Photovoltaic Imaging in Standard BiCMOS with an Open-Circuit Voltage Pixel

A pixel unit cell leveraging the photovoltaic regime of the detector and a subthreshold common-source amplifier is proposed. A prototype $128 \times 128$ front-side illuminated visible image sensor fabricated in standard $0.13 \mu \mathrm{~m}$ BiCMOS was developed to validate the pixel topology. Additionally, singleelement photodiode arrays compatible with standard CMOS or BiCMOS processes were fabricated, characterized, and evaluated for photodetector performance. The standard photodiodes exhibit dark current densities and resistance-area product in the range of $0.82-1.99 \mu \mathrm{~A} / \mathrm{cm}^{2}$ and $6.1-22 \Omega \cdot \mathrm{~cm}^{2}$, respectively. The $\boldsymbol{p}+/ n$-well photodiodes show peak quantum efficiency of 14.5% at $0.7 \mu \mathrm{~m}$ peak wavelength. The open-circuit voltage pixel (VocP) improves effective responsivity of the photodiode enabling sensitive imaging in standard CMOS. Noise-equivalent power (NEP) of ${\lt}3^{p W} / \sqrt{H z}$ is demonstrated for the prototype array. The proposed pixel and detector techniques are compatible with low-cost, standard CMOS.