High Electric Field Conditions Research Articles

Superelastic electromechanical behaviors in ferroelectric PbTiO[formula omitted] ceramics under coupled mechanical-electric fields: Higher-order piezoelectric constitutive equations from first-principles

With the recent discovery of superelastic behaviors of ferroelectric (piezoelectric) ceramics, understanding their non-linear mechanical and electromechanical responses under high stress and electric field conditions is crucial for engineering and designing advanced piezoelectric devices, such as ultrasmall actuator systems. In this study, we carry out first-principles finite electric field calculations to clarify the mechanical and electromechanical properties under the electric field for typical ferroelectric ceramics of PbTiO3. Superelastic-like non-linear deformation behavior is enhanced or suppressed depending on the electric field direction, suggesting the possible design of superelasticity. We clarified that positive and negative electric fields to spontaneous polarization promote and inhibit deformation due to strain loading, thereby providing tunable superelasticity. We also investigate the mechanical loading and electric field dependence of the piezoelectric coefficient of PbTiO3. The tunable piezoelectric response can be provided with a coupling of mechanical loading and electric field. Finally, we present higher-order piezoelectric constitutive equations applicable for superelastic-like non-linear deformations under an electric field. The present results will open promising paradigms for functional piezoelectric devices, and the proposed piezoelectric constitutive equations broaden the design scope through finite element method analysis.

Improved Energy Density at High Temperatures of FPE Dielectrics by Extreme Low Loading of CQDs.

Electrostatic capacitors, with the advantages of high-power density, fast charging-discharging, and outstanding cyclic stability, have become important energy storage devices for modern power electronics. However, the insulation performance of the dielectrics in capacitors will significantly deteriorate under the conditions of high temperatures and electric fields, resulting in limited capacitive performance. In this paper, we report a method to improve the high-temperature energy storage performance of a polymer dielectric for capacitors by incorporating an extremely low loading of 0.5 wt% carbon quantum dots (CQDs) into a fluorene polyester (FPE) polymer. CQDs possess a high electron affinity energy, enabling them to capture migrating carriers and exhibit a unique Coulomb-blocking effect to scatter electrons, thereby restricting electron migration. As a result, the breakdown strength and energy storage properties of the CQD/FPE nanocomposites are significantly enhanced. For instance, the energy density of 0.5 wt% CQD/FPE nanocomposites at room temperature, with an efficiency (η) exceeding 90%, reached 9.6 J/cm3. At the discharge energy density of 0.5 wt%, the CQD/FPE nanocomposites remained at 4.53 J/cm3 with an efficiency (η) exceeding 90% at 150 °C, which surpasses lots of reported results.

Interface engineering of polymer composite films for high-temperature capacitive energy storage

Polymer film capacitors encounter challenges in harsh conditions of high temperatures and electric fields because of large conduction loss and degraded breakdown strength (Eb). Herein, an interface engineering strategy is proposed to fluorinate the interfaces between the polyetherimide (PEI) matrix and wide bandgap boron nitride nanosheets (BNNSs) fillers. The composite films exhibit high-performance capacitive energy storage with a remarkable energy density of 5.73 J/cm3 and an ultrahigh efficiency of 91.22 % in conditions of 575 kV/mm and 150 °C. By adopting interfacial fluorination, the band structure of BNNSs is tailored to achieve a type II band alignment with PEI, promoting the dual trapping for both electrons and holes. It highly suppresses leakage current and reduces conduction loss. Typically, introducing fillers can compromise the properties of interfacial layers, creating weak points that trigger breakdown. Conversely, fluorinated interfaces exhibit an increased Young’s modulus and a reduced dielectric constant. According to the electromechanical breakdown theory, the interfacial Eb is increased. The breakdown phase propagation along the interfaces is thereby impeded, ultimately resulting in a further increase in overall Eb, reaching up to 589 kV/mm at 150 °C. Fluorinated interface engineering addresses interfacial challenges posed by fillers, enabling high-temperature energy storage capability in PEI-based capacitors.

The Influence of Measurement Conditions on the Electrocaloric Effect in Ferroelectric Ceramics of Modified Barium Titanate.

