Peak Electric Field Research Articles

Current collapse suppression in AlGaN/GaN HEMTs using dual-layer SiNx stressor passivation

In this work, a dramatic reduction in current collapse is achieved in GaN-based high-electron-mobility transistors (HEMTs) using dual-layer SiNx stressor passivation (DSSP), and the related mechanism is proposed. The SiNx compression neutralizes the inherent piezo polarization caused by the lattice mismatch at the heterojunction and effectively mitigates the peak electric field crowding at the drain-side gate edge, as supported by technology computer-aided design simulation. Thus, the inverse piezoelectric effect is suppressed and the trapped charge density is reduced under high electrical stress. As a result, the current collapse effect can be significantly restrained. Upon pulsing (Vg = −6 and Vds = 20 V), the device with DSSP exhibits a negligible current collapse (∼3%), which is significantly lower than the baseline device (∼34%). Moreover, it shows a one-order-of-magnitude reduction in gate leakage and a significant enhancement in gate stability. These results prove that the DSSP process is an attractive technique to facilitate high-reliability GaN-on-Si HEMTs.

Differences Between Far Electric Field Waveforms of Triggered Return Strokes and Natural Return Strokes From Nine Thunderstorms

The far electric field waveforms of natural first return strokes (FRSs), natural subsequent return strokes (SRSs), and triggered return strokes (TRSs) from nine thunderstorms measured by the same device were compared. The results were as follows: The far electric field peaks of TRSs were 31% smaller than that of SRSs. The geometric means of 10-to-90% risetime and half-peak width of SRS far electric fields are 2.4 μs and 5.4 μs, respectively, while those of TRSs are significantly smaller, i.e., 1.5 μs and 3.2 μs, respectively. Three possible reasons cause the differences between the SRS and TRS far electric field waveforms: TRS and SRS occur in different cloud conditions; triggering experiments are more likely to be successful when the thunderstorm electric field is in a stable period; the rise of the TRS current is steeper. Two possible reasons cause the steeper rise in TRS current: the lower part of the TRS channel is more conductive; the lower part of the TRS channel is shorter than that of the SRS channel.

AlGaN/GaN superlattice-based multichannel RF transistors for high linearity and reliability: a simplified simulation approach

Multichannel RF power amplifiers offer high frequency operation, high current and RF power, combined with excellent linearity. 3D and 2D simulation is used to investigate how changes in device architecture impact both the linearity and off-state reliability, allowing an improved linear design which does not compromise reliability. Linearity is assessed by extraction of , and third order intercept (TOI) as a function of gate bias, using a straightforward 2D approximation which is computation time and resource efficient compared to the full 3D simulation normally used for these devices. Off-state reliability is assumed to be linked to dielectric failure, and hence peak electric field as a measure of reliability is evaluated at gate corners and edges using a full 3D simulation. It is found that introducing a channel number-dependent doping in the AlGaN/GaN-based superlattice structure can be used to enable an improved transconductance–linearity. It is also found that there is a strong increase in TOI as gate dielectric thickness or fin width is increased. On the other hand, in order to maintain reliability, increased fin height is found to be essential in order to reduce electric field as dielectric thickness is increased. Finally, a device architecture for improving linearity, power and reduced OFF-state field is suggested.

Potential and electric field analysis of field plated AlGaN/GaN HEMT for high voltage applications using 2-D analytical approach

A physics-based 2-D analytical model is developed for field plated AlGaN/GaN high electron mobility transistor (HEMT) and the effect of field plate on potential and electric field is analyzed. The complete generalized theory developed includes the dependence of electric field and electric potential distribution on (i) different dielectric materials and (ii) dielectric thickness below the field plate. An extensive study of the effect of various non-field plate parameters such as doping concentration in the AlGaN layer, drain source voltage, and gate source voltage has also been carried out. It is observed that with the introduction of field plate, primary peak of electric field gets reduced and redistribution of electric field occurs in a better way with the introduction of much smaller secondary electric field peak. This leads to improved breakdown voltage thus making the device suitable for high voltage applications. The analytical results are also compared with the simulated results extracted with ATLAS 2D device simulation. The good agreement validates the analytical approach.

