A unique sub-micron scanning system use for CMOS APS crosstalk characterization

This paper presents the pioneer use of our unique Sub-micron Scanning System (SSS) for point spread function (PSF) and crosstalk (CTK) measurements of focal plane CMOS Active Pixel Sensor (APS) arrays. The system enables the combination of near-field optical and atomic force microscopy measurements with the standard electronic analysis. This SSS enables full PSF extraction for imagers via sub-micron spot light stimulation. This is unique to our system. Other systems provide Modulation Transfer Function (MTF) measurements, and cannot acquire the true PSF, therefore limiting the evaluation of the sensor and its performance grading. A full PSF is required for better knowledge of the sensor and its specific faults, and for research - to enable better optimization of pixel design and imager performance. In this work based on the thorough scanning of different "L" shaped active area pixel designs (the responsivity variation measurements on a subpixel scale) the full PSF was obtained and the crosstalk distributions of the different APS arrays are calculated. The obtained PSF points out the pronounced asymmetry of the diffusion within the array, mostly caused by the certain pixel architecture and the pixels arrangement within the array. We show that a reliable estimate of the CTK in the imager is possible; the PSF use for the CTK measurements enables not only its magnitude determination (that can be done by regular optical measurements), but also to discover its main causes, enabling the design optimization per each potential pixel application.