應用於液晶顯示器之銦鎵鋅氧化物薄膜電晶體與堆疊型矽控整流器之特性研究

Abstract

銦鎵鋅氧化物(InGaZnO, IGZO)薄膜電晶體具有高透光度、高均勻度、低成本以及低製程溫度等優點，由於這些特性可與非晶矽和多晶矽薄膜電晶體相抗衡，因而吸引了許多在顯示器應用方面的關注，另一方面此材料也利於發展可繞性與穿戴式裝置。即使是非晶態銦鎵鋅氧化物都不因無序的結構排列而影響其傳輸特性，其高的驅動電流滿足應用於有機發光二極體、主動陣列式液晶顯示器及主動陣列式有機發光二極體顯示器的需求。一般來說，化合物半導體通常會依其原子成分的相對含量而影響到其元件的載子傳輸特性。然而，在先前我們團隊曾以非晶態的氧化鈦薄膜覆蓋在IGZO薄膜電晶體成功的改善其元件電性。 在此篇論文中，我們證實了低氧含量的氧化鈦薄膜在非晶態的IGZO及IZO薄膜上的氧空缺吸附效應。藉由氧化鈦的吸附效應(gettering effect)，IGZO通道層的氧空缺濃度受到調變且成功大幅增加其載子濃度與載子遷移率。元件電性方面如次臨界擺幅達到79 mV/dec，載子遷移率達到68 cm2/Vs，另外開關的電流比值也來到5.61x106。但IZO通道由於奈米微晶相的產生極缺乏鎵原子的摻雜，在過度的氧化鈦吸附效應後使氧化鈦產生較大的通道寄生電阻，也因而限制了IZO薄膜電晶體的輸出電流。這也顯示在產生吸附效應的過程中，鎵原子扮演了一個重要的角色可穩定氧原子的擴散行為。 此外，我們也研究了結晶性對IGZO薄膜電晶體的影響，我們利用不同In含量的IGZO研究其熱穩定度，當沉積後退火溫度升高到700度C時，結晶狀況更趨明顯且電性也因此改善了，透過X光繞射分析與穿透電子顯微鏡分析，我們得到一個清楚的(0 0 16)繞射峰並觀測得到六重對稱的IGZO層狀結構。元件電性經測量後次臨界擺幅值降低到130 mV/dec與漏電流也減少到2.4x10-14 A/m。 在此論文後段，我們與LCD驅動IC設計公司奇景光電合作研究了應用於電視面板驅動IC內的ESD箝位電路。我們應用了高壓製程中多重井(muti-well)結構於不連續型射極結構的矽控整流器中，成功的解決此技術伴隨的觸發電壓(triggered voltage)上升的問題。另外，藉由電阻觸發堆疊型矽控整流器的技術，我們成功的在0.11微米32V製程製造出一個擁有33.4V高維持電壓的靜電防護電路。其觸發電壓與失效電流分別為51V和3.3A. 根據我們的實驗結果，整合低成本的缺氧型氧化鈦薄膜至IGZO薄膜電晶體中適合未來發展高速且高解析度的平面顯示器。使用電路學的分壓定理，可協助我們設計一個具高栓鎖效應免疫力的矽控整流器於功率箝位電路中執行有效的靜電防護。

InGaZnO thin-film transistor has attracted much attention for TFT-LCD applications because of its superior characteristics such as high transparency, good uniformity, relatively low cost, and low thermal budget compared to the -Si and poly-Si TFTs. These features is benefit to develop flexible or wearable displays. Even in amorphous phase, the device mobility is insensitive to structure disorder. Its high driving capability is more suitable to apply on OLED, AMLCD, and AMOLED products. In general, the transport properties usually have significantly depend on elements composition in compound semiconductors. The relative cation proportion of the cations directly control the back ground carrier concentration within a broad range. In previous study, we had already employed -TiOx layer capped on IGZO TFTs to improve the device electrical performance. However, the detailed mechanism of gettering effect is still unclear and it should be further investigate in other oxide TFTs. In this thesis, we demonstrate the gettering effect of oxygen-deficient TiOx in -IGZO and IZO TFTs by material analysis. After the TiOx gettering process, the oxygen vacancies in IGZO channel were successfully modified and the carrier concentration and device mobility were increased. The superior transfer characteristics such as low sub-threshold swing of 79 mV/decade, high mobility of 68 cm2/Vs, and good on/off-current ratio of 5.61×106. However, the IZO channel showed unfavorable transistor characteristics due to lack of Ga atom doping. After gettering process. IZO film exhibit a nano-crystallized grains in TEM image. The severe oxidized TiOx capping layer leads to an additional channel parasitic resistance that limits the output driving current. Therefore, we believe that the existence of Ga-O bonds among IGZO channel would be helpful to stabilize oxygen diffusion behavior and electric structure during the gettering process. Furthermore, we investigate the impact of orientated crystalline InGaZnO (IGZO) thin film transistor. To evaluate interface thermodynamic stability of temperature-sensitive IGZO film, the film-structural stabilities of high- and low-indium-content InGaZnO were studied. With increasing annealing temperature up to 700 °C, the crystallinity becomes more pronounced and device electrical characteristics are further improved. The off-state leakage is reduced and it can be attributed to the formation of c-axis-orientated crystalline located at the X-ray diffraction peak of (0 0 16). A superior performance improvements include a very low turn-on voltage close to zero voltage, a small subthreshold swing of 130 mV/dec, and a low off-state current of 2.4x10-14 A/μm at low operating voltage of 4 V. At the end of this thesis, we co-work with a LCD driver IC company to study the ESD power clamp circuit which applied on panel driver. A body-tied blocking layer is inserted into the segmented SCR structure to increase the holding voltage and no tradeoff on triggered boltage. By using resistor triggered technique, we successfully obtain a high holding voltage SCR which has Vhold of 33.4V in 0.11m 32V process. Other characteristics such as the Vt1 and It2 are 51V and 3.3A m, respectively. According to our experiment results, the integration of low-cost a-TiOx film into IGZO TFTs are suitable to develop high speed and high resolution FPDs in the future. Using a divided voltage theorem can help us to design a high latchup immunity stacked SCR device in HV ESD power clamp circuit.