Very good energy resolution (in the order of 135 eV at 6 keV) and good timing resolution (about 500 ns FWHM) are the main features of Silicon Drift Detectors (SDDs)^a. But, up to now no large area devices were available (available sizes up to 10 mm², first prototypes with an active area of 30 mm²). Therefore, the SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Applications) collaboration was formed to develop large area SDD devices within the 6^th-framework program of the EU (I3-Hadron Physics). The goal is to build SDD-chips with total active area of 300 mm², consisting of 3 individual elements on one chip. Finally, a detector system with a total active area of more than 200 cm² is envisioned. This unique detector system will be used to perform precision measurements of kaonic atoms at the percent level.

The X-ray timing signal from the kaonic atom transition of interest can be used together with the time signal of the back-to-back K⁺K^- pair to set up a triple coincidence. With this coincidence method it will be possible to suppress the continuous background as well as fluorescence X-rays by almost three orders of magnitude, compared with the background in the DEAR experiment.
The SDD-chips were produced at the MPI-Halbleiterlabor, München. After a test series of 8 SDD-chips to evaluate the gluing and bonding technique, in the first half of 2006 the first 10 SDD-chips were mounted in ceramic holders and bonded under the supervision of SMI at the Fraunhofer Institut (IZM-Berlin).
These chips were successfully tested in Vienna - first an optical inspection of all delivered chips took place, then the electrical characteristic of each chip was determined and compared with the MPI data. Finally spectroscopic measurements were performed, showing very good energy resolution of about 140 eV at 6 keV.
To make use of the good performance of SDDs a new pre-amplifier chip (source follower configuration) is under development at Poltichnico Milano, to achieve better rate and long-term stability. Tests in the second half of 2006 have shown promising results.
After having successfully tested 10 SDD-chips we started in the second half of 2006 the assembly of the 70 SDD-chips, foreseen to be used in SIDDHARTA. Until end of 2006, 25 chips were mounted, bonded and finally electrically characterized at SMI. The spectroscopic test measurements are running.

Outlook

Preparing the SDD ceramic holders for mounting and bonding of the SDDs will be continued as well as electronic and spectroscopic test measurements of the finished SDD devices. The goal is to finish the test measurements of all 70 chips within spring 2007. Long-term measurements are going on in parallel with a set of 4 chips at SMI and at LNF.
A test at the BTF (beam test facility) at LNF is planned for end of March 2007. The installation of 6 SDD-chip at the DAFNE machine is foreseen for the second half of 2007 and first beam, but only for machine development, is expected in November 2007. In this period debugging of the SDD system and background measurements might be possible.

^a J. Kemmer, G. Lutz, Nucl. Instr. and Meth. A 253 (1987) 365