應用於主動畫素感測器 之元件的雜訊分析與補償方法

Abstract

主動畫素感測器因可將感測電壓加以放大，故可提供較強的輸出訊號，但仍需符合高解析度及低雜訊的要求。由於輸出訊號受畫素感測電路中薄膜電晶體間的差異如截止電壓偏移或載子移動率不同等的影響，會造成感測誤差，需要加以補正。此外，目前有數種薄膜電晶體技術可供選擇，我們以雜訊的觀點來比較其特性。 本篇論文研究重點有兩個部分，第一部分對不同材質之電晶體雜訊加以量測及分析，之後利用其提出之雜訊公式計算各個受測元件的訊雜比值，並且說明何種材料的電晶體具有較好的特性，以利用於電路設計。第二部分則基於利用兩個薄膜電晶體、兩個儲存電容以及兩條控制掃描線的最簡設計下，提出輸入已知電流的校正方法，以達到補償截止電壓、載子移動率等元件變動的目的，並利用實際操作來驗證其功能。 經由此研究，我們可確認此高解析度、高敏感性與高精確度的主動式感測電路設計，並以所提出的元件雜訊分析的方法，判斷出最適合感測電路使用的薄膜電晶體技術。

The active pixel sensor can amplify sensing voltage, and it can provide a stronger output signal. However, it still needs to meet the requirements of high-resolution and low noise. Because the output signal can be affected by the variation of thin film transistor, such as the threshold voltage shift or the difference in mobility, the sensing error can be induced and needs to be corrected. In addition, currently, there are kinds of thin film transistor technologies. Their characteristics are studied in the view point of noise performance. This thesis focuses on two parts. The first is the noise measurement and analysis for the transistors made of different materials. A noise formula is newly proposed to calculate the signal-to-noise ratios for the devices under test. Based on that analysis, we explain how the transistor technology suitable for the application in active pixel sensing circuit can be properly determined. The second part is based on the simplest sensing circuit containing only two thin film transistors, two storage capacitors and two scan lines. The calibration method of applying bias currents is proposed to compensate the variations in threshold voltage, mobility, etc. The method is verified in its function experimentally. In this study, we confirm the active X-ray sensing array can be high resolution, high sensitivity and high accuracy. In addition, the analysis of noise helps to determine the appropriate thin-film transistor technology for the sensing circuit.