混合PVD/ALD多层薄膜沉积提升未来航空高压电子器件介电击穿强度方向博士职位

Faced with the urgent challenges of climate change and the need to drastically reduce global CO2 emissions, the electrification of transport has emerged as a key lever for reducing reliance on fossil fuels [1-3]. With 13.9% of transport emissions, aviation is the second biggest source of greenhouse gas emissions in the transport sector after road transport [4], and air-traffic is going to continue to rise over the next decades [5]. Against this backdrop, the aviation industry is reinventing itself around the concepts of the "More Electric Aircraft" (MEA) and, in the longer term, "All Electric Aircraft" (AEA). Historically, the sector has transitioned from onboard network voltages of 14/28 V DC to 115 V AC (400 Hz) networks, and subsequently—on the most recent long-range aircraft programs—to 270 V DC [6]. Ongoing studies are now exploring 800 V DC architectures for power electric propulsion systems ranging from a few hundred kilowatts to the megawatt level [7]. In the longer term beyond 2050, aeronautic aims to move beyond the megawatt range, with onboard voltage levels expected to range 1,000 V to 3,000 V DC [7]. This evolution presents new challenges regarding electrical insulation for onboard AC/DC high-power density conversion systems. Wide-bandgap power semiconductors (GaN, SiC) are central to these issues. Thanks to their high switching speeds and ability to withstand electric fields exceeding 3 MV/cm, they now enable the design of double-side cooling inverters with higher power density (50-100 kW/L) capable of operating at voltages up to 800 V nowadays [8, 9], and above 1 kV in the future. However, to operate safely and reliably, the top surface of semiconductor devices, as well as any critical metal part in the device package, must be appropriately insulated with high dielectric strength materials to separate high-voltage contacts from ground contacts, and using a compatible technological process. Thin metal oxides (SiO2, Al2O3, HfO2 …) or silicon (oxy)nitrides (SiN x , SiO x N y ) are traditional thin film dielectrics —namely surface passivants— for electronic devices and are typically deposited by thermal growth (few ~10 nm) complemented by chemical vapor deposition (CVD) (few ~100 nm) [10, 11]. While they exhibit good short term dielectric breakdown strength ( EBD ) with values ranging between 3-10 MV/cm, they are still suffering of long term high-field reliability issues [12], that will make critical the emergence of the next generation of high-voltage power devices. The reason is usually related to the introduction of defects (pinholes) within the films during the deposition process that lead to high leakage currents from electric field of only a few ~MV/cm [13, 14], and act as nuclei location for irreversible electrical degradation processes [15]. Therefore, reinforcing inorganic films by engineering them with advanced deposition processes to reach an initial dielectric breakdown strength and eradicating any leakage current will enable to delay the early degradation processes and to considerably improve the long term high-field reliability of electronic devices, participating to the adoption of higher voltage converters in aeronautics. Physical vapor deposition (PVD), particularly reactive magnetron sputtering, is a well-suited alternative to grow thick dielectric coatings. As a precursor-free process, it avoids carbon-, hydrogen- and hydroxyl-containing residues associated with CVD chemistries that can promote charge trapping and leakage [13]. It is above all fast: deposition rates of tens of nm/min at low substrate temperature deliver micrometer-thick coatings in minutes. At the University of Nottingham (UK), PVD-grown AlN films (~15–150 nm) have already demonstrated EBD > 15 MV/cm together with high thermal conductivity of λ ~ 300 W/m·K [16]. The limitation arises at greater thickness. Sputtered films typically develop a columnar microstructure in which grain boundaries, pinholes, and aligned defects can form continuous leakage pathways through the dielectric, reducing EBD down to ~1–5 MV/cm. Multilayering partially addresses this problem: chemically distinct interfaces force re-nucleation, interrupt columnar boundaries, and hinder charge transport. The University of Nottingham has demonstrated this approach in sputtered oxide multilayers, achieving 4.7–5.1 MV/cm [17]. However, because every layer is still sputtered, the interfaces disrupt defect propagation without eliminating the pinholes from which it originates. Atomic layer deposition (ALD) provides the complementary capability. Its self-limiting surface chemistry produces highly conformal, continuous, and effectively pinhole-free layers with sub-nanometer thickness control [18,19]. ALD Al2O3 reaches ~8.3 MV/cm [20], while recent high-voltage C-AFM measurements by the University of Nottingham and University of Toulouse (France) showed that ~6 nm ALD AlN can sustain local fields approaching 40 MV/cm [21]. The cost, however, is throughput: at ~1 nm/min, an order of magnitude below PVD, ALD alone cannot build the micrometer-thick insulation a power device needs. Speed and perfection have therefore remained mutually exclusive. Breaking that deadlock is the novelty of this proposal. In a hybrid [PVD/ALD] nanolaminate, PVD deposits the bulk at an industrial rate while a 2-10 nm ALD interlayer, pinhole-free and perfectly conformal, caps the columnar boundaries of the layer beneath, so that every sputtered sublayer re-nucleates on a flawless surface instead of inheriting the defect network of the one before it. Defects are no longer merely separated from one another: they are prevented from ever lining up. Neither process achieves this alone, and although hybrid PVD/ALD stacks are already established for wear and corrosion protection [22,23], not a single study has examined their dielectric behaviour — the fabrication risk is therefore low while the insulation science is entirely unexplored , and the concept has never been attempted on nitrides . By delaying the onset of leakage beyond 15 MV/cm, such an architecture is expected to deliver an unprecedented dielectric strength >20 MV/cm at micrometre thickness and industrial deposition rate, unachievable by either process alone.

