PUBLICATIONS & PRESENTATIONS

Electrical Characterization of Si capacitor with TSV electrode

Maiko Hatano

The 71st JSAP Spring Meeting 2024

Mode-dependent variations of eigenfrequencies in the one-dimensional Su–Schrieffer–Heeger electrical circuit: Experimental demonstration

Fumiya Nagasawa

The 71st JSAP Spring Meeting 2024

Control of the morphology and the number of layers of graphene on SiC

Keiju Sato

The 71st JSAP Spring Meeting 2024

Fracture Mechanism of Sintered Silver Film Revealed by in-situ SEM Uniaxial Tensile Loading

Keisuke Wakamoto

IEEE Transactions on Components, Packaging, and Manufacturing Technology

Toward the Practical Application of Terahertz Resonant Tunneling Diodes

Yosuke Nishida

Symposium on Frontier of Terahertz Science Ⅹ

Low-Power and Fast-Response Limiting Current-Type Oxygen Microsensor with a Wide Range Oxygen Concentration

Shunsuke Akasaka

IEEJ Transactions on Electrical and Electronic Engineering

Development of In-Situ Measurement Method for Wire-Bonding Lifetime Utilizing the 4-terminal Method

Kento Kariya

Journal of Smart Processing for Materials Environment & Energy, Volume: 12, Issue: 5, pp. 251-256

Comparison of Sintered Silver Die Attach Failure between Thermal Shock Test and Mechanical Cycling Test

Keisuke Wakamoto

Japanese Journal of Applied Physics, Volume: vol. 61, pp. SD1029

Degradation Mechanism of Silver Sintering Die Attach Based on Thermal and Mechanical Reliability Testing

Keisuke Wakamoto

IEEE Transactions on Components, Packaging and Manufacturing Technology, Volume:13, pp. 197-210

Nine Point Bending Test Technique for Understanding of Sintered Silver Die Bonding Failure Mechanism

Keisuke Wakamoto

Experimental techniques

Sputtered β-Ga2O3 Crystallization by High Temperature Annealing on AlN/Si

Akira Sagawa

SSDM2023

Effect of the Forward and Reverse Conduction Resistance of SiC MOSFET on the Harmonic Voltage of the Full-Bridge Inverters of Wireless Power Systems for Electric Vehicles and Its Suppression Method

Tatsuya Yanagi

EPE 2023 ECCE Europe

The improved scheme of estimating embedded gate resistance to reproduce SiC MOSFET circuit performance

Shogo Ogawa

IEEE TRANSACTIONS ON ELECTRON DEVICES

Application of remote epitaxy for SiC wafer cost reduction

Takuji Maekawa

Workshop on Advanced Epitaxy for Freestanding Membranes and 2D Materials

EXTREMELY SMALL LIMITING-CURRENT-TYPE OXYGEN SENSOR WITH A WIDE RANGE PROPORTIONALITY OF THE OXYGEN CONCENTRATION

Shunsuke Akasaka

We succeeded in demonstrating an oxygen microsensor with a good linear relationship in a wide-range oxygen concentration.

Transducers2023

Suppression of Leakage Current in Wireless Charging Systems Using N-legged Inverters

Yusaku Takagi (Tokyo university)

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)

Simplified Open-Loop Transfer Functions to Analyze Influential Parasitic Parameters for Oscillation Caused by Parallel Connected Transistors

Hiroto Sakai

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

Autonomous Minimization of Power Loss by Switching Frequency Adjusting Function for a DC–DC Converter

Junichi Kashiwagi

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

PCIM2023

A Unified Model of MIS and Ridge HEMTs for Fast and High-Power Switching Applications.

Hitoshi Aoki

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)

Performance Comparison of Si IGBT and SiC MOSFET Power Module driving IPMSM or IM under WLTC

Hirokatsu Umegami

World Electric Vehicle Journal, Volume: 14, Issue: 4, Apr. 2023, pp.

SiC wafer cost reduction with remote epitaxy technology

Takuji Maekawa

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

Principal Component Analysis based GaN transistor live health monitoring

Florian Chalvin

A method using PCA to track GaN transistors degradation in real time with no need for prior failure data is investigated. Based on the fatigue experiment carried out we suggest a graphical representation and associated threshold to easily detect when a device is damaged.

