Reliability of thin-film IGZO transistors for logic and memory applications

In the last decade, oxide semiconductors have emerged as a higher performance replacement for standard amorphous silicon thin-film transistors (TFT’s) in display back-plane and flexible electronics. Among different material candidates, Indium-Gallium-Zinc Oxide (IGZO) is the most promising, providing high performance with large area uniformity, low off-currents and low-temperature processing. As a result of the exceptional electrical characteristics of this material, it is envisaged to use it in applications where standard Silicon technology cannot be employed due to process temperature constraints (power gating in the Back-End of Line) or has fundamental limitations such as leakage current (selector transistors in DRAM arrays). However, the long-term reliability of IGZO devices is one of the most important aspects to be still fully characterized and understood before full deployment.  The aim of this PhD research is hence to study the overall IGZO TFT electrical reliability, targeting both logic and memory applications. To this end, this novel device must be fully characterized and modelled, from which fundamental understanding and possible reliability limitations are extracted, allowing for further process optimization and eventually the employment of these devices in real products. The PhD student will play a key role in understanding the device degradation by combining electrical characterization and modelling. Electrical characterization will take place within imec labs, in which the student will be responsible for developing his measurements routines and analyzing the subsequent measured data. The empirical activity will be followed by a fundamental modelling study. The student will model the defect generation and simulate the degraded devices using state-of-the-art device simulators. All the degradation mechanisms will be integrated within a comprehensive physics-based simulation framework which will be calibrated over a wide range of stress conditions. This approach is expected to shed light on physical mechanisms behind degradation of IGZO transistors and provide unprecedented accuracy for reliability modeling. The student will therefore be able to develop a solid measurement/characterization expertise, but also a deep understanding of the device degradation at the atomistic level.