第四章 垂直入射式折射率顯微術與其應用
4.4 討論
4.4.1 量測 GRIN lens
(Model 2700, Keithley Instrument Inc.)分別在 ITO 樣本進行撓曲前後量測其電阻 值，量測電阻時的接觸電極位置如同Fig. 4.6(a)所示。當樣本處於上述三種情形 下，所測得的電阻值分別為2.613 kΩ、2.623 kΩ 以及 2.674 kΩ，因此樣本撓曲 後之電阻值分別改變了0.38 %以及 2.33 %。為了便於瞭解，我們將本方法的平 均值、現有量測電阻值的方法，以及本方法的標準差等上述三種量測結果一齊進行比較，並繪於Fig. 4.10 中。由於電阻的量測以及折射率平均值的量測，都是屬 於導電區域面積內的平均效應，因此在Fig. 4.10 中可知道上述二者具有相似的變 化量；然而由於本方法能觀察局部微小區域的變化量，從Fig. 4.10 中可知當改以 二維折射率之標準差做為判斷指標時，觀察ITO 薄膜的撓曲特性則會更加靈敏，
因此我們可以說，二維折射率之標準差可以用做 ITO 薄膜的耐久性測試指標，
本方法較現有的電阻值量測方法更加靈敏。
Fig. 4. 10 在 1000 次與 4000 次撓曲後，比較本方法平均值(符號■)、標準差(符號●)以及 電阻(符號
♦
)等量測結果之變化情形4.5 小結
本文提出一種垂直入射的折射率顯微術，用來量測GRIN lens 以及不同撓曲 次數狀態下的 ITO 層的表面二維折射率的分佈。利用一外差光束準直後進入一 類似 Twyman-Green 干涉儀的光學架構中，全場干涉訊號則可由一快速 CMOS 相機取得，每個像素皆記錄一序列的弦波訊號的取樣光強度，這些光強度再經由 擬合運算而得到相關的弦波訊號，則可獲得該像素的相位，而其他像素的相位都 按照上述方法而得到。之後由 Fresnel 公式可推得測得之相位與折射率之間的關 係，進而解得二維折射率分佈。本方法具有光學架構簡單、高靈敏度、高量測解 析度以及高重現性等優點。
參考文獻
1. R. Oven, “Measurement of two dimensional refractive index profiles of channel waveguides using an interferometric technique,” Appl. Opt. 48, 5704-5712 (2009).
2. N. M. Dragomir, X. M. Goh, and A. Roberts, “Three-dimensional refractive index reconstruction with quantitative phase tomography,” Microsc. Res. Tech. 71, 5-10 (2008).
3. Y. Youk and D. Y. Kim, “A simple reflection-type two-dimensional refractive index profile measurement technique for optical waveguides,” Opt. Commun. 262, 206-210 (2006).
4. D. Vazquez, E. Acosta, G. Smith, and L. Garner, “Tomographic method for measurement of the radient refractive index of the crystalline lens. II The rotationally symmetrical lens,” Opt. Soc. Am. A 23, 2551- 2565 (2006).
5. Y. F. Chao and K. Y. Lee, “Index Profile of Radial Gradient Index Lens Measured by Imaging Ellipsometric Technique,” Jpn. J. Appl. Phys. 44, 1111-1114 (2005).
6. Z. Liu, X. Dong, Q. Chen, C. Yin, Y. Xu, and Y. Zheng, “Nondestructive measurement of an optical fiber refractive-index profile by a transmitted-light differential interference contact microscope,” Appl. Opt. 43, 1485- 1492 (2004).
7. M. Ray, S. K. Sarkar, A. Basuray, and N. SoodBiswas, “Measurement of refractive index profile of GRIN glasses,” Proc. SPIE 4417, 483- 488 (2001).
8. H. C. Hsieh, Y. L. Chen, W. T. Wu, and D. C. Su, “Method for measuring the refractive index distribution of a GRIN lens with heterodyne interferometry,” Proc.
SPIE 7390, 73900G (2009).
9. Y. L. Chen and D. C. Su, “A method for determining full-field absolute phases in the common-path heterodyne interferometer with an electro-optic modulator,” Appl.
Opt. 47, 6518-6523 (2008).
10. E. Hecht, “Optics,” 4th ed., (Addison-Wesley), pp.376-379 (2002).
11. C. Sujatha, G. M. Rao, and S. Uthanna, “Characteristics of indium tin oxide films deposited by bias magnetron sputtering,” Mater. Sci. Eng. B94, 106-110 (2002).
12. H. Y. Tsai, H. Yangm C. T. Pan, and M. C. Chou, “Laser patterning indium tin oxide (ITO) coated on PET substrate,” Proc. SPIE 4230, 156-163 (2000).
13. S. Grego, J. Lewis, E. Vick, and D. Temple, “Development and evaluation of bend-testing techniques for flexible-display applications,” J. Soc. Inf. Display 13, 575-581 (2005).
14. S. P. Gorkhali, D. R. Cairns, and G. P. Crawford, “Reliability of transparent conducting substrates for rollable displays: A cyclic loading investigation,” J. Soc.
Inf. Display 12, 45-49 (2004).
15. M. H. Lee, K. Y. Ho, P. C. Chen, C. C. Cheng, S. T. Chang, M. Tang, M. H. Liao, and Y.-H. Yeh, “Promising a-Si:H TFTs with high mechanical reliability for flexible display,” Tech. Dig. IEDM, 299-302 (2006).
16. B. J. Wen, T. S. Liu, C. H. Chen, H. Y. Ko, Z. Y. Chung, and S. C. Liao, “P-72:
optical-characteristic measurement of flexible display for reliability test,” SID Symp.
Dig. Tech. Papers 40, 1378-1381 (2009).
17. J. R. Lee, D. Y. Lee, D. G. Kim, G. H. Lee, Y. D. Kim, and P. K. Song,
“Characteristics of ITO films deposited on a PET substrate under various deposition conditions,” Met. Mater. Int. 14, 745-751 (2008).
18. IEEE, “Standard for Terminology and Test Methods for Analogto-Digital Converters”, IEEE Std 1241-2000, 25-29, Dec. (2000).