a novel maps based vertex detector for the star experiment ... · l. greiner slac instrumentation...

L. Greiner 1SLAC Instrumentation – May 22, 2013

STAR HFTSTAR HFT

LBNLLeo Greiner, Eric Anderssen, Giacomo Contin,Thorsten Stezelberger, Joe Silber, Xiangming

Sun, Michal Szelezniak, Chinh Vu, Howard Wieman

UT at AustinJerry Hoffman, Jo Schambach

IPHC StrasburgMarc Winter CMOS group

A novel MAPS based vertex detector for the STAR experiment at RHIC

2SLAC Instrumentation – May 22, 2013L. Greiner

STAR HFTTalk Outline

• STAR vertex detector upgrades at RHIC.• Pixel detector requirements, design and characteristics.• Overview of detector design.• Detector development and construction flow path. Novel

sensors and mechanics.• Detector assembly, integration and installation for

engineering run.• Summary and plans.

The primary focus of this talk is technical and on instrumentation.


STAR HFTVertex Detector Motivation

Direct topological reconstruction of Charm

Detect charm decays with small c, including D0 K

Method: Resolve displaced vertices (100-150 microns)

200 GeV Au-Au collisions


STAR HFTPXL in STAR Inner Detector Upgrades

TPC – Time Projection Chamber(main tracking detector in STAR)

HFT – Heavy Flavor Tracker SSD – Silicon Strip Detector

r = 22 cm IST – Inner Silicon Tracker

r = 14 cm PXL – Pixel Detector

r = 2.5, 8 cm

We track inward from the TPC with graded resolution:

TPC SSD IST PXL~1mm ~300µm ~250µm vertex<30µm


STAR HFTPXL Detector Requirements and Design Choices

• -1 ≤ Eta ≤ 1, full Phi coverage (TPC coverage)• ≤ 30 µm DCA pointing resolution required for 750 MeV/c kaon

– Two or more layers with a separation of > 5 cm.– Pixel size of ≤ 30 µm– Radiation length as low as possible but should be ≤ 0.5% / layer (including

support structure). The goal is 0.37% / layer (limits MCS)• Integration time of < 200 μs (limit pile-up, occupancy of ~250 hits/inner sensor)• Sensor efficiency ≥ 99% with accidental rate ≤ 10-4.• Survive radiation environment.

• Air cooling• Thinned silicon sensors (50 μm thickness)• MAPS (Monolithic Active Pixel Sensor) pixel technology

– Sensor power dissipation ~170 mW/cm2

– Sensor integration time <200 μs (L=8×1027)• Quick detector installation or replacement (1 day)

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es


STAR HFTPXL Detector Design

Mechanical support with kinematic mounts (insertion side)

Insertion from one side2 layers5 sectors / half (10 sectors total)4 ladders/sector

Aluminum conductor Ladder Flex Cable

Ladder with 10 MAPS sensors (~ 2×2 cm each)

carbon fiber sector tubes (~ 200 µm thick)

20 cm


STAR HFT

2 m (42 AWG TP)11 m (24 AWG TP)

100 m (fiber optic)

Highly parallel system

4 ladders per sector 1 Mass Termination Board (MTB) per sector 1 sector per RDO board 10 RDO boards in the PXL system

RDO motherboard w/ Xilinx Virtex-6 FPGA

RDO PC with fiber link to RDO board

Mass Termination Board (signal buffering) + latch-up protected power

PXL Detector Basic Unit (RDO)

Clk, config, data, powerClk, config, data

PXL built events

Trigger, Slow control,Configuration,etc.

