Journal of the Institute of Electronics Engineers of Korea SD (대한전자공학회논문지SD)

The Institute of Electronics and Information Engineers (대한전자공학회)
권호 표지

Performance enhancement of Organic Thin Film Transistor using $C_{60}$ hole injection layer

$C_{60}$(buckminsterfullurene) 홀주입층을 적용한 유기박막트랜지스터의 성능향상

  • Yi, Moon-Suk (School of Electrical Engineering, Pusan National University)
  • 이문석 (부산대학교 전자전기통신공학부)
  • Published : 2008.05.25
Download PDF
⟨ Previous Next ⟩

Abstract

In this study, we fabricated Organic Thin Film Transistors(OTFTs) with $C_{60}$ hole injection layer between organic semiconductor(pentacene) and metal electrode, and we compared the electrical characteristics of OTFTs with/without $C_{60}$. When the $C_{60}$ hole injection layer was introduced, the mobility and the threshold voltage were improved from 0.298 $cm^2/V{\cdot}s$ and -13.3V to 0.452 $cm^2/V{\cdot}s$ and -10.8V, and the contact resistance was also reduced. When the $C_{60}$ is inserted, the hole injection was enhanced because the $C_{60}$ prevent the unwanted chemical reaction between pentacene and Au. Furthermore, we fabricated the OTFTs using Al as their electrodes. When the OTFTs were made by only aluminum electrode, the channel were not mostly made because of the high hole injection barrier between pentacene and aluminum, but when the $C_{60}$ layer with an optimal thickness was applied between aluminum and pentacene, the device performances were obviously enhanced because of the vacuum energy level shift of Al and the consequent decrease of the hole injection barrier which was induced by the interface dipole formation between $C_{60}$ and Al. The mobility and $I_{ON}/I_{OFF}$ current ratio of OTFT with $C_{60}/Al$ electrode were 0.165 $cm^2/V{\cdot}s$ and $1.4{\times}10^4$ which were comparable with the normal Au electrode OTFT.

본 연구에서는 유기반도체인 펜타센과 소스-드레인 금속전극사이에 $C_{60}$을 홀주입층으로 적용한 유기박막트랜지스터를 제작하여 $C_{60}$을 삽입하지 않은 소자와의 전기적특성을 비교하였다. $C_{60}/Au$ 이중전극을 사용한 소자의 경우 Au단일전극을 사용한 소자와 비교하였을 때 전하이동도는 0.298 $cm^2/V{\cdot}s$에서 0.452 $cm^2/V{\cdot}s$ 문턱전압의 경우 -13.3V에서 -10.8V로 향상되었으며, contact resistance를 추출하여 비교하였을 경우 감소함을 확인할 수 있었다. 이러한 성능의 향상은 $C_{60}$을 Au와 pentacene 사이에 삽입하였을 경우 Au-pentacene 간의 원하지 않는 화학적 반응을 막아줌으로써 홀 주입장벽를 감소시켜 홀 주입이 향상되었기 때문이다. 또한 Al을 전극으로 적용한 OTFT도 제작하였다. 기존에 Al은 OTFT에 단일전극으로 사용하였을 경우 둘간의 높은 홀 주입장벽으로 인해 채널이 거의 형성되지 않았으나, $C_{60}/Al$ 이중전극을 사용한 소자의 경우 전하이동도와 전류점멸비은 0.165 $cm^2/V{\cdot}s$, $1.4{\times}10^4$ 으로써 Al를 단일전극으로 사용하는 소자의 전기적 특성에 비해 크게 향상되어진 소자를 제작할 수 있었다. 이는 $C_{60}$과 Al이 접합시에 interface dipole의 형성으로 Al의 vacuum energy level이 변화로 인한 Al의 work function이 증가되어 pentacene과 Al간의 hole injection barrier가 감소되었기 때문이다.

Keywords

References

  1. C. D. Dimitrakopoulos and P. R. L. Malenfant, 'Organic Thin Film Transistors for Large Area Electronics,' Adv. Mater. Weinheim, Ger. Vol. 14, pp. 99 ,January 2002 https://doi.org/10.1002/1521-4095(20020116)14:2<99::AID-ADMA99>3.0.CO;2-9
  2. L. Zhou, S. Park, B. Bai, J. Sun, S. Wu, T.N. Jackson, S. Nelson, D. Freeman and Y. Hong, 'Pentacene TFT Driven AM OLED Displays,' IEEE Electron Device Lett. Vol. 26, pp. 640, September 2005 https://doi.org/10.1109/LED.2005.853654
  3. C. D. Sheraw, L. Zhou, J. R. Huang, D. J. Gundlach, T. N. Jackson, M. G. Kane, I. G. Hill, M. S. Hammond, J. Campi and B. K. Greening, J. Francl and J. West, 'Organic thin-film transistor-driven polymer-dispersed liquid crystal displays on flexible polymeric substrates,' Appl. Phys. Lett. Vol 80, pp. 1088, February 2002 https://doi.org/10.1063/1.1448659
  4. F. C. Chen, L. Kung, T. Chen and Y. Lin, 'Copper phthalocyanine buffer layer to enhance the charge injection in organic thin-film transistors,' Appl. Phys. Lett. Vol 90, pp. 073504, February 2007 https://doi.org/10.1063/1.2535741
  5. W. Hu, Y. Zhao, C. Ma, J. Hou and S. Liu, 'Improving the performance of the organic thin-film transistors with thin insulating lithium fluoride buffer layer,' Microelectronics Journal, Vol 38, pp. 632, February 2007 https://doi.org/10.1016/j.mejo.2007.02.007
  6. N. Hayashi, H. Ishii, Y. Ouchi and K. Seki, 'Examination of band bending at buckminsterfullerene $(C_{60})/metal$ interfaces by the Kelvin probe method,' J. Appl. Phys. Vol. 92, pp. 3784, July 2002 https://doi.org/10.1063/1.1504495
  7. A. Kahn, N. Kocha and W. Gao, 'Electronic Structure and Electrical properties of interfaces between Metals and ${\varpi}-Conjugated$ Molecular Films,' J. Polymer Science. Vol. 41, pp. 2529, May 2003 https://doi.org/10.1002/polb.10642
  8. S. T. Zhang, X. Ding, J. M. Zhao, H. Z. Shi, J. He, Z. H. Xiong, H. J. Ding, E. G. Obbard, Y. Q. Zhan, W. Huang and X. Y. Hou, 'Role of hole playing in improving performance of organic light-emitting devices with an $Al_2O_3$ layer inserted at the cathode-organic interface,' A. Phys. Lett., Vol. 89, pp. 043502, July 2006 https://doi.org/10.1063/1.2220013
  9. D. J. Gundlach, L. Zhou, J. A. Nichols, T. N. Jackson, P.V. Necliudov and M. S. Shur, 'An experimental study of contact effects in organic thin film transistors,' J. Appl. Phys., Vol. 100, pp. 024509, July 2006 https://doi.org/10.1063/1.2215132
  10. J. Y. Lee, 'Efficient hole injection in organic light-emitting diodes using C60 as a buffer layer for Al reflective anodes,' Appl. Phys. Lett. Vol 88, pp. 073512, February 2006 https://doi.org/10.1063/1.2174838
  11. J. H. Seo, S. J. Kang, C. Y. Kim, S. W. Cho, K. -H. Yoo, C. N. Whang. 'Energy level alignment between C60 and Al using ultraviolet photoelectron spectroscopy,' A. Surface Sience, Vol. 252, pp. 8015, January 2006 https://doi.org/10.1016/j.apsusc.2005.12.095