快速表征非晶铟镓锌氧薄膜晶体管的可靠性研究

Recently, amorphous In–Ga–Zn–O thin-film transistors (a-IGZO TFTs) have attracted many interests in the world wide for applications in transparent and flexible electronics, due to their unique characteristics such as good electrical uniformity, high field-effect mobility, visible light transparency, low processing temperature. However, the reliability of a-IGZO TFTs cannot meet the requirements of practical applications and these is a sever measurement delay in conventional methods, which may mislead the understanding of degradations. In this work, we will study the reliability of a-IGZO TFTs by using fast measurement techniques such as fast pulse I-V measurement, where the devices are subjected to stress conditions of bias, illumination, temperature, moisture, and so on. We will obtain comprehensive information of device degradations, distinguish the fast and slow components of degradations caused by the trapping effect and thus build the comprehensive physical model. We will clarify the micro-mechanism of carrier trapping induced by the optical excitation. We will understand the possible mechanism of interface trapping for devices degraded under the conditions of bias stress, temperatures, environment, etc. This will provide us with helpful scientific basis and solutions for improving the device performance.

近来，非晶铟镓锌氧薄膜晶体管由于电学均匀性好、高场迁移率、可见光透明、低温工艺等优异特性在透明和柔性显示中具有重要的应用价值，在世界范围内引起了广泛的兴趣。然而，非晶铟镓锌氧薄膜晶体管的可靠性仍然不能满足实际应用的要求，并且传统测量方法存在严重延迟而使得我们对器件的退化机理产生偏颇的理解。本项目针对非晶铟镓锌氧薄膜晶体管在偏压、光照、温度、水气等应力条件下的器件性能退化存在严重低估的实际情况，采用新的快速测量手段进行表征，以获取器件退化的完整信息，在此基础上建立可靠性物理模型。通过采用新的测量手段（如快速脉冲I-V测量等）来评估器件性能变化情况，深入全面地理解造成器件性能退化的陷阱电荷俘获的快慢成分；阐明光照偏压应力下的载流子俘获及光激发引起的缺陷俘获的微观机理；理解界面态电荷俘获与光照、温度等内在作用机制，最终为改善器件性能提供科学依据和解决思路。

本项目针对金属氧化物半导体非晶铟镓锌氧薄膜晶体管(a-IGZO TFTs)的可靠性问题，研究了偏压应力、光照应力、工艺退火条件等对器件稳定性的影响，并对作用关系和物理机制进行了深入探讨。探究了非晶铟镓锌氧薄膜晶体管在正偏栅压应力(PGBS)和负偏栅压应力(NGBS)下的退化行为，分析并提出了相应的物理机制来解释退化现象。结果表明在PGBS下，器件的阈值电压发生正向漂移，这是由于电荷注入和电荷俘获效应共同造成的；在NGBS下，阈值电压的负向漂移是由电荷俘获效应引起的。阐明了a-IGZO TFTs在恢复阶段电学特性的变化规律，即施加PGBS后撤除应力，发现器件的阈值电压仍有轻微的正向漂移，这是由于被栅绝缘层中的缺陷俘获的电子在回到沟道层前会被界面处的缺陷俘获并重新分布或者是因为在表征器件电学特性的过程中诱导了一些电子俘获。在施加NGBS后撤除应力的情况下，器件的阈值电压发生了正向漂移，这是因为声子辅助电荷脱陷造成的。进一步，我们研究了低热预算微波退火（MWA）工艺对对a-IGZO TFTs器件性能及电学稳定性的作用，并系统地进行了PGBS和NGBS测试。研究结果表明，840 W-MWA器件具有最佳的电学稳定性。这些发现为制造高性能金属氧化物 TFTs 提供了非常有用的策略，尤其是在低热预算的情况下。此外，由于a-IGZO有源层能有效吸收微波能量，因此具有低热预算的MWA不仅可以提高器件性能和可靠性，同时也降低了制造成本。研究结果将为改善对氧化物薄膜晶体管器件性能提供科学依据和解决思路。