Fabrication of Relative Humidity Sensors based on Polyimide Nanoparticles

A capacitive relative humidity sensor fabricated with electrosprayed polyimide nanoparticles is proposed in this thesis. The goal has been to fabricate a humidity sensor with small size and simple structure in order to decrease the fabrication cost. Polyimide is used as the sensing material and deposited on top of the electrodes in two methods: spin-on and electrospraying. Performance of the sensors made through these two deposition methods is compared. The effect of different electrospraying parameters on the sensor performance are studied and discussed. The sensor output was measured and compared using a capacitance sensing circuit, an oscillator circuit, and a standard LCR meter. Experimental results show that the humidity sensors proposed in this thesis provide stable data in a short time with low hysteresis when increasing and decreasing humidity. The technique is flexible and can be used to build relative humidity sensors directly on printed circuit board, thus reducing manufacturing costs of such sensor systems.