High-power Devices Research Articles

Significantly Enhanced Interfacial Thermal Conductance across GaN/Diamond Interfaces Utilizing AlxGa1-xN as a Phonon Bridge.

Improving the thermal conductance at the GaN/diamond interface is crucial for boosting GaN-based device performance and reliability. In this study, first-principles calculations and molecular dynamics simulations were employed to explore the interfacial thermal conductance of GaN/diamond interfaces with AlxGa1-xN transition layers. The AlxGa1-xN alloy exhibits a lower thermal conductivity than GaN, primarily due to enhanced anharmonic phonon scattering. However, for the interfacial thermal conductance at the GaN/diamond interface, we discovered that introducing an AlxGa1-xN with a high Al concentration (x > 0.5) as a phonon bridge between GaN and diamond can significantly enhance the interfacial thermal conductance. In particular, it increases from 4.79 MW·m-2 K-1 to a maximum of 158 MW·m-2 K-1 at x = 0.75, surpassing the 152 MW·m-2 K-1 achieved by AlN. The AlxGa1-xN alloy has been confirmed computationally as a more efficient phonon bridge, which can provide a valuable theoretical reference for experimentally investigating the thermal management and thermal design of high-power electronic devices based on the GaN/diamond interface.

Synergistically Constructing High-Dielectric Poly(m-phenylene isophthalamide)/Silica/Cellulose Nanofiber Composite Insulation Paper through Dynamic Covalent Chemistry and Hydrogen Bonding.

The rapid advancement of modern power equipment and high-power devices has imposed increasingly stringent demands upon the mechanical and dielectric properties of electrical insulation materials. Herein, we report a poly(m-phenylene isophthalamide) (PMIA) composite insulating paper with excellent dielectric breakdown strength, reliable mechanical properties, and high thermal stability. Enhanced surface activity of PMIA is achieved through surface modification, facilitating the synergistic integration of modified PMIA (MPMIA), bovine serum albumin (BSA)/silica (SiO2), and cellulose nanofiber (CNF) into composite paper using dynamic covalent bonds and hydrogen bonding. The prepared MPMIA-BSA/SiO2-CNF composite paper exhibits a laminated stacked structure with high tensile strength (32.68 MPa) and strain at break (9.57%). Meanwhile, MPMIA-BSA/SiO2-CNF composites have excellent dielectric breakdown strength (24.75 kV/mm) and good temperature resistance. Therefore, the MPMIA-BSA/SiO2-CNF composite paper has a broad application prospect in the field of high-voltage and high-power electrical equipment insulation.

Excellent Low-Frequency Microwave Absorption and High Thermal Conductivity in Polydimethylsiloxane Composites Endowed by Hydrangea-Like CoNi@BN Heterostructure Fillers.

The advancement of thin, lightweight, and high-power electronic devices has increasingly exacerbated issues related to electromagnetic interference and heat accumulation. To address these challenges, a spray-drying-sintering process is employed to assemble chain-like CoNi and flake boron nitride (BN) into hydrangea-like CoNi@BN heterostructure fillers. These fillers are then composited with polydimethylsiloxane (PDMS) to develop CoNi@BN/PDMS composites, which integrate low-frequency microwave absorption and thermal conductivity. When the volume fraction of CoNi@BN is 44 vol% and the mass ratio of CoNi to BN is 3:1, the CoNi@BN/PDMS composites exhibit optimal performance in both low-frequency microwave absorption and thermal conductivity. These composites achieve a minimum reflection loss of -49.9dB and a low-frequency effective absorption bandwidth of 2.40GHz (3.92-6.32GHz) at a thickness of 4.4mm, fully covering the n79 band (4.4-5.0GHz) for 5G communications. Meanwhile, the in-plane thermal conductivity (λ∥) of the CoNi@BN/PDMS composites is 7.31W m-1 K-1, which is ≈11.4 times of the λ∥ (0.64W m-1 K-1) for pure PDMS, and 32% higher than that of the (CoNi/BN)/PDMS composites (5.52W m-1 K-1) with the same volume fraction of CoNi and BN obtained through direct mixing.

