高效能矽披覆層非晶銦鎵鋅氧化物薄膜電晶體

Abstract

非晶氧化金屬半導體比起傳統的非晶矽半導體而言，由於具有高載子移動率(~10 cm2/Vs)，較低的工作電壓(<5V)，以及其小的次臨界電壓擺幅，近年來被視為深具潛力的半導體材料。其可在低溫(常溫)製程下成膜與高透光的特性，也使得在顯示科技領域上有很好的運用發展性。然而非晶氧化銦鎵鋅薄膜電晶體如果想發展低功率損耗、高頻率操作的電路，則增加其載子移動率，並降低其寄生電容是必要的。 本研究中發現藉由覆蓋層矽的引入會造成載子移動率大幅的提升，推測是a-IGZO主動層中的氧轉移至覆蓋層矽上，使得a-IGZO氧空缺的數目增加，載子濃度大幅提高，導致載子移動率(mobility)變大。因此，我們提出一個加入矽做為覆蓋層的結構來提升元件的特性而不會造成元件效能的折損與漏電，此法可作為一簡單而有效的製程來提升元件效能。另外我們以共濺鍍的方式成長出更高載子移動率的非晶氧化金屬半導體，再搭配上述的覆蓋層矽，並利用改變覆蓋層的覆蓋比例與位置，探討其背後的物理機制。本研究中也試著在不影響電特性的情況下成長保護層，以期能提升元件的穩定度而能實際應用目前的顯示技術上。

With a high mobility (>10 cm2/Vs) than conventional amorphous silicon semiconductor and a low operating voltage (< 5 V) and small sub-threshold voltage swing, amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) draw a lot of attentions. Besides, due to a low temperature process and high transparency, a-IGZO TFTs is suitable to develop on flexible displays. However, when a-IGZO TFTs are developed for low-power consumption, high-frequency operating of circuit, improved electron mobility and a low parasitic capacitance are required. In this study, we found the carrier mobility significantly increase by a silicon capping layer on the back channel. We presume that the oxygen in IGZO films be captured by silicon and transfer to the silicon surface or bulk. Therefore the oxygen vacancy is created to dramatically increase the carrier concentration and leaded the mobility significantly improved. Hence, we propose a structure with silicon capping layer onto the active layer of bottom-gate a-IGZO TFT to provide a powerful solution of enhancement of device performance that would not cause current leakage and performance degradation. The method of Si capping layer is a simple and effective approach to fabricate a feasible metal oxide transistor. Besides, we also use co-sputtered a-IGZO/IZO to improve the mobility, incorporating with the Si capping layer and changing the capping ratio or position to find the physics behind. Moreover, we try to passivate the device without changing the characteristics to improve the stability so that we could apply to the present display technology.