A real-time humidity sensor based on a microwave oscillator with conducting polymer PEDOT:PSS film

• Published in: Sensors and actuators. B, Chemical Vol. 282; pp. 145 - 151
• Main Authors: Kang, Tae-Gyu, Park, Jin-Kwan, Yun, Gi-Ho, Choi, Hyang Hee, Lee, Hee-Jo, Yook, Jong-Gwan
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-03-2019; Elsevier Science Ltd
• Subjects: Conducting polymer; Conducting polymers; Ground plane; Humidity; Microstrip transmission lines; Microwave; Microwave oscillators; Negative resistance circuits; Oscillating circuit; PEDOT:PSS; Polymer films; Polymers; Real time; Real-time humidity sensing; Relative humidity; Sensors; Thin films; Microwave; Oscillating circuit; Conducting polymer; PEDOT:PSS; Real-time humidity sensing
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2018.09.080

•Electrical properties of the PEDOT: PSS due to changes in the humidity level.•Negative resistance circuit combined with the microstrip sensor creates a negative resistance for high frequency oscillations.•Microstrip sensor has a grounded microstrip line structure with a CP polymer film as a part of signal line.
In this paper, we propose a humidity sensor based on a negative resistance oscillator using conducting polymer (CP) PEDOT:PSS film at room temperature. The proposed humidity sensor basically consists of a microstrip line and a negative resistance circuit, which creates a negative resistance for high-frequency oscillation. The microstrip line has a circuit structure that is connected through a via hole between the ground plane and the signal line with a CP thin film. From our experimental results, we find that the oscillation frequency of the sensor gradually decreases as the relative humidity (RH) increases. Owing to the conductivity variation of the CP film with the RH value, the oscillation frequency of the sensor sensitively changes in real time. Therefore, we suggest that our microwave-oscillator-based sensor scheme is a good candidate for the design of a robust and stable humidity sensor.