论文/学会发表

Harmonics in the inverter output of wireless power transfer are affected by the difference in conduction resistance in the forward and reverse directions of the device. We clarified this effect through theoretical equations, circuit simulations, and experiments, and confirmed that harmonics can be suppressed by reducing the conduction resistance difference.

EPE 2023 ECCE Europe

Wireless power transfer systems using N-leg inverters are known to cause leakage current to flow to the non-driven legs when some of the legs are driven, which is caused by charging and discharging to the depletion capacitance of the device. We found that the suppression effect differs depending on the pulse length. This pulse length dependence was confirmed by circuit simulations and experiments.

IEEE Wireless Power Technology Conference and Expo (WPTCE)

Oscillation may occur during parallel connection in switching devices. The authors have established a method to easily derive an approximate formula for the open-loop transfer function to evaluate the stability of the oscillation phenomenon. The derived approximate formula enables us to analyze the influence of parasitic parameters of both devices and modules on the oscillation, including their interaction. The dependence on the parameters identified by the formula was confirmed to be correct by simulation and experiment.

ISPSD 2023

SiC chip die bonding with sintered nano silver layer was evaluated by thermal cycle test and nine point bending test (NBT). NBT is an original bending test that can mecahnically apply out-of-plane deformation to the die attached assembles as TST like. We propose the new damage parameter associated with both experiments, and we will clarify the overall sintered silver die degradation mechanism during reliability tests.

日本実装学会春季講演大会

We report the results of a spiral coil using a new anisotropic magnetic material.

電気学会全国大会

The authors present a DC-DC converter that autonomously adjusts the switching frequency and reduces losses.

PCIM2023

INVITED PAPER: AlGaN/GaN MIS-HEMT and AlGaN/GaN Ridge HEMT are implemented in one Verilog-A compact model. The theory and practice of modelling features for each normally-off device will be discussed. In addition, the issues of parasitic device characteristics and scaling by ESFPs are raised and solutions are presented. This paper presents the key technologies for a number of papers that have been published so far.

12th International Conference on Communications, Circuits and Systems (ICCCAS)

Photonic crystal lasers (PCSELs) enable both high-power operation and high-quality beam, thus they are useful for various application. In a certain optical system, linear polarization of the beam can be important. Thus, based on optimization by quantum annealing, we realized the beam with high polarization degree by control of the lattice-point shape and current-density distribution.

第70回応用物理学会春季学術講演会

SiC industry is growing fast and delivering highly efficient and compact power electronics. The main contributor of SiC device cost is SiC substrate. Other costs such as epitaxy and fabrication costs are low compared to SiC substrate cost. In this talk, the author introduces the first application of remote epitaxy technology through graphene to SiC alternative substrates with epi membranes. The author believes that this epi-based substrate is the solution to cost savings for SiC wafers.

ACerS EMA 2023 / Electronic Materials and Applications

Wide-gap semiconductors have recently been attracting much attention, but it is still not easy to claim that what values new-semiconductor devices are capable of providing for power applications. The authores set up the research and development project that bridge the gap between applications and devices. The team drive a electric vehicle motor with silicon carbide (SiC) transistors, simulated driving according to an internationally common driving mode, and calculate its electric mileage. The results showed that SiC is superior to Si devices in all the driving modes.

先進パワー半導体分科会第9回講演会

A new circuit topology is proposed to realize a boost mode in a secondary-side resonant LLC converter by utilizing the magnetizing inductance of a coupled inductor placed on the secondary side, and its effectiveness is verified by simulation and actual measurement.

SPEC2022 (Southern Power Electronics Conference)

This reseach investigates the two types of sintered silver (s-Ag) die layer (NP: Nano paste, NMP, Nano to micro paste) delamination speed main cause by compating thermal shocked test (TST) and nine point bending test (NBT). NBT can mechcanically apply out-plane deformation for s-Ag die part as TST provides. The obtained results suggest that NBT could organize delamination ratio during TST. That was, mechanical stress was main contribution to the failure of s-Ag die layer during TST.

ICMR2022

This reseach introduces new mechanical bending test technique called nine-point-bending test (NBT). NBT can mechanically provide out-ou-plane deformation as TST provides. In the presentation, state the technical components in NBT, then the sintered silver die failure mechanism during TST will be discussed by comparing the results of NBT.

