silicon microfluidic scintillation detectors
DESCRIPTION
Silicon Microfluidic Scintillation Detectors. 1 Physics Department , European Organization for Nuclear Research (CERN), Switzerland 2 Microsystems Laboratory , Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland - PowerPoint PPT PresentationTRANSCRIPT
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
1
SILICON MICROFLUIDIC SCINTILLATION
DETECTORS
1 Physics Department, European Organization for Nuclear Research (CERN), Switzerland2 Microsystems Laboratory, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
3 Sezione di Roma 1, Istituto Nazionale di Fisica Nucleare (INFN), Italy
10.10.2013 // [email protected]
P. Maoddi1,2, A. Mapelli1, P. Bagiacchi3, B. Gorini1, M. Haguenauer1, G. Lehmann Miotto1, R. Murillo Garcia1, F. Safai Tehrani3, L. Serex1, S.
Veneziano3, P. Renaud2
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
2
OUTLINE
• 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 // [email protected]
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
3
OPERATING PRINCIPLE
10.10.2013 // [email protected]
• 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)
microfluidicsPhotodetector array
Microchannel
Scintillation
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
4
FIRST PROTOTYPE
10.10.2013 // [email protected]
DAQ syste
m
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
𝑁 𝑝𝑒=1.6(200 µm deep channel)
MAPMT
~8 mm-1
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
5
ADVANTAGES AND APPLICATIONS
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 // [email protected]
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
6
Thin microfluidic detector
Particle beam
Patient under treatment
ONLINE BEAM MONITORING• 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 // [email protected]
Real-time monitoring of the beamduring patient irradiation
• Safer treatment• Optimized beam time use• Treatment cost reduction
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
7
WHY SILICON?
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 withsemiconductor devices (photodetectors, electronics, …)
All microfabrication activities performed at theEPFL Center for Micronanotechnology cleanroom
10.10.2013 // [email protected]
Photo: V. Floraud
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
8
DRY ETCHING AND SMOOTHING
• RF plasma reactor alternating SF6 (etching) and C4F8 (polymer coating) plasmas
• Vertical etching profile but resulting in «scalloping»
• Wet oxidation SiO2 has larger volume than Si surface features loss
• SiO2 removal with hydrofluoric acid smooth silicon
10.10.2013 // [email protected]
2 µm 5 µm
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
9
DRY ETCHING OF MICROCHANNELS
• Starting substrate: silicon wafer• Etching of microchannels via DRIE process
10.10.2013 // [email protected]
2. Deep Reactive Ion Etching(alternated etching and passivation steps)
3. Smoothing by thick SiO2 growthand removal surfaces with suitable optical quality
1. Patterning of silicon oxide asetching mask 200 µm
Microchannels etched in silicon
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
10
OPTICAL COATING AND BONDING
• Deposition of reflective aluminum layer• Wafer-level bonding of metallized glass top
10.10.2013 // [email protected]
5. Preparation of top cover(aluminum patterning on glass wafer)
6. Anodic bonding
4. Reflective coating by aluminumsputtering
0.5 mm
0.5 mm
Bonded channels section
Pyrex 100 µm
Total thickness~0.96 mm
Two devices superimposed and staggered
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
11
20 m
m15 mm
OPTICAL AND FLUIDIC PACKAGING
10.10.2013 // [email protected]
7. DicingChannel ends are cut open
8. «Packaging»Thin glass window and fluidicconnectors glued on chip
Finished device
Microchannels cut open
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
12
CHARACTERIZATION WITH PMTS
10.10.2013 // [email protected]
PMT
PMT
QDC
β-
Radioactivesource (90Sr )
Scintillating fiber(trigger)
Photoelectron spectrum fitted with:
𝑆=𝑃+𝒫∗𝒩Signal Pedestal Gaussians
convoluted with Poisson distribution(PMT response)
𝑁 𝑝𝑒=1.4
Charge signal
Event
count
(180µm deep channel)
~7.8 mm-1
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
13
LIGHT YIELD
• Expected light yield consistent with PMT measurements
10.10.2013 // [email protected]
2.07 (measured: 1.42)
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 indexdielectric cladding
50 µm
Effects of surface roughness and defects at the liquid/glue/glass interface (lowering ) not calculated!
