Silicon Carbide Semiconductor Research Articles

Effect of Surface Microstructure on Joints Using Nanoporous Cu Sheet for Power Devices

Wide-bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are being developed as promising replacements for Si-based semiconductors. The operating temperature of SiC semiconductor is expected to be much higher. The replacement of soldering with new bonding process has been needed for WBG semiconductor devices. We have proposed a solid-state bonding process using nanoporous metal sheet, as a die-attach bonding method for WBG semiconductor devices. In this study, the bonding process using nanoporous Cu sheet as an insert metal was investigated to achieve a Cu disk/Cu disk bonding without solvent and flux. The shear strength of the joint using nanoporous Cu sheet at 350 and 300°C in formic acid atmosphere exceeded the shear strength of conventional Pb–5Sn solder joints which was approximately 18 MPa.

Prospects for silicon being replaced by other materials in integratedcircuit applications

Currently, silicon is the most widely used semiconductor material. However, in recent years, the development of integrated circuits has encountered more and more limitations, among which the physical characteristics of single-crystal silicon materials are an important reason. With the expansion of integrated circuit scale and the continuous reduction of manufacturing processes, silicon has gradually reached its physical limit. At the same time, silicon has a higher calorific value and a higher performance loss. Therefore, people are actively seeking alternatives to silicon in integrated circuits. This paper reviews the characteristics of three new semiconductor materials, graphene, silicon carbide, gallium nitride, and current research on their applications. Silicon carbide and gallium nitride materials have shown outstanding performance in power-integrated circuits, while graphene has many applications. However, they still have many defects before being used on a large scale. In short, in integrated circuit applications, when new materials replace silicon, many problems remain to be solved.

High-Frequency Modelling of Electrical Machines for EMC Analysis

The trend towards electrification in mobility has led to the increased use of silicon carbide (SiC) semiconductors. These semiconductors are more efficient but also present challenges related to electromagnetic interference (EMI) due to their higher voltage derivatives. This paper introduces a new high-frequency impedance model for electrical machines. The proposed model distinguishes itself from existing approaches by being entirely derived from Finite Element Method (FEM) simulations, which include capacitances in the magnetic simulation. This approach achieves a balance between computational efficiency and high accuracy across the entire frequency spectrum, ranging from 100 Hz to 50 MHz. The model provides valuable insights during the design phase and was rigorously validated using data from 28 samples of an industrial machine.

A Comparative Study of Silicon and Silicon Carbide Semiconductors

A Comparative Study of Silicon and Silicon Carbide Semiconductors

Comparative Analysis of Sic and Gan: Third-Generation Semiconductor Materials

This article delves into a comprehensive comparative analysis of two prominent third-generation semiconductor materials, silicon carbide (SiC) and gallium nitride (GaN). It explores their foundational theories, practical applications, future prospects, and the hurdles they face in the realm of materials science. SiC is characterized by its impressive thermal conductivity and a wide bandgap, while GaN showcases remarkable electron mobility and high electron saturation velocity. Both materials have demonstrated outstanding capabilities in high-temperature, high-frequency, and high-power electronic devices, finding utility in power conversion, automotive systems, and optoelectronics. Looking forward, SiC and GaN hold tremendous potential in emerging fields such as new energy sources, advanced optoelectronic devices, and semiconductor packaging. Nevertheless, they encounter challenges, including manufacturing costs and the control of crystal defects. In conclusion, these third-generation semiconductors offer extensive possibilities across various domains, although overcoming significant challenges is essential for their widespread integration.

