具C軸結晶之氧化銦鎵鋅薄膜電晶體特性研究

Abstract

銦鎵鋅氧化物(InGaZnO, IGZO)薄膜電晶體具有高載子遷移率、低成本、低製程溫度以及高均勻度等優點，可整合軟性顯示器或積體電路等應用，其特性能與非晶矽和多晶矽薄膜電晶體相抗衡，因此近幾年來已引起全球產學研各方的關注。本論文研究沿C軸結晶之IGZO(CAAC-IGZO)薄膜電晶體，跟一般IGZO薄膜電晶體相較起來，其優點為具有較低的關閉電流，可以應用在低功耗的顯示器上。 本論文研究了不同基板溫度、退火溫度以及通道厚度對元件電性與結晶特性的影響。由x光繞射分析儀可得到在較高的基板溫度(約200度)、較高的退火溫度和較厚的通道厚度下，能達到較強的C軸結晶；另一方面，由穿透式電子顯微鏡、可看出在退火溫度500、600℃時有小範圍的結晶，而退火溫度700℃時，在剖面圖發現CAAC的層狀結構及在俯視圖發現了六角環狀結構。此外我們成功地做出最好的元件，其特性具有陡峭的次臨界擺幅(130 mV/decade)、低臨界電壓(-0.7 V)、低漏電(2.5×10-14 A/um)及低操作電壓(4 V)。 然而為了彌補CAAC-IGZO薄膜電晶體低載子遷移率之缺點，本研究提出了在通道層覆蓋上二氧化鈦來增進載子遷移率的結構，其元件特性：次臨界擺幅為 244 mV/decade、臨界電壓為1.9 V，載子遷移率成功地從0.5提升至13.6 cm2/Vs。

InGaZnO-based thin film transistors have attracted increasing attention in recent years because of the relatively low cost and good uniformity compared to the amorphous-silicon and poly-silicon TFTs. Besides, IGZO TFTs can be processed with a low thermal budget that has the capability of integrating flexible displays. In this thesis, we demonstrate CAAC-IGZO TFTs, which exhibit low off current that can apply to future low power consumption displays. We investigate the relationship between substrate temperature/PDA temperature/ channel layer thickness and crystallization/electrical properties. According to XRD spectra, we find that high substrate temperature (~200℃), high PDA temperature, and thick channel layer can facilitate highly c-axis crystallization. On the other hand, cross-sectional and top view TEM images show the layerd structure and hexagonal structure, respectively. In this work, we have demonstrated CAAC-like IGZO TFTs having performance of small S.S. of 130 mV/dec., low VT of -0.7 V, Ioff of 2.5x10-14 A/um, and Vop of 4 V . In order to promote the mobility, which is a disadvantages of CAAC-IGZO TFTs. We cap TiO2 passivation layer on the IGZO channel layer. The devices demonstrate good performance, which shows a small S.S. of 244 mV/dec, a low VT of 1.9 V. The mobility is improved from 0.5 to 13.6 cm2/Vs.