- 學位論文
非晶相銦鎵鋅氧化物光學特性分析及雙閘極薄膜電晶體穩定度測試
Optical Analysis and Reliability Testing of Dual gate Thin-Film Transistor of Amorphous Indium-Gallium-Zinc-Oxide
摘要
近年來，利用非晶相銦鎵鋅氧化物(α-IGZO)做為薄膜電晶體(TFT)通道材料於Active Matrix Organic Light Emitting Diode (AMOLED)已經成為研究的趨勢。相較於傳統的非晶矽薄膜電晶體(α-Si TFTs)，α-IGZO有高的開/關比(on/off ratio) > 108和電子遷移率(Carrier Mobility) > 10 cm2/V-s。在製程上，可以在室溫中利用RF-sputter沉積通道材料α-IGZO並且可以有效的控制薄膜的均勻性。因此， α-IGZO 是下一代薄膜電晶體很好的通道材料。 在α-IGZO薄膜特性上，會隨著不同的成長環境以及退火處理有所差別。這樣的差別在不僅在對於電性操作會有很大的影響，甚至可從其光特性表現看出變化。我們利用廣波長的光源，量測在不同波段α-IGZO薄膜的吸收係數。配合Tauc plot的作圖計算，定義出α-IGZO薄膜的光能帶隙 (optical band gap)，並計算出α-IGZO薄膜的Urbach energy 以分析不同製程參數下的tail states分布。 對於元件穩定度測試，探討由於偏壓應力施加導致元件失真的原因以及物理機制。我們將對元件做一系列的量測分析，例如：電性分析、偏壓應力分析等等。然而，元件的可靠度測試以及物理特性分析就變得特別重要，對於N型α-IGZO TFTs而言，本研究將對於元件NBTI以及PBTI做基本的測試，並探討元件電性衰減的物理機制。對於下列量測方式與結果的分析對於元件的穩定度非常重要。然而，在先前已發表的文獻中已提出幾項原因以及模型理論，例如：電荷被氧化層捕捉、能帶間產生新的缺陷分布等等，解釋偏壓應力產生的臨界電壓偏移、汲極電流、電子遷移率次臨界斜率的衰退。在本研究上，將對於α-IGZO薄膜電晶體正偏壓和負偏壓的穩定度測試做詳細的量測以及分析。本研究使用負偏壓或於上閘極絕緣層中儲存負電荷可將通道中載子推離遷移率低之通道層並屆此增強通道載子遷移率。
並列摘要
Recently, there has been increasing interest in amorphous indium – gallium - zinc oxide (α-IGZO) thin-film transistors (TFTs) for Active Matrix Organic Light Emitting Display (AMOLED). The α-IGZO TFTs have higher on/off current ratio and higher carrier mobility as compared to amorphous Si (α-Si) TFTs, and is suitable for the high performance applications. The defects within the bandgap especially tail states and shallow states affect the electrical characteristic of α-IGZO TFTs. The absorption coefficient measurement is used to measure the width of tail states (Urbach energy) and inspect the quality of α-IGZO films in early stage of fabrication. α-IGZO films with different process conditions were analyzed. In convenience to control the threshold voltage of α-IGZO TFT, dual gate TFT is consider to be one of the solutions. We can get larger negative threshold voltage by applying positive bias at top gate and larger positive threshold voltage by applying negative bias at top gate. Thus the instability test for dual gate α-IGZO TFT has become an important issue. The characteristics of α-IGZO TFT such as SS, mobility, Ion, and on/off ratio could be affected during instability test. The bottom channel has a higher mobility than the top channel due to the process difference. Either to store negative charges in the top gate insulator or to apply negative bias at the top gate, the electrons in the channel can be pushed toward the bottom SiOX/α-IGZO interface by coulomb repulsion force, and the mobility enhancement is observed. The storage of negative charge in the top insulator can be obtained by applying positive voltage at the top gate for controllable time.