雙閘極氧化物半導體薄膜電晶體應用於X光主動感測陣列之研究

Abstract

生醫光電設備的研究開發，朝向更低成本、更精確及更安全的目標前進。以成熟的薄膜電晶 體(TFT)技術製成主動式X光感測器可降低製作成本，且其感測解析度可精確至30微米，並使用較 安全的低劑量X光。然而，如何進一步降低X光劑量而仍能讀取到此更微弱之訊號，是本計畫欲 克服的課題。 本計畫提出利用新型雙閘極氧化物(IGZO) TFT來建構X射線感測系統。利用雙閘極IGZO TFT 受上下二個閘極控制之效應，以及上閘極電容極小的特性，可利用感光元件將低劑量X光所產生 的微小電荷累積，改變上閘極電壓，再藉由適當的下閘極操作，可使得TFT的輸出電流訊號有較 大的變化。我們可妥善設計電路操作模式，進一步將此電流變化轉換成更高敏感度的變化信號。 為完成整體X光感測系統的設置，考量X光實驗有安全上之顧慮，本計畫擬與加拿大滑鐵盧大 學的Karim 教授團隊進行國際合作。Karim 教授在X光感測領域上有豐富的經驗及設備，將與 Karim 教授協同開發對應之X光感光元件，完成相關電路設計與後端處理系統，並進行X光實測。 此計畫雖以Ｘ光感測器為目標，但其技術重點在極低電荷讀取電路，其應用性不只限於X光 感測，只要找到相對應之感測材料，此電路可應用在其他感測系統上，如UV光、有毒氣體、重 金屬汙染感測等。

The development of bio-medical optics equipments is aiming at lower cost, higher precision, and higher level of safety. Using the well-developed thin film transistor (TFT) technology, the active matrix X-ray sensor can be made at lower cost. In addition, its resolution can be as small as 30um and the X-ray dose can be lowered. However, how to further reduce the X-ray dose but read the small signal is still an issue, which is the goal of this project. In this project, we propose to use a new device of dual-gate indium-gallium-zinc-oxide (IGZO) TFT to make the X-ray sensing system. Since the characteristic of IGZO TFT can be controlled by both the top and bottom gate electrodes and the capacitance of the top gate is very small, the top gate electrode can be used to accumulate the extremely small amount of charge generated by low dose X-ray to induce a significant voltage change at the top gate. By properly operating the bottom gate of the TFT, we can get a more significant current signal. Designing a more advanced circuit, we can further transform the current to a more sensitive signal. In order to implement the X-ray sensing system, considering the safety issue of X-ray experiments, we plan to cooperate with professor Karim at University of Waterloo, Canada. Professor Karim’s group has many years of experience in X-ray sensing and possesses adequate equipments. We will work together to develop the sensing devices, circuits, read out system, as well as conduct the system test. Although this project focuses on X-ray sensors, the core techniques of small-charge sensing circuit can be applied to other kinds of sensors such as UV, toxic gases, heavy metal contaminations, …etc., if appropriate sensing materials are applied.