Cradle-to-Gate Life Cycle Assessment (LCA) of GaN Power Semiconductor Device

Wide Band Gap (WBG) semiconductors have the potential to provide significant improvements in energy efficiency over conventional silicon (Si) semiconductors. While the potential for energy efficiency gains is widely researched, the relation to the energy and resource use during manufacturing processes remains insufficiently studied. In order to appraise the performance of the technology thoroughly, issues such as raw material scarcity, toxicity and environmental impacts need to be investigated in detail. However, sparse Life Cycle Assessment (LCA) data are available for the two currently most widespread WBG semiconductor materials, gallium nitride (GaN or GaN/Si) and silicon carbide (SiC). This paper, for the first time, presents a cradle-to-gate life cycle assessment for a GaN/Si power device. To allow for a full range of indicators, life cycle assessment method EF 3.1 was used to analyze the results. The results identify environmental hotspots associated with different materials and processes: electricity consumption for the processes and clean room facilities, direct emissions of greenhouse gases, gold (when used), and volatile organic chemicals. Finally, we compare this result with publicly available data for Si, GaN and SiC power devices.

On-Chip Circularly Polarized Circular Loop Antennas Utilizing 4H-SiC and GaAs Substrates in the Q/V Band.

This paper presents a comprehensive assessment of the performance of on-chip circularly polarized (CP) circular loop antennas that have been designed and fabricated to operate in the Q/V frequency band. The proposed antenna design incorporates two concentric loops, with the outer loop as the active element and the inner loop enhancing the CP bandwidth. The study utilizes gallium arsenide (GaAs) and silicon carbide (4H-SiC) semiconductor wafer substrates. The measured results highlight the successful achievement of impedance matching at 40 GHz and 44 GHz for the 4H-SiC and GaAs substrates, respectively. Furthermore, both cases yield an axial ratio (AR) of less than 3 dB, with variations in bandwidths and frequency bands contingent upon the dielectric constant of the respective substrate material. Moreover, the outcomes confirm that utilizing 4H-SiC substrates results in a significantly higher radiation efficiency of 95%, owing to lower substrate losses. In pursuit of these findings, a 4-element circularly polarized loop array antenna has been fabricated for operation at 40 GHz, employing a 4H-SiC wafer as a low-loss substrate. The results underscore the antenna's remarkable performance, exemplified by a broadside gain of approximately 9.7 dBic and a total efficiency of circa 92%. A close agreement has been achieved between simulated and measured results.

Energy Spectrum and Properties of SiC: Using Two-Photon Absorption for Different Harmonics

This paper describes a methodology for studying the energy spectrum and characteristics of Silicon Carbide (SiC) semiconductor materials, utilizing various harmonics for two-photon absorption (TPA). The approach involves developing theoretical models to simulate the energy levels and transitions of SiC, based on the TPA process. By analyzing the resulting spectra obtained by varying the harmonic order, the energy spectrum, and properties of SiC are explored. In this work also includes a comparison of the energy spectrum and properties of SiC for single and two-photon absorption, providing insights into the distinctive features of SiC under these conditions. In particularly absorption co-efficient of the material was calculated from optical transmittance and reflectance measurements at room temperature (300 K) in the wavelength range of 200 -900 nm. In addition, Gaussian functions centered at different energies were modeled using TPA in SiC materials and their contribution to the Harmonic Generation (HG) signal was calculated.

Reliability evaluation of thick Ag wire bonding on Ni pad for power devices

In recent years, silicon carbide (SiC) semiconductors have gained traction in high-performance power devices due to their ability to operate at high temperatures (above 200 °C). However, traditional interconnection materials are not sufficiently reliable at such elevated temperatures. Typically, in power devices, thick Al wires with diameters of 200 μm or larger are commonly used to bond Al electrodes of semiconductor chips to their corresponding Cu leadframes or substrates. Nevertheless, the low melting point of Al can lead to recrystallization at high temperatures, thereby raising concerns about reliability and a decrease in wire strength and fatigue properties. Although thick Cu wires with higher melting points have been explored as potential solutions, their high hardness and susceptibility to work hardening during bonding can damage the chip beneath the bonding area, making them impractical. In response to these challenges, we investigated the use of thick Ag wires. However, direct bonding of thick Ag wires to Al pads can form intermetallic compounds (IMC) in the bonding area, leading to concerns about decreased reliability. To address this issue, we experimented with a bonding method that utilized thick Ag wires on Ni pads. In this study, we evaluated the reliability of thick Ag wire bonding under various stress conditions, including high-temperature storage tests (HTST) and temperature cycling tests (TCT). Our results showed that thick Ag wire bonding on Ni pads exhibited high bond strength and prevented IMC formation after HTST. Nonetheless, bond failure of the Ag wires could occur after TCT due to the mismatch in the coefficient of thermal expansion (CTE) between the Ag wire and SiC chip, particularly under extremely severe TCT conditions. We found this issue could be mitigated by introducing a soft metal layer, such as Al, between the Ni pad and the SiC chip. This reduced internal stress and enabled the device to pass TCT under harsher conditions with reliable performance.