In this work, the electrocaloric effect (ECE) and electrocaloric strength (ΔT/E) were measured and thermal and dielectric studies were performed on Pb-modified BaTiO3 (BPT). The saturated hysteresis loops and normal ferroelectric behavior of the ferroelectric ceramics allow the utilization of the indirect method to estimate the electrocaloric properties. The electrocaloric measurements were performed under high (18 kV/cm) versus low (8 kV/cm) electric field conditions. These conditions were chosen to notice and then eliminate an artificial negative electrocaloric effect in the tested ceramics. At the same time, relatively high values of positive electrocaloric temperature change ΔT (~ 2.19 K) and electrocaloric strength ΔT/E (~0.27-0.11 K·cm/kV) were obtained.

Impact of doping with organic dopants and mixed doping with alkali metals and organic dopants on the absorption, electronic, optoelectronic, thermodynamic and nonlinear optical properties of dibenzo[b,def]chrysene in gaseous media: DFT and TD-DFT studies.

In this study, we evaluate the geometrical, absorption, optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of dibenzo[b,def]chrysene molecule derivatives by means of DFT and TD-DFT simulations. In view of the aim of producing new high-performance materials for non-linear optics (NLO) by doping test, two types of doping were used. We obtained six derivatives by doping with organic dopants (Nitro, amide and ticyanoethenyl) and mixed alkali metal (potassium) and organic dopants. Doping with organic dopants produced molecules A, B and C, respectively when substituting one hydrogen with nitro (NO2), amide (CONH2) and tricyanoethenyl (C5N3) groups, while mixed doping involved considering A, B and C and then substituting two hydrogens with two potassiums to obtain compounds D, E and F respectively. The negative values of the various interaction energies calculated for all the doped molecules show that they are all stable, but also that molecules C and F are the most stable in the case of both dopings. The gap energies calculated at the B3LYP level of theory are all below 3eV, which means that all the molecules obtained are semiconductors. Better still, compounds C and F, with gap energies of 1.852eV and 1.204eV, respectively, corresponding to decreases of 35.67% and 58.18% in gap energy compared with the pristine molecule, are more reactive than the other doped molecules. Mixed doping is therefore a highly effective way of narrowing the energy gap and boosting the semiconducting character and reactivity of organic materials. Optoelectronic properties have also been improved, with refractive index values higher than those of the reference material, glass. This shows that our compounds could be used under very high electric field conditions of the order of 4.164 109V.m-1 for C and 7.410 109V.m-1 for F the highest values at the B3LYP level of theory. The maximum first-order hyperpolarizability values for both types of doping are obtained at the CAM-B3LYP level of theory by C: 10-30esu and by F: 10-30esu, and second-order values are also given by these same compounds. These values are higher than the reference value, which is urea, making our compounds potential candidates for high-performance NLO applications. In dynamic mode and at a frequency of 1064nm, at the CAM-B3LYP level of theory, the highest dynamic hyperpolarizability coefficients were obtained by C and F. Hyper-Rayleigh scattering , coefficients of the electro-optical Pockel effect (EOPE), EFISHG, third-order NLO-response degree four-wave mixing , quadratic nonlinear refractive index n2 were also calculated. The maximum values of n2 are obtained by C (6.13 10-20 m2/W) and F (6.60 10-20 m2/W), these values are 2.24 times higher than that of fused silica which is the reference for degenerate four-wave mixing so our molecules could also have applications in optoelectronics as wavelength converters, optical pulse modulators and optical switches. Using the DFT method, we were able to determine the optimized and stable electronic structures of doped dibenzo[b,def]chrysene derivatives in the gas phase. We limited ourselves to using the proven B3LYP and CAMB3LYP levels of theory for calculating electronic properties, and non-linear optics with the 6-311G + + (d,p) basis set, which is a large basis set frequently used for these types of compound. Gaussian 09 software was used to run our calculations, and Gauss View 6.0.16 was used to visualize the output files. TD-DFT was also used to determine absorption properties at the B3LYP level of theory, using the same basis set.

