The microScint Project

Silicon Microfluidic Scintillation Detectors1 Physics Department, European Organization for Nuclear Research (CERN), Switzerland2 Microsystems Laboratory, Ecole Polytechnique Fdrale de Lausanne (EPFL), Switzerland3 Sezione di Roma 1, Istituto Nazionale di Fisica Nucleare (INFN), Italy10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20131P. Maoddi1,2, A. Mapelli1, P. Bagiacchi3, B. Gorini1, M. Haguenauer1, G. Lehmann Miotto1, R. Murillo Garcia1, F. Safai Tehrani3, L. Serex1, S. Veneziano3, P. Renaud21OutlineIntroductionMicrofluidic scintillation detectors: concept and previous workAdvantages and applications

Single layer devicesFabrication technologyExperiments

Double layer devicesFabrication technologyExperiments

Conclusions and outlook10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201322

Operating Principle10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20133

Microfluidic channel filled with liquid scintillator defining an array of waveguidesPhotodetector pixel coupled to each channel endScintillation light guided along microchannel and detectedFor fine spatial resolution:small channels (10 m 1 mm) microfluidicsPhotodetector arrayMicrochannelScintillation3First Prototype10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20134

DAQ systemA. Mapelli PhD thesis (2011)

Photo: J. Daguin20 mm15 mmFirst prototype ( first shown at IPRD08 )Microchannels made by SU-8 photolithographyGold reflective coating(200 m deep channel)MAPMT4Advantages And ApplicationsAdvantagesIncreased radiation resistance(liquid scintillator can be easily circulated in microchannels)Microfabrication technology allows to make very thin detectors

Potential applications individuatedTracking/calorimetry in high energy physicsBeam monitoring in hadron therapy10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20135

Thin microfluidic detectorParticle beamPatient under treatmentOnline Beam MonitoringHadron therapyCancer treatment using hadron beams

Microfluidic detectorsVery thin detectors can be made with microfabrication techniquesVery good radiation resistance expected10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20136

Real-time monitoring of the beamduring patient irradiationSafer treatmentOptimized beam time useTreatment cost reduction

Why Silicon?SU-8 photosensitive polymerEasy micropatterning (one-step photolithography)Good radiation resistance (comparable to Kapton)Main challenge: incompatible with high temperature processing(required for other materials in the device, e.g. metal bonding)

SiliconMany reliable microfabrication techniques availableBetter thermal and mechanical resistancePossibility of tight integration of microchannels withsemiconductor devices (photodetectors, electronics, )

All microfabrication activities performed at theEPFL Center for Micronanotechnology cleanroom10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20137Photo: V. FloraudDry Etching and SmoothingRF plasma reactor alternating SF6 (etching) and C4F8 (polymer coating) plasmasVertical etching profile but resulting in scallopingWet oxidation SiO2 has larger volume than Si surface features lossSiO2 removal with hydrofluoric acid smooth silicon10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20138

2 m

5 mDry Etching of MicrochannelsStarting substrate: silicon waferEtching of microchannels via DRIE process

10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201392. Deep Reactive Ion Etching(alternated etching and passivation steps)3. Smoothing by thick SiO2 growthand removal surfaces with suitable optical quality1. Patterning of silicon oxide asetching mask

200 mMicrochannels etched in silicon9Optical Coating and BondingDeposition of reflective aluminum layerWafer-level bonding of metallized glass top10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013105. Preparation of top cover(aluminum patterning on glass wafer)6. Anodic bonding4. Reflective coating by aluminumsputtering0.5 mm

0.5 mmBonded channels section

Pyrex 100 mTotal thickness~0.96 mmTwo devices superimposed and staggered10

20 mm

15 mmOptical and Fluidic Packaging10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013117. DicingChannel ends are cut open8. PackagingThin glass window and fluidicconnectors glued on chipFinished device

Microchannels cut open11Characterization with PMTs

10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201312PMTPMTQDC-Radioactivesource (90Sr )Scintillating fiber(trigger)Photoelectron spectrum fitted with:

SignalPedestalGaussians convoluted with Poisson distribution(PMT response)

Charge signalEvent count(180m deep channel)12Light YieldExpected light yield consistent with PMT measurements10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201313Average scintillation photons (~307)Light transport efficiency (~0.03)Interface optical efficiency (~0.9)PMT quantum efficiency (~0.25)Needs improvement!