ISSM2022

Sintered Silver Degradation Assessment by Thermal and Mechanical Cyclic Tests

Keisuke Wakamoto

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

A Secondary-Side Resonant LLC converter for Reducing Resonance Voltage with Boost Mode Operation Using Resonance Including Current Doubler Rectifier

Hayato Nakamura（Okayama University）

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)

Dominant Model-Parameter Determination for the Analysis of Current Imbalance Across Paralleled Power Transistors

Yohei Nakamura

IEEE Transactions on Power Electronics

Nine Point Bending Test Technique for Evaluating the Sintered Silver Die Degradation

Keisuke Wakamoto

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

Compact and cost-effective solution for terahertz applications

Beziko Mikhail

Overview of Resonant tunneling diode devices developed at ROHM. Key advantages and characteristics.

Electronica 2022 Embedded Platforms Conference

Degradation Mechanism Comparison of Sintered Silver Die in Thermal and Mechanical Cycling Tests

Keisuke Wakamoto

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

Oxygen and humidity sensing property of a limiting current-type thin-film YSZ-based sensor on a micro-hotplate

Shunsuke Akasaka

Sensing properties of MEMS oxygen and humidity sensor

IEEE Sensors 2022

Evaluating Sintered Silver Die-attach Thermal Cycling Degradation

Keisuke Wakamoto

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

SiC wafer cost reduction strategy with remote epitaxy

Takuji Maekawa

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

Performance Comparison of Si IGBT and SiC MOSFET Power Module driving IPMSM or IM under WLTC

Hirokatsu Umegami

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

Effect of N2-Anneal Temperature on Silicon Nitride film:(Ⅱ) Fine Structures of ESR Spectrum and FTIR

Hayato Miyagawa (Kagawa University: Joint research with ROHM Hamamatsu Co., Ltd.)

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

R&D Bridging over Device and System Engineers Through the Electric-Mileage Estimation of a Motor System.

Ken Nakahara

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

An evaluation of a new type of High Efficiency Hybrid Gate Drive Circuit for SiC- MOSFET suitable for Automotive Power Electronics System Applications

Masayoshi Yamamoto（Nagoya university）

J-STAGE, Volume: E105.A, Issue: 5, May.2022, pp. 834-843

High efficiency 3-Phase Power Inverter Using SiC MOSFETs and Trans-Linked Neutral-Point-Clamped Topology

Tatsuya Miyazaki

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

Temperature Characterizations of Multi-Unit and Multi-finger Dependencies on AlGaN/GaN

Hitoshi Aoki (Teikyo Heisei University)

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)

Evaluation of Thermal Couple Impedance Model of Power Modules for Accurate Die Temperature Estimation up to 200℃

Yohei Nakamura

Japanese Journal of Applied Physics, Volume: 61, Issue: SC, Mar.2022

Zn-doped GaN Comprising the Gate Structure of Normally Off AlGaN/GaN-HFETs

Norikazu Ito

IEEE Electron Device Letters, Volume: 43, Issue: 2, Dec.2021, pp. 192-195

Elucidation of Adhesive Interaction between the Epoxy Molding Compound and Cu Lead Frames

Naoaki Tsurumi

ACS Omega, Volume: 6, Issue: 49, Dec.2021, pp. 34173–34184

Observation of a flat band and bandgap in millimeter-scale twisted bilayer graphene

Keiju Sato(Nagoya University)

Communications Materials, Volume: 2, Issue: 117, Dec.2021

Comparison in Sintered SiIver Die Attach Failure between Thermal Shocked Test and Four-point Bending Test

Keisuke Wakamoto

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

Dominant Model Parameter Extraction for Analyzing Current Imbalance in Parallel Connected SiC MOSFETs

Yohei Nakamura

https://ieeexplore.ieee.org/document/9595345

ECCE2021

Observation of a flat band in millimetre-scale magic-angle twisted bilayer graphene

Wataru Norimatsu (Nagoya university)

The electronic states of twisted bilayer graphene (TBG) vary with its twist angle. In this study, we obtained 5 × 5 mm^2 TBG samples with various twist angle, using epi-graphene on SiC. Furthermore, angle-resolved photoemission spectroscopy revealed their energy band structures.