Basic Mechanisms of Single-Event Occurrence in Silicon Carbide Semiconductor under Terrestrial Atmospheric Neutron Irradiation

This numerical simulation work investigates the basic physical mechanisms of single events induced in a target layer composed of silicon carbide exposed to natural radiation with atmospheric neutrons at the terrestrial level. Using direct calculations and extensive Geant4 simulations, this study provides an accurate investigation in terms of nuclear processes, recoil products, secondary ion production and fragment energy distributions. In addition, the thorough analysis includes a comparison between the responses to neutron irradiation of silicon carbide, carbon (diamond) and silicon targets. Finally, the consequences of these interactions in terms of the generation of electron–hole pairs, which is a fundamental mechanism underlying single-event transient effects at the device or circuit level, are discussed in detail.

Silicon carbide based traction inverter cooling in electric vehicle using heat pipes

Power train in electric vehicles is provided with assortment of power electronics including traction inverter to control, monitor and deliver electric power from battery system to electric motor as per vehicle needs. Inverter technology based on Silicon Carbide (SiC) semiconductor provide lower switching losses, can handle high power densities and can operate at very high junction temperatures ∼ 200 °C, which enables air cooling for such system viable. This project investigates the technical feasibility and the potential of an air-cooled traction inverter, for mid-sized passenger vehicles, with very high heat fluxes (∼35 W/cm2) and heat loads exceeding ∼ 2.2 kW. Heat pipe based air cooled heat sink has been evaluated for thermal management of SiC inverter for traction purposes in electric vehicles. Traction inverter was equipped with 3x SiC power modules, each with 350 W heat load (∼17 W/cm2 heat flux) totaling 1050 W, and operating in 85 °C ambient. Based on analysis of different design options, remote heat pipe heat exchanger was chosen as optimal design with best performance and volume/area ratio. Heat pipe system with copper–water heat pipe configuration and air cooled aluminum sheet metal based heat sink arrangement was designed in segmented form to dissipate asymmetric heat loads (65 % top, 35 % bottom) output by two faces of each SiC power module. Top surface of each chip was cooled by separate heat sink, each with 2x U-shape heat pipes while bottom faces of three chips have common heat sink with 6x L-shape heat pipes. Complete cooling system was put together using system of copper blocks that provide housing for SiC power modules while allowing for integration of cooling module into inverter housing, keeping IP6 K4K sealing requirements. Proposed solution was able to keep junction temperature < 142 °C against requirement of 175 °C, provide thermal uniformity within ∼ ±5 °C, was able to handle maximum power surges double of nominal loads, qualify for start-up from frozen state and was able to handle temperature cyclic loading without showing any performance degradation. Heat pipe based air cooling system for traction inverter, in particular, and overall vehicular power electronics, in general, will provide dedicated and modular cooling system approach, which can be located with relative ease and simplicity as compared to liquid cooled system while achieving lower system cost. Furthermore, such systems will provide operational safety against leaks, runtime reliability and lifetime longevity which is critical in automotive.

