High Power Electronics Research Articles

Balancing Interfacial Toughness and Intrinsic Dissipation for High Adhesion and Thermal Conductivity of Polymer-Based Thermal Interface Materials.

In recent years, adhesive thermal interface materials have attracted much attention because of their reliable adhesion properties on most substrates, preventing moisture, vibration impact, or chemical corrosion damage to components and equipment, as well as solving the heat dissipation problem. However, thermal interface materials have a huge contradiction between strong adhesion and high thermal conductivity. Here, we report a polymer-based thermal interface material consisting of polydimethylsiloxane/spherical aluminum fillers, which possesses both adhesion properties (adhesion strength of 3.59 MPa and adhesion toughness of 1673 J m-2 and enhanced thermal conductivity of 3.90 W m-1 K-1). These excellent properties are attributed to the modified chain structure by introducing acrylate accelerators into the polydimethylsiloxane network, thereby striking a balance between interfacial toughness and intrinsic dissipation. The addition of thermally conductive aluminum fillers not only increases the thermal conductivity but also improves the bulk energy dissipation of the thermal interface material. This work provides a novel strategy for designing a novel thermal interface material, leading to new ideas in long-term applications in high-power electronics.

Device Structural Engineering and Modelling of Emerging III-Nitride/β-Ga2O3 Nano-HEMT for High-Power and THz Electronics

Abstract III-nitrides, such as gallium nitride (GaN) and aluminium nitride (AlN), possess a wide bandgap, a high breakdown voltage, and a high thermal conductivity, making them an attractive choice for high frequency and high-power applications. A further benefit of III-nitride-based HEMTs is their high current density, low noise figure, and higher electron mobility, which enable efficient radio-frequency signal amplification. In this research work, the polarization induced graded buffer technique and improved lattice matched β-Ga2O3 substrate is employed to minimize the buffer-related issues in III-Nitride Nano-HEMTs (high electron mobility transistors), such as reduction in the buffer leakage current losses. The polarization-induced doping in buffer region can considerably reduce the buffer leakage current, enhance breakdown voltage and RF characteristics, and bend the conduction band upwardly convex, improving two-dimensional electron gas (2DEG) confinement. A detailed comparison between the graded buffer technique of the HEMT and the HEMT having normal buffer has been conducted. The results demonstrated that the suggested HEMT demonstrated better DC and RF characteristics up to the Tera (1012) hertz range of frequencies. The improved characteristics of the proposed HEMT allow it to be a feasible solution for emerging technologies and cutting-edge communication systems that require efficient signal processing at very high frequencies.

Supression of Shielding Effect of Large Area Field Emitter cathode in Radio Frequency Gun environment

Abstract Using large area field emitters (LAFE) as cathodes for RF gun injectors offers significant potential for creating compact, high-power, and high-brightness electron beams, crucial for advanced accelerator technologies. However, when subjected to DC electric fields, LAFEs face significant challenges due to the shielding effect, which limits emission from central emitters and decreases overall current density. Overcoming the shielding effect in an RF gun environment is essential to meet the required beam quality in accelerators. The current distribution of LAFE under DC conditions is influenced by several geometric parameters, such as emitter height, inter-emitter distance, aspect ratio, and the number of emitters. Moreover, in an RF gun setup, LAFEs experience varying macroscopic electric fields at different emitter positions, altering the current distribution compared to DC fields. In this study, we have systematically examined the impact of various LAFE parameters on their field emission performance in an RF gun environment. We have adopted a semi-analytical approach to estimate the current distribution of LAFE, combining analytically calculated field enhancement factors (γ) with numerically calculated applied RF field values. After validating the method with COMSOL simulations, we have applied it to estimate the current distribution of an LAFE cathode integrated into a ½ cell S-band (2856 MHz) gun. The simulation results indicate that, under favorable conditions, a Gaussian spatial beam distribution can be achieved with LAFE, thus mitigating the shielding effect typical in DC fields. By optimizing various LAFE parameters, the desired current and beam distribution patterns can be attained. This study highlights a promising approach for designing LAFE cathodes for RF guns, which could advance accelerator-related technologies.

