ATLAS Semi Conductor Tracker Operation and Performance

ATLAS Semi Conductor Tracker Operation and Performance

Dave RobinsonCavendish Laboratory, Cambridge, UK

on behalf of the SCT Collaboration

Dave Robinson - 8th International Hiroshima Symposium, Academica Sinica, Taipei, 5-8 December 2011 2

ATLAS was fully commissioned in 2008 and has been fully exploiting

the physics potential of the LHC sincethe first 7TeV pp collisions in 2009

The ATLAS Detector

Tracking : The Inner Detector


5.6m

1.4m

• C3F8 Cooling (-7oC to +4.5oC silicon) to limit radiation damage• Radiation hard: tested to 2x1014 1-MeV neutron equivalent/cm2 • Lightweight: 3% X0 per layer

The Semi Conductor Tracker (SCT)• 61 m2 of silicon with 6.2 million readout channels• 4088 silicon modules in 4 Barrels and 18 Disks (9 each end)• Barrels : |h| < 1.1 to 1.4, End-caps : 1.1 to 1.4 <|h| < 2.5• 30cm < R < 52cm, space point resolution rf ~16mm / R~580mm

The SCT Sensors

• 8448 barrel sensors• 64.0 x 63.6mm• 80mm strip pitch• all supplied by Hamamatsu

• Single sided p-on-n• <111> substrate, 285mm thick• 768+2 AC-coupled strips• Polysilicon (1.5MW) Bias• Strips reach-through protection 5-10mm• Strip metal/implant widths 22/16mm

• 6944 wedge sensors• 56.9-90.4mm strip pitch• 5 flavours• 82.8% Hamamatsu• 17.2% CiS (some oxygenated)

5

The SCT Modules• Back-to-back sensors, glued to highly thermallyconductive substrates for mech/thermal stability,wire-bonded to form ~12cm long strips• 40mrad stereo angle between strips on opposite sides• 1536 channels (768 on each side)• 5.6W/module (rising to ~10W after 10 yrs LHC)• up to 500V sensor bias (nominal 150V)

• 1976 end-cap modules• 3 shapes

• 2112 barrel modules• one shape

6

• 128 channel ASIC with binary architecture• Radiation-hard DMILL technology• 12 chips per module (6 each side)• glued to hybrid (Cu/polyimide flex circuit)• 40MHz (25ns) clock• 20ns front end shaping time

DAC

Binary Pipeline (132 deep)Comparator

PreAmp+Shaper

Threshold Voltage

Edge-Detect circuit

Readout Buffer

Test-Input

Data Compression

Circuit

t

t

v

“Shaped” input pulse to Comparator

“Logic” output of comparator

• 3 pipeline bins read out, centred on L1A trigger• Hits contained in 1 or 2 bins• Timing optimised using pattern of hits in the 3 time bins

The ASICs (ABCD Chips)

7

Optical Link Redundancy Schemes

VCSELVCSELP-I-N

VCSELVCSELP-I-N

VCSELVCSELP-I-N

VCSELVCSELP-I-N

VCSELVCSELP-I-N

Standard operationAll chips, VCSELs and fibres ok

Dead chip bypassedAll fibres ok

Broken RX fibre or dead RX VCSEL(for barrels, lose master chip of lost link)

Broken TX fibre or dead TX VCSELClock and control from neighbouringmodule

Typical snapshot in SCT

Link0 DataLink1 Data

TTC


TTC


TTC


TTC


TTC


The SCT TimelinePrototyping & Production

to LHC Physics

92010 2011200920082007200620052004≤2003

Prototyping and Production

102010 2011200920082007200620052004≤2003

Assembly of Barrels and End-Caps

Barrel modules attached by robot at Oxford

Endcap modules attachedmanually at NIKHEF and Liverpool

• mount services - cooling pipes - powering & optical harnesses• mount modules• connect to services

Cool, power and test all modules after assemblyand compare with pre-assembly data

112010 2011200920082007200620052004≤2003

Reception Tests & Assembly at CERN

• Stability & uniformity of cooling and module temperatures• Stability of power supplies and optical communication• Digital functionality, response and noise from all modules

