VCI2010 Photonic Crystals: A Novel Approach to Enhance the Light Output of Scintillation Based Detectors 11/19/2015 Arno KNAPITSCH a, Etiennette AUFFRAY a, Paul LECOQ a a PH-CMX,CERN, Geneva, Switzerland

/ 26 VCI2010 Outline: – Introduction Scintillating Crystals Motivation Photonic Crystals – Simulations Monte Carlo A Frequency- Domain Eigenmode Solver Results – PhC Fabrication Sputter Deposition Electron Beam Lithography Reactive Ion Etching Results – Conclusion 11/19/20152

/ 26 VCI2010 Scintillating Crystals What is scintillation? – Emission of light due to an ionizing event What kind of scintillators are there? – Intrinsic (BWO, BGO) or extrinsic(LYSO:Ce, LuAG:Ce) scintillators – Organic, inorganic, liquid-, plastic, gaseous Common scintillators in HEP and medical imaging – LYSO:Ce(Lu 2-x Y x SiO 5 ), BGO(Bi 4 Ge 3 O 12 ), LuYAP:Ce(Lu x Y 1-x AlO 3 ), LuAG:Ce(Lu 3 Al 5 O 7 ) 11/19/20153 ionizing radiation Light emission Scintillating Crystal Cerium-doped Lutetium-Yttrium Aluminum Perovskite Cerium-doped Lutetium Yttrium Orthosilicate Bismuth germinateCerium-doped Lutetium Aluminum Garnet

/ 26 VCI2010 Motivation: Application Field of application of heavy inorganic scintillators – High energy physics (HEP), medical imaging (e.g. PET), spectroscopy 11/19/20154

/ 26 VCI2010 Motivation: Increase Nr. of detected Photons Main factors governing energy- and time resolution: Detected number of photoelectrons N pe 11/19/20155 Main limiting factor for the light collection efficiency : Total reflection due to a mismatch of the refractive index of crystal and detector Snell’s Law: Efficiency:

/ 26 VCI2010 Motivation: Photonic Crystal How can a photonic crystal help to overcome those limits ? Light extraction due to a periodic grating of the interface: 11/19/20156 incident light reflected light extracted modes

/ 26 VCI2010 Photonic Crystals (PhCs) Photonic crystal basics: Periodic arrangement of two materials with different index of refraction, in one-, two-, or three dimensions 11/19/ D2D3D [3] J. D. Joannopoulos, Photonic crystals – Molding the flow of light, 2008

/ 26 VCI2010 How does the Photonic Crystal Work? Diffracted modes interfere constructively in the PhC- grating and are therefore able to escape the Crystal 11/19/20158 Plain crystal- air interface: (EM – fieldplot [5] ) Crystal- air interface with PhC grating: Plane Wave θ>θcθ>θc Total Reflection at the interface since Extracted Mode (~60% Transmission) θ>θcθ>θc crystalaircrystalair (0% Transmission)

/ 26 VCI2010 Outline: – Introduction Scintillating Crystals Motivation Photonic Crystals – Simulations Monte Carlo A Frequency- Domain Eigenmode Solver Results – PhC Fabrication Sputter Deposition Electron Beam Lithography Reactive Ion Etching Results – Conclusion 11/19/20159

/ 26 VCI2010 Simulation: A two Step Approach 1.Look at the angular distribution at the crystal- detector interface with a Monte- Carlo simulation tool (LITRANI [5]) 2.Take the light distribution from the Monte-Carlo program and simulate the light extraction of a scintillator- PhC- air interface with an eigenmode expansion software (CAMFR [4]) 11/19/ θcθc

/ 26 VCI2010 Optimize the PhC Design PhC crystal parameters: – Lattice constant: a – Hole diameter: D – Hole depth: d Optimize the parameters for maximal light transmission over all angles: Parameters in case of LYSO: – a = 340nm – D = 200nm – d = 300nm 11/19/ x z y Scintillator ITO Si 3 N 4 a hole depth: d hole diameter: D

