Large Negative Shift Research Articles

Investigation of Threshold Voltage Instability and Bipolar Degradation in 3.3 kV Conventional Body Diode and Embedded SBD SiC MOSFET

The 3.3 kV SiC MOSFETs are essential for traction applications, so it is important to investigate the reliability of the recently developed high voltage MOSFETs and power modules as they are believed to be more susceptible to the effects of basal plane dislocations (BPDs). This paper presents measurement results and analysis of bipolar degradation and threshold voltage instability in 3.3 kV SiC MOSFETs having two distinct kinds of integrated diode, conventional body diode and embedded Schottky Barrier Diode (SBD). No bipolar degradation was observed both in MOSFET with conventional body diode and with embedded SBD after accumulated test with 100 hours each of 200%, 400% and 600% rated current stress in the 3rd quadrant of operation. However, the output characteristics show 1% (~0.2 mΩ) and 2% (~0.4 mΩ) increase in on resistance (RDS(on)) and 11% (0.23 V) and 5% (0.1 V) increase in threshold voltage (VTH), respectively, after total bipolar degradation test in the case of the MOSFET with conventional body diode and up to 74 hrs of 600% rated current stress in the case of the MOSFET with embedded SBD at 70°C. A rapid large negative VTH shift was observed in the MOSFETs with embedded SBD after ~ 74 hrs of 600% rated current stress. After accumulated Bias Temperature Instability (BTI) test at 150°C, the VTH value at 25°C has increased by 9.7% (0.14 V) and 14.5% (0.2 V) for the MOSFET with conventional body diode and with embedded SBD, respectively, while RDS(on) increased by 1mΩ at 25°C and by 5mΩ at 150°C, for both types of MOSFETs.

Influence of Di-n-butyl Phosphoric Acid on Cerium Redox and Speciation in Tri-n-butyl Phosphate.

The effects of simulated radiolytic degradation of tri-n-butyl phosphate (TBP) on the chemical speciation of cerium were studied by spectrophotometry and electrochemistry of TBP solutions containing increasing amounts of di-n-butyl phosphoric acid (HDBP), a common degradation product of TBP. Tetravalent cerium was found to exchange coordinated nitrate for the dibutyl phosphate anion, forming dinuclear complexes of the formula (CeOCe)(NO3)(6-d)(DBP)d·3TBP (d = 0-3). Compared to Ce(IV), Ce(III) was complexed less strongly by HDBP in TBP, but HDBP displaced both nitrate and TBP to form the series of mononuclear complexes Ce(NO3)(3-d)(HDBP·DBP)d·(3-d)TBP (d = 0-3). Dibutyl phosphate coordination caused large negative shifts in the Ce(IV/III) reduction potential in TBP, indicating a strong stabilization of the tetravalent state. Electrochemical investigation of the reduction of Ce(IV) in TBP revealed it to be a two-electron process in accordance with the dinuclear nature of the organic-phase Ce(IV) complexes. The diffusion coefficients of the d = 0 dinuclear Ce(IV)-nitrate-TBP complex and mononuclear Ce(III)-nitrate-TBP complex in TBP equilibrated with 7 M HNO3 were determined to be (1.16 ± 0.06) × 10-7 cm2/s and (1.9 ± 0.4) × 10-7 cm2/s, respectively, which also is consistent with the larger molecular volume of the dinuclear Ce(IV) complexes.

Retention time prediction for post-translationally modified peptides: Ser, Thr, Tyr-phosphorylation

The development of a peptide retention prediction model for reversed-phase chromatography applications in proteomics is reported for peptides carrying phosphorylated Ser, Thr and Tyr-residues. The major retention features have been assessed using a collection of over 10,000 phosphorylated/non-phosphorylated peptide pairs identified in a series 1D and 2D LC-MS/MS acquisitions using formic acid as ion pairing modifier. Single modification event on average results in increased peptide retention for phosphorylation of Ser (+ 1.46), Thr (+1.33), Tyr (+0.93% acetonitrile, ACN) on gradient elution scale for Luna C18(2) stationary phase. We established several composition and sequence specific features, which drive deviations from these average values. Thus, single phosphorylation of serine results in retention shifts ranging from -2.4 to 5.5% ACN depending on position of the residue, nature of nearest neighbour residues, peptide length, hydrophobicity and pI value, and its propensity to form amphipathic helical structures. We established that the altered ion-pairing environment upon phosphorylation is detrimental for this variability. Hydrophobicity of ion-pairing modifier directly informs the magnitude of expected shifts: (most hydrophilic) 0.5 % acetic acid (larger positive shift upon phosphorylation) > 0.1 % formic acid (positive) > 0.1 % trifluoroacetic (negative) > 0.1 % heptafluorobutyric acid (larger negative shift). The effect of phosphorylation has been also evaluated for several separation conditions used in the first dimension of 2D LC applications: high pH reversed-phase (RP), hydrophilic interaction liquid chromatography (HILIC), strong cation- and strong anion exchange separations.