Graphene Week 2021

Auto Structural Optimization of Toroidal Coils Based on Neural Network and Genetic Algorithm

Junichi Kashiwagi

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

EPE2021

Degradation Mechanism of Pressure-Assisted Sintered Silver by Thermal Shocked Test

Keisuke Wakamoto

Energies, Volume: 14, Issue: 17, Sep.2021, pp. 5532

Integrated Resonant Tunneling Diode with Rectangular Waveguide I/O using Photonic Crystal Interface

Yuma Kawamoto（Osaka University）

We have developed a technology to integrate terahertz devices in rectangular waveguides with low loss by using dielectric transmission lines.
A module in which a resonant tunneling diode is packaged using a photonic crystal waveguide was fabricated, and wireless communication was demonstrated.

46th International Conference on Infrared, Millimeter and Terahertz Waves

Terahertz RTD Chip Backside-coupled to Photonic-crystal Waveguide

Ratmalgre Koala（Osaka University）

We proposed a backside-coupling structure for efficient and broadband coupling of terahertz resonant tunneling diodes and phoonics-crystal waveguides, and demonstrated its operation in the 300-GHz band.

46th International Conference on Infared, Millimeter and Terahertz Waves

SiC wafer cost reduction with remote epitaxy technology through graphene

Takuji Maekawa

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

Geometry Independent Hole Injection Current Model of GaN Ridge HEMTs

Hitoshi Aoki (Teikyo Heisei University)

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)

EV driving pattern simulation with PLECS

Ryosuke Ishido

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

Metalens mounted on a resonant tunneling diode for collimated and directed terahertz waves

Takehito Suzuki（Tokyo University of Agriculture and Technology）

Optics Express, Volume: 29, Issue: 12, June.2021, pp. 18988-19000

TLP Bonding process using In coated Cu sheet for high-temperature dieattach

Hiroshi Nishikawa（Osaka University）

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

Development of the Third-Generation Wireless In-wheel Motor

Osamu Shimizu(Tokyo university)

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

A High-Speed and High-Accuracy SiC MOSFET Model for Simulating Practical Power Circuits

Yohei Nakamura

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

Characterization of Mechanical Properties of Pb-2Sn-2.5Ag Solder Using Instrumented Indentation Microscopy with Optically Transparent Indenter

Kento Kariya

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

Study of the Microstructure and the Mechanical Properties of Pb-2.0Sn-2.5Ag Solder Joint

Kento Kariya

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

Prominent luminescence of silicon‑vacancy defects created in bulk silicon carbide p–n junction diodes

Fumiya Nagasawa

Scientific Reports, Volume: 11, Issue: 1, Jan. 2021, pp. 1497

Power Conversion Efficiency Prioritized AC Filter Inductor Design for Three-Phase PWM Inverter

Hiroaki Matsumori (Nagoya Institute of Technology)

AIP Advances, Volume: 11, Issue: 015338, Jan. 2021, pp. 1-4

Limiting current type yttria-stabilized zirconia thin-film oxygen sensor with spiral Ta₂O₅ gas diffusion layer

Shunsuke Akasaka

Sensors and Actuators B: ChemicalVolume: 327 , Issue:1 , Jan.2021 , pp. 128932-128939

Ageing Monitoring of GaN Transistores using Recurrent Neural Networks

Florian Chalvin

Developping a method to track GaN transistor degradation over time with recurrent neural networks. From measurements easily obtained during the normal operation of the transistor we can detect if the behavior is standard or if there is an anomaly. This method should enable live monitoring of device health.

ISSM2020

Imaging Applications with a Single Resonnant Tunneling Diode Transceiver at 300GHz Band

Li Yi（Osaka University）

We employed a single resonant tunneling diode as both a transmitter and a receiver simultaneously, and demonstrated its impact in terahertz imaging applications.It leads to simplify terahertz imaging systems.