Low Inductive Characterization of Fast-Switching SiC MOSFETs and Active Gate Driver Units

Accurate switching device characterization is necessary for effectively utilizing the technological ad-vantages of Silicon Carbide (SiC) Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) over their Silicon (Si) Insulated-Gate Bipolar Transistor (IGBT) counterparts. With switching times of few nanoseconds, the unprecedented switching speed of SiC semiconductor devices challenges today's converter and characterization setup designs in regard to parasitic layout inductances for optimal conversion and reliable characterization data. Fur-thermore, active gate driving is a key to unlock the potential of SiC MOSFETs, but requires performance assessment prior to integration. This paper presents a low-inductive test platform for flexible and high-accuracy characterization of fast-switching SiC MOSFETs and active gate drivers evalu-ation. The test circuit delivers high quality characterization data that is comparable with a commercial dynamic power device characterizer. In addition to the conventional hard-switching double-pulse tests with a two-level voltage source gate driver, the test circuit offers soft-switching and gate driver evaluation capability in addition. This test platform is a valuable tool for obtaining reliable characterization data to develop more accurate SiC MOSFET simulation models, and evaluate the combination of gate driver and MOSFET prior to the prototyping phase of a converter.

Crack Formation Reduction on Diamond-Paste Abrasive Processing of Silicon-Carbide Semiconductor Wafers

Crack Formation Reduction on Diamond-Paste Abrasive Processing of Silicon-Carbide Semiconductor Wafers

Clarification of the Reaction Mechanism of the Photoassisted Anodic Oxidation of SiC in a Newly Developed Inverted Rotating Disk Electrode Cell Setup

Due to the distinctive chemical and physical properties of silicon carbide (SiC), interest in the material as a substrate for semiconductor industry has risen significantly during the past two decades. As a wide bandgap semiconductor SiC is known to be highly chemically inert. Still, under specific conditions SiC takes part in a number of electrochemical reactions that lead to a rapid oxidation of the surface. The goal of this work is to understand the fundamental factors driving this process for n-type SiC crystals in aqueous electrolytes.In alkaline solutions, the photoelectrochemical behaviour of n-type SiC is determined by two partial reactions (oxidation/dissolution) 1 :(1a) SiC + 6h+ (hν) + 6OH- → SiO2 + CO + 3H2O(1b) SiC + 8h+ (hν) + 8OH- → SiO2 + CO2 + 4H2O(2) SiO2 + 2OH- → [Si(OH)2O2]2- For the investigation of such photoassisted or photoelectrochemical reaction mechanisms involving mass transfer, we specifically developed a new inverted rotating disk electrode (IRDE) cell setup 2 that allows to control the most essential experimental parameters (i.e. potential, diffusion conditions and light intensity).In this setup, rotation of the disk electrode is achieved by magnetic coupling between a driver magnet (i.e. a magnetic stirrer) and the follower magnet included in the sample holder. The cell allows a homogeneous illumination and removal of gaseous reaction products, while still providing leak tightness. The surface of the semiconductor electrode is illuminated with UV light (λ = 365 nm) from a high-power LED. The distance between light source and sample is minimized to achieve maximum surface illumination of the sample.To investigate mass transport phenomena, electrolytes with relatively low solubility of SiO2 are preferable. Therefore, we used potassium hydroxide solutions in a concentration range where mass transport of hydroxide ions plays a major role.Performing cyclic voltammetry in this newly developed IRDE cell allows to distinguish different reaction regimes that are either limited by mass transport, photon flux or hole transport. For low light intensities (either through a large distance between the sample and the LED or through low driving currents through the LED) the number of photon-induced holes is limiting. At low electrolyte concentrations, the transport of hydroxyl ions and the dissolution of the oxidation products determine the reaction rate. At low potentials, hole transport limits the overall current flow. Each of these reaction regimes was studied individually to conduct a potential reaction mechanism.[1] D. H. van Dorp und J. J. Kelly, „Photoelectrochemistry of 4H–SiC in KOH solutions,“ Journal of Electroanalytical Chemistry, Bd. 599, Nr. 2, pp. 260-266, 2007.[2] K. Mairhofer, P. Mayr, S. Radl, M. Nelhiebel, S. Larisegger, G. Fafilek, „An Inherently Leakage-Free Inverted Rotating Disk Electrode Setup“, 2022. Figure 1

