Development of 2nd prototype of novel silicon Stripixel detector for PHENIX upgrade

A novel detector type, named "Stripixel" detector developed at BNL, has been applied in the development of a prototype Si strip detector system for the PHENIX Upgrade at RHIC. This novel detector type can generate X- Y two-dimensional position sensitivity with single-sided processing and readout. The prototype Si Stripixel detector has an active area of about 3cm × 6cm, which is divided into two identical halves. Both X and Y pitches are 80 μm, with a stereo angle of 4.6°. There are 384 X strips and 384 Y strips on each half of the detector. The first prototype Si Stripixel detectors have been produced at BNL. The initial tests of detector properties have yielded good results on position resolution in both X and Y coordinates. The design and mask set production of the 2nd prototype Si strip detectors were completed in December 2003. In the 2nd prototype design, the maximum distance between the X and Y interleaving pixels is shortened significantly to solve the asymmetry in charge sharing between X and Y pixels and strips observed in the first prototype Stripixel detectors. Also, a novel pixel inter-connection scheme with overlapping pixels is implemented, which can generate the same position resolution with twice of the pitch size as in the tradition scheme. In this novel scheme, for the same position resolution, one may just use half of the number of strips (in a given detector size), thus saving the readout channels by a factor of two. The first batch of the fabrication run of the 2nd prototype Stripixel detectors have been completed in February 2004. Preliminary electrical tests have revealed good results. Laser, source and beam tests are planned.