@phdthesis{oai:kyutech.repo.nii.ac.jp:00007896,
 author = {河野,  洋志 and Kono, Hiroshi},
 month = {2023-02-22},
 note = {1 Overview of power electronics and power semiconductor||2 Oscillation phenomena in power semiconductor operation||3 Theory of oscillation analysis with a signal flow graph and a scattering parameter||4 Analysis of Oscillation phenomena of SiC MOSFETs||5 Analysis of Oscillation phenomena of Si-IGBTs||6 Conclusions, Technological innovation in power electronics is desired to realize the social demand for the spread of renewable energy and the promotion of electrification of automobiles to achieve carbon neutrality. Power devices are key components in power electronics, and their performance has been improving. As their performance improves, the occurrence of unstable behaviors such as oscillation and noise in power device packages and circuits can cause system failures. Hence, a new design technology to ensure the stable operation is required. In this study, a novel design method is proposed and applied to oscillation phenomena of SiC-MOSFETs and Si-IGBTs during short-circuit operation. The effectiveness of the method is demonstrated by comparing the results calculated using the proposed method and the results obtained using conventional methods and experimental results. In chapter 1, the requirements for power semiconductors in the international effort to achieve zero CO2 emissions in 2050 are summarized. Then, the trend of research and development on the improvement of power device characteristics for smaller and higher efficiency power conversion systems is discussed, focusing on Si-IGBT and SiC-MOSFET. In chapter 2, previous studies on oscillation phenomena and its suppression are summarized, which can become issues as the power devices are improved. These previous studies can be classified into two categories: one based on equivalent circuits and the other based on device physics. However, there has not been sufficient discussion on the oscillation phenomenon that strongly couples circuits and devices, which is becoming more important as power devices become more high-performance. Technology computer aided design （TCAD） mixed mode simulation can handle both circuits and device physics, however, it is difficult to use it for realistic device design due to the large amount of calculation. In Chapter 3, a new method based on the S-parameter and the signal flow graph （SFG） is introduced to analyze the circuit stability. This method allows us to calculate the frequency response of the output current to the external field maintaining the response of the carrier distribution and electric field inside the device. The signal gain for the focused operating mode can be easily calculated by applying Mason’s rule to the SFG. Additionally, the stability analysis using the Nyquist plot enables not only the judgment of the system stability with respect to the design parameters but also the quantitative evaluation of the stable/unstable margin. In Chapter 4, the usefulness of the proposed method is verified by applying it to the oscillation phenomenon of SiC-MOSFETs during Type II short-circuit operation. The S-parameters are calculated from the TCAD model for a commercial SiC-MOSFET, and stability analysis is carried out using the SFG. The dependence of the gate resistance required for oscillation suppression obtained from the mixed mode simulation of TCAD is compared with the results obtained from the proposed method. The agreement between the proposed method and the results of TCAD mixed mode simulation is confirmed. Stability analysis is conducted for both the mode in which a single switching device oscillates by coupling with parasitic elements of the circuit and the mode in which oscillation occurs through switching devices connected in parallel. The characteristics of each mode during short-circuit operation are clarified, and the stability phase diagram in the design parameter space is calculated for each mode by taking advantage of the