/ 26 VCI2010 Light Gain Light Gain when comparing to an unstructured Crystal: 11/19/ Crystal Type: LYSO Crystal measurements: 1.3x2.6x8mm Wrapping: Tyvek

/ 26 VCI2010 Results of different Crystals: CrystalLYSOLuYAPBGOLuAG Light gain Angular distribution of the extracted light 11/19/201513

/ 26 VCI2010 Outline: – Introduction Scintillating Crystals Motivation Photonic Crystals – Simulations Monte Carlo A Frequency- Domain Eigenmode Solver Results – PhC Fabrication Sputter Deposition Electron Beam Lithography Reactive Ion Etching Results – Conclusion 11/19/201514

/ 26 VCI2010 PhC Fabrication Nano Lithography PhC is produced in cooperation with the INL (Institut des Nanotechnologies de Lyon) Three step approach: 1.Deposition of a pattern transfer material 2.Patterning of the resist using a scanning electron Microscope 3.Pattern transfer using reactive ion etching (RIE) 11/19/ Reactive ion etching reactor Scanning electron Microscope

/ 26 VCI2010 Sputter Deposition Sputtering of two different Materials: 1.~70nm of ITO (Indium Tin Oxide) 2. ~300nm of Si 3 N 4 (Silicon Nitride) 11/19/ x z y Scintillator ITO 70nm x z y Scintillator ITO Si 3 N 4 70nm 300nm

/ 26 VCI2010 Electron Beam Patterning 1.Deposit of an resist material (PMMA) by spin coating 2.Writing the PhC pattern into the resist with a scanning electron microscope (SEM) 3.Removing the exposed areas on the resist with an chemical solvate 11/19/ x z y Scintillator ITO Si 3 N 4 PMMA x z y Scintillator ITO Si 3 N 4 PMMA Resist x z y Scintillator ITO Si 3 N 4 PMMA Resist Electron beam

/ 26 VCI2010 Reactive Ion Etching (RIE) 1.Chemically reactive plasma removes Si 3 N 4 not covered by the resist 2.Change the composition of the reactive plasma to remove the resist (PMMA) without etching the Si 3 N 4 11/19/ x z y Scintillator ITO Si 3 N 4 a Hole depth: 300nm hole diameter: 200nm x z y Scintillator ITO Si 3 N 4 Ion Bombardment PMMA Resist

/ 26 VCI2010 PhC Results Scanning Electron Images: 11/19/ a = 340nm D = 200nm

/ 26 VCI2010 Outline: – Introduction Scintillating Crystals Motivation Photonic Crystals – Simulations Monte Carlo A Frequency domain Eigenmode Solver Results – PhC Fabrication Sputter Deposition Electron Beam Lithography Reactive Ion Etching Results – Conclusion Outlook Acknowledgement 11/19/201520

/ 26 VCI2010 Conclusion – Simulations show an light yield enhancement between 80% and 120% 11/19/ % and 110%

/ 26 VCI2010 Conclusion 2. The PhC- production process has been adapted to the requirements of the crystal – Due to the ITO layer we have good electrical connectivity from the Si 3 N 4 to the surrounding – The RIE parameters were adapted to the required etching depth without having anisotropic effects on the pattern – Lattice parameters of the PhC could be verified 11/19/201522

/ 26 VCI2010 Outlook Optical Characterization of the PhC – Light Yield Measurements – Angular Distribution Compare the measurement- results to the simulations and classify possible deviations Use the knowledge obtained by the measurements to further optimize the PhC pattern of the next samples 11/19/201523

/ 26 VCI2010 Acknowledgments Many thanks to the staff of the INL – Lyon, especially to J.-L. Leclercq and C. Seassal for their support and advice during my stays in Lyon. 11/19/201524

/ 26 VCI /19/ References [1] [2] [3] J. D. Joannopoulos, Photonic crystals – Molding the flow of light, 2008 [4] Photonic crystal LEDs - designing light extraction, C. Wiesmann, 2009 [5] CAMFR, (CAvity Modelling FRamework), [6] LITRANI,