非晶與低溫多晶薄膜電晶體電氣特性與遷移率之研究

The Electrical Characteristics and Mobility of Amorphous and Low-Temperature Poly-Crystalline Thin-Film Transistors

胡祐銘(You-Ming Hu)

指導教授 ： 陳雙源 ； 王木俊

國立臺北科技大學/機電學院/機電整合研究所/碩士(2012年)

摘要

應用在平面顯示器的薄膜電晶體，大部分使用非晶矽薄膜電晶體作為電路控制開關，但其電子遷移率過低 (~ 1 cm2/V-sec) ，導致驅動電流較低，電晶體之開關速度也相對地較慢，阻礙大尺寸螢幕的發展，無法使一個大畫面其反應時間小於8 毫秒.。由於有這些阻礙，因而有低溫多晶矽(low-temperature poly-silicon, LTPS)之開發，可將電子遷移率拉升至~ 100 cm2/V-sec或以上。
　　本論文中採用非晶矽薄膜電晶體、爐管退火及連續式綠光雷射退火多晶矽薄膜電晶體，對臨界電壓、載子遷移率、次臨界擺伏、晶粒陷阱缺陷、表面陷阱缺陷等特性進行探討，及溫度對於這些特性的變化曲線有何影響。
　　本研究重要性在於能得知，高溫會導致元件特性的改變，當溫度從25 ℃提高至125 ℃，綠光雷射退火的多晶矽薄膜電晶體其臨界電壓變化最嚴重的下降0.4 V，另外，關閉電流增加5倍及次臨界擺幅增加 25%；爐管退火的多晶薄膜電晶體變化最嚴重的臨界電壓下降0.24 V，關閉電流大約增加170倍及次臨界擺幅增加 80 %；非晶矽薄膜電晶體變化最嚴重的的臨界電壓上升1.7 V，關閉電流大約增加2倍及次臨界擺幅降低 17 %。而非晶矽薄膜電晶體對於熱活化產生的變化不同於多晶矽薄膜電晶體，隨著溫度升高，使得元件缺陷因再結晶而修復，讓元件性能變得更好。

關鍵字

連續式綠光雷射退火結晶 ； 薄膜電晶體 ； 低溫多晶矽 ； 遷移率

並列摘要

Thin film transistor is applied in flat-panel displays, most of display products adopt the amorphous-silicon thin-film transistors (TFTs) to control the signal circuit. Because of the low electron mobility (~ 1 cm2/V-sec), the drive current is also low and the transistor switching speed relatively is slow. This electrical characteristic, which can not provide the response time < 8 msec, will block the development of big-size display products. Due to this concern, the low-temperature poly-silicon (LTPS) technology was developed. The electron mobility could be promoted to or over 100 cm2/V-sec.
In this research, the tested devices are the amorphous-Si TFT, and poly-Si annealed by furnace and annealed by green laser. Comparing the transfer characteristics of the tested devices and discussing the temperature effect on threshold voltage Vth, field effect mobility μFE, and subthreshold swing S.S. are also provided in this work.
The significance of this study is to know that higher temperature was resulted in the variation of the electrical characteristics. When the temperature rise from 25 ℃ to 125 ℃, the worst case of threshold voltage decreases 0.5 V, OFF current increases 5 times and the subthreshold swing increases 25% in the poly-Si TFTs annealed by green laser ; The worst case of threshold voltage decreases 0.24 V, OFF current increase 170 times and the subthreshold swing increase 80% in the poly-Si TFTs by furnace; The worst case of threshold voltage decreases 1.7 V, OFF current increases 2 times and the subthreshold swing decreases 17% in the a-Si:H TFT. However the variation of the transfer characteristics of a-Si:H TFT by thermal activated is very different than the poy-Si TFTs. The bulk traps recover by crystallized with increasing temperature, and the transfer characteristics become better than the initial.

並列關鍵字

continuous-wave green-laser-crystallization ； thin-film transistor ； mobility ； green laser activation ； LTPS

參考文獻

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