改善TFT-LCD中串扰的工艺研究
摘要
近年来,薄膜晶体管液晶显示器产业在基础研究和应用方面急速扩展,特别是在中小尺寸领域逐渐成为平板显示器的主流。但是,若想真正全面取代其它平板显示技术,大面板尺寸和高解析度及高画面品质的要求则是必然要克服的挑战。然而,面板尺寸加大对宽视角提出更高要求。解析度要求越来越高,而解析度的增加要求TFT线宽更窄,像素间距也更小。这会导致串扰(CrosstaIk)、闪烁(Flicker)、影像残留等问题,成为困扰提升画面品质的几个主要挑战。特别是继TN型液晶显示器后新开发的VA型及IPS型液晶显示器,由于采用新型电极结构设计,更容易导致画面串扰的问题。
然而从驱动上改善串扰一直是工业界采用的主要方法,主要是对串扰进行补偿,但是通过驱动改善是不稳定的,而且针对不同型号产品,甚至同一款产品也要有多种驱动方案,这显然是不高效的；结构上改善串扰主要是通过增加线间距,但是这样降低了开口率,与高解析度的发展方向是相悖的。为了能从根本上解决串扰,如何从制造工艺上找到与串扰强相关的因素并加以优化就非常重要。
本论文通过对生产工艺中与串扰强相关工艺的DOE试验及分析,找出工艺上改善和控制串扰的方向。第一章主要是对串扰的现象及原因进行了研究,并介绍了TFT-LCD的基本工作原理；第二章介绍了制备及测试方法；第三、四章主要是对与串扰强相关工艺的试验验证并有针对性的优化工艺改善串扰：
1.垂直串扰的改善
论文首先通过对垂直串扰屏幕的反向解析,确定了TFT关态特性异常是导致垂直串扰的原因。接着理论分析了TFT关态特性异常的原因,认为干刻工艺是造成异常的主要工艺因素。对干刻工艺进行DOE试验,验证了干刻工艺对关态特性的影响；发现了造成大玻璃上存在I-off较大的异常区域的原因,并最终通过试验找到了改善I-off均匀性的最佳干刻工艺条件,从而进一步改善了垂直串扰。
2.水平串扰及耦合电容的改善
论文通过改变PVD金属成膜工艺,降低了公共电极的线电阻,从而降低了公共电极线线延时,解决了水平串扰；本部分还对影响耦合电容的主要因素进行了分析,通过试验验证了耦合电容对串扰的影响,确定了像素电极(ITO)和信号线(S/D)的最小间距,为提高像素开口率提供了数据支持。
The thin film transistor liquid crystal display (TFT-LCD) industry is rapidly developing, particularly in the field of small and medium size flat-panel displays. However, if TFT-LCD technology can comprehensively replace other flat panel display technologies, some challenges like large panel size, high resolution and high picture quality requirements still need to be overcomed. The reduction of panel size will result in many problems, e.g., the TFT width is narrower and the pixel spacing is smaller, which will increase the impact of crosstalk, flicker, image sticking, etc.. These become several major challenges to upgrade picture quality. Particularly following the TN-LCD technology, newly developed VA and IPS-type LCDs with new electrode design will more easily lead to crosstalk problems.
However, improvent of LCD drivers has been the main method used to suppress crosstalk. But it is unstable, and for different types of products even for one kind of product it also needs a specific drive code. This is obviously not efficient. Using new structures to improve the crosstalk is mainly by increasing the line spacing, but it will reduce the aperture ratio and high resolution,which is contrary to the direction of TFT-LCD development. To fundamentally solve the crosstalk, it is more and more important to find the relationship between fabrication process and crosstalk.
This paper studies the origin of crosstalk through the analysis of its strong correlation processes. The first chapter introduces the basic principles of TFT-LCD and crosstaIk phenomena. The second chapter introduces the preparation and testing methods of TFT-LCD, and the third and fouth chapters are mainly to find the strong correlations between crosstalk and processes:
1. Vertical crosstalk improvement
Firstly, this section analyzes the LCD screen with vertical crosstalks and determines the characteristics of the TFT off-state anomalies leading to vertical crosstalks. Then the theoretical analysis of the off-state TFT reaveals the main process factor which causes the abnormal TFT characteristics is dry etch process. Dry etch DOE tests are carried out to verify the impact of dry etch on the off-state TFT characteristics. This section also studies the large anomalies of I-off in a large glass and eventually improves the I-off uniformity. Finally the best dry etch conditions is determined.
2. The improvement of horizontal crosstalk and the coupling capacitance
The common electrode line resistance is reduce by increasing the the PVD metal film thickness, which further reduces the common electrode line delay and eliminates the horizontal crosstalk. This section also analyzes the coupling capacitance and the relationship between coupling capacitor and crosstalk. The minimum distance between the pixel electrode (ITO) and the signal line (S/D) is then determined, which provides data for further pixel aperture ratio improvement.
