DEVELOPMENT OF MICROFLUIDIC SCINTILLATION DETECTOR PMMA MICROCHANNELS FABRICATION

Outline  Introduction and Objectives  Development pathways  Working schedule Luca Müller PH-DT

INTRODUCTION and OBJECTIVES Luca Müller PH-DT

Scintillation Detectors  Instruments used for detecting and measuring ionizing radiation  Main applications:  High Energy Physics experiments:  Tracking, calorimetry, triggering and time-of-flight measurements  Medical applications:  Imagining  Hadron therapy  Industrial application:  Homeland security  Physical measurements Luca Müller PH-DT Hadron therapy in children, an update of the scientific evidence for 15 paediatric cancers, R. Leroy et Al, 2015 KCE report 235, Health Technology Assessment. 4

Scintillators  The type of radiation detected and detector properties depend of the scintillator material:  Inorganic crystals: scintillation due to the band structure of the crystal lattice.  Organic: crystal, plastic and liquid. Scintillation due to molecule’s free electrons excitation. Luca Müller PH-DT A.Mapelli.ScintillationParticleDetectorsBasedonPlasticOpticalFibresandMicroflu- idics. PhD thesis, École Polytechnique Fédérale De Lausanne,

Scintillation Detectors: working principle Luca Müller PH-DT Electric pulses Scintillator Photocathode Photomultiplier tube Anode Impinging particle/radiation Photons Dynodes 6

Microfluidic scintillation detector (microscint)  SU-8 photoresist support  EJ-305 Liquid scintillator  Metallic coating of microchannels  Orthogonal array of microchannels for x-y high spacial resolution Luca Müller PH-DT P. Maoddi. Microfluidic Scintillation Detectors for High Energy Physics. PhD thesis, École Polytechnique Fédérale De Lausanne, 2015 A.Mapelli.ScintillationParticleDetectorsBasedonPlasticOpticalFibresandMicroflu- idics. PhD thesis, École Polytechnique Fédérale De Lausanne, Comparison with the other scint. detectors Advantages: -Thin detector, -High spacial resolution, -Good radiation resistance -Good reproducibility Drawback: -Microfabrication limits the size of detector. -The size can limit the signal intensity Main drawback of this microfluidic scintillator: -Al coating for multiple reflection gives a short attenuation length: ~ 20mm 7

Total Internal Reflection Luca Müller PH-DT n1n1 n2n2 θ1θ1 θ2θ2 θcθc 8

New microscint: PMMA microchannels Luca Müller PH-DT  PMMA as new support material due to its properties:  Good compatibility with the scintillator  Good radiation resistance  92% of transparency, n= at 425nm  Process flow developed by J. Bronuzzi and P.Maoddi: J. Bronuzzi. Microfluidic Scintillation Detectors for High Energy Physics. PdM thesis, École Polytechnique Fédérale De Lausanne, 2015 P. Maoddi. Microfluidic Scintillation Detectors for High Energy Physics. PhD thesis, École Polytechnique Fédérale De Lausanne, 2015 Solution preparation (MMA) Pouring on mold and polymerization Molded PMMA Pressure and heat Two main issues: 1)Demoulding: Sample clamping and mould fracture 2)Bonding: parameters not well defined Dicing Bonding and Sealing 9

Objectives  To reproduce Bronuzzi’s process flow  To solve the demoulding issues  To define bonding and sealing parameters Luca Müller PH-DT

DEVOLPMENT PATHWAYS Luca Müller PH-DT

Thermal process of demoulding Luca Müller PH-DT Cu Si PMMA Cold source  25°C:  Cu /K  PMMA /K  Si /K  Thermal 25°C:  Cu 400 W/mK  PMMA 0.23 W/mK  Si W/mK  Playing with cooling time, it might be possible to decrease Cu channels size and hence extract the PMMA plate. 12

Thermal process of demoulding Luca Müller PH-DT  Approximated FEA of thermal behavior of the system:  Investigation on ΔT: 20, 40, 60, 80.  Due to the high conductivity of Cu the mould channels size decreases of ~100 nm more than PMMA in the first 5ms.  Thermal internal stresses not simulated yet. 13

Thermal process of demoulding Luca Müller PH-DT  First experimental setup Cu Si PMMA Cold source Suction cups Tensile load 14

Moulding under pressure Luca Müller PH-DT J. Bronuzzi. Microfluidic Scintillation Detectors for High Energy Physics. PdM thesis, École Polytechnique Fédérale De Lausanne, 2015  In situ polymerization under pressure:  Pressure between: MPa  The main idea is to counterbalance the effect of shrinkage  Problem: not enough data on our PMMA’s shrinkage 15

Plasma etching with O 2 Reactive Ion Etching (RIE)  Reusable Si mask  PMMA etch rate around 1μm/min  No reported transparency loss  Surface Roughness R rms below 10nm  Thermal bonding can be plasma assisted Luca Müller PH-DT Si PR Quartz PMMA Photolithography Deep RIE SF 6 / C 4 F 8 Deep RIE O 2 / O 2 -CF 4 Jinan Chai et al Langmuir 2004, 20, ; J.H. Park et al. Thin Solid Films 518 (2010) 6465–6468; Hirofumi Nabesawa et al. Sensors and Actuators B 132 (2008) 637–643; Zhiyong Wu et al. Electrophoresis 2002, 23, 782–790 16

Working schedule Luca Müller PH-DT

Working schedule (1) Luca Müller PH-DT J. Bronuzzi. Microfluidic Scintillation Detectors for High Energy Physics. PdM thesis, École Polytechnique Fédérale De Lausanne, 2015  To reproduce the Bronuzzi process flow of polymerization.  To make polymerization shrinkage measurements on 15 samples.  To create 5 samples of PMMA plates for optical properties characterization:  Transmittance and absorbance at 425 nm of wavelength radiation  Refractive index measurement:  Refractometer  Calculations from transmittance and absorbance  Physical characterization:  Surface roughness  Viscosity during polymerization 18

Working schedule (2) Luca Müller PH-DT J. Bronuzzi. Microfluidic Scintillation Detectors for High Energy Physics. PdM thesis, École Polytechnique Fédérale De Lausanne, 2015  To reproduce the Bronuzzi process flow of moulding.  To develop on 5 samples the thermal demoulding  To define bonding parameters  To characterize moulded samples optically and physically.  Parallel work:  To apply pressure during moulding, definition of moulding parameters.  To characterize moulded samples optically and physically.  To develop the RIE of the PMMA plates 19

Discussion time Luca Müller PH-DT