Highly Conductive Paths in Diamond and their Application in High Pressure Measurements.

Diamonds possess exceptional properties such as high mechanical strength, thermal conductivity, and electrical resistance, making them suitable for various applications, including high-power electronics and optoelectronics. However, fabricating conductive structures in diamond remains a significant technological challenge. In this publication, we present a controlled process for fabricating precise amorphous conductive paths in a monocrystalline diamond using a focused ion beam (FIB) technique. The resistivity and thickness of the fabricated structures were determined, and their morphology was carefully characterized. The results showed that the optimal charge dose for achieving the lowest resistance was found to be 1017 ions/cm2. The fabricated structures exhibited amorphous morphology. Elemental analysis confirmed the presence of gallium ions in the modified material. The resistivity of the conductive paths was determined to be 30 μΩm, which is remarkably low compared to previous studies and only 1-2 orders of magnitude higher than in metals. Additionally, it is shown that this technology has potential applications in high-pressure chambers and the development of high-pressure sensors within diamond anvils. Overall, this study provides valuable insights into fabricating conductive structures on diamonds using FIB and opens up possibilities for diamond electronics.

Hardware Testing Methodologies for Wide Bandgap High-Power Converters

Wide bandgap (WBG) power semiconductor devices are increasingly replacing silicon IGBTs in high-power and high-voltage power electronics applications. However, there is a significant gap in the literature regarding efficient testing methodologies for high-power and high-voltage converters under constrained laboratory resources. This paper addresses this gap by presenting comprehensive, hardware-focused testing methodologies for high-power and high-voltage WBG power semiconductor-based converter bring-up before the control validation phase steps in. The proposed methods enable thorough evaluation and validation of converter hardware, including device switching characteristics, driving circuit functionality, thermal management performance, insulation integrity, and sustained operation at full power. We utilized the double pulse test (DPT) to characterize switching performance in a two-level phase leg configuration, extract circuit parasitics, and validate magnetic components. The DPT was further applied to optimize gate driving circuits, validate overcurrent protection mechanisms, and measure device on-resistance. Additionally, a multicycle test was introduced to rapidly assess steady-state converter performance and estimate efficiency. Recognizing the critical role of thermal management in high-power converters, our methodologies extend to the experimental extraction of key thermal parameters—such as junction-to-ambient thermal resistance and thermal capacitance—via a heat loss injection method. A correlation method between temperature sensor measurements and junction temperature is presented to enhance the accuracy of device temperature monitoring during tests. To ensure reliability and safety, dielectric withstand tests and partial discharge measurements were conducted at both component and converter levels under conventional 60 Hz sinusoidal and high-frequency PWM waveforms. Finally, we highlight the importance of testing converters under full voltage, current, and thermal conditions through power circulating tests with minimal power consumption, applicable to both non-isolated and isolated high-power converters. Practical examples are provided to demonstrate the effectiveness and applicability of these hardware testing methodologies.

Sputtering of (111) highly-oriented nanotwinned Ag on polycrystalline Si3N4 substrates for high-power electronic packaging

Nanotwinned silver (NT-Ag) exhibits excellent mechanical and electrical properties, attributed to its high-density and (111) highly-oriented twinning structure in nanoscale. Therefore, it has recently drawn much attention in the field of electronic packaging, where it can be utilized as interconnection or metallization materials. However, it has been a critical challenge to fabricate the high-density and highly-oriented NT-Ag onto polycrystalline ceramic substrates, whose crystal structure does not support the epitaxial growth of NT-Ag films. In the current work, a high-density and highly-oriented NT-Ag film has been fabricated onto a polycrystalline ceramic substrate, i.e., NT-Ag on silicon nitride (NT-Ag@Si3N4), using the magnetron sputtering method. As results, a close-packed arrangement of high-density NT-Ag has been observed within columnar grains aligned along its growth direction, whereas the nanoindentation hardness of the NT-Ag film reached 1.82 GPa, with an electrical resistivity of 2.06 μΩ‧cm. Moreover, this study has discussed and explained the growth kinetics and mechanism of NT-Ag films, by controlling magnetron sputtering process parameters, such as sputtering power and argon flow rate. Additionally, the differences in the growth mechanism of NT-Ag on (100) Si and polycrystalline Si3N4 have also been investigated. With its superior material properties, NT-Ag@Si3N4 holds great promise in the applications of advanced packaging technology for high-power electronics.

