Abstract
Recently, humidity sensors have been investigated extensively due to their broad applications in chip fabrication, health care, agriculture, amongst others. We propose a capacitive humidity sensor with a shielding electrode under the interdigitated electrode (SIDE) based on polyimide (PI). Thanks to the shielding electrode, this humidity sensor combines the high sensitivity of parallel plate capacitive sensors and the fast response of interdigitated electrode capacitive sensors. We use COMSOL Multiphysics to design and optimize the SIDE structure. The experimental data show very good agreement with the simulation. The sensitivity of the SIDE sensor is 0.0063% ± 0.0002% RH. Its response/recovery time is 20 s/22 s. The maximum capacitance drift under different relative humidity is 1.28% RH.
Highlights
In addition to daily applications, such as air conditioners and humidifiers, humidity sensors are widely used in industrial process control, medical science, food production, agriculture, and meteorological monitoring [1,2,3,4,5,6,7,8,9]
2.5 μm-thick negative photoresist is patterned. (b) An e-beam-evaporated Ti/Au layer is deposited and selectively removed by a lift-off process to form the bottom shielding electrode. (c) A layer of 1 μm silicon dioxide is deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition). (d) interdigital electrode (IDE) are fabricated on the silicon dioxide by the same sequence of lithography, e-beam evaporation, and lift-off
The sensitivity of the shielding electrode under the interdigitated electrode (SIDE) structure is 3.82 times bigger than that of the IDE. These results show the significant improvement of sensitivity brought by the shielding electrode, that minimizes the large constant capacitance of the substrate
Summary
In addition to daily applications, such as air conditioners and humidifiers, humidity sensors are widely used in industrial process control, medical science, food production, agriculture, and meteorological monitoring [1,2,3,4,5,6,7,8,9]. The many manufacturing processes, such as semiconductor manufacturing and chemical gas purification, rely on precisely controlled humidity levels. Environmental humidity needs to be controlled during operations and pharmaceutical processing. In meteorological monitoring, weather bureaus and marine monitoring applications rely on accurate humidity sensing. For modern agriculture [10] and weather stations [11,12], accurate and fast measurement of humidity is becoming more and more important. Electronic sensors have to become faster and more accurate
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