Many coating applications depend on the monitor and control of film's physical properties. Particularly important are the thermal and/or residual stresses, which mainly occur in the hard coating deposition process. These stresses can affect the optical, electrical, magnetic and mechanical properties of the film. The need to measure and control the stress it is vital for the success of the final device. The development of in situ analysis not only provides the possibility of a feedback control during deposition, but also give a more efficient evaluation of the best conditions to achieve particular properties. Recently, a considerable research has been focused on fiber Bragg gratings (FBG), particularly on systems using these devices for sensing applications. FBG which can be operated in a wavelength-coding manner has become an important component for optical sensing devices in measuring temperature and stress principally in systems where electrical measurements are not allowed. In this work, we present a new optical FBG strain sensor which can be utilized to measure in situ the induced substrate strain caused by the film stress. The fiber optical sensor is interfaced to an analyzer to determine the wavelength shift of the reflected signal due to strain and temperature effect. The technique was used during the deposition of silicon carbide (SiC) and Indium Tin Oxide (ITO) thin films by rf magneto sputtering, onto silicon and glass substrates. The direct measurement of the wavelength shift (Δλ = 0.7 nm) for the ITO films provides a strain value ε = 5.8e^-4 which can be used to found the tensile stress σ = 70 MPa presents in the film/substrate interface. These preliminary results are in agreement with other works reported in the literature. The research is under way to improve the accuracy and study the possibility to develop a more compact device.

This work is supported by RENAMI, CNPq, and FAPERJ.