Frequency and humidity dependent sensing properties of 3-(4, 5-diphenyl-1H-imidazol-2-yl)phenol based humidity sensor.

In this study the semiconducting properties of imidazole based organic compound 3- (4, 5-diphenyl-1H-imidazol-2-yl) phenol (DHIP) was investigated as an active sensing material to further fabricate surface-type humidity sensor. Aluminum (Al) having thickness of 100 nm was deposited on 25 × 25 mm2 glass substrate by vacuum thermal evaporator. The gap between electrodes was kept ~ 40 micrometer (µm). The DHIP material was deposited between the Al-electrodes in order to form Al/DHIP/Al sensor. The SEM image of the DHIP material shows that the structure consists of petals and needles like structure having pores and pore channels. The change in capacitance of the device as a function of relative humidity (RH) was measured at applied frequencies of 120 Hz and 1 kHz. The capacitance of the device was increased from 15 pF to 22 pF, and from 15 pF to 17.1 pF when humidity was changed from 45% RH to 95% RH at applied frequencies of 120 Hz, and 1 kHz, respectively. The response time of the device was 22 s and recovery time of the device was 54 s at applied frequencies of 120 Hz. The values of R2, i.e. goodness of fit, were 0.96 and 0.98 for the chemisorbed and physisorbed layers, respectively. These R2 values are close to unity, which showed highest response in comparison to the reported sensors based on different materials. [ABSTRACT FROM AUTHOR]