Computational study of cathode plasma dynamics in high-power electron beam diodes by particle-in-cell simulations

Plasma dynamics are essential in high-power electron beam diodes, as they influence the current density and can even cause gap closure because of fast expansion velocity during operation. In this study, the formation and expansion of the cathode plasma in a high-power planar diode has been investigated by particle-in-cell simulations. The results indicate that the expansion velocity of the cathode plasma in the planar diode is ∼2.5 cm/μs operating with a 340 kV peak voltage and 1.5 kA current, which possesses a maximum pressure of 1 Torr pressure and a gas desorption rate of 38 molecules per electron. Moreover, the enhanced emission on the edge causes a faster growth rate of the gas pressure and formation of plasma, which possesses a higher plasma density than other regions. A higher gas desorption rate and total amount of outgoing gas can cause a larger velocity of plasma expansion, and the expansion velocity is proportional to the logarithm of the rising speed of the diode voltage, while the amplitude of diode voltage did not show a clear correlation with plasma velocity. Finally, a combined dependence of the plasma velocity on the gas desorption rate, total gas volume, rising speed of the diode voltage, and diode voltage is concluded. This work provides new insights into the dynamics of cathode plasma in high-power diodes and may be helpful for engineering design.

Fabrication of through alumina vias (TAV) by ultrasonic micromachining for advanced packaging applications

This article presents the fabrication of a high aspect ratio through alumina-vias (TAV) by combining ultrasonic micromachining (USM), electroless plating, and copper electrodeposition. Various horn designs, i.e., tapered, stepped, exponential, and hybrid horns, were analyzed to achieve a uniform longitudinal vibration in a 6 × 6 multi-tip tool assembly. The modal analysis determined the horn length, and harmonic analysis provided the stress distribution and vibrational amplitude. The tapered horn design was selected for its superior vibration amplification and reduced stresses. Finite element modeling predicted the geometric profiles of the microvias at various USM parameters. Experimental validation showed less than 5 % error in the depths of the microvias. Using the optimized USM parameters, a 6 × 6 array of blind and through-holes was created in a 3 mm thick alumina substrate with an average feed rate of 180 μm/min. The average tool wear was observed to be 0.5 mm when drilling through 3 mm thick alumina. Electroless deposition created a ∼100 nm seed layer on the alumina substrate and achieved good adhesion with via sidewalls. The through-holes were partially filled with a 60 μm thick copper layer by electrodeposition to create through-alumina vias (TAV) that can be used as 3D interconnects in the packaging of high-power electronics.

Thermal Transport at the AlN-SiC Interface and Grain Boundary of AlN.

AlN is deposited on silicon carbide (SiC) for high-power electronics; in these devices, AlN acts as both a buffer layer for the growth of the active device and a thermal conductor. However, the mechanism of thermal transport through the AlN-SiC interfaces and through grain boundaries of AlN has not been clearly analyzed, even though AlN forms grain boundaries during the deposition process. The thermal properties of the AlN-SiC interface and the inversion domain boundaries (IDBs) of AlN were examined by a phonon transport model based on a nonequilibrium Green function formalism and first-principles calculations. The interface and grain boundary models were designed, and the thermal resistances (TRs) and origins of TR were examined. The TRs of the AlN-SiC interface and the IDB of AlN are much higher than the TRs of AlN and SiC of relevant thickness. Elemental intermixing and vacancy formation were modeled. The formation of charge-balanced defect of VAl + 3ON is thermodynamically favorable compared to other defects, indicating that ON induces formation of VAl. The charge-balanced defect combining VAl and ON increases the TRs of both AlN-SiC interfaces and AlN grain boundaries because vacancy defects induce larger changes in mass than all other defects, and TRs are proportional to changes in mass. In addition, VAl defects are increased by excess ON, resulting in a continuous increase in TR, and then, the calculated thermal boundary resistance (TBR) of the AlN-SiC interface with increased density of VAl by excess ON reaches the experimental TBR. Therefore, it is expected that the large increase in TR by the formation of VAl + ON would be suppressed by controlling the low O density during synthesis.

