X-ray area detectors for synchrotron experiments Characteristics and Technologies Cyril Ponchut ESRF Instrumentation Services and Development Division ESI school 16-20 May 2011 X-ray area detectors for SR 1
Outline Introduction 2D detector parameters 2D detector principles 2D detector technologies Eiroforum school on Instrumentation - 16-20 May 2011 2
Introduction The beamline user problem X-ray area detector on a SR beamline Eiroforum school on Instrumentation - 16-20 May 2011 3
The beamline user problem Introduction What is the optimum detector for a given (range of ) experiment(s)?? Image : The ATLAS experiment at CERN Eiroforum school on Instrumentation - 16-20 May 2011 4
X-ray area detection on a SR beamline Introduction detector sample y S i (x,y,t,e) Φ o (t,e) X-ray beam x Eiroforum school on Instrumentation - 16-20 May 2011 5
Detector parameters and characterization 2D detector parameters 2D detector model Gain Noise Dynamic range Eiroforum school on Instrumentation - 16-20 May 2011 6
2D detectors parameters Detector parameters and characterization Gain Noise Dynamic range Linearity X-ray area detector = device that measures the intensity of an incident X-ray flux with a certain efficiency, as a function of position, time, energy. MTF Frame rate Energy resolution QE LSF Readout dead time Energy threshold DQE spatial distortions Decay time Eiroforum school on Instrumentation - 16-20 May 2011 7
Gain Detector parameters and characterization G = output input G = image level (ADU) per incident X-ray ADU : analog to digital units Measuring G : G = integrated pixel signal in the exposed region X-ray counts through pinhole measured with a counter G includes X-ray interaction probability => depends on energy Eiroforum school on Instrumentation - 16-20 May 2011 8
Noise Detector parameters and characterization Image noise : N o = Var( I( i, j)) ( i, j) ROI ADU/pixel r.m.s. Noise components : 2 2 2 2 N = N Q + N R + N P + quantum readout proportional stochastic spatial 2 D DSNU N r.m.s. image noise 1000 100 10 quantum readout proportional DSNU total incoming photons (Poisson) electronics inhomogeneities (fixed pattern noise) dark pattern 1 1 10 100 1000 10000 X-ray photons/pixel Eiroforum school on Instrumentation - 16-20 May 2011 9
Dynamic range DR = S S 0 max 0 min DR bits = log 2 DR DR = 10000 = 80 db = 13.2 bits Detector parameters and characterization Not to be confused with ADC range = log 2 I max energy integrating photon counting I Xmax I Xmax image level I d S 0max input X-ray flux S 0min image level 1 0 S 0max S 0min input X-ray flux I X I max d DR = N 0 ( S 0min N o = readout noise ) DR = I X max Eiroforum school on Instrumentation - 16-20 May 2011 10
Linearity Detector parameters and characterization Integral non-linearity max( G( Si ) < G > ) INL = < G > <G> Quick non-linearity test S i max S i Eiroforum school on Instrumentation - 16-20 May 2011 11
Quantum efficiency Detector parameters and characterization QE = X-ray interaction probability = characteristic of the X-ray conversion medium QE can be deduced from knowledge of detection material, but not measurable directly QE does not take into account signal degradation across the system Need for a general and measurable quantity for detection efficiency : DQE (Detective Quantum Efficiency) Eiroforum school on Instrumentation - 16-20 May 2011 12
Detective Quantum Efficiency (DQE) Detector parameters and characterization DQE = SNR out2 /SNR in2 = (S o2 / N o2 ) / (S i2 / N i2 ) (Gruner, 1978) Measuring the DQE : S o / S i = G N i2 = S i (Poisson statistics) DQE = G S N 0 2 0 Eiroforum school on Instrumentation - 16-20 May 2011 13
DQE approximated expression Detector parameters and characterization signal X-rays incident X-rays detected output signal S i variance (Poisson) S i Q S o = S i Qg Q g S i S i Q S i Qg 2 + n e- 2 (Poisson) DQE 1+ Q g 2 e 2 n QS i Input-equivalent noise N eq = n e- /gq : perfect detector (n e- = 0) => DQE = Q Q DQE 2 QN eq 1+ S i Eiroforum school on Instrumentation - 16-20 May 2011 14