Optimized energy storage performances via high-entropy design in KNN-based relaxor ferroelectric ceramics

Dielectric capacitors play an irreplaceable role in complex and integrated electronic systems. However, attaining ultrahigh recoverable energy storage density (Wrec) alongside energy storage efficiency (η) poses a formidable challenge, impeding the advance towards the miniaturization and integration of cutting-edge energy storage devices. In this work, a high-entropy strategy with a viscous polymer process is adopted, bringing about ultrafine grains and polar nanoregions (PNRs) accompanied by enhanced electrical homogeneity and polarization relaxation characteristics. As a result, an ultrahigh Wrec ∼ 7.51 J/cm3 is achieved in a high-entropy KNN-based energy storage ceramic with a high η ∼ 88.4% at 750 kV/cm. Moreover, the ceramic capacitor exhibits a colossal power density reaching approximately 420 MW/cm3 and a discharge energy density of approximately 4.85 J/cm3 at 160 ℃. Impressively, it maintains low variation rates of less than 4% across a broad temperature range from 20 ℃ to 160 ℃. The new approach opens avenues for the design and development of superior dielectric materials used in next-generation high-power pulse devices.

Achievement of ductile-regime removal in fabricating Gaussian curved microstructure processed by micro ball-end milling on soft-brittle KDP surface

Laser-induced damage points (known as defects) would seriously reduce the service life of large-aperture KDP optics in high-power laser devices. The ball-end milling procedure is recognized as an efficient method for creating a Gaussian mitigation pit (GMP) to restore the optical transmission performance of functional KDP crystals by removing defects. Nevertheless, achieving smooth and flawless Gaussian curved microstructures is a massive challenge for soft-brittle KDP crystals. Herein, a judging criterion of the ductile-regime machining for the GMP is developed by the models of uncut chip thickness (UCT) and critical milling depth. Simultaneously, the obtained judging criterion can be validated by the microstructure fabrication experiments. Besides, considering the spindle vibration, plowing effect, and machined surface texture, the influence of spindle speed (n), feed rate (f), and tool mark interval (d) on the surface formation mechanism of the GMP is analyzed, respectively. It can be discovered that the n of up to 60,000 r/min can lead to severe velocity fluctuation of the motion system, increasing the UCT and causing brittle fractures on the KDP surface. A low f can result in an undesirable plowing phenomenon, and a large number of crystal materials are accumulated in the up-cut process. Once the f reaches 72 mm/min, the tool path would fluctuate significantly, resulting in poor GMP surface texture. When the d exceeds 15 μm, the surface quality of the GMP can no longer meet the engineering requirements of the Ra ≤ 50 nm. Moreover, the optimized processing parameters of the microstructure fabrication are 47,800 r/min in the n, 30 mm/min in the f, and 5 μm in the d. This study can provide crucial guidance for obtaining the ultra-smooth and defect-free GMP processed in the ductile regime, which would resultantly possess significant theoretical importance and practical value in enhancing the optical properties of flawed KDP crystals.

Insights into pressure-driven depolarization in PLZST-based antiferroelectric ceramics

Materials showing field-driven antiferroelectric to ferroelectric transformation are interesting for the design of pyroelectric, high strain actuator and high-power dielectric energy storage and discharge devices. The stability of the antiferroelectric and ferroelectric states at room temperature can be chemically tuned by La and Ti co-modification of the antiferroelectric system Pb(Zr1-ySny)O3. Here, we have chosen a composition Pb0.982La0.012(Zr0.60Sn0.30Ti0.10)O3 (PLZST) at the threshold of the antiferroelectric-ferroelectric instability at room temperature and investigated the effect of electric field, temperature and pressure on the stability of the structural-polar states. We show that electric poling transforms irreversibly the antiferroelectric state into a ferroelectric state. Application of hydrostatic pressure ∼100 MPa on the field-stabilized ferroelectric phase, however, restores the antiferroelectric state and depolarizes the system.

