1. S ILICON M ICROFLUIDIC S CINTILLATION D ETECTORS 1 Physics Department, European Organization for Nuclear Research (CERN), Switzerland 2 Microsystems Laboratory, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland 3 Sezione di Roma 1, Istituto Nazionale di Fisica Nucleare (INFN), Italy 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 1 P. Maoddi 1,2, A. Mapelli 1, P. Bagiacchi 3, B. Gorini 1, M. Haguenauer 1, G. Lehmann Miotto 1, R. Murillo Garcia 1, F. Safai Tehrani 3, L. Serex 1, S. Veneziano 3, P. Renaud 2

2. O UTLINE Introduction Microfluidic scintillation detectors: concept and previous work Advantages and applications Single layer devices Fabrication technology Experiments Double layer devices Fabrication technology Experiments Conclusions and outlook 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 2

3. O PERATING P RINCIPLE 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 3 Microfluidic channel filled with liquid scintillator defining an array of waveguides Photodetector pixel coupled to each channel end Scintillation light guided along microchannel and detected For fine spatial resolution: small channels (10 µm – 1 mm)  microfluidics Photodetector array Microchannel Scintillation

4. F IRST P ROTOTYPE 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 4 DAQ system A. Mapelli PhD thesis (2011) Photo: J. Daguin 20 mm 15 mm First prototype ( first shown at IPRD08 ) Microchannels made by SU-8 photolithography Gold reflective coating (200 µm deep channel) MAPMT

5. A DVANTAGES A ND A PPLICATIONS Advantages Increased radiation resistance (liquid scintillator can be easily circulated in microchannels) Microfabrication technology allows to make very thin detectors Potential applications individuated Tracking/calorimetry in high energy physics Beam monitoring in hadron therapy 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 5

6. Thin microfluidic detector Particle beam Patient under treatment O NLINE B EAM M ONITORING Hadron therapy Cancer treatment using hadron beams Microfluidic detectors Very thin detectors can be made with microfabrication techniques Very good radiation resistance expected 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 6 Real-time monitoring of the beam during patient irradiation Safer treatment Optimized beam time use Treatment cost reduction

7. W HY S ILICON ? SU-8 photosensitive polymer Easy 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) Silicon Many reliable microfabrication techniques available Better thermal and mechanical resistance Possibility of tight integration of microchannels with semiconductor devices (photodetectors, electronics, …) All microfabrication activities performed at the EPFL Center for Micronanotechnology cleanroom 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 7 Photo: V. Floraud

8. D RY E TCHING AND S MOOTHING RF plasma reactor alternating SF 6 (etching) and C 4 F 8 (polymer coating) plasmas Vertical etching profile but resulting in «scalloping» Wet oxidation  SiO 2 has larger volume than Si  surface features loss SiO 2 removal with hydrofluoric acid  smooth silicon 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 8 2 µm 5 µm

9. D RY E TCHING OF M ICROCHANNELS Starting substrate: silicon wafer Etching of microchannels via DRIE process 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 9 2. Deep Reactive Ion Etching (alternated etching and passivation steps) 3. Smoothing by thick SiO 2 growth and removal  surfaces with suitable optical quality 1. Patterning of silicon oxide as etching mask 200 µm Microchannels etched in silicon

10. O PTICAL C OATING AND B ONDING Deposition of reflective aluminum layer Wafer-level bonding of metallized glass top 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 10 5. Preparation of top cover (aluminum patterning on glass wafer) 6. Anodic bonding 4. Reflective coating by aluminum sputtering 0.5 mm Bonded channels section Pyrex 100 µm Total thickness ~0.96 mm Two devices superimposed and staggered

11. 20 mm 15 mm O PTICAL AND F LUIDIC P ACKAGING 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 11 7. Dicing Channel ends are cut open 8. «Packaging» Thin glass window and fluidic connectors glued on chip Finished device Microchannels cut open

12. C HARACTERIZATION WITH PMT S 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 12 PMT QD C β-β- Radioactive source ( 90 Sr ) Scintillating fiber (trigger) Photoelectron spectrum fitted with: Signal Pedestal Gaussians convoluted with Poisson distribution (PMT response) Charge signal Event count (180µm deep channel)

13. L IGHT Y IELD Expected light yield consistent with PMT measurements 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 13 Average scintillation photons (~307) Light transport efficiency (~0.03) Interface optical efficiency (~0.9) PMT quantum efficiency (~0.25) Needs improvement! Possible solution: low refractive index dielectric cladding 50 µm

