| Summary: | 碩士 === 國立中興大學 === 光電工程研究所 === 104 === The last fifteen years have witnessed a phenomenal growth in thin film transistor (TFT) technology, driven by an insatiable demand for larger and larger displays. Indeed the flat panel display has been making rapid progress in providing interactive information retrieval as opposed to one-way information delivery. To keep up with this paradigm shift, the display must integrate in situ sensors to detect the external signal and yet maintain the thin and large area form factor, high resolution at low cost. In order to meet these myriad of technological challenges, there has been an active interest in high performance sensors based on the TFT structure, for process compatibility with the switching TFT in active matrix and offer the interactive solution. For the next generation display, a promising alternative is the photo sensing approach since it has the potential to eliminate RC delay issues, as long as the photo-sensor has high responsivity and high sensing speed enabling high frame rate applications. Most of the time because the displays are placed in visible light, the application in visible range is the most direct way.
In this work, we fabricated visible light phototransistors based on the integration of graphene nano-clusters(called graphene dots following) as light absorption layer by sol-gel and the active semiconductor layer of amorphous indium−gallium−zinc−oxide (a-IGZO) in conventional bottom-gate TFT configuration. Phototransistors can have high gain through the transistor action. So, performance of pristine a-IGZO TFTs will play an important role in graphene dots/a-IGZO phototransistors. Thus, we discussed electricity characteristics of a-IGZO TFTs depend on thicknesses of a-IGZO and oxygen ratio at deposition process. We discovered thicknesses 40nm and oxygen ratio 0.2% at deposition process are the best process conditions for a-IGZO TFT. In addition to the performance of a-IGZO, graphene dots concentration also a key to graphene dots/a-IGZO phototransisitors. Excessive and/or too little graphene dots concentration will effect the photogenerated carriers density in phototransistor, especially in the near ultraviolet range (405nm). We observed the phototransisitors were spin-coated graphene solution concentration 0.1wt%, exhibited the best sensing capability in the visible range. Under illumination, applied bias VDS = 10V and VGS = -1V. The photoresponsivity achieve 124.3 A/W in 405nm, 1.8 A/W in 532nm, and 0.058 A/W in 650nm. In dynamic photosensing measurement, under short-wave illumination(405nm), the response times is decreased , which is contributed to the photogenerated electrons inject from graphene dots.
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