Line-spread function (LSF) Detector parameters and characterization Measuring the LSF : Slit aperture << pixel size Tilted slit (Fujita, 1992) : oversampling 1/sinθ => Provides the presampling LSF For non-isotropic spatial response : PSF (point-spread function) IEEE TNS 52 (2005) Eiroforum school on Instrumentation - 16-20 May 2011 15
Contrast Transfer Function (CTF) Detector parameters and characterization CTF( ν ) = I I max max ( ν ) I ( ν ) + I Measuring the CTF : min min ( ν ) ( ν ) (square modulation) I max contrast modulation I min Eiroforum school on Instrumentation - 16-20 May 2011 16
Modulation Transfer Function (MTF) Detector parameters and characterization MTF I max min = (sine modulation) Not measurable directly I max I + I min Indirect measurement from LSF : MTF( ν ) 2 jπνx = LSF( x)exp dx Eiroforum school on Instrumentation - 16-20 May 2011 17
DQE in the Fourier domain Detector parameters and characterization Frequency-dependent DQE 1,0 DQE DQE( ν ) = G 2 So MTF ( ν ) N. NPS ( ν ) o DQE 0,5 Noise power spectrum NPS ( k, l) = FFT ( I( i, j)) angular averaging NPS( ν ) = π NPS(ν, θ)dθ 0 2 2 nps (Xph/pixel -1 ) 0,0 0,0 0,5 1,0 frequency (normalized) 0,5 nps 0,0 0,0 0,5 1,0 frequency (normalized) Eiroforum school on Instrumentation - 16-20 May 2011 18
Time resolution Detector parameters and characterization frame rate T cycle T decay F = 1/T cycle exposure T exp readout triggered acquisition experiment T cycle T readout exposure T exp T jitter Eiroforum school on Instrumentation - 16-20 May 2011 19
Detector parameters and characterization Summary : basic area detector specification list Detection field, pixel size, LSF Gain, noise, dynamic range Linearity DQE at a given energy Frame rate, readout dead time, minimum exposure time Energy range Eiroforum school on Instrumentation - 16-20 May 2011 20
2D X-ray detection principles Indirect conversion X-ray converters Optical coupling Direct conversion Eiroforum school on Instrumentation - 16-20 May 2011 21
Indirect conversion X-ray 2D detection principles Impinging X-ray photon X-ray to light converter optical coupling image sensor Eiroforum school on Instrumentation - 16-20 May 2011 22
X-ray to light converters 2D X-ray detection principles reflective layer phosphor powder + binder Gd 2 O 2 S:Tb (P43), YAG:Ce (P46), spatial resolution e e=5 100 µm spatial resolution < e growth substrate columnar CsI e = 100 500 µm scintillator layer transparent substrate microscope objective α e=1 25 µm LuAG, YAG:Ce, LAG:Ce, NA=n.sin α spatial resolution = 0.5 5 µm Martin, Koch, JSR (2006) Eiroforum school on Instrumentation - 16-20 May 2011 23
Absorption efficiencies X-ray 2D detection principles 1.E+00 CsI 100 µm GOS 40 µm YSO 10 µm absorption 1.E-01 1.E-02 YAG 10 µm Phosphor powder screens High-resolution single crystal film scintillators 1.E-03 0 50 100 150 kev Absorption efficiency / spatial resolution trade off Eiroforum school on Instrumentation - 16-20 May 2011 24
Decay times 2D X-ray detection principles Afterglow depend on exposure time GGG: Eu 14 bit dynamic @ 80ms 16-17 bit are resolved Bit depth 1 Relative amplitude 0.1 0.01 0.001 0.0001 1s 10s 12 bit 14 bit 16 bit Data from Thierry Martin (ESRF) 10-5 100ms 10-6 1 10 100 1000 10 4 Time (ms) speed / dynamic range trade off Eiroforum school on Instrumentation - 16-20 May 2011 25
Decay times Phosphors with peak emission in the 530-550 nm range : 60 efficiency (ph/kev) 40 20 P46 P43 P20 0 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 decay time at 1% (s) speed / sensitivity trade off Eiroforum school on Instrumentation - 16-20 May 2011 26
Optical coupling 2D X-ray detection principles Lens Fiberoptic taper Direct coupling Eiroforum school on Instrumentation - 16-20 May 2011 27
Optical coupling efficiency 2D X-ray detection principles Single lens p p G = p /p Improvable using tandem lenses : η opt N = f D = T NA 2 = + T + 2 1 4N (1 1/ G G = 1:1 and N = F/2 : η opt = 0.015 G = f /f ) 2 f f Magnification (G > 1 ) => coupling efficiency NA 2 ~1/N 2 Demagnification (G < 1 ) => coupling efficiency 1/N 2 G 2 Field width / sensitivity trade-off Eiroforum school on Instrumentation - 16-20 May 2011 28