Optimization of technological parameters when polishing sic materials by magnetic compound fluid with the straight electromagnetic yoke

Crystallized silicon carbide (SiC) wafers are widely used in the field of integrated circuits as well as essential in the epitaxial growth of graphene and are one of the promising materials for applications in electronics at future high capacity. The surface quality of the required ultra-fine crystalline silicon wafer is the most essential factor in achieving graphene's desired electronic properties. Aiming to produce superfine surface quality SiC wafers, in this study, a new algorithm is developed to solve optimization problems with many nonlinear factors in ultra-precision machining by magnetic liquid mixture. The presented algorithm is a collective global search inspired by artificial intelligence based on the coordination of nonlinear systems occurring in machining processes. A new algorithm based on the optimization collaborative of multiple nonlinear systems (OCMNO) with the same flexibility and high convergence was established in optimizing surface quality when polishing the SiC wafers. To show the effectiveness of the proposed OCMNO algorithm, the benchmark functions were analyzed together with the established SiC wafers polishing optimization process. To give the best-machined surface quality, polishing experiments were set to find the optimal technological parameters based on a new algorithm and straight electromagnetic yoke polishing method. From the analysis and experimental results when polishing SiC wafers in an electromagnetic yoke field when using a magnetic compound fluid (MCF) with technological parameters according to the OCMNO algorithm for ultra-smooth surface quality with Ra=2.306 nm. The study aims to provide an excellent reference value in optimizing surface polishing SiC wafers, semiconductor materials, and optical devices

A highly sensitive filterless narrowband 4H-SiC photodetector employing a charge narrowing strategy

Silicon carbide (SiC) semiconductors with a wide bandgap have attracted much attention because they can endure harsh environments and high temperatures. SiC photodetectors based on conventional principles usually detect ultraviolet (UV) light without the ability to discriminate wavelength. Here, using the charge narrowing collection principle, we realize a highly sensitive filterless narrowband 4H-SiC photodetector. The 4H-SiC layer is sufficiently thick to facilitate charge collection narrowing of the device’s external quantum efficiency spectrum, inducing a full width at half-maximum of 14.5 nm at the peak wavelength of 355 nm. Thanks to the Fermi level pinning effect, the proposed photodetector can fully eliminate the injection current; thus it works as a photovoltaic type device with a remarkably low dark current. Consequently, the device has a photo-to-dark current ratio as high as 4 × 107, superior to the performance of most reported 4H-SiC UV photodetectors. In addition, the device can detect light signals with a power density as low as 96.8 pW cm−2, more than two orders of magnitude superior to that of the commercial product based on the photodiode principle. Moreover, it can endure high temperatures of 350 °C, demonstrating bright prospects in harsh industrial conditions.

Fabrication of 4H-SiC piezoresistive pressure sensor for high temperature using an integrated femtosecond laser-assisted plasma etching method

The processing, particularly, etching of brittle, hard, and anti-corrosion materials represented by the third-generation wide bandgap semiconductor silicon carbide (SiC), is a significant challenge. Although SiC has excellent electrical, mechanical, and chemical properties, the difficulty of processing limits its application in various sensor devices. To solve this problem, in this study, an integrated processing method of femtosecond laser-assisted SiC dry etching is proposed, which realizes high surface quality and high rate etching of the SiC microstructure. Specifically, the effects of different laser processing parameters on the processing effect were first studied through orthogonal experiments. Experiments indicate that compared with laser power and laser scan times, laser processing speed has a more obvious impact on the processing effect. Subsequently, considering the elastic modulus anisotropy of SiC, a 5 MPa piezoresistive pressure sensor chip was designed. Using the proposed composite processing method, a chip sensitive diaphragm was obtained. The diaphragm thickness and diameter are 76 μm and 1700 μm respectively. The overall sensor chip dimension was 4000 μm × 4000 μm × 350 μm. Static tests demonstrated that the sensor have excellent performance with sensitivity of 6.8 mV/MPa, linearity of 0.69% FS, and repeatability of 0.078% FS. In addition, by designing high-temperature packaging, the sensor achieved a pressure test at 400 °C. This study verifies the feasibility of the composite processing method, realizes the fabrication and measurement of high-temperature pressure sensors, and provides a reference for the micro-and nanostructure processing of various SiC sensors.

