Improving the manufacturing technology of sensing gas sensors based on zinc oxide by using the method of magnetron sputtering on direct current

Abstract

A gas sensor based on zinc oxide obtained by magnetron spraying at direct current was investigated. There are methods of deposition of zinc oxide nanostructures such as thermal evaporation, chemical vapor deposition, organometallic chemical vapor deposition, magnetron sputtering, pulsed laser deposition, and hydrothermal process. The least investigated is magnetron sputtering. To obtain films, a vacuum unit VUP-5M with an original material-saving magnetron was used. Studies into the sensitivity and speed of the gas sensor based on ZnO with respect to the target gas – ethanol of different concentrations – were carried out. The resulting experimental dependences of the sensitivity of the gas sensor on the concentration of the target gas demonstrate that with increasing concentration of the target gas, the resistance decreased while the sensitivity of the sample increased. It was established that the change in the resistance of the test sample is proportional to the change in the concentration of the target gas. After the sensor surface becomes saturated with adsorbed molecules, the resistance no longer decreases, even if the gas concentration continues to increase. The reaction of the gas sensor to the target gas – ethanol – at concentrations above 150 ppm was almost absent. The time required to achieve the maximum response value should be lower at higher target gas concentrations. Sensitivity reaction repeatability studies were conducted to measure the resistance of a gas sensor based on ZnO in a target gas atmosphere with a concentration of 150 ppm. It was found that the gas sensor demonstrates excellent stability and consistent sensitivity reaction when re-exposed to the target gas – ethanol. It was established that the reaction time of a gas sensor based on ZnO to the target gas at each repeated exposure does not exceed 10 s. This repeatability index allows us to assert the stability of the ZnO-based gas sensor in an ethanol atmosphere under standard conditions

Design of ammonia sensor based on ZnO for analyzing hazards at critical infrastructure

“…In contrast to the results reported in [8,9], the ammonia gas sensor demonstrates a high efficiency of detecting the target gas under standard conditions (operating temperature 25 °С) and a low concentration of 25 ppm. In [8], a gas sensor based on ZnO demonstrates sensitivity to the target gas ethanol only when the substrate is heated to a temperature above 200 °С, which negatively affects its degradation resistance.…”

“…In [8], a gas sensor based on ZnO demonstrates sensitivity to the target gas ethanol only when the substrate is heated to a temperature above 200 °С, which negatively affects its degradation resistance. In [9], a gas sensor based on ZnO demonstrates sensitivity to NH 3 of the target gas only at its concentration of 150 ppm.…”

“…From the point of view of fire and explosion hazard, the mass lower concentration limit of flame spread was determined. According to [9], the lower concentration limit of flame propagation is 16.2 %. Using expression (1), the volume concentration of NH 3 was converted into mass:…”

“…The main performance characteristics of the sensor include sensitivity, selectivity, response and recovery time, stability upon repeated exposure to the target gas, ease of manufacturing, and low energy consumption [8]. Most of the commercially available gas sensors have high sensitivity only at elevated operating temperatures, therefore the instrument structures are equipped with microheaters [9]. But frequent switching between heating and normal atmospheric conditions leads to structural transformation of the sensitive layer, phase separation, grain growth of the sensitive element.…”

Devising technological solutions for gas sensors based on zinc oxide for use at critical infrastructure facilities

“…These parameters optimize the sensitivity of the sensor. In work [18], the deposition parameters were as follows: the working pressure of the argon-air mixture during the spraying process is (2.1-2.6)×10 -2 mmHg. The substrate temperature was 300 °C.…”