Turn-off Dynamics Research Articles

Modelling and mitigating oscillation in E-mode GaN HEMT: A simulation-based approach to parasitic inductance optimization

The escalating demands in energy conversion necessitate the evolution of efficient power electronic devices beyond the limitations of traditional silicon (Si) counterparts. This research delves into the intricacies of the Enhancement mode Gallium Nitride High Electron Mobility Transistor (E-mode GaN HEMT). A focus is placed on its static characterization, parameter analysis, and the influence of external parasitic inductances, particularly regarding oscillation challenges during its hard switching process. Forward and revise bias are conducted through comparison with Si-MOSFET and Cascade-GaN HEMT, along with its static on-resistance and transfer characteristics. Through rigorous half-bridge double pulse circuit LTSPICE simulations, this study deciphers the turn-on and turn-off dynamics of the E-mode GaN HEMT. By scrutinizing various parasitic inductances, the research elucidates mechanisms instigating high-frequency voltage and current oscillations. Significantly, the research presents a hierarchy of parasitic inductance influences, employing an energy loss comparison. This analysis underscores the prominent impact of the common source parasitic inductance, which exhibits energy loss increases of 23.6 % and 22.7 % at junction temperatures of 25 °C and 75 °C, respectively. Building on these insights, the study recommends strategies to mitigate the effects of external parasitic inductance, underscoring the pivotal role of oscillation suppression in advanced GaN Printed Circuit Board (PCB) and Integrated Circuit (IC) designs. This comprehensive inquiry provides a blueprint for enhancing GaN circuit designs, paving the way for their optimal application in the evolving realm of power electronics.

Realising SiC MOSFET switching speed control based on a novel series variable-resistance gate driver

Silicon carbide (SiC) MOSFETs feature salient characteristics such as higher breakdown voltage, lower losses and higher switching speed when compared to Silicon (Si) MOSFETs. However, due to the high switching speed and parasitic parameters, the SiC MOSFET turn-on and turn-off dynamics lead to overvoltage, overcurrent and electromagnetic interference (EMI) issues. This paper proposes a SiC MOSFET switching speed control concept based on a gate driver that features dynamically changeable gate resistance allowing microcontroller-based adjustment of the SiC MOSFET switching speed. This function therefore enables a closed-loop SiC MOSFET switching speed control, which is suited to device safety and EMI control. The configuration and operation of the proposed concept are presented. Both simulation and experimental results are provided to verify the proposed circuit.

Voltage-dependent photocurrent transients of PTB7:PC70BM solar cells: Experiment and numerical simulation

Transient photocurrent measurements on efficient polymer/fullerene solar cells based on a blend of the donor polymer PTB7 with the fullerene acceptor PC70BM are reported. In particular, we examine the light intensity dependence and voltage dependence of the turn-on and turn-off photocurrent dynamics of devices in response to a 200 μs square light pulse. At short circuit, subtle changes in the turn-on and turn-off dynamics are observed consistent with charge-density-dependent transport phenomena. As the working voltage is moved from short circuit to open circuit, we observe the appearance of an initial transient photocurrent peak a few microseconds after turn-on before the device settles to steady state. Furthermore, we observe only a weak dependence of the charge extraction dynamics on the working voltage, with the amount of charge extracted monotonically decreasing as the working voltage is moved from short circuit to open circuit. This collection of features is interpreted with the aid of numerical simulations in terms of charge trapping, with increased trap-assisted recombination closer to open circuit. The operation of devices fabricated with and without the solvent additive di-iodooctane is also compared. Charge trapping features are reduced for optimized devices fabricated with the solvent additive compared to devices fabricated without. The use of the solvent additive di-iodooctane in this system is therefore important in minimizing trap-assisted recombination.

Thermoreflectance imaging of sub 100 ns pulsed cooling in high-speed thermoelectric microcoolers

Miniaturized thin film thermoelectric coolers have received considerable attention as potential means to locally address hot spots in microprocessors. Given the highly dynamic workload in complex integrated circuits, the need arises for a thorough understanding of the high-speed thermal behavior of microcoolers. Although some prior work on transient Peltier cooling in pulsed operation is available, these studies mostly focus on theoretical modeling and typically deal with relatively large modules with time constants well into the millisecond range. In this paper, we present an extensive experimental characterization of 30×30 μm2 high-speed coplanar SiGe superlattice microcoolers subjected to 300 ns wide current pulses at ≈ 300 kHz repetition rate. Using thermoreflectance imaging microscopy, we obtain 2D maps of the transient surface temperature and constituent Peltier and Joule components over the 50–750 ns time range with submicron spatial and 50 ns temporal resolutions. Net cooling of 1 K–1.5 K is achieved within 100–300 ns, well over an order of magnitude faster compared to previous reports on microcoolers in high-speed operation. We also point out ambiguities in separating Peltier and Joule signals during the device turn-off. Overall, our measurements provide substantial insight into ultrafast turn-on and turn-off dynamics in thin film thermoelectrics.

