金屬氧化物薄膜電晶體電路設計與分析

Design and Analysis of Metal Oxide Thin-Film Transistor Circuits

林欣穎(Hsin-Ying Lin)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10298

摘要

薄膜電晶體已在平面顯示器的應用上發展了十數年。然而，非晶矽薄膜電晶體的低載子遷移率與不穩定性及多晶矽薄膜電晶體的不一致性限制了大面積面板和電流驅動之電路的發展。高載子遷移率、大面積製作、低成本…等益處使得非晶態氧化物半導體成為量產薄膜電晶體的新興材料。
在本論文中，高溫成膜的氧化鋅薄膜電晶體有超過9次方的電流開關比，並且製作和比較不同退火時間下元件在閘極偏壓之下的穩定性，也導入定量萃取出元件的生命期的Stertched-Exponential Time Dependence，更進一步的將生命期最長(1.26x106s)的元件在變溫下作穩定性測驗，成功的萃取出0.57eV的元件活化能。
此外我們製作了氧化銦鎵鋅薄膜電晶體以克服氧化鋅的缺陷問題，並進一步將飽和載子遷移率推進至16.5 cm2/Vs以利電路的應用。以此材料製作的增強型反向器的直流增益達到2.5，且環形震盪器可在20伏特之下操作在8.7MHz的頻率以及0.37伏的峰對峰值。與其他研究團隊的增強型電路相比，這是目前最快的操作頻率。我們也引入頻率和一些製程參數的關係式，以便於進一步調整其操作頻率，其中元件通道層的長度對頻率有最大的影響。總體而言，如要更加推進電路的品質，電路的匹配設計以及電路參數的最佳化都是不可或缺的。

關鍵字

薄膜電晶體 ； 電路 ； 環形震盪器

並列摘要

Thin-film transistor (TFT) has been developed to be applied on the flat panel display (FPD) in decades. However, the low mobility and instability of a-Si:H TFTs and the poor uniformity of poly-Si TFTs are insufficient to applied on large size substrate and current driving circuits. The amorphous nature of amorphous oxide semiconductor (AOS) is attractive for manufacturing because of their high mobility (> 10 cm2/Vs), large-area, low-cost, transparent, and possibly flexible electronics applications.
In this thesis, a high temperature deposited ZnO film is deposited to fabricate the high performance TFT, including an on-off ratio over 109. The effects of gate bias and thermal stress induced threshold voltage shift for ZnO TFTs are discussed. We compared three samples with various post ZnO growth annealing durations. The best result shows that the threshold voltage shift (ΔVth) is only 2.2V after a 1.3×104s stress at the gate bias 20V. And the ΔVth can be correlated to the stress time following the charge trapping mechanism. The characteristic trapping time τ was calculated to be 1.26×106 s. Finally, the characteristic trapping time was extracted at different temperatures and obtaining an average effective energy barrier Eτ of 0.57eV.
The a-IGZO TFTs are employed to overcome the drawback of ZnO film forming defects and grain boundaries. The a-IGZO TFT reaches a higher saturation mobility of 16.5 cm2/Vs than ZnO TFT and has a better and more suitable performance than ZnO-based TFTs to develop the TFT circuits. The transconductance and extraction of resistivity in a-IGZO film by TLM method are also discussed.
The design and implementation of the enhancement-mode inverter and the corresponding ring oscillator using a-IGZO TFTs are presented in the last part of this thesis. The DC gain and transient response are both extracted to examine the potential on realizing ring oscillators. An inverter DC gain of 2.5 biased at a supply voltage of 15V and a slew rate of 0.41V/μs are achieved separately. And an a-IGZO TFT ring oscillator with a channel length of 2μm and a beta ratio of 5 possesses an oscillator frequency 8.7 MHz and Vp-to-p = 0.37V biased at 20V. The operational frequency is expressed in a simple equation to further develop the frequency tuning method. It is mainly influenced by the channel length of the a-IGZO TFTs. Other design rules of thumb to improve the frequency are discussed. At last, the matching work by adding extra passive elements is required between circuit networks to minimize signal reflection at their interfaces. In summary, the device parameters can be sophisticated designed and optimized to improve the circuit performance.

並列關鍵字

Thin-film-transistor ； a-IGZO ； circuit ； ring-oscillator

參考文獻

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