然而从驱动上改善串扰一直是工业界采用的主要方法,主要是对串扰进行补偿,但是通过驱动改善是不稳定的,而且针对不同型号产品,甚至同一款产品也要有多种驱动方案,这显然是不高效的；结构上改善串扰主要是通过增加线间距,但是这样降低了开口率,与高解析度的发展方向是相悖的。为了能从根本上解决串扰,如何从制造工艺上找到与串扰强相关的因素并加以优化就非常重要。
本论文通过对生产工艺中与串扰强相关工艺的DOE试验及分析,找出工艺上改善和控制串扰的方向。第一章主要是对串扰的现象及原因进行了研究,并介绍了TFT-LCD的基本工作原理；第二章介绍了制备及测试方法；第三、四章主要是对与串扰强相关工艺的试验验证并有针对性的优化工艺改善串扰：
1.垂直串扰的改善
论文首先通过对垂直串扰屏幕的反向解析,确定了TFT关态特性异常是导致垂直串扰的原因。接着理论分析了TFT关态特性异常的原因,认为干刻工艺是造成异常的主要工艺因素。对干刻工艺进行DOE试验,验证了干刻工艺对关态特性的影响；发现了造成大玻璃上存在I-off较大的异常区域的原因,并最终通过试验找到了改善I-off均匀性的最佳干刻工艺条件,从而进一步改善了垂直串扰。
2.水平串扰及耦合电容的改善
论文通过改变PVD金属成膜工艺,降低了公共电极的线电阻,从而降低了公共电极线线延时,解决了水平串扰；本部分还对影响耦合电容的主要因素进行了分析,通过试验验证了耦合电容对串扰的影响,确定了像素电极(ITO)和信号线(S/D)的最小间距,为提高像素开口率提供了数据支持。
The thin film transistor liquid crystal display (TFT-LCD) industry is rapidly developing, particularly in the field of small and medium size flat-panel displays. However, if TFT-LCD technology can comprehensively replace other flat panel display technologies, some challenges like large panel size, high resolution and high picture quality requirements still need to be overcomed. The reduction of panel size will result in many problems, e.g., the TFT width is narrower and the pixel spacing is smaller, which will increase the impact of crosstalk, flicker, image sticking, etc.. These become several major challenges to upgrade picture quality. Particularly following the TN-LCD technology, newly developed VA and IPS-type LCDs with new electrode design will more easily lead to crosstalk problems.
However, improvent of LCD drivers has been the main method used to suppress crosstalk. But it is unstable, and for different types of products even for one kind of product it also needs a specific drive code. This is obviously not efficient. Using new structures to improve the crosstalk is mainly by increasing the line spacing, but it will reduce the aperture ratio and high resolution,which is contrary to the direction of TFT-LCD development. To fundamentally solve the crosstalk, it is more and more important to find the relationship between fabrication process and crosstalk.
This paper studies the origin of crosstalk through the analysis of its strong correlation processes. The first chapter introduces the basic principles of TFT-LCD and crosstaIk phenomena. The second chapter introduces the preparation and testing methods of TFT-LCD, and the third and fouth chapters are mainly to find the strong correlations between crosstalk and processes:
1. Vertical crosstalk improvement
Firstly, this section analyzes the LCD screen with vertical crosstalks and determines the characteristics of the TFT off-state anomalies leading to vertical crosstalks. Then the theoretical analysis of the off-state TFT reaveals the main process factor which causes the abnormal TFT characteristics is dry etch process. Dry etch DOE tests are carried out to verify the impact of dry etch on the off-state TFT characteristics. This section also studies the large anomalies of I-off in a large glass and eventually improves the I-off uniformity. Finally the best dry etch conditions is determined.
2. The improvement of horizontal crosstalk and the coupling capacitance
The common electrode line resistance is reduce by increasing the the PVD metal film thickness, which further reduces the common electrode line delay and eliminates the horizontal crosstalk. This section also analyzes the coupling capacitance and the relationship between coupling capacitor and crosstalk. The minimum distance between the pixel electrode (ITO) and the signal line (S/D) is then determined, which provides data for further pixel aperture ratio improvement.
引文
[1]W. E. Howard, P. M. Alt and R. L. Wisnieff. Eliminating crosstalk in thin-film transistor/ liquid-crystal displays[J]. Electron Devices,1989,36:19-38.
[2]Frank R. Libsch and A. Lien. A low power driving method for reducing cross-talk in high resolution TFT-LCDs[A]. AMLCD95,1995:72.