The 19th International Conference on Precision Engineering

We proposed nine-point bending test technique that can apply out-of-plane deformation to the assembly, which is similar with the defomation morphorogy during TST. By comparing NBT and TST, degradation during TST was mainly given rise by the mechanical stress.

MNC 2022, 35th International Microprocesses and Nanotechnology Conference

In this paper, we investigated the sintered silver (s-Ag) degradation mechanism during thermal shocked test (TST).
During TST, the s-Ag degradation was multiply given rise by thermal and mechanical stress. To clarify the main degradation cause during TST, reliability study separately should be performed to focus on the main degradation cause. Hereby, nine-point bending test that can be applied out-ou-plane deformation to the assemble is proposed. By comparing between NBT and TST, s-Ag degradation mechanism is discussed.

SSDM2022

Photonic crystal lasers (PCSEL) are characterized by being capable of large-area single-mode operation. However, when the current becomes high, it may become multimode depending on the lattice point shape. Therefore, in order to suppress multimode oscillation and improve the robustness of the design, theoretical analysis was performed by making the injection current density distribution Gaussian. As a result, it was found that the Gaussian current density distribution suppressed multimode oscillation compared to the normal electrode.

第83回応用物理学会秋季学術講演会

熱信頼性試験(TST)中の面外変形を機械的負荷によって再現する九点曲げ試験技術(NBT)を開発。NBTとTSTの両試験後の接合劣化比較した結果について述べる。TST中の破壊は、機械応力と材料劣化の二つに分けれることが新たに分かった。

日本機械学会年次記念大会

The dependence mechanism of SiN film breakdown on the N2 annealing temperature was investigated using TDDB and ESR. We proposed two types of TDDB modes at 900℃ and over 1000℃. At the first mode of 900℃, SiN film breakdown frequency due to the generation of Si dangling bonds with one oxygen and two silicon back bonds. At the second mode over 1000℃, SiN film breakdown frequency, caused by the E’center, which is Si dangling bonds with three oxygens. In previous paper, Si reconstruction occur in H2 or Ar annealing at from 850℃ to 1200℃. To determine the effect of SiN/Si interface reconstruction behavior at 900℃, we add Si annealing before SiN film deposition.

第83回応用物理学会秋季学術講演会

This paper reports on the current power devices used in electric vehicles.

電気学会産業応用部門大会

電気学会産業応用部門大会

SiC industry is growing fast and delivering highly efficient and compact power electronics. The main contributor of SiC device cost is SiC substrate. Other costs such as epitaxy and fabrication costs are low compared to SiC substrate cost. In this talk, the author introduces the first application of remote epitaxy technology through graphene to SiC alternative substrates with epi membranes. The author believes that this epi-based substrate is the solution to cost savings for SiC wafers.

Workshop on Advanced Epitaxy for Freestanding Membranes and 2D Materials

Infineon Si IGBT and Rohm SiC MOSFET of 2, 3 and 4 generation is compared by evaluating characteristic of powertrain loss and energy consumption with IPMSM and IM under road load of Nissan Leaf and BMW i4 eDrive.

EVS35

The dependence mechanism of SiN film breakdown on the N2 annealing temperature was investigated using TDDB and ESR. We proposed two types of TDDB modes at 900℃ and over 1000℃. At the first mode of 900℃, SiN film breakdown frequency due to the generation of Si dangling bonds with one oxygen and two silicon back bonds. At the second mode over 1000℃, SiN film breakdown frequency, caused by the E’center, which is Si dangling bonds with three oxygens.

241ST ECS Meeting

The dependence mechanism of SiN film breakdown on the N2 annealing temperature was investigated using TDDB, ESR and FTIR. We proposed two types of TDDB modes at 900℃ and over 1000℃. At the first mode of 900℃, SiN film breakdown frequency due to the generation of Si dangling bonds with one oxygen and two silicon back bonds. At the second mode over 1000℃, SiN film breakdown frequency, caused by the E’center, which is Si dangling bonds with three oxygens.