Ultrasensitive Carbon Monoxide Gas Sensor at Room Temperature Using Fluorine-Graphdiyne.

Currently, most carbon monoxide (CO) gas sensors work at high temperatures of over 150 °C. Developing CO gas sensors that operate at room temperature is challenging because of the sensitivity trade-offs. Here, we report an ultrasensitive CO gas sensor at room temperature using fluorine-graphdiyne (F-GDY) in which electrons are increased by light. The GDY films used as channels of field-effect transistors were prepared by using chemical vapor deposition and were characterized by using various spectroscopic techniques. With exposure to UV light, F-GDY showed a more efficient photodoping effect than hydrogen-graphdiyne (H-GDY), resulting in a larger negative shift in the charge neutral point (CNP) to form an n-type semiconductor and an increase in the Fermi level from -5.27 to -5.01 eV. Upon CO exposure, the negatively shifted CNP moved toward a positive shift, and the electrical current decreased, indicating electron transfer from photodoped GDYs to CO. Dynamic sensing experiments demonstrated that negatively charged F-GDY is remarkably sensitive to an electron-deficient CO gas, even with a low concentration of 200 parts per billion. This work provides a promising solution for enhancing the CO sensitivity at room temperature and expanding the application of GDYs in electronic devices.

Tuning In-Plane Magnetic Anisotropy and Interfacial Exchange Coupling in Epitaxial La2/3Sr1/3CoO3/La2/3Sr1/3MnO3 Heterostructures.

Controlling the in-plane magnetocrystalline anisotropy and interfacial exchange coupling between ferromagnetic (FM) layers plays a key role in next-generation spintronic and magnetic memory devices. In this work, we explored the effect of tuning the magnetocrystalline anisotropy of La2/3Sr1/3CoO3 (LSCO) and La2/3Sr1/3MnO3 (LSMO) layers and the corresponding effect on interfacial exchange coupling by adjusting the thickness of the LSCO layer (tLSCO). The epitaxial LSCO/LSMO bilayers were grown on (110)o-oriented NdGaO3 (NGO) substrates with a fixed LSMO (top layer) thickness of 6 nm and LSCO (bottom layer) thicknesses varying from 1 to 10 nm. Despite the small difference (∼0.2%) in lattice mismatch between the two in-plane directions, [001]o and [11̅0]o, a pronounced in-plane magnetic anisotropy was observed. Soft X-ray magnetic circular dichroism hysteresis loops revealed that for tLSCO ≤ 4 nm, the easy axes for both LSCO and LSMO layers were along the [001]o direction, and the LSCO layer was characterized by magnetically active Co2+ ions that strongly coupled to the LSMO layer. No exchange bias effect was observed in the hysteresis loops. In contrast, along the [11̅0]o direction, the LSCO and LSMO layers displayed a small difference in their coercivity values, and a small exchange bias shift was observed. As tLSCO increased above 4 nm, the easy axis for the LSCO layer remained along the [100]o direction, but it gradually rotated to the [11̅0]o direction for the LSMO layer, resulting in a large negative exchange bias shift. Therefore, we provide a way to control the magnetocrystalline anisotropy and exchange bias by tuning the interfacial exchange coupling between the two FM layers.

Dynamic emotional states shape the episodic structure of memory

Human emotions fluctuate over time. However, it is unclear how these shifting emotional states influence the organization of episodic memory. Here, we examine how emotion dynamics transform experiences into memorable events. Using custom musical pieces and a dynamic emotion-tracking tool to elicit and measure temporal fluctuations in felt valence and arousal, our results demonstrate that memory is organized around emotional states. While listening to music, fluctuations between different emotional valences bias temporal encoding process toward memory integration or separation. Whereas a large absolute or negative shift in valence helps segment memories into episodes, a positive emotional shift binds sequential representations together. Both discrete and dynamic shifts in music-evoked valence and arousal also enhance delayed item and temporal source memory for concurrent neutral items, signaling the beginning of new emotional events. These findings are in line with the idea that the rise and fall of emotions can sculpt unfolding experiences into memories of meaningful events.

