Papers by Keyword: Hysteresis

Abstract: Bias-temperature instability (BTI) is one of the primary sources of parameter drift in silicon and SiC MOSFETs and consequently can determine device lifetime. Most studies of BTI in SiC MOSFETs have characterized the threshold voltage (V_T) but not the interface trap density (N_it), leaving uncertainty about the relative contributions of carrier capture and trap creation to the V_T shift. In this study, to lend insight into the physical mechanisms responsible for BTI in SiC MOSFETs, we measure N_it during positive bias-temperature stress (BTS) using the charge pumping (CP) technique. We also characterize the shift in V_T and hysteresis using the triple-sense method [1], [2] for comparison with the N_it changes to evaluate whether the changes in N_it are responsible for the V_T and/or hysteresis changes, and demonstrate the utility of the technique for reliable characterization of V_T and hysteresis in SiC MOSFETs.

Abstract: This work investigates the impact of different gate oxide fabrication schemes on the electrical characteristics of 4H-SiC planar MOSFETs. Three processes were implemented: (1) 50 nm thermal oxidation with NO annealing at 1350°C, (2) 50 nm ALD-grown oxide with NO annealing at 1250°C, and (3) a stacked 20 nm thermal/30 nm ALD oxide structure with NO annealing at 1250°C. Electrical characterization included I_dV_g, CV, and I_gE_ox measurements. Results show that Condition 1 exhibits the lowest leakage and best uniformity, and demonstrates strong oxide integrity without soft breakdown events. In contrast, Condition 2 and 3 show increased leakage, higher variability, and evidence of soft breakdown, suggesting greater interfacial weakness. However, a surprising trend was observed in the CV analysis: Condition 2’s flat band voltage (VFB​) is closest to the ideal 0V, indicating a lower fixed charge density than Condition 1 [1], which has the most negative VFB​ (≈ -2V). The hysteresis results further highlight differences, with Condition 3 showing the largest hysteresis window (ΔVth​=0.13V). These findings suggest that while the ALD process coupled with a lower-temperature NO anneal (Condition 2) can effectively reduce fixed charges, it does not fully eliminate interfacial defects responsible for increased leakage and soft breakdown. Our results underscore the complex trade-offs in different fabrication schemes, emphasizing that careful interface engineering beyond conventional NO annealing is required to ensure reliable performance in SiC MOSFETs.

Abstract: Classical linear contact mechanics, formulated with small strain and displacement assumption, struggles to accurately describe experiments involving rubbers and elastomers. Indeed, under high loads, these materials undergo large deformations and exhibit constitutive behaviors that deviate from a linear relationship between stress and strain. In such cases, it is essential to move beyond linear elasticity to account for nonlinearity caused by large deformations and displacements. Despite efforts to develop numerical tools capable of incorporating these non-linearities in contact problems, our understanding of their impact on contact mechanical responses remains limited. In this study, we investigate the basic case of normal contact between a wavy rigid indenter and a flat, deformable substrate. We examine the influence of geometric non-linearities, arising from large deformations and displacements, alongside material non-linearities, under both frictionless and frictional interfacial conditions. To this end, we developed a finite element model, and we compared its predictions with those of Westergaard’s fully linear theoretical model. The results indicate that even in frictionless contact scenarios, non-linearities produce a mechanical response that differs significantly from predictions based on linear theory. This discrepancy becomes more pronounced as the aspect ratio of the wavy indenter increases, thereby invalidating the small-displacement assumption inherent in linear models. Moreover, the presence of friction, coupled with geometric non-linearities, induces contact hysteresis during loading and unloading cycles a phenomenon often attributed to other interfacial behaviors such as adhesion and plasticity.

Abstract: In this paper, the ferrimagnetic mixed spins (1, 5/2) Blume-Capel model is proposed to investigate the phase diagrams and hysteresis behaviors of a magnetic cylindrical nanotube with a core-shell structure using the mean-field approximation based on the Bogoliubov inequality for the Gibbs free energy. The core sites are occupied by σ= ±1, 0 spins, whereas the shell sites are filled by S= ±5/2, ±3/2, ±1/2 spins. The effects of exchange couplings (J_in, J_S) and single-ion anisotropies (D_C, D_S) on core, shell, and total magnetizations are investigated, as well as hysteresis behaviors. The entropy, free energy, and specific heat are analyzed to establish the stability of the solutions. The presentation and discussion of phase diagrams is detailed. The system shows a first-order and second-order phase transitions, as well as tricritical and critical end- points. In addition, the system shows compensation and reentrant behaviors. Various multiple hysteresis loop behaviors are seen according on the Hamiltonian parameters, such as the presence of triple, quintuple, and septuple hysteresis loops.