[3]F. R. Libsch and A. Lien. A new driving method for reducing crosstalk in high resolution TFT-LCD[J]. Jpn. J. Appl. Phys,1995,34:63-64.
[4]Ahn et al. Thin Film Transistor And Flat Panel Display Including The TFT[p]美国专利:Patent No:US7550766 B2,2009.
[5]Koo et al. Thin Film Transistor And Flat Panel Display Device Comprising The Same[p]美国专利:Patent No:US7692245 B2,2010.
[6]黄瑶秋.液晶显示器之串音研究[D].台湾：中华大学.1997.26-38
[7]戴亚翔.TFT-LCD液晶面板的驱动与设计[M].台湾：2008.120-135.
[8]谷志华.薄膜晶体管(TFT)阵列制造技术[M].复旦大学出版社.2007.304-328
[9]甄汉生.等离子体加工技术[M].北京：清华大学出版社.1990.1～2
[10]Yamaji Y, Ikeda M, Akiyama M, Endo T. Characterization of photo leakage current of amorphous silicon thin-film transistors[J]. Jpn J Appl Phys Part 1,1999,38:6202-6.
[11]杜海波.光刻胶剥离工艺IPA消减方法研究[D].2010.
[12]崔宏清.四分之一波长延迟膜在向列相液晶显示器件中的应用[D].2008
[13]S. Ono, Y. Kobayashi, Japanese Journal of Applied Physics Part 1 [C].2004,43:7947-7952.
[14]J.Y. Nahm, T. Goda, B.H. Min, T.K. Chou, J. Kanicki, X.Y. Huang, N. Miller, V. Sergan, P. Bos, J.W. Doane. Proceedings of the 18th International Display Research Conference, Asia Display 98[C].1998:979-982.
[15]YH. Song, C.S. Hwang, YR. Cho, B.C. Kim, S.D. Ahn, C.H. Chung, D.H. Kim, H.S. Uhm, J.H. Lee, K.I. Cho. ETRI Journal[A].2002,24:290-298.
[16]J.H. Kim, J. Kanicki. Proceedings of the SPIE-The International Society for Optical Engineering[A].2001, vol.4319:306-318.
[17]Kuo Y. Electrochemical Society Proceedings of the Thin Film Transistor Technologies Ⅳ[A]. 1998, vol. PV-98-22:191.
[18]M. C. Kwan, K. H.Cheng, P. T. Lai, C.M. Che. Improved carrier mobility for pentance TFT by NH3 annealing of gate dielectric [J]. Solid-state Electronics,2007,51:77.
[19]Wang Changan, Xiong Zhibin, Zhang Shaoqiang. Influnce of a-SiNx:H film on the Threshold Voltage of a-Si:H TFT[J].光电子学报,1997, VOL.17 NO1:45.
[20]A. KUO, T. K. Won, J. Kanicki. Back channel etch chemistry of advanced a-Si:H TFTs[J]. Microelectronic Engineering,2010:612
[21]A. Kuo, T.K. Won, J. Kanicki, Japanese Journal of Applied Physics 47 (5) (2008) 3362-3367. A.M. Miri, S.G. Chamberlain. Proceedings-Materials Research Society Symposium, Amorphous Silicon Technology[A].1995, vol.377:737-742.
[22]赵颖熊绍珍.H处理对a-Si TFT矩阵性能的改善作用[J].半导体学报.1997,Vol.18：p59.
[23]H. K. Jang, C. E. Lee, S. J. Noh. Poly-Si thin film transistor with a souce overlap and a drain offset:leakage current characteristics[J]. Thin Solid Films,341 (1999). pp.148-151.
[24]G.Lavareda,C. Nunes de Carvalho, A. Amaral, E. Fortunato, P. Vilarinho. a-Si:H TFT enhancement by plasma processing of the insulating/semiconductor interface[J]. Materials Science and Engineering,2004, B109:264-268.
[25]Tae Hyung Kim, Soon Shin Jung, Jae Woo Park and Jong Sun Choi Simulations of Crosstalk and Flicker in TFT-LCDs[J]. Journal of the Korean Physical Society, July 2001,Vol.39, No.1: 67-71.
[26]Nathan A, Austin M, Pereira D. Correlation between Leakage Current and Overlap Capacitance in a-Si:H TFTs. Proc of IEEE Workshop on Charge Coupled Devices vid advanced Image Sensor[J]. Japan Karuizawa,1999,6:10-12,126.
[27]Angelis T, Dimitriadis C A, Samaras I, et al. Study of Leakage Current in n-channel and P-channel Polycrystalline Silicon Thin-film Transistors by Conduction and Low Frequency Noise Measurements[J]. J appl Phys,1997,82(8):4095.
[2]Frank R. Libsch and A. Lien. A low power driving method for reducing cross-talk in high resolution TFT-LCDs[A]. AMLCD95,1995:72.