Superior energy storage performance in Bi0.5Na0.5TiO3 based ceramics via synergistic design of multi-size domain construction and multiple phase structures

Lead-free dielectric ceramics, as the crucial materials for the development of eco-friendly high pulse power devices, have faced limitations in achieving energy storage performance comparable to lead-based counterparts. A novel strategy was adopted to enhance the energy storage capability of Bi0.5Na0.5TiO3 based ceramics by constructing multiple phase structures and multi-size domain. An ultrahigh energy storage density of 8.0 J·cm−3 and a large efficiency of 88.9 % were achieved. The superior energy storage properties can be attributed to the synergistic effects of multiple phase structures and multi-size domain construction resulted from a significant polarization intensity difference upon Sr(Zr0.2Ti0.8)O3 doping. Even more surprising, the 0.6Bi0.5Na0.5TiO3-0.4Sr(Zr0.2Ti0.8)O3 ceramic exhibited excellent aging resistance, with variation in discharge energy density (Wd) < ±7% over a temperature range from 20 to 150°C, variations in recoverable energy density (Wrec) < ±8.3 %, and efficiency (η) < ±5.6 % over a frequency range from 1 to 50 Hz and across 105 cycles. The finding in this work not only provides an effective candidate for high power pulse capacitors, but also provides ideas for the study of high energy storage performance of BNT and the related lead-free ceramics.

Synergetic effect of diamond particle size on thermal expansion of Cu-B/diamond composite

Diamond particles reinforced Cu matrix (Cu/diamond) composites have promising applications for heat dissipation of high-power electronic devices because of their high thermal conductivity and suitable coefficient of thermal expansion. The effect of diamond particle size on thermal conductivity has been addressed; however, the effect of diamond particle size on thermal expansion still needs to be clarified. In this study, Cu-B/diamond composites with various diamond particle sizes ranging from 66 μm to 701 μm were fabricated to assess the impact of diamond particle size on the thermal expansion behavior. The composites exhibit low and adjustable coefficient of thermal expansion (CTE) values of 4.58–6.63 × 10−6 K−1, which align with 4–8 × 10−6 K−1 of widely employed semiconductors. The CTE of the Cu-B/diamond composites first decreases and then increases with increasing diamond particle size, which arises from a synergetic effect of interfacial bonding strength and matrix strengthening effect. As the diamond particle size is smaller than 272 μm, the interfacial bonding strength rises with increasing particle size, enabling the diamond particles to restrain the expansion of the Cu matrix more effectively and to reduce the CTE. As the diamond particle size exceeds 272 μm, the dislocation density in the Cu matrix continually decreases with increasing particle size, reducing the strength increment in the Cu matrix and increasing the CTE. The effect of thermal cycling on the thermal expansion of the Cu-B/diamond composites was also investigated, and all the composites show an increase in the CTE after 100 thermal cycles. Notably, the composite with 272 μm diamond particle size exhibits the lowest CTE increment. It shows a CTE value of 5.29 × 10−6 K−1 after thermal cycling, still compatible with the semiconductors for electronic packaging applications.

Effect of trace silver on the conductivity and softening temperature of high conductivity and high heat resistance pure copper

As a conductor material for high-power electronic devices, pure copper requires both conductivity and softening temperature. The effects of 0% (7NCu), 0.015% (Ag150), 0.030% (Ag300), 0.045% (Ag450) and 0.059% (Ag590) Ag on the microstructure, conductivity and softening temperature of pure copper were studied. The results show that trace Ag can refine the microstructure of pure copper and improve the mechanical properties at room temperature and high temperature. The hardness values of 7NCu, Ag 150, Ag 300, Ag 450 and Ag 590 were 112, 119.06, 122.14, 123.54 and 125.68HV, respectively, and the softening temperatures were 195, 310, 336, 344 and 345 °C, respectively. At the same time, the conductivity of the samples with different Ag content was more than 100.5 %IACS. The similar structure of Ag and Cu has little effect on the conductivity. On the one hand, the trace Ag element soluble in the matrix causes lattice distortion, inhibits recrystallization nucleation and grain boundary migration. On the other hand, the Ag element is polarized at the grain boundary, which reduces the grain boundary energy, decreases the atomic diffusion and increases the recrystallization temperature.

