Thermocouple Fabrication by Cold Plasma Spray

Fraunhofer IST and University of Applied Sciences and Arts (HAWK) have recently developed a Cold Plasma Spray (CPS) coating technique providing for superior assembly of microsensors and other delicate substrates or devices. In CPS systems pulsed voltages at low currents ignite transient arc discharges that result in thermally moderate plasmas. Further, CPS allows for the use of air or nitrogen as plasma gas and provides a considerably gentle coating deposition process enabling the metallization of heat-sensitive or mechanical-weak objects. This is in contrast to conventional High-Temperature Thermal Plasma Spray or High Velocity Oxygen Fuel Spraying. The CPS process extends to a myriad of delicate surface applications, including the fabrication of electrically conductive bars and thermal sensors such as accurate thermocouples. These elements can be deposited onto thin polymer foils, e.g., ≤10 µm-thick PET, glass optics, or organic coatings; the so-called “cathodic dip paint” which is common in the automotive industry. Moreover, depending on the substrate, the CPS process allows for device extensions permitting robot-based metallization without the need for masking. The hereinafter presented work elucidates the fabrication of thin-film thermocouples by means of the unique CPS plasma spray process at Fraunhofer IST with emphasis on two use-cases.