SAW sensor based on ZnO thin film for ultraviolet light measurement

This research is focusing on SAW (Surface Acoustic Wave) Sensor based on ZnO (Zinc oxide) thin film for ultraviolet light sensing. ZnO is a semiconductor and has a characteristic of wide-bandgap. ZnO material is used as an... [ view full abstract ]

This research is focusing on SAW (Surface Acoustic Wave) Sensor based on ZnO (Zinc oxide) thin film for ultraviolet light sensing. ZnO is a semiconductor and has a characteristic of wide-bandgap. ZnO material is used as an optical sensor for measuring the intensity of ultraviolet light [1]. A mechanical stress generates propagating mechanical waves on SAW sensor as an electric field is applied on piezoelectric substrate. SAW sensor is composed of a sensing area in the middle, called the delay line, of the wave propagation. When an electrical conductivity is changed in the sensing film, Propagated saw speed changes and is measured as a frequency change [2]. In this study, a SAW based ultraviolet light sensor using ZnO thin film as a sensing film was researched and a change of frequency were measured according to the thickness of the sensing area.ZnO, which is a sensing area in the delay line, was deposited at a thickness of 50 to 430 nm by RF(Radio Frequency) sputter. The RF sputter conditions are T:26°,100W, 10mTorr, and Ar:O2 = 10:2 of gas ratio. When ZnO thin film thickness was 100nm, the linear characteristics were observed up to 1.94 mw/cm2 light intensity and the sensitivity was 4.8x10-5/mW. ZnO was used as a material to detect the intensity of light, and the sensor showed a linear characteristic up to 1.9426 mw/cm2 on the SAW sensor. As this ultraviolet light sensor is expected to be a notable technology in smart phone that can replace sensor of photodiode type which  has been various researched.