Research methodology: - Multilayer deposition and structural characterization at the University of Nottingham (UK): At Nottingham, hybrid PVD/ALD nanolaminates (both on AlN/AlN-base and on Al2O3/Al2O3-base) will be fabricated by combining multi-target reactive magnetron sputtering with ALD. The PVD process will be systematically optimized by varying RF/DC/pulsed-DC target power, Ar/N₂ or Ar/O2 atmosphere, substrate temperature, bias, and target-to-substrate distance to control film stoichiometry, crystallinity, texture, and defect density. Individual PVD layers of approximately 10–100 nm will be alternated with ultrathin ~2–10 nm ALD interlayers, with the number and thickness of layers progressively varied to determine the optimum architecture for disrupting columnar grain boundaries and continuous defect pathways. Deposition will initially be optimized on Si-based substrates before producing complete multilayer stacks for electrical testing. Film composition, stoichiometry, and chemical bonding will be analysed by XPS, SEM/EDX, FTIR and Raman spectroscopy, while AFM and profilometry will quantify surface roughness, thickness, and deposition rate; cross-sectional SEM/HR-TEM will be used to assess layer continuity and interface quality. This will be complemented with state-of-the-art co-localized AFM-Raman and Tip-Enhanced Raman Spectroscopy (TERS) to map chemical and structural changes at breakdown sites before and after failure with diffraction-limited and sub-10nm resolution, respectively. This correlated approach will provide unique insights into defect-induced phase transformations since chemical information from individual defects present in the as-grown film and from the areas where breakdown occurs can be extracted. The resulting structure–composition relationships will guide iterative optimisation of the deposition process before the optimized samples are transferred to Toulouse for macroscopic dielectric testing, ageing and lifetime measurements. - Electrical characterization at the University of Toulouse (France): At Toulouse, a diverse array of diagnostic techniques (I-V, dielectric spectroscopy, breakdown strength) will be used to evaluate the electrical properties of the multilayered PVD/ALD films (AlN/AlN-base and Al2O3/Al2O3-base), all of which conducted using a state-of-the-art 20kV probe station with thermoregulated chuck (–50°C/+300°C). This will contribute to producing a large database of electrical properties both types of nanolaminates depending on deposition conditions and film structural layering. I-V and field-dependent complex permittivity will be probed to identify the threshold field of nonlinear properties and correlation with breakdown field will guide design optimization to reach ultra-high- EBD stacks. Post-mortem analysis of the failure made by SEM or TEM/FIB will enable to understand how defect are capped by the interfacial ALD nanolayers and will serve for further process optimization at Nottingham. To evaluate the long-term reliability of the multilayer PVD/ALD hybrid stacks, the PhD student will perform in Toulouse accelerating electrical aging at wafer-level using stress induced leakage current (SILC) measurement over time, and under various high field, waveform, polarity, frequency and temperature. Time-to-failure will be evaluated as a function of the film layered structure and the applied stress conditions. Finally, the benefits of the ALD nanolayers on the defect propagation limitation and on the stack resilience to breakdown will be established. Expected outcomes: This combination of multidisciplinary expertise’s between the University of Toulouse and the University of Nottingham will leverage a unique opportunity to understand how defects propagate within dielectric thin films (oxides and nitrides) and how they degrade electrically and chemically during aging under high fields, with complementary multiscale diagnostic techniques on both sides. A successful integration of ALD nanolayers in between PVD layers will be validated upon leakage current threshold delay to high fields of >15 MV/cm. Finally, this new collaboration will enable the development of completely novel dielectric materials with unprecedented dielectric strength performance (>20 MV/cm), highly expected for future electronic devices. Thesis schedule and practical arrangements: The 3-year PhD thesis duration will be split as follows: The first 18 months (from M1-M18) at the University of Nottingham aim to develop the material deposition process and the chemical analysis. The last 18 months (from M19-M36) will be at the University of Toulouse (at the LAPLACE Institute), where the electrical and dielectric breakdown characterizations and electrical aging and lifetime assessment of the multilayer samples will be performed.

