Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
권호 표지
DOI QR코드

DOI QR Code

Experimental and Finite Element Study of Tribological Characteristics of SU-8 Thin Film

실험 및 유한요소해석에 의한 SU-8 박막의 Tribological 특성 연구

  • 양우열 (한남대학교 기계공학과) ;
  • 신명근 (한남대학교 기계공학과) ;
  • 김형만 (한남대학교 기계공학과) ;
  • 한상철 (한남대학교 기계공학과) ;
  • 성인하 (한남대학교 기계공학과)
  • Received : 2012.07.17
  • Accepted : 2012.12.02
  • Published : 2013.04.01
Download PDF
⟨ Previous Next ⟩

Abstract

In this study, two-dimensional finite element models were developed and experiments were conducted using an atomic force microscope to investigate the tribological characteristics of an SU-8 layer coated on a patterned wafer for microsystem applications. The results revealed that both the adhesion and the friction forces measured by the atomic force microscope were lower for the SU-8 coated surface than for the bare silicon surface. This is attributed to the hydrophobicity of SU-8. Another important result derived from the finite element analysis was the critical load required to fracture the SU-8 film with respect to the thickness. The critical loads for thicknesses of 200, 400, and 800 nm were approximately 13, 22, and 28 mN, respectively, which corresponded to a Hertzian contact pressure of 1.2-1.8 GPa. These results will aid in the design of a suitable SU-8 thickness for microsystem components that are in contact with one another.

본 연구에서는 SU-8 박막의 마이크로시스템으로의 트라이볼로지적 응용을 목적으로 하여, 원자간 힘 현미경(AFM) 과 콜로이드 프로브를 이용한 실험 및 유한요소해석 기법을 이용하여 SU-8 코팅층의 두께에 따른 트라이볼로지적 특성을 고찰하였다. SU-8 시편은 스핀 코팅기법을 이용하여 두께를 다르게하여 제작하였다. 실험결과 코팅두께가 증가함에 따라 마찰력과 점착력이 감소하여 박막두께에 따른 차이가 존재함을 알 수 있었고, SU-8 표면이 Si 표면에서보다 더 낮은 점착력과 마찰력을 보여주었다. 또한, 시뮬레이션을 통해 두께별로 박막 파손을 유발시키는 임계하중(압력)이 존재하며, 본 연구에서의 200~800 nm 두께범위에서는 1.2~1.8 GPa 로 측정되었다.

