A 55 CM(2) CYLINDRICAL SILICON DRIFT DETECTOR

AZTEC, a large area cylindrical silicon drift detector was designed, p roduced and tested. AZTEC will be the building block of the NA45 and W A98 micro vertex detectors at CERN. Two AZTEC detectors are placed dow n stream from the target to measure trajectories of charged particles produced in the forward direction. The active area of AZTEC is practic ally the full usable surface of a 100 mm diameter wafer. The electrons drift radially from the center towards the outside. The sensing anode s are located at a radius of 42 mm. The center of the wafer is cut out and forms a passage for the non interacting beam, With a minimal radi us for this hole the active region of the drift detector starts at an inner radius of 3.1 mm. Any larger radius can be selected if necessary . With this geometry and a typical operating voltage the maximum drift time is less than 4 mu s. Due to constrains in the mask layout the re adout region and field electrodes are designed along the 360 sides of a symmetric polygon. All structures on one surface of the wafer are ro tated by 0.5 degrees with respect to the other surface, In the middle plane of the detector, where the electrons are mostly transported, the effective geometry is close to a smoothed polygon with 720 sides, can celling practically ail effects of the non-perfect cylindrical symmetr y. The radial position of fast charged particles is measured by the el ectron drift time within the detector. The drift velocity can be monit ored by 48 injection points at three different radii. The azimuthal an gle is measured by the 360 readout anodes. Each anode is subdivided in to five segments, which are interlaced with the neighbouring anodes. B y this methode the azimuthal resolution is improved and corresponds to a 720 channel read out.