully explained by the advanced inhomogeneous stray‐field energy model, which simulates the dynamic evolution of polarization and screening charges. Therefore, an NCFET with a metal interlayer is impractical.
The experiment confirms that negative capacitance (NC) effect in metal–ferroelectric–dielectric–metal structure does not appear in metal–ferroelectric–metal–dielectric–metal structure. These results are inconsistent with the phenomenological NC model. In contrast, the suppression of NC effect in the structure is fully explained by the advanced electrostatic energy model, which simulates the dynamic evolution of polarization and screening charges.
The negative capacitance (NC) effect, recently discovered in a fluorite‐based ferroelectric thin film, has attracted great attention as a rescue to overcome the scaling limitations of the ...conventional memory and logic devices of highly integrated circuits. The NC effect manifesting an S‐shaped polarization–voltage (P–V) curve is initially interpreted by a 1‐dimensional Landau Ginzburg Devonshire (LGD) model. However, a series of recent studies have found that this effect can also be explained by the inhomogeneous stray field energy (ISE) model. In this study, by extending the ISE model in the ferroelectric (FE)‐dielectric (DE) layered structure, an analytical model that considers the influence of the interfacial screening charge distribution is presented. This model showed that the NC effect in the FE‐DE heterostructure can be manifested in various forms other than a single S‐shaped P–V curve. In particular, a double S‐shaped P–V curve is expected from the fully compensated anti‐parallel domain structure, confirmed experimentally in the actual Al2O3/(Hf0.5Zr0.5)O2/Al2O3 triple‐layer structure. Furthermore, to reveal the origin of the double S‐shaped P–V curve, a multidomain LGD model is presented. It is confirmed that this phenomenon is attributed to the evolution of inhomogeneous stray field energy.
The inhomogeneous stray field energy model for the metal‐insulator‐ferroelectric‐insulator‐metal structure where the ferroelectric bound charge of the anti‐parallel domain structure is compensated by the symmetrical screening charges at the lower and upper interfaces (the schematics is shown in ToC Figure (a)) reproduces the various double S‐shaped polarization – voltage curves (shown in ToC figure (b)) depending on the compensation factor λ.
This work investigates the evolution of the ferroelectric (FE) performance of the sputtered aluminum scandium nitride (AlScN) thin film, which has a high remanent polarization (Pr, > 100 µC cm−2) and ...coercive field (Ec, > 6 MV cm−1), with the electric field cycling. The work aims at elucidating the underlying origin of the severe fatigue behavior, even with a relatively small number of endurance cycles (<105). When cycled with a low electric field, an internal field is created by charges trapped between the FE layer and the interfacial dielectric layer (non‐FE). On the other hand, fatigue is observed when cycled with a high electric field cycling. This work proposes a new method to simulate a switching current utilizing an inhomogeneous field mechanism and the appropriate circuit model to assess the thickness change of the non‐FE layer. It is concluded that the thickened non‐FE layer after the field cycling results in fatigue.
This work discovers that the thickening of the non‐ferroelectric (FE) layer causes the fatigue phenomenon of aluminum scandium when subjected to a high electric field cycling. The non‐FE layer thickness variation is investigated by simulating the switching current using an inhomogeneous field distribution and the appropriate circuit model.
To investigate the effects of customized biomechanical foot orthosis (BFO) on kinematic data during gait in patients with hallux valgus (HV) deformities and compare the results with those of a normal ...control group.
Ten patients with HV deformities and 10 healthy volunteers were enrolled in this study. HV deformity was diagnosed using biomechanical and radiological assessments by a rehabilitation physician. Patients received the customized BFO manufactured at a commercial orthosis laboratory (Biomechanics, Goyang, South Korea) according to the strictly defined procedure by a single experienced technician. The spatiotemporal and kinematic data acquired by the Vicon 3D motion capture system (Oxford Metrics, Oxford, UK) were compared between the intervention groups (control vs. HV without orthosis) and between the HV groups (with vs. without orthosis).
The temporal-spatial and kinematic parameters of the HV group were significantly different from those of the control group. After applying BFO to the HV group, significantly increased ranges of plantar flexion motion and hindfoot inversion were observed. Furthermore, the HV group with BFO showed improved gait cadence, walking speed, and stride length, although the results were not statistically significant.
Our results suggest that it is imperative to understand the pathophysiology of HV, and the application of customized BFO can be useful for improving kinematics in HV deformities.
The aim of this study was to compare the clinical effectiveness of robot-assisted therapy with that of conventional occupational therapy according to the onset and severity of stroke.
In this ...multicenter randomized controlled trial, stroke patients were randomized (1:1) to receive robot-assisted therapy or conventional occupational therapy. The robot-assisted training group received 30 min of robot-assisted therapy twice and 30 min of conventional occupational therapy daily, while the conventional therapy group received 90 min of occupational therapy. Therapy was conducted 5 days/week for 4 weeks. The primary outcome was the Wolf Motor Function Test (WMFT) score after 4 and 8 weeks of therapy.
