Full-Field Measurement of Nonuniform Stresses of Thin Films at High Temperature

AML, Department of Engineering Mechanics, Tsinghua University, Beijing, China.
Optics Express (Impact Factor: 3.49). 07/2011; 19(14):13201-8. DOI: 10.1364/OE.19.013201
Source: PubMed


Coherent gradient sensing (CGS), a shear interferometry method, is developed to measure the full-field curvatures of a film/substrate system at high temperature. We obtain the relationship between an interferogram phase and specimen topography, accounting for temperature effect. The self-interference of CGS combined with designed setup can reduce the air effect. The full-field phases can be extracted by fast Fourier transform. Both nonuniform thin-film stresses and interfacial stresses are obtained by the extended Stoney's formula. The evolution of thermo-stresses verifies the feasibility of the proposed interferometry method and implies the "nonlocal" effect featured by the experimental results.

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    • ". One can see that the higher the temperature is, the weaker the thermal effect is on the refractive index. Thus, the thermal effect on the refractive index of the air can be neglected and the CGS at high temperature developed by Dong et al. [11] is also used in the single medium. This paper presents the theoretical analysis on the curvature measurements of the thin film systems in multiple-media with different refractive indexes. "
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    ABSTRACT: The Coherent Gradient Sensor (CGS) system has many merits, such as full field, real time, nondestructive, vibration insensitivity, etc., which is developed to measure the curvatures and nonuniform curvatures changes of film-substrate systems in multiple media with different refractive indexes. The general calculation formula for the curvatures in multiple media are obtained. Take the CGS applied in two types of medium as an example, the presented theoretical analysis has been verified by experimental measurements when the specimen is immerged into water or silicone oil. Moreover, the influences of wave length on the measurement error of this system are reported.
    Full-text · Article · Feb 2015 · Optics and Lasers in Engineering
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    • "Compared with other methods, the coherent gradient sensor (CGS), one type of shear interferometry, has distinguished advantages, including full field, real-time, noninstrusive, noncontact, and vibration insensitivity , which is based on the observation of substrate curvature induced by this stress, and is gaining increasingly widespread use as diagnostic procedures [8] [9] [10]. According to the mismatch in thermal expansion coefficient between the film and substrate subjected to a changing temperature environment(especially high temperature), Dong et al. [11] developed the CGS system to high temperature and presented the analysis expression of the stress based on the Stoney's formula [12] and its expansions [13] [14] [15] [16] [17]. In addition, CGS system is always used to investigate the deformation of crack tip and facture characteristics in the facture-mechanics [3,18–20], such as the crack tip deformation, stress intensity factor, etc. "
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    ABSTRACT: A general coherent gradient sensor (CGS) system without temperature constraint has been investigated for the measurement of curvatures and nonuniform curvatures changes in film-substrate systems. According to a strict mathematical derivation with the wave nature of light, systematic absolute error limit and relative error limit of the CGS system are presented at arbitrary temperature. It is found that with the decrease of the ambient temperature, the systematic relative error limit increases with a negative exponential law.
    Full-text · Article · Jul 2013 · Optics and Lasers in Engineering
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    ABSTRACT: Thin film technology is an area of great importance in current applications of opto-electronics, electronics, MEMS and computer technology. A critical issue in thin film technology is residual stresses that arise when the coating is deposited onto a substrate. Residual stresses can be very large in magnitude and have detrimental effects on the role that the thin film must play. To save development time on coating deposition processes it is important to perform accurate residual stresses measurements in situ in real time where the deposition is made. A novel optical set up is developed in this study to measure deflections and residual stresses generated in coated specimens that can be applied directly in the reactor utilized in the deposition process. Experimental results are in good agreement with other measurements carried out independently and other data reported in literature for thin films like those tested in the experiments.
    Full-text · Article · Jul 2013 · Experimental Mechanics
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