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"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 ’internal gates’ 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 µm) 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).