Effect of high static electric field on germination and early stage of growth of Avena sativa and Raphanus sativus

Presented study investigated the impact of a stationary electric field with an average value of 185 kV/m on the germination process and early growth of radish (Raphanus sativus – a eudicot plant) and oat (Avena sativa – a monocot plant). Electric field stimulation may prove to be one method to sustainably increase crop efficiency. The research is aimed to increase knowledge of the effect of a static electric field on the plant growth process, because understanding of the topic is still limited. The plants were grown on a viscose substrate in a dark room without any light. Studies have shown that the electric field can affect the germination and growth process depending on the plant species. The findings indicate a positive influence of the electric field on radish germination. The presence of the electric field accelerates the germination process and growth of young plants. On the first day of germination (the 3rd day of cultivation), about 3.2 times as many plants germinated in the samples exposed to a stationary electric field compared to the control samples. On the last day of the experiment (the 8th day of cultivation), the tallest plants in the samples subjected to the electric field were 8 % higher, compared to the tallest plants in the control samples. On the other hand, the results demonstrate a negative impact of the electric field on oat seed germination. The presence of an electric field delays the germination process and reduces the number of germinated seeds. On the last day of the experiment (the 11th day of cultivation), about 1.25 times fewer oat plants germinated in the samples exposed to a stationary electric field compared to the control samples. The tallest plants in the samples subjected to the electric field were 1.1 times smaller than the tallest plants in the control samples.

Bounce and contact mode regimes for drop impact on smooth surfaces: The influence of gas kinetics and electrostatics

When liquid drops impact on solid surfaces, an air layer forms in between the drop and the surface, acting as a cushion to mitigate the impact. In this work, we focus on delineating the bounce and contact mode regimes of impacting drops on smooth surfaces, specifically discerning whether drops rebound from the air layer or make contact with the solid surfaces, and pinpointing the precise contact modes between the drop and solid surfaces by resolving the gas film evolution and rupture. Our simulation model incorporates gas kinetics and electrostatics effects, both of which have been validated by experiments documented in the literature or theoretical models regarding thin film instabilities. We undertake a comprehensive review and categorization of the contact modes and elucidate how they change under different conditions of impact velocities, ambient pressures, and electric field intensities. We also provide some perspectives on the regime map for the lubricated surfaces, which contains an unresolved issue that the critical Weber number for bouncing-wetting transition is significantly reduced compared to the solid smooth surfaces like mica. These insights have noteworthy practical implications offering guidance for a wide range of scenarios, from normal-pressure environments to low-pressure conditions at high altitudes, encompassing high electric field conditions such as nanogenerators as well as low electric field conditions resembling glass surfaces with static electricity.

Sandwich-structured BOPET films with high energy density and low loss for high temperature film capacitors

Film capacitors have widely been used in modern electrical/electronic equipment because of their high insulation property and high-power density. However, the traditional dielectric films suffered a high conduction loss under high temperature and electric field conditions, which leads to the depression of high temperature energy storage properties. Herein, sandwich-structured composite films using biaxially oriented polyethylene terephthalate (BOPET) as the outer layers were prepared to construct the interfacial barrier, which was beneficial for hindering the propagation of breakdown path. In addition, epoxy resin was applied as the adhesive inner layer to bind the outer layers up tightly, while the boron nitride nanosheets (BNNSs) in the inner layer further improved the breakdown strength of the film and inhibited the conduction loss, especially under high temperature and electric field conditions. The composite film with optimized BNNSs content had a high discharged energy density of 9.11 J/cm3 and a ultrahigh charge–discharge efficiency of 95% at 25 °C, while the values were 6.45 J/cm3 and 70% at 150 °C, respectively, of which both were much higher than those of pure BOPET. Thus, the sandwich-structure method points out a promising way of preparing dielectric films with excellent energy storage performances.

Reliability Assessment of On-Wafer AlGaN/GaN HEMTs: The Impact of Electric Field Stress on the Mean Time to Failure.

We present the mean time to failure (MTTF) of on-wafer AlGaN/GaN HEMTs under two distinct electric field stress conditions. The channel temperature (Tch) of the devices exhibits variability contingent upon the stress voltage and power dissipation, thereby influencing the long-term reliability of the devices. The accuracy of the channel temperature assumes a pivotal role in MTTF determination, a parameter measured and simulated through TCAD Silvaco device simulation. Under low electric field stress, a gradual degradation of IDSS is noted, accompanied by a negative shift in threshold voltage (ΔVT) and a substantial increase in gate leakage current (IG). Conversely, the high electric field stress condition induces a sudden decrease in IDSS without any observed shift in threshold voltage. For the low and high electric field conditions, MTTF values of 360 h and 160 h, respectively, were determined for on-wafer AlGaN/GaN HEMTs.

First-Principles Modeling of Preferential Solvation in Mixed-Modifier Differential Mobility Spectrometry.

