Study on the Amorphous Indium – Gallium – Zinc Oxide Flexible Thin Film Transistors and High performance Phototransistors

• Main Authors: Hsin-Cheng Lai, 賴信誠
• Other Authors: 裴靜偉
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/66026744705629871560

博士 === 國立中興大學 === 電機工程學系所 === 103 === Flexible flat panel display (FPD) has been recently attracting extensively attention due to its light-weight, cheaper, rugged in shape and potentially rollable based on the plastic substrate. However, the low mobility and high processing temperature of hydrogenated amorphous Si (a-Si:H) limit the flexible can only rugged and fabricate on expensive plastic substrate. In this thesis, we demonstrate an flexible amorphous Indium-Gallium-Zinc Oxide (a-IGZO) thin-film transistor (TFT) on polyethylene naphthalate (PEN) plastic substrate. The a-IGZO TFT could be operated well with almost unchanged performance after banding at radius of 4 mm (strain~1.5%) for more than 100 times. This was implemented the utilization of polymer gate dielectric, poly(4-vinylpheonol) (PVP). The PVP was then demonstrated with no damage after plasma process equivalent the the a-IGZO deposition process. Due to the large Young’s modulus difference, the stress was believed mainly within polymer gate dielectric. Therefore, after bending, the a-IGZO was not damaged.The mobility could be further increase by fine-tuning the a-IGZO deposition condition. The Al2O3 nanoparticles were incorporated into polymer as a nanocomposite dielectric for used in a flexible a-IGZO TFTs on a polyethylene naphthalate (PEN) substrate by solution process. The process temperature was well below 100 °C. The a-IGZO TFT exhibit a mobility of 5.13 cm2/V.s. on the flexible substrate. After bending for more than 100 times, the performance of this a-IGZO TFT was nearly unchanged. The electrical characteristics are less altered after positive gate bias stress at 10V for 1,500s. Thus, combing the flexibility and the acceptable performance, this technology is suitable to integrate into Liquid Crystal Display (LCD) or Organic Light-Emitting Diode (OLED) implementing flexible display. In addition, the high performance of a-IGZO TFTs Al2O3 with dielectric demonstrated on glass substrate was investigated. The typical mobility for a-IGZO TFT is 10.2 cm2/V.s. The current on/off ratio and subthreshold swing are 108 and 0.35V/dec., respectively. An a-IGZO layer based thin film phototransistor incorporating Graphene absorption layer was proposed to enhance the responsivity and sensitivity simultaneo usly for photodetection from ultra-violet to visible regime. The spin-coated Graphene dots absorb incident light, transferring electrons to the underlying a-IGZO establish a photo-channel. The 5 A/W responsivity and 1,000 photo-to-dark current ratio were achieved for Graphene phototransistor at 500 nm. As compared to the less than 1 % absorption, the Graphene phototransistor indicates a more than 2700 transistor gain. The highest responsivity and photo-to-dark current ratio is 897 A/W and 106, respectively under 340 nm light illumination. Such an excellent light sensing performance paves a way for high definition image sensors from entertainment to biomedical applications.