SiC Materials Research Articles

Numerical simulation and optimization of heat dissipation structure for high power insulated gate bipolar transistor (IGBT)

With the increasing integration level of IGBT components, heat dissipation capacity determines whether its working state is stable. The third-generation semiconductor chips are expected to be made of SiC or GaN materials, with lower power loss and higher thermostability. Currently, the widely used backplane heat dissipation schemes cannot meet the heat dissipation requirements of high-power IGBT modules. In this study, an aluminium alloy shell with an AlN column is proposed to replace the traditional plastic shell to further improve the heat dissipation of IGBT devices. 180°C is set as the expected maximum temperature of the module, and finite element modelling and analysis of the heat dissipation structure of the IGBT device is carried out. Four types of design schemes are compared and the heat dissipation structure is optimized. AlN heat-transfer blocks and Ag sintering are introduced to realise the novel design. The results show that traditional single-side heat dissipation can not meet the requirements. The improved double-side dissipation scheme meets the requirement when the heat sink fin height is more than 15mm. And the optimized heat sink shall have 14 fins of 20mm in height. The results of this study can provide a reference for the thermal management and design of high-power third-generation semiconductor devices.

Numerical study on methane/air combustion characteristics in a heat-recirculating micro combustor embedded with porous media

Micro-combustor is a portable power device that can provide energy efficiently, heat recirculating is considered to be an important factor affecting the combustion process. For enhancing the heat recirculating and improving the combustion stability, we proposed a heat-recirculating micro-combustor embedded with porous media, and the numerical simulation was carried out by CFD software. In this paper, the effect of porous media materials, thickness and inlet conditions (equivalence ratio, inlet velocity) on the temperature distribution and exhaust species in the micro combustor are investigated. The results showed that compared with the micro combustor without embedded porous media (MCNPM), micro-combustor embedded with porous media (MCEPM) can improve the temperature uniformity distribution in the radial direction and strengthen the preheating capacity. However, it is found that the embedding thickness of porous media should be reasonably arranged. Setting the thickness of porous media to 15 mm, the combustor can obtain excellent comprehensive capacity of steady combustion and heat recirculating. Compared the thermal performance of Al2O3, SiC, and ZrO2 porous media materials, indicating that SiC due to its strong thermal conductivity, its combustion stabilization and heat recirculating capacity are obviously better than that of Al2O3 and ZrO2. With the porous media embedded in the micro combustor, the combustion has a tempering limit of more than 10 m/s, and the flame is blown out of the porous media area over 100 m/s. The reasonable equivalence ratio of CH4/air combustion should be controlled within the range of 0.1–0.5, and “super-enthalpy combustion” can be realized.

A perspective on multi-channel technology for the next-generation of GaN power devices

The outstanding properties of Gallium Nitride (GaN) have enabled considerable improvements in the performance of power devices compared to traditional silicon technology, resulting in more efficient and highly compact power converters. GaN power technology has rapidly developed and is expected to gain a significant market share in an increasing number of applications in the coming years. However, despite the great progress, the performance of current GaN devices is still far from what the GaN material could potentially offer, and a significant reduction of the device on-resistance for a certain blocking voltage is needed. Conventional GaN high-electron-mobility-transistors are based on a single two-dimensional electron gas (2DEG) channel, whose trade-off between electron mobility and carrier density limits the minimum achievable sheet resistance. To overcome such limitations, GaN power devices including multiple, vertically stacked 2DEG channels have recently been proposed, showing much-reduced resistances and excellent voltage blocking capabilities for a wide range of voltage classes from 1 to 10 kV. Such devices resulted in unprecedented high-power figures of merit and exceeded the SiC material limit, unveiling the full potential of lateral GaN power devices. This Letter reviews the recent progress of GaN multi-channel power devices and explores the promising perspective of the multi-channel platform for future power devices.

Fabricating porous ceramic materials via phase separations in blends of cellulose acetate and ceramic nanoparticles

AbstractAs applications of porous ceramic materials have gradually expanded, the novel technologies for the fabrication of porous ceramic materials with a delicate and controllable structure are still attractive. In this work, three types of porous monolithic ceramic materials, including Al2O3–SiO2, TiO2, and SiC, have been fabricated by thermally impacted and non‐solvent‐induced phase separations in blends of cellulose acetate and ceramic nanoparticles. These materials possessed three‐dimensional interconnected porous structures with low densities, high porosities, and hierarchical pores ranging from 5 nm to 6 μm. The relationships between microstructures and phase separations were systematically investigated. Furthermore, electromagnetic shielding effectiveness of 20 dB from 5 to 18 GHz in porous SiC materials has been achieved, revealing that those materials have potential applications in the electromagnetic shielding. This work provides a powerful and general approach to fabricate porous monolithic ceramic materials with a wide range of various ceramic nanoparticles.

