主動矩陣式有機發光二極體顯示器之畫素電路利用薄膜電晶體作為驅動與開關元件，然而採用不同製程的薄膜電晶體元件其臨界電壓會因為主動層材料晶粒特性產生空間性的變異或者因長時間的使用而產生漂移。此外，有機發光二極體材料隨著長時間使用而老化的現象導致臨界電壓上升和發光效率下降以及電源線寄生電阻導致的壓降，皆會造成面板亮度不均勻或衰減。
為了解決上述問題，本論文即提出五個新式畫素補償電路。第一個電路採用非晶矽薄膜電晶體之4T1C畫素架構並結合外部偵測電路，利用自我補償架構補償薄膜電晶體臨界電壓漂移現象，並藉由外部偵測電路預測有機發光二極體元件亮度衰減百分比進而調整驅動電流來補償亮度衰減的現象。藉由量測結果的驗證，可知本電路較傳統2T1C電路具有更高的畫素電流和亮度穩定性。由於目前主動矩陣式有機發光二極體顯示器相關產品所採用的背板主要是以具有較高電子遷移率和穩定性的低溫多晶矽薄膜電晶體為主，然而其空間上不一致的電子特性仍會造成面板亮度不均勻的現象。因此，第二個電路即採用此製程設計3T1C精簡畫素架構以符合高解析度和高開口率面板的需求並且能夠補償驅動薄膜電晶體的臨界電壓變異。由模擬結果可知當驅動薄膜電晶體的臨界電壓變異±0.5 V時，本電路的畫素電流相對誤差在所有資料電壓範圍之內皆在1.2%以下。第三個電路則是可適用於三維顯示模式之4T1C畫素架構並結合同步式發光驅動法以及交流式反向偏壓法來改善有機發光二極體元件亮度衰減現象。由模擬結果可知在240 Hz之高速三維顯示模式操作下，本電路可有效改善驅動薄膜電晶體的臨界電壓變異以及電源線寄生電阻所造成的影響。此外，由實驗結果可知本電路所採用的交流式反向偏壓法可有效增長有機發光二極體元件的生命週期。此外，由於目前大部分的電壓式畫素補償電路皆無法有效改善低溫多晶矽薄膜電晶體元件其電子遷移率變異所造成的影響，本論文第四個電路即採用3T2C電壓式畫素補償架構來改善電子遷移率變異所造成面板亮度不均勻的現象。藉由實際量測電路操作中驅動電晶體各節點電壓的暫態波形以及相關模擬結果可知本電路確實可同時補償低溫多晶矽薄膜電晶體的臨界電壓和電子遷移率變異。此外，本電路也可改善電源線寄生電阻所造成的影響進而達到高面板亮度均勻性的目標。至於論文中的第五個電路則是採用非晶相銦鎵鋅氧化物薄膜電晶體 結合同步式發光驅動法設計適用於三維顯示模式之精簡3T1C畫素架構。由模擬結果可知本電路可成功補償增強/空乏型之非晶相銦鎵鋅氧化物薄膜電晶體的臨界電壓漂移，且當驅動薄膜電晶體的臨界電壓變異±1 V時，本電路的畫素電流相對誤差在所有資料電壓範圍之內皆在2%以下。總結來說，第一個電路因為必須實現較複雜之外部系統因此在實際應用上會有成本較高之缺點。至於第二、三、四個電路，因為採用低溫多晶矽薄膜電晶體且具有精簡的畫素架構因此可適用於高解析度的顯示器產品上。由於非晶相銦鎵鋅氧化物薄膜電晶體跟低溫多晶矽薄膜電晶體比較起來，具有較均勻的電性、較好之尺寸可伸縮性、以及較低之漏電流，因此採用此新式薄膜電晶體製程的第五個電路可望使得三維顯示模式之主動矩陣式有機發光二極體顯示器的畫面品質更加細緻。

For active-matrix organic light-emitting diode (AMOLED) displays, the pixel circuit utilizes thin film transistors (TFTs) as the driving and switching components. However, variation in the threshold voltage (VTH) of the driving TFT due to inherent grain boundaries or long-term operation, and luminance decay caused by OLED degradation as well as power line current-resistance (IR) voltage drop directly influence the image quality of the AMOLED displays.
This dissertation proposes five novel pixel circuits and verifies their effectiveness by simulations and experiments. The first pixel circuit is a 4T1C hydrogenated amorphous silicon (a-Si:H) structure that compensates for the threshold voltage shift of TFT using an internal compensated structure and reduces luminance decay by external detection method, based on the interdependence between the luminance degradation of OLED and the decrease in current under constant voltage bias stress. Experimental results demonstrate that the luminance of the OLED device with the proposed external detection method is more stable than that with the conventional 2T1C pixel circuit. Due to high mobility and stability of low-temperature polycrystalline-silicon thin film transistors (LTPS TFTs), the second 3T1C structure uses all p-type TFTs for panel requirements of high resolution and high aperture ratio. According to the results of a simulation, over the entire range of tested data voltages (4.5 to 2.5 V), the relative errors of the OLED current of the proposed circuit are below 1.2% when the driving TFT threshold voltage varies from 0.5 to -0.5 V. The third pixel circuit is a 4T1C LTPS structure with a novel driving scheme that is based on the simultaneous emission and reverse-biased methods. During high-speed three-dimensional (3D) operation at 240 Hz, the proposed circuit can successfully compensate for the TFT threshold voltage variation and improve the effects of IR voltage drop in the power line. Simulation and experimental results confirm the stability of the OLED current and the amelioration of the OLED lifetime. Since most prior voltage-programmed methods can not solve the impacts of mobility variation in LTPS TFTs, the fourth 3T2C pixel circuit uses the voltage-programmed method to compensate for the electrical characteristic variations in LTPS TFTs and the IR voltage drop in the power line. Based on the measurement results of the transient waveforms of the source and gate nodes in the driving TFT, the functionality of the proposed pixel circuit can be operated correctly during each operation phase. Moreover, the simulation results demonstrate that the pixel current exhibits high uniformity against the threshold voltage and mobility variations in TFTs. As for the last pixel circuit, an amorphous indium-gallium-zinc-oxide (a-IGZO) pixel circuit with 3T1C structure is proposed for large-sized and high-resolution 3D AMOLED displays. The proposed pixel circuit can compensate for the threshold voltage shifts in both enhancement-mode and depletion-mode a-IGZO TFTs. Based on the simulation results with ±1 V threshold voltage shifts of the driving TFT, the relative errors of the OLED current are less than 2% for the entire range of tested data voltages.
In conclusion, a complex external system must be designed to achieve practical application of the first pixel circuit, ultimately increasing the system costs. The second, third, and fourth pixel circuits use LTPS TFTs and a simple structure for the application of high-resolution displays. The last pixel circuit is promising for use in large-sized and high-resolution 3D AMOLED displays, owing to its improved large area uniformity, superior scalability with a low production cost, and lower leakage current than LTPS TFTs.

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