Experimental study on the thermal performance of a novel vapor chamber manufactured by 3D-printing technology

Vapor chamber holds great application potential in the field of heat dissipation for high-power electronic devices. This study developed a novel vapor chamber using 3D-printing technology to enhance heat dissipation for compact electronic devices. The vapor chamber was constructed from aluminum alloy with a structural dimension of 60×60×30mm3. In this work, the extended condensation structure of the vapor chamber was combined with an external cooling structure, resulting in a 729 % increase in the external heat dissipation area compared to the evaporation area in a limited space. Extensive experiments were conducted using deionized water as the working fluid under various cooling conditions and heat loads. The results showed that the vapor chamber was capable of maintaining a low thermal resistance at high power and high heat flux conditions, with a minimum thermal resistance of 0.087 °C/W when the heat load was 1000 W. At a cooling water flow rate of 0.1 L/s, the vapor chamber demonstrated the capacity to withstand a critical heat load of up to 1600 W, with the heat flux of 326 W/cm2. Compared to conventional vapor chambers, this novel vapor chamber is better able to achieve stable and efficient heat dissipation under high power and high heat flux conditions, especially in a limited space.

Experimental investigation of steady state power balance in double null and single null H mode plasmas in MAST Upgrade

Global power balance calculations in steady state H mode plasmas varying the distance between separatrices (drsep) and the divertor configuration have been performed in MAST Upgrade. As drsep becomes more negative, more of the power crossing the separatrix goes to the lower divertor. The inner divertor receives a higher fraction of the power exhaust in a Super-X divertor plasma compared to a conventional divertor plasma at similar negative drsep, which is a concern for high power devices employing alternative divertor configurations for power exhaust handling. Global power accounting suggests >30% of the input power is unaccounted for with the power loss channels quantified in this work. Charge exchange and orbit losses from the NBI could account for a large fraction of unaccounted power but it is not possible to precisely determine this without further diagnostic calibration.

Gas-Generation Mechanism of Silicone Gel in High-Temperature Thermal Decomposition for High-Voltage and High-Power Device Encapsulation

Gas-Generation Mechanism of Silicone Gel in High-Temperature Thermal Decomposition for High-Voltage and High-Power Device Encapsulation

Properties Investigation and Damage Analysis of GaN Photoconductive Semiconductor Switch Based on SiC Substrate.

The GaN photoconductive semiconductor switches (PCSSs) with low leakage current and large on-state current are suitable for several applications, including fast switching and high-power electromagnetic pulse equipment. This paper demonstrates a high-power GaN lateral PCSS device. An output peak current of 142.2 A is reached with an input voltage of 10.28 kV when the GaN lateral PCSS is intrinsically triggered. In addition, the method of retaining the AlGaN/GaN heterostructure between electrodes on PCSSs is proposed, which results in increasing the output peak current of the PCSS. The damage mechanism of the PCSS caused by a high electric field and high excitation laser energy is analyzed. The obtained results show that the high heat generated by the large current leads to the decomposition of GaN, and thus, the Ga forms a metal conductive path, resulting in the failure of the device.

Leaf-like Multiphase Metal Phosphides as Bifunctional Oxygen Electrocatalysts toward Rechargeable Zinc-Air Batteries.