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
14
BEAM MONITORING
10.10.2013 // [email protected]
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
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
15
EXPERIMENTS WITH PHOTODIODES
10.10.2013 // [email protected]
Plastic support
Microchannels
Microchannels windowon photodiodes
Hamamatsu S8866-128-02photodiode array(connected to DAQ board)
90Sr source(2.4 MBq)
β-
Readout system developed incollaboration with INFN Rome
x
0.8
0.7
0.8
(mm)
. . . 0.18
Microchannel section
Photodiode (pixel)
Pixel number(0 … 127)
Inte
gra
ted lig
ht
signal
Long integration time used (1 sec)
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
16
EXPERIMENTS WITH PHOTODIODES
Problem: flux from radioactive source too low for scintillation photons to «sum-up» in the photodiodes• Test 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
photodiodes• Test with actual beam envisioned to validate this kind of
application10.10.2013 // [email protected]
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
17
DOUBLE LAYER MICROCHANNELS
10.10.2013 // [email protected]
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
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
18
WET ETCHING OF XY MICROCHANNELS
10.10.2013 // [email protected]
• 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 aluminumSputtering on both sides
1. Patterning of etching mask on bothsides of the wafer
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
19
PACKAGING OF DOUBLE LAYER CHIPS
• One-step bonding of 3 wafers stack• Dry etching for inter-layer connection
10.10.2013 // [email protected]
4. Bonding of 3 wafers stack byaluminum thermocompression
Si
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
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
20
EXPERIMENTS WITH XY DEVICES
10.10.2013 // [email protected]
β-
Trigger PMT
Trigger fiber
Y PMT X PMT
Radioactivesource (90Sr )
X layer (150 µm)𝑁 𝑝𝑒=1.0
Y layer (150 µm)𝑁 𝑝𝑒=0.9
Data acquisition from both layers at the same time
(Glass windows and tubing not shown)
~6 mm-1
(preliminary)
(preliminary)
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
21
CONCLUSIONS AND OUTLOOK
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 // [email protected]
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
22
OTHER TECHNOLOGIES
10.10.2013 // [email protected]
110 µm total thickness(30 + 50 + 30)
200 µm
20 x 20 mm
... aside from silicon, research on polymeric microchannels also ongoing!
~0.03% X0
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
23
THANK YOU
10.10.2013 // [email protected]
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
24
STAGGERING
• Staggered channels for improved geometrical coverage
10.10.2013 // [email protected]
Pyrex grindedto 100 µm
(focal plane in the middle)Total thickness~0.96 mm
100 µm staggering
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
25
MATERIAL BUDGETX0
(mm)Single layer thickness (mm)
Double layer thickness (mm)
Silicon 94 0.2 (0.21% X0) 0.58 (0.62% X0)
Pyrex 126 0.5 (0.4% X0) 0.5 (0.21% X0)
EJ-305 ~500 0.18 (0.04% X0) 0.3 (0.06% X0)
Aluminum 89 0.0002 (negligible) 0.0004 (negligible)
Total 0.65% to 0.8% X0 0.89% to 1.2% X0
10.10.2013 // [email protected]
0.5 mm Excess material can be ground down to 100 – 50 µm Single layer: 0.12% to 0.28% X0
Double layer: 0.24% to 0.5% X0
maxmin
13th Topical Seminar on Innovative Particle and Radiation Detectors, Siena 2013
26
FLUIDIC OPERATION
Detector area
(mm2)Depth(mm)
Width(mm)
N channels
Internal volume
(µL)
Hydraulic Resistance (bar s
µL-1)
Refill time @ ΔP = 1
bar
12.8 x 12.8 0.18 0.7 16 25.8 0.0042 ~ 100 ms
12.8 x 12.8 0.18 0.1 64 14.7 0.5 ~ 7 s
204.8 x 204.8
0.18 0.7 256 6450 1.1 ~ 2h
10.10.2013 // [email protected]
24h operation at ΔP = 1 bar:less than 80 mL of scintillator neededChannel section
width
depth