Wearable temperature sensors based on lanthanum-doped aluminum-oxide dielectrics operating at low-voltage and high-frequency for healthcare monitoring systems

Abstract The incorporation of lanthanum (La) into sol-gel based aluminum-oxide (Al2O3) dielectrics is investigated by analyzing the dielectric properties obtained from electrical capacitive measurements of metal-insulator-metal. The optimized La doping results in significantly suppressed variation of frequency-dependent capacitance of sol-gel based La-doped Al2O3 (LaAlO3) dielectrics even at high frequencies of ∼ MHz. In addition, flexible temperature sensors with sol-gel based LaAlO3 dielectrics on polyimide substrates are demonstrated through investigations on the capacitive responses to different temperatures ranging from 30 to 200 °C at various frequencies from 100 Hz to 1 MHz. Without any buffer or passivation film, the proposed flexible temperature sensors achieved a high mechanical stability against cyclic bending tests with curvature radii from 10 to 5 mm. Finally, the feasibility of a healthcare monitoring system incorporated with a smartphone is demonstrated by utilizing wearable body-temperature sensor arrays consisting of sol-gel based LaAlO3 dielectrics. High-performance temperature sensor system is capable of analyzing interfacial temperature characteristics on human body between 30 and 40 °C in real-time and displaying them on the use's smartphone through wireless communication. We believe that this study is expected to significantly contribute to the field of wearable bioelectronics consisting of solution-processed metal-oxide dielectrics for healthcare monitoring systems based on the Internet-of-things.