Production testing and quality assurance of CMS silicon microstrip tracker readout chips

The APV25 is the 128 channel CMOS chip developed for readout of the silicon microstrip tracker in the CMS experiment at the CERN Large Hadron Collider. The detector is now under construction and will be the largest silicon microstrip system ever built, with ∼200 m2 of silicon sensors. 75,000 chips are required to instrument the system, which must operate for 10 years in a high radiation environment with little or no possibility of replacement of any component. The readout chip is a crucial components, which must provide low noise and reliable operation. Thus, each readout chip must be carefully tested prior to installation in CMS modules and assurance of long-term performance of the readout electronics, especially verification of radiation tolerance, is highly desirable. This has been achieved by means of automated probe testing of every chip on the silicon wafers from the foundry, followed by studies of sample die to evaluate in more detail properties of the chips, which cannot easily be examined at the wafer level. production, it was observed that the yield of good die varied unexpectedly from one production lot to another. This was investigated with significant help from the manufacturer and the process was optimised to ensure consistent high yield. A fraction of the dies, which successfully passed the wafer screening, are subjected to short-term X-ray irradiation to levels equivalent to that expected in CMS and are then annealed. s are presented here and illustrate the excellent performance of APV25 under all expected operating conditions.