Structural Evolution
The rate at which internal mechanical stresses in a thin film are relieved over time under thermal or mechanical exposure determines the long term stability of the sensor. Analyzing the stress relaxation kinetics of deposited films helps engineers predict how the material will behave during high temperature operation. This analysis is critical for maintaining the calibration of strain gauges.
By measuring the stress decay over continuous thermal cycles, developers can determine the stability of the physical bonds at the interface.
Relaxation Mechanism
Atomic diffusion and dislocation climb are the primary microscopic mechanisms that drive the relaxation of residual stresses. When the film is exposed to elevated temperatures, the thermal energy allows atoms to migrate, which reduces the local lattice distortion. This process leads to a reduction in the compressive or tensile stress within the film.
Thermal Effect
Operating temperatures directly influence the rate of this relaxation process, which accelerates exponentially with increasing thermal energy. High temperatures speed up the atomic transport, causing rapid stress reduction during the initial hours of thermal exposure. This behavior requires that the sensor undergo pre stabilization heat treatment before being deployed in the field.
Analytical Measurement
Wafer curvature and x ray diffraction are used to monitor the changes in stress over time at specific temperatures. These measurements provide the data needed to calculate the activation energy of the relaxation process. This activation energy helps determine the lifetime and drift rates of the sensor under field conditions.
