Evaluation of the Impacts of V_th Variation and Leakage Current on the Signal-to-Noise Ratio of a Single-Shot HDR Image Sensor with a Lateral Overflow Transistor

We developed a pixel that achieves high dynamic range (HDR) under a single exposure condition for an organic photoconductive film complementary metal–oxide–semiconductor (CMOS) image sensor. A lateral overflow transistor (LO-Tr) was employed to modulate the conversion gain, and the effects of the threshold voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf>) variations of the LO-Tr and leakage current toward the substrate (I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</inf>) on the signal-to-noise ratio (SNR) were evaluated. SNR degradation at the gain switching point (SP) was suppressed by applying a device structure to LO-Tr, which reduced the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> variation and I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</inf>, and an SNR of 33 dB was obtained at the SP. We successfully improved the number of saturation electrons from 52 ke<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> to 230 ke<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> and the DR from 71 dB to 86 dB by employing HDR pixels with LO-Trs.