Study on the Transient Electroluminescence of Phosphorescent OLEDs

We have studied the turn-off dynamics of phosphorescent organic light-emitting diodes (OLEDs) by investigating the temperature, pulse width, and voltage dependences of the radiative triplet lifetime with the dispersive parameter γ, calculated from the second luminescence of the transient electro-luminescence. This behavior is caused by the redistribution and recombination of electrons and holes accumulated near the interfaces. The lifetime increases with increasing carrier density and with decreasing temperature. This is due to the decrease in the hopping and the triplet-triplet annihilation rates. The experimental data satisfy the relationship between the dispersive parameter γ and temperature T, γ − 1 ∝ exp(−A/T ), with a constant A.

Multiple Slope Switching Waveform Approximation to Improve Conducted EMI Spectral Analysis of Power Converters

An improved and simplified electromagnetic interference (EMI) modeling method based on multiple slope approximation of device-switching transitions for EMI analysis of power converters is presented. The traditional noise source modeling method, which uses single slope for rise and fall transition, is studied, and the criteria for reasonable modeling in the frequency range is analyzed. The turn-on and turn-off dynamics are investigated by dividing the nonlinear transitions into several stages based on an insulated gate bipolar transistor (IGBT) behavior circuit model. Real device-switching voltage and current waveforms are approximated by piece-wise linear lines and modeled by multiple dv/dt and di/dt slopes. The predicted EMI spectra suggest that high-frequency EMI noise is modeled with an acceptable accuracy. The proposed method was verified experimentally for a dc-dc buck converter

Power Converter EMI Analysis Including IGBT Nonlinear Switching Transient Model

It is well known that very high dv/dt and di/dt during the switching instant is the major high-frequency electromagnetic interference (EMI) source. This paper proposes an improved and simplified EMI-modeling method considering the insulated gate bipolar transistor switching-behavior model. The device turn-on and turn-off dynamics are investigated by dividing the nonlinear transition by several stages. The real device switching voltage and current are approximated by piecewise linear lines and expressed using multiple dv/dt and di/dt superposition. The derived EMI spectra suggest that the high-frequency noise is modeled with an acceptable accuracy. The proposed methodology is verified by experimental results using a dc-dc buck converter

Electroluminescence spikes, turn-off dynamics, and charge traps in organic light-emitting devices

The strong electroluminescence (EL) spikes and long tails occurring at the turn-off of a bias pulse in high-quality guest-host small molecular organic light-emitting devices are described and analyzed. The observed behavior of the spikes is found to be in excellent agreement with a model based on correlated charge pairs, with average charge pair separation of 20\char21{}50 \AA{}. Immediately following the spike is a long EL tail which decays as $1/t.$ This tail is due to the recombination of initially independent charges. Hence the EL decay is determined by the dynamics of trapped charges in the recombination zone.

Resonant and off-resonant transients in electromagnetically induced transparency: Turn-on and turn-off dynamics

This paper presents a wide-ranging theoretical and experimental study of non-adiabatic transient phenomena in a $\Lambda $ EIT system when a strong coupling field is rapidly switched on or off. The theoretical treatment uses a Laplace transform approach to solve the time-dependent density matrix equation. The experiments are carried out in a Rb$^{87}$ MOT. The results show transient probe gain in parameter regions not previously studied, and provide insight into the transition dynamics between bare and dressed states.

Analysis of the turn-off dynamics in polymer light-emitting diodes

We present experimental techniques to analyze the electroluminescence (EL) of polymer light-emitting diodes following the removal of an applied voltage pulse. We explain the fast modulation of the EL intensity at turn-off in terms of the sudden reduction of the Langevin recombination rate, and extract the time evolution the device’s internal electric field at the recombination zone during the application of a voltage pulse. The results are compared to, and found to be consistent with, those of simple numerical modeling. The subsequent long-lived EL tail is analyzed to give the time evolution of the carrier distributions at the recombination zone once the voltage pulse has been removed.

Dynamic characteristics of bistable laser diodes

A stability analysis of bistable laser diodes, which gives a first analytical explanation of the recently observed high-speed bistable switching and self-pulsation, is presented by introducing two key parameters. It is shown that switching and self-pulsation are associated with two time scales. Turn-on and turn-off dynamics can be characterized by two different sets of eigenvalues which are used to analytically explain the switch-off and switch-on transients observed in experiments. It is also shown that the gain function profile can significantly affect the performance of self-pulsation operation of bistable laser diodes. The analysis also proves that the existence of two critical points has an important effect on the switching time if switching occurs around one of them. The results of the present analysis agree well with those of an exact numerical simulation. In addition, the analysis can be applied to study dynamic characteristics of a bistable laser diode (BLD) with other more complicated structures such as distributed feedback (DFB) laser diodes, multiquantum-well (MQW) laser diodes, etc.

A Unified SCR Model for Continuous Topology CADA

The principle of SCR model parameter estimation from device specification sheets [7] is combined with a reduced version of the intrinsic SCR model [2] to provide improved computational efficiency and better simulation of device turn-off dynamics. The small element count makes computer-aided design and analysis (CADA) of circuits containing several SCR's more feasible. The easy to understand intrinsic model and analytical parameter estimation procedure produce a user-oriented model with common topology applicable to popular CADA programs such as SPICE2 and SUPER-SCEPTRE.