Thermomechanical and Creep Behaviors of Multilayered Metallization Systems Developed for High‐Temperature Surface Acoustic Wave Sensors

Abstract

The structural stability and durability of a sensing device at high‐temperatures (HT) have important effects on its functionality and reliability. This becomes more critical in the devices that work based on the surface acoustic waves (SAW). In this study, the thermomechanical and creep behaviors of the metallization systems, RuAl, MoLa, and Mo suggested for the electrodes of HT‐SAW sensors are investigated. Several experiments are designed to obtain the state and the value of stress in the films deposited on a Si [100] substrate caused by the fabrication process and the operational conditions. Results show that after the film deposition, the intrinsic compressive stress in the MoLa film is significantly lower than the other films. However, after annealing the samples, the lowest residual stress is reached in the Mo. Linear stress variations during the thermal cycling of the annealed samples are obtained for all metallizations. To study the durability of the films at HT, the creep behavior of the samples is investigated by keeping them at a temperature of 600 °C for 10 h. The creep rate and its constitutive equation for the films are obtained. It is observed that the creep rate of MoLa and Mo films is much lower than RuAl.

A Practical Approach for Determination of Thermal Stress and Temperature-Dependent Material Properties in Multilayered Thin Films

“…The alloy layer 3 is the functional part. By deposition, it is composed of a stack of alternating RuAl and Al layers as shown in Figure b, which combine during the annealing process and form one layer of RuAl alloy. ,, …”

“…However, the closed-form solution is too complicated for engineering calculations, and the simplified solution requires multiple experiments to obtain the required parameters. Alternatively, the modified Stoney equation for the biaxial stress state can be applied directly to multilayered thin films as a whole stack to acquire the average thermal stress throughout the film layers. , This approach is engineering-doable without multiple experiments, but the detailed distribution of thermal stress within film layers remains unknown.…”

“…A five-layered sample of RuAl metallization system − was sputter-deposited as a multilayered thin film system and analyzed. To acquire the thermal stress or mechanical properties of thin films, the curvature variations of the sample under thermal load are determined by an in situ multibeam optical sensor (MOS) system in an ultrahigh vacuum (UHV) pressure chamber equipped with an automated heating system . In addition, a numerical model of the multilayered thin films system is built and validated by the experimental curvature results in a temperature range from 20 to 600 °C.…”

“…Alternatively, the modified Stoney equation for the biaxial stress state can be applied directly to multilayered thin films as a whole stack to acquire the average thermal stress throughout the film layers. 9 , 15 This approach is engineering-doable without multiple experiments, but the detailed distribution of thermal stress within film layers remains unknown.…”

“…To acquire the thermal stress or mechanical properties of thin films, the curvature variations of the sample under thermal load are determined by an in situ multibeam optical sensor (MOS) system in an ultrahigh vacuum (UHV) pressure chamber equipped with an automated heating system. 15 In addition, a numerical model of the multilayered thin films system is built and validated by the experimental curvature results in a temperature range from 20 to 600 °C. The stress in each film layer obtained from the validated numerical simulation is compared with the results calculated from the multilayer-adapted Stoney equation.…”