Book Description

Thin-film pressure sensors have received widespread attention in recent times due to its ease of manufacture, characterization, and fatigue strength. Commercial fabrication of these sensors is inexpensive and compatible with the current manufacturing technologies. It has been found that the sensitivity of the flexible pressure sensor depends on the sensing pressure, the microstructural dispersion of nanoparticles, and the compatibility of the binder and the nanoparticles. The binder/particle dispersion should be such that it facilitates the formation of a greater number of conduction paths with a slight change in sensing pressure. The objective of this thesis includes the fabrication and characterization of a thin-film pressure sensor using different novel materials. The first material to be investigated was ZnO. ZnO thin-film materials that have received a great deal of attention due to its unique properties of being a semiconductor with wide bandgap and piezoelectric effect. The sensor characteristic of ZnO was compared with barium-titanate (BaTiO3) Gallium arsenic (GaAs) and Polyvinylidene fluoride (PVDF). The second material to be investigated was aluminum-doped zinc oxide (AZO). AZO has attracted a great deal of attention in many applications because of its nontoxicity, abundancy, and lower cost than other materials such as indium tin oxide (ITO). The AZO films were deposited on polyethylene (PE) substrates by a radiofrequency (rf) magnetron sputtering method. The piezoresistive sensor was tested for different pressures in vacuum and gage pressure conditions. The response characteristics indicated that resistance increased with the bending of the AZO layer in both compressive and tensile operation modes. The sensor characteristics exhibited that the AZO piezoresistive sensor can be used to measure ambient pressure quantitatively. This investigation indicated that AZO can be used as an alternative material for the fabrication of pressure sensors. Lastly, the materials that were investigated are carbon black/ Poly (vinylidene fluoride) (CB/PVDF), graphene/PMMA, and graphene/PVDF composites. The conductive CB/PVDF material was prepared by the wet-cast method and deposited into a flexible polyethylene (PE) substrate, while the graphene composites were prepared by the solvent cast method. The surface morphology, crystal structure, and material properties were studied using SEM and X-ray diffraction methods. Sensitivity, response time, and recovery time were analyzed by testing the sample in the deferent pressure range and vibration modes. The repeatability and reproducibility characteristics of the sensor were studied and found that the sensor exhibits excellent characteristics. The sensors were subjected to different loading/unloading pressures. The resistance of the sensor remained stable indicating that the sensor had a high degree of reproducibility.