Stability Of Humidity Sensor Based On Black Phosphorous

There is a huge demand for High-performance humidity sensors nowadays for the diverse applications as it has been already extensively used in many fields,like meteorology monitoring,industry control and agriculture.In recent years,the application of new materials in humidity sensing has become a possible direction after the discovery of many new sensing materials with different properties.Black Phosphorous belongs to the family of 2-D material with its brilliant properties for electronics devices.According to its structure,at room temperature/pressure it is the most stable form.Stability of black phosphorous is presented in this thesis.The major disadvantage of black phosphorous is that its open-air life is very shorter than other materials.When it exposed in open air,it reacts with water present in the air in the presence of light and degrades in hours.A humidity sensor using black phosphorous as a sensing layer was used to observe its stability.Moreover,a glass wafer was used as a substrate and interdigitated electrodes were made of Al which was deposited over the substrate by using the method of sputtering.A(software)Tanner EDA tool was used to design the structure of interdigitated electrodes.After that,as a final step exfoliated black phosphorous was used as a sensing layer which was deposited over electrodes by using spin coating technique and tape was used to protect the pads from black phosphorous.By using different thicknesses for two different samples,results were observed.The thicknesses of both samples were controlled by using different layers of BP by two times over one sample and four times on another sample.Spin Coating was done at the rate of 3000 rpm to deposit BP layers.To observe the results of the fabricated devices,a climatic chamber was used to conduct tests under different conditions of humidity.The temperature was constant at 25℃.An LCR meter was used to measure the values of Cp and Rp.The Sensitivity of two layers sensor was 0.158PF/%RH,Hysteresis was 10.3%RH,Response time and Recovery time was 4.46 sec and 4.79 sec.For four layers sample sensitivity was 2.010PF/%RH,hysteresis was 16.03%RH,response time and recovery time was 20.45sec and 9.51 sec.Testing in low humidity it was observed that the samples constantly degraded on a slow rate for 48 hours.In higher humidity condition,thinner sample constantly degrades for 48 hours while thicker sample becomes stable after degrading for 10 hours.By Long-term stability test in the low humidity of 15%RH for 144 hours,it was observed that the thinner sample degrade till 60 hours and then become stable and thicker sample degraded for 40 hours and then showed a stable response.Then we changed the condition of low humidity to higher humidity at once in the same test for 6 hours and it was noticed that both samples were also stable in the high humidity of 90%RH.