High-sensitivity NIR Sensing with Stacked Photodiode Architecture

Near-infrared (NIR) sensing technology using CMOS image sensors is used in many applications, including automobiles, biological inspection, surveillance, and mobile devices. An intuitive way to im-prove NIR sensitivity is to thicken the light absorption layer (silicon). However, thickened silicon lacks NIR sensitivity and has other disadvantages, such as diminished optical performance (e.g. crosstalk) and difficulty in processing. In this paper, a pixel structure for NIR sensing using a stacked CMOS image sensor is introduced. There are two photodetection layers, a conventional layer and a bottom photodi-ode, in the stacked CMOS image sensor. The bottom photodiode is used as the NIR absorption layer. Therefore, the suggested pixel structure does not change the thickness of the conventional photodiode. To verify the suggested pixel structure, sensitivity was simulated using an optical simulator. As a result, the sensitivity was improved by a maximum of 130% and 160% at wavelengths of 850 nm and 940 nm, respectively, with a pixel size of 1.2 mu m. Therefore, the proposed pixel structure is useful for NIR sens-ing without thickening the silicon.

Automated summary

This paper presents a near-infrared (NIR) sensing technology using a stacked CMOS image sensor, which is widely employed in various applications. By adding a bottom photodiode as the NIR absorption layer in the stacked CMOS image sensor, the sensitivity of the sensor is improved without increasing the thickness of the conventional photodiode, overcoming the issues of decreased optical performance and processing difficulties.