Research On Sensing Structure Of Micro-sized Capacitive Humidity Sensor

Humidity sensors are not only absolutely necessary for traditional industry,agriculture, business, medical science and meteorology, and also playing an importantrole in modern military, micro-electronics, aerospace. With rapidly development ofMEMS and integrated circuit, humidity sensors make progress in integration,micromation and multi-functionalization, micro capacitive humidity sensors producedin the base of these technologies, detect moisture depending on the change of sensitivecapacitance. Compared to the traditional humidity sensors, micro capacitive humiditysensors made much progress in process technology, manufacturing cost and humiditysensing property. This paper is Open Foundation project funded by Nanjing Universityof Information Science&Technology.The sensing material of humidity sensor in this paper is sandwiched between theelectrodes, the dielectric constant changes along with the change of ambient humidity,the change influences output capacitance, therefore, the humidity detection is finishedby detecting capacitance, using external circuit. The most important factors impactingon humidity sensing property are humidity sensitive materials, sensitive structure andprocessing technology, this paper takes polyimide as humidity sensing material, andintroduces its excellent property, then, gets moisture characteristic curve by simulatingtwo models of capacitor, at last, it manufactures a suspended interdigital capacitivehumidity sensor and tests its property. The main contents of this paper are as follow.First, this paper chooses polyimide as sensing material by comparative analysis ofair, porous oxide, high-molecular polymer and nanometer materials, introduces theproperties and manufacturing process of polyimide, gets principle of sensing humidityon the base of several physical models.Second, this paper improves existing capacitor models, and designs a suspendinginterdigital structure to reduce the impact of parasitic capacitance, simulates moisturecharacteristic curve by COMSOL. Third, this paper designs a manufacturing process for suspending interdigitalstructure, and finishes performance testing.