Existing STAR infrastructure


STAR HFTDetector Characteristics

Pointing resolution (12 19 GeV/pc) mLayers Layer 1 at 2.5 cm radius

Layer 2 at 8 cm radiusPixel size 20.7 m X 20.7 m Hit resolution 6 mPosition stability 6 m rms (20 m envelope)Radiation length per layer X/X0 = 0.37%Number of pixels 356 MIntegration time (affects pileup) 185.6 s

Radiation environment 20 to 90 kRad / year2*1011 to 1012 1MeV n eq/cm2

Rapid detector replacement ~ 1 day

356 M pixels on ~0.16 m2 of Silicon


STAR HFT

2 2

GEANT: Realistic detector geometry + Standard STAR trackingincluding the pixel pileup hits at RHIC-II luminosity

Hand Calculation: Multiple Coulomb Scattering + Detector hit resolutionPXL telescope limit: Two PIXEL layers only, hit resolution only

Mean pT

30 m

Expected DCA resolution performance


STAR HFTPXL Detector Production Path (post CD – 2/3)

Sensor development

Readout development

Mechanical development

Cable development

Pre-production prototype

UltProbe tests

Infrastructure development

Ult sensorprototype

10 sensorCu+kapton pre-prod

Eng run Sector

prototype

Final Ladder readout

Final individual readout

Update mech for

size

Prod readout

production sensors

ProdProbe tests

10 sensorAl+kapton

prod

prod Sector

Eng run detector

prod detector

May 2013

Dec 2013

Culmination of >9 years of development


STAR HFTPXL Detector Highlights• The HFT upgrade to STAR received DOE CD-2/3 approval in

September 2011 and became a construction project.• We installed a 3 sector engineering run detector into the STAR

experiment on May 8, 2013. • The production detector is scheduled to be installed in December of

2013.

I will give a brief overview of the PXL detector design details, components and assembly in the following areas:

• Sensors• Ladders• Sectors• Detector Half• Insertion mechanics• RDO System• Engineering run


STAR HFT

• Sensors


STAR HFT

• Standard commercial CMOS technology

• Room temperature operation• Sensor and signal processing are

integrated in the same silicon wafer• Signal is created in the low-doped

epitaxial layer (typically ~10-15 μm) → MIP signal is limited to <1000 electrons

• Charge collection is mainly through thermal diffusion (~100 ns), reflective boundaries at p-well and substrate.

• High resistivity epi for larger depleted region → more efficient charge collection, radiation tolerance.

• 100% fill-factor • Fast readout• Proven thinning to 50 micron

MAPS pixel cross-section (not to scale)

Monolithic Active Pixel Sensors


STAR HFTSensor generation and RDO attributes

Pixel

Sensors CDS

ADC Data

sparsification

readout

to DAQ

analogsignals

Complementary detector readout

MimoSTAR sensors 4 ms integration time

PXL final sensors (Ultimate) < 200 μs integration time

analog

digital digital signals

Disc.

CDS

Phase-1 sensors 640 μs integration time

Sensor and RDO Development Path

9 year program with IPHC – Strasbourg, France

3 generation program with highly coupled sensor and readout development

1

2

3


STAR HFTPixel signal extraction and operation

GND

VDD

select

outputoutputin equilibrium

time

pote

ntia

l on

the

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g no

de

chargecollection

chargecollectingdiode

Capacitor Storage for Correlated Double Sampling (CDS)

~ 100s ms

Discriminator

Zero suppression and memory

LVDS outputs 160 MHz

1 2 3

(Sample 1 – Sample 2) > threshold => hit(Sample 2 – Sample 3) < threshold => no hit

CDS

Simplified description

O

Self-biasedconfiguration


STAR HFTPXL detector Ult -1/2 Sensor• Reticle size (~ 4 cm²)

• Pixel pitch 20.7 μm • 928 x 960 array ~890 k pixels

• Power dissipation ~170 mW/cm² @ 3.3V• Short integration time 185.6 μs• In pixel CDS• Discriminators at the end of each column

(each row processed in parallel)• 2 LVDS data outputs @ 160 MHz• Zero suppression and run length encoding on

rows with up to 9 hits/row.• Ping-pong memory for frame readout (~1500

hits deep)• 4 sub-arrays to help with process variation• JTAG configuration of many internal

parameters.• Individual discriminator disable, etc.• Built in automated testing routines for sensor

probe testing and characterization.• High Res Si option – significantly increases

S/N and radiation tolerance.

