This study presents the fabrication and investigation of humidity sensors based on orange dye (OD) and polyaniline (PANI) composite films. A blend of 3 wt.% OD with 1 wt.% PANI was prepared in 1 ml water. The composite films were deposited on glass substrates between pre-deposited silver electrodes. The gap between the electrodes was 45 μm. The sensing mechanism was based on the impedance and capacitance variations due to the absorption/desorption of water vapor. It was observed that with the increase in relative humidity (RH) from 30% to 90%, the impedance decreases by 5.2×104 and 8.8×103 times for the frequencies of 120 Hz and 1 kHz, respectively. The impedance—humidity relationship showed a more uniform change compared to the capacitance—humidity relationship in the RH range of 30% to 90%. The consequence of annealing, measuring frequency, response and recovery time, and absorption—desorption behavior of the humidity sensor were also discussed in detail. The annealing resulted in an increase in sensitivity of up to 2.5 times, while the measured response time and recovery time were 34 s and 450 s, respectively. The impedance—humidity relationship was simulated.

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A novel surface-type nonvolatile electric memory elements based on organic semiconductors CuPc and H 2 Pc are fabricated by vacuum deposition of the CuPc and H 2 Pc films on preliminary deposited metallic (Ag and Cu) electrodes. The gap between Ag and Cu electrodes is 30-40 µm. For the current-voltage (I-V ) characteristics the memory effect, switching effect, and negative differential resistance regions are observed. The switching mechanism is attributed to the electric-field-induced charge transfer. As a result the device switches from a low to a high-conductivity state and then back to a low conductivity state if the opposite polarity voltage is applied. The ratio of resistance at the high resistance state to that at the low resistance state is equal to 120-150. Under the switching condition, the electric current increases ∼ 80-100 times. A comparison between the forward and reverse I-V characteristics shows the presence of rectifying behavior.

In this work, the elastic layered rubber-graphene composite based multi-functional sensor has been fabricated by rubbing-in technology. The effects of temperature, displacement, pressure and humidity on the impedance of the multi-functional sensor has been investigated in the frequency range of 0–200 kHz. The impedance of the samples decreased under the effect of uniaxial compressive displacement and under the effect of pressure. The temperature coefficient of the samples was found to be −0.836 and −0.862 %/°C with the increase in temperature from 29 °C to 54 °C, respectively, while the impedance of the samples decreased 1.26 ± 0.01 times with the increase in temperature from 29 °C to 54 °C while, respectively. The humidity dependent cross-sensitivity of the samples was investigated in the relative humidity range of (58–93) %RH and no effect of humidity on the performance of the sensor has been observed. The elastic layered rubber-graphene composite potentially can be used as displacement, frequency, temperature and pressure sensors.

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