241ST ECS Meeting

For oscillations between parallel switching devices in power modules, the open loop transfer function was derived approximately by extracting the dominant circuit elements for each frequency band from the equivalent circuit considering the high frequency parasitic component. In addition, the effect of each parameter on the poles and zeros on the Bode plot was clarified from the derived approximation formula, and the parameter dependence was demonstrated by circuit simulation.

電気学会　産業応用部門　家電・民生研究会

自動車技術会 2022年春季大会

The team experimentally showed how different power devices change the efficiency of a motor system. This reserach aims at optimizing the design of the whole system, not focusing only on the device characteristics.

IPEC2022

A report about high efficiency hiblid gate driver for SiC MOSFET

電子情報通信学会

A 50kW three-phase inverter using SiC MOSFETs achieves a maximum conversion efficiency of 99.1%. The inverter utilizes a neutral-point-clamped (NPC) topology combined with a trans-linked circuit. These combined technologies successfully reduce the reactor loss and enable high efficiency operation.

APEC2022

令和4年度 電気学会全国大会

The authors discuss the measurements and simulations of the transconductance characteristics for the compact model of AlGaN/GaN Ridge type HEMTs that we have developed, focusing on the dependence on temperature, number of gate fingers and number of units. In particular, we proposed model equations for the increased drain current due to gate injection and discuss in detail the analysis results of the change in the gate injection current characteristics with device size and temperature.

34th IEEE International Conference on Microelectronic Test Structures (ICMTS2022)

Sintered silver (s-Ag) has attracted so many researchers due to its high heat conductivity. Applying power module products for die attach part, the degradation has been evaluated by thermal shocked test (TST). Therefore, understanding of the degradation mechanism during TST is an eseential role for designing power modules. The objective of this study is to compare degradation mechanism between TST and four-point bending test to understand s-Ag die attach failure in power module products under operation.

MNC2021

ECCE2021

The dependence mechanism of SiN film breakdown on the N2 annealing temperature was investigated using TDDB and ESR. We proposed two types of TDDB modes at 900℃ and over 1000℃. At the first mode of 900℃, SiN film breakdown frequency due to the generation of Si dangling bonds with one oxygen and two silicon back bonds. At the second mode over 1000℃, SiN film breakdown frequency, caused by the E’center, which is Si dangling bonds with three oxygens.

第82回応用物理学会秋季学術講演会

The dependence mechanism of SiN film breakdown on the N2 annealing temperature was investigated using TDDB, ESR and FTIR. We proposed two types of TDDB modes at 900℃ and over 1000℃. At the first mode of 900℃, SiN film breakdown frequency due to the generation of Si dangling bonds with one oxygen and two silicon back bonds. At the second mode over 1000℃, SiN film breakdown frequency, caused by the E’center, which is Si dangling bonds with three oxygens.

第82回応用物理学会秋季学術講演会

The toroidal coil shape was automatically optimized using neural networks and genetic algorithm.

EPE2021

日本機械学会

SSDM2021

Expanding SiC power device market requires lowering wafer prices for the majority of device costs. In this talk, the author reports the application of remote epitaxy technology to alternative substrate with epi-membrane. SiC remote epitaxy needs high growth temperature with hot-wall chemical vapor deposition around 1873 K, which is a harsh environment for graphene survival. By replacing the carrier gas from hydrogen to argon, graphene etching was suppressed and peeling was successful. The author believes this approach represents a significant step toward the fabrication of high quality and low cost substrate with epi.

Epitaxy on 2D materials for layer release and their applications

The Compact model of GaN Ridge HEMTs, especially the drain current increase due to gate injection, has been improved from the one presented at APEC2020, and a scalable model equation has been derived by considering the physical generation mechanism. In addition, we analized the effect of the current gain H21 on the frequency response when the device is operated in AC. With this model, the H21 characteristics in the current-increasing region due to gate injection agreed with the actual measurement with high accuracy.

30th International Symposium on Industrial Electronics (ISIE2021)

We propose a results of a simple motor inverter simulation with WLTC droving mode using PLECS. PLECS is the simulation platform of power electric systems.

APEC2021

In coated Cu substrate was used as a low melting temperature bonding. We optimized the joint condition such as a temperature, pressure and process.