Differential mobility spectrometry (DMS) separates ions based on mobility differences between high and low electric field conditions. To enhance resolution, solvents such as water and acetonitrile are often used to modify the collision environment and take advantage of differing dynamic clustering behavior between analytes that coelute in hard-sphere environments (e.g., N2). When binary solvent mixtures are used to modify the DMS environment, one solvent can have a dominant influence over the other with respect to ion trajectories. For example, for quinoline derivatives, a 9:1 water:acetonitrile solvent mixture exhibited identical behavior to an environment containing only acetonitrile as a modifier. It was hypothesized that this effect arises due to the significantly different binding strengths of the two solvents. Here, we utilize a first-principles model of DMS to study analytes in single and binary solvent mixtures and explore the effects governing the dominance of one solvent over the other. Computed DMS dispersion curves of quinoline derivatives are in excellent agreement with those measured experimentally. For mixed-modifier environments, the predicted cluster populations show a clear preferential solvation of ions with the stronger binding solvent. The influence of ion-solvent binding energies, solvent concentration, and solvent molecule size is discussed in the context of the observed DMS behavior. This work can guide the usage of binary solvent mixtures for improving ion separations in cases where compounds coelute in pure N2 and in single-solvent modifier environments. Moreover, our results indicate that binary solvent mixtures can be used to create a relative scale for solvent binding energies.

A Reactive Molecular Dynamics Study on Crosslinked Epoxy Resin Decomposition under High Electric Field and Thermal Aging Conditions.

To reveal the microscopic mechanism of synergetic thermal-electrical degradation during a partial discharge process in epoxy insulation materials, the decomposition of crosslinked epoxy resin is investigated using reactive molecular dynamics simulations under high electric field and thermal degradation conditions. Bond-boost acceleration method is employed in reactive molecular dynamics simulations to successfully establish epoxy polymer models with a crosslink degree of 93%. Active molecular species derived from electrical partial discharges are considered in the current work. Small molecule products and decomposition temperature in the degradation process under an electric field are calculated to elucidate the effect of nitric acid and ozone molecules, being the active products generated by electrical partial discharges, on the synergetic thermal-electrical degradation of epoxy resin. Both nitric acid and ozone exacerbate thermal impact decomposition of crosslinked epoxy polymer by decreasing initial decomposition temperature from 1050 K to 940 K and 820 K, respectively. It is found that these active products can oxidize hydroxyl groups and carbon-nitrogen bridge bonds in epoxy molecular chains, leading to the aggravation of epoxy resin decomposition, as manifested by the significant increase in the decomposed molecular products. In contrast, thermal degradation of the epoxy resin without the active species is not expedited by increasing electric field. These strongly oxidative molecules are easily reduced to negative ions and able to obtain kinetic energies from electric field, which result in chemical corrosion and local temperature increase to accelerate decomposition of epoxy insulation materials.

Frenkel-Poole Mechanism Unveils Black Diamond as Quasi-Epsilon-Near-Zero Surface.

A recent innovation in diamond technology has been the development of the "black diamond" (BD), a material with very high optical absorption generated by processing the diamond surface with a femtosecond laser. In this work, we investigate the optical behavior of the BD samples to prove a near to zero dielectric permittivity in the high electric field condition, where the Frenkel-Poole (FP) effect takes place. Zero-epsilon materials (ENZ), which represent a singularity in optical materials, are expected to lead to remarkable developments in the fields of integrated photonic devices and optical interconnections. Such a result opens the route to the development of BD-based, novel, functional photonic devices.

Modelling of a shear-type piezoelectric actuator for AFM-based vibration-assisted nanomachining

Recent research investigations have reported the benefit of enhancing conventional AFM-based nanoscale machining operations by the introduction of high frequency vibrations between the AFM tip and the processed material. The technique relies on piezoelectric actuation and is relatively straight forward to implement in practice. However, the non-linearity of piezoelectric actuators when operated under high electric field and frequency conditions can affect the dimensional accuracy of the fabricated nanostructures. To address these issues, the paper reports a method based on coupled mechanical-electrical Finite Element (FE) modelling to predict the relative motion between an AFM tip and a workpiece for vibration-assisted AFM-based nanomachining applications. In particular, the novelty of the proposed method is that it combines two classical approaches for modelling the nonlinear behaviour of piezoelectric materials. More specifically, two sources of non-linearity are considered simultaneously by combining the field-dependant model from Muller and Zhang with the frequency-dependant model from Damjanovic. The resulting combined model is employed to establish the piezoelectric constitutive equations implemented in the developed coupled field FE model. A further distinguishing characteristic of the work is that the proposed approach was subsequently validated by comparing the predicted widths of nanoscale grooves against those machined with a custom AFM-based vibration-assisted nanomachining configuration.