• Assembly of all 4 barrels

122010 2011200920082007200620052004≤2003

Integration with TRT and combined tests

Insertion of SCT barrels within the TRT

First cosmic rays recorded through SCT and TRT

132010 2011200920082007200620052004≤2003

Installation and Commissioning in ATLAS cavern

SCT+TRT Barrel installation

Connectivity tests

SCT+TRT End-cap installation

142010 2011200920082007200620052004≤2003

Single Beam : “Beam Splash” Events

152010 2011200920082007200620052004≤2003

First Collisions at 450 GeV

162010 2011200920082007200620052004≤2003

First Collisions at 7 TeV

172010 2011200920082007200620052004≤2003

Routine pp Data Taking at 7TeV and 1380 bunches

Typical event with 11 vertices(Smallest separation here 3.2mm)


SCT Performance

Data Quality and Data taking efficiencyData Acquisition

TimingHit EfficiencyLorentz Angle

AlignmentOperational Issues


Data Quality & Operational Efficiency2011

2010


Typical SCT Configuration Status

21

Data TakingSeveral enhancements to DAQ during 2010/11 to maximise data taking efficiency: “Stopless” reconfiguration and re-integration of RODs in case of (rare) BUSY Auto reconfiguration & recovery of modules which have non-zero errors Auto reconfiguration of entire SCT to counter SEUs

Typical data link error rate


Hit Efficiency

• #Hits/#Possible hits on tracks• Require PT>1GeV/c• Require ≥7 hits for SCT standalone• Require ≥ 6 hits for ID combined Hit efficiency well above 99% design requirement


Lorentz Angle• Carrier drift direction is deflected in B-field• Lorentz angle - track incidence angle at which the minimum cluster size (#hits in cluster) is detected • Lorentz angle is function of B-field, voltage and temperature

Prediction sensitive to:• model of signal digitisation in simulation• radiation damage

Measurements with cosmic ray and collision data both compatible with model predictions


Alignment

Alignment performed using a track based algorithm (minimise c2 of track-hit residuals). Initial alignment from survey and cosmic ray data, then isolated high Pt tracks for collision data. Continues to improve and approach design values.


Calibration

• Charge injection circuitry in ABCD• Measures hits vs threshold (S-curve)• Fit by complementary error function• Noise parameterised by width SCT noise < 1500 electrons (Hit threshold ~6000 electrons)

• Online method• Counts hits in empty bunches Noise occupancy ~10-5

Design < 5x10-4


TX VCSEL issues

• SCT has experienced poor reliability and frequent failures of the VCSEL arrays in the TX optical transmitters• Initially attributed to poor ESD precautions at factory• New batch was installed in 2009 manufactured with improved ESD precautions• New batch had improved lifetime, but again started to fail, this time attributed to exposure to humidity• Gradually being replaced by TXs with VCSELs from new vendor with improved resistance against humidity

Use of redundancy has minimised impact on SCT operations, and BOCs now operate in lower humidity environment

Radiation Damage• Radiation damages sensors and components. Effects are monitored constantly to predict future performance.• Fluence is measured on-detector• Observe excellent agreement between measured leakage current and predictions from MC based on measured fluence

Operationally, we see a gradual and continuous increase in leakage current for each module, both at 50V standby and 150V operation.Trips limits incremented (so far from 5mA to 50mA) appropriately as required. So far expect negligible shift in depletion voltage. Typical module current evolution at 50V and 150V

50V

150V

27Dave Robinson - 8th International Hiroshima Symposium, Academica Sinica, Taipei, 5-8 December 2011

28

Summary

• The SCT has enjoyed an outstanding first two years of LHC physics 99.6% overall data taking efficiency for 2011 99.0% of the 6 million channels are operational Fulfilled design requirements for noise, hit efficiency, tracking and

alignment• Significant effects of radiation damage are in very good

agreement with expectations• Only significant operational issues have been related to TX VCSEL

deaths Minimal effect on acceptance due to availability of redundancy Replacement program underway with improved resistance to humidity

(and now operate in lower humidity environment)• We look forward to many more years of successful tracking at

higher energy and luminosity

Dave Robinson - 8th International Hiroshima Symposium, Academica Sinica, Taipei, 5-8 December 2011


Backup Slides

30

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

ROD

RX chans

TX Chans

ROD

BOC

Optical Communication & Power Supplies

DATA

LV:- Vdd

- Vcc

- Vvcsel

- Vpin

HV:- Vbias

TTC

VCSELVCSELP-I-N

ROD

RX chans

TX Chans

ROD

BOC

SCT Module

48 modulesper

ROD/BOC

ROD crate (DAQ)