ECTC

The third-generation wireless in-wheel motor (W-IWM3) which has the capability of the Dynamic Wireless Power Transfer (D-WPT) on its wheel side has been developed for the Electric Vehicles. Developing concepts of W-IWM3 targeting “all components in wheel” is realized. One of the factors for “all components in wheel” is the small silicon-carbide (SiC) power device authors have developed. This paper showed the test result that the more than 18kW output with 95.2% DC to DC efficiency was achieved.

EVTeC 2021 5th International Electric Vehicle Technology Conference 2021

We propose a SiC MOSFET model for circuit simulation. We validated the accuracy of the proposed model by measured switching waveforms of an inductive load switching evaluation circuit. Simulation speed of the model has been validated by a three-phase inverter simulation. Excellent results have been observed for both accuracy and speed.

PCIM2021

Pb-2Sn-2.5Ag alloy solder is one of the most popular materials for die attach in electronic devices, however its mechanical properties have not been reported. In this study, we measured the visco-elasto-plastic properties of Pb-2Sn-2.5Ag solder using Instrumented Indentation microscopy with an optically transparent indenter.

22nd International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems

Since high lead solder has been used in industry for many years, few basic studies have been reported that discuss the microstructure and mechanical properties. In this study, the relationship between the microstructure and mechanical properties of high lead solder joints was investigated.

2021 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM

Influence of device parameter variation on current sharing between SiC MOSFETs connected in parallel has been studied. From the simulation results, we reveal the device parameters which mainly affetct the static and dynamic current sharing behavior of the devices. We also evaluate the effect of the current sharing mismatch on energy loss for each device.

ATS2020 (Asian Test Symposium 2020)

The presentation reveals the pore size and shape dependences on sintered silver mechanical durabilities.
From stress-strain results, uniform crystal structure make sphere and small pore shape. In terms of thermal cycle reliability using sintered silver materials, uniform structure with small and sphere pore state is essential.

MNC2020

The Id-Vd charactaristic in high-Id and high-Vd range of SiC-MOSFET shows incremental trend instead of saturated Id behavior. By TCAD simulation, the self-heating at measurement reproduce well this incremental trend.

SSDM2020

In the evaluation of the impurity level depth in Zn-doped GaN, it was found that Zn behaves as an acceptor impurity in GaN by forming the state at 0.3 eV from the top of the valence band. Normaly-off operation was confirmed in an AlGaN/GaN HFET with a 0.1 μm mesa shape using Zn-doped GaN as the gate layer.

SSDM2020

To maximise the switching capability of SiC-MOSFET, we introduce a current and voltage hybrid source gate driver and design method.

WiPDA Asia 2020

The adoption of small Qoss and small Qg GaN transistors was found to be a useful option to solve both the miniaturization and high power conversion efficiency of switching power supplies. Isolated 48 V-12 V LLC converter with a switching frequency of 2 MHz and 100 W class was fabricated, and the maximum power conversion efficiency reached 95.3%.

WiPDA Asia 2020

The basic characteristics of the latest generation of ROHM's SiC-MOSFETs are presented and compared with the current generation of devices in production. On the other hand, it is often assumed that better power device characteristics improve power-circuit performace, but it is not that simple. For better system-level performance, our researches of power applications and the related simulations are also presented.

WiPDA Asia 2020

日本機械学会2020年度年次大会

日本機械学会2020年度年次大会

日本機械学会2020年度年次大会

This research investigates how the mechanical properties of sintered silver (s-Ag) as a die attach material influence its heat-cycle reliability. s-Ag mechanical fatigue life was 500 times under elastic stress. To investigate the correlation between fatigue mechanical test and thermal shocked test (TST), we performed TST with different temperature patterns. From TST results, higher TST gives faster degradation of s-Ag.

IEEE　ISPSD2020

Twisted bilyaer graphene can be mocified the energy band structure by changing the rotation angle. Especially, the 1.1degree called as a magic angle can be shown the superconductivity. However, the next challenge is to obtain big scale (millimeter-scale) TBG samples. This research was shown to obtain it with using transfer graphene after annealing.

応用物理学会

応用物理学会

This paper presents a semi-theoretical method for predicting the turn-off surge voltage (Vsurge) in double-pulse test (DPT) using a power module (PM) with SiC MOSFETs and an embedded DC-link decoupling capacitor. In this scheme, multiple Kirchhoff’s laws-based equations are simultaneously solved, and drain-source voltage and drain current are mathematically expressed. This calculation process is semi-theoretical, and sufficiently predicts the Vsurge observed in DPT performed under various conditions.

