Accurate Ruby Sensor for Stress Analysis in Electronics

In this work, we present a simple and cost-effective method to produce a stress sensor based on the luminescence response of ruby thin films. The proposed sensor has a multilayer configuration between the target film of YBa2Cu3O7-delta (YBCO), the nickel tape substrate, and a ruby thin film, among others. The ruby film is deposited by sputtering, and the YBCO was deposited by A-MOCVD on the opposite surface on the top of the Ni-tape substrate. The performance of the sensor is estimated by calculating the residual stresses of the YBCO thin film after deposition. The analysis is conducted using Raman spectroscopy, where the shift of the luminescent lines of ruby are used to determine the residual stress built up, which is extrapolated by means of the Stoney equation to the REBCO film. The calculated residual stress in the ruby sensor is from 0.56 to 0.625 GPa, which translates to 1.50-1.68 GPa in the REBCO film. Further confirmation of the residual stress value in the REBCO film is done using the Stoney equation, resulting in a stress value of 1.55 GPa. This demonstrates the accuracy of the method. The sensitivity, easy processing, reliability, and low cost of the ruby thin films make of them a highly desirable option for their application as stress sensors for a wide variety of applications, including electronics.