Advancing industry 4.0 with microfabrication of K-type TFTCs on stainless steel 316 L substrates: A study on SiO2 insulation, substrate thickness, and surface roughness optimization

Abstract Thin-film thermocouples (TFTCs) are critical for real-time temperature monitoring in advanced manufacturing processes where conventional sensors fail due to spatial constraints or complex geometries. This study develops K-type TFTCs on stainless steel 316 L substrates with optimized SiO₂/SiO insulation layers for industrial deployment. In particular, two types of stainless steel substrates were investigated: thick and rigid substrates designed for stationary applications requiring durability, and thin, flexible substrates tailored for dynamic environments such as robotics and other moving systems. We systematically investigate the impact of substrate thickness (flexible − 50 μm to rigid − 500 μm), surface roughness (Ra = 20 nm to 0.210 μm), and insulation deposition techniques (PECVD, SOG, PVD) on sensor performance. TFTCs on 50-µm substrates achieved a 71% faster response time (0.95 s) than conventional designs, with sensitivities of 0.041142 mV/°C, demonstrating excellent agreement with the theoretical K-type thermocouple sensitivity of 0.041 mV/°C. The sensor mechanical robustness, corrosion resistance, and flexibility enable direct integration into manufacturing equipment for in-situ monitoring of machining, forging, and additive manufacturing processes. These advances address Industry 4.0 demands for embedded sensing in harsh industrial environments, enhancing predictive maintenance and energy efficiency in automotive, aerospace, and energy sectors.