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[image: projection of tracks in a telescope]

This is the image which demonstrated the potential of hybrid silicon pixel detectors for tracking applications in High Energy Physics. It shows 153 high energy particle tracks flying through a telescope of half a million pixels in the WA97 experiment back in 1995. Every red dot in this image signifies a pixel which has been hit by a track and there are no pixels giving false hits. Therefore this image - which was taken with a 1 microsecond shutter time - is noise free! That was the key parameter which drove almost all of the LHC experiments to adopt hybrid pixel technology for their vertex detectors. It is also why this technology is so unique for imaging applications.

With the Medipix family of chips we have striven to disseminate a technology which was developed because of the needs of the Large Hadron Collider experiments at CERN to other fields of science.

The activity started in the 90's when a small Collaboration of 4 institutes produced the Medipix1 or Photon Counting Chip (PCC) demonstrating the potential of the new technology to provide noise-free single photon counting.

At the end of the 1990's the Medipix2 Collaboration was formed with the aim of taking advantage of the potential of deep sub-micron CMOS to shrink the pixel size and to increase the number of pixels per chip. The Medipix2 chip is the outcome of that effort.

During the extensive characterisation of that chip we recognised that charge diffusion within the sensor ultimately limits the performance of the chip for small pixel sizes. With access to very deep sub-micron CMOS processes it is now possible to mitigate the effects of charge diffusion by allowing pixels to communicate with each other on an event-by-event basis. Moreover is becomes possible to integrate 2 counters on a single small pixel permitting one image to be taken while the previous one is being read out. This is what the Medipix3 Collaboration hopes to achieve.