A Novel Capacitive Low-Humidity Sensor Based on a Double-Sided Structure

Abstract

The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\alpha }$ </tex-math></inline-formula> -Al2O3 sensor has low sensitivity, and its capacitance value only slightly changes in low-humidity environment. To improve the characteristics of such sensors in the field of low humidity, a sensor with a double-sided structure was designed for measuring ppm levels. In this article, the principle of increasing the total effective surface area of the sensing film is investigated based on a conventional sensor. The sensor consists of a parallel-plate capacitive structure with a porous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\alpha }$ </tex-math></inline-formula> -Al2O3-nanostructured sensing film fabricated on an aluminum substrate using an anodic oxidation method. First, the background and objectives of the work are presented. Next, the mathematical model of the sensor with a double-sided structure and its equivalent circuit is briefly described. A simulation in COMSOL is also presented. Then, the process of manufacturing the moisture-sensitive film and sensor is briefly explained. Finally, the performance of the double-sided <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\alpha }$ </tex-math></inline-formula> -al2O3 low-humidity sensor is tested and compared. The results show that the output response of the sensor increases by 2–3 times, and the sensitivity increases by nearly two times to 1.68%/ppm in the range of 1–1000 ppm. The sensor’s temperature dependence, response time, and measurement range are improved.