[3]F. R. Libsch and A. Lien. A new driving method for reducing crosstalk in high resolution TFT-LCD[J]. Jpn. J. Appl. Phys,1995,34:63-64.
[4]Ahn et al. Thin Film Transistor And Flat Panel Display Including The TFT[p]美国专利:Patent No:US7550766 B2,2009.
[5]Koo et al. Thin Film Transistor And Flat Panel Display Device Comprising The Same[p]美国专利:Patent No:US7692245 B2,2010.
[6]黄瑶秋.液晶显示器之串音研究[D].台湾：中华大学.1997.26-38
[7]戴亚翔.TFT-LCD液晶面板的驱动与设计[M].台湾：2008.120-135.
[8]谷志华.薄膜晶体管(TFT)阵列制造技术[M].复旦大学出版社.2007.304-328
[9]甄汉生.等离子体加工技术[M].北京：清华大学出版社.1990.1～2
[10]Yamaji Y, Ikeda M, Akiyama M, Endo T. Characterization of photo leakage current of amorphous silicon thin-film transistors[J]. Jpn J Appl Phys Part 1,1999,38:6202-6.
[11]杜海波.光刻胶剥离工艺IPA消减方法研究[D].2010.
[12]崔宏清.四分之一波长延迟膜在向列相液晶显示器件中的应用[D].2008
[13]S. Ono, Y. Kobayashi, Japanese Journal of Applied Physics Part 1 [C].2004,43:7947-7952.
[14]J.Y. Nahm, T. Goda, B.H. Min, T.K. Chou, J. Kanicki, X.Y. Huang, N. Miller, V. Sergan, P. Bos, J.W. Doane. Proceedings of the 18th International Display Research Conference, Asia Display 98[C].1998:979-982.
[15]YH. Song, C.S. Hwang, YR. Cho, B.C. Kim, S.D. Ahn, C.H. Chung, D.H. Kim, H.S. Uhm, J.H. Lee, K.I. Cho. ETRI Journal[A].2002,24:290-298.
[16]J.H. Kim, J. Kanicki. Proceedings of the SPIE-The International Society for Optical Engineering[A].2001, vol.4319:306-318.
[17]Kuo Y. Electrochemical Society Proceedings of the Thin Film Transistor Technologies Ⅳ[A]. 1998, vol. PV-98-22:191.
[18]M. C. Kwan, K. H.Cheng, P. T. Lai, C.M. Che. Improved carrier mobility for pentance TFT by NH3 annealing of gate dielectric [J]. Solid-state Electronics,2007,51:77.
[19]Wang Changan, Xiong Zhibin, Zhang Shaoqiang. Influnce of a-SiNx:H film on the Threshold Voltage of a-Si:H TFT[J].光电子学报,1997, VOL.17 NO1:45.
[20]A. KUO, T. K. Won, J. Kanicki. Back channel etch chemistry of advanced a-Si:H TFTs[J]. Microelectronic Engineering,2010:612
[21]A. Kuo, T.K. Won, J. Kanicki, Japanese Journal of Applied Physics 47 (5) (2008) 3362-3367. A.M. Miri, S.G. Chamberlain. Proceedings-Materials Research Society Symposium, Amorphous Silicon Technology[A].1995, vol.377:737-742.
[22]赵颖熊绍珍.H处理对a-Si TFT矩阵性能的改善作用[J].半导体学报.1997,Vol.18：p59.
[23]H. K. Jang, C. E. Lee, S. J. Noh. Poly-Si thin film transistor with a souce overlap and a drain offset:leakage current characteristics[J]. Thin Solid Films,341 (1999). pp.148-151.
[24]G.Lavareda,C. Nunes de Carvalho, A. Amaral, E. Fortunato, P. Vilarinho. a-Si:H TFT enhancement by plasma processing of the insulating/semiconductor interface[J]. Materials Science and Engineering,2004, B109:264-268.
[25]Tae Hyung Kim, Soon Shin Jung, Jae Woo Park and Jong Sun Choi Simulations of Crosstalk and Flicker in TFT-LCDs[J]. Journal of the Korean Physical Society, July 2001,Vol.39, No.1: 67-71.
[26]Nathan A, Austin M, Pereira D. Correlation between Leakage Current and Overlap Capacitance in a-Si:H TFTs. Proc of IEEE Workshop on Charge Coupled Devices vid advanced Image Sensor[J]. Japan Karuizawa,1999,6:10-12,126.
[27]Angelis T, Dimitriadis C A, Samaras I, et al. Study of Leakage Current in n-channel and P-channel Polycrystalline Silicon Thin-film Transistors by Conduction and Low Frequency Noise Measurements[J]. J appl Phys,1997,82(8):4095.