A High Near-Infrared Sensitivity Over 70-dB SNR CMOS Image Sensor With Lateral Overflow Integration Trench Capacitor

This article presents a 16-μm pitch CMOS image sensor (CIS) exhibiting a high near-infrared (NIR) sensitivity and a 71.3-dB signal-to-noise ratio (SNR) with a linear response for high-precision absorption imaging. A 1.6-pF lateral overflow integration trench capacitor (LOFITreC) was introduced in each pixel to achieve a very high full well capacity (FWC), and a very low impurity concentration p-type Cz-Si substrate with a low oxygen concentration was employed for improving the NIR sensitivity. The developed CIS operated at a single exposure linear response wide dynamic range (DR) mode and a dual reset voltage mode for high SNR absorption imaging and achieved the maximum 24.3 Me
^-
FWC, a wide spectral sensitivity from 200 to 1100 nm, and a photodiode quantum efficiency of 89.7%, 78.2%, and 26.7% at 860, 940, and 1050 nm, respectively. Both the spatial resolution and light sensitivity toward the NIR light were further improved by thinning the Si substrate and by applying a negative backside bias. Due to the LOFITreC, a record spatial efficiency of 95 ke
^-
/μm
²
with a 130-dB DR was achieved. As one of the applications of the developed CIS, the NIR absorption imaging toward a noninvasive blood glucose measurement was experimented and a diffusion of 5 mg/dl glucose was clearly visualized at 1050 nm in real time.