The present technique to find a dark current source in an image sensor, i.e., Dark Current Spectroscopy, is not sufficient to conclusively differentiate between the contribution of interface and bulk defect generation in a pixel. Also, the dark current data is available only post-fabrication. In this work, the Dark current vs Transfer Gate-off voltage curve is used to extract the defect density-cross-section product, activation energy and maximum carrier lifetime for two important device generation sites, i.e., interface under the Transfer Gate and Pinned Photodiode depletion region. A comprehensive analytical dark current model is formulated and validated using TCAD simulation and experimental data reported in the literature. The temperature variation is incorporated using the Arrhenius relation corresponding to the specific activation energy level. The proposed model along with the Arrhenius relation provides a sufficient pre-fabrication dark current estimate.
Low-light imaging is an essential characteristic of Space and Quanta sensing applications. For an accurate design and optimization of image sensor pixels, the analysis of Dark Current generation mechanisms including effects of Temperature, Trap concentration and Trap Cross-section is essential. TCAD optoelectrical simulations are used to calculate the thresholds of the above generation effects and the corresponding Dynamic Pinned Photo-Diode (PPD) capacitance variations. An interfacial Trap model with various generation models activated allows comparison of variations in PPD capacitance on a widely used PPD model both in light and dark. This allows the remodeling of existing CMOS image sensor compact models to capture the Dark Current effects in a Low illumination regime. The compact model shows a deviation of 6.85% from the physical device.
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