透明金屬氧化物導體及半導體之成長與光電元件應用

在低溫製程及軟性薄膜電晶體的發展上，透明金屬氧化物半導體薄膜電晶體備受關注。金屬氧化物半導體在非晶態下依然能保持足夠高的載子遷移率，使其可以於較低溫甚至室溫環境下進行製程。此外，其在可見光波段具有高穿透率，可應用於透明電子或提升顯示器的開口率。可低溫製程的介電材質亦是實現低溫製程及軟性薄膜電晶體的重要關鍵，將有機矽分子HMDSO和氧作為前驅物，通入電感式耦合電漿化學氣相沉積(ICP-CVD)系統中以低溫環境成長出的矽基有機-無機複合薄膜具有優良的電性，其漏電流及崩潰電場可媲美PECVD所成長出的SiOx薄膜。在第一部份研究中，我們利用HMDSO所成長之有機-無機複合介電膜應用於下閘極非晶系氧化銦鎵鋅薄膜電晶體(a-IGZO TFT)的閘極介電層、蝕刻停止層及鈍化層，並且利用雙主動層結構成功製作出下閘極薄膜電晶體，得到次臨界斜率小於0.4 V/decade，且電流開關比大於108，具有優良開關特性的電晶體。此外，透明導體對於高效率有機發光二極體 (OLED) 的應用相當關鍵，目前常用氧化銦錫 (ITO) 作為OLED之透明電極，然而其含有昂貴的稀有金屬元素銦，因此須研究替代型之透明導體。此外，若透明導體具高折射率的特性，並搭配合適的元件結構，將可使得元件具有較強微共振腔效應，達到增加外部出光效率之效果。常見的高折射率透明金屬氧化物為二氧化鈦(TiO2)，若在此材料中摻雜鈮(Nb)，將使得成為TixNb1-xO2 (TNO)之材料，並具有一定的導電特性。在第二部份研究中，我們利用濺鍍的方式成長TNO薄膜，並探討其在不同基板溫度、不同氧氣濃度及不同退火氛圍及時間下，TNO薄膜的導電特性、光學特性、結晶結構與表面粗糙度。TNO薄膜電阻率可低至約1.7×10-3 ohm-cm，最後將其應用於OLED元件陽極上，並配合模擬之最佳結構，將外部量子效率比利用ITO為陽極時之元件高約5.5 %，達成可取代ITO電極並同時增加出光效率之效果。

關鍵字

透明氧化物導體；透明氧化物半導體；有機發光元件；薄膜電晶體

並列摘要

In the development of low-temperature-processed and flexible TFTs, transparent oxide semiconductors draw wide attention. Because of their adequate carrier mobility in the amorphous state, they are compatible with low temperature processes. In addition, the high transparency permits it to be applied in transparent displays or raise the display aperture ratio. On the other hand, low-temperature-deposited dielectric films are also key to realize low-temperature and flexible TFTs. Using HMDSO and oxygen as precursors, silicon-base organic-inorganic hybrid films deposited by ICP-CVD provides good electrical properties. The leakage current and breakdown field are comparable with SiOx films grown by PECVD. In the first study, we applied the organic-inorganic hybrid films grown with HMDSO as the bottom gate insulator, the etch-stop layer and the passivation layer in the bottom-gate staggered a-IGZO TFTs with the etch-stop. By adopting the double active layer structure, we successfully realized an a-IGZOI TFT with a subthreshold swing less than 0.4 V/decade and an on/off ratio more than 108. On the other hand, transparent conductors are essential for high-efficiency OLED. The transparent conductor indium tin oxide (ITO) has been extensively used in OLED as the transparent electrodes. However, there is a need to replace currently widely used ITO due to its high cost and rarity. In addition, if transparent conductor has higher refractive index, with suitable device structure to induce appropriate microcavity effects, it will increase the external quantum efficiency (EQE) of OLEDs. The generally high- refractive-index transparent metal oxide, titanium oxide (TiO2), when doped with niobium (Nb), it could provide a high-index transparent conductive oxide TixNb1-xO2 (TNO). In the second study, we investigated sputtering deposition of TNO films using the Ti0.94Nb0.06O2 target. The effects of the substrate temperature, oxygen ratio, annealing atmosphere and annealing time on electrical properties, optical properties, structure, and morphology of deposited TNO films were studied. The resistivity of TNO film is lowered to 1.7×10-3 ohm-cm. OLEDs using TNO as the anode can exhibit 5.5 % higher EQE than OLEDs using the ITO as anode.