AlGaN/GaN HEMTs의 신뢰성 평가와 퇴화 물리학에 관한 연구

Abstract

The widespread adoption of Gallium Nitride High-Electron-Mobility Transistor (GaN HEMT) technology has faced significant challenges, primarily related to its electrical reliability. While GaN HEMTs demonstrate remarkable resilience against a range of electrical overstress conditions, guaranteeing their long-term reliability has emerged as a critical concern. The pivotal parameter for evaluating device longevity, the Mean Time To Failure (MTTF), has often eluded precise estimation, despite extensive long-term reliability tests conducted under varying temperature conditions. This doctoral thesis undertakes a comprehensive exploration of the profound impact of electrical field stress on long-term reliability, with a particular focus on GaN HEMTs. It delves deep into the intricate physical mechanisms underpinning device degradation, with a primary focus on the effects of hot electron-induced trap phenomena and impact ionization. Emphasizing that MTTF values are influenced not only by temperature but also by the specific electric field stress conditions, this research seeks to provide a profound understanding of these degradation mechanisms and their broader implications. This understanding lays the groundwork for the intentional design of device structures that optimize both performance and reliability. To unravel these intricate complexities, a systematic analysis of the degradation of critical parameters in GaN HEMTs, including drain current (IDS), threshold voltage shift (ΔVT), transconductance (GMAX), on-resistance (RON), and gate leakage current (Ig_leak) under various bias conditions within the High-Temperature Operating Life (HTOL) test, is conducted. The unique proposition of a combined acceleration factor that considers both voltage and temperature facilitate precise MTTF determination, recognizing that AlGaN/GaN HEMTs exhibit a complex interplay between electric field/voltage and temperature for reliability. Finally, an in-depth analysis of three distinct HEMT technologies, including hot electron and hot electron-induced impact ionization, reveals that these mechanisms are predominant during On-stress testing and contribute significantly to electrical degradation.