非晶相銦鎵鋅氧化物薄膜電晶體之電性分析與以深埋氧化層電荷改善短通道效應之超薄體金氧半電晶體

Electrical Characteristics of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors and Enhanced Ultra-Thin-Body MOSFETs by Charged Buried Oxide

林軒毅(Hsuan-Yi Lin)

指導教授 ： 劉致為

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.10169

摘要

於未來顯示器技術中，高解析度顯示器所需之通道載子遷移率(Mobility)的需求亦將隨之增加。近年來，將非晶相銦鎵鋅氧化物薄膜電晶體(a-IGZO TFT)利用於Active Matrix Organic Light Emitting Diode (AMOLED)已經成為研究的趨勢。相較於傳統的通道材料非晶矽之載子遷移率(Mobility ~1cm2/V-s)，非晶相銦鎵鋅氧化物有著較高之載子遷移率(Mobility~10cm2/V-s)。因此，非晶相銦鎵鋅氧化物被視為是可用於次世代薄膜電晶體之理想的通道材料。
在a-IGZO中，因為不同製程條件的影響，因而會造成下層通道較上層通道有較高之載子遷移率。在本論文中，我們提出了以原子層沉積(ALD)之三氧化二鋁(Al2O3)鈍化保護層(passivation layer)可增加以底部閘極所操作(bottom gate operation)之非晶相銦鎵鋅氧化物薄膜電晶體之載子遷移率，並且改善其操作穩定度(reliability)。藉由在三氧化二鋁鈍化保護層中之固定負電荷(negative fixed charge)，在非晶相銦鎵鋅氧化物通道中之電子可被庫倫斥力(coulomb repulsion)推離品質較差之上通道，進而可觀察到載子遷移率提升的現象。此外，以三氧化二鋁鈍化保護層覆蓋之非晶相銦鎵鋅氧化物薄膜電晶體亦展現出比以二氧化矽(SiO2) 鈍化保護層覆蓋之非晶相銦鎵鋅氧化物薄膜電晶體有著較高之載子遷移率以及較佳之操作穩定度。
為了追求更快的電晶體操作速度以及更高的封裝密度，近年來金氧半場效電晶體(MOSFET)之尺寸持續地微縮。全空乏型超薄體金氧半電晶體(FD Ultra-thin body MOSFET)被視為是符合國際半導體技術藍圖(International Technology Roadmap for Semiconductors)制定之微縮需求的理想元件。然而，當閘極長度持續地被微縮下去，通道的閘極控制(gate control)將會被劣化，並且全空乏型超薄體金氧半電晶體之電性表現亦將因短通道效應(short-channel effects)而被損害。在本論文中，我們提出了帶有深埋氧化層電荷之超薄體金氧半電晶體(UTB MOSFET with charged buried oxide)的新型結構。藉由此新型結構，短通道效應將得以改善。在此結構中，帶有電荷之深埋氧化層為汲極電場之收集者，利用此效應可進一步改善超薄體金氧半電晶體中的短通道效應。本研究中以二維電腦輔助模擬技術(two-dimensional technology computer-aided design simulation)來對改善之短通道效應進行原理分析，並且藉以驗證此新型元件結構。

關鍵字

非晶相銦鎵鋅氧化物 ； 薄膜電晶體 ； 短通道效應 ； 金氧半場效電晶體

並列摘要

In future displays, the required channel mobility of thin-film transistors is higher for displays with higher resolution. Recently, there has been increasing research in amorphous indium – gallium - zinc oxide (a-IGZO) thin-film transistors (TFTs) for Active Matrix Organic Light Emitting Display (AMOLED). As compared with the mobility of hydrogenated amorphous silicon (a-Si) (~1cm2/V-s), the mobility of a-IGZO (~10cm2/V-s) is much higher, and therefore a-IGZO is considered as a promising channel material for next generation thin-film transistors.
In a-IGZO, the bottom channel has a higher mobility than the top channel due to the various process conditions. Negative charges in the Al2O3-passivation layer deposited by atomic layer deposition (ALD) can enhance the saturation mobility and reliability of the bottom gate operation α-IGZO TFTs. By negative fixed charges in the Al2O3-passivation layer, the electrons in the channel can be pushed away from the top insulator/channel interface by coulomb repulsion, and the mobility enhancement is observed. The Al2O3-passivated α-IGZO TFT also reveals higher mobility and better reliability than the conventional SiOX-passivated α-IGZO TFT.
In order to pursue higher operation speed and higher packing density for transistors, the dimensions of MOSFETs have continued to shrink rapidly over the years. Fully-depleted (FD) ultra-thin body (UTB) MOSFETs are considered as one of the most promising candidates for scaling capability requested by International Technology Roadmap for Semiconductors (ITRS). However, as the gate length is reduced, the gate control on the electrostatic potential in the channel becomes less effective and the performance of the UTB MOSFET deteriorates due to short-channel effects. We propose a new device structure “Ultra-Thin body MOSFET with charged buried oxide”. In the proposed device structure, the charged buried oxide act as a collector to the drain electric field, leading to the improved short-channel effects in ultra-thin body MOSFET. Two-dimensional technology computer-aided design (TCAD) simulation is used to verify the new device structure and the characteristics of improved short-channel effects such as DIBL and subthreshold slope are demonstrated.

並列關鍵字

a-IGZO ； TFT ； short-channel effects ； MOSFET

參考文獻

[1] T. Kamiya, K. Nomura, and H. Hosono, “Present status of amorphous In–Ga–Zn–O thin-film transistors,” Science and Technology of Advanced Materials, vol. 11, Aug. 2010, p. 044305.

[2] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, “Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors.,” Nature, vol. 432, Nov. 2004, pp. 488-92.

[3] International Technology Roadmap for Semiconductors, 2012. [Online]. Available: http://www.itrs.net/

[4] A. Chaudhry and M. J. Kumar, “Controlling short-channel effects in deep-submicron SOI MOSFETs for improved reliability: A review,” IEEE Trans. Device Mater. Rel., vol. 4, no. 1, pp. 99–109, Mar. 2004.

[5] T. Kamiya, K. Nomura, and H. Hosono, “Present status of amorphous In–Ga–Zn–O thin-film transistors,” Science and Technology of Advanced Materials, vol. 11, Aug. 2010, p. 044305.