APEC2020

令和2年電気学会全国大会

第34回　エレクトロニクス実装学会講演大会

第34回　エレクトロニクス実装学会講演大会

The modeling method developed in SiC DMOS was applied to the SiC UMOS and its versatility was verified. The model was also evaluated by comparing the switching waveforms fo a power module with SiC UMOS chip. As a result, the SiC UMOS model reproduced the measurement data with high accuracy as well as the SiC DMOS.

International Conference on Materials and Systems for Sustainability

Demonstrate the dynamic on-state resistance of GaN-HEMT and estimate inpact of loss of devices.

ICMass2019

The fatigue mechanical property of sintered silver plays a critical role to estimate the reliability of systems. The tensile fatigue test is performed for the sintered silver with p=5% and the bulk silver. The fatigue lifetime of the silver films is shorter than that of the bulk silver one.

Material Science Conference 2019

This study report that high speed switching gate drive circuit for SiC MOSFETs. The provided gate drive circuit adapted subsidery capacitor in order to add gate voltage, enables increase gate current. This allows fast charge and discharge and reduced switching losses. This study confirmed that the provided gate drive circuit reduce switching loss compared to conventional one.

ICSCRM2019

A novel measurement method to extract high voltage and high current I-V characteristics (HVHC I-V)of SiC MOSFET is proposed in this paper. The method could extract the HVHC I-V with extremely reduced self heating of the device. By using the method, we can measure higher voltage and current I-V characteristics than those extracted by the conventional method. It is possible for us to measure the HVHC I-V of the next generation SiC MOSFET, whose rated volatge and current is more than those of the conventional device.

ICSCRM2019

The internal gate resistance of SiC MOSFET effects its switching behavior larger than Si devices because it can switch at high speed with low external gate resistance. However, the convention mesurement method of internal gate resistance is not accurate. Then, we devised the new measurement method of it at switching operation by the switching waveforms.

ECCE2019

銀焼成は、空孔率がその引張り機械特性に影響することがわかっている。ところが、銀焼成の疲労機械特性について未だ不明である。今回我々は多孔質銀焼成の薄膜試験片と銀膜の疲労試験を実施した。銀焼成膜は、高加圧条件(60MPa)で成膜し、空孔率は5％であった。疲労試験結果から、焼成膜の引張疲労強度は銀膜と比較して低下しやすいことが分かった。

日本機械学会

第57回日本接着学会年次大会

SiC,GaNのパワーデバイスを開発するだけでなく、それらを使いこなすための技術も伴わないと社会貢献することはできない。本講演では、アプリケーションの実例、それを支える設計技術、ノイズの予測について紹介する

先端パワー半導体分科会第14回研究会

The precise modeling of SiC MOSFETs are difficult by means of conventional modeling method of Si devices because of the device characteristics. Then, we invented the new modeling method for SiC MOSFETs which can reproduce its switching behavior precisely.

PCIM2017

20th Annual International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE2019)

A 3-phase15kW using SiC MOSFETs and trans-linked topology achieved maximum efficiency of 99.2%, and verified the benefit of combining SiC MOSFET with trans-linked technology.

APEC2019

電流形と電圧形を組み合わせたSiC-MOSFET用ハイブリッド形ゲート駆動回路の実機実験により、ターンオン損失が50%、ターンオフ損失が35%低減できることを実証した。

平成31年電気学会全国大会

SiC-MOSFETを高速に駆動できるゲート駆動回路についての報告。本ゲート駆動回路は補助キャパシタを用いており、この補助キャパシタを介してゲートに通常よりも高い電圧を印加することができ、ゲート電流を増加させることができる。これにより高速にゲートを充放電し、スイッチング損失を低減できる。実測でもこの効果を確認し、本回路の優位性を実証した。

平成31年電気学会全国大会

IEEE CPMT Symposium Japan 2018

This paper investigates the porosity-dependent tensile mechanical properties of porous 8-10 μm thick silver films. The silver films are fabricated by pressure press, the variety of which changes the porosity (p) ranging 5% to 25%. p is determined by use of scanning electron microscopy cross-section images of the films. Stress-strain (S-S) curves are obtained by tensile tests performed for the porous and bulk silver films.Breaking strain and Ultimate tensile strengh decrease almost linearly with increase of p.

