Polymer-electrolyte-film-based Humidity Sensor With Integrated Signal Conditioner

This paper describes a humidity sensor, whose sensing element is an ionic polymer film the resistance of which is measured by a dedicated signal conditioning circuit implemented in 0.35um CMOS. In addition to providing excitation and measurement of the film resistance, the implemented signal conditioning circuit detects the temperature of the sensing film by way of an on-chip temperature sensor in order to perform the necessary compensation for the influence of the temperature upon the measured relative humidity. The sensing polymer film is 10.4 μm thick deposited on glass by casting using a solution of P(EO-EPI)84-16+NaI on top of the interdigitated gold electrodes. The signal conditioning circuit excites the sensing element with a 50% duty-cycle, 1KHz, 700nA, square wave. Samples of the sensor have been measured in the range 25 to 85% RH, varying the temperature from 10 to 50°C. At 55%RH/30°C the mean value of resistance per square of the measured samples is 16.9k Ω/□.Traversa, E., (1995) Ceramic Sensor for Humidity Detection: State-ofthe- Art and Future Developments, pp. 135-156. , Sensors and Actuators B: 23, Issues 2-3, FebruarySakai, Y., Sadaoka, Y., Matsuguchi, M., (1996) Humidity Sensors Based on Polymer Films, 35, pp. 85-90. , Sensors and Actuators B: Issues 1-3, SeptemberGazotti, W.A., Spinacé, M.A.S., Girotto, E.M., De Paoli, M.A., Polymer Electrolytes Based on Ethylene Oxide-Epichlorohydrin Copolymers (2000) Solid State Ionics, 130, pp. 281-291Nogueira, A.F., Spinacé, M.A.S., Gazotti, W.A., Girotto, E.M., De Paoli, M.-A., Poly(ethilene oxide-co-epichlorohydrin)/NaI: A Promising Polymer Electrolyte for Photoelectrochemical Cells (2001) Solid State Ionics, 140, pp. 327-335Harsányi, G., Polymer Films in Sensor Applications: Technology, Materials, Devices and their Characteristics, (C1995). , Lancaster, Pa, Technomic Pub. CoConnolly, E.J., O'Halloran, G.M., Pham, H.T., Sarro, P.M., French, P.J., (2002) Comparison of Porous Polysilicon and Porous Silicon Carbide as Materials for Humidity Sensing Applications, pp. 25-30. , Sensors and Actuators A: 99, Issues 1-2, 30 Apri