Charge collection and field profile studies of heavily irradiated strip sensors for the ATLAS inner tracker upgrade

Hara, K. and Chilingarov, Alexandre and Fox, Harald (2016) Charge collection and field profile studies of heavily irradiated strip sensors for the ATLAS inner tracker upgrade. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 831. pp. 181-188. ISSN 0168-9002

Abstract

The ATLAS group has evaluated the charge collection in silicon microstrip sensors irradiated up to a fluence of 1×10161×1016 n eqeq/cm2 , exceeding the maximum of 1.6×10151.6×1015 n eqeq/cm2 expected for the strip tracker during the high luminosity LHC (HL-LHC) period including a safety factor of 2. The ATLAS12, n+-on-p type sensor, which is fabricated by Hamamatsu Photonics (HPK) on float zone (FZ) substrates, is the latest barrel sensor prototype. The charge collection from the irradiated 1×1 cm2 barrel test sensors has been evaluated systematically using penetrating β-rays and an Alibava readout system. The data obtained at different measurement sites are compared with each other and with the results obtained from the previous ATLAS07 design. The results are very consistent, in particular, when the deposit charge is normalized by the sensor's active thickness derived from the edge transient current technique (edge-TCT) measurements. The measurements obtained using β-rays are verified to be consistent with the measurements using an electron beam. The edge-TCT is also effective for evaluating the field profiles across the depth. The differences between the irradiated ATLAS07 and ATLAS12 samples have been examined along with the differences among the samples irradiated with different radiation sources: neutrons, protons, and pions. The studies of the bulk properties of the devices show that the devices can yield a sufficiently large signal for the expected fluence range in the HL-LHC, thereby acting as precision tracking sensors.