Turnaround Behavior Research Articles

Gate Oxide Reliability in Silicon Carbide Planar and Trench Metal-Oxide-Semiconductor Field-Effect Transistors Under Positive and Negative Electric Field Stress

This work investigates the gate oxide reliability of commercial 1.2 kV silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) with planar and trench gate structures. The performance of threshold voltage (Vth) and gate leakage current (Igss) in SiC MOSFETs is evaluated under positive and negative gate voltage stress. The oxide lifetimes of SiC planar and trench MOSFETs at 150 °C are measured using constant voltage Time-Dependent Dielectric Breakdown (TDDB) testing. From the test results, it is found that electron trapping and hole trapping in SiO2 caused by oxide electric field (Eox) stress affect the Vth of SiC MOSFETs. The saturation and turnaround behavior of the Vth shift during positive and negative gate voltage stresses indicates that the influence of charge trapping in the gate oxide varies with stress time. The Igss under positive and negative gate voltages depends on the tunneling barrier height for electrons and holes, respectively, which can be calculated using the Fowler–Nordheim (FN) tunneling mechanism. Moreover, the presence of near-interface traps (NITs) affects the barrier height for holes under negative gate voltages. The behavior of Vth shift and Igss under high-temperature gate bias reflects the charge trapping occurring in different regions of the gate oxide. In addition, compared to SiC planar MOSFETs, SiC trench MOSFETs with thicker gate oxide tend to exhibit higher lifetimes in TDDB tests.

32.4: Abnormal Turnaround Phenomenon of Threshold Voltage Shifts in Bias‐Stressed a‐Si:H Thin Film Transistor under Extremely High Intensity Illumination

The abnormal threshold voltage (Vth) turnaround behavior of a‐Si:H TFTs was investigated when biased under extremely high intensity illumination. TFTs with various compositions of gate insulator (SiNx) interface layer were fabricated to avoid this abnormal behavior and enhance reliability upon high intensity illumination. 500‐hours RA results confirmed that our optimization strategy can effectively improve the reliability of TFT‐LCDs.

P‐16: Turnaround Phenomenon of Threshold Voltage Shifts in Bias‐Stressed a‐Si:H Thin‐Film Transistor under Extremely High Intensity Illumination

The abnormal threshold voltage (Vth) turnaround behavior of a‐Si:H TFTs was investigated when biased under extremely high intensity illumination. TFTs with various compositions of gate insulator (SiNx) were fabricated to avoid this abnormal behavior and enhance reliability upon high intensity illumination. 500‐hours RA results confirmed that our optimization strategy can effectively improve the reliability of TFT‐LCDs.

Microscopic origin of breakdown of Stokes-Einstein relation in binary mixtures: Inherent structure analysis.

Aqueous binary mixtures often exhibit dramatic departure from the predicted hydrodynamic behavior when transport properties are plotted against composition. We show by inherent structure (IS) analysis that this sharp composition dependent breakdown of the Stokes-Einstein relation can be attributed to the non-monotonic variation in the average inherent structure energy of these mixtures. Further IS analysis reveals the existence of a unique ground state, stabilized by both the formation of an optimum number of H-bonds and a favorable hydrophobic interaction at this composition. The surprisingly sharp turnaround behavior observed in the effective hydrodynamic radius also owes its origin to the same combination of these two factors. Interestingly, the temperature dependence of isothermal compressibility shows a minimum at the particular composition. Extensive studies on water-dimethyl sulfoxide and water-ethanol mixtures using two different force-fields of water reveal many features that are nearly universal. A justification of this quasi-universal behavior is provided in terms of a mode-coupling theory (MCT) of viscosity, which can serve as the starting point of a remarkable correlation observed with the nearest neighbor structure, as captured by the first peaks of the radial distribution function, and the slowdown in the intermediate scattering function at intermediate wavenumbers. Therefore, the formation of the local structure captured through IS analysis can be correlated with the MCT.

Effect of Simultaneous Mechanical and Electrical Stress on the Electrical Performance of Flexible In-Ga-Zn-O Thin-Film Transistors.

We investigated the effect of simultaneous mechanical and electrical stress on the electrical characteristics of flexible indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). The IGZO TFTs exhibited a threshold voltage shift (∆VTH) under an application of positive-bias-stress (PBS), with a turnaround behavior from the positive ∆VTH to the negative ∆VTH with an increase in the PBS application time, whether a mechanical stress is applied or not. However, the magnitudes of PBS-induced ∆VTH in both the positive and negative directions exhibited significantly larger values when a flexible IGZO TFT was under mechanical-bending stress than when it was at the flat state. The observed phenomena were possibly attributed to the mechanical stress-induced interface trap generation and the enhanced hydrogen diffusion from atomic layer deposition-grown Al2O3 to IGZO under mechanical-bending stress during PBS. The subgap density of states was extracted before and after an application of PBS under both mechanical stress conditions. The obtained results in this study provided potent evidence supporting the mechanism suggested to explain the PBS-induced larger ∆VTHs in both directions under mechanical-bending stress.

