Highly segmented large-area hybrid photodiodes with bialkali photocathodesand enclosed VLSI readout electronics

We report on the principles, design, fabrication, and operation of a highly segmented, large-area hybrid photodiode, which is being developed in the f ramework of the LHCb RICH project. The device consists of a cylindrical, 12 7 mm diameter vacuum envelope capped with a spherical borosilicate UV-glass entrance window, with an active-to-total-area fraction of 81%, A fountain- focusing electron optics is used to demagnify the image onto a 50 mm diamet er silicon sensor, containing 2048 pads of size 1 x 1 mm(2). The sensor pad s are read out by 16 analogue multiplexed readout chips enclosed in the vac uum envelope. A large ultra-high vacuum plant for the evaporation of visibl e-light transmittive bialkali (K2CsSb) photocathodes and subsequent tube en capsulation has been built and successfully operated. The characteristics a nd performance of the first HPDs have been measured to be in full agreement with expectations. (C) 2000 Elsevier Science B.V. All rights reserved.