Abstract: This paper explores the versatility of Bouc-Wen hysteresis model in simulating the dynamic behaviour of magnetorheological elastomer (MRE) material. Bouc-Wen model have been used in many field of science including modelling the hysteresis phenomenon happen in magnetic material, elastomer, base isolation of structures and many more. Introduced by the Robert Bouc, this nonlinear hysteretic model has been modified by many researchers to suit different applications. Compression testing of MRE material under high strain amplitude produces nonlinear hysteresis curve based on stress-strain data. Bouc-Wen hysteretic model has been found to be able to simulate the hysteresis curve of MRE material using parameter identification method within MATLAB Simulink.

Abstract: In the recent past, lots of efforts have been put into further developing SiC power MOSFETs. In addition to optimization of device geometry, i.e., vertical device structure, various post-oxidation anneals have been studied to improve carrier mobility by reducing trap density. Nevertheless, a considerable number of traps remain, which are the central origin for dynamic changes in the threshold voltage of up to several volts during DC and AC operation. To explain the threshold voltage instability, an effective two-state defect model has been recently applied. In this work, we give an overview of modeling efforts to explain the impact of defects on the device threshold voltage and discuss the hysteresis of voltage sweep and bias temperature instabilities in SiC transistors. Based on the combination of measurements and computer simulations, a list of potential defect candidates responsible for the observed threshold voltage instabilities is discussed.

Abstract: We investigated oxide and interface defects of lateral 4H-SiC MOSFETs through capacitance-voltage (C-V) and conductance-voltage (G-V) characterization at various frequencies and temperatures. By employing consecutive up and down sweeps of the gate voltage at three different temperatures, we experimentally characterized the hysteresis width as the difference between up and down sweeps in the depletion to accumulation (d-a) and depletion to inversion (d-i) regions. We observed an increase in the hysteresis width with decreasing temperature. Although the hysteresis width is not affected by the small-signal frequency, at the same time, increasing the frequency leads to a strong stretch-out effect, especially in the d-i region.Our measurement results indicate that the hysteresis deformation of the C-V curves is dominated by three different trap types. First, interface acceptor-like defects located close to the conduction band can follow the small-signal frequency. Slower acceptor-like border traps with trap levels both close to the conduction band and in the middle of the band gap are however responsible for the increase of trapped negative charge with increasing gate voltage. Finally, we assume the presence of a fixed positive charge.

Abstract: Hysteresis response of epitaxially grown graphene nanoribbons devices on semi-insulating 4H-SiC in the armchair and zigzag directions is evaluated and studied. The influence of the orientation of fabrication and dimensions of graphene nanoribbons on the hysteresis effect reveals the metallic and semiconducting nature graphene nanoribbons. The hysteresis response of armchair based graphene nanoribbon side gate and top gated devices implies the influence of gate field electric strength and the contribution of surface traps, adsorbents, and initial defects on graphene as the primary sources of hysteresis. Additionally, passivation with AlO_x and top gate modulation decreased the hysteresis and improved the current-voltage characteristics.

Abstract: The magnetic and thermal properties of a ferrimagnetic mixed spin-1 and spin-2 cubic Ising nanowire are studied by using the Monte Carlo simulation. The influences of the nearest (J_AB) and next-nearest neighbor (J_A and J_B) exchange interactions and the single-ion anisotropies (D_A and D_B) on the critical and compensation temperatures are illustrated. Moreover, the phase diagrams on the (temperature, anisotropy) plane are plotted for several values of J_A/|J_AB|. The system shows very rich and interesting behaviors, namely first and second order phase transitions, tricritical points and compensation phenomenon. Finally, the dependence of hysteresis loops on the anisotropies, the exchange interactions and the temperature is also investigated.

Abstract: Carbon nanotube yarns (CNTYs) are twisted hierarchical fibers which exhibit a strong property-structure relationship. Understanding of the property-structure relationship of CNTYs will allow their use in structural and energy dissipation (damping) applications. For this reason, the morphology and structure of dry-spun CNTYs are characterized by means of Raman spectroscopy mapping, atomic force microscopy, and scanning electron microscopy and correlated to their quasi-static and dynamic mechanical properties. The continuous CNTYs present some degree of structural variability, which explains the variability measured in their dynamic mechanical response. Under tension, 42.3 μm diameter (0.71 porosity) CNTYs reach specific strengths of ~0.8 N/tex and ultimate strains ranging from 4% to 7%. Mechanical hysteresis tests under incremental cyclic strain show that the CNTYs exhibits high energy dissipation, which concur with dynamic mechanical analysis (DMA). DMA shows that CNTYs are unconventional materials with high specific stiffness (per unit weight) as well as a very high damping ratio. The damping ratio increases with temperature and reach ~0.6 at 60 °C. The mechanical response of the CNTYs under tension can be explained mainly from changes in the hierarchical structural conformation of the yarn, rather than from changes in the carbon nanotube bond distance or inherent material properties.