Ion-implanted triple-zone graded junction termination extension for vertical GaN p-n diodes

We demonstrate an ion-implanted triple-zone junction termination extension (JTE) for vertical GaN p-n diodes. Due to the spatial distribution of fixed charge in the triple-zone JTE structure, the peak electric fields at the contact metal edge and at the edge of the JTE are significantly reduced compared to conventional approaches. The forward and reverse characteristics of diodes with conventional single-zone JTE and the triple-zone JTE explored here have been studied and compared experimentally. GaN p-n diodes fabricated using the triple-zone JTE obtain an experimentally measured maximum breakdown voltage of 1.27 kV, appreciably higher than the 1.01 kV achieved using the single-zone JTE structure. The triple-zone JTE design also provides a wider window for fabrication processing and epitaxial wafer growth to achieve the high breakdown voltage compared to single-zone designs. The triple-zone JTE is promising for cost-effective fabrication of GaN power electronics.

Investigation of 4H-SiC UMOSFET Architectures for High Voltage and High Speed Power Switching Applications

A comparative TCAD (Technology Computer Aided Design) simulation study of various 4H-SiC trench gate MOSFET (Metal Oxide Semiconductor Field Effect Transistor) (or U-shaped trench gate MOSFET abbreviated for UMOSFET) architectures for high voltage and high-speed switching applications is reported. The DC (Direct Current) and AC (Alternating Current) characteristics of the different trench gate structures are investigated. Particularly, compared to conventional 4H-SiC UMOSFETs, the breakdown voltage of the UMOSFET having a p-type implanted bottom shield is increased by 44%. However, due to the extra JFET (Junction Field Effect Transistor) region, the specific on resistance also increases by 6%. Furthermore, under 1000 V drain bias, the peak electric field at the bottom oxide of the shielded trench gate is below 0.3 MV/cm. In contrast, the peak electric field of conventional UMOSFETs can be as high as 8 MV/cm, which might cause reliability issues. On the other hand, when the bottom oxide thickness of the trench gate is increased, the UMOSFET exhibits 22% less total gate charge, leading to 76% and 71% shorter switching delay time, compared to conventional UMOSFETs and bottom shield UMOSFETs, respectively. As revealed by the simulation results, the UMOSFETs with the p-type implanted bottom shield or thick bottom oxide are advantageous for high voltage and high-speed power switching applications.

Human Exposure to Non-Ionizing Radiation from Indoor Distributed Antenna System: Shopping Mall Measurement Analysis.

It is crucial to monitor the levels of Non-Ionizing Radiation (NIR) to which the general population may be exposed and compare them to the limits defined in the current standards, in view of the rapid rise of communication services and the prospects of a connected society. A high number of people visits shopping malls and since these locations usually have several indoor antennas close to the public, it is therefore a kind of place that must be evaluated. Thus, this work presents measurements of the electric field in a shopping mall located in Natal, Brazil. We proposed a set of six measurement points, following two criteria: places with great the flow of people and the presence of one or more Distributed Antenna System (DAS), co-sited or not with WiFi access points. Results are presented and discussed in terms of the distance to DAS (conditions: near and far) and flow density of people in the mall (scenarios: low and high number of people). The highest peaks of electric field measured were 1.96 and 3.26 V/m, respectively corresponding to 5% and 8% of the limits defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Brazilian National Telecommunication Agency (ANATEL).

Suppression of hot electron effect in AlGaN/GaN HEMT with multi-grooves barrier-etched structure

A multi-grooves barrier-etched structure between barrier layer and passivation layer is proposed in this paper to suppress the hot electron effect at the gate edge on the drain side in the p-GaN gate AlGaN/GaN high-electron-mobility transistor. In the TCAD simulations, the groove structure induces extra electric field concentration region and AlGaN/SiN interface area, which can lower the high electric field peak and electron temperature in the channel at the gate edge, leading to the alleviated capture and release of hot electrons. The static I–V characteristic and dynamic switching performance and breakdown characteristic show that the multi-grooves barrier-etched structure improves the current collapse and switching time and breakdown voltage. Our work exhibits the great potential of multi-grooves barrier-etched structure on the stability and reliability of the AlGaN/GaN HEMT.

Generation of 13.9-mJ Terahertz Radiation from Lithium Niobate Materials.

