An advanced CMOS imager employing modified AR and ACS methods

In this work we present measurements from two generations of fully operational 128times128 CMOS image sensor arrays. In these imagers, we have modified two existing design techniques, the active reset (AR) technique and the active column sensor (ACS) readout technique, and combined them together to achieve low-noise reset and improved spatial gain fixed pattern noise (FPN). In addition, we have implemented three different types of pixels, employing nwell/psub photodiodes to examine the influence of the shallow trench isolation (STI) on dark currents of the photodiodes. While the first fabricated imager served as a basis for different pixels and techniques examination, the second sensor was designed based on the conclusions drawn from the measurements of the first imager. Measurements from both sensors are presented, showing that the proposed architecture achieves column-level FPN of 0.05%, pixel level FPN of 0.16% and SNR of 15 dB at illumination level as low as 4 nW/mm², making it suitable for applications, where low light detection is required. Other imager attributes are also presented.