CERN Accelerating science

Researchers from CERN and some external collaborating groups saw the opportunity to transfer the technology being developed for the LHC experiments to applications outside the field of high-energy physics. The Medipix1 Collaboration was born. 

The Medipix1 chip, a large CMOS imaging chip, was designed at CERN in the micro-electronics group following specifications from the Medipix1 collaboration. The chip was received in 1997, characterised and bump-bonded to Si and GaAs sensors which provide direct charge conversion of photons and therefore minimum image blurring.

The Medipix1 chip, or photon counting chip, was the first large area single photon counting CMOS imaging chip. It comprises a matrix of 64 x 64 identical pixels each measuring 170 μm x 170 μm. Each pixel contains a preamplifier, comparator and a 15-bit pseudorandom counter. It operates like an electronic camera counting hits above threshold while the shutter is open and permitting readout of the acquired image when the shutter is closed. It was bump bonded to identically segmented sensors of both silicon and GaAs. Although the number of pixels was rather low, the pixel pitch was rather high and it could not be abutted to neighbouring chips it demonstrated the potential of single photon counting X-ray imaging.