Abstract
This article presents a 16- $\mu \text{m}$ 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 $^{-}/\mu \text{m}^{{2}}$ 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.
Highlights
T HE sensing technology utilizing a CMOS image sensor (CIS) is expected to be useful in the healthcare, medical, Manuscript received November 7, 2019; revised January 17, 2020 and February 6, 2020; accepted February 15, 2020
Converted at the small capacitance floating diffusion (FD) in a low light illumination and the high saturation voltage signal S2 converted at FD + LOFITreC in a high light illumination are read out, whereby the wide dynamic range (WDR) performance is achieved under a single exposure
Using the WDR mode, an over 130-dB dynamic range (DR) with a linear response was obtained under a single exposure
Summary
T HE sensing technology utilizing a CMOS image sensor (CIS) is expected to be useful in the healthcare, medical, Manuscript received November 7, 2019; revised January 17, 2020 and February 6, 2020; accepted February 15, 2020. Several CISs with advanced device technologies have been reported to be useful to achieve a high FWC so far, such as the CISs with a lateral overflow integration capacitor (LOFIC) to accumulate the overflow photoelectrons from the PD [4]–[6], organic photoconductive film (OPF) CISs [7], [8] with a large FD capacitance using a high-k metal-insulator-metal (MIM) capacitors [8], [9], and a complementary carrier collection CIS using an Si accumulation layer of the capacitive trench isolation in-pixel as a photocharge storage [10]. The combination of a front-side illumination and a trench capacitor employing high-integrity SiO2 dielectric film was chosen so as to achieve both the high QE for the UV-visible-NIR waveband and high saturation.
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