Module Production for The ATLAS Silicon Tracker (SCT)

The SCT requirements:• Hermetic lightweight tracker.

• 4 space-points detection up to pseudo rapidity angle (η) of 2.5 (9º).

• Small stereo angle in order to avoid ambiguities.

• Each detector to provide resolution of 20 μm.

• Effective z resolution of space-point better than 1 mm.

• Two-hit resolution of the order of 200 μm.

• Each detector has at least 97% efficiency.

• All layers to operate for full lifetime of Atlas – design is challenged by hostile radiation environment and the 25 ns LHC bunch crossing time.

An ATLAS Silicon module:

• A module is the basic readout unit of the SCT.

• Wedge shaped Silicon sensors with an average pitch of 80μm, 285μm thick(~22000 electron-hole pairs / MIP).

•The modules are double-sided with 2 single-sided silicon strip sensors per side.

• Sensors are glued on a SPINE – a mechanical support skeleton that has a high thermal conductivity, also used to remove heat essential for power detector dissipation.

• Sensors on the two sides of the module are glued back to back with a 40 mrad stereo angle, providing space-points with a resolution of about 16μm in rφ and 500μm in Z.

The chosen design:

• A Silicon micro-strip p on n detector.

• ~16000 sensors with a total active surface of over 60m².

• 6.3 million readout channels built into 4088 modules.

• Modules are arranged in 4 barrel layers and 9 disks covering each of the forward regions up to η=2.5.

• Operation temperature is -7º.

• Bias voltage up to 500V.

• Binary readout electronics.

- Amplification of the small detector signal

- Discrimination of the signal from the background noise

- Storage of the signal in temporary storage area (pipeline).

SCT Electronics

- Data from pipeline readout through links to the off-detector electronics.

- Serial transmission lines of optical fibres.

- Power cables made from Aluminium plated on Kapton.

The Inner Detector

SCT

Forward Module Production in Geneva

Shulamit Moed

Thickness profile of the module

Surface profile of the front and back side of the module

Tests of components before assembly to a module

• Visual inspection and electrical tests of hybrid performance.

• IV measurements of silicon sensors.

• Inspection of spines, far-end washers, pad locators and fan-ins.Tests during module assembly

• IV measurements of silicon sensors after they are glued on the spine.

• IV measurements of silicon sensors after hybrid gluing.

• IV measurements of silicon sensors after wire bonding.

Tests after module assembly:

• Metrology – measurements of module profile before thermal cycling.

• Thermal cycling – in a climate chamber the module is put through a temperature cycle between -30º and +35º within ~17 hours in order to check that different temperatures do not effect the module parameters in a way which damages its performance.

• Metrology – measurements of module profile after thermal cycling.

• Electrical readout tests of the module.

Electrical tests of the modules:

• Done once the module is completed and went through the thermal cycling.

• Module electrical performance is characterized via measurements of its gain, response curve, noise occupancy, IV curve and time resolution of the readout signal.

Production Statistics

• In order to get an overview of the production a statistics tool based on query of the SCT database has been developed.

• Plots of the characteristic module parameters and the measured values from the readout tests are made.

• Plots show specification limits and distributions of the desired parameters, thus enabling identification of problems and trends during the production.

The setup for electrical readout tests

IV curve of a module from final electrical test

A module before shipment to CERN QA site

IV measurements of a module during different assembly stages

The limit on noise hits has been set so as to make them a negligible addition to the expected real signal hit occupancy.

For the ATLAS operation conditions a limit of 0.0005 is set on the noise occupancy.

Typical noise occupancy plots for front and back side of the module (logarithmic scale). The blue dot indicates the 1 fC ATLAS operating threshold.

Silicon sensors:

Semiconductor ionisation tracking detector

Sensors are based on a junction diode. The diodes are reversed biased until fully depleted.

Binary readout scheme

Block diagram of the SCT ABCD readout chip.