IEEE Workshop on High-Power Electronics for Decarbonizing Energy Grids

IEEE Workshop on High-Power Electronics for Decarbonizing Energy Grids

Analysis of the Stability and System Participation Factors of Grid-Connected Converters

When the sources of renewable energy and numerous power electronic gadgets are introduced into the power system, which is related to the negative resistance features of power electronic gadgets, the power system with high power electronics often exhibits weak inertia. Also the stability of multi-converter grid-connected systems is adversely affected. To address these issues, a process of small disturbance stability analysis is proposed in this paper for the grid-connected systems of multiple grid-forming converters based on impedance ratio criterion. The Nyquist trajectory map of the system ratio of impedance in the complex plane is used in the suggested analytical method to estimate the quantity of RHPs in the right half-plane of the system, and the stability at the common points of the system is evaluated against the Nyquist criterion. In addition, the instability of grid-forming converters in grid-connected systems is reproduced by using grid-forming converters state space equation. Unlike the traditional methods of analysis, the method proposed in this paper can be applied to specifically judge the key equipment or control link of instability of the system, which provides guidance on optimizing the parameters of the system. Finally, simulation analysis is conducted to confirm that the model is accurate and that the proposed approach is applicable.

SiC GAA MOSFET Concept for High Power Electronics Performance Evaluation through Advanced TCAD Simulations

In this work a groundbreaking SiC power MOSFET based on innovative vertical Gate All Around (GAA) concept is presented. Extensive TCAD simulations are performed to analyze the performance in forward as well as in reverse conditions for this new device concept. The proposed design has a target rating voltage of 1200V, suitable for e-mobility applications.

Low contact resistivity at the 10−4 Ω cm2 level fabricated directly on n-type AlN

Ultrawide bandgap aluminum nitride (AlN) stands out as a highly attractive material for high-power electronics. However, AlN power devices face performance challenges due to high contact resistivity exceeding 10−1 Ω cm2. In this Letter, we demonstrate achieving a low contact resistivity at the 10−4 Ω cm2 level via refined metallization processes applied directly to n-AlN. The minimum contact resistivity reached 5.82 × 10−4 Ω cm2. Our analysis reveals that the low contact resistance primarily results from the stable TiAlTi/AlN interface, resilient even under rigorous annealing conditions, which beneficially forms a thin Al–Ti–N interlayer, promotes substantial nitrogen vacancies, enhances the net carrier density at the interface, and lowers the contact barrier. This work marks a significant milestone in realizing superior Ohmic contacts for n-type AlN, paving the way for more efficient power electronic and optoelectronic devices.

(Invited) Development of Single Crystal Nbn Superconductor on Wide Bandgap GaN By Sputtering and Thermal Annealing

