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

Abstract

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. Index Terms-Absorption imaging, CMOS image sensor (CIS), lateral overflow integration trench capacitor (LOFITreC), near-infrared (NIR) light, signal-to-noise ratio (SNR).

Self-Reset Image Sensor With a Signal-to-Noise Ratio Over 70 dB and Its Application to Brain Surface Imaging

“…For SNR, Murata and Fujihara et al presented a pixel with a high SNR of 70 dB ( Murata et al, 2020 ; Fujihara et al, 2021 ). The pixel size was 16 × 16 μm, and ultra-large capacitances were achieved with in-pixel capacitors.…”

Polarization Image Sensor for Highly Sensitive Polarization Modulation Imaging Based on Stacked Polarizers

“…Thus, there is potential to make the circuit configuration per pixel more complex. This strategy can increase the effective pixel capacitance and improve the SNR using a self-resetting circuit [24], [25] or a self-resetting circuit [26]- [28]. In the case of high spatial resolution, techniques for reducing crosstalk, such as a vertical waveguide structure deep trench isolation, are required.…”

A 70-dB SNR High-Speed Global Shutter CMOS Image Sensor for in Situ Fluid Concentration Distribution Measurements

“…The concentration of DPW was optimized to suppress the leakage and to obtain a high uniformity of the capacitance value over the operating voltage range. Detailed information of optimizations of trench capacitor formation process and DPW conditions as well as transmission electron microscope (TEM) images of the trench capacitors can be seen elsewhere [11], [12]. In addition, distances between adjacent edges of PDs are arranged equally in all the directions to reduce the variation of crosstalk by making the potential between pixels symmetrical.…”

“…For instance, to achieve 70-dB SNR, over 10-Me − FWC is needed. There are several technologies to increase FWC, such as using organic photoconductive with high-density capacitors [6], [7], complementary carrier collection [8], and lateral overflow integration capacitor (LOFIC) [9]- [11]. In the LOFIC method, PD, FD, and LOFIC can be optimized independently.…”