Comparison of Global Shutter Pixels for CMOS Image Sensors

In this paper we are presenting preliminary results from 4T technology based CMOS image sensors with global shutter, i.e. all pixels in the active array integrate light simultaneously. The global shutter operation mode is particularly important for high-speed video applications, where the more commonly implemented rolling line shutter creates motion blur. Our chips were fabricated using a 0.18 micron 4T, CIS technology with pinned photodiode and transfer gate. Different from conventional 3T type CMOS image sensors with global shutter pixel, in these 4T technology based global shutter pixels, the charge is transferred, not just sampled, onto the sense node. This translates into very high sensitivity and low readout noise at low power. For an imager with 7 transistors per pixel that is operated in global shutter, “Integrate While Read” mode, we measure an input referred noise of 10 electrons. The extinction ratio at full well signal charge is ~ 97.7%.