Humidity sensors for a pulmonary function diagnostic microsystem

The work reported here is a part of an European research project. The aim of the project is the implementation of a multisensor microsystem for pulmonary diagnostic functions for chronic obstructive pulmonary diseases and asthma patients. The proposed microsystem is required to measure simultaneously peak expiratory flow, temperature, relative humidity and pressure. We have in charge the realisation of the humidity sensor. The structure realised with compatible CMOS technology consists in two coplanar electrodes covered by a humidity sensing dielectric. Interdigitated sensors have been realised using silicon as substrate, aluminium as conductor and polyimide Ultradel as dielectric. Sensors responses show that we have a quick absorption of humidity (less than 1 s) and a longer desorption (15 s). The influence of the geometry and the dielectric material on the performance of the sensor (sensitivity, response time) will be reported. Specially, we will demonstrate that a plasma etching of the dielectric surface notably increases the sensitivity.