近來，平板顯視用途的領域，利用非晶矽薄膜電晶體當作光感側元件的運用及發展越來越多元化。主要配合主動式液晶顯示器的運用通常需要多加的元件如電阻式、電容式 或是電感式的接觸平板元件，這不僅增加元件的材料成本也相對的影響顯示器的光穿透效率。如果利用平面顯示器前段製程技術上的設計，將光感側元件製作在每一個影像畫素中，利用相同驅動液晶的非晶矽薄膜電晶體來當感測光信號的元件，每一個光信號將透過光感測電晶體被儲存下來，經過循序的電路定址輸出所要的信號，達到所需要的功能。
近幾年許多研究報告提及到，未來影像消費性產品的運用越來越廣，例如掃描器、名片閱讀機、指紋辨識機等。我們都知道，非晶矽的薄膜電晶體在可見光的波長環境下有相當高的光電流輸出，所以將其運用在光感知元件上有其優越之處。在液晶顯示器面板整合光感測元件電路，將可簡單的利用手指、光筆、一般的筆尖或是雷射筆等輸入設備得知感應位置，達到各種不同的運用。當然光感測元件必須具備低的暗電流、高的光電流、高的信號雜訊比或光增益值、靈敏度及反應速度。本篇論文將探討如何提高非晶矽薄膜電晶體光感測元件之光電流與暗電流比值，已達到較高的信號雜訊比及較快的反應速度。
如何提高非晶矽薄膜電晶體光感測元件之光電流與暗電流比值是一大挑戰。本論文利用模擬軟體試圖改變及計算元件的物理參數，即透過各種薄膜電晶體的結構設計來達到我們所需求的目的。在模擬過程中發現透過階梯式的電晶體通道參雜可得到較高的光電流與暗電流比值。除此，利用不同的薄膜電晶體光感測元件設計，如對稱式的、非對稱式的、不同通道的寬度及長度或是電晶體上方製作微小的聚光透鏡等方式。再透過儀器量測及分析的結果，我們可以得到光電流與暗電流比值在白光LED14500lx的曝光強度下大於105至106 。
近幾年相關研究的報告中，和本篇論文得到的光電流與暗電流比值比較，通常晶矽薄膜電晶體光感測元件之光電流與暗電流比值約103左右。此篇論文透過不同結構的討論設計及實際實驗驗證，大大的提高的矽薄膜電晶體光感測元件的限制，相信將來會有更寬廣、更多采多姿的消費性產品運用。

Recently, new imaging devices that take advantage of the TFT array have been developed in the non-display field. The majority of touch-enabled AMLCDs , active matrix liquid crystal display, are based on resistive, capacitive or inductive touch technology. All these solutions require externally added components or screens, which add cost and reduce optical performance. A photodiode integrated into each pixel of the TFT array, or a photoconductive layer formed on the TFT array. In this device, the electric charge is generated in the photo-detective and is stored in the pixel, depending on the outside of light signals. The charge information is then read out as the imaging data by sequential line-addressing.
In consumer application, several types of imaging devices have been reported, for example, the document imager, name card reader, and fingerprint reader. It is well known that a-Si TFTs has a high photocurrent under exposure to visible light. The advantages of the photosensitivity of a- Si TFT is integrated an optical sensor array into the AMLCD display for example for touch location detection by finger, stylus, light pen or laser pointer. So, A good photo sensor should possess low dark-current, high photo- current, high optical gain, high sensitivity and fast response time. In this thesis, we try to use the simulation software to optimize the a-Si TFT device and realize the TFT device.
Enhancing the Photo/dark current of a-Si TFT device that is real challenge. We used the simulation software to evaluate the TFT device and verified some physical of TFT parameters. After work- station simulation, we obtained the gradient of channel doping that can enlarge the photo current because of the electronic field. Otherwise, we design several shapes of the TFT devices, like symmetry structure、non-symmetry structure、differential channel width and length of the TFT devices、micro lens array lie on top of the TFT devices. After analysis of these devices by HP 4156, the best result of photo/dark current is about 5 ~ 6 orders.
Comparing with the previous papers, the common photo/dark ratio is around 3 orders. In this research, we largely improve the performance of Photo sensors. We believe that the consumer application will be further evolved widely base on this development.

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