銦鎵摻雜之非晶態氧化鋅薄膜電晶體在環境與照光偏壓下穩定度之研究

Abstract

近年來，隨著液晶顯示器的尺寸越來越大，用來使液晶旋轉的電晶體所需要的電子遷移率(mobility)也必須越來越高，但是傳統的非晶矽薄膜電晶體的電子遷移率太低(< 1 cm2/V s) ，因此擁有高電子遷移率(<10 cm2/V s)的非晶金屬氧化物薄膜電晶體對於未來顯示器的應用上非常有潛力，故銦鎵摻雜之非晶態氧化鋅(α-InGaZnO)薄膜電晶體是我們所要研究的重點。 雖然α-IGZO薄膜電晶體有非高的電子遷移率，但往往會受到環境、照光以及長時間操作偏壓而對元件產生起始電壓(threshold voltage)的偏移，故我們的實驗分成兩大部分來探討，第一部分主要是針對α-IGZO薄膜電晶體對氣氛的關係，我們可以發現到氧氣在含水的環境中或者是較高的溫度下可以更有效率的吸附在α-IGZO薄膜電晶體上，造成起始電壓向右飄移。第二部主要為測試元件在照光以及負偏壓下不穩定性的探討，在照長波常以及負偏壓的條件下可以看到電容有一個提早抬升的趨勢，我們將這個現象歸因於有donor-like 型態的缺陷產生於介面，但是這個現象在照短波長以及負偏壓下並看不到，這是因為照短波長的光可以產生大量的電洞，這些電洞累積在介面，當在量測的時候這些累積的電洞屏蔽掉了介面donor-like 型態的缺陷，導致在C-V的量測上沒有提早抬升的趨勢。

In recent years, the higher mobility is needed for thin film transistor (TFT) mainly used to twist the liquid crystal for the larger size display. The mobility of traditional amorphous silicon TFT is too low (< 1 cm2/V s), while the amorphous metal oxide has mobility higher than 10 cm2/V s, which is a very promising material for the future display application. Therefore, the amorphous Indium-Gallium-Zinc-Oxide (α-InGaZnO) is the main topic that we want to research. Although the α-IGZO TFT has very high mobility, it is always suffer from the instability of environment, illumination and long term bias stress which cause the threshold voltage (VTH) shift. We can separate our study into two parts. The first part we want to discuss is the relation between the α-IGZO TFT and oxygen. We found that oxygen absorbs on α-IGZO is much more efficiently under water-containing or higher temperature condition, causing a positive threshold voltage shift. The second part is mainly the examination of α-IGZO TFT instability under the negative bias stress with light. We can find that the stretch-out phenomenon of C-V transfer curve under negative bias stress with long wavelength of light. We contribute this phenomenon to the donor-like traps creation at the interface between gate insulator and channel. However, the C-V transfer curve stretch-out phenomenon disappeared under the negative bias stress with short wavelength of light. It may be due to the huge amount of holes generated through illumination with short wavelength of light. These holes could accumulate at the interface and screen the donor-like traps.