New results from fast timing iLGAD sensor on Timepix4

Abstract

With the High-Luminosity Large Hadron Collider (HL-LHC) the number of collisions per bunch crossing increases. To cope with these high rates in the pixel trackers, per-pixel time measurements are required, which implies the need for fast sensors. The inverse Low-Gain Avalanche Detector (iLGAD) is one of the fast sensor options that is being investigated. This paper will show the results of an inverse Low-Gain Avalanche Detector (iLGAD) with a pitch of 55 $μ$m, a thickness of 250~$μ$m and a large-area (2~cm$^2$), bump bonded to a Timepix4 ASIC. Timepix4 has 195~ps time binning on each pixel and therefore an excellent ASIC to test the sensor. The sensor is characterised with radio-active source measurements in the lab, and during beam test at the CERN SPS North Area H8 beamline, where the Timepix4 telescope was used. The telescope has a time reference of 12~ps and a pointing resolution of 2.4 $\pm$ 0.1~$μ$m. The iLGAD shows an almost uniform gain of approximately 4 and an efficiency of 99.6 $\pm$ 0.1\%. Without any corrections the obtained time resolution is about 750~ps. After timewalk and clock corrections the time resolution becomes 377 $\pm$ 7~ps. Grazing angle measurements have been done, which allow to measure the time resolution as function of depth of the charge deposition in the sensor. This provides more insight for the perpendicular time resolution.