Developed by IPHC, Strasbourg France


STAR HFTUltimate 1 efficiency vs. fake hit rate

Tested for STAR Operating conditions

Developed and tested by IPHC Marc WinterCMOS GroupIPHC, Strasbourg, France


STAR HFT

• Building sensors into ladders


STAR HFT

• Probe card with readout electronics – derived from individual sensor test card

• Analog and digital sensor readout• Full speed readout at 160 MHz• Full sensor characterization at full speed

– Test results used for initial settings in ladder testing and PXL detector configuration

• 2nd generation for production testing– only digital readout pins loaded

Yield modeling makes probe testing critical to the goal of assembling functional 10 sensor ladders.We test thinned and diced 50 µm thick sensors (curved). This is hard.

Assembling sensors into ladders – Probe Testing


STAR HFTAssembling sensors into ladders – Probe Testing• Vacuum chuck for testing 20 thin

sensors (50 µm)– Thin sensors are sensitive to chuck

surface imperfections– Need a special probe pin design and

to work in clean environment• Testing up to 18 sensors per batch

– Optimized for sensor handling in 9-sensor carrier boxes

• Manual alignment (18 sensors ~ 1 hr)– Testing time is ~ 15 minutes per

sensor (3 supply voltages)

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x5)

Column number

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hold


STAR HFTPXL Sensor selection• Automated interface to a database (18 config + 68 result parameters)• Sensors are binned according to performance

Example of wafer maps for Ultimate-2 wafers with DRIE processing (ion etching)

~65% - 70% yield


STAR HFTAssembling sensors into ladders – Hybrid Cable• The cable is needed to deliver power and ground and provide signal routing to and from

the sensors on the ladder with minimal radiation length.• Production aluminum conductor flex cables are being fabricated in the CERN PCB shop.

(difficult to produce, only one real vendor)

Hybrid Copper / Aluminum conductor flex cable design concept

Low mass region calculated X/X0 for Al conductor = 0.079 %Low mass region calculated X/X0 for Cu conductor = 0.232 %

• 20 differential signal pairs• JTAG, 2 temp diodes, CLK, START• VDD, VDA, GND - ~1.8 A / ladder

Layout (in copper)


STAR HFTAssembling sensors into ladders – Assembly

• We use precision vacuum chuck fixtures to position sensors and assemble ladders.

• Sensors are positioned with butted edges. Acrylic adhesive mechanically decouples sensors from the cable and prevents CTE difference based damage.

• Weights taken at all assembly steps to track material and as QA.

Reference pins for cable/sensor alignment



• Hybrid cable with carbon fiber stiffener plate on back in position to glue on sensors.

• The cable reference holes are used for all aspects of assembly of ladders and sectors.



Early optimizationTesting results (ladder with 2 bad sensors)

Assembled ladder on FR-4 handling piece

Sensor noise performance only minimally degraded with all sensors running


STAR HFT

• Ladders to sectors


STAR HFTLadders to sectors


STAR HFTLadders to sectors

Sector in optical metrology machine

• Sensor positions on sector are measured and related to tooling balls.

• After touch probe measurements, sectors are tested electrically for damage from metrology.

Radiation Length of active area

NOTE: Does not include sector tube side walls


STAR HFTsectors to detector half

Sectors are mounted in dovetail slots on detector half.Metrology is done to relate sector balls to each other and to kinematic mounts.


STAR HFT

• PXL detector mechanics


STAR HFTPXL detector – insertion mechanics

• Unusual mechanical approach.• Cantilevered and insertable (1 day)• Pre-surveyed and mechanically stable to a level that preserves the survey.• Detector inserts and initiates a clamshell closing around beam pipe, and is

locked into position on kinematic mounts.• Cooling vibration and displacement stability, thermal stability, humidity stability.


STAR HFTPXL insertion mechanics

Interaction point view of the PXL insertion rails and kinematic mount points

Carbon fiber rails

Kinematic mounts


STAR HFTPXL insertion mechanics

PXL detector half with complete insertion mechanism


STAR HFT

• RDO electronics


STAR HFTRead-out Electronics1. The detector is 10 parallel sector chains.2. Each sector is configured and delivers data to the RDO boards

continuously into a data pipeline.3. The receipt of a trigger opens an event buffer for 1 frame of data.