Anomalous Positive Bias Stress Instability in MoS2 Transistors With High-Hydrogen-Concentration SiO2 Gate Dielectrics

For the first time, in this letter, the anomalous positive bias stress instability of the back gated monolayer polycrystal molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) field-effect transistors with high-hydrogen-concentration SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics is reported. It is found that the threshold voltage shifts exhibit a pronounced turnaround behavior from a positive shift to a negative shift when enlarging the stress voltage and stress time. We relate this anomalous positive bias instability to two physical processes, charge trapping and hydrogen release and migration.

Abnormal behavior with hump characteristics in current stressed a-InGaZnO thin film transistors

We investigated the degradation mechanism of a-InGaZnO TFTs under simultaneous gate and drain bias stress. Gate and drain bias of 20V were applied simultaneously to induce current stress, and abnormal turn-around behavior in transfer characteristics with a hump phenomenon were identified. Hump characteristics were interpreted in terms of parasitic current path, and the degradation itself was found to be caused dominantly by the electrical field and to be accelerated with current by Joule heating. The mechanism of asymmetrical degradation after current stress was also investigated. By decomposing the curves into two curves and measuring the relaxation behavior of the stressed TFTs, we also found that abnormal turn-around behavior in the transfer characteristics was related to acceptor-like states.

Cosmological evolution with the cubic order field derivative coupling

We investigate cosmological evolution in the scalar–tensor theory with the field derivative coupling to the double-dual of the Riemann tensor (the cubic-type theory). The theory can be seen as the straightforward extension of the scalar–tensor with the quadratic order field derivative coupling to the Einstein tensor (the quadratic-type theory). Both the field derivative couplings to the Einstein tensor and the double-dual of the Riemann tensor have been argued in terms of the successful realization of the self-tuning of the cosmological constant within the Horndeski theory. Assuming the constant potential given by the sum of the cosmological constant and the quantum vacuum energy, the shift symmetry for the scalar field and no matter fields, in the spatially-flat Friedmann–Lemaitre–Robertson–Walker spacetime, we can reduce the set of the field equations to the first-order ordinary nonlinear differential equation for the Hubble parameter, showing the existence of the self-tuned and runaway de Sitter solutions, in addition to the standard de Sitter solutions in general relativity and the finite Hubble singularities which can be reached within the finite time. We then argue the possible cosmological evolution in terms of the values of the effective cosmological constant, the kinetic coupling constants and the initial Hubble parameter. Although the behavior of the universe around each of the de Sitter solutions as well as the finite time singularities is very similar in both theories, we find that the crucial difference appears in terms of no bounce or turnaround behavior across the vanishing Hubble parameter as well as no limitation for the range of the Hubble parameter in the cubic-type theory.

Abnormal positive bias stress instability of In–Ga–Zn–O thin-film transistors with low-temperature Al2O3 gate dielectric

Low-temperature atomic layer deposition (ALD) was employed to deposit Al2O3 as a gate dielectric in amorphous In–Ga–Zn–O thin-film transistors fabricated at temperatures below 120 °C. The devices exhibited a negligible threshold voltage shift (ΔVT) during negative bias stress, but a more pronounced ΔVT under positive bias stress with a characteristic turnaround behavior from a positive ΔVT to a negative ΔVT. This abnormal positive bias instability is explained using a two-process model, including both electron trapping and hydrogen release and migration. Electron trapping induces the initial positive ΔVT, which can be fitted using the stretched exponential function. The breakage of residual AlO-H bonds in low-temperature ALD Al2O3 is triggered by the energetic channel electrons. The hydrogen atoms then diffuse toward the In–Ga–Zn–O channel and induce the negative ΔVT through electron doping with power-law time dependence. A rapid partial recovery of the negative ΔVT after stress is also observed during relaxation.

Abnormal Threshold Voltage Shifts in P-Channel Low-Temperature Polycrystalline Silicon Thin Film Transistors Under Negative Bias Temperature Stress.

In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiNx dielectrics. A negative gate bias temperature instability (NBTI) stress was applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (Vth). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNx/SiO2 dielectric interface being dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the Vth switches to the negative voltage direction, which is "turn-around" behavior. In the second stage, the Vth moves from -1.63 V to -2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps.

