新型纳米器件的电学特性和可靠性研究

【作者】 刘志英；

【导师】 黄大鸣； 张世理；

【作者基本信息】 复旦大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 集成电路按照摩尔定律和按比例缩小的规律持续发展。在器件小型化的过程中,出现了许多新的问题。其中,纳米MOSFET的关键可靠性问题：偏压温度不稳定性(Bias Temperature Instability或BTI),便是其中之一。另外,传统Si工艺正在接近物理极限。因此,各种新型电子器件应运而生。其中,基于碳纳米管网络的薄膜晶体管(Carbon Nanotube Network-based Thin-Film Transistors或CNN-TFTs)以其优良的电学性能、工艺可控性和独特的柔性引起了广泛关注。随着新材料、新工艺和新器件的开发,传统的电学测量手段在纳米器件的研究中也面临很多新的问题,例如BTI中恢复效应的准确表征,目前在国际上尚未很好地解决。除此之外,对新型纳米器件CNN-TFT的电学特性如栅电容和迁移率也缺乏深入的研究。本论文针对新型纳米器件的制备、表征方法、电学特性以及可靠性展开前瞻性的研究。具体内容包括：(1)针对纳米MOSFET中BTI效应的恢复现象,我们建立了快速脉冲ID-VG测量(Fast Pulsed Measurement或FPM)系统,用于表征应力过程中的阂值电压漂移(△Vt)；发展了改进的电荷泵(Modified Charge Pumping或MCP)方法,用于准实时地测量应力下产生的界面态(△Nit)。(2)结合上述新型测量方法,我们系统地研究了纳米MOSFET的BTI效应,包括pMOSFET的NBTI、pMOSFET的PBTI、nMOSFET的NBTI和nMOSFET的PBTI效应。(3)我们采用滴涂工艺和光刻技术,制备了CNN-TFTs.并且结合交变脉冲ID-VG和C-V测量方法,系统地研究了CNN-TFT的栅电容和转移特性。论文工作的主要结果有：(1)结合FPM和MCP两种方法,我们定量地区分了各种不同应力条件下,纳米MOSFET中界面态和氧化层电荷对BTI的贡献。(2)我们发现在BTI中,除了界面态的影响,氧化层电荷的俘获/释放效应也很重要,在建立BTI模型中必须加以考虑。(3)结合交变脉冲ID-VG和C-V测量,我们获得了无电滞特性的CNN-TFT的转移曲线,给出了器件栅电容随碳纳米管密度的变化关系。在此基础上,建立了一种提取CNN-TFT沟道迁移率的新的方法。论文工作为新型纳米器件的制备、电学表征、特性分析和可靠性研究提供了新的方法、模型和结果,对新型纳米器件的研究开发具有重要的科学意义和应用价值。更多还原

【Abstract】 The Moore’s Law and the rule of scaling-down have been the guiding principles for the development of Integrated Circuits (ICs) over the last 50 years. With the geometric shrinkage, many new effects appear, such as the most important reliability issue of nano MOSFETs-Bias temperature instability (BTI). In addition, traditional Si technology is approaching its physical limit and a variety of innovative electronic devices emerge. As one among them, carbon nanotube network based thin-film transistors (CNN-TFTs) have gained enormous attentions for their superior electrical properties, improved process controllability and unique flexibility.With the development of novel materials, technology and devices, the conventional electrical characterization methods face many new challenges, such as the characterization of the recovery effect in BTI, which are still not well-dissolved yet. In addition to the characterization methods, the electrical properties of the emerging deceives, for instance, the effective gate capacitance (CG) and the carrier mobility (μ) of the CNN-TFTs are still lack of complete studies.This thesis has launched some frontier researches mainly focusing on the fabrication, electrical characterization, electrical properties, and reliability of the nano-devices. It includes:(1) For the recovery effect of BTI in nano-MOSFETs, much effort was spent on building a new type of fast pulsed ID-VG measurement (FPM) system to accurately extract the stress induced threshold voltage shift (ΔVt) and developing a modified charge pumping (MCP) method to quasi real-time examining the generations of interface trapped charges (ΔNit). (2) By the new measurement techniques, the BTI effects of nano-MOSFETs have been systematically studied, including all four different configurations:NBTI of pMOSFETs, PBTI of pMOSFETs, NBTI of nMOSFETs and PBTI of nMOSFETs. (3) By the combination of drop-casting process and lithography technique, CNN-TFTs were fabricated. A pulsed ID-VG method with gate pulses of alternating polarities (AP) and conventional C-V measurements were innovatively employed to the CNN-TFTs. we have systematically investigated the effective gate capacitance and the transfer characteristics of the CNN-TFTs. Our main results are:(1) Combing FPM and MCP methods, we have quantitatively decomposed the contributions of interface trapped charges and oxide charges in BTI effects of nano-MOSFETs under different stress conditions. (2) We found that:in BTT effects, expect for the influence from interface traps, the contribution from the trapping/detrapping of oxide charges is also curial, which must be taken into account when modeling BTI effects. (3) With the AP pulsed ID-VG and C-V measurements on CNN-TFTs, we have obtained hysteresis-free transfer characteristics and the strong correlation between the gate capacitance and nanotube density. Based on these, a new methodology to obtain the apparent carrier mobility has been established.These studies have provided new methods, models and results for device fabrication, electrical characterization, electrical property analysis and reliability evaluation of nano-MOSFETs. It is of important scientific significance and practical value for the research and development of emerging devices.更多还原