The field of quantum computing is rapidly evolving, and Niobium Nitride (NbN) superconductors have emerged as a pivotal component in the field of quantum computing due to their unique properties. NbN possesses relatively higher superconducting transition temperature (Tc = 15-17 K) as compared to traditional superconductors, making it a promising material for various applications, including superconductor quantum computers, single photon detectors, and hot electron bolometers [1]. The investigation of NbN's superconductivity has been a subject of extensive research over the past few decades. Given that the properties of NbN are intricately linked to its crystal structure, lattice constant, and nitrogen content, precise control of the structural and electrical characteristics of NbN films is essential for the realization of NbN based quantum devices. The (111) planes of δ-NbN exhibit relatively small lattice mismatches with group-III nitride semiconductors (~0.2% for AlN and ~2.7% for GaN) [2], suggesting the potential for integrating crystalline NbN superconductors with nitride semiconductors on a single wafer. Notably, N-polar AlGaN/GaN high electron mobility transistors have been successfully fabricated on NbN films, operating under Tc with a negative differential resistance [3], indicating that the integration of nitride semiconductors and superconductors can be harnessed to create Josephson junctions. To achieve high-quality all-nitride NbN/group-III nitride/NbN Josephson junctions, a comprehensive understanding of the NbN/GaN heterointerfaces is crucial. Despite limited reports on the epitaxial growth of NbN films on nitride semiconductors, little is known about the structural and transport properties of such NbN films. Previously, MBE growth of NbN films have been demonstrated on GaN substrate, showing superconducting critical temperatures exceeding 10 K [4]. In this presentation, our efforts on the development of single crystal NbN thin films on wide bandgap GaN substrate using cost efficient sputtering technique followed by a subsequent high-temperature annealing will be presented. Commercially available single-crystalline GaN (0001)/sapphire templates as well as differently oriented (c and a-planes) sapphire substrates are used as the substrates for the sputtered deposition of NbN films at 20 °C. After the deposition, a high temperature annealing was performed separately at 950 °C for 30 mins under Ar as well as N2 atmosphere. While the as-deposited NbN film on GaN did not exhibit a discernible peak in the high-resolution XRD measurement, a high-intensity, single crystal (111)-oriented NbN film emerged prominently after annealing in both N2 and Ar environments. This suggests a notable enhancement in the crystalline quality of the superconducting material attributable to the thermal annealing process. Although the crystallinity of the NbN layer improves post-annealing, there is an associated increase in grain size and surface roughness. Preliminary findings indicate a reduction in the critical temperature of the NbN film from 12.82 K to 8.69 K after high-temperature annealing, potentially linked to the incorporation of impurities and crystallographic defects during this process. Further investigations using atomic resolution transmission electron microscopy, secondary ion mass spectrometry and X-ray photoelectron spectroscopy will be performed to investigate the influence of annealing duration, temperature, and conditions on the critical temperature, impurity incorporation and defect formation in NbN films deposited with different thickness.In continuation of our recent exploration into depositing crystalline superconducting NbN films on III-nitride semiconductors, this presentation will also focus on our recent advancement of ultrawide bandgap semiconductor materials such as the growth of high-quality quality β-Ga2O3 films and its ternary (AlxGa1-x)2O3 alloys, using metalorganic (MOCVD) and low-pressure (LPCVD) chemical vapor deposition growth techniques. Ga2O3 and (AlxGa1-x)2O3 have emerged as a promising semiconductor material platform for applications in high-power electronics and ultraviolet optoelectronics due to their excellent chemical and thermal stability, as well as high breakdown field strengths. The structural and electrical characteristics of Si-doped β-Ga2O3 and (AlxGa1-x)2O3 thin films will be presented. Additionally, we will present recent findings on achieving phase-pure β-(AlxGa1-x)2O3 films with a record-high Al composition (< 99%) [5]. Our research efforts into understanding the orientation-dependent Al incorporation in β-(AlxGa1-x)2O3 thin films and the determination of band offsets at β-(AlxGa1-x)2O3/β-Ga2O3 heterostructures will be presented. Furthermore, the presentation will touch upon the heteroepitaxial development of other phases of Ga2O3 and (AlxGa1-x)2O3, including α, γ, and κ. Acknowledgment: Dr. Bhuiyan acknowledges the support and guidance of his PhD advisor- Dr. Hongping Zhao at The Ohio State University for the MOCVD growth and characterization of β-Ga2O3 and (AlxGa1-x)2O3 films conducted in Zhao's group. Reference: Yamashita et al., Phys. Rev. Appl. 8, 054028 (2017).Kobayashi et al., Appl. Phys. Express 13, 061006 (2020).Yan et al., Nature 555, 183 (2018).G. Wright et al., APL Mater. 10, 051103 (2022).Bhuiyan et. al, Phys. Status Solidi RRL 17, 2300224 (2023). Figure 1