DCS

8 ROD crates (90 ROD/BOC pairs) 88 Power Supply Crates

P-I-N receives Timing, Trigger & ControlVCSEL* for each link (side) returns data

* VCSEL=Vertical Cavity Surface Emitting Laser

32

TimingThe ABCD chip is a binary chip - “hit” or “no hit” above 1fC threshold. It samples hits in 3 consecutive time bins (25ns LHC clock cycles), and is configured to flag a

“hit” in the readout depending on the pattern of hits in those 3 bins

Three bin sampling provides means to time in the SCT, and provide rejection of ghost tracks from hits associated with collisions 25ns or 50ns earlier.

• XXX for timing in, cosmic rays and ≥75ns bunch trains• X1X used currently for 50ns bunch trains• 01X will be used for 25ns bunch trains

Dedicated timing scans in first low lumi pp collisions of the year, with each of the 4088 modules optimised for 01X (1ns precision) Mean of 3bit hit pattern across SCT

Dave Robinson - 8th International Hiroshima Symposium, Academica Sinica, Taipei, 5-8 December 2011

33

Occupancy and Rate Limitations

• We expect around 1% peak SCT occupancy for 23 interactions per BX at 14TeV• Rate limit at 1% occupancy is ~90kHz, comfortably above ATLAS nominal peak trigger rate of 75kHz

(*) Complex Dead-Time: Maximum number of triggers within a given number of bunch crossings

-> Imposed by ABCD 8-deep event buffer

(*ATLAS 7/415)


Cooling & Environment

• C3F8 Compressor Issues– Worries about long term reliability have motivated the

Thermosiphon project• Gravity fed C3F8 system, to be commissioned in long 2013/14 shutdown

• Cooling temperatures– Pressure gradient in long delivery lines means the SCT silicon

cannot reach the design operating temperature of -7oC• Fluorocarbon blends (C3F8-C2F6) will allow is to reach target

temperature

• Thermo-heater Pad issues– Some non-operational heater pads (between SCT and TRT)

requires us to run barrel 6 (outermost barrel) at elevated temperature

The C3F8 evaporative cooling system has operated very reliably all year. But….


Frequency Scanning Interferometry• Optical alignment system to monitor the long term SCT mechanical stability• 842 fibre coupled interferometers• Typical deviations associated with solenoid cycle: - before ~11nm - during <3mm - after ~49nm


The SCT CiS Sensors – “Same spec, different species”

Hamamatsu CiS

Bias Resistors (1.5MW) Polysilicon Implant

Strip metal/implant widths (mm) 20/16 16/20

Guard design Single floating Multi-guard

Barrels supplied 8448 0

Wedges supplied 6944 1196


The CIS Leakage Current Problem• It become clear that the CIS SCT sensors were very sensitive to

humidity– A significant subset displayed poor IV and early (<150V) breakdown in

dry conditions– Need humidity to maintain a ‘healthy looking’ IV– Became more apparent during module tests which (unlike sensor QA)

were typically conducted in nitrogen environment– Problem identified as microdischarge from strips, due to lack of field

plate (strip metal narrower than implant)• As this became an issue rather late in the delivery program, SCT

adopted a pragmatic strategy:– Only accept sensors with no sign of breakdown below 150V in dry air– OK for the short term, and then strip micro-discharge becomes less

relevant after type inversion


CIS Leakage Current ProblemConsequences during SCT operation

• We have had a small but significant (~30) number of modules which have developed anomalously high leakage currents this year

• Almost all were constructed with CIS sensors, and all showed IV breakdown above 150V during production QA tests

• We believe that oxide charge buildup from ionising radiation is shifting the breakdown voltage downwards– Decreasing HV and increasing current limits means we can

keep operating these devices with full efficiency so far


Comparison of 1MeV neutron equivalent fluences determined from SCT leakage current measurements with simulated FLUKA

Snapshot corresponding to 2010 7TeV data with integrated luminosity of 48.6pb-1

Excellent agreement for barrels. Reasonable agreement for end-caps

ATLAS Semi Conductor Tracker Operation and Performance

Documents

Transcript of ATLAS Semi Conductor Tracker Operation and Performance