2020 International Topical Meeting on Microwave Photonics

Influences of Device Parameters Variability on Current Sharing of Parallel-Connected SiC MOSFETs

Yohei Nakamura

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)

Pore Size and Shape Dependences on Quasi-Static Tensile Characteristics of Sintered Silver Films

Keisuke Wakamoto

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

Anisotropic temperature distribution causing the incremental saturated drain-current observed in the I-V characteristic of the SiC MOSFET

Shogo Ogawa

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

Zn-doped GaN Mesa Structure As a Gate for Normally-Off AlGaN/GaN-HFET

Norikazu Ito

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

Current-and-Voltage Hybrid Source Gate Driver for Maximizing the Switching Capability of SiC-MOSFETs

Ryosuke Ishido

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

WiPDA Asia 2020

Miniaturized 48 V‒12 V insulation-type DC/DC converter miniaturized by using GaN transistors operating at 2-MHz switching frequency

Koki Sakamoto

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

Research Activities to Maximize the Capability of New Power Devices

Ken Nakahara

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

The Influence of Mechanical Property on the Heat-Cycle Reliability of Sintered Silver Die Attach

Keisuke Wakamoto

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

Development of practical terahertz package for resonant tunneling diode oscillators and detectors

Kazuisao Tsuruda

We have devloped the world's first small general-purpose PLCC package and a high-gain antenna integrated package for terahertz devices. There are promising as a high-frequency package form that are functional and can be mass produced.

IEEE RFIT2020

Temperature Dependence on Tensile Mechanical Properties of Sintered Silver Film

Keisuke Wakamoto

MaterialsVolume: 13 , Issue:4061 , Sep.2020

Formation of quantum dots in GaN/AlGaN FETs

Tomohiro Otsuka (Tohoku University)

scientific reportsVolume: 10 , Issue:1 , Sep.2020 , pp. 15421

Comparative study of the ideal and actual adhesion interfaces of the die bonding structure using conductive adhesives

Naoaki Tsurumi

The Journal of AdhesionVolume: 0 , Issue:0 , Aug. 2020 , pp. 1-25

Electrothermal Co-simulation for Predicting the Power Loss and Temperature of SiC MOSFET Dies Assembled in a Power Module

Yohei Nakamura

IEEE Transactions on Power Electronics, Volume: 35, Issue: 3, Jul.2020, pp. 2950 - 2958

Magnetic Near-Field Strength Prediction of a Power Module by Measurement-Independent Modeling of Its Structure

Junichi Kashiwagi

IEEE Access, Volume:8, Issue:28,May 2020, pp.101915-101922

Deep-Donor-Induced Suppression of Current Collapse in an AlGaN-GaN Heterojunction Structure Grown on Si

Taketoshi Tanaka

IEICE Transactions on Electronics
Volume: E103.C , Issue: 4 , Apr. 2020 , pp. 186-190

Semi-Theoretical Prediction of Turn-off Surge Voltage in a SiC MOSFET Power Module with an Embedded DC-link Decoupling Capacitor

Tatsuya Miyazaki

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

High-Voltage and High-Current Id–Vds Measurement Method for Power Transistors Improved by Reducing Self-Heating

Yohei Nakamura

IEEE Electron Device Letters
Volume: 41, Issue: 4 , Apr. 2020 , pp. 581 - 584

Dynamic On-State Resistance Measurement of GaN-HEMT by Double Pulse Test

Ryosuke Ishido

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

ICMass2019

Modeling of SiC UMOS chip and its application to Power Module

Hiroyuki Sakairi

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

Mechanical Property of Nano Porous Sintered Silver: Toward Reliability Estimation

Keisuke Wakamoto

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

Dry and wet etching for β-Ga₂O₃ Schottky barrier diodes with mesa termination

Hironori Okumura (University of Tsukuba)

Japanese Journal of Applied Physics, Volume: 58, Number: 12, pp.120902

A gate Driver Maximizing the Switching Capability of SiC MOSFETs

Yusuke Nakakohara

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

Dynamic Measurement Method to Extract High Voltage and High Current I-V Characteristics of SiC MOSFET with Reduced Self Heating

Yohei Nakamura

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

Switching behavior based method to estimate the intrinsic gate resistance of a transistor by using gate plateau voltage