Improving the Rotational Freedom of Polyetherimide: Enhancement of the Dielectric Properties of a Commodity High-Temperature Polymer Using a Structural Defect

Dielectric polymers that can withstand harsh conditions of simultaneous high electric field and elevated temperature are widely used in electrical and electronic systems. However, traditionally, the thermal stability of polymers is engineered based on highly conjugated aromatic molecular structures, giving rise to soring charge transport and thus poor charge–discharge efficiency under concurrent high electric field and elevated temperature. Here, we locally improved the rotational flexibility of the phenylenediamine linkage structure in polyetherimide (PEI) to decouple the conjugation of the organic molecule. p-Phenylenediamine (5 mol %) as a low-energy rotation repeat unit within PEI significantly optimized its dielectric properties, exhibiting substantially suppressed electrical conduction (more than 1 order of magnitude lower) and polarization loss (<1%). The new PEI has a largely improved charge–discharge efficiency of 91% at 400 MV/m 200 °C, outperforming the best-reported polymer-based dielectrics without any modification of the cost of goods. The high-throughput facile processing of the new PEI provides a potential candidate for energy storage applications under elevated temperatures. This work unveils a scalable approach to exploring polymer dielectrics by introducing a small amount of local structural modifications.

Significantly improved high-temperature charge-discharge efficiency of all-organic polyimide composites by suppressing space charges

In order to satisfy the miniaturization trends of power electronic devices and safe operation in harsh environments, high-temperature dielectric polymers with excellent energy density and great reliability are desired in advanced electronic and power systems as electrostatic capacitors. Herein, the all-polymer dielectric composite films, consisting of ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as filler and linear polymer polyimide (PI) as matrix, were fabricated by in situ polymerization method for electrostatic energy storage scenarios. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicated that the P(VDF-HFP) was successfully compounded into the PI matrix. The dielectric permittivity of PI/P(VDF-HFP) energy storage composites was enhanced, while the breakdown strength and electrical resistivity values were wrecked slightly with enhancive mass fraction of P(VDF-HFP). Consequently, the discharged energy density (Ud) of PI-10, PI-20 and PI-30 were 2.60, 2.90, and 3.16 J/cm3 at 30 ℃ and 400 MV/m, respectively, which were 1.05, 1.17 and 1.27 times than those of neat PI film (2.48 J/cm3). Notably, an interesting phenomenon was observed that the charge-discharge efficiency (η) of all-organic composites was dramatically improved situated in high-temperature conditions. When the mass ratio of P(VDF-HFP) to PI was 1:4, the corresponding Ud and η of PI-20 could be significantly improved to 2.25 J/cm3 and 76.9% at 382 MV/m and 150 ℃, which were 6.7 and 10.5 times than those of neat PI film (0.336 J/cm3 and 7.3%) at 300 MV/m, respectively. Impressively, PI-30 film delivers an enhanced Ud of 1.81 J/cm3 and η of 71% at 200 ℃ and 308 MV/m. The significant improvement in the efficiency of composites under high-temperature environment is attributed to the suppression of space charges, which was verified by the TSDC results. In addition, the all-polymer composites exhibited outstanding cycling stability under harsh conditions of high temperature and high electric field. Our fabricated PI/P(VDF-HFP) composite films present potential energy storage applications in the high temperature environments with demand for flexible dielectric materials with upgraded permittivity, excellent energy density as well as reliable cycling stability.

Flexible polyolefin dielectric by strategic design of organic modules for harsh condition electrification

A paradigm-shifting design strategy is demonstrated that unifies the treatment of electronic and conformational properties of polymer dielectrics for concurrent high electric field and elevated temperature harsh conditions.

