Soft X-ray sensitivity of a photon-counting hybrid pixel detector with a silicon sensor matrix

We have tested a CMOS pixel readout circuit bump-bonded to a high resistivity silicon sensor to study the noise properties of the system and to determine the lower limit in energy for the detection of X-rays at room temperature. Our test shows that single photon counting is possible down to about 5 keV, and we obtain a mean total noise equivalent to142 electrons on the electronics input.