Influences of annealing temperature on the thermoelectric properties of thin film thermocouples based on a flexible substrate by RF magnetron sputtering

Thin film thermocouples (TFTCs) made up of indium tin oxide (ITO) and indium oxide (In2O3) are designed and fabricated on a flexible substrate (polyimide) by radio frequency magnetron sputtering to satisfy the application needs of real-time monitoring of the surface temperature of non-planar objects. The microstructure and thermoelectric property of TFTCs are investigated under different annealing temperatures and the results show that the best annealing treatment result is achieved at 200 °C for 1 h. After the annealing treatment, the temperature resolution of the flexible TFTCs can reach 0.1 °C, and the hysteresis error and repeatability error can reach 2.06% and ±1.287%, respectively. An electromotive force (EMF) experiment shows that the average Seebeck coefficient of flexible TFTCs annealed at 300 °C can reach 56.90 µV °C−1 which is more than 8.5 times higher than the unannealed ones when the temperature difference is 200 °C. In addition, different output characteristics are obtained when TFTCs are placed on the inner and outer surfaces with different curvatures. Keeping the temperature difference between the hot and cold ends of the TFTCs constant, the flexible TFTCs also have the ability to measure the angle by measuring the EMF. The sensors show good application potential in temperature measurement in a curved plane and the measurement of the curvature of a curved surface.