The PhD student will be registered and hired at the University of Toulouse (through the MSCA COFUND BEST funding) but will be fully integrated into the two host research groups (both Toulouse and Nottingham) working in collaboration. Remote weekly meetings will be organized to follow up on the thesis progress with the counterpart. Comprehensive institutional support will provide access to research administration, grant management (UT), technology transfer, advanced laboratories and high-voltage testing facilities, lab consumables, software licenses, laptop and internal cloud access, IT support, budget for external communication activities (conference and publication fees). The Fellow will also benefit from mentorship, career-development workshops and language training (French class for daily-life integration in Toulouse will be provided and funded). Regular progress reviews and access to academic and industrial networks will support successful project implementation, professional development and transition preparation towards research job prospects.

As the University of Toulouse will bring the PhD grant, the University of Nottingham shows its financial engagement in this study by co-funding the environment contribution at Nottingham, corresponding to full access to the magnetron sputtering multi-target and ALD deposition tools and the state-of-the-art material characterization facilities (SEM/HR-TEM, EDX, FTIR, Raman, TERS etc.), which also includes providing all the samples necessary for the study. LAPLACE Institute at the University of Toulouse will provide full access to the high-voltage characterization facilities for integrated dielectric materials. The PhD student will be trained on various aspects of electrical insulation (dielectric spectroscopy, I-V measurement), dielectric breakdown (in AC/DC), electrical ageing (TDDB, lifetime, QBD) and reliability assessment. She/he will pass safety certifications related to high voltage that are required by industry for future job applications.

Dissemination and Communication objectives: The results of the PhD thesis will be disseminated in two ways: ( i ) through journal and conference publications and ( ii ) through research internal and external events organization/participation. For journal publications, a minimum of 3 peer-reviewed papers in Q1-journals in Materials Science ( Nature Mater., Adv. Mat., ACS Nano … ) and Applied Physics ( APL, JAP, … ) will be targeted. The results will also be presented at the main international conferences on Dielectrics ( IEEECEIDP , IEEE ICD …), Materials Science (MRS and E-MRS Spring and Fall meetings…) and Device Reliability ( IEEE IRPS , ESREF , REPP …) with 6 conference papers expected in total over the thesis course. Moreover, internal dissemination of the results will take place at the two host institutions: ( i ) LAPLACE Scientific’ Days (attended by all staff), ( ii ) Annual Celebrating Engineering Research Showcase event at Nottingham, and ( iii ) during the internal group’s seminars. During the annual French networking Workshop on Dielectrics and during the biannual French Conference of Electrical Engineering ( SGE ), the results will be presented to all the French research community.

Supervision of the thesis: The PhD thesis will be supervised by Dr. Sombel Diaham , Associate-Professor HDR in Electrical Engineering and High-Voltage Insulation at the University of Toulouse and LAPLACE Institute, France, and co-supervised by Dr. Zakhar Kudrynskyi , Lecturer-Researcher in Materials Science at the University of Nottingham, UK. Dr. S. Diaham is one of the world experts in dielectric breakdown in insulation in relation to their applications in integrated and power electronics. His interests concern the physics of polymer and inorganic dielectrics (charge injection, breakdown in the context of high electric field, high frequency and high temperature), electrical characterizations, process-structural-properties relationships, and multi-stress aging of insulation and their application to devices and systems. He has been the Principal Investigator of >20 projects with a total funding of €6.5M. He was awarded a prestigious industrial MSCA-IF fellowship ( 2019-21 , H2020) with the Analog Devices company, Ireland. He was awarded also with 3 selective national project fundings from the French ANR ( 2013-17 , 2018-22 , 2025-29 ) on insulation for HV electronics. He authored > 150 papers (+2500 citations), holds 12 granted patents and supervised 15 PhD students. He will take care of HV breakdown and aging testing at microscale. | Dr. Z. Kudrynskyi has established a unique expertise in PVD deposition of multilayer inorganic thin-films with high dielectric strength and/or high thermal conductivity for applications as electrical insulation, as well as nano-resolved characterization of layered nanomaterials and heterostructures, including mapping of (i) dielectric breakdown with CAFM, and (ii) chemical composition with co-localised AFM-Raman and TERS. Dr. Kudrynskyi is a leading researcher in the Advanced Materials Research Group . He currently holds a prestigious personal Nottingham Research Fellowship in the Faculty of Engineering and leads the Thin Films lab. He has a background in physics of semiconductors and dielectrics and 16 years of experience in experimental materials science of layered materials and functional heterostructures. He has published >100 papers (+5300 citations) and holds 10 patents. References: • J Y. Liang, W. Zhang, and C. Li, “Assessing the Deployment of Electric Aircraft from Energy, Environmental, and Economic Perspectives,” Sustainability , vol. 17, No. 12, pp. 5453, 2025. https://doi.org/10.3390/su17125453 • X. Zhao, H. Hu, H. Yuan, X. Chu, “How does adoption of electric vehicles reduce carbon emissions? Evidence from China,” Heliyon , Vol. 9, No. 9, e20296, 2023. https://doi.org/10.1016/j.heliyon.2023.e20296 • E. Smith, M. Woody, T. J. Wallington, C. Hitt, H. Chul Kim, A. I. Taub, G. A. 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