Effect of Interdigited in the Sensed of Carbon Monoxide Using ZnO Films
Authors: Hernández Yazmin Mariela , Avila García Alejandro , Paredes Rubio Gabriel Romero , Peña Sierra Ramón 
Published: May 2020

Carbon monoxide (CO) gas is colorless, odorless, highly toxic and extremely dangerous. Natural sources account for 40% of the CO in the environment while 40% is the result of human activities. It is produced by the incomplete combustion of fuels and exhaust emission [1]. The Zinc oxide (ZnO) is an n-type metal oxide semiconductor (MOS) that has been widely used for gas sensors along many years because of their chemical response to different adsorbed gases, high chemical stability, amenability to doping, non-toxicity, affordability and relative fabrication simplicity. It has a wide range of electronic, chemical and physical characteristics and has become a well-known commercial sensor because of the sensitivity of its properties to variations in its chemical environment [2,3]. In the present work we use ZnO films for sensing of carbon monoxide, The ZnO films are deposited by a Sputtering system using radiofrequency (RF), on substrates of silicon (001) p-type with a size of 1.5 x 1.5 cm2, the substrates were washed using a conventional washing method. ZnO was deposited on the substrate during a fixed deposit period of 45 minutes with a thickness of approximately 150 nm, at a base pressure of 7.1 mTorr, a power of 125 W and an Ar flow of 10%, the blank of ZnO has purity of 99.99%, the deposit was made at room temperature. After the deposit of ZnO films, the metallic interdigitated was definite using lithography, whose design presents variations between the distance of the fingers of 200, 400 and 800 microns as well as the metal thereof, for which aluminum was used, with a thickness of 50 nm, gold with thickness of 25 nm and gold /aluminum with 25 nm and 50 nm thickness respectively, this to be able to study the effect of metals, as well as the distance between the fingers of the interdigitate. The deposited films are applied to measure the detection properties of the gas.

The gas detection properties are evaluated by measuring the changes of the resistance of the sensor in air and CO gas. The metallic interdigitate definite on the ZnO films using two different metals. As expected, the films with a distance between fingers of 800 micros in the interdigitate, were those that presented the greatest response to the gas of interest, this because the surface exposed to gas was larger with respect to the other two designs. The best response to different concentrations of CO was found with the use of Al as the metallic interdigit contact, the difference being greater at high concentrations of CO, and at a relatively low measuring temperature of 240 ° C with respect to the other two metal contacts, as can be observed in Fig. 1.

References

[1] Wright J 2002 Chronic and occult carbon monoxide poisoning: we don´t know what we´re missing Emerg Med J 19 386-390.

[2] S. Ghanem, A. Telia, C. Boukaous, M.S. Aida, Humidity sensor characteristics based on ZnO nanostructure grown by sol-gel method Int, J. Nanotechnol. 12(2015) 697–707.

[3] D. Zhu, T. Hu, Y. Zhao, W. Zang, L. Xing, X. Xue, High-performance self-powered/active humidity sensing of Fe-doped ZnO nano array nanogenerator, Sens. Actuators B Chem. 213 (2015) 382.

[4] X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, H. Ning, A survey on gas sensing technology, Sensors 12 (2012) 9635.

Figure 1