Tatsuya Yanagi

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

Ultrahigh temperature platinum microheater encapsulated by reduced-TiO₂ barrier layer

Shunsuke Akasaka

"Sensors and Actuators A: Physical
Volume: 296 , Issue: 1 , Sep. 2019 , pp. 286-291"

Measurement scheme to model an SiC MOSFET for simulating its switching behaviors

Tatsuya Yanagi

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

Tensile mechanical propertiees of sintered porous silver films and their dependence on porosity

Keisuke Wakamoto

Japanese Journal of Applied Physics Volume: 58 , Number SD , Jun. 2019 , SDDL08-1-5

Terahertz fibre transmission link using resonant tunnelling diodes integrated with photonic-crystal waveguides

Xiongbin Yu（Osaka University）

Electronics Letters Volume: 55 , Issue: 7 , Apr. 2019 , pp. 398-400

Thermal Warpage Behavior Analysis of Semiconductor Package of Semiconductor Packaging Structure

Kento Kariya

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

A High Efficiency 3-Phase 400V 15kW Power Inverter Using SiC MOSFETs and Trans-Linked Topology

Tatsuya Miyazaki

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

A 130-nm Ferroelectric Nonvolatile System-on-Chip With Direct Peripheral Restore Architecture for Transient Computing System

Yongpan Liu(Tsinghua University)

IEEE Journal of Solid-State Circuits Volume: 54 , Issue: 3 , Mar. 2019 , pp. 885-895

A Study of Adhesion Interface about Die Bonding Structure with Conductive Silver Paste

Naoaki Tsurumi

IEEE CPMT Symposium Japan 2018

Influence of porosity on Tensile Mechanical Properties of Sintered Porous Silver Films

Keisuke Wakamoto

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

Development of Resonant Tunneling Diodes for Terahertz Applications

Jaeyoung Kim

Workshop: Introduced RTD devices for THz communication and sensing. With comparison with other terahertz device, RTDs are compact and power-efficient.

APMC2018

Measurement Methodology for Accurate Modeling of SiC MOSFET Switching Behavior over Wide Voltage and Current Ranges

Hiroyuki Sakairi

IEEE Transactions on Power ElectronicsVolume: 33 , Issue:9 , Sep.2018 , pp. 7314-7325

Application of PZT thin film devices to realize IoT society

Yoshiaki Oku

A number of IoT applications are rapidly growing. Among others, smart factory, smart infrastructure and digital medicine/health are major IoT markets. ROHM also succeeded in demonstration of healthcare monitoring utilizing non-volatile PZT devices. The essentials for IoT society and ROHM’s device applications of PZT thin film were described.

The 12th Japan-Korea Conference on Ferroelectrics (JKC-FE12)

A Small Signal AC Model Using Scalable Drain Current Equations of AlGaN/GaN MIS Enhancement HEMT

Hitoshi Aoki (Teikyo Heisei University)

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 5-kW Inverter Using SiC MOSFETs to Achieve Fan-less Operation

Tatsuya Miyazaki

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

Electro-Thermal Simulation for Predicting the Temperature of SiC Dies in the Power Module of a High Frequency Operating Power Converter

Yohei Nakamura

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 Modeling a Power Module Independent of Measurement Data

Junichi Kashiwagi

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

A Newly Developed high performance PZT thin films by using sputtering and sol-gel hybrid method for Piezo-MEMS device

Tomohiro Date

We have proposed a new hybrid structure of the PZT film which we made by sol-gel method of construction on the PbTiO3 seed layer made by rf magnetron sputtering. These hybrid PZT films showed high (100)/(001) orientation and had high breakdown voltage.

2018 ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP2018)

Application of PZT thin film devices to realize IoT society

Yoshiaki Oku

ROHM has developed PZT thin film devices, such as non-volatile ferroelectric memory, highly-sensitive sensors, highly-accurate actuators, high-speed space light modulators and ultra-low-power-consumption non-volatile flip-flop devices so far. ROHM also succeeded in demonstration of healthcare monitoring utilizing non-volatile PZT devices (memory and logic). In this presentation, ROHM’s device applications of PZT thin film were described.