Developing a bifunctional oxygen electrocatalyst is crucial to improve the reversibility and cycle life of a rechargeable zinc-air battery (RZAB). Here, transition metal phosphides (TMPs) with a leaf-like hierarchical structure and multiphase composition can be synthesized by the "alloying-dealloying-phosphating" strategy. The as-prepared P-NiCo(1:1) electrode takes advantage of its internal dense nanoholes and synergistic effects induced by NiCoP-containing polyphase to reveal multifunctional catalysis, such as OER and ORR. In combination of these advantages, P-NiCo(1:1) exhibits an extremely low OER overpotential of 220 mV at 10 mA cm-2, a higher half-wave potential of 0.79 V for ORR, and a smaller potential difference (ΔE) of 0.66 V. The liquid RZAB with P-NiCo(1:1) as a cathodic bifunctional catalyst delivers a higher open-circuit voltage (OCV), a larger power density of 175 mW cm-2, and longer cycling life for more than 180 h. Even when applied in solid-state flexible RZABs, the lightweight module could start high-power devices. With theoretical confirmation, the major phase NiCoP of P-NiCo(1:1) is helpful to increase the density of states, regulate the d-band center, and decrease the energy barrier to 2.13 eV, which are significantly superior to those of Co2P and Ni2P. It is believable that the synthetic strategy and activity-promoting mechanism acquired from this research can offer a guide to designing a promising rechargeable zinc-air battery system.

Excellent energy storage performance of Nd-modified lead-free AgNbO3 ceramics via triple collaborative optimization

Lead-free Dielectric capacitors that possess high power density as well as swift charging/discharging speed are in tremendous requirement in pulse/high power fields, but the lower recovery energy density and efficiency restrict their applications. Herein, via triple collaborative optimization, we designed Nd-modified AgNbO3 antiferroelectric ceramics with excellent energy storage performance. First, Nd3+ ions are smaller than Ag+ ions, which effectively inhibits cation displacements and the tilting of oxygen octahedra, leading to an optimized phase composition, the suppressed ferroelectricity and enhanced antiferroelectricity. Second, the valence of Nd3+ ions are higher than that of Ag+ ions, which help to lower the content of oxygen vacancies. Third, the random substitution of Nd3+, extrinsic ions, cause the chemical disorder, thus dwindling the grain size. Both of the latter could boost the breakdown field. Eventually, the synchronously boosted energy density of 7.16 J/cm3 and efficiency of 72 %, together with excellent frequency stability, temperature tolerance, ultrafast charging/discharging time of 45 ns and superhigh power density of 354.2 MW/cm3, are achieved in Ag0.91Nd0.03NbO3. All these merits manifest Nd- AgNbO3 as a promising candidate for lead-free high-power energy storage devices. Our work brings forward a good reference for developing the capabilities of antiferroelectric capacitors.

Innovative configurations for heat sink integrated with piezoelectric fans

Piezoelectric (PE) fans are gradually replacing conventional axial flow fans in the field of heat dissipation for microelectronics due to small size and high efficiency. However, the flow characteristic of PE fans was seldom considered when arranging heat sink fins, which could not utilize the fans’ advantages. Here, the design of fin arrangement based on the transient flow field generated by the vibration of dual PE fans in the channel was calculated and analyzed by CFD simulation and dynamic grid technology. Four zones with different flow field characteristics were found: Zones 1 and 4 which located inlet and outlet of the channel were Parallel flow zone. Zone 2 with vortices corresponds to the area ranges from the waist of blades to middle section of the channel was Multiple vortices flow zone. Zone 3 with high-speed vortices and jet flows corresponds to the area ranges from middle section of the channel to halfway downstream of blades region was Diffuse flow zone. Innovative configurations of heat sinks where fins arranged at the inlet and surrounding blades were designed according to the flow field characteristics: the loss of high-speed airflow to the inlet was prevented effectively and heat dissipation in the downstream heat sinks was dispersed by fins arranging in Parallel flow zone and Multiple vortices flow zone. The development and merging of high-speed vortices were strengthened by the inhomogeneous pin-fins arranging in Diffuse flow zone. The optimal coordination between the velocity field and the temperature gradient field among innovative configurations was found based on the field coordination analysis. Heat transfer performance was enhanced by new designs where the average temperature compared to conventional heat sink with PE fans was reduced by 16.7°. Our work provided a new fins arrangement to achieve uniform temperature distribution and high heat transfer performance for heat sink integrated with PE fans and would benefit the application in thermal management of high power devices integrated with PE fans.

