Investigations into the impact of locally modified sensor architectures on the detection efficiency of silicon micro-strip sensors

L Poley,I Pape,M Warren,C Lacasta,K Lohwasser,D Sperlich,Marko Milovanovic ,Kawal Sawhney ,M Benoit,Sergio Cañas Díez ,P W Phillips ,J S Keller ,D Maneuski,A Blue,I M Gregor ,C Sawyer,L Rehnisch,V Fadeyev,A Greenall,Y Unno,I Bloch,E Yildirim,L Meng,M Stegler,B J Gallop

doi:10.1088/1748-0221/12/07/p07006

Abstract

The High Luminosity Upgrade of the LHC will require the replacement of the Inner Detector of ATLAS with the Inner Tracker (ITk) in order to cope with higher radiation levels and higher track densities. Prototype silicon strip detector modules are currently developed and their performance is studied in both particle test beams and X-ray beams. In previous test beam measurements of prototype modules, the response of silicon sensors has been studied in detailed scans across individual sensor strips. These scans found instances of sensor strips collecting charge across areas on the sensor deviating from the geometrical width of a sensor strip. The variations have been linked to local features of the sensor architecture. This paper presents results of detailed sensor measurements in both X-ray and particle beams investigating the impact of sensor features (metal pads and p-stops) on the sensor strip response.

Highlights

In the current layout for silicon strip sensor modules for the future ATLAS Inner Tracker, modules consist of silicon strip sensors, printed circuit boards [1] and binary readout chips (ABC130 ASICs [2])
The number of recorded particle hits per sensor position showed that the presence of bond pads leads to a statistical effect on the number of recorded hits: sensor strips with bond pads show an increased number of hits in the bond pad area, while sensor strips without bond pads show fewer hits in the same area
After the previous test beam results had indicated that bond pads might lead to different widths over which a sensor strip responds, the findings from this test beam showed a similar effect: the presence of a bond pad on a sensor strip results in this strip collecting hits over a larger area than intended

Summary

Introduction

In the current layout for silicon strip sensor modules for the future ATLAS Inner Tracker, modules consist of silicon strip sensors, printed circuit boards (hybrids) [1] and binary readout chips (ABC130 ASICs [2]). The connection of ASICs and sensor strips by wire bonds requires the addition of electrically conductive bond pads to the aluminium layer on top of each strip implant. By investigating which sensor strip responded with a signal and relating this to the expected hit position on the sensor given the parameters of the particle track reconstructed in the beam telescope, charge collection from individual strips can be mapped in the x-y plane. Both the ALiBaVa daughterboard (used for signal readout) and the sensor board (holding the miniature sensors) were mounted on a copper plate cooled down to 10 °C. The sensor was operated fully depleted at a bias voltage of -250 V

Results

Conclusion and Outlook