LOW COST SILICON RADIATION DETECTORS

THE USE OF SILICON (SI) RADIATION DETECTORS IN HIGH ENERGY PHYSICS, ENVIRONMENTAL MONITORING, NEUTRON AND X-RAY IMAGING, ETC., IS RESTRICTED BY THEIR COST. HIGH COSTS BECOMES AN ACUTE PROBLEM IN APPLICATIONS LIKE HIGH ENERGY PHYSICS SAMPLING CALORIMETERS, WHICH REQUIRE VERY LARGE ARRAYS OF DETECTOR ELEMENTS. ALTHOUGH SOME IMPROVEMENT RESULTS FROM LARGE VOLUME THROUGHPUT, THIS IMPACT IS NOT AS LARGE AS MIGHT BE EXPECTED BECAUSE SOME OF THE COST ARE ALREADY COMMON TO LARGE VOLUME LARGE SCALE INTEGRATION (LSI)MANUFACTURING OPERATIONS. TO REDUCE MAJOR COSTS FURTHER, BASIC DESIGN AND PROCESSING CHANGES ARE REQUIRED BEFORE COSTOBJECTIVES CAN BE MET. THE COST PROBLEM HAS THE FOLLOWING SEGMENTS: GOOD QUALITY AND HIGH RESISTIVITY SI CRYSTALS, CUTTING AND POLISHING OPERATIONS, WAFER FABRICATION OPERATIONS FOR CONVERTING THE POLISHED WAFERS INTO DETECTORS, AND TESTING AND QUALITY CONTROL. IT IS POSTULATED THAT THE LSI STYLE OF WAFER CUTTING AND POLISHINGCURRENTLY IN USE IS NOT OPTIMAL FOR RADIATION DETECTORS AND IS THEREFORE A GOOD TARGET FOR MAJOR COST REDUCTION, PARTICULARLY IF COORDINATED WITH CHANGES IN THE WAFER FABRICATION DESIGN. IT IS ALSO SUGGESTED THAT THE DETECTOR DESIGNS AND FABRICATION PROCESSES IN COMMON USE ARE TOO COMPLICATED FOR SIMPLE PAD AND PIXEL DETECTORS AND THAT MAJOR COST IMPROVEMENTS CAN BE ACHIEVED BY SIMPLIFYING THE DESIGN AND THE MANUFACTURING PROCESS. CHANGES IN CUTTING AND POLISHING AND IN DETECTOR DESIGN CAN ALSO BE USED TO REDUCE SI CRYSTAL COST. PHASE I OF THIS PROJECT CONCENTRATES ON DEVELOPMENT OF LOWER COST CUTTING AND POLISHING TECHNIQUES, ON DESIGN OF AN IMPROVED DETECTOR CONFIGURATION AND MANUFACTURING PROCESS, ON THEIR COMBINED IMPACT ON SI MATERIAL COST, AND ON AN ESTIMATE OF THE COST ADVANTAGES INHERENT IN IMPLEMENTING THESE CHANGES.