Possible solution:low refractive indexdielectric cladding50 m13Beam Monitoring10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201314

Particle beam

xxEnergy distributionHigh flux of relatively high energy particles

High light output expected

No need for high sensitivity photodetectors

Hamamatsu S8866-128-02 photodiode arrayExperiments with Photodiodes10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201315Plastic supportMicrochannelsMicrochannels windowon photodiodesHamamatsu S8866-128-02photodiode array(connected to DAQ board)90Sr source(2.4 MBq)

-Readout system developed incollaboration with INFN Romex0.80.70.8(mm). . . 0.18Microchannel section Photodiode (pixel)

Pixel number(0 127)Integrated light signalLong integration time used (1 sec)Experiments with PhotodiodesProblem: flux from radioactive source too low for scintillation photons to sum-up in the photodiodesTest setup 90Sr source: ~104 e-/sec @ ~2 MeV/e-For comparison, proton therapy: ~1011 p+/sec @ ~100 MeV/p+

Conclusions:Test setup with 90Sr source not suitable for readout with photodiodesTest with actual beam envisioned to validate this kind of application10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20131616Double Layer Microchannels10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201317xyAdding an orthogonal microchannel layer XY position resolutionTechnological solution: patterning both sides of the silicon substrateX sideY sidePatent filed in 2012, PCT/EP201200198017Wet Etching of XY Microchannels10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201318Starting substrate: silicon waferEtching of microchannels on both sidesat the same time2. Etching of both sides of the wafer3. Reflective coating by aluminumSputtering on both sides1. Patterning of etching mask on bothsides of the wafer18Packaging of Double Layer ChipsOne-step bonding of 3 wafers stackDry etching for inter-layer connection10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201319

4. Bonding of 3 wafers stack byaluminum thermocompressionSiSiAlBonding interfaceFluid inlet5. Channel cutting and gluing of two glass windows and fluidic connectors as before200 nmTop layerBottom layer80 m inter-layer SiSilicon or pyrex cover wafers19Experiments with XY devices10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201320

-Trigger PMTTrigger fiberY PMTX PMTRadioactivesource (90Sr )

X layer (150 m)

Y layer (150 m)Data acquisition from both layers at the same time(Glass windows and tubing not shown)(preliminary)(preliminary)20Conclusions and OutlookConclusionsDifferent processes for microchannel patterning on silicon developedSingle and double layer devices demonstrated with PMT readoutIssues on tests with photodiode array readout

PerspectivesBeam tests with photodiode readoutIntegration of on-chip a-Si:H photodiodes Readout system based on SiPMs10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201321Other Technologies

10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201322

110 m total thickness(30 + 50 + 30)200 m 20 x 20 mm... aside from silicon, research on polymeric microchannels also ongoing!~0.03% X0Thank You 10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201323StaggeringStaggered channels for improved geometrical coverage10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201324

Pyrex grindedto 100 m(focal plane in the middle)Total thickness~0.96 mm100 m staggeringMaterial BudgetX0 (mm)Single layer thickness (mm)Double layer thickness (mm)Silicon940.2 (0.21% X0)0.58 (0.62% X0)Pyrex1260.5 (0.4% X0)0.5 (0.21% X0)EJ-305~5000.18 (0.04% X0)0.3 (0.06% X0)Aluminum890.0002 (negligible)0.0004 (negligible)Total0.65% to 0.8% X00.89% to 1.2% X010.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 201325

0.5 mmExcess material can be ground down to 100 50 m Single layer: 0.12% to 0.28% X0Double layer: 0.24% to 0.5% X0maxminFluidic OperationDetector area(mm2)Depth(mm)Width(mm)N channelsInternal volume(L)Hydraulic Resistance (bar s L-1)Refill time @ P = 1 bar12.8 x 12.80.180.71625.80.0042~ 100 ms12.8 x 12.80.180.16414.70.5~ 7 s204.8 x 204.80.180.725664501.1~ 2h10.10.2013 // pietro.maoddi@cern.ch13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 20132624h operation at P = 1 bar:less than 80 mL of scintillator neededChannel sectionwidthdepth