Low Frequency Electronic Noise Characterization of Au-W/β-Ga2O3 Schottky Diodes

Ultra-wide bandgap (UWBG) semiconductors have attracted tremendous amount of interest for applications in high-power electronics and solar-blind UV photodetectors. In particular, β-Ga2O3 has attracted significant research attention in recent years due to its promising electrical and optical characteristics including a large bandgap, high breakdown electrical field, and large Baliga’s figure of merit compared to well-established wide-bandgap technologies such as GaN and SiC [1].Low frequency electronic noise, which is present in all electronic devices, can be used as a diagnostic tool for semiconductor material and device characterization. By studying the low frequency noise in semiconductor materials and devices, the physics associated with the noise properties of bulk and interface defects and traps can be investigated [2]. Measurement of low frequency noise is also crucial for evaluating material quality and device reliability.In this work, we investigate the forward-bias diode parameters and low-frequency electronic noise in Au-W/β-Ga2O3 Schottky barrier diodes. The Schottky contact is formed by depositing 20 nm of Tungsten (W) using dc sputtering followed by 340 nm of Gold (Au) using e-beam evaporation, and subsequent annealing [3].We first measure the I-V characteristics and extract important diode parameters, such as the Schottky barrier height, ideality factor, and series resistance from room temperature forward-bias current-voltage characteristics. The extracted Schottky barrier height for these devices is in the range 0.7-0.8 eV and the ideality factor is approximately 1.2.We next measure the low-frequency electronic noise in Au-W/β-Ga2O3 Schottky diodes at different forward bias voltages at room temperature. We find that the current noise spectral density exhibits 1/f-type behavior for all forward bias voltages at low frequency with an exponent ranging from 0.75 to 1.15, indicating that the low frequency noise of these devices is dominated by excess (flicker) noise. No Lorentzian-shaped generation-recombination (G-R) noise is observed. At low frequencies, the shot noise contribution is found to be negligible for the values of the current in our devices, and the total noise is 1/f-limited.We also investigate the dependence of the current noise spectral density on forward bias current, revealing different relationships in different current regimes. At low currents, the noise spectral density is found to scale approximately as the square of current, whereas at high currents, the noise spectral density begins to saturate. Such noise behavior can be attributed to different noise sources dominating in different current regimes. Furthermore, using the noise figure of merit adapted for ultra-wide bandgap semiconductor devices [4], we find that the Au-W/β-Ga2O3 devices have lower noise levels compared to other emerging UWBG materials and similar noise levels as well-established technologies such as GaN.These results provide important insights into the electronic noise properties of Au-W/β-Ga2O3 Schottky diodes and show that low frequency noise characterization is an important diagnostic tool for assessing the quality and reliability of gallium oxide based wide-bandgap materials and device technologies.

(Invited) Wbg and Uwbg Photoconductors and Applications

Wide band gap and ultra wide band gap photoconductive semiconductors are of increasing interest for a number of applications including high power switching, high speed electronics, electromagnetic isolation, power electronics, and optical beam control. We will present work characterizing a number of semi-insulating semiconductors including GaN, SiC, Diamond, AlN, Ga2O3, their relative performance metrics, and examples of realized and proposed devices and applications. We will further discuss selection criteria based on first principles analysis for promising new photoconductors.

Variable Area Jet Impingement for Enhanced Junction Temperature Control of High-Power Electronics

Abstract Convective heat transfer by jet impingement cooling offers a suitable solution for high heat flux applications. Compared to techniques that rely on bulk conduction in series with convection, direct liquid impingement reduces the thermal resistance between power device hot spots and the coolant. Although capable of highly efficient cooling, static impingement devices must be designed for the worst-case cooling requirements for a transient power profile. This can result in wasted hydraulic performance. Aircraft, highway vehicles, and heavy machinery fall into this category where a substantial factor of safety is required. This work proposes a method for improving power electronics reliability by limiting temperature fluctuations at reduced coolant pressure requirements during transient power cycling using a variable area jet. Single phase jet impingement cooling is implemented in an active control scheme using a variable diameter iris mechanism as the primary nozzle architecture. In addition to pressure drop and temperature control, the active nozzle structure introduces the ability to create pulsating jet flows to further enhance the heat transfer compared to fixed-geometry nozzles. The key underlying fluid mechanics characteristic of pulsating flows is the effect of disrupting the thermal boundary layer on the electrical device surface. By introducing a variable diameter jet, eddy formation can be fine-tuned for optimal boundary layer disruption. Using the definition of the Strouhal number, vortex shedding created by the non-steady jet flows is directly correlated with the resulting Nusselt number as a function of the iris kinematics. An experimental apparatus for jet impingement thermal-fluid testing is used to evaluate the Nusselt number versus Strouhal number for a parametric study of variable diameter iris configurations. The apparatus utilizes a voice coil actuator to achieve sine and square waveforms, to vary the amplitude of actuation, and to vary the mean of actuation. Finally, power cycling with a single emulated hot spot is performed to estimate the reliability increase as a result of maintaining constant junction temperatures with the active jet impingement scheme.

