The coherent gradient sensor for film curvature measurements at cryogenic temperature

Cong Liu,Youhe Zhou,Xingyi Zhang,Xue Feng,Jun Zhou

doi:10.1364/oe.21.026352

Abstract

Coherent Gradient Sensor (CGS) system is presented for measurement of curvatures and nonuniform curvatures changes in film-substrate systems at cryogenic temperature. The influences of the interface of refrigerator and itself on the interferograms which are accounting for the temperature effect are successfully eliminated. Based on the measurement technique, the thermal stresses (including the radial stress, circumferential stress and shear stress) of superconducting YBCO thin-film are obtained by the extended Stoney's formula during the heating process from 30K to 150K. Take the superconducting YBCO thin film as an example, the thermal stresses of which are gained successfully.

Highlights

Thin films deposited on various types of substrates are applied in many technologies, such as microelectronics, optoelectronics, thermal barrier coating technology, and microelectromechanical systems (MEMS), etc
The coherent gradient sensor (CGS), one type of shear interferometry, has distinguished advantages, including full field, real-time, non-destructive, 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 high temperature environment, 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]

Summary

Introduction

Thin films deposited on various types of substrates are applied in many technologies, such as microelectronics, optoelectronics, thermal barrier coating technology, and microelectromechanical systems (MEMS), etc. Fabrication of such a film-substrate structure inevitably gives rise to stress in the film due to lattice mismatch, different coefficients of thermal expansion, chemical reactions, or other physical effects. The coherent gradient sensor (CGS), one type of shear interferometry, has distinguished advantages, including full field, real-time, non-destructive, 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].

Methods

Results

Conclusion