R&D activity in Bari for the ALICE Inner Tracking System upgrade Referee Meeting, 24 Giugno 2011 Vito Manzari INFN Bari (vito.manzari@cern.ch)
ALICE Pixel Material Budget Ø Contributions to one current Pixel layer Carbon fiber support: 200 µm Cooling tube (Phynox): 40 µm wall thickness Grounding foil (Al-Kapton): 75 µm Silicon pixel chip: 150 µm ² 0.16% X 0 Bump bonds (Pb-Sn): diameter ~15-20 µm Silicon sensor: 200 µm ² 0.22% X 0 Multilayer Al/Kapton pixel bus: 280 µm ² 0.48% X 0 SMD components Glue (Eccobond 45) and thermal grease Two main contributors: silicon and multilayer flex (pixel bus) 2
Hybrid Pixel R&D: Material Budget Ø How can the material budget be reduced? Reduce silicon front-end chip thickness Reduce silicon sensor thickness Reduce interconnect bus contribution - reduce power Reduce edge dead regions on sensor - reduce overlaps to avoid gaps Review also other components - average contribution ~0.02% Ø What can be a reasonable target Hybrid pixels overall material budget: 0.5 % X 0 ü silicon: 0.16% X 0 overall (100µm sensor + 50µm front end chip), at present 0.38% ü bus: 0.24% X 0, at present 0.48% ü others: 0.1% X 0 overall, at present 0.24% Monolithic pixels: 0.3 0.4% X 0 (e.g. STAR HFT) 3
Hybrid Pixel R&D: Material Budget Ø To reduce the silicon contribution to the overall material budget Threefold activity Thin Planar Sensor based on the current ALICE layout ü bump-bonded to present ALICE front-end chip for testing Thin Planar Active Edge Sensor based on the current ALICE layout ü bump-bonded to present ALICE front-end chip for testing Thinning the existing ALICE front-end chip ü Bump-bonded to standard ALICE sensor 200 µm thick for testing And then combine them 4
Hybrid Pixel R&D: Thin Planar Sensor Ø Procurement, Processing and Handling of 100µm thick wafers is an issue Ø Alternative: Epitaxial Wafers to be thinned during the bump-bonding process Epitaxial wafers provide a mean to use very thin sensor wafers carrier wafer included for free First tests of epitaxial sensors by PANDA (D. Calvo et al.) [see NIM A 595(2008)] Ø ALICE Epi-Pixel sensor Goal: achieve a sensor thickness of 100 µm (~ 0.11% X 0 ) Test with the ALICE pixel front-end chip (optimized for 200µm sensor) Epitaxial wafers produced by ITME (Poland) - Substrate thickness 525µm, doping n/sb, resistivity 0.008-0.02 Ωcm, <111> - Epitaxial layer thickness 95-105µm, doping n/p, resistivity 2000±100 Ωcm 5
ALICE Epi-Pixel Sensor Ø 5 sensor wafers fabricated at FBK Ø 3 wafers processed at VTT - successfully through all process steps, including thinning and back side patterning - Overall thickness: 105-115 µm (i.e. epi layer + 10 µm) Ø 5 singles flip-chip bonded to the current ALICE pixel front-end chip - electrical tests: ~30 na at 20V at RT, min. threshold ~ 1500 el., ~30 missing pixels 6
Beam Test of Epi-Pixel detector Ø Beam test of ALICE Epi-Pixel detector November 2010 CERN SPS: positive beam (pions, protons), 350 GeV/c, up to 10 4 particles/spill Duty cicle 49s, Flat top 9s, Trigger rate 3KHz ALICE 3D-Pixel detector samples were also tested - Double-sided Double-Type Column (DDTC) from FBK multi-project wafer Ø Tracking Telescope 4 ALICE standard Pixel detector arranged in 2 stations - each station contains 2 pixel detectors arranged in cross-geometry ü pixel cell dimensions 50 x 425 µm 2 - Estimated tracking precision 10µm both in x and y directions Ø Trigger Self-triggering: FastOr logic combining the information from the tracking planes 7
Beam Test Set-up Single assembly mounted on test card SPS beam test set-up 8
Beam Test Measurements Track Efficiency Cluster size Space accuracy Objectives vs Depletion Voltage Threshold Particle Crossing Angle Online beam spot Tracking Station 1 3D-sensor Epi-sensor Tracking Station 2 9
Residuals and Efficiency ALICE SPD Ø NIM paper in preparation Thr (DAC) Thr (el.) 200 3000 190 3600 180 4200 170 4800 10
Planar Pixel Sensor with Active Edge Ø Standard detectors Dead region (cracks and damages) a + d 500 µm Ø Active edge to limit dead region Cut lines not sawed but etched with Deep Reactive Ion Etching (DRIE) and doped Standard Detector Active Edge Detector Ø R&D in collaboration with FBK Within the MEMS2 agreement FBK-INFN Epitaxial wafer in order to achieve an Active Edge 100µm thick Planar Sensor 11
