Cr2O3-modified ZnO thick film resistors as LPG sensors

Thick films of pure ZnO were obtained by screen-printing technique. Surface functionalized ZnO thick films by Cr2O3 were obtained by dipping pure ZnO thick films into 0.01 M aqueous solution of chromium trioxide (CrO3). The dipped films were fired at 500 °C for 30 min. Upon firing, the CrO3 would reduce to Cr2O3. Cr2O3-activated (0.47 mass%) ZnO thick films resulted in LPG sensor. Upon exposure to 100 ppm LPG, the barrier height between Cr2O3 and ZnO grains decreases markedly, leading to a drastic decrease in resistance. The sensor was found to sense LPG at 350 °C and no cross sensitivity was observed to other hazardous, polluting and inflammable gases. The quick response (∼18 s) and fast recovery (∼42 s) are the main features of this sensor. The effects of microstructures and dopant concentrations on the gas sensing performance of the sensor were studied and discussed.