  The Skipper-in-CMOS image sensor integrates the non-destructive readout
capability of Skipper Charge Coupled Devices (Skipper-CCDs) with the high
conversion gain of a pinned photodiode in a CMOS imaging process, while taking
advantage of in-pixel signal processing. This allows both single photon
counting as well as high frame rate readout through highly parallel processing.
The first results obtained from a 15 x 15 um^2 pixel cell of a Skipper-in-CMOS
sensor fabricated in Tower Semiconductor's commercial 180 nm CMOS Image Sensor
process are presented. Measurements confirm the expected reduction of the
readout noise with the number of samples down to deep sub-electron noise of
0.15rms e-, demonstrating the charge transfer operation from the pinned
photodiode and the single photon counting operation when the sensor is exposed
to light. The article also discusses new testing strategies employed for its
operation and characterization.