Band alignment of TiO2/SiC and TiO2/Si heterojunction interface grown by atomic layer deposition

Silicon carbide (SiC) is regarded as a promising semiconductor owing to its wide band gap and high thermal conductivity. Meanwhile, it possesses issues such as interface properties, which may affect the performance of SiC substrate power devices (e.g. MOSFET), especially when compared with similarly structured silicon appliances. Given that the development of SiC semiconductor devices has a number of commonalities with conventional silicon-based semiconductors, titanium dioxide (TiO2), a material that has a great track record in Si-based semiconductor devices, has been chosen for investigation in this work. Although TiO2 is not capable of being a gate dielectric alone on the SiC substrate because of its relatively narrow band gap, it can be adopted into composite or multilayer gate dielectrics to reach satisfying characteristics. As such, the interfacial state and heterostructure between TiO2 and SiC remain worthy being researched. In the present study, the properties of atomic layer deposited (ALD) TiO2 films on silicon substrates were compared with those on 4H-SiC substrates via x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray reflectometry. It is shown that the interface state between ALD TiO2 film and both types of substrates as-deposited have similar chemical conditions, whereby TiO2 layer barely react with substrates, containing great amount of oxygen vacancies. According to band alignment calculations, heterostructure of both samples are type-II heterojunctions with negatively shifted conduction band. Although the large bandwidth of 4H-SiC hinders the use of TiO2 as a gate dielectric in power devices, this structure has the potential for other semiconductor products.

High-Resolution Alpha Spectrometry Using 4H-SiC Detectors: A Review of the State-of-the-Art

Silicon Carbide (SiC) semiconductor radiation detectors were first demonstrated in 1957, however, meaningful progress was delayed until the mid-1990s when high-quality epitaxially-grown SiC became available. Rapid progress ensued, and detection of alpha particles, gamma and X-rays, protons, fission fragments, heavy ions, beta particles, minimum-ionizing particles, and neutrons were all demonstrated. In the case of alpha-particle detection and spectrometry, the obtainable energy resolution is dependent on the design characteristics of the SiC detector as well as on the material and electronic properties of the SiC material. In this paper, we review the history of SiC alpha-particle detector development as well as the factors affecting detector performance and the prospects for further improvements. Detector design factors, including active-volume and entrance-window effects, are discussed in detail. Materials and electronic factors that influence the quality of alpha-particle detection are also discussed. These factors include SiC lattice defects, charge-carrier mobility, charge trapping, and the energy required to produce an electron-hole pair. Since the first demonstration of alpha-particle spectrometry, SiC detectors have evolved to the point that an energy resolution of 0.29% (15.9 keV FWHM for 5485.7-keV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">241</sup> Am alpha particles) has been reported. This resolution is comparable to the best obtainable with Silicon alpha-particle detectors. The prospects for further improvements in alpha spectrometry with SiC detectors are also discussed.

REDUCTION OF CRACK FORMATION DURING ABRASIVE TREATMENT WITH DIAMOND PASTES OF SILICON CARBIDE SEMICONDUCTOR PLATES

The results of diamond-abrasive treatment of the reverse side of silicon carbide semiconductor plates of polytypes 4H and 6H are presented. Dimensions of surface microcracks of ceramic plates after abrasive treatment with pastes with diamond powder of different grain size are investigated, and also relationship between length of surface microcrack and rate of material removal depending on technological modes of diamond-abrasive treatment is established. As a result, a new method of single-sided abrasion treatment of thin ceramic plates is proposed, which ensures reduction of crack formation.