MNC 2018, 31st International Microprocesses and Nanotechnology Conference

SiC,GaNのパワーデバイスを開発するだけでなく、それらを使いこなすための技術も伴わないと社会貢献することはできない。本講演では、アプリケーションの実例、それを支える設計技術について紹介する

先端パワー半導体分科会第5回講演会

The mechanical properties of die-attach materials are a decisive factor in determing the reliability of the system. Sintered porous silver is attracting much attention as a next-generation die-attach material,however still do not clalify the mechanical properties. Authors prepared thin sintered silver and bulk silver films.Sintered silver films were fabricated under various pressure. From tensile tests, Sintered porous silver films exhibit brittle characteristic in comparison with silver films and show high strength under high process pressure.

日本機械学会

A Scalable drain current model and a small-signal AC model have been developed for AlGaN/GaN MIS HEMTs with embedded source field plate. The model was found to reproduce the device characteristics well by comparing the Id-Vds, Id-Vgs, S11and H21 characteristics of the device.

RF-IC2018

A trans-linked 5kW interleaved inverter using SiC MOSFETs drastically reduced both tansistor loss and reactor losses, resulting in high efficiency over 99% and fanless operation.

PCIM2018

The accurate electro-thermal simulation is presented by using a new SiC die model to predict the power loss and temperature of SiC MOSFET dies in a power module. The new model incorporates a temperature dependent I-V model and body diode model which is dependent on the gate-voltage. The simulation using the model yields an accurate power loss and temperature estimate of the SiC module in a buck converter.

PCIM2018

S-parameter based simulation model for power module (PM) except for the semiconductor chips was created with electromagnetic simulation. This PM model was combined with the chip model in order to build the model of the whole structure. As a result of verifying the model by the double pulse test, the simulation waveforms which reproduce the measurement results well were obtained.

PCIM2018

電流形と電圧形を組み合わせたSiC-MOSFET用ハイブリッド形ゲート駆動回路を提案し、シミュレーションにてゲート電圧の安定性とスイッチング損失の低減ができることを確認した。

平成30年電気学会全国大会

The high speed switching of SiC MOSFET is affected by the parasitic elements of circuit board. Therefore, we analyzed the impact of stray capacitance in circuit board on the switching behavior and tried circuit simulation of the effect by use of precise model and electromagnetic simulation results of circuit board.

APEC2018

エレクトロニクス実装学会 MES2017

This study report that a three-phase, 5-kW LLC series resonant dc/dc converter utilizing SiC MOSFETs. The high-break down voltage of SiC MOSFETs, enables increasing the input voltage up to 800 V. Around 160kHz switchig frequency successfully reduces the volume of isolation transformers. Current-balancing transformers among each phases effectively suppress a peak current from arising in the circuit and contributed that miniaturizes the input and output capacitances. The proposed power supply weighs 1.55 kg with dimensions including a width of 18 cm, a length of 12 cm, and a height of 12.5cm. The conversion efficiency of the converter reaches 98.1% at 5-kW operation.

PCIM Europe 2017

14th European Conference on Thermoelectrics

平成28年電気学会基礎・材料・共通部門大会

Until now, the transientcharacteristics of circuit simulations using the SiC device model have not been consistent. Since EMC must be considered when using SiC Devices, it is important to reproduce their transient characteristics. Therefore, we have developed a novel SiC devie model by measureing the Id-Vds characteristics with the high-voltage and high-current region and the on-state capacitance of the SiC MOSFET to reproduce the transient characteristics. As a result the novel SiC device model successfully reproduce the switching taransient waveform with high accuracy.

第29回回路とシステムのワークショップ

The self-sustained oscillations are sometimes obserbed when SiC MOSFETs switch at high speed in the half bridge configuration. The oscillation is regard as nonlinear self-excited oscillation as a result of its device characteristics. We tried to analyze it from the aspects of device characteristics of MOSFET and trajectory of the oscillation in the I-V plane.

NOLTA2015

電気学会マグネティックス研究会