lbnl leo greiner , eric anderssen, giacomo contin,
DESCRIPTION
Assembly and testing of a MAPS based vertex detector for the STAR experiment at RHIC. LBNL Leo Greiner , Eric Anderssen, Giacomo Contin, Thorsten Stezelberger, Joe Silber, Xiangming Sun, Michal Szelezniak, Chinh Vu, Howard Wieman, Sam Woodmansee UT at Austin Jerry Hoffman, Jo Schambach - PowerPoint PPT PresentationTRANSCRIPT
L. Greiner 1ATLAS Workshop LBL - September, 2013
STAR HFTSTAR HFT
LBNLLeo Greiner, Eric Anderssen, Giacomo Contin,Thorsten Stezelberger, Joe Silber, Xiangming
Sun, Michal Szelezniak, Chinh Vu, Howard Wieman, Sam Woodmansee
UT at AustinJerry Hoffman, Jo Schambach
IPHC StrasburgMarc Winter CMOS PICSEL group
Assembly and testing of a MAPS based vertex detector for the STAR
experiment at RHIC
2ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTTalk Outline
•Short overview of detector design.•Design of ladders, sectors, insertion mechanism.•Detector assembly, yields, integration and installation for engineering run.•In progress production, assembly and QA for the primary detector.
The primary focus of this talk is technical and on instrumentation.
3ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPXL in STAR Inner Detector UpgradesTPC – 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 = 2.7, 8 cm
We track inward from the TPC with graded resolution:
TPC SSD IST PXL~1mm ~300µm ~250µm <30µm
Direct topological reconstruction of Charm
vertex
4ATLAS Workshop LBL - September, 2013L. Greiner
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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5ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPXL Detector Design
Mechanical support with kinematic mounts (insertion side)
Insertion from one side2 layers (tiled)5 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
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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 RDO board per sector 10 Sector chains in the PXL system
RDO motherboard w/ Xilinx Virtex-6 FPGA
DAQ 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
7ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTDetector Characteristics
Pointing resolution (12 19 GeV/pc) m
Layers Layer 1 at 2.7 cm radiusLayer 2 at 8 cm radius
Pixel size 20.7 m X 20.7 m
Hit resolution 6 m
Position stability 6 m rms (20 m envelope)
Radiation length per layer X/X0 = 0.37%
Number of pixels 356 M
Integration 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
8ATLAS Workshop LBL - September, 2013L. Greiner
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 and ran the detector until June 10, 2013. • The production detector is scheduled to be installed in December of 2013.• We will build 2 complete detectors and enough good ladders to build a third.
These serve as spares for rework if necessary.
I will give a brief overview of the PXL detector design details, components and assembly in the following areas:
• Sensors• Ladder assembly and QA• Sector assembly and QA• Detector Half• Insertion mechanics• RDO System• Engineering run
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STAR HFT
• Sensors
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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
11ATLAS Workshop LBL - September, 2013L. Greiner
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
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STAR HFTUltimate 1 efficiency vs. fake hit rate
Tested for STAR Operating conditions
Developed and tested by IPHC Marc WinterCMOS GroupIPHC, Strasbourg, France
13ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
• Ladder assembly• Sector assembly• Half detector assembly
14ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTLadder Design• Ladder assembly is the primary task for the detector fabrication.• We assemble ladders by edge bumping sensors on a vacuum
chuck (the soft acrylic adhesive provides mechanical decoupling for CTE mismatches)
• DRIE needed for precise sensor size. (most engineering run sensors were saw cut and this gave significant variations in the assembled length of the 10 sensor array, after DRIE, length variation in butted edge sensor array is ~50um)
• Wire bonding is very sensitive to small sensor position variations (small displacements cause the bonding pads on the ladder to displace wrt bonding pads on the sensors and wire bonds then require steep angles).
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STAR HFTLadder Design
Ladder cable concept
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STAR HFTLadder assembly work flow chart
Probe tested sensors
Electrically tested low mass cables
Electrically tested driver boards
Dimensionally checked composite backer
Ladder assembly
Ladder wire bonding
Wire bond encapsulation
Quick test
Full functionality test
Complete ladder
• Ladder characterization
• Reworking and troubleshooting
• Quality assessment• Initial validation
1 day without problem
sFull functionality testbias optimizationThreshold scanNormal readout mode testAccidental hit rate scan
Quick testThreshold scan @ nominal bias settings
17ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTSector/half-detector work flow chart
TestedLadders
SizedSector Tubes
machined Dovetail/D-tube
Elect testedMTB/cables/insertion
Sector assembly
Full functionality test
Quick test
Half detector headassembly
Sector metrology
½ HFT PXL
Quick test
Half detector head metrology
Full Half detector assembly
Quick test
18ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTOverall detector design factors (metrology)
• We intend to insert a fully mapped detector with all pixel positions known and stable.
• We have gone to great lengths to ensure that the ladder/sector/half detector mechanics are stable to 30um for all forces (gravity, vibration and deflection due to air cooling (~10 m/s), thermal distortion, mechanical stress from cable loading, etc.) anticipated during running.
• We map each sector using fiducials on the sensors and relate pixel positions to tooling balls on the sectors.
• We then assemble half detectors and map the sector tooling balls to give the pixel positions for each half detector.
19ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTSensor Thinning• We use sensors thinned to 50 µm thickness.• We use DRIE processing on the wafers to give accurate sensor dimensions
and edge quality.• Wafers are delivered with DRIE trenches 70 µm deep. The wafers are back-
thinned and polished at Aptek to release the dies from the wafer (yield started quite low, but is now significantly improved).