2018 ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP2018)

Hysteretic Control Embedded Boost Converter Operating at 25-MHz Switching

Junichi Kashiwagi

IEEE Transactions on Circuits and Systems II: Express Briefs Volume: 66 , Issue: 1 , Jan. 2019 , pp. 101-105

External Feedback Effect in Terahertz Resonant Tunneling Diode Oscillators

Luong Duy Manh (Osaka University)

IEEE Transactions on Terahertz Science and Technology Volume: 8 , Issue: 4 , Jul. 2018 , pp. 455-464

Circuit Simulation of a Silicon-Carbide MOSFET Considering the Effect of the Parasitic Elements on Circuit Boards by Using S-parameters

Tatsuya Yanagi

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

A Fanless Operating Trans-Linked Interleaved 5kW Inverter Using SiC MOSFETs to Achieve 99% Power Conversion Efficiency

Tatsuya Miyazaki

IEEE Transactions on Industrial Electronics Volume: 65 , Issue: 12 , Dec. 2018 , pp. 9429-9437

Resonant Tunneling Diodes for THz Applications

Jaeyoung Kim

Present the recent advance of RTD-based terahertz devices. Based on a well-defined equivalent circuit model, circuits like mixer, detector, and oscillators have been integrated.

ALT 2017

High-Temperature Characteristics of 3-kV 4H-SiC Reverse Blocking MOSFET for High-Performance Bidirectional Switch

Seigo Mori

IEEE Transactions on Electron Devices Volume: 64 , Issue: 10 , Oct. 2017 , pp. 4167-4174

800 V Three-Phase LLC Series Resonant DC/DC Converter Using SiC MOSFETs

Yusuke Nakakohara

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

Terahertz Sensor Using Photonic Crystal Cavity and Resonant Tunneling Diodes

Kazuma Okamoto (Osaka University)

Journal of Infrared, Millimeter, and Terahertz Waves, Volume: 38, Issue: 9, May.2017, pp. 1085-1097

Extraction of net acceptor type trap density in semi-insulating GaN layers grown on Si substrate by DC I-V measurement

Taketoshi Tanaka

physica status solidi (a) Volume: 214, Issue: 8 , Aug. 2017

Thermoelectric enhancement in the two-dimensional electron gas of AlGaN/GaN heterostructures

Kazuya Nagase

14th European Conference on Thermoelectrics

Modeling and simulation of terahertz resonant tunneling diode based circuits

Sebasitian Diebold (Osaka University)

IEEE Transactions on Terahertz Science and Technology Volume: 6 , Issue: 5 , Sep. 2016 , pp. 716-723

Terahertzsensing based on photonic crystal cavity and resonant tunneling diode”,Progress in Electromagnetics Research Symposium

Kazuisao Tsuruda

Progress In Electromagnetics Research Symposium 2016 China

PIERS 2016 China

Thin film YSZ-based limiting current-type oxygen and humidity sensor on thermally oxidized silicon substrates

Shunsuke Akasaka

Sensors and Actuators B: Chemical
Volume: 236 , Issue: 29,June 2016 , pp. 499-505

Self-Sustained Oscillation in Half Bridge Circuit of Silicon Carbide Devices with Inductive Load

Tatsuya Yanagi

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

Millimeter-wave and terahertz-wave applications enabled by photonics

Prof. Tadao Nagatsuma (Osaka University)

IEEE Journal of Quantum Electronics Volume: 52 , Issue: 1 , Jan. 2016

Extremely low-loss terahertz waveguide based on silicon photonic-crystal slab

Kazuisao Tsuruda

Optics Express Volume: 23 , Issue: 25, 2015 , pp. 31977-31990

Three Phase LLC Series Resonant DC/DC Converter Using SiC MOSFETs to Realize High Voltage and High Frequency Operation

Yusuke Nakakohara

IEEE Transactions on Industrial Electronics Volume: 63 , Issue: 4 , Apr. 2016 , pp. 2103-2110

Terahertz-wave integrated circuits based on photonic crystals

Kazuisao Tsuruda

Progress In Electromagnetics Research Symposium 2015 Czech