Degradation assessment of 1.2-kV SiC MOSFETs and comparative study with 1.2-kV Si IGBTs under power cycling

Although SiC MOSFETs has better performance than Si IGBTs, some obvious differences between SiC materials and devices and Si equivalents affect the robustness and reliability of SiC MOSFETs. In this paper, an in-depth comparison of degradation assessment of 1.2-kV SiC MOSFETs and 1.2-kV Si IGBTs under the same power cycling test condition is presented. The variations of electrical and thermal characteristics of the two kinds of devices are investigated comparatively. Both devices chip-related and package-related degradation analysis is provided to explain each parameter variation. And a detailed physical analysis is conducted to have a better understanding of the root cause of the aging. From test results, SiC MOSFETs with the same package process will fail earlier than Si IGBTs. After a long period of PCT, Si IGBTs are not observed other failure modes except for solder layer degradation, but SiC MOSFETs are successively observed three failure modes: solder layer crack and delamination, bond crack, threshold voltage shift. However, chip-level degradation failures are much later than package-level degradation failures for SiC MOSFETs. It is shown that although chips still have unresolved reliability problems for SiC MOSFETs, the package reliability is the shortcoming that limits their long-term service life.

Stacked Single‐Gate Silicon on Insulator 4H‐SiC Junctionless Field‐Effect Transistor with a Buried P‐Type 4H‐SiC Layer

This study describes a single‐gate silicon on insulator junctionless metal–oxide–semiconductor field‐effect transistor (SJL‐MOSFET) with inserted buried 4H‐SiC p‐type layer (B‐SJL‐MOSFET). The embedded p‐type layer is placed at the bottom of the active regions, achieving the full depletion of the channel in the off‐state mode. The p‐type layer affects the depletion region of the channel, which helps us have a full depletion area with a lower gate electrode work function. The main reason for using SiC material instead of silicon is the higher electrostatic integrity and a shorter natural length than silicon, resulting in a better short channel effect (SCE). In addition, the high‐k oxide is stacked for achieving lower natural length and better subthreshold swing (SS). The p‐type layer improves the leakage current (Ioff) by ≈105 in the event that it slightly diminishes the on‐state current (Ion) and improves the SS. Improvement of off‐current is due to higher barriers between source‐channel side and reduces the parasitic BJT in the off‐mode.

SiC Monolayers as Promising Substrates for the Development of Highly Stable Palladium Single Atom Catalysts: A Density Functional Theory Study

Single-atom catalysts have been touted as highly efficient catalysts, but the catalytic single-atom sites are unstable and tend to aggregate into nanoparticles during chemical reactions. In this study, we show that SiC monolayers are promising substrates for the development of highly stable single-atom catalysts (Pd1 /SiC) within the density functional theory. In presence of a Si-vacancy, the diffusion barrier energy of a Pd1 atom embedded in the SiC monolayer is substantially enhanced from 2.3 to 7.8 eV, which is much higher than the reported diffusion barrier energies of graphene, boron nitride and defective MgO of the same catalytic system. Ab initio molecular dynamic calculations at 500 K also confirm the enhanced stability of Pd1 /SiC monolayer (Si-vacancy) such that the Pd1 atom remains embedded in the vacancy. Additionally, the Pd1 /SiC monolayer (Si-vacancy) catalysts show a ∼34 % reduction of activation barrier energy for CO oxidation as compared to pristine catalysts. This work implies that nanostructured SiC materials are promising substrates for the synthesis of highly stable single-atom catalysts.

Modeling of Bipolar Degradations in 4H-SiC Power MOSFET Devices by a 3C-SiC Inclusive Layer Consideration in the Drift Region

The reliability of 4H-SiC power devices account not only to power packages but as well to SiC materials which contain defects that impact the performance of power converters. A detrimental material defect that is still hindering the development of high power MOSFET devices is the so-called bipolar degradation. It is mainly due to Shockley stacking sequence faults (SFs) within the hexagonal SiC structure lattice creating 3C-SiC- regions embedded within the main 4H-SiC structure. In this paper, we have modelled the bipolar degradation of a power MOSFET device rated at 1.7kV by considering the drift layer formed by a 4H-3C-4H heterojunction. In term of electrical parameters, the bipolar degradation which manifests itself as the increase of the forward voltage of the device, TCAD simulation results showed an increase of 0.7 V and 1 V of the forward voltage at a current level of -3A and 4A for the body diode and the MOSFET operating in the first quadrant respectively. These were of the same order of magnitude as experimental results obtained on degraded power MOSFET devices. Additionally, we have presented a novel method to ascertain the presence of SFs within the power device by measuring the electroluminescence of the body diode.