Electric-Field-Dependence Mechanism for Cosmic Ray Failure in Power Semiconductor Devices

This article describes an analysis of the electric-field-dependence mechanism for cosmic ray failure in power semiconductor devices. Two major modes for the failure have been reported. One is bipolar transistor activation caused by carrier generation from impact ionization at the n−/n+ boundary. The other is Joule heating generated by an avalanche current in high electric fields. We clarified that a bipolar transistor activation mode had not occurred even under high electric field conditions for the drift layer width used in lower-voltage-class insulated-gate bipolar transistors (IGBTs) by evaluating the drift layer thickness dependence of the failure in time (FIT) in 1700 V devices from punchthrough to non-punchthrough with and without a p+ collector layer. We also clarified that the electric field averaged over the depletion layer width (applied voltage divided by the depletion layer width) is the critical factor for failure, rather than the maximum electric field, for the first time by observing a universal curve of the average electric field dependence of FIT in 750–6500 V IGBTs and diodes. To improve the cosmic ray durability of power semiconductor devices, lowering the electric field averaged over the depletion layer width is effective for device design.

Experimental study of the effect of water vapor on dynamics of a high electric field non-equilibrium diffuse discharge in air

We report results on the influence of relative humidity (RH) on the propagation speed, the intensity of the emitted light, the energy and the gas temperature of a pin-to-plane nanosecond pulsed discharge at atmospheric pressure in synthetic air. The discharge is generated under very high overvoltage (several tens of kilovolts) so that it propagates with a voluminous, diffuse, and stable pattern. It is shown that the water vapor content has a strong impact on the discharge dynamics for gas mixtures with high RH and for the highest electric field values. In particular, for voltage pulse amplitudes higher than 65 kV and RH higher than 30%, the propagation abruptly slows down and the light intensity profiles show a stronger emission at the pin which weakens in the rest of the gap. The electric energy is slightly lower in humid air, independently of water vapor concentration. Also, time and spatially resolved gas temperature measurements carried out for different voltages show a late and significant heating at the pin whatever the water vapor content. An evaluation of the energy consumed in fast heating processes is proposed, showing an increased energy consumption at the pin in highly humid air. Besides, the hypotheses allowing for the consideration of the rotational temperature of the second positive system (SPS) of nitrogen (N2(SPS)) as the gas temperature under high electric field conditions are discussed.

Nonlinear dynamic response of an L-shaped beam-mass piezoelectric energy harvester

Piezoelectric energy harvesters (PEHs) have been taken considerable attention in decades. To evaluate the performance of the harvester in large deformation and high electric field conditions, nonlinear effects (geometric, material and damping nonlinearities) should be involved in analyzing the characteristic of the harvesters. In this article, the unimorph L-shaped harvester is investigated and influence of the geometric and material nonlinearities to the responses of the proposed L-shaped harvester is also studied. Based on extended Hamilton principle and Gauss law, the distributed parameter model of the L-shaped harvester is established and validated with experiments. Moreover, influence of some key parameters such as excitation amplitude abx and nonlinear material coefficients α1-α4 to the dynamic responses and voltage outputs of the L-shaped harvester are also analyzed. Besides, four different harvesters, which contain linearity only, geometric nonlinearity only, material nonlinearity only and both geometric and material nonlinearities, are investigated to embody the difference and importance of the two nonlinearities (geometric and material nonlinearities). Results show that as the excitation amplitude abx increases, effect of geometric nonlinearity becomes more obvious and leads to the softening phenomenon, and part of nonlinear material coefficients have greater influence to the peak value of the dynamic responses and the nonlinear phenomena (softening or multiple-frequency). Thus, consideration of nonlinear effects (geometric and material nonlinearities) can improve the prediction accuracy of the performance of the harvester which will be helpful for design and application of the harvester in large amplitude excitation and high electric field conditions.

Improving the GaN-on-GaN Schottky Barrier Diode by ALD-AlN Tunneling Barrier Layer and Multi-Fins Structure

In this paper, we report a 1.84 kV GaN-on-GaN Schottky barrier diode (SBD) corresponds to a low on-resistance of 1.98 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The GaN epi-layer was etched to the multi-fins-structure with optimized bevel angle. The fins structure enables to improve the breakdown voltage by means of the uniforme electric field distribution. Afterwards, the GaN fins were capped by atomic layer deposition (ALD)-grown AlN film. The AlN served as a tunneling-barrier layer, which not only passivated the GaN surface but also decreased the turn-on voltage. The AlN-capped SBD shows a turn-on voltage at 0.18 V. Furthermore, the temperature-dependent transfer characteristics suggest the different current tunneling mechanisms at low and high electric field conditions, respectively. The time-dependent dielectric breakdown (TDDB) measurement suggests the surface traps were well passivated by ALD-AlN, which implies that the AlN cap-layer enables to improve the device reliability.