| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 106 === With the rapid development of science and technology, Low temperature poly-silicon thin film transistor (LTPS TFTs) play an important role in small and medium-sized panels. The biggest difference between LTPS TFTs and Amorphous- silicon TFTs display is that LTPS speed of operation is faster and better. Besides, LTPS have high luminance, high resolution, low power consumption and lightweight and short. Therefore, LTPS will be the mainstream of small-size wearable display in the future.
It pointed out that reliability has been the research emphases of Low-temperature poly-silicon thin film transistor. Under high bias, high current and light illumination operation can cause electrical characteristic degradation. Especially, hot-carrier effects and self-heating effects. These are important issues in practical TFTs operation.
In this paper, we studies hot-carrier effects and self-carrier effect in p-type flexible LTPS TFTs. Using different measurement, changing sizes of devices and different frequency of operation. Finding out the deterioration caused by different operating environments, and to further analyze and bring up solutions.
In the first part, the abnormal electrical characteristics after Hot-carrier Stress in p-type flexible LTPS TFTs is investigated. It was found out the electrical characteristics changes mainly caused by Hot-carrier induced electron trapping in small channel width. The channel of device become shorter is due to electron trapping in oxide layer, and on current rising let C-V transfer earlier. In addition, OFF current decrease can verify the changing characteristics of the device is due to hot-carrier stress induce electron trapping.
In second part is going to investigate self-heating effect cause characteristics changing in device. The self-heating effect is affected by the size of the channel width. After stress, the negative threshold voltage shift and OFF current decreases mainly caused by Self-heating effect and Hot-carrier effect. As the channel width getting lager, the condition of heat dissipation is poor and the distance from border gets further which make the degradation more obviously. Due to the high current operation, the channel will induce Joule heating and electric field during self-heating stress is strong near the source, and the NBTI is induced that descend the thickness of buffer layer which can abstract the heat effectively. By discussing the condition of Self-heating effect at different substrate further, we found out that the heat conductivity of PI is lower than the Glass. Therefore, the deterioration of PI with Self-heating effect is bigger than Glass.
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