Electron tomography for sintered ceramic materials by a neural network algebraic reconstruction technique

The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality. The artifacts produced in tomographic reconstruction of bulk materials can be very severe, particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features. Here, we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones. The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise. The information in the missing wedge can be partly recovered by this technique. Thus, both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image. Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography, in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.

Analysis of radiation effect of a novel SOI-Like LDMOS structure

This study proposes a new SL LDMOS structure similar to a silicon-on-insulator. The P+/N structure is used to replace the buried oxygen layer of traditional SOI LDMOS devices. The N-type layer is made of SiC material, and the highly doped P-type layer is used to partially deplete the SiC layer to achieve the SOI Like effect. At the same time, the highly doped buried layer is formed by ion implantation in the SiC layer to adjust the electric field in the drift region and improve the breakdown voltage. The Silvaco TCAD software is used to conduct a two-dimensional simulation of the proposed structure. The breakdown voltage of the device is 306 V. Compared with the SOI LDMOS under the same withstand voltage, the proposed SL LDMOS has about 32.9% lower the on-resistance and better electrical characteristics. In the study of radiation effects, the burnout threshold of the proposed structure is LET = 0.93 pC/μm and Vd = 222 V, which shows that the device has good anti-single event burnout performance. In the study of the total-ionizing-dose, when the total dose is higher than 119 Krad(Si), the breakdown voltage of the proposed device is significantly higher than that of the SOI LDMOS device. This can effectively address the shortcomings of SOI LDMOS devices regarding the total-ionizing-dose. Therefore, the proposed structure is suitable for application in harsh environments such as those with high radiation.

Low Switching Loss Split-Gate 4H-SiC MOSFET With Integrated Heterojunction Diode

A 4H-SiC MOSFET with p-type region injection and integrated split gate and heterojunction diode is proposed in this paper. Compared with the conventional MOSFET, the proposed structure has a lower on-resistance and switching loss. And the gate oxide layer has been well protected by the p-type region, which reduces the electric field in gate oxide layer at the off-state. The on-resistance of device can be greatly reduced by increasing the doping concentration of current spreading layer and will not cause a huge electric field in gate oxide layer. The specific on-resistance is decreased by about 27.8% and the static characteristic (BV/Ron,sp) of the device is improved about 37.3%. SiC material has a high third quadrant turn-on voltage due to its wide band gap characteristics. The use of heterojunction integration can take place of parasitic body diode and reduce its turn-on voltage, avoid the bipolar degradation effect, and improves the reverse recovery characteristics. To evaluate the dynamic performance, the reverse transmission capacitance (Crss) and gate-drain charge (Qgd) of the proposed structure have been studied in this paper via numerical simulations. Based on the simulation, the HF-FOM (Crss×Ron,sp) and HF-FOM (Qgd×Ron,sp) of the proposed structure are decreased by about 87% and 86%, respectively. Meanwhile, the reverse turn-on voltage and reverse recovery characteristics are also improved, and the total energy loss decreases by about 37.3%.

A novel 4H-SiC ESD protection device with improved robustness

In 2020, Korean scholars proposed a new electrotatic discharge (ESD) protection device HHFGNMOS(high holding voltage floating gate nMOSFET) based on 4H-SiC material, which can significantly improve the severe snapback phenomenon of 4H-SiC GGNMOS due to the characteristics of SiC material. However, there still exists a problem that the current distribution is too dense in the HHFGNMOS structure. In this work, the comb-like structure is used for the HHFGNMOS protection device for the first time. The bottom of the drain region of the device is comb transformed, and the current distribution is made uniform by making full use of the current edge effect. The influence of design variables of comb-like structure on structure performance is given by TCAD simulation. The transient simulation results of GGNMOS, HHFGNMOS and comb-like HHFGNMOS based on 4H-SiC under TLP pulse show that the secondary failure current <i>I</i><sub>T2</sub> of comb-like HHFGNMOS increases from 17 to 22 A i.e. by 29%, compared with that of GGNMOS and HHFGNMOS. In addition, the comb-like HHFGNMOS snapback is reduced by 55.2% and 5% compared with GGNMOS snapback and HHFGNMOS snapback, respectively. Therefore, the robustness of the device is greatly improved and the snapback effect is reduced under the condition of constant area and compatible process.

