Single-Exposure High Dynamic Range Image Sensor Using Thin-Film Photodiode Pixel

Abstract

This letter presents a single-exposure high dynamic range (HDR) image sensor based on a thin-film pinned photodiode (TF-PPD) pixel structure. The proposed technique efficiently exploits the unique structural features of the TF-PPD architecture to achieve high dynamic range operation while retaining the inherent advantages of thin-film photodiodes, such as wavelength extensibility and ease of integration. Specifically, the photodiode (PD) under the photogate (PG) is utilized as a large photodiode (LPD), while the PD in the floating diffusion (FD) region is employed as a small photodiode (SPD). This enables single-exposure HDR imaging without requiring additional circuitry or complex fabrication steps. Furthermore, by adjusting the integration-time ratio between the LPD and SPD, an additional effective dynamic range can be achieved. The prototype image sensor demonstrates an effective dynamic range of 100 dB with an integration-time ratio of 5:1 between the LPD and SPD. The proposed technique successfully reproduces both bright and dark regions under single-exposure conditions, confirming its capability for efficient HDR imaging within a compact pixel design.