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URN etd-0615118-154724
Author Bo-Wei Chen
Author's Email Address No Public.
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Department Electro-Optical Engineering
Year 2017
Semester 2
Degree Ph.D.
Type of Document
Language English
Title Development and Physical Mechanisms Establishment of Flexible Thin Film Transistors
Date of Defense 2018-07-06
Page Count 129
Keyword
  • Self-Heating Effects
  • Flexible Display
  • Low Temperature Polycrystalline Silicon
  • Mechanical Bending Stress
  • Negative Bias Temperature Instability
  • Thermal Expansion Stress
  • Abstract Recently, flexible thin film transistor applications are widely used, both academics and industry have invested considerable resources in research and development. From the application depth of the flexible display, the application of small curvature (R = 2mm) bending and high resolution is still not yet mature. From the application breadth, the application of the repetitive mechanical bending and fully flexible applications also have a lot of room for progress.
    The first section of this dissertation will discuss the performance and reliability issues of the low-temperature polysilicon fabricated on the polyimide substrate. The Poly-Si TFTs fabricated on Polyimide will face several challenges. For example, coefficient of thermal expansion (CTE) of polyimide is higher than the glass, which means that in the process of the temperature will produce thermal expansion and then the TFT Poly-Si and gate insulator (GI), which can affect the performance and reliability (NBTI). Therefore, the thickness of the buffer layer is adjusted to alleviate the substrate thermal expansion of the deterioration.
    The second section systematically studies high current-induced effects, hot-carrier effects, and self-heating effects in flexible low temperature polycrystalline silicon thin film transistors (LTPS TFTs) fabricated on polyimide (PI). By utilizing I-V and various-frequency C-V measurements, the exact location of defects generated by self-heating effects can be clarified
    In the third section, we are going to discuss the degradation mechanism of flexible LTPS TFTs after undergoing long-term bend mechanical stress. This section investigates the stress distribution while undergoing long-term mechanical stress and the influence of stress on electrical characteristics. Surface morphology in polycrystalline silicon (poly-Si) film is an issue regardless of whether conventional excimer laser annealing (ELA) or the newer metal-induced lateral crystallization (MILC) process is used To eliminate the influence of surface morphology in poly-Si, three kinds of laser energy density were used during crystallization to control the protrusion height.
    The fourth section investigates the effect of repeated uniaxial mechanical stress on bias-induced degradation behavior in polycrystalline thin film transistors. After 10,000 and 100,000 iterations of channel-width-direction mechanical compression, serious threshold voltage degradation and an abnormal hump are observed.
    The fifth section investigates flexible low temperature polycrystalline silicon thin film transistors suffer from strong mechanical stress and demonstrate severe degradation of electrical characteristics at bending radii smaller than 2mm. Our previous study showed repetitive mechanical bending damages the gate insulator, causing carriers to trap into it. Here, degradation after channel width-axis direction bending was found to be more pronounced than after channel length-axis bending. In order to alleviate this degradation, an organic structure flexible LTPS TFT was proposed to enhance mechanical stress endurance.
    Advisory Committee
  • Jeng-Tzong Sheu - chair
  • Hung-Che Liao - co-chair
  • Ting-Chang Chang - co-chair
  • Hung-Wei Li - co-chair
  • Terry Tai-Jui Wang - co-chair
  • Yu-Ju Hung - advisor
  • Files
  • etd-0615118-154724.pdf
  • Indicate in-campus at 3 year and off-campus access at 3 year.
    Date of Submission 2018-07-15

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