Development of a humidity microsensor with thermal reset

The present project is aimed at developing a capacitive humidity microsensor to measure humidity profiles inside the human respiratory tract. The ultimate goal of the project is to design the sensor with minimum size and with maximum sensitivity providing minimum response time. The sensor will allow determination of humidity variation in different generations of the human lung during a breath. The design process involves an appropriate simulation of the sensor to investigate the influence of several parameters on its sensitivity, and to develop a microheater that would be used to thermally reset the sensor. This sensor consists of interdigitated electrodes formed as a capacitor using aluminum as conductor and polyimide as dielectric built on a silicon substrate. For the thermal resetting, a polysilicon microheater will be built just underneath the sensor. The system should have quick absorption of moisture and ideally have a response time of less than 1 s. This specific requirement would allow for several measurements during one breath period. In order to meet these constraints a capacitive sensor was designed with a dielectric sensitive to humidity. Other parameters such as shapes of air contact surfaces, domain dimensions, properties of materials, etc. are analyzed and results are shown as well.