Overall, 113 and 115 patients received robot-assisted and conventional therapy, respectively. The WMFT score after robot-assisted therapy was not significantly better than that after conventional therapy, but there were significant improvements in the Motricity Index (trunk) and the Fugl-Meyer Assessment. After robot-assisted therapy, wrist strength significantly improved in the subacute or moderate-severity group of stroke patients.
Robot-assisted therapy improved the upper-limb functions and activities of daily living (ADL) performance as much as conventional occupational therapy. In particular, it showed signs of more therapeutic effectiveness in the subacute stage or moderate-severity group.
HfNx films were deposited by atomic layer deposition (ALD) using HfN(CH3)(C2H5)4 (TEMAHf) and NH3 as the Hf-precursor and reactant gas, respectively. A precleaning step using TEMAHf as a reducing ...agent was devised to minimize the oxygen concentration in the as-deposited film. Consequently, the oxygen concentration in the film was reduced by ∼66%. In addition, the carbon impurity concentration caused by the side effects of the precleaning step and the remaining oxygen concentration were effectively reduced through post-NH3 annealing. The oxygen concentration inside HfNx decreased as the annealing temperature increased. HfNx films annealed under 900 °C showed dielectric properties similar to hafnium oxynitride (HfOxNy). However, films annealed over 950 °C transformed into a more electrically conducting HfN film, showing a resistivity of ∼106 μΩ cm.
Charge injection from the near-by-electrode can occur during ferroelectric switching in the ferroelectric-dielectric bilayer due to the high field applied to the adjacent dielectric layers. The aim ...of this study is to investigate the effect of the charge injection by separating the amount of switched polarization and the injected charge density. A dynamic model of the injection-involved switching is developed and exploited to elucidate the mechanism. The model demonstrates that the amount of injected charges, which compensates for the bound charge of the polarization, can be larger, smaller, or identical to that of the polarization. This model further describes the analytical conditions of this compensation state. The model predictions are validated by the newly introduced ramping pulse measurements involving the serially connected TiN/Hf
0.5
Zr
0.5
O
2
/TiN and TiN/amorphous Al
2
O
3
/TiN, which are capable of separating the injected charge from the switched polarization. The dynamic model, along with the electrical measurements, enables the quantitative prediction and estimation of the internal potential and the effective charge, which is the sum of the bound and injected charges in the bilayer. This work provides fundamental insights into field-effect devices such as the next-generation ferroelectric-field-effect-transistors with NAND architecture based on uncompensated ferroelectric charges.
Charge injection meditated switching of the ferroelectric-dielectric bilayer is quantitatively investigated by the compact model and newly introduced pulse measurement.
Abstract
The negative capacitance (NC) effect, recently discovered in a fluorite‐based ferroelectric thin film, has attracted great attention as a rescue to overcome the scaling limitations of the ...conventional memory and logic devices of highly integrated circuits. The NC effect manifesting an S‐shaped polarization–voltage (
P–V
) curve is initially interpreted by a 1‐dimensional Landau Ginzburg Devonshire (LGD) model. However, a series of recent studies have found that this effect can also be explained by the inhomogeneous stray field energy (ISE) model. In this study, by extending the ISE model in the ferroelectric (FE)‐dielectric (DE) layered structure, an analytical model that considers the influence of the interfacial screening charge distribution is presented. This model showed that the NC effect in the FE‐DE heterostructure can be manifested in various forms other than a single S‐shaped
P–V
curve. In particular, a double S‐shaped
P–V
curve is expected from the fully compensated anti‐parallel domain structure, confirmed experimentally in the actual Al
2
O
3
/(Hf
0.5
Zr
0.5
)O
2
/Al
2
O
3
triple‐layer structure. Furthermore, to reveal the origin of the double S‐shaped
P–V
curve, a multidomain LGD model is presented. It is confirmed that this phenomenon is attributed to the evolution of inhomogeneous stray field energy.
Charge injection from the near-by-electrode can occur during ferroelectric switching in the ferroelectric–dielectric bilayer due to the high field applied to the adjacent dielectric layers. The aim ...of this study is to investigate the effect of the charge injection by separating the amount of switched polarization and the injected charge density. A dynamic model of the injection-involved switching is developed and exploited to elucidate the mechanism. The model demonstrates that the amount of injected charges, which compensates for the bound charge of the polarization, can be larger, smaller, or identical to that of the polarization. This model further describes the analytical conditions of this compensation state. The model predictions are validated by the newly introduced ramping pulse measurements involving the serially connected TiN/Hf0.5Zr0.5O2/TiN and TiN/amorphous Al2O3/TiN, which are capable of separating the injected charge from the switched polarization. The dynamic model, along with the electrical measurements, enables the quantitative prediction and estimation of the internal potential and the effective charge, which is the sum of the bound and injected charges in the bilayer. This work provides fundamental insights into field-effect devices such as the next-generation ferroelectric-field-effect-transistors with NAND architecture based on uncompensated ferroelectric charges.
Ferroelectric 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.
Increase of coercive field with c0/a0 ratio of 45 nm Al0.7Sc0.3N films deposited under different deposition conditions, where c0 and a0 mean the c‐ and a–axis lattice constant. Remanent polarization of Al0.7Sc0.3N films with different thicknesses are measured through 1 µs positive up negative down square pulse.