Fitted Difference Scheme on a Non-uniform Mesh for Singularly Perturbed Parabolic Reaction–Diffusion with Large Negative Shift and Non-local Boundary Condition

Fitted Difference Scheme on a Non-uniform Mesh for Singularly Perturbed Parabolic Reaction–Diffusion with Large Negative Shift and Non-local Boundary Condition

An efficient numerical approach for solving singularly perturbed parabolic differential equations with large negative shift and integral boundary condition

In this study, we consider singularly perturbed large negative shift parabolic reaction–diffusion with integral boundary condition. The continuous solution's properties are discussed. On a non-uniform Shishkin mesh, the spatial derivative is discretized using the tension spline method, and the temporal derivative is discretized using the Crank–Nicolson method. In order to handle the integral boundary condition, Simpson's rule is used. After conducting an error analysis, it was determined that the method was uniformly convergent. To support the theoretical findings, numerical examples are taken into account and solved for different values of the perturbation parameter and mesh sizes. It is proved to be uniformly convergent to almost second order.

A robust numerical scheme for singularly perturbed differential equations with spatio-temporal delays

In this article, we proposed and analyzed a numerical scheme for singularly perturbed differential equations with both spatial and temporal delays. The presence of the perturbation parameter exhibits strong boundary layers, and the large negative shift gives rise to a strong interior layer in the solution. The abruptly changing behaviors of the solution in the layers make it difficult to solve the problem analytically. Standard numerical methods do not give satisfactory results, unless a large mesh number is considered, which needs a massive computational cost. We treated such problem by proposing a numerical scheme using the implicit Euler method in the temporal variable and the nonstandard finite difference method in the spatial variable on uniform meshes. The stability and uniform convergence of the proposed scheme have been investigated and proved. To demonstrate the theoretical results, numerical experiments are carried out. From the theoretical and numerical results, we observed that the method is uniformly convergent of order one in time and of order two in space.

Effect of Gate Bias Stress on the Electrical Characteristics of Ferroelectric Oxide Thin-Film Transistors with Poly(Vinylidenefluoride-Trifluoroethylene).

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and a large positive shift under positive gate bias stress (PBS) in transfer characteristic curves. In contrast, the FeOxTFTs show a small positive shift and a large negative shift under NBS and PBS, respectively. It was confirmed that sufficient changes in the electrical characteristics are obtained by 10 min NBS and PBS. The changed electrical characteristics such as threshold voltage shift, memory on- and memory off-current were maintained for more than 168 h after NBS and 24 h after PBS. It is deduced that, since the dipole alignment of the ferroelectric layer is maximized during GBS, these changes in electrical properties are caused by the remnant dipole moments still being retained during the gate sweep. The memory on- and memory off-current are controlled by GBS and the best on/off current ratio at 107 was obtained after NBS. By repeatedly alternating NBS and PBS, the electrical characteristics were reversibly changed. Our results provide the scientific and technological basis for the development of stability and performance optimization of FeOxTFTs.

Accelerated parameter-uniform numerical method for singularly perturbed parabolic convection-diffusion problems with a large negative shift and integral boundary condition

The singularly perturbed parabolic convection–diffusion equations with integral boundary conditions and a large negative shift are studied in this paper. The implicit Euler method for the temporal direction and the exponentially fitted finite difference scheme for the spatial direction are applied to formulate a parameter-uniform numerical method. The Simpson’s integration rule is used to handle the integral boundary condition. The Richardson extrapolation technique is applied to enhance the order of convergence of the method. The stability and uniform convergence analysis of the proposed method are studied. It is shown that the method is uniformly convergent with a convergence order of two in both temporal and spatial direction after Richardson extrapolation. Two test examples are considered to verify the validity of the proposed numerical scheme. The obtained numerical results confirm the theoretical estimates. The proposed method provide more accurate results and a higher order of convergence than methods available in the literature.

A Systematic Review on the Solution Methodology of Singularly Perturbed Differential Difference Equations

This review paper contains computational methods or solution methodologies for singularly perturbed differential difference equations with negative and/or positive shifts in a spatial variable. This survey limits its coverage to singular perturbation equations arising in the modeling of neuronal activity and the methods developed by numerous researchers between 2012 and 2022. The review covered singularly perturbed ordinary delay differential equations with small or large negative shift(s), singularly perturbed ordinary differential–differential equations with mixed shift(s), singularly perturbed delay partial differential equations with small or large negative shift(s) and singularly perturbed partial differential–difference equations of the mixed type. The main aim of this review is to find out what numerical and asymptotic methods were developed in the last ten years to solve such problems. Further, it aims to stimulate researchers to develop new robust methods for solving families of the problems under consideration.

