Comparison of Three Humidity Sensors for a Pulmonary Function Diagnosis Microsystem

Three capacitive humidity sensors developed for a portable clinical application are presented and compared. The first structures consist in interdigitated electrodes covered by a polyimide sensitive layer. The second structures have the same geometry but include a benzocyclobutene sensitive layer and a heating resistor. The third structures have been developed with a new geometry, the electrodes being stacked. Humidity measurements results are presented, in particular sensors response time in absorption that must be very small (inferior to 500 ms). The influence of the heating on the response time is described. In conclusion, the three sensors are compared and the more adapted structure for our application is pointed out. Although polyimide has been widely used for realization of capacitive humidity sensors, we demonstrate here that it is not the best sensitive material for our application.