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Research Papers

Influences of Specimen Size and Temperature on Viscoelastic Tensile Properties of SU-8 Photoresist Films

[+] Author and Article Information
Takahiro Namazu

Associate Professor
Department of Mechanical Engineering,
University of Hyogo,
2167 Shosha,
Himeji, Hyogo 671-2201, Japan
e-mail: namazu@eng.u-hyogo.ac.jp

Kenichi Takio, Shozo Inoue

Department of Mechanical Engineering,
University of Hyogo,
2167 Shosha,
Himeji, Hyogo 671-2201, Japan

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received June 5, 2015; final manuscript received December 14, 2015; published online January 21, 2016. Assoc. Editor: Hareesh Tippur.

J. Eng. Mater. Technol 138(2), 021002 (Jan 21, 2016) (5 pages) Paper No: MATS-15-1127; doi: 10.1115/1.4032320 History: Received June 05, 2015; Revised December 14, 2015

In this paper, the influences of specimen size and test temperature on the viscoelastic properties of SU-8 photoresist films are described. Films with the thicknesses of 1 μm and 10 μm are subjected to quasi-static uniaxial tensile tests and stress relaxation tests at temperatures ranging from 293 K to 473 K. The average glassy modulus at 293 K is 3.2 GPa, which decreases with an increase in the test temperature irrespective of specimen size. The mean fracture strain depends on film thickness as well as temperature. The fracture strain of the 1-μm thick films is approximately half of that of the 10-μm thick films at each temperature. Stress relaxation tests are conducted for constructing the master curves of the relaxation moduli. There is no apparent thickness dependence on the master curve. Above glass transition temperature, Tg, apparent activation energies for the two films are almost identical, whereas the activation energy for the thinner films is smaller than that for the thicker films below Tg. This size effect is discussed using Fourier transform infrared spectroscopy (FTIR).

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Figures

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Fig. 1

Photograph of fabricated SU-8 specimen used for uniaxial tensile test. The photo was shot after Pt coating on SU-8.

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Fig. 2

Photographs of specially developed uniaxial tensile test equipment for thin films. The equipment is able to precisely apply tensile force to a film specimen. A CCD camera is set in the overhead of a specimen for tensile elongation measurement without contact. The equipment is set in a vacuum chamber to conduct quasi-static tensile tests and stress relaxation tests at intermediate temperatures without oxidation.

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Fig. 3

Representative tensile stress–strain relations of the SU-8 specimens. It is found that both the test temperature and specimen thickness dependences on the stress–strain behaviors.

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Fig. 4

The Young's modulus and fracture strain for SU-8 as a function of test temperature

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Fig. 5

Constructed master curves of relaxation modulus for SU-8 specimens by means of stress relaxation tests. Reference temperature was set to be 411 K.

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Fig. 6

Relationship between test temperature and time-temperature shift factor used for making the master curves of relaxation modulus based on the time-temperature reduction law. The slopes for each specimen indicate apparent activation energies in glassy and rubbery states.

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Fig. 7

Representative FTIR spectra for the SU-8 specimens. There are two differences, transmittances for epoxy radical and ether linkage, in the spectra.

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