First test measurements of a 64 k pixel readout chip working in single photon counting mode

The Medipix2 chip is a pixel detector readout chip consisting of 256 multiplied by 256 identical elements, each working in single photon counting mode for positive or negative input charge signals. The chip is designed and manufactured in a six-metal 0.25 mum CMOS technology. This paper describes several electrical measurements which have been carried out on the chip prior to detector bump bonding using a dedicated readout system. Threshold linearity and variation has been measured for both electron and hole collection. The noise is similar to 100 e**- RMS and the threshold can be adjusted to similar to 120 e **- RMS for both polarities. The minimum operating threshold is similar to 1000 e**-.