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Interpretation and Regulation of Electronic Defects in IGZO TFTs Through Materials & Processes

机译：通过材料和工艺解释和调节IGZO TFT中的电子缺陷

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摘要

The recent rise in the market for consumer electronics has fueled extensive research in the field of display. Thin-Film Transistors (TFTs) are used as active matrix switching devices for flat panel displays such as LCD and OLED. The following investigation involves an amorphous metal-oxide semiconductor that has the potential for improved performance over current technology, while maintaining high manufacturability. Indium-Gallium-Zinc-Oxide (IGZO) is a semiconductor material which is at the onset of commercialization. The low-temperature large-area deposition compatibility of IGZO makes it an attractive technology from a manufacturing standpoint, with an electron mobility that is 10 times higher than current amorphous silicon technology. The stability of IGZO TFTs continues to be a challenge due to the presence of defect states and problems associated with interface passivation.;The goal of this dissertation is to further the understanding of the role of defect states in IGZO, and investigate materials and processes needed to regulate defects to the level at which the associated influence on device operation is controlled. The relationships between processes associated with IGZO TFT operation including IGZO sputter deposition, annealing conditions and back-channel passivation are established through process experimentation, materials analysis, electrical characterization, and modeling of electronic properties and transistor behavior. Each of these components has been essential in formulating and testing several hypotheses on the mechanisms involved, and directing efforts towards achieving the goal. Key accomplishments and quantified results are summarized as follows:;• XPS analysis identified differences in oxygen vacancies in samples before and after oxidizing ambient annealing at 400 °C, showing a drop in relative integrated area of the O-1s peak from 32% to 19%, which experimentally translates to over a thousand fold decrease in the channel free electron concentration.;• Transport behavior at cryogenic temperatures identified variable range hopping as the electron transport mechanism at temperature below 130 K, whereas at temperature greater than 130 K, the current vs temperature response followed an Arrhenius relationship consistent with extended state transport.;• Refinement of an IGZO material model for TCAD simulation, which consists of oxygen vacancy donors providing an integrated space charge concentration NVO = +5e15 cm-3, and acceptor-like band-tail states with a total integrated ionized concentration of NTA = -2e18 cm-3. An intrinsic electron mobility was established to be micron = 12.7 cm2/V·s.;• A SPICE-compatible 2D on-state operation model for IGZO TFTs has been developed which includes the integration of drain-impressed deionization of band-tail states and results in a 2D modification of free channel charge. The model provides an exceptional match to measured data and TCAD simulation, with model parameters for channel mobility (microch = 12 cm2/V·s) and threshold voltage (V T = 0.14 V) having a close match to TCAD analogs.;• TCAD material