WORKSHOP PAPER
Improved Design of 1T Charge-Modulation Pixel Structure for Small-Size and Low-Dark-Current Achievements
Abstract
A ring-gate design of 1T (single-transistor) charge-modulation pixel structure is proposed, obviating the need for STI (shallow trench isolation) to avoid crosstalk, enabling achievements of smaller pixel size and/or higher fill factor, and reducing dark current by limiting peripheral leakage current contribution and minimizing band-to-band tunneling effect. A test chip integrating an array of 1.4µm-pitch, 50%-fill-factor pixels is designed in a 0.13µm CMOS technology, showing improved conversion gain, substantial reductions in dark current, temporal noise, and FPN, though with a degraded full well capacity, hence improving dynamic range.Keywords
1T charge-modulation pixel structure, ring-gate design, small pixel size,References
1) G. Agranov et al., "Optical-electrical characteristics of small, sub-4µm and sub-3µm pixels for modern CMOS Image Sensors", Proc. IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors, Nagano, 2005
2) S.-H. Lee et al., "The features and characteristics of 5M CMOS image sensor with topologically Unique 1.7x1.7µm² pixel", Symposium on VLSI Technology Dig. Tech. Papers, Honolulu, 2006. https://doi.org/10.1109/vlsit.2006.1705257
3) K-B Cho et al, "A 1/2.5 inch 8.1Mpixel CMOS Image Sensor for Digital Cameras", International Solid-State Circuits Conference (ISSCC) Dig. Tech. Papers, San Francisco, 2007. https://doi.org/10.1109/isscc.2007.373517
4) M. Cohen et al., "Fully Optimized Cu based process with dedicated cavity etch for 1.75µm and 1.45µm pixel pitch CMOS Image Sensors", IEEE International Electron Devices Meeting (IEDM) Dig. Tech. Papers, San Francisco, 2006. https://doi.org/10.1109/iedm.2006.346976
5) K. Matsumoto et al., "The Operation Mechanism of a Charge Modulation Device (CMD) Image Sensor", IEEE Trans. Electron Devices, vol. 38, May 1991. https://doi.org/10.1109/16.78370
6) J. Hynecek, "BCMD - An Improved Photosite Structure for High-Density Image Sensors", IEEE Trans. Electron Devices, vol. 38, May 1991. https://doi.org/10.1109/16.78373
7) T. Miida et al., "A 1.5MPixel Imager with Localized Hole-Modulation Method", International Solid-State Circuits Conference (ISSCC) Dig. Tech. Papers, San Francisco, 2002. https://doi.org/10.1109/isscc.2002.992092
8) A. Tournier et al., "Implementation and electrical characterization of CMOS single-transistor charge-modulation pixel structure", Proc. 8th International Conference on Solid-State and Integrated-Circuit Technology (ICSICT), Shanghai, 2006. https://doi.org/10.1109/icsict.2006.306345