Etching of SiC–SiC-composites by a laser-induced plasma in a reactive gas

The precise machining of silicon carbide composite (SiC–SiC) as a high-tech material with extraordinary characteristics is required for different applications in aerospace, light weight construction and car industry. Laser machining enable new approaches for fabrication processes but the regularly applied ablation processes can cause damage to the SiC–SiC material. Here we propose and demonstrate a new approach for gentle SiC–SiC machining making use of a laser-induced plasma for reactive species generation enabling chemical material removal processes. A fs-laser (775 nm, 150 fs, 1 kHz) was focussed to a CF 4 /O 2 gas mixture igniting a laser-induced plasma (LIP) approximately 100 μm in front of a SiC–SiC sample. This LIP initiate material removal processes of the textured, multiphase SiC–SiC sample without a mechanical damage of the SiC–SiC composite structure. Different surface features such as etching of the cover SiC layer, etching of the SiC matrix and exposure, thinning and sharpen of the SiC fibres, underetching of the fibres has been observed. Across the whole etched area, no mechanical damage such as cracks, delamination's, broken fibres were observed so that a gentle machining process can be expected. • Etching of superhard SiC–SiC by a reactive, laser-induced plasma (LIP) was achieved. • Preferential etching of the matrix causes the exposure of fibres due to processing. • Selective etching of the various SiC–SiC phases causes specific surface morphologies. • Damage-free machining of the SiC–SiC composites by lasers is shown.

Loofah-derived eco-friendly SiC ceramics for high-performance sunlight capture, thermal transport, and energy storage

Emerging integrated solar thermal conversion and latent heat storage has a great potential in harvesting solar energy continuously and efficiently by avoiding redundant energy transfer processes. However, the energy harvesting performance is limited by weak solar absorption and low thermal conductivity of phase change materials (PCMs). Here, loofah-derived eco-friendly SiC ceramics is proposed for fast, efficient, and compact solar thermal energy storage beyond state-of-the-art. We design a facile way to fabricate eco-friendly porous SiC ceramics with robust structure and tunable porosity by impregnating flour paste into loofah followed by carbonization and molten silicon reaction processes. After impregnation with NaCl-NaF eutectics, broadband sunlight capture with average solar absorptance of 95.25%, rapid thermal transport with thermal conductivity of 20.7 W/mK, and compact latent heat storage with energy storage density of up to 424 kJ/kg are demonstrated simultaneously. Highly conductive light SiC materials, hierarchical continuous loofah skeleton structure, and high energy density eutectics are attributed to this superior performance. This work opens new routes for efficient harvesting solar thermal energy based on biomimetic eco-friendly ceramics.

SiC, titanium, nickel, and ferric acid reinforcement materials to enhance mechanical properties in aluminium alloys: A critical review

The purpose of this review is for the examination of the impact of reinforcement particles on the microstructural properties and mechanical characteristics of aluminium alloys produced by friction stir processing (FSP). Reinforcement material filling methods will be explored to assess the amount at which grain refinement takes place. Comparison is done between the tool that is employed to produce the said composites as well as different reinforcement materials that have been studied and tested. Surface flaws and the major issues in friction stir procedures are porosity and reinforcement clusters. Solid-state FSP improves characteristics in MMCs by fine-tuning grain size and uniformly dispersing reinforcement. This review is focused on literatureapproaches for improving existing materials through friction stir processing. The properties of the improved material can be an answer to various industrial needs. This paper presents a review of recent models for microstructural change in alloys through the FSP process. The effectiveness of the present techniques will be highlighted to show their adequacies andinadequacies in the study to propose new ways for future material advancements.

The effects of atomic arrangements on mechanical properties of 2H, 3C, 4H and 6H-SiC

As a typical polytypic compound, silicon carbide has various atomic arrangements; however, the role of atomic arrangements in the plastic deformation mechanisms remains unclear. In this article, the relationship between atomic arrangements and mechanical properties in single crystal and polycrystalline SiC is revealed by first-principle calculations and molecular dynamics simulations. We found that the twin boundary can delay the fracture of the single crystal 6H-SiC chemical bonds, could account for its excellent tensile toughness. The plastic deformation of polycrystalline SiC is dominated by dislocation nucleation and propagation under compressive strain, and by intergranular fracture under tensile strain. In addition, when the temperature exceeds 1200 K, the yield stress of polycrystalline SiC gradually stabilizes. Hexagonal SiC (2H, 4H and 6H) have stronger strain resistance than cubic one (3C) due to the hierarchical resistance of twinning and stacking fault structures to external stress. These results can provide insight into the relationship between atomic arrangements and stress response in SiC materials.