and device models for bottom-gate and double-gate TFT configurations have been developed which depict the role of defect states on device operation, as well as provide insight and support of a presented hypothesis on DIBL like device behavior associated with back-channel interface trap inhomogeneity. This phenomenon has been named Trap Associated Barrier Lowering (TABL).;• A process integration scheme has been developed that includes IGZO back-channel passivation with PECVD SiO2, furnace annealing in O2 at 400 °C, and a thin capping layer of alumina deposited via atomic layer deposition. This process supports device stability when subjected to negative and positive bias stress conditions, and thermal stability up to 140 °C. It also enables TFT operation at short channel lengths (Leff ~ 3 microm) with steep subthreshold characteristics (SS ~ 120 mV/dec).;The details of these contributions in the interpretation and regulation of electronic defect states in IGZO TFTs is presented, along with the support of device characteristics that are among the best reported in the literature. Additional material on a complementary technology which utilizes flash-lamp annealing of amorphous silicon will also be described. Flash-Lamp Annealed Polycrystalline Silicon (FLAPS) has realized n-channel and p-channel TFTs with promising results, and may provide an option for future applications with the highest performance demands. IGZO is rapidly emerging as the candidate to replace a-Si:H and address the performance needs of display products produced by large panel manufacturing.
机译：消费类电子产品市场的近期兴起推动了显示器领域的广泛研究。薄膜晶体管（TFT）用作LCD和OLED等平板显示器的有源矩阵开关器件。以下研究涉及一种非晶态金属氧化物半导体，该半导体具有比现有技术更高的性能，同时又保持了较高的可制造性。铟镓锌氧化物（IGZO）是一种商业化的半导体材料。从制造的角度来看，IGZO的低温大面积沉积兼容性使其成为一种有吸引力的技术，其电子迁移率是当前非晶硅技术的10倍。由于存在缺陷状态和与界面钝化有关的问题，IGZO TFT的稳定性仍是一个挑战。本论文的目的是进一步了解缺陷状态在IGZO中的作用，并研究所需的材料和工艺将缺陷调整到可以控制对设备操作的相关影响的水平。通过工艺实验，材料分析，电特性以及电子特性和晶体管行为的建模，可以建立与IGZO TFT操作相关的工艺之间的关系，包括IGZO溅射沉积，退火条件和反向沟道钝化。这些要素中的每一个对于制定和检验所涉及机制的若干假设以及指导实现目标的努力都是至关重要的。关键成就和量化结果总结如下：•XPS分析确定了在400°C下进行环境退火氧化前后样品中氧空位的差异，表明O-1s峰的相对积分面积从32％下降至19 ％，这在实验上转化为沟道自由电子浓度降低了1000倍。；•在低温下的传输行为将可变范围跳跃确定为低于130 K的温度下的电子传输机制，而在高于130 K的温度下，电流与温度响应之​​间的关系遵循与扩展态传输相一致的Arrhenius关系。；•完善了用于TCAD模拟的IGZO材料模型，该模型由氧空位供体组成，提供了积分的空间电荷浓度NVO = + 5e15 cm-3，并具有受体样带尾态，总积分电离浓度为NTA = -2e18 cm-3。建立的本征电子迁移率为微米= 12.7 cm2 / V·s。；•已开发出适用于IGZO TFT的SPICE兼容2D导通状态操作模型，该模型集成了带尾态的漏极-去离子去离子和导致免费频道费用的2D修改。该模型提供了与测量数据和TCAD模拟的出色匹配，其通道迁移率（microch = 12 cm2 / V·s）和阈值电压（VT = 0.14 V）的模型参数与TCAD类似物非常匹配。已开发出用于底栅和双栅TFT配置的器件模型，该模型描述了缺陷状态在器件操作中的作用，并提供了对DIBL假设假设的洞见和支持，例如与反向通道接口陷阱相关的器件行为不均匀性。这种现象已被称为陷阱关联势垒降低（TABL）。；•已开发出一种工艺集成方案，其中包括使用PECVD SiO2进行IGZO反向通道钝化，在400°C的O2中进行炉退火以及沉积氧化铝薄覆盖层通过原子层沉积。此工艺可在受到负和正偏置应力的情况下支持器件的稳定性，以及高达140°C的热稳定性。它还使TFT能够在短沟道长度（Leff〜3 microm）处具有陡峭的亚阈值特性（SS〜120 mV / dec）。;在IGZO TFT的电子缺陷状态的解释和调节中，这些贡献的细节也将一一列举。在文献报道中最好的器件特性的支持下。也将描述利用非晶硅的闪光灯退火的补充技术上的其他材料。闪光灯退火多晶硅（FLAPS）已实现n沟道和p沟道TFT，并取得了可喜的结果，并可能为性能要求最高的未来应用提供一个选择。 IGZO正迅速成为替代a-Si：H并满足由大型面板制造生产的显示产品的性能需求的候选者。

著录项

  • 作者

    Mudgal, Tarun.;

  • 作者单位

    Rochester Institute of Technology.;

  • 授予单位 Rochester Institute of Technology.;
  • 学科 Electrical engineering.;Materials science.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 252 p.
  • 总页数 252
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 公共建筑;
  • 关键词

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