Spin-orbit-coupled spinor gap solitons in Bose-Einstein condensates

Spin-1 spin-orbit-coupled spinor Bose-Einstein condensates have been realized in experiment. We study spin-orbit-coupled spinor gap solitons in this experimentally realizable system with an optical lattice. The spin-dependent parity symmetry of the spin-orbit coupling plays an important role in properties of gap solitons. Two families of solitons with opposite spin-dependent parity are found. Using an approximating model by replacing the optical lattice with a Harmonic trap, we demonstrate the physical origination of these two families. For a large negative quadratic Zeeman shift, we also find a type of gap solitons that spontaneously breaks the spin-dependent parity symmetry due to the ferromagnetic spinor interactions.

Parameter-uniform cubic spline method for singularly perturbed parabolic differential equation with large negative shift and integral boundary condition

Parameter-uniform cubic spline method for singularly perturbed parabolic differential equation with large negative shift and integral boundary condition

Detection of defect levels in vicinity of Al2O3/p-type GaN interface using sub-bandgap-light-assisted capacitance–voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance–voltage (C–V) method. For metal–oxide–semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C–V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C–V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7–0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C–V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C–V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures.

Capacitance-Dependent VTH Instability Under a High dVg/dt Event in p-GaN Power HEMTs

In this work, we report that the VTH stability in p-GaN power HEMTs under a high dVg/dt event is highly correlated with the capacitance for the first time. The different dVg/dt event is performed by using fast sweep characterization with sweeping time (tsweep) varied from 10ms to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~\mu \text{s}$ </tex-math></inline-formula> . As the tsweep is decreased, i.e., high dVg/dt, p-GaN HEMTs show a negative VTH shift and a high measured gate current. The higher measured gate current is mainly due to the displacement current with respect to a high dVg/dt. To further understand the impacts of capacitance on VTH stability, p-GaN power HEMTs are connected with different additional capacitance (Cadditional) between gate-to-source terminals. The results indicate that the negative VTH shift and the gate current are highly correlated with the Cadditional, i.e., a large negative VTH shift and a high measured gate current in the device with a large Cadditional, suggesting that the charging capacitance caused by the displacement current during a high dVg/dt event can influence the VTHstability. Therefore, the optimization of the capacitance is crucial to improve the VTH stability during a high-speed gate operation.

Cryogenic-temperature investigation of negative bias stress inducing threshold voltage instabilities on 4H-SiC MOSFETs

We investigate the effect of Negative-Bias-Temperature-Instability on 4H-Silicon Carbide MOSFETs at room and cryogenic temperature and found a large negative threshold voltage shift at T < 250 K. For T < 140 K, both capture and emission follow an almost ideal exponential transient. Cryogenic temperatures reveal fast interface traps, otherwise difficult to probe at relatively high temperatures; we attribute the threshold voltage shift to a high density of hole traps located: 1) close to the SiC valence band and able to emit within the measurement time window; 2) above the SiC valence band, responsible of the slow transient at low temperature. Finally, the extraction of the emission time constant via Capture Emission Time map analysis allowed to extract the activation energy of mechanism 2 (82 meV).

An optimal fitted numerical scheme for solving singularly perturbed parabolic problems with large negative shift and integral boundary condition

This paper deals with numerical solution of singularly perturbed parabolic partial differential equations with large negative shift on the spatial variable and integral boundary condition on the right side of the domain. For small values of perturbation parameter ɛ, solution of the problem exhibits an interior layer besides a parabolic boundary layers. The numerical methods combine the Crank–Nicolson difference scheme for the temporal direction on the uniform mesh and exponentially fitted operator finite difference method in spatial discretization. The integral boundary condition is treated using numerical integration techniques. The rate of convergence of the scheme is optimized by applying Richardson extrapolation technique. The stability and uniform convergence analysis has been carried out. To validate the applicability of the scheme, numerical examples are presented and the method is more accurate and shown to be second order uniformly convergent in both direction, and it also improves the results of the methods (Elango et al., 2021; Gobena and Duressa, 2021) existing in the literature.

Uniformly convergent numerical method for singularly perturbed parabolic differential equations with non-smooth data and large negative shift

Uniformly convergent numerical method for singularly perturbed parabolic differential equations with non-smooth data and large negative shift

Computational method for singularly perturbed parabolic differential equations with discontinuous coefficients and large delay

This paper deals with the computational method for a class of second-order singularly perturbed parabolic differential equations with discontinuous coefficients involving large negative shift. The formulated method comprises the implicit Euler and the cubic-spline in compression methods for time and spatial dimensions, respectively. Intensive numerical experimentation has been done on some model examples and the results are tabulated. The results depict that the present method is more accurate than some methods existing in the literature. Further, the layer behavior of the solutions is presented using graphs and observed to agree with the existing theories. Finally, error analysis of the scheme is done and observed that the proposed method is parameter uniform convergent with the order of convergence (Δt+h2).