Non-contact grinding/thinning of silicon carbide wafer by pure EDM using a rotary cup wheel electrode

The significantly increased stability of third-generation semiconductors, both mechanically and chemically, presents a significant challenge to traditional wafer grinding. This study develops pure electrical discharge machining as an alternative for non-contact wafer grinding and thinning to achieve high precision and low cost. This method employs a copper-made rotary cup wheel as the tool electrode to replace the conventional diamond wheel to realize electrical discharge grinding. A prototype is built to evaluate the new process with single-crystal SiC. Aiming at ultra-precision machining, the material response of SiC to both single and consecutive discharge is elucidated. The influencing mechanism of pulse conditions on hard, brittle crystalline SiC material is demonstrated via experiments and simulation. Further, the material removal behavior, grinding stability, surface integrity, wafer shape accuracy, and process-induced subsurface damage are comprehensively investigated via single and consecutive discharge experiments under various conditions. In addition, the extreme precision that is achievable by contemporary EDM technology is explored. As a result, a 30 μm thin Φ20 mm SiC wafer with a subsurface damaged layer <1 μm was obtained, showing the potential of EDM for the processing of third-generation semiconductor wafers.

Backwashable dynamic membrane made of anchored CNT on SiC microfiltration membranes applied to oil in water emulsion filtration

Produced water is the highest liquid stream generated by the petroleum industry. It is most of the time saline water extracted with the petroleum or gas which contains<30 ppm of emulsified oil. SiC membrane material seems promising to treat such industrial wastewater and remove oil droplets but its development is still hindered by fouling phenomena. The present study investigates the filtration performances at lab-scale of a commercial flat sheet SiC membrane (55 cm2) and the positive impact of CNTs synthesis by C-CVD process. The SiC pristine membrane exhibited a sharp flux decline of about 96 % for a low filtration volume (i;e : 4 L h−1 m−2 for 20 L m−2). Results demonstrate that well anchored CNTs were successfully synthesized and functionalized on the SiC material. The hydrid SiC-CNTs materials showed permeate flux improvement with a higher permeate flux during O/W emulsion separation (i.e: 45 L h−1 m−2 for the same filtration conditions). Whatever the considered membrane, rejection values were excellent and above 90 %. Results also showed that the hydrophobic properties of SiC-CNTs membrane might be easily tuned by CNTs surface coating (i.e: iron oxide coating). Moreover, the synthesized CNTs were well anchored and might be backwashed keeping their positive impact on deposited oil. However, results emphasized that irreversible fouling tended to accumulate at the CNTs surface due to oil adsorption despite intensive chemical cleaning.

Method for the modification of graphite subsurface layer to a solid mixture of SiC and graphite

We studied the interaction of molten Si and graphite surface during annealing in different atmospheres (CO, vacuum, Ar). The studies have shown that during annealing in CO atmosphere a composite material of SiC and graphite in a thick subsurface layer of the graphite is being formed, whereas at vacuum and Ar atmosphere the modified layer is either thin or absent. The composition and structure of both the composite material itself and the interface between the composite material and the graphite matrix were investigated using the methods of scanning electron microscopy and Raman spectroscopy. Studies have shown that the composite material obtained by this method has a branched fibrous structure consisting of small tubular layers of silicon carbide interspersed with large monocrystalline grains of silicon carbide of the cubic polytype, which leads to significant strengthening of the material. Thus the proposed method can be used to form a thermal protective, chemically resistant coating on graphite surface.

Numerical investigation on combustion characteristics of premixed hydrogen/air in a swirl micro combustor with twisted vanes

The combustion characteristics of the swirl micro combustor with twisted vanes (Swirl-MC-TV) and the conventional micro combustor (Conventional-MC) are investigated and compared under different inlet velocities (8–40 m/s), wall materials (quartz, steel, and SiC), and equivalence ratios (0.6–1.4). The results show that the larger area of recirculation zones and the stronger recirculation intensity are the key factors for Swirl-MC-TV to stable combustion. When the inlet velocity is 40 m/s, compared with the Conventional-MC, the wall heat loss of the Swirl-MC-TV is reduced by 15.9%, and the reaction heat and combustion efficiency of the Swirl-MC-TV are increased by 17.5% and 5.9%, respectively. When the wall materials of steel and SiC, combustors have a better preheating effect and higher combustion intensity. When the equivalence ratio is greater than 0.6, the wall heat loss of Swirl-MC-TV is larger but the combustion efficiency and the reaction intensity are still higher than Conventional-MC.