Keywords

References

  1. Williams, J. A. and Le, H. R., 2006, "Tribology and MEMS," Journal of Physics D: Applied Physics, Vol. 39, pp. 201-204. https://doi.org/10.1088/0022-3727/39/12/R01
  2. Kim, D.E., Cha, K. H. and Sung, I. H., 2002, "Design of Surface Micro-Structures for Friction Control in Micro-Systems Applications," CIRP Annals, Vol. 51, No. 1, pp. 495-498. https://doi.org/10.1016/S0007-8506(07)61569-8
  3. Baumgart, P., Krajnovich, D. J., Nguyen, T. A. and Tam, A. C., 1995, "A New Laser Texturing Technique for High Performance Magnetic Disk Drives," IEEE Transactions on Magnetics,Vol. 31, pp. 2946-2951. https://doi.org/10.1109/20.490199
  4. Abgrall, P., Conedera, V., Camon, H., Gue, A. M. and Nguyen, N. T., 2007, "SU-8 as a Structural Material for Labs-on-Chips and Microelectromechanical Systems," Electrophoresis, Vol. 28, pp. 4539-4551. https://doi.org/10.1002/elps.200700333
  5. Foulds, I. G. and Parameswaran, M., 2006, "A Planar Self-Sacrificial Multilayer SU-8-Based MEMS Process Utilizing a UV-Blocking Layer for the Creation of Freely Moving Parts," Journal of Micromechanics and Microengineering, Vol. 16, pp. 2109-2115. https://doi.org/10.1088/0960-1317/16/10/026
  6. Tay, N. B., Minn, M. and Sinha, S. K., 2011, "Polymer Jet Printing of SU-8 Micro-Dot Patterns on Si Surface: Optimization of Tribological Properties," Tribology Letters, Vol. 42, pp. 215-222. https://doi.org/10.1007/s11249-011-9765-y
  7. Tay, N. B., Minn, M. and Sinha, S. K., 2011, "A Tribological Study of SU-8 Micro-Dot Patterns Printed on Si Surface in a Flat-on-Flat Reciprocating Sliding Test," Tribology Letters, Vol. 44, pp. 167-176. https://doi.org/10.1007/s11249-011-9835-1
  8. Jiguet, S., Judelewicz, M., Mischler, S., Hofmann, H., Bertsch, A. and Renaud, P., 2006, "SU-8 Nanocomposite Coatings with Improved Tribological Performance for MEMS," Surface & Coatings Technology, Vol. 201, No. 6, pp. 2289-2295. https://doi.org/10.1016/j.surfcoat.2006.03.041
  9. Singh, R. A., Satyanarayana, N., Kustandi, T. S. and Sinha, S. K., 2011, "Tribo-Functionalizing Si and SU8 Materials by Surface Modification for Application in MEMS/NEMS Actuator-Based Devices," Journal of Physics D: Applied Physics, Vol. 44, 015301. https://doi.org/10.1088/0022-3727/44/1/015301
  10. Son, Y., Lim, T. W., Yang, D. Y., Yi, S. W., Kong, H. J. and Park, S. H., 2008, "Study on Process Parameters of a SU-8 Resin in Two-Photon Stereolithography for the Fabrication of Robust Three-dimensional Microstructures," Journal of the Korean Society of Precision Engineering, Vol. 25, No. 1, pp. 130-137.
  11. Choi, I., Wang, H., Choi, K. S. and Kim, H. M., 2010, "Numerical Analysis-Based Design of PEMFC Channel, Fabrication of Channels, and Performance Test Using SU-8," Trans. Korean Soc. Mech. Eng. B, Vol. 34, No. 4, pp. 349-354. https://doi.org/10.3795/KSME-B.2010.34.4.349
  12. Lawrence, C. J., 1988, "The Mechanics of Spin Coating of Polymer Films," Physics of Fluids, Vol. 31, No. 10, pp. 2786-2795. https://doi.org/10.1063/1.866986
  13. Sader, J. E., Chon, J. W. M. and Mulvaney, P., 1999, "Calibration of Rectangular Atomic Force Microscope Cantilevers," Review of Scientific Instruments, Vol. 70, pp. 3967-3969. https://doi.org/10.1063/1.1150021
  14. Green, C. P., Lioe, H., Cleveland, J. P., Proksch, R., Mulvaney, P. and Sader, J. E., 1995, "Normal and Torsional Spring Constants of Atomic Force Microscope Cantilevers," Review of Scientific Instruments, Vol. 75, pp. 1988-1996.
  15. Ogletree, D. F., Carpick, R. W. and Salmeron, M., 1996, "Calibration of Frictional Forces in Atomic Force Microscopy," Review of Scientific Instruments, Vol. 67, pp. 3298-3306. https://doi.org/10.1063/1.1147411
  16. De, S., Hong, J. and Bathe, K., 2003, "On the Method of Finite Spheres in Applications: Towards the use with ADINA and in a Surgical Simulator," Computational Mechanics, Vol. 31, No. 1, pp. 27-37. https://doi.org/10.1007/s00466-002-0390-3
  17. Cappella, B. and Dietler, G., 1999, Force-Distance Curves by Atomic Force Microscopy, Surface Science Reports, Vol. 34, No. 1-3, pp. 5-104.
  18. Waltman, R. J. and Guo, X.-C., 2012, "AFM Force-Distance Curves for Perfluoropolyether Boundary Lubricant Films as a Function of Molecular Polarity," Tribology Letters, Vol. 45, No. 2, pp. 275-289. https://doi.org/10.1007/s11249-011-9887-2
  19. Rymuza, Z., 2007, "Tribology of Polymers," Archives of Civil and Mechanical Engineering, Vol. VII, No. 4, pp.177-184.
  20. Yamaguchi, Y., 1990, Tribology of Plastic Materials, Tribology Series, Vol. 16, Elsevier, New York.
  21. Imperial College Press ed., Polymer Tribology, Chapter 1, World Scientific Publishing, 2009.
  22. Hammerschmidt, J. A., Gladfelter, W. L. and Haugstad, G., 1999, "Probing Polymer Viscoelastic Relaxations with Temperature-Controlled Friction Force Microscopy," Macromolecules, Vol. 32, pp. 3360-3367. https://doi.org/10.1021/ma981966m
  23. Forrest, J. A., Dalnoki-Veress, K. and Dutcher, J. R., 1997, "Interface and Chain Confinement Effects on the Glass Transition Temperature of Thin Polymer Films," Physical Review E, Vol. 56, pp. 5705-5716. https://doi.org/10.1103/PhysRevE.56.5705
  24. Yu, H., Balogun, O., Li, B., Murray, T. W., and Zhang, X., 2006, "Fabrication of Three-Dimensional Microstructures Based on Singled-Layered SU-8 for Lab-on-Chip Applications," Sensors and Actuators A: Physical, Vol. 127, No. 2, pp. 228-234. https://doi.org/10.1016/j.sna.2005.08.033
  25. Yu, H., Balogun, O., Li, B., Murray, T. W., and Zhang, X., 2004, "Building Embedded Microchannels Using a Single Layered SU-8 and Determining Young's Modulus Using a Laser Acoustic Technique," Journal of Micromechanics and Microengineering, Vol. 14, No. 11, pp. 1576-1584. https://doi.org/10.1088/0960-1317/14/11/020