Humidity sensors for a pulmonary function diagnostic microsystem

The work reported here is a part of an European research project. The aim o f the project is the implementation of a multisensor microsystem for pulmon ary diagnostic functions for chronic obstructive pulmonary diseases and ast hma patients. The proposed microsystem is required to measure simultaneousl y peak expiratory flow, temperature, relative humidity and pressure. We hav e 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 realise d using silicon as substrate, aluminium as conductor and polyimide Ultradel as dielectric. Sensors responses show that we have a quick absorption of h umidity (less than 1 s) and a longer desorption (15 s). The influence of th e geometry and the dielectric material on the performance of the sensor (se nsitivity, response time) will be reported. Specially, we will demonstrate that a plasma etching of the dielectric surface notably increases the sensi tivity. (C) 2001 Elsevier Science B.V. All rights reserved.