14. B EAM M ONITORING 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 14 Particle beam x x Energy distribution High flux of relatively high energy particles High light output expected No need for high sensitivity photodetectors Hamamatsu S8866-128-02 photodiode array

15. E XPERIMENTS WITH P HOTODIODES 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 15 Plastic support Microchannels Microchannels window on photodiodes Hamamatsu S8866-128-02 photodiode array (connected to DAQ board) 90 Sr source (2.4 MBq) β-β- Readout system developed in collaboration with INFN Rome x 0.8 0.7 0.8 (mm)... 0.18 Microchannel section Photodiode (pixel) Pixel number (0 … 127) Integrated light signal Long integration time used (1 sec)

16. E XPERIMENTS WITH P HOTODIODES Problem: flux from radioactive source too low for scintillation photons to «sum-up» in the photodiodes Test setup 90 Sr source: ~10 4 e - /sec @ ~2 MeV/e - For comparison, proton therapy: ~10 11 p + /sec @ ~100 MeV/p + Conclusions: Test setup with 90 Sr source not suitable for readout with photodiodes Test with actual beam envisioned to validate this kind of application 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 16

17. D OUBLE L AYER M ICROCHANNELS 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 17 x y Adding an orthogonal microchannel layer  XY position resolution Technological solution: patterning both sides of the silicon substrate X side Y side Patent filed in 2012, PCT/EP2012001980

18. W ET E TCHING OF XY M ICROCHANNELS 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 18 Starting substrate: silicon wafer Etching of microchannels on both sides at the same time 2. Etching of both sides of the wafer 3. Reflective coating by aluminum Sputtering on both sides 1. Patterning of etching mask on both sides of the wafer

19. P ACKAGING OF D OUBLE L AYER C HIPS One-step bonding of 3 wafers stack Dry etching for inter-layer connection 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 19 4. Bonding of 3 wafers stack by aluminum thermocompression Si Al Bonding interface Fluid inlet 5. Channel cutting and gluing of two glass windows and fluidic connectors as before 200 nm Top layer Bottom layer 80 µm inter-layer Si Silicon or pyrex cover wafers

20. E XPERIMENTS WITH XY DEVICES 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 20 β-β- Trigger PMT Trigger fiber Y PMT X PMT Radioactive source ( 90 Sr ) X layer (150 µm) Y layer (150 µm) Data acquisition from both layers at the same time (Glass windows and tubing not shown) (preliminary)

21. C ONCLUSIONS AND O UTLOOK Conclusions Different processes for microchannel patterning on silicon developed Single and double layer devices demonstrated with PMT readout Issues on tests with photodiode array readout Perspectives Beam tests with photodiode readout Integration of on-chip a-Si:H photodiodes Readout system based on SiPMs 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 21

22. O THER T ECHNOLOGIES 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 22 110 µm total thickness (30 + 50 + 30) 200 µm 20 x 20 mm... aside from silicon, research on polymeric microchannels also ongoing! ~0.03% X 0

23. T HANK Y OU 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 23

24. S TAGGERING Staggered channels for improved geometrical coverage 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 24 Pyrex grinded to 100 µm (focal plane in the middle) Total thickness ~0.96 mm 100 µm staggering

25. M ATERIAL B UDGET X 0 (mm) Single layer thickness (mm) Double layer thickness (mm) Silicon940.2 (0.21% X 0 )0.58 (0.62% X 0 ) Pyrex1260.5 (0.4% X 0 )0.5 (0.21% X 0 ) EJ-305~5000.18 (0.04% X 0 )0.3 (0.06% X 0 ) Aluminum890.0002 (negligible)0.0004 (negligible) Total0.65% to 0.8% X 0 0.89% to 1.2% X 0 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 25 0.5 mm Excess material can be ground down to 100 – 50 µm Single layer: 0.12% to 0.28% X 0 Double layer: 0.24% to 0.5% X 0 max min

26. F LUIDIC O PERATION Detector area (mm 2 ) Depth (mm) Width (mm)N channels Internal volume (µL) Hydraulic Resistance (bar s µL -1 ) Refill time @ ΔP = 1 bar 12.8 x 12.80.180.71625.80.0042~ 100 ms 12.8 x 12.80.180.16414.70.5~ 7 s 204.8 x 204.8 0.180.725664501.1~ 2h 10.10.2013 // pietro.maoddi@cern.ch 13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013 26 24h operation at ΔP = 1 bar: less than 80 mL of scintillator needed Channel section width depth