主動式有機發光二極體顯示器之畫素電路以薄膜電晶體作為驅動與開關元件，然而薄膜電晶體元件的電氣特性變異，例如臨界電壓的變異或漂移，會導致驅動有機發光二極體的電流產生無法忽視的偏差量。更甚者，有機發光二極體材料會隨著長時間的使用而老化，使得整體面板的亮度下降，進而影響顯示器的使用壽命。目前已經有許多相關畫素補償電路被提出來改善畫面品質及增加使用壽命。由於非晶相銦鎵鋅氧化物薄膜電晶體具有極佳的電氣特性，因此被視為應用於主動式有機發光二極體顯示器的選擇之一。然而不同製程下的非晶相銦鎵鋅氧化物薄膜電晶體會有常關型與常開型兩種不同特性，而常開型的非晶相銦鎵鋅氧化物薄膜電晶體對於畫素電路設計將是相當重要的考慮因素。
本論文針對上述問題提出三個新式畫素補償電路，並且使用HSPICE軟體驗證其性能。第一個提出的電路適用於小尺寸、高解析度的顯示器，其3T2C之電路架構對於低溫多晶矽薄膜電晶體臨界電壓的變異具有相當的抗擾性。從模擬結果可知，當薄膜電晶體臨界電壓變異量為±0.5V時，所有資料電壓對應電流誤差率皆低於5%。然而由於此電路無法補償有機發光二極體的亮度衰減，因此提出第二個採用非晶相銦鎵鋅氧化物薄膜電晶體的5T1C電路，以偵測驅動薄膜電晶體及有機發光二極體臨界電壓的方式，能同時補償常關型與常開型非晶相銦鎵鋅氧化物薄膜電晶體的臨界電壓飄移，並進一步改善有機發光二極體材料老化所造成之亮度衰減。此電路之驅動薄膜電晶體電氣特性被實際量測出來，其電氣特性之模擬數據也被建立來進行HSPICE模擬。由模擬結果可知此5T1C電路之常關型與常開型薄膜電晶體臨界電壓飄移所造成的電流誤差在整個資料電壓範圍內皆低於5%。此外，此電路亦在有機發光二極體劣化時提供額外驅動電流來維持亮度穩定。然而第二個電路結構極易受薄膜電晶體的寄生電容影響而使儲存電容的電壓失真，降低此電路的補償性能。為了提高電路之穩定度，因此提出第三個採用非晶相銦鎵鋅氧化物薄膜電晶體之畫素電路來補償薄膜電晶體的臨界電壓飄移和改善有機發光二極體的亮度衰減。在常關型與常開型驅動薄膜電晶體之臨界電壓飄移1V的情況下，模擬結果顯示第三個電路的電流誤差率皆在3.5%以下。並且在輸入不同資料電壓時的對應亮度誤差在5%以內。根據上述模擬結果，第三個畫素電路展現對元件特性衰減的抗擾性。

For the pixel circuits of active-matrix organic light-emitting diode (AMOLED) displays, thin-film transistors (TFTs) are used as the driving and switching devices. However, variations in the electrical characteristics of TFTs, such as threshold voltage variations and shifts, cause non-negligible deviations in OLED currents. Furthermore, the luminance of OLED devices degrades over time, which shortens the life-time of AMOLED displays. Therefore, several compensating pixel circuits have been developed to improve the image quality as well as extend the life-time of the displays. Recently, the amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs are regarded as one of the candidates employed in AMOLED displays for superior electrical characteristics. While they may be normally-off or normally-on depending on the fabrication process, the normally-on characteristic of the a-IGZO TFTs is a critical issue for the design of the pixel circuits.
This thesis proposes three new pixel circuits and verifies their performance by HSPICE simulations. The first proposed 3T2C pixel circuit has immunity against the threshold voltage variations of the low temperature polycrystalline-silicon (LTPS) driving TFT for small-size and high-resolution AMOLED displays. Based on simulation results, relative current error rates among the entire data voltage range all fall below 5% with ±0.5 V threshold voltage variations of the driving TFT. However, this pixel circuit is incapable of compensation for the OLED luminance drop. Therefore, the second proposed 5T1C pixel circuit adopting a-IGZO TFTs is designed to compensate for both the threshold voltage shift of the driving TFT and luminance drop of the OLED by internally detecting the threshold voltages of the driving TFT and the OLED. The electrical characteristics of the driving a-IGZO TFT are experimentally measured and the simulation parameters are extracted for HSPICE simulations. The simulation results demonstrate that the fluctuations of OLED currents resulting from the threshold voltage shifts of the normally-off and normally-on driving TFTs are suppressed below 5%. Furthermore, the maintenance of the normalized luminance is also achieved by increasing the driving current for OLED. Nevertheless, the structure of the proposed 5T1C pixel circuit is sensitive to the parasitic capacitance of the TFTs, which easily affects the stored voltage in the storage capacitor and therefore reduces the compensation performance of the proposed 5T1C pixel circuit.
To improve circuit stability, the third 5T2C pixel circuit adopting a-IGZO TFTs is proposed with compensations for the threshold voltage shifts of the driving TFT and the luminance drop of OLED. According to simulation results, the current error rates are within 3.5% for the proposed 5T2C pixel circuit, with 1V shift in the threshold voltage of normally-off and normally-on driving TFTs. Moreover, the deviations of the normalized luminance of the proposed pixel circuit fall 5% for different data voltages. Thus, the proposed 5T2C pixel circuit has high immunity against the VTH shifts of a-IGZO driving TFTs and the luminance drop of OLED devices.

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