A SEMI-EMPIRICAL MASS-LOSS RATE IN SHORT-PERIOD CATACLYSMIC VARIABLES

The mass-loss rate of donor stars in cataclysmic variables (CVs) is of paramount importance in the evolution of short-period CVs. Observed donors are oversized in comparison with those of isolated single stars of the same mass, which is thought to be a consequence of the mass loss. Using the empirical mass-radius relation of CVs and the homologous approximation for changes in effective temperature T_2, orbital period P, and luminosity of the donor with the stellar radius, we find the semi-empirical mass-loss rate M2_dot of CVs as a function of P. The derived M2_dot is at ~10^(-9.5)-10^(-10) Msun/yr and depends weakly on P when P > 90 min, while it declines very rapidly towards the minimum period when P < 90 min, emulating the P-T_2 relation. Due to strong deviation from thermal equilibrium caused by the mass loss, the semi-empirical M2_dot is significantly different from, and has a less-pronounced turnaround behavior with P than suggested by previous numerical models. The semi-empirical P-M2_dot relation is consistent with the angular momentum loss due to gravitational wave emission, and strongly suggests that CV secondaries with 0.075 Msun < M_2 < 0.2 Msun are less than 2 Gyrs old. When applied to selected eclipsing CVs, our semi-empirical mass-loss rates are in good agreement with the accretion rates derived from the effective temperatures T_1 of white dwarfs, suggesting that M2_dot can be used to reliably infer T_2 from T_1. Based on the semi-empirical M2_dot, SDSS 1501 and 1433 systems that were previously identified as post-bounce CVs have yet to reach the minimal period.

Investigation of Hot-Carrier-Induced Degradation Mechanisms in p-Type High-Voltage Drain Extended Metal–Oxide–Semiconductor Transistors

Hot-carrier-induced degradation in p-type drain extended metal–oxide–semiconductor (DEMOS) devices is investigated. The gate voltage biased at the second substrate current peak produces the most device degradation. The generation of interface state (ΔNit) in the channel region, ΔNit in the drift region under poly-gate, and negative oxide-trapped charge (ΔNot) in the drift region outside poly-gate are responsible for device parameter degradation. ΔNit in the channel region causes threshold voltage and maximum transconductance degradation. ΔNot in the drift region outside poly-gate leads to the increase of linear drain current (Idlin) at the beginning of stress. ΔNit in the drift region under poly-gate results in the turnaround behavior of |Idlin| shift as the stress time is longer.

Improvement in Mobility and Negative-Bias Temperature Instability in Metal–Oxide–Semiconductor Field-Effect Transistors with Atomic-Layer-Deposited Si–Nitride/SiO2 Stack Dielectrics

Carrier mobility and negative-bias temperature instability (NBTI) characteristics were studied for p+ polycrystalline Si-gated metal–oxide–semiconductor field-effect transistors (MOSFETs) with various gate dielectrics: atomic-layer-deposited (ALD) Si–nitride/SiO2 stack, plasma-nitrided SiON, and pure-SiO2 dielectrics. MOSFETs with the ALD Si–nitride/SiO2 stack dielectrics offer the lowest interface trap density and highest carrier mobility among the three samples owing to their superior ability to suppress boron penetration. P-channel MOSFETs with the ALD stack dielectrics exhibit an abnormal NBTI behavior: threshold voltage shift (ΔVth) is positive at the early stress stage and then becomes negative at longer stress times. Such a turnaround behavior may be attributed to the presence of preexisting neutral electron traps in the Si–nitride/SiO2 stack dielectrics, which may lead to the net ΔVth of the stack dielectrics stressed at a low voltage to be even smaller than that of the pure-SiO2 dielectrics. The above-mentioned findings suggest that the ALD Si–nitride/SiO2 stack dielectrics are very promising for sub-0.1-µm MOSFETs.

Impact of hot-carrier stress on gate-induced floating body effects and drain current transients of thin gate oxide partially depleted SOI nMOSFETs

The impact of hot-carrier (HC) stress on thin gate oxide PD SOI nMOSFETs is investigated by analyzing the front and back channel current–voltage characteristics and the switch-off drain current transients. A particular hot-carrier degradation mode, characterized by a turn-around behavior for front gate threshold voltage degradation, is analyzed for devices with different geometries, bias conditions and source/drain architecture. A significant positive back gate threshold voltage shift is also observed after long HC stress. The maximum hot-carrier degradation (HCD) is obtained for the highest front gate biases, corresponding to the conditions of maximum electron valence band injection of majority carriers into the floating body. The presence of the HCD is found to reduce both the generation and the recombination switch-off drain current transient times. Unbiased thermal annealing in the range of 200–250 °C significantly reduces the hot-carrier-induced damage affecting the back channel characteristics. Whereas front gate direct tunnel stress is not causing any significant degradation for stress biases up to about two times the power supply for this technology node and reasonably short stress times, for the highest stress conditions the drain current transients are found to be progressively faster till front gate dielectric breakdown occurs.