An X-band coaxial relativistic klystron oscillator with a novel diode structure packaged with permanent magnet

To achieve compactness and miniaturization for high-power microwave devices, this paper proposes an X-band permanent magnet-packaged coaxial relativistic klystron oscillator (RKO) with a novel diode structure featuring a stair-step cathode. First, by adopting a large-radius anode structure, the emission of beam currents from the side of the cathode surface is diminished, thereby reducing the proportion of the backward current in the beam current from 10% to 7%. Second, a stair-step cathode is used to inhibit the return flow of electron beams from striking the anode and generating plasma. Concurrently, a radially non-uniform coaxial resonant cavity structure is employed to enhance the fundamental wave modulation depth of the electron beam and improve the beam–wave interaction's efficiency. The experimental results show that the novel device outputs a microwave with a frequency of 9.46 GHz and a pulse width of 55 ns. It generates a power output of 1.5 GW with an efficiency of approximately 30.5%, in the case in which the diode voltage is 505 kV, the beam current is 9.7 kA, and the guiding magnetic flux density is 0.4 T. This novel structure surpasses traditional diode configurations by enhancing the beam-to-wave conversion efficiency by roughly 10%, thereby offering substantial support for the compactness and miniaturization of RKO.

The impact of LSM pretreatment on the growth behavior, electrical insulation and corrosion resistance properties of PEO coating on 6061 aluminum alloy

This work reported the influence of laser surface melting (LSM) pretreatment on the growth behavior, electrical insulation and corrosion resistance of plasma electrolytic oxidation (PEO) film on 6061 aluminum alloy. It is found that the LSM pretreatment refines the surface structure of original Al metal, generating defects that store excessive energy, thereby enhancing reaction kinetics and phase transition during the PEO process. By LSM pretreatment, uniform electrical discharge and film growth can be obtained, resulting in fewer defects and lower porosity in PEO layers. Additionally, a large amount of columnar crystals comprising of SiO2 phase are observed, which transformed from the SiO32− deposited on the surface, and the LSM pretreatment significantly improves the electrical insulation, corrosion resistance, and substrate adhesion of following PEO layer. Under the same PEO treatment duration, the breakdown voltage of coating increased by 100 V, and icorr decreased from 3.26 × 10−4 to 9.13 × 10−6 A cm−2. It is expected that the combination of LSM and PEO processes can not only enhance the surface properties of Al metal, but also expand the practical application of aluminum alloy in high-power electronic devices and related fields.

Review of Nanosecond Pulse Generator With High-Power Switching Devices

Review of Nanosecond Pulse Generator With High-Power Switching Devices

Construction of rGO-MXene@FeNi/epoxy composites with regular honeycomb structures for high-efficiency electromagnetic interference shielding

With the rapid development of 5G communication technology and wearable electronic devices, the demand for low-reflection electromagnetic interference (EMI) shielding materials is becoming increasingly urgent. In this work, reduced graphene oxide-MXene (rGMH) @FeNi/epoxy EMI shielding composites with a regular honeycomb structure were successfully prepared by the combination of surface functionalization modification, sacrificial template, and freeze-drying. The effects of magnetic FeNi alloy particle loading mode and loading amount on the EMI shielding performance of composites were investigated. The results show that rGMH@FeNi/epoxy EMI shielding composites have the highest EMI shielding effectiveness (EMI SE) and the lowest reflection shielding effectiveness when magnetic FeNi alloy particles are loaded only on the graphene skeleton. In this composite, the EMI SE value of the composite is 61 dB when the rGMH@FeNi mass fraction is 5.4 wt% (f-FeNi mass fraction is 0.9 wt%), which is 4.7 times that of the blended rGO/MXene/FeNi/ epoxy resin composite (13 dB) with the same mass fraction. At the same time, the rGMH@FeNi/epoxy composite has excellent thermal stability (heat-resistance index of 190.3 °C) and mechanical properties (energy storage modulus of 8606.7 MPa). These polymer-based EMI shielding composites with excellent EMI shielding properties and low reflection effectiveness have great potential in the protection of high-power, portable and wearable electronic devices against electromagnetic pollution.