-

Performance Studies & Productionof the LHCb Silicon Tracker

Stefan Koestner (University Zurich)

on behalf of the Silicon Tracker Collaboration

IT - modules:• p-n silicon micro-strip sensors (Hamamatsu)• 384 AC coupled readout strips, 108 mm long • 197µm pitch, w/p=0.25, 320(410) µm thickness• readout hybrid with 3 Beetle chips • cooling “balcony” for mounting and positioning of the ladder on the supporting cooling rod which is connected to the liquid cooling system• Carbon Fibre (CF) support produced out of high thermal conductive fibre used to cool the sensors and the detector box

TT- modules:• modules are connected to 14 sensor long ladders (4-3-3-4 and 4-2-1-1-2-4) • To reduce material inside sensitive area readout hybrids are located at the edges of detector boxes• inner sensors connected via Kapton interconnect cable (up to 55cm long) • supported by carbon/glass fibre rail• high load capacitance: 3 sensor + flex 55 pF• inter-strip capacitance 0.17 pF/cm

minimize R/O channels & radiation length: large pitch O(200m) (charge collection) long strips 33cm (noise) “thin” sensors (little charge) 40MHz, fast readout (noise)

Pulse-Shaping• fast readout in O(charge collection time)• variable shaper feedback setting in Beetle (Vfs) adapt to different detector capacitances

signal remainder 25ns after peak

specification: remainder < 0.5

(TT)< 0.3 (IT)

Signal

Noise

•Sensors•Kapton•Carbon Fibre•AIREX faom•Carbon Fibre

The LHCb experiment: Single-arm forward spectrometer dedicated to B-physics• acceptance: 15-300(250)mrad• pp@14 TeV, luminosity=2·1032 cm-2s-1

• 1012 bb/year, full B spectrum

The Silicon Tracker:consists of the Trigger Tracker (TT) in front of the magnet and the Inner Tracker (IT) behind the magnet. • spatial resolution requirements ~60µm pitch ~200µmTT-station:Measures transverse momentum of large impact parameter tracks in L1• active area: 8.2m2, readout channels: ~180k, cooled to ~5°C• modules: 1,2,3-sensor-sectors (11cm, 22cm,33cm )• 4 layers in 2 half stations, 2 layers with ±5º stereo angle

The Inner Tracker:Provides granularity in the high multiplicity region around the beam pipe - 1.3% of sensitive area 20% of tracks• active area: 4.3m2, readout channels: ~130k• modules: 1, 2sensor-ladders (11 and 22cm) • 3 stations with 4 boxes, 4 layers per box (2 stereo): 336modules

Testbeam Results:

• 120 GeV pions ~MIP (minimum ionizing particle)• 3 sensor ladders with CMS, GLAST, LHCb sensors (~30cm) • 2, 1 sensor ladders with LHCb multigeometry sensors

S/N interpolation of on-strip data:• ENC = 542 + 49.83·Ctot • total capacitance linear with w/p (independent of thickness)• parameterization for 320 µm thick sensor

S/N interpolation of inter-strip data:• charge loss in inter-strip region (trapped on surface) • linear as a function of (pitch-width)/thickness (in the range of interest)• dominates for pitch wider than ~200 µm

Electrical Tests:

• internal calibration pulses reliable to detect common defects (broken, short, pinhole) in final modules• simulated defects (artificial bonds) show similar behaviour than real ones

peakheight remainder

3σ short

broken bond

• high leakage (irradiation) affects dc-coupled readout • easy test for pinholes (bias voltage @ -0.5V & 0V)

-0.5 Volts No bias voltage

• 1.6·1015 primary pp-collisions (after 10 years)• average flux up to ~4·1013 1MeV neutron equivalent/cm2

for 1 sensor sector - (safety factor 2)

Other losses in S/N (pessimistic scenario):• charge traps • increase of total capacitance

• up to 1·1013 1MeV neutrons/cm2 close to beam pipe

Sensor Positioning Precision

0

10

20

30

40

50

60

70

80

TT1 TT2 TT3 TT4 TT5

[m

]

0

50

100

150

200

250

300

[ra

d]

offset

flatness

angle

GFKCFK

S/N

S/N

Module Production:• Readout hybrid and sensors are glued using custom made positioning jigs • parallel module production in several jigs

Burn-in and Final Readout Test:• temperature cycling and readout for module testing•IV measurements, Test-pulses, etc

IV curve for 2nd, 3rd ladders at T=20C,10C,0C,-10C

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400 450 500

Sensor bias (V)

Sen

sor

curr

ent

(nA

)

l2t20h44

l2t20

l2t10

l2t0

l2t-10

l3t20h44

l3t20

l3t10

l3t0

l3t-10

Production tested on 4 IT and 7 TT modules so far, almost ready for full production !

Leakage current:• I = α·Φ·V @ 20°C

•

• ENC2=11.56·τ·I

21

21

2

1

2

1

2

2exp

TTk

TTE

T

T

I

I

B

g

Expected depletion voltage according to the “Hamburg Model”:• 410µm thick sensors• bulk resistivity 4-9 kΩ/cm

Low material budget for cooling inside sensitive area:

•liquid (C6F14) cooling for hybrids and module support

•natural convection on sensor surface to prevent thermal runaway (~5 Wm-2K-

1)

-