Extremely strong-field terahertz (THz) radiation in free space has compelling applications in nonequilibrium condensed matter state regulation, all-optical THz electron acceleration and manipulation, THz biological effects, etc. However, these practical applications are constrained by the absence of high-intensity, high-efficiency, high-beam-quality, and stable solid-state THz light sources. Here, the generation of single-cycle 13.9-mJ extreme THz pulses from cryogenically cooled lithium niobate crystals and a 1.2% energy conversion efficiency from 800nm to THz are demonstrated experimentally using the tilted pulse-front technique driven by a home-built 30-fs, 1.2-Joule Ti:sapphire laser amplifier. The focused peak electric field strength is estimated to be 7.5MVcm-1 . A record of 1.1-mJ THz single-pulse energy at a 450 mJ pump at room temperature is produced and observed that the self-phase modulation of the optical pump can induce THz saturation behavior from the crystals in the substantially nonlinear pump regime. This study lays the foundation for the generation of sub-Joule THz radiation from lithium niobate crystals and will inspire more innovations in extreme THz science and applications.

Nonadiabatic tunneling ionization of atoms in few-cycle elliptically polarized laser pulses

We theoretically investigate nonadiabatic effects in tunneling ionization of a hydrogen atom induced by a few-cycle elliptically polarized laser pulse. We find a deflection angle between the maximum of the photoelectron momentum distribution and the direction of the negative vector potential corresponding to the electric-field peak. This deflection angle mainly originates from the fact that the instant of the maximal ionization rate does not exactly correspond to the instant of the electric-field peak in the few-cycle elliptically polarized laser pulse, revealing an ionization time shift between those two instants. The ionization time shift is a result of the nonadiabatic effect induced by the envelope of the few-cycle elliptically polarized laser pulse, which disappears in a long-pulsed laser. Our study is useful for understanding attoclock experiments using few-cycle elliptically polarized laser pulses.

Intense narrowband terahertz pulses produced by obliquely colliding laser pulses in helium gas

A practical configuration for generating narrowband terahertz (THz) pulses based on plasma dipole oscillations (PDOs) is studied using two-dimensional particle-in-cell simulations. In this scheme, two slightly detuned laser pulses collide obliquely in a helium gas. Plasma strips are generated along the paths of the laser pulses by field ionization. The PDO created in the overlap region of the two laser pulses emits a THz pulse with a peak electric field strength of a few gigavolt per meter. An energy conversion efficiency of 0.542 × 10 − 3 is achieved for laser pulse intensities 4.82 × 10 16 W / c m 2, a spot radii of 5 μ m, and a collision angle of 10.8 °. A force balance model is extended for the obliquely colliding configuration of the pulses. As the complications, such as generating plasmas separately or aligning the beams with preformed plasma, are eliminated from our new configuration, this makes a future experimental study of PDO more straightforward.

Broadband Spintronic Terahertz Source with Peak Electric Fields Exceeding 1.5 MV/cm

Spintronic terahertz emitters (STEs) are desirable broadband terahertz sources, but their limited signal strength has hindered practical application. By optimizing the photonic and thermal environment, the authors present an STE that could overcome this obstacle. Benchmarking against the state-of-the-art terahertz emitters based on optical rectification, this STE delivers strong terahertz pulses with comparable peak electric field and fluence, and offers additional features such as broadband radiation, easy alignment, and rotation of the terahertz polarization plane without power loss. This work will open up a promising pathway to nonlinear terahertz spectroscopy with spintronic sources.

Ultra-low-frequency waves for below threshold and thousand times threshold flux events

A recent study by Shah et al. [Astrophys. Space Sci. 366(2), 22 (2021)] explored the effects of large-scale solar wind structures on relativistic electron fluxes in the slot region and categorized the flux events into four classes, including those with the events of maximum peak fluxes, TTF (thousand times threshold flux), and the events of smallest fluxes, BTF (below threshold flux). This study compares ultra-low-frequency (ULF) waves inside a magnetosphere and at the magnetopause boundary for the BTF and TTF events. It is found that during the TTF event, the electron radial drift velocity peaked very early at the position of an inner Van Allen radiation belt (L = 2–3). The delay between the radial velocity peak and the peak of the toroidal mode electric field was 12 min. For the BTF event, strong ULF waves were absent in the outer Van Allen radiation belt. In contrast, peak powers of ULF waves in the outer radiation belt approached 80 (mV/m)2/Hz for the TTF event, and this peak exceeded the peak power of the toroidal mode electric field at the magnetopause boundary (L = 11) for the BTF event. Our findings are critical for understanding the transport of ULF wave-driven charged particles from the magnetopause boundary to the inner magnetosphere.

