Development And Fabrication Of Polyimide Capacitive Humidity Sensors

Humidity sensor is widely used in many fields including meteorology, industry, agriculture, medicine, and in our everyday life. With the fast development in technology, the humidity sensor is changed from simple to smarter and more integrated, the humidity sensors which fabricated by IC technology show many advantages, such as higher accuracy and higher reliability.The paper studied capacitive humidity sensor which based on two different electrode structures (the strap type and the grid type) and two different humidity-sensitive layers (the insoluble polyimide and the soluble polyimide). This paper carries out theory researching, manufacturing, testing and analyzing onto different capacitive humidity sensors. We analyses various parameters have influence on device performance from the changes of the concentration of water molecules in the static and dynamic response process. This paper carries out manufacturing, pressure welding and package onto the capacitive humidity sensors, and obtained a great deal of data, analyzed the different from the performance parameters, such as the sensitivity, response time, then did a comparative analysis.The results showed that when the devices were in the same size, the smaller the minimum line width of the upper electrode, the shorter response time of the humidity sensors are. When we use the same kind of materials as the humidity-sensitive layer, the output capacitances of the humidity sensors with the grid type electrode were larger than the strap type humidity sensors, and have higher sensitivity, the sensitivity of humidity sensor which based on grid type electrode was 0.882 pF/%RH,instead, the sensitivity of humidity sensor which based on strap type electrode was 0.65 pF/%RH. Soluble polyimide is more compact, more solid than the insoluble polyimide, but it was difficult to etch. Soluble polyimide humidity sensors have faster response time than insoluble polyimide humidity sensor, the response time of Soluble polyimide humidity sensors was 880 ms, but the response time of insoluble polyimide humidity sensors was 3 s. Regardless of what kind of structure and materials we use, the humidity hysteresis was generally small, which shows that the parameters we select is reasonable.