CMOS image sensors: Two-dimensional MTF for anisotropic resolution characterization

In this paper, the meaning and appropriateness of complementary metal-oxide-semiconductor image sensor (CIS) modulation transfer function (MTF) is reconsidered. Two-dimensional (2-D) submicrometer spot scanning results are presented for industrial CIS, 2-D-MTF, characterizing CIS performance and resolution abilities is extracted and compared with the ideal one-dimensional (1-D) MTF profile estimation calculated for all spatial frequencies. "Inter" and "intra" pixel MTFs emphasizing pixel structure dependencies are defined. The domain of applicability of traditional 1-D sensor characterization methods is shown to be ambiguous and insufficient for modern anisotropic CIS designs, resembling the inability to account for the sensor internal structural effects. Furthermore, it was shown that 2-D characterization provides reliable information and enables better understanding and the most accurate description of device performance. In addition, the advantages (over the commonly referred 1-D-MTF) and necessities of 2-D-MTF are verified experimentally and clearly demonstrated in this paper.