Convection Cooling of Power Electronics Operating in Deep-Space

Abstract Since most traditional spacecraft are designed to operate in a vacuum environment, forced convection cooling has seen limited use in space-applications. This paper considers an ideal candidate–the Dragonfly Lander, a rotorcraft being sent into Deep-space to conduct experiments on Saturn's largest moon, Titan. A forced convection based thermal management solution is presented for the Rotor Drive Electronics (RDE) unit, a high-power electronics box responsible for controlling the rotors that allow the Lander to fly on Titan. A thermal flow model was built in Solidworks Flow Simulation to evaluate the effectiveness of a fan system integrated into the packaging design and used as the primary method for cooling the RDE. The model was validated with temperature data collected from custom designed ground support equipment. It was found that utilizing forced convection allows temperatures of the electronics within the tightly packaged RDE to remain within operational limits when conductive and radiative heat transfer alone are insufficient. Titan's dense atmosphere results in greater mass flow rates through fans compared to on Earth, making forced convection a particularly efficient method of heat transfer. This research may guide the use of forced convection in future space missions, or non-traditional environments.

Physico-chemical characterization of polyimide passivation layers for high power electronics applications

Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, high-power and high-temperature applications. However, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer. Thanks to their high operating temperature and dielectric strength, spin coated polyimide (PI) layers are considered ideal candidates for SiC devices passivation and insulation. In this view, a robust methodology for the physico-chemical characterization of such PI layers is required. Thanks to the use of time of flight-secondary ion mass spectrometry (ToF-SIMS), a SIMS-based surface-sensitive technique that provides specific identification of molecules, it was possible to distinguish different types of PIs employed in commercial SiC devices and postulate their molecular structure. This was obtained after careful selection of the analytical conditions used for the characterization of the specimens.The results attained in this study open the way for further improvements in one of the most key issues in the development of higher SiC power devices.

Performance of a novel loop heat pipe coupled with micro vapor-driven jet injector – An experimental and numerical study

Loop heat pipe (LHP) is an efficient phase-change heat transfer device which has been widely applied in cooling high-power electronics on ground and in spacecraft. In previous work, a novel LHP coupled with vapor-driven jet injector (VDJI) has been proved to be feasible and shows excellent performance, namely LHPI. However, due to the lack of pressure data during LHP operation, the coupling mechanisms of VDJI and LHP remain unknown. Especially, the heat-mass transfer between high-speed vapor and subcooled liquid inside VDJI, which has great influence on the LHPI, need to be investigated to guide the design of the LHPI. In this paper, the start-up process, steady-state operation characteristic of LHPI and internal flow field of VDJI were investigated experimentally and numerically. By using the pore-forming sintering and integrated sintering method, the bi-porous wick was prepared and embedded on the base plate surface of evaporator, which brought a significant improvement in its performance. The results indicated that the LHPI could operate under a power of 600 W (50.0 W/cm2) without dry-out. Maintaining the heating wall temperature within 85 °C, the minimum thermal resistance of the LHPI with bi-porous and integrated sintered wick was below 0.18, and the maximum heating power can reach up to 404 W, which are 60% lower and 52.5% higher than mono-porous wick, respectively. In addition, four operation modes of VDJI were classified as low-efficiency mode, normal-injection mode, restricted expansion mode and superheated mode. The operation modes of VDJI had great influence on the performance of LHPI. In normal-injection mode, the entrainment ratio of VDJI exceeded 100, which resulted in the lowest thermal resistance of LHPI. For long-term operation of LHPI, the VDJI is suggested keep operating in normal-injection mode. Moreover, by using 3D numerical simulation method, the internal flow structure of the VDJI was obtained to gives an insight into mechanisms of these four operation modes. The numerical results showed the profile of compression waves and confirmed the existence of condensation shock wave in VDJI.