Ultraviolet CMOS Image-Sensor Via Energy Down Shift Mechanism of Blue-Light Emitting Quantum-Dots for Environment Analysis

Abstract

The application market of ultraviolet (UV) technology has been growing in various fields such as sanitation, sterilization, medicine, and environment, which lead the increase of the demand for UV sensors. In particular, air pollution management has recently attracted social attention. According to the Ministry of Environment, NO2 accounts for 27.2% of air pollutants. An UV sensor can detect NO2 because NO2 absorbs UV lights. The Si based CMOS image sensor (CIS), which is widely used for light sensing, is not suitable for sensing a UV light because of its low quantum efficiency in UV region. Therefore, conventional UV sensors measure reflected, transmitted, and fluorescent UV by using methods with a high sensitivity to UV lights. However, these UV sensors have a limitation in the location of installation because those are single-cell devices or can measure only a small area of several mm2. Therefore, in our research, we propose the quantum-dot (QD) UV-CIS that overcomes these issues and detects NO2 gas quantitatively by imaging UV lights. In addition, we investigated how to increase quantum efficiency and UV sensitivity in Si-CIS by applying a blue-emitting QD film to conventional CIS, which convert UV to blue light through an energy-down-shift mechanism. The UV-CIS demonstrated much higher sensitivity (maximum 118.9 times) in detecting NO2 gas under UV illumination at 365-nm-wavelength than conventional CIS, as shown in Fig. 1. In addition, the difference in UV sensitivity between the conventional CIS and the UV-CIS increased with decreasing the gas UV intensity, as shown in Fig. 2. In particular, under the UV intensity of 100 μW/cm2, the sensitivity of UV CIS to detect NO2 increased by 118.9 times compared to the conventional CIS. Finally, the difference in the UV sensitivity of conventional CIS and UV-CIS and the sensing mechanism of UV lights in UV-CIS will be presented in detail. Figure 1