Numerical simulation of streamer discharge with different electrode shapes in C4F7N

In recent years, the environmentally friendly gas, C4F7N, has been recognized as a potential SF6 alternative gas due to its excellent insulation. To study the streamer discharge characteristics of different electrode shapes in C4F7N, a fluid model was established by COMSOL, and simulations were performed. Streamer discharge as a function of varying electrode shapes was analyzed, and the variation law of electric field intensity and photon flux was obtained, which serves as a theoretical basis for optical detection and reliable diagnosis of partial discharge. Simulation results demonstrate that under the same discharge conditions, the electric field inhomogeneity of the needle–plane model, rod–plane model, and ball–plane model decreased successively and the breakdown difficulty increased. With the increase in the applied voltage, the peak electric field intensity of the streamer head was found to increase, whereas an increase in the electrode spacing was found to decrease this property. The change in photon flux was found to be similar to the change in the electric field intensity.

Si3 N4 Passivation and Side Illumination of High-Power Photoconductive Semiconductor Switch Based on Free-Standing SI-GaN

To meet the needs of wide band gap (WBG) gallium nitride (GaN)-based photoconductive semiconductor switch (PCSS) in high-voltage and high-power microwave systems. Herein, silicon nitride (Si3N4) dielectric films were deposited on GaN PCSS using plasma-enhanced chemical vapor deposition (PECVD) and illuminated from the side of the device. A high refractive index of 2.03 and a high permittivity of 7.97 were obtained from Si3N4 films, which are characterized by high optical and dielectric properties. According to the electrostatic field simulation, Si3N4’s high permittivity minimizes the peak electric field at the electrode boundary of GaN PCSSs. When the 532-nm incident light is side illuminated for the device, the output peak power and rise time are 59.8 kW and 0.52 ns, respectively. At a future date, the proposed GaN-based PCSS will have a practical application for radio frequency microwave systems.

Simulation study on single-event burnout reliability of 4H-SiC trench gate MOSFET with combined P-buried layer

In this article, the purpose of this numerical study is to investigate the rated 3.3-kV SiC power gate trench MOSFET structure with ground and float p-buried layer (DGF-MOS). The simulation results show the introduction of ground and float p-buried layer and upper drift layer optimized breakdown voltage (BV) the specific on-resistance (Ron,sp), and gate drain charge (Qgd,sp), thus the figure of merit (BV2/Ron,sp) is improved by 130 % and the figure of merit (Ron,sp × Qgd,sp) is reduced 173 % compared with the conventional SiC power gate trench MOSFET (CT-MOS). Additionally, the single-event burnout (SEB) simulation results show that the critical degradation threshold of CT-MOS structure is 900 V at LET = 0.5 pC/μm. The robustness of the DGF-MOS structure design to heavy ions was simulated. The results show that the maximum temperature peaks around the gate trench and substrate junction of the DGF-MOS structure could both be effectively suppressed due to the decrease in electric field peak. Consequently, the DGF-MOS structure showed a severe denaturation threshold of 1500 V, which was 66.6 % higher than that of the CT-MOS structure.

Electric field simulations of transcranial direct current stimulation in children with perinatal stroke.