Processing w thicknesses Active Edge Detector www.vtt.fi www.vtt.fi/detectors www.micronova.fi Ø Main process steps and critical issues Attach support wafer ü provides mechanical Various detector support designs after trench on 6 etching inch wafer (SOI, wafer bonding, ) Trench opening by Deep Reactive Ion Etching (DRIE) - 5 x 5 cm ü dimensional aspect 1/20, 2 deep etching (200-230 µm) Inside trench doping ü solid source technology Wafer Layout and Detector Struc Main edgeless strip detectors - 50 µm edge distance Baby edgeless strip detectors - 1 x 1 cm 2-20µm, 50µm, 100µm edge distance Trench filling with Medipix polysilicon edgeless pixel detectors: ü spin coating with standard photoresist is challenging due to trench - 1.4 x 1.4 cm 2 Remove devices from - support 20 µm & 50 wafers µm edge (after distance bumping in case of pixel sensors) 50µm, 10 Edge implan 12
Active Edge Detector 13
Active Edge Detector 14
Active Edge Detector 15
Active Edge Detector 16
ALICE Pixel with Active Edge Ø Recall ALICE Epi-Pixel detector Planar pixel sensor on epitaxial high resistivity silicon wafer ü Remove the bulk by back-grinding after the bumping to achieve a 100 µm thick sensor Ø Combine with the capability to etch a trench to achieve an Active Edge Thin pixel detector Scribe Line Trench 17
ALICE Pixel with Active Edge trench Guard ring pixel Scribe line passivazione N+ ossido P+ P+ epi substrato Dead area 18
Front-end Chip Thinning Ø Current ALICE chips: 150 µm thinned during bump bonding process Ø Thickness reduction will make inherent stresses come out stronger Ø First experience during the ALICE production Ø Thinning process needs to be well studied and tuned to produce coherent results S. Vahanen, VTT 19
Front-end Chip Thinning R&D Ø Study using dummy components with IZM Berlin Hybrid detector dummy components, i.e sensors and chips, based on ALICE layout Specific IZM process for thinning: - Glass support wafer during full process - Laser release of the support wafer Sensor wafers (200 µm) in processing, ASIC wafers ready in 4 weeks First components back by end July 2011 Si sensor [μm] X0 [%] ASIC [μm] X0 [%] X 0 total [%] First R&D step 200 0.22 50 0.05 0.27 R&D target 100 0.11 50 0.05 0.16 20
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Polyimide MicroChannel cooling Wtot = 1.6 cm OUT IN q = 0.4 W/cm 2 Ltot = 20 cm Pyralux PC 1020 (polyimide) 200µm Pyralux LF7001 (Kapton ) 24µm Pyralux LF110 (Kapton ) 50µm 1 2 4 3 5 SENSOR READOUT CHIP SMD COMP 1 2 4 3 5 SENSOR READOUT CHIP SMD COMP CARBONFIBER SUPPORT COOLING TUBE 24
MicroChannel Simulation (Fluent 6.2) Ø Assuming ΔT max = 3 C Leakless (underpressure) system Top Layer T water in 15 C L = 20 cm W= 1.6 cm T water out 18 C T water in 15 C 16.65 C 20.62 C T water out 18 C 16 channels 800 x 200 µm 2 IN OUT Axonometric view of a single channel Inlet section Middle section Outlet section 25
MicroChannel Production Ø Main fabrication process steps (R. De Oliveira, CERN TM-MPE-EM) Sheet 50 µm of LF110 Lamination 200 µm photoimageable coverlay (4 layers of PC1020) Creation of the grooves (800 x 200 µm 2 ) by photolithography process @ 180 C Gluing by hot pressing the LF7001 24 µm lid cured @ 180 C for 10h Pyralux PC 1020 (polyimide) 200µm Pyralux LF7001 (Kapton ) 24µm Pyralux LF110 (Kapton ) 50µm 26
MicroChannel Material Budget Material Radiation length [cm] Kapton 28.6 H 2 O 36.1 % Xo 0.094 0.085 0.094 Single channel Cross section 0 100 900 1000 µm Ø Material budget of the ALICE Pixel cooling (Phynox tube + C4F10) O.8 % X 0 27
Richieste finanziarie Ø Richieste straordinarie 2011 ü Sviluppo di sensori sottili per rivelatori a pixel ibridi ü Produzione di un run di sensori a pixel epitassiali planari sottili di tipo active edge presso la ditta FBK nell ambito dell accordo MEMS2 con l INFN - 25 keur Cons. ü Sviluppo di microcanali in polietilene per il raffreddamento ü Sviluppo e realizzazione dei raccordi per la connessione del bus di microcanali al sistema di test, valvole pneumatiche e non, misuratori di pressione e temperature, modulo di lettura per PLC - 5 keur Cons. ü Acquisto di un flussimetro integrato con valvola di regolazione, pompa micro gear, microfiltro, scambiatore di calore - 4 keur Inv. 28
Richieste finanziarie Ø Richieste Preventivi 2012 ü ü ü ü Completamento R&D sensori sottili active edge con layout ottimizzato: Run FBK - 25 keur Cons. Test dei microcanali di geometria reale: Produzione componenti, componentistica ed allestimento laboratorio - 5 keur Cons., 4 keur Inv. Assemblaggio di rivelatori per test di laboratorio e su fascio e di moduli dummy - 5 keur Cons. Test beam al CERN: 2 settimane x 3 persone = 6 settimane + 6 viaggi XX keur ME 29