Work Function Effects of Nano Structured ZnO Thin Film on the Acetone Gas Sensitivity
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1174-V06-23
Work Function Effects of Nano Structured ZnO Thin Film on the Acetone Gas Sensitivity Seung Hyun Jee 1, Nitul Kakati 1, Soo Ho Kim 2, Dong-Joo Kim 3 and Young Soo Yoon 1,* School of Advanced Material Engineering, Yonsei University, Seoul, Korea. 2 Department of Advanced Technology Fusion, Konkuk University, Seoul, Korea. 3 Materials Research and Education Center, Dept. of Mechanical Engineering, Auburn University, AL, USA 1
ABSTRACT We deposited various nano structured ZnO thin films with plasma treatment on an alumina substrate and fabricate ZnO sensors for acetone gas detection. The ZnO sensors with various nano structures and the plasma treatment (PT) were deposited by radio frequency (RF) magnetron sputtering method with RuO2 micro heater and Ru electrode. In order to control the work function intentionally, the various deposition conditions and the plasma treatment were used. Sensitivities of the ZnO sensor were measured in acetone vapor and air at 250℃. In conclusion, we suggested that not only plasma treatment can enhance the work function but also the sensitivity of ZnO sensors for acetone be improved on the work function increase of the plasma treated ZnO thin films with nano structures. INTRODUCTION Many researchers have recently focused on ZnO thin film because it is an inexpensive n-type and wide band gap (3.2 eV) semiconductor with high transmittance, good electrical conductivity and high gas sensing property.[1,2,3] These properties make the ZnO a multifunctional material that can be applied to sensing material of gas sensors and a transparent electrode of optical devices. [4,5]. Even though the ZnO thin film shows relatively high sensitivity for acetone gas, the operation temperature and detectable minimum acetone gas concentration are still high when we consider the real commercial application of the ZnO thin film based gas sensor. [6,7] The electron transfers on surface depends on work function [8]. However, influence of work function of ZnO thin film on acetone gas sensitivity has not been reported yet. In this study, the ZnO thin films with various deposition conditions and plasma treatment were fabricated by radio frequency (RF) magnetron sputtering on an alumina substrate with a RuO2 micro heater and a Ru electrode. In order to control the work function intentionally, different deposition conditions and the plasma treatment were used. In this study, we investigated relations between sensitivity and the work function in the ZnO sensor for acetone with various work functions by various deposition conditions and the plasma treatment. EXPERIMENT The RF magnetron sputtering system with Zn target was used to deposit ZnO thin film on alumina substrate by reactive method. The sputtering gas was used to a mixture of Ar-O2, and the rate of oxygen was varied from 10% to 50%. Thickness of ZnO thin films was 400nm. The chamber had a base pressure of 5 x 10-6 torr and a working pressure of 8.0 x 10-3 torr. Distances from target to substrate were 6.5 cm (in plasma) and 10 cm (out plasma). Table I
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