• First 25 production wafers, 5 were lost completely during thinning as process was refined. Last 17 wafers thinned had >99% yield.
• Die position on the wafer and wafer # are preserved through the thinning process and this identifies the die in our database.
• We select dies based on probe testing of thinned sensors.• 50 um thick sensors are curved, up to 2 mm out of plane, this has
implications.
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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 probe card 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 not easy.
Assembling sensors into ladders – Probe Testing
21ATLAS Workshop LBL - September, 2013L. Greiner
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) (4.5 hr testing time)
Thr
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cou
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x5)
Column number
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22ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTExamples of failures
D07_w_12E01_w_8 (@3.0V)
E05_w_12 E06_w_12
E05_w_08 C04_w_12
OK
Faultycolumns
Sub-arrays
Faulty rows
3.3 or 3.0 V
23ATLAS Workshop LBL - September, 2013L. Greiner
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 (Tier 1-3)
40% Tier 1-2
24ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
• Building sensors into ladders
25ATLAS Workshop LBL - September, 2013L. Greiner
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 output pairs• JTAG, 2 temp diodes, CLK, START• VDD, VDA, GND - ~1.8 A / ladder
Layout (in copper)
26ATLAS Workshop LBL - September, 2013L. Greiner
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
27ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTAssembling sensors into ladders – Assembly
• 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.
28ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTQA/QC for Sector Production
Completed ladder in anti-static carrying box with follower and check off list.
Assembled ladder with driver board, wire bonded and encapsulated
29ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTEngineering Run Ladder Yield• The assembly of ladders and sectors for the PXL Engineering Run has been
crucial for process optimization and we have dealt with a number of unexpected issues.
• Thanks to this experience, we were able to refine the assembly procedure and to develop effective tools for troubleshooting ladders.
• The final ladder assembly statistics for the engineering run detector are:
Quality assessment (03/20/2013) # %Fully operating ladders 15 55.6
Lower quality operating ladders (>8 operating chips) 4 14.8
Recoverable not operating ladders (need fix or workaround)
4 14.8
Dead ladders (not recoverable) 4 14.8
Total 27 100.0• The primary lessons learned had to do with the need for coverlay on the
cable, modification of tooling that was damaging sensors, adjustment of adhesive sizes and backing plates, proper adjustment of sensor array on the cable.
30ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
• Ladders to sectors
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STAR HFTLadders to sectors
32ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTLadders to sectorsSector in optical metrology machine
• Sensor fiducial positions on sector are measured optically and related to tooling balls.
• Surface profiles of sensors (sensors are not flat) are measured using feather touch probe CMM and pixel positions are related to sensor fiducials using thin plate spline fit. Now we have pixel positions related to the tooling balls.
• After touch probe measurements, sectors are tested electrically for damage from metrology.
33ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTsectors to detector half (ER)
• Sectors are mounted in dovetail slots on detector half.• Metrology is done to relate sector balls to each other and
to kinematic mounts. We now have pixel positions for the half detector object.
34ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
• PXL detector mechanics
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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
36ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
Power ~340 W Airflow 10.1 m/s
Thermal camera image of sector 1 (composite image):
Mechanical Development
unsuported endmid-section fixed 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.
37ATLAS Workshop LBL - September, 2013L. Greiner
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.
38ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPXL insertion mechanics
Interaction point view of the PXL insertion rails and kinematic mount points
Carbon fiber rails
Kinematic mounts
39ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPXL insertion mechanics
PXL detector half with complete insertion mechanism
40ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTEngineering Run
Left detector half being inserted
Right detector half being inserted
41ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTEngineering Run
PXL eng detector inserted, cabled and working in 1 day access
42ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTEngineering Run
• PXL system working with 3 sectors
• Integrated with STAR trigger, DAQ, slow controls, online event pool.
• Software and firmware for performing data quality checks were modified and optimized.
Hit display for PXL engineering run detector.
43ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPreliminary results from Engineering Run• First tracking results show
good matching of TPC tracks to hits on PXL sensors
• Residuals compatible with TPC track resolutions on the sensors (~1-2 mm)
• 3mm beam shift reflects the PXL&TPC relative position
44ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTLessons learned• “Full dress rehearsals” are critical to success.• We discovered a mechanical conflict in the ladder driver
board section that necessitated a sector tube redesign.• Tooling that would fracture sensors during assembly
was modified.• Our ladder temperature monitoring system didn’t work
properly and was re-designed.• Other electronics / sensor issues are still under
investigation and will require further updating of the existing systems.
45ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTProduction detector
• We are currently building ladders for the production detector.
• Mechanical thinning yields are now close to 100%.• Current ladder yields are much better.• 36 ladders produced, 26 tested, 1 ladder has 1
damaged sensor, all others tested are fully functional.
• Production sector assembly will start in mid-September.
46ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
• end
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STAR HFT
• Extra slides
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STAR HFT
49ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTRead-out Electronics
1. 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
50ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFT
Tier1 yield Vs position in wafer
0
5
10
15
Chip Position
Coun
ts
Tier2Tier1
First 25 production wafers.
Radiation Length of active area
NOTE: Does not include sector tube side walls
52ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTHFT PXL status – fabrication and tooling
L. Greiner 53ATLAS Workshop LBL - September, 2013
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
54ATLAS Workshop LBL - September, 2013L. Greiner
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
55ATLAS Workshop LBL - September, 2013L. Greiner
STAR HFTPixel signal extraction and operation
GND
VDD
select
outputoutputin equilibrium
time
pote
ntia
l on
the
char
ge c
olle
ctin
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
56ATLAS Workshop LBL - September, 2013L. Greiner
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
57ATLAS Workshop LBL - September, 2013L. Greiner
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