Nanoporous Humidity-Sensitive Thick Films Derived from Spinel MgAl2O4 Ceramics: Sintering, Structural Analysis and Electrophysical Investigations

One-layered thick films utilizing spinel MgAl2O4 ceramics were meticulously crafted to be sensitive to humidity levels. The research delved into the intricate structural and electrophysical characteristics, particularly focusing on how electrical resistance varied in response to changes in relative humidity. This investigation was conducted both prior to and following a degradation cycle, simulated at 40 ℃ under 95% relative humidity conditions. The findings revealed a remarkable sensitivity of the thick films within the relative humidity range of 55% to 99%. However, an intriguing observation emerged: the sensitivity was notably poorer in regions characterized by lower relative humidity values. This deficiency was attributed to the presence of imperfect porous structures within the thick films, particularly affecting the contact area. This underscores the critical role of the film’s microstructure in dictating its sensitivity across different humidity levels. To improve the properties of thick films two techniques for creating contact areas are showcased: employing Ag or Ag-Ru paste and utilizing conductive thermistor ceramic thick films. It is confirmed that the resultant thick-film structures exhibit sensitivity across a broad range of relative humidity levels. However, it’s observed that thick films deposited on Ag-Ru contacts experience a loss in sensitivity over time due to natural physical aging, leading to degradation of the contact area. Functionality can be reinstated through the re-formation of contacts. The resistance alteration in thick films with applied contacts, in the form of a thermistor film, is found to be significant, approximately one order of magnitude.