Study of surface properties of ATLAS12 strip sensors and their radiation resistance

Abstract

A radiation hard n þ -in-p micro-strip sensor for the use in the Upgrade of the strip tracker of the ATLAS experiment at the High Luminosity Large Hadron Collider (HL-LHC) has been developed by the "ATLAS ITk Strip Sensor collaboration" and produced by Hamamatsu Photonics.Surface properties of different types of end-cap and barrel miniature sensors of the latest sensor design ATLAS12 have been studied before and after irradiation. The tested barrel sensors vary in "punch-through protection" (PTP) structure, and the end-cap sensors, whose stereo-strips differ in fan geometry, in strip pitch and in edge strip ganging options. Sensors have been irradiated with proton fluences of up to 1 Â 10 16 n eq /cm 2 , by reactor neutron fluence of 1 Â 10 15 n eq /cm 2 and by gamma rays from 60Co up to dose of 1 MGy. The main goal of the present study is to characterize the leakage current for micro-discharge breakdown voltage estimation, the inter-strip resistance and capacitance, the bias resistance and the effectiveness of PTP structures as a function of bias voltage and fluence. It has been verified that the ATLAS12 sensors have high breakdown voltage well above the operational voltage which implies that different geometries of sensors do not influence their stability. The inter-strip isolation is a strong function of irradiation fluence, however the sensor performance is acceptable in the expected range for HL-LHC. New gated PTP structure exhibits low PTP onset voltage and sharp cut-off of effective resistance even at the highest tested radiation fluence. The inter-strip capacitance complies with the technical specification required before irradiation and no radiation-induced degradation was observed. A summary of ATLAS12 sensors tests is presented including a comparison of results from different irradiation sites. The measured characteristics are compared with the previous prototype of the sensor design, ATLAS07.

Detailed studies of full-size ATLAS12 sensors

“…Soft breakdown will occur across this gap as soon as a threshold potential is exceeded. The PTP structure is of the "fully gated" design, where the bias rail implant extends over the gap, covering the PTP gap entirely, see [5]. A static measurement to determine the threshold voltage consists of monitoring the current whilst increasing the voltage imposed on the strip implant.…”

“…The goal of the ITk Strip Sensor collaboration is to develop a silicon microstrip sensor that is suitable for use in the new ITk. Results of detailed studies of properties of full-size sensor prototypes are presented in this paper, whereas studies of radiation damage of 1×1 cm 2 miniature sensors are reported in [5], [6].…”

Investigation of HV/HR-CMOS technology for the ATLAS Phase-II Strip Tracker Upgrade

“…This is natural, 224 since the top-side biasing is implemented in these devices with doped areas between the 225 pixel n-wells, called "guard rings". The guard rings provide a strong isolation, similar to 226 "p-stop" technique in conventional sensors [7]. A test structure without intentional guard 227 ring still showed similarly high resistance indicating a presence of similar structure 228 between the n-wells.…”

Underpinning UK high-value manufacturing: Development of a robotic re-manufacturing system

“…Orbital GTAW or Tungsten Inert Gas welding (TIG) was well established in the 1960s and the technology advanced by the space race. Numerous failures in space vehicle propulsion fuel systems, failed welds [17], [18] and subsystem electronic component damage [19], [20], [21], [22], [23], [24], [25], [26], [27] induced from stray electrical arcs all looked to be avoidable. The journey from concept to improve detector construction to later a full joint technology development programme was underway with a simple, "yes we can do it" from the VBCie Directors.…”