(2 actual frames with address selection performed to give one compete frame based on the time the trigger is received)

4. The data is formed into an event and shipped to the DAQ receiver PCs.

Full PXL RDO fits into 1 crate


STAR HFTEngineering Run

Left detector half being inserted

Right detector half being inserted



PXL eng detector inserted, cabled and working in 1 day access



• PXL system working with 3 sectors

• Integrated with STAR trigger, DAQ, slow controls, online event pool.

• Doing data quality checks and tweeking firmware and software.

Hit display for PXL engineering run detector.

More to come…


STAR HFTSummary

• The PXL detector simulations and prototyping indicate that we should be able to achieve a very high resolution and low radiation length vertex detector.

• The STAR PXL detector will be the first MAPS based vertex detector used at a collider accelerator experiment.

• We have produced and inserted a three sector prototype detector on May 8.

• Construction on the production detector is beginning. The first batch of 25 wafers of sensors has arrived and been sent for thinning.

• The final PXL detector along with the rest of the HFT upgrades will be installed for the December 2013 run.


STAR HFT

• Extra slides


STAR HFTHFT PXL status – fabrication and tooling


STAR HFTMechanical Development

Silicon power: tested at 170 mW/cm2 (~ power of sunlight) 350 W total in the ladder region (Si + drivers)

computational fluid dynamics

Air-flow based cooling system for PXL to minimize material budget.

Detector mockup to study cooling efficiency

ladder region


STAR HFT

Power ~340 W Airflow 10.1 m/s

Thermal camera image of sector 1 (composite image):

Mechanical Development

unsuported endmid-sectionfixed endSolid – inner layerOpen – outer layer

340 W with ambient air = 26.8 C

NTC thermistors(averaged at same “Z” position)

• Measurement results agree with simulations and meets calculated stability envelope tolerance.

• Air flow-induced vibrations (≤ 10 m/s) are within required stability window.


STAR HFT

Driver section ~ 6 cm

Sensor section ~20 cm

Kapton cables with copper traces forming heaters allow us to dissipate the expected amount of power in the detector

6 NTC thermistors on each ladder

Sector 1 was equipped with 10 thinned dummy silicon chips per ladder with Pt heaters vapor deposited on top of the silicon and wire bonded to heater power.

Power ~340 W Airflow 10.1 m/s

Thermal camera image of sector 1 (composite image):

Mechanical Development


STAR HFTAlternate Technologies Considered

• Hybrid– X0 large (1.2%)– Pixel Size large (50 m x 450 m)– Specialized manufacturing - not readily available

• CCDs– Limited radiation tolerance– Slow frame rate, pileup issues– Specialized manufacturing

• DEPFET– Specialized manufacturing– very aggressive unproven technology

MAPS sensors are the technology selected


STAR HFTFast, column-parallel architecture

VREF1 PWR_ON

MOSCAP

RESET

VREF2 VDD

PWR_ON

VR1VR2

READ

CALIB

ISF

PIXEL

COLUMN CIRCUITRY

OFFSET COMPENSATED COMPARATOR

(COLUMN LEVEL CDS)

SOURCEFOLLOWER

latch

Q

Q_

READ

READ

+

+

+

+

+ +

-

- -

-

LATCH

CALIB

READ

PWR_ON

RESET

READ

CALIB

LATCH

CDS at column level (reduces Fixed Pattern Noise belowtemporal noise)

122 , inrefCsfrefCALIB VVVVVV

)( 122

122

2

ininsfref

inrefsfin

sfCinREAD

VVVV

VVVV

VVVV

VREAD,CALIB

VCVin1,2

12122

2_ 1 offRREADoffREADS VVVAV

AAV

READSoffoffRCALIBout VVVVVAAV _21112

1212 RRREADCALIBout VVVVAAV

VS_READ

A1 Voff1

A2, Voff2

Developed in IPHC - DAPNIA collaboration


STAR HFTLadder 3 (separated VDA and VDD)

Results consistent with previous ladders (L1, L2)

- Faulty sensors and/or fine-wire cable issues (under investigation)

(slight improvement?)

(From previous IPHC-LBL phone meetings)


STAR HFTMimosa-26 in HR

a novel maps based vertex detector for the star experiment ... · l. greiner slac instrumentation...

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