Effects of TCE concentration on oxide-charge and interface properties of SiO 2 thermally grown on SiC

The effects of trichloroethylene (TCE) concentration on the thermal oxidation of SiC are studied in terms of the oxide quality and the properties of the SiO 2/SiC interface. It is found for the first time that as TCE concentration increases, the flat-band voltage, oxide-charge density and interface-state density all exhibit a turnaround behavior. For TCE ratio (flow rate of N 2 + TCE to flow rate of O 2) less than 0.01, the flat-band voltage increases with TCE concentration while the oxide-charge and interface-state densities decrease. However, for TCE ratio larger than 0.05, opposites occur with the flat-band voltage decreasing and the two densities increasing. The TCE-induced reductions of the oxide charges and interface states at 0.1–0.5 eV below the conduction-band edge are 93% and 24–99%, respectively, for a TCE ratio of 0.05. Moreover, as TCE ratio increases from 0 to 0.2, the oxide resistance against stress-induced damage increases. In summary, the TCE oxidation with appropriate TCE concentration can reduce the oxide charges and improve the interface properties and oxide reliability.

Study of the multicritical point in the vortex phase diagram(H‖c)of a weakly pinned crystal ofYBa2Cu3O7−δ

dc magnetization studies on a high quality ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ crystal show that the flux-line lattice melting line extends beyond the notional ``tricritical point'' in the intermediate field region $(\ensuremath{\sim}10 \mathrm{T}),$ which broadly agrees with a recent theoretical proposal. The magnetization hysteresis data reveal the presence of both the peak effect (PE) and the fishtail effect in isothermal scans in the temperature interval 66--75 K. The broad anomaly in the magnetization hysteresis observed at lower temperatures $(T&lt;50 \mathrm{K}),$ splits into two well separated peaks above 65 K. The upper peak closely resembles the classical PE phenomenon and the locus of the peak fields shows a turnaround behavior. On the other hand, the lower peak progressively moves to smaller fields as $\stackrel{\ensuremath{\rightarrow}}{T}{T}_{c}.$

Improvement on 1/f noise properties of nitrided n-MOSFETs by backsurface argon bombardment

The 1/f noise properties of nitrided MOSFETs bombarded by low-energy (550 eV) argon-ion beam are investigated. It is found that after bombardment, 1/f noise, and its degradation under hot-carrier stress are reduced, and both exhibit a turnaround behavior with bombardment time for a given ion energy and intensity. The physical mechanism involved is probably enhanced interface hardness resulting from bombardment-induced stress relief in the vicinity of the oxide/Si interface. Moreover, from the frequency dependence of the noise, it is revealed that the nitrided devices have a nonuniform trap distribution increasing toward the oxide/Si interface which can be modified by the backsurface bombardment.

A comparison between the interface properties of N 2O-nitrided and N 2O-grown oxides

The interface and bulk qualities of N 2O-based oxides are investigated by means of backsurface Ar + bombardment and hot-carrier stressings. It is deduced that there exists a large mechanical stress near the oxide/Si interface for N 2O-grown oxide which might result from its initial accelerated growth phase, while the residual stress is negligible for N 2O-nitrided oxide. Therefore, in view of another stress induced by the bombardment, the interfacial properties can be improved for N 2O-grown oxide through stress compensation, but deteriorate for N 2O-nitrided oxide due to increased mechanical stress, indicating fresh N 2O-nitrided oxide itself has excellent interfacial and bulk qualities for high-performance devices. Moreover, for N 2O-grown oxide, the improvement exhibits a turnaround behavior for long bombardment times due to stress over-compensation.

Suppression of hot-electron-induced interface degradation in metal-oxide-semiconductor devices by backsurface argon bombardment

Low-energy (550 eV) argon-ion beam was used to bombard directly the backsurface of polysilicon-gate metal-oxide-semiconductor (MOS) capacitors after the completion of all conventional processing steps. The effects of this extra step on the interface characteristics of the MOS capacitors before and after hot-electron injection were investigated. After the backsurface argon-ion bombardment, the MOS capacitors showed improved interface hardness against hot-electron-induced degradation. A turn-around behavior was observed, indicating that an optimal bombardment time should be used. The physical mechanism involved could possibly be stress compensation at the Si/SiO 2 interface, induced by the backsurface bombardment.

A study on interface and charge trapping properties of nitrided n-channel metal-oxide-semiconductor field-effect transistors by backsurface argon bombardment

A low-energy (550 eV) argon-ion beam was used to directly bombard the backsurface of nitrided n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) after the completion of all conventional processing steps. The interface and oxide-charge trapping characteristics of the bombarded MOSFETs were investigated as compared to nonbombarded and reoxidized-nitrided n-MOSFETs. It was found that after bombardment, interface state density decreases and interface hardness against hot-carrier bombardment enhances, and oxide charge trapping properties were also improved. The improvements exhibit a turnaround behavior depending on bombardment conditions and could be attributed to stress compensation in the vicinity of the Si/SiO2 interface and an annealing effect.