We present a study of a CMOS test sensor which has been designed, fabricated and characterised to investigate the parameters required for a binary readout electromagnetic calorimeter. The sensors were fabricated with several enhancements in addition
to standard CMOS processing. Detailed simulations and experimental results of the performance of the sensor are presented. The sensor and pixels are shown to behave in accordance with expectations and the processing enhancements are found to be essential to achieve the performance required.