computational speed. It is shown that which mode becomes unstable depends on the design parameters. In Chapter 5, the proposed method is applied to the oscillation phenomenon of Si-IGBTs under Type II short-circuit operation and the oscillation mechanism is investigated. Experimental results revealed that the oscillation occurred during Type II short-circuit operation and it can be suppressed by increasing the gate resistance. The resistance required for oscillation suppression decreases as the collector voltage increases. The stability analysis is conducted using the proposed method. It is confirmed that the calculated critical gate resistance decreases as the collector voltage increases. The results are in good agreement with the experimental results. The internal behavior of the device under the oscillation state is also analyzed. During the short-circuit operation, a high electric field region is formed at the boundary between the base and drift layers, and the carrier distribution at both ends of the plasma region is modulated through the electron-hole plasma. This modulation becomes more responsive when the collector voltage is smaller. In Chapter 6, the development potential of the proposed method and future challenges are discussed. This study presents a new method for accelerating the development of power devices and power electronics systems that contribute to CO2 reduction, which is becoming an international effort. This method provides an integrated approach for managing the multilevel design hierarchy, from devices to power conversion systems. It is expected that this achievement will make it possible to fully use the potential of power devices and contribute to expanding the application field of power electronics., 再生可能エネルギーの普及，自動車などの電動化を推進するため，パワーエレクトロニクスの技術革新が期待されている．パワーデバイスはそのキーとなる部品であり高性能化が進んでいる．高性能化に伴いパワーデバイスのパッケージや回路で生じる発振・ノイズなどの不安定動作が課題となっている．このような不安定動作はシステムの故障や誤動作の原因となるため，安定動作を担保する新しい設計技術が求められている．本研究ではパワーデバイスの内部動作から回路やシステムまでを統一的に安定化する新たな設計手法を提案する．第1章では，2050年のCO2排出量実質ゼロに向けた国際的な取り組みの中でパワーエレクトロニクスの効率改善，適用範囲拡大に向けた取り組みのまとめを行った．さらに電力変換システムの小型化・高効率化に向けた炭化ケイ素-金属酸化膜電界効果トランジスタ（SiC-MOSFET）とシリコン-絶縁ゲート型バイポーラートランジスタ（Si-IGBT）の高性能化の現状をまとめた．第2章では，パワーデバイスの高性能化に伴い顕在化する発振現象と，その抑制に関する先行研究の到達点を整理した．先行研究は等価回路に基づく研究と，デバイス物理に基づく研究に分類される．しかし，パワーデバイスの高性能化に伴い顕在化する回路とデバイスがより強く結合する発振現象について十分な議論がされていなかった．Technology computer aided design（TCAD）のmixed modesimulationは回路とデバイス物理の双方を取り扱えるが計算量が多く，現実の素子設計への適用は難しく，課題となっている．第3章では，パワーデバイスの内部動作から回路やシステムまでを統一的に設計する手法を提案する．本手法では，デバイスモデルを元に，TCADシミュレーションの結果から求めたS-parameterと回路を，signal flow graph（SFG）を用いて統一的に取り扱い安定性を解析する．この手法では，デバイス内部のキャリア分布や電界の外場応答を維持したモデル化が可能である．SFGに対してMason’s ruleを適用することで着目した動作モードに対する信号ゲインを容易に計算することができる．安定性解析にNyquist plotを用いることで，設計パラメータに対する安定・不安定の判定を行うだけでなく，設計者が定量的にマージンを設定することが可能になる．第4章では，提案手法をSiC-MOSFETのType II短絡動作時の発振現象に適用することで手法の有用性を示した．市販のSiC-MOSFETの動作を模擬したTCADモデルからS-parameterを計算し，SFGを使って安定性解析を実施した．TCAD mixed mode simulationから求めた発振抑制に必要なゲート抵抗の回路パラメータ依存性と提案手法から求められた計算結果を比較し，提案手法とTCAD mixed mode simulationの結果が一致する事を確認した．また，単素子が回路の寄生要素と結合して発振するモードと，並列接続された素子を通じて発振するモードの双方についてそれぞれ安定性解析を実施した．短絡動作時の各モードの特徴を明らかにするとともに，計算速度を生かし，モード毎に設計パラメータ空間内での安定性の相図を計算し，設計パラメータにより不安定になるモードが異なる事を示した．第5章では，提案手法をSi-IGBTのType II短絡動作時の発振現象に適用した．はじめに，Si-IGBTのType II短絡動作時の発振を実験的に調べ，提案手法による計算結果が実験結果と一致することを示した．また，発振状態でのデバイス内部動作の解析により，短絡動作時にベースとドリフト層境界に，キャリア密度が低下した高電界領域が形成され，外場によってこの領域が伸縮する際，電子正孔プラズマを介して，プラズマ領域両端のキャリア分布が変調されることがわかった．この変調はコレクタ電圧が小さく，高電界領域が狭いほど大きいことが分かった．実験結果の対応から，短絡時に生じる高電界領域とプラズマ領域の外場に対する応答が，外部回路との結合により発振を引き起こすと考えられる．以上のように本手法は，簡易な計算で回路安定性評価とデバイス内部状態解析を同時に行うことができる．第6章では，本研究のまとめを行い，本手法の発展性について述べた．電磁界解析と本手法を組み合わせたモジュール構造最適化などについて触れた．本論文は，今後国際的な取り組みが高まるCO2削減に貢献するパワーエレクトロニクスシステムの開発を加速し，デバイスからシステムまでの全体設計を行うための新しい手法を示したものである．本手法は，これまでその特性を十分に生かしきれていなかったパワーデバイスの特性活用を進め，パワーエレクトロニクスの適用範囲拡大に貢献することが期待される．, 九州工業大学博士学位論文 学位記番号：工博甲第542号 学位授与年月日：令和4年3月25日, 令和3年度},
 school = {九州工業大学},
 title = {Novel TCAD-based Signal-Flow Graph Approaches for the Stability Analysis of Power Semiconductor Devices},
 year = {},
 yomi = {コウノ,  ヒロシ}
}