The Medipix2 Collaboration was formed in 1999 with the aim of developing a single photon counting pixel detector readout chip using a 0.25 μm CMOS process. The work of the Collaboration was initially foreseen to take four years, it is still active now almost two decades later. A major reason for this is the number and variety of applications to which the technology has been applied. Moreover, the development and immediate success of the Timepix chip in 2006 has led to a second wave of applications. 

There are two chips deriving from the Medipix2 Collaboration, the Medipix2 chip and the Timepix chip.

The Timepix2 Chip

Timepix2 is a programmable, general purpose hybrid pixel detector readout ASIC. The Timepix2 ASIC consists of a matrix of256x256 pixels with pixel pitch of 55μm, and is applicable to a wide range of applications including X-ray imaging, particle tracking and material analysis.

The Timepix2 pixel can be programmed to operate in one of several modes depending on the application requirement, offering increased complexity compared to the predecessor Timepix ASIC. Readout is frame-based. The arrival time (Time-of-Arrival – ToA) and charge deposit information (Time-over-Threshold – ToT) can be recorded for each hit when used in sequential read/write mode. In continuous read/write mode one can chose between ToT, ToA or event counting. There are a total of 28 bits per pixel which can be allocated depending on the read/write mode chosen and the requirements of the application.

Key Facts

Collaboration Partners: View page

Intellectual Property Status:
Timepix2 is available for licensing.

Relevant documents:

The Medipix2 Chip

The Medipix2 ASIC, the successor of the Medipix1 chip, is a high spatial, high contrast resolving CMOS pixel read-out chip working in single photon counting mode. It benefits from the quick progress of CMOS technology which allows enhanced functionality of the pixel cell at the same time as providing a significant reduction in pixel size. The chip can be combined with different semiconductor sensors which convert the X-rays directly into detectable electric signals. This represents a new solution for various X-ray and gamma-ray imaging applications.

Key Facts

Intellectual Property Status:
It is no longer possible to get a licence on the Medipix2 or Timepix chip.

Relevant documents:

The Timepix Chip

The Timepix chip evolved from the Medipix2 development. The pixels have identical size to those of Medipix2 but the functionality within each pixel has been changed. In Timepix each pixel can be programmed to count hits like Medipix2, or to record Time-Over-Threshold (providing rough analog information), or to measure arrival time of the first particle to impinge on the pixel. The Timepix development was driven by the requirements for TPC readout and supported by the EUDet project.

Relevant Documents:
  • Medipix2 and Timepix: Design and Characterization of 64K Pixels Chips Working in Single Photon Processing Mode, Thesis by Llopart Cudie, X(CERN; Mid Sweden Univ.) ;Frojdh, C (dir.) ;Campbell, M(dir.);
  • Timepix2: W.S. Wong, J. Alozy, R. Ballabriga, M. Campbell, I. Kremastiotis, X. Llopart, T. Poikela, V. Sriskaran, L. Tlustos, D. Turecek, Introducing Timepix2, a frame-based pixel detector readout ASIC measuring energy deposition and arrival time, Radiation Measurements, Volume 131, 2020,