Perinatal stroke (PS) is a focal vascular brain injury and the leading cause of hemiparetic cerebral palsy. Motor impairments last a lifetime but treatments are limited. Transcranial direct-current stimulation (tDCS) may enhance motor learning in adults but tDCS effects on motor learning are less studied in children. Imaging-based simulations of tDCS-induced electric fields (EF) suggest differences in the developing brain compared to adults but have not been applied to common pediatric disease states. We created estimates of tDCS-induced EF strength using five tDCS montages targeting the motor system in children with PS [arterial ischemic stroke (AIS) or periventricular infarction (PVI)] and typically developing controls (TDC) aged 6-19 years to explore associates between simulation values and underlying anatomy. Simulations were performed using SimNIBS https://simnibs.github.io/simnibs/build/html/index.html using T1, T2, and diffusion-weighted images. After tissue segmentation and tetrahedral mesh generation, tDCS-induced EF was estimated based on the finite element model (FEM). Five 1mA tDCS montages targeting motor function in the paretic (non-dominant) hand were simulated. Estimates of peak EF strength, EF angle, field focality, and mean EF in motor cortex (M1) were extracted for each montage and compared between groups. Simulations for eighty-three children were successfully completed (21 AIS, 30 PVI, 32 TDC). Conventional tDCS montages utilizing anodes over lesioned cortex had higher peak EF strength values for the AIS group compared to TDC. These montages showed lower mean EF strength within target M1 regions suggesting that peaks were not necessarily localized to motor network-related targets. EF angle was lower for TDC compared to PS groups for a subset of montages. Montages using anodes over lesioned cortex were more sensitive to variations in underlying anatomy (lesion and tissue volumes) than those using cathodes over non-lesioned cortex. Individualized patient-centered tDCS EF simulations are prudent for clinical trial planning and may provide insight into the efficacy of tDCS interventions in children with PS.

Epitaxial κ-Ga2O3/GaN heterostructure for high electron-mobility transistors

GaN power technology, especially AlGaN/GaN high electron-mobility transistors (HEMTs), has made significant progress in recent years. However, the performance of HEMTs is still limited due to a trade-off between on-resistance and off-state breakdown voltage (BV). Integrating a polar gate dielectric with GaN HEMTs can potentially improve both sheet resistance of the two-dimensional electron gas channel and the field distribution between gate and drain. In this regard, orthorhombic κ-Ga2O3 has attractive properties since it is predicted to be strongly polar and highly dielectric while it grows epitaxially on GaN. By successfully integrating crystalline κ-Ga2O3 on GaN HEMTs, the channel sheet resistance is reduced by 20% from a reference device with amorphous Al2O3 gate dielectric. As a result, the cut-off frequency increases from 4.8 to 9.1 GHz. The dielectric property of κ-Ga2O3 also improves BV from 354 to 380 V by reducing the peak electric field in the gate-drain region.

Physical Mechanism of the β‐Ga2O3 PN Tunneling Diode with a Low Specific On‐Resistance

This study proposes a β‐Ga2O3 pn tunneling diode (PNT‐diode) in which the p‐type region is obtained by sputtering a thin NiOx layer in the pure argon atmosphere. The diode exhibits good characteristics: a high current density of 1530 A cm−2 at 10 V and a low specific on‐resistance of 0.56 mΩ cm2. Moreover, its breakdown voltage of is about four times compared to a conventional diode, and its Baliga's figure of merit (BFOM) is as high as 3.25 GW cm−2. Ni/NiOx diodes are simulated by Silvaco simulation software to investigate the physical mechanism of the low specific on‐resistance of the PNT‐diode, and the results demonstrate that Ni and NiOx can form a reverse diode, and that PNT‐diode is equivalent to the Ni/NiOx reverse diode and the NiOx/β‐Ga2O3 forward diode connected in series. Finally, the electric field distribution of the PNT‐diode is simulated, and it is found that p‐type NiOx can significantly reduce the peak electric field at the anode edge.

Single-event burnout hardening evaluation with current and electric field redistribution of high voltage LDMOS transistors based on TCAD Simulations

—A single-event burnout (SEB) hardened design based on high voltage lateral double-diffused metal-oxide-silicon (LDMOS) devices with an optimal partial buried oxide (BOX) layer and a N-buffer layer is firstly proposed in this paper. By analyzing the response of surface electric field and transient current, the optimal parameters of hardened layers are selected. Simulation results reveal that an optimal buffer layer can suppress the peak electric field from 4.5 MV/cm to 2 MV/cm, recreate the position of peak electric field and an optimal BOX layer can reconstruct the path of electron and hole currents, reducing the risk of parasitic bipolar-junction-transistor (BJT). By contrast, the SEB triggering voltage can be improved from 197 V to 396 V, with an increase of 100%. And the ratio of safe operating area (SOA) with SEB to breakdown voltage (BV) can be increased from 30% to 69%. In the case of heavy-ions with different energies, the SEB hardened LDMOS also has better performance than the conventional one.