Interdigitated humidity sensors for a portable clinical microsystem

Presents and compares two capacitive humidity sensors with interdigitated electrodes for a portable clinical application. The first structures are covered by a polyimide sensitive layer and the optimised ones include a BCB sensitive layer and a heating resistor. Humidity measurements results are presented, in particular sensors response time in absorption which are very small (inferior to 500 ms). Then, mechanisms of absorption and adsorption in a polymer layer are described and the two structures are compared. The suitability of optimised sensors for the authors' application is discussed: new structures permit to increase sensitivity and decrease response time. When the structure is maintained at 40/spl deg/C by its heater, the response time is 200 ms and the total desorption time is 11 s.