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Vectors, Voxels, Submicron, Tricks for Tracking in Silicon Detectors

Abstract: Some of the microelectronics technologies under development in industry could play an important role in tracking detectors for future particle physics experiments. Wafer thinning, chip stacking, 3-dimensional interconnections, integrated cooling are among the developments of interest. The question is where our focus should be, depending on the aims of the instrument. In the Super LHC hadron collider the emphasis is expected to be on high occupancy, high event rates and enhanced trigger selectivity. It is important there to have means of tagging secondary vertices, and linking them to their own primary vertex, but also to identify electrons and muons already close to the interaction. In a linear electron collider the tracking precision and resolution within jets with a low mass instrument seem to be the most important. Small pixels will be needed in both cases, which imposes the use of signal processing circuits in advanced CMOS, maybe 90 nm rather than 130nm. For precision tracking the use of space points in the form of voxels, e.g. 20 Ám or 50 Ám cubes, is desirable. Correlation of hits in close, parallel pixel planes could result in track vectors rather than single points. This can help in fast reconstruction algorithms, ultimately even at the first trigger level. This approach also could alleviate problems when a large proportion of pixels would experience signals related to energy deposits from background radiation. The pixel detector development by the Medipix collaboration with membership of 17 institutes and the design team at CERN has led to a series of instruments that explore new approaches in this domain. The Medipix2 matrix with 55 Ám square pixels has been operated at ~800 electrons equivalent threshold, and with GeV muons a submicron tracking accuracy has been achieved by using the diffusion of the charge during the drift to the contacts. Disturbing effects from delta electrons can be studied. Vectors have been determined with < mradian precision over a few mm length. The most recent Timepix chip allows analog signal measurements with Time-Over-Threshold circuits in each of the 65536 pixels. In the Medipix collaboration one has also studied Gbit transmission over traditional copper wires, and the use of standard USB components to achieve miniaturization of the readout. Finally, in the Medipix3 design is introduced signal processing and communication between neighboring pixels, so that charge sharing between small pixels can be exploited on-chip.
Speaker: Erik Heijne - CERN
Speaker Bio: Dr Erik H.M. Heijne is instrumentation physicist at CERN, where he has worked on silicon devices since he came there in 1973. Most of his innovations were derived from ongoing technology developments in industry. At first a few hundred classical silicon diode particle detectors were installed in the neutrino beams, for measuring the muon flux and calculating the neutrino cross section. In 1980 he built with Paul Burger in Strasbourg the first silicon microstrip detectors, for which Pierre Jarron designed miniaturized readout amplifiers. In 1988 the UA2 inner Si pad detector was the first to use CMOS readout chips in a particle collider. In 1991 the first operational hybridized silicon pixel detector telescope was used in the CERN Omega spectrometer for tracks from lead ion interactions. Around 1990 Erik also developed the ideas for radiation hard CMOS chips in deep submicron together with Nelson Saks from NRL. Most recently, quantum particle imaging devices such as Medipix and Timepix have been used to record direct images of interactions and particle trajectories, with precisions well below 1 um.
Poster Link: Poster
Presentation: Presentation on 6/27/2007 (PDF)