Up until now it has been possible to make pixel detector read-out chips that can be abutted on three sides only. The fourth side is used for on-chip peripheral logic and wire-bond pads that permit electronic read-out. Because of this structure, large detector areas can be covered, but only with gaps in the coverage, or by using sophisticated roof-tile mechanics. Through-silicon-via (TSV) technology provides the possibility of reading the chips through copper-filled holes that bring the signals from the front side of the chip to its rear. Developments based on the Medipix3 chips have demonstrated that this has now become a viable option for pixel detector read-out. However, the TSV processing of Medipix3 only allows a reduction in the peripheral area by avoiding the use of wire bonds. The peripheral logic is still present.
The Medipix4 Collaboration launched in 2016. The aim of the collaboration is designing pixel read-out chips that for the first time are fully prepared for TSV processing and may be tiled on all four sides. In other words, all of the communication with the pixel matrix will now go through the rear of the chip - the peripheral logic and control elements will be integrated inside the pixel matrix. This will not only enable large areas to be covered seamlessly, but will also permit the development of new read-out architectures by avoiding the need to send all of the data to one side of the chip for read-out.
Two new chips are foreseen: Medipix4, which will target spectroscopic X-ray imaging at rates compatible with medical CT scans, and Timepix4, which will provide particle identification and tracking with higher spatial and timing precision.