非晶銦鎵鋅氧化物薄膜電晶體之背通道調製效應

Abstract

非晶銦鎵鋅氧化物半導體(a-IGZO)所構成的薄膜電晶體，可在低溫製程(常溫濺鍍)成膜，並具有高於非晶矽薄膜電晶體(a-Si:H TFT)的電子遷移率(>10cm2/VS)，故在顯示科技領域上具有很大運用潛力。此外由於IGZO在大氣環境下非常穩定，複合式IGZO生化感測器(Hybrid IGZO bio-chemical sensor)成為極有潛力之氣體感測器。本研究之感測器結構為原本的金屬氧化物電晶體上多覆蓋生化物質感測層，利用a-IGZO當電子訊號傳輸層，感測層用於提升感測效能，對於特定或多種生化物質(bio-chemical material)具有靈敏的反應。推測反應機制為生化物質與下層的金屬氧化物a-IGZO主動層有載子的轉移，或是a-IGZO載子與具有極性的生化分子之間有電場交互作用，使其能偵測不同生化物質與其濃度。複合式a-IGZO薄膜電晶體具有相當的潛力應用在非侵入性、低成本的呼氣診療上。 此外，a-IGZO 薄膜電晶體的臨界電壓位置可經由一系列不同費米能階的金屬覆蓋層來有效的調變，由於a-IGZO 主動層後通道與不同費米能階之覆蓋層間形成不同程度與極性的電偶極，此會感應出不同的基體電壓(基體效應)來改變元件臨界電壓值。因此，我們提出一個加入金屬覆蓋層的結構來提升元件效能與調變其臨界電壓值而不會造成元件效能的折損與漏電。於此更發現元件遷移率(mobility)可經由覆蓋層的引入而大幅提升，尤其以易氧化之材料提升幅度最大，推測是易氧化的覆蓋層影響a-IGZO薄膜的氧含量，使載子濃度與導電度大幅提升，進而獲得較高的載子遷移率，此方法可應用於目前顯示器的製程技術。

With a high mobility (>10 cm2/Vs) and a low threshold voltage (< 5 V) under a low temperature process, transparent amorphous oxide semiconductor thin-film transistors (AOS TFTs) draw considerable attention due to their applications on flexible displays. Beside, a-IGZO is very stable in atmosphere, which makes it an ideal material in sensor technology. In this study, the sensor structure is based on a-IGZO TFT with an additional sensing layer capped above it. a-IGZO active layer is act as electrical transport layer, and the sensing layer can improve sensitivity significantly to diverse bio-chemical molecules. The sensing mechanism might be due to carrier transfer or field effect interaction between sensing layer and a-IGZO active layer under sensing process and influenced by the concentration of specific molecules. This work opens a route to develop low-cost large-area bio/chemical sensor array based on the commercialized a-IGZO TFT technology. Furthermore, we proposed a structure with capping metal layer onto the active layer of bottom-gate a-IGZO TFT to provide a solution to enhance device performance and threshold voltage modulation, which does not cause leakage current degradation. In addition, the device mobility increases significantly after introducing the metal capping layer, and easily oxidized material caused higher mobility in comparison. It is possibly due to variation of oxygen concentration in a-IGZO film causing higher conductivity and carrier concentration in region near the edge and under capping layer assisting carrier transportation. We also propose a defect reduction effect based on reducing weak-bonded oxygen in a-IGZO film. The results enable the development of a-IGZO TFT for the applications like RFID and display driving.