Determining Heat Treatment Effects on the TCR of NiCr thin film sensors

Advancements in data collection and automation have become critical to maintaining the growth of key industries, including automotive manufacturing, and medical robotics. To facilitate this data collection, thin film sensors are used due to their versatility and customization. The key challenges with the use of thin film sensors are the change in resistance due to the temperature coefficient of resistance (TCR) at higher use temperatures. This change in resistance can cause skewed results at higher temperatures, necessitating the need for compensative circuits. This research investigates the heat treatment process for a common metal sensing element, Evanohm a nickel chromium alloy, to reduce its TCR as close to 0 as possible with increasing testing temperature. This study involves heat treating the alloy at temperatures ranging from 315°C to 600°C, with varying times, then fabricating thin film sensors with the materials using UV laser ablation. The sensors are then mounted onto the aluminum substrate, and resistance is measured across a temperature range of -10°C to 150°C to determine the TCR. Mechanical properties and micro-structural changes are also analyzed to determine the mechanism for change in TCR. The results demonstrate the effectiveness of heat treatment in reducing the TCR of the sensing element, minimizing the impact that testing temperature has on resistance change. This research contributes to the development of more customizable sensors for industries requiring accurate data collection under thermal cycling conditions.