"DEPFET vertex detector"
DEPFET pixels offer the unique possibility for a high resolution pixel vertex
detector as the innermost component of the tracking system in an ILC
detector. The key idea of DEPFET sensors is the integration of amplifying
transistors into a fully depleted bulk in such a way that all signal charges are
collected in the Âinternal gatesÂ of the transistors. The excellent noise performance
obtained through the low input capacitance in combination with the
full primary signal leads to a large S/N ratio. The sensor itself can therefore
be made very thin (50 Âµm) without loss of efficiency. Readout is performed
by cyclic enabling of transistor rows in a large matrix. The total system,
including readout and sequencing chips, is expected to dissipate about 4W
for a 5 layer geometry assuming a 1:200 power duty cycle. Like all of the technologies
proposed for the vertex detector at the ILC, the DEPFET apporach is applicable to
all three of the overall detector concepts (SID, LDC, and GLD).
Presently, there are three German institutes participating in this project.
The MPI Semiconductor Laboratory is developing the DEPFET sensor and its technology,
and is responsible for the production of the matrices, which takes place in the clean room
of the MPI Semiconductor Laboratory. The Universities of Bonn and Mannheim are
responsible for the readout chip CURO and the steering chip for the row wise read out of the
matrix. System design and evaluation is also part of the responsibilties of these two
Unversities. A group form Aachen University has recently joined the project.
The most important achievements are the realization of several prototype
sensor matrices using double metal technology, the design, fabrication and
characterization of fast steering and readout chips, the realization of an ILC
suited prototype system, the preliminary measurement of its performance in
the lab as well as in the test beam, progress in and validation of the thinning
technology and studies on the radiation tolerance of DEPFET sensors. In
particular, DEPFET pixel sensors have proven to be radiation tolerant in
excess of 1Mrad ionizing dose. In 2005 a 64 x 128 DEPFET pixel matrix system with close to ILC specs has been tested and evaluated in test beams with excellent results regarding noise and hit reconstruction performance.
After the successful evaluation of the first prototype system, the project will
move 2006 in the next phase with the production of optimized larger matrices and new submissions
of the readout and steering chips. An important step towards a full size demonstrator with thinned
DEPFET matrices, planned for 2009, is also the elaboration of an engineering model for the vertex detector at the ILC.
The project is currently sufficiently supported by the German Ministry for Research (BMBF), the European Union through the EUDET program, and the Max-Planck-Society (MPG and MPI fuer Physik in Munich).
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Topic revision: 21 Nov 2005, LadislavAndricek
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