Signal propagation in indirect detection 2D X-ray detection principles X-ray converter optical system image sensor charge signal signal processing image 10 kev 500 hν 5 hν 3 e- 1 ADU ~50 hν/kev QE ~ 65% ~0.01 hν/hν (demag.lens) S X-ray ~ n e- : single-photon discrimination (generally) not possible Eiroforum school on Instrumentation - 16-20 May 2011 29
Signal propagation in direct detection 2D X-ray detection principles perfect material (e.g. Si) : depleted semiconductor pixel sensor charge signal signal processing image 10 kev X-ray 2760 e- ε h+/e- = 3.62 ev Imperfect material ( Si ) incomplete depletion incomplete charge collection polarization S X-ray >> n e- : single photon detection possible reduced DQE reduced sensitivity image afterglow GaAs CdTe CdZnTe a-se HgI 2 PbI 2 Eiroforum school on Instrumentation - 16-20 May 2011 30
LSF : indirect vs direct detection 2D X-ray detection principles 2 different detectors with identical pixel sizes and X-ray absorptions : Lens-coupled CCD Direct detection in Si Intensity (ADU) 10 7 10 6 10 5 10 4 10 3 10 2 10 1 MPX CCD (b) IEEE TNS 52 (2005) 10 0-3 0 3 Distance to slit centre (mm) Eiroforum school on Instrumentation - 16-20 May 2011 31
Summary : indirect vs. direct detection 2D X-ray detection principles indirect wide range of spatial resolutions versatile low gain at large input fields direct sharp LSF high gain (=> photon counting) fixed spatial resolution dynamic range limitations Eiroforum school on Instrumentation - 16-20 May 2011 32
2D X-ray detector technologies Image sensors : CCD, CMOS Optically-coupled CCD detectors Photon-counting ASICS and detectors Flatpanels Image plates Gas filled multiwire proportional chambers Eiroforum school on Instrumentation - 16-20 May 2011 33
CCD image sensors 2D X-ray detector technologies MOS gate structure, 3-phase CCD +V 1 +V 2 +V 3 poly-si electrodes SiO 2 pixel wells p Si bulk Image credit : DALSA Full frame transfer vertical shift exposure during readout => SMEARING output node V=q/C horizontal shift output video signal Eiroforum school on Instrumentation - 16-20 May 2011 34
Electron-multiplication CCD 2D X-ray detector technologies Self-amplification in horizontal shift register High gain Excess noise at high gain Dark noise amplification Eiroforum school on Instrumentation - 16-20 May 2011 35
CMOS image sensor 2D X-ray detector technologies Example layout Example characteristics (MICRON): row addressing column ADC memory MUX active pixel matrix Active Array 1,280H x 1,024V Imaging Area 15.36mm(H) x 12.29mm(V) Pixel Size 12.0µm Dynamic Range 59dB Responsivity 1600 LSB/lux-sec Frame Rate 0-500+ fps Shutter type TrueSNAP Data Rate 660 Mp/s Master Clock 66 MHz Data Format 10-bit digital Eiroforum school on Instrumentation - 16-20 May 2011 36
CCD vs. CMOS in brief 2D X-ray detector technologies CCD CMOS High dynamic range Low readout noise readout time smearing (full frame) High frame rate Short exposures Readout noise Fixed pattern noise Eiroforum school on Instrumentation - 16-20 May 2011 37
Variable field CCD detector 2D X-ray detector technologies Application : high-energy imaging (ESRF ID15) camera Adjustable field size with zoom lens Field size 7-19 mm Pixel size 3.8-9.4µm Converter YAG 280 µm Gain 2.4 ADU/keV LSF FWHM 13-25 µm Frame rate ~10 Hz Design : ESRF manual zoom setting folding mirror screen holder with motorized focusing Eiroforum school on Instrumentation - 16-20 May 2011 38
CCD detector for EDXAS 2D X-ray detector technologies Field size 50x3 mm 2 Pixel size 25µm Noise 4 ADU/pixel rms Dynamic range 14 bits Frame rate 1 k Hz (kinetics mode) Based on ESRF FReLoN CCD camera RSI 78 (2007) CCD sensor Lens MCP (fast shutter) Lens Image : ESRF ID24 http://www.esrf.fr/usersandscience/experiments/xasms/id24/ Phosphor screen Eiroforum school on Instrumentation - 16-20 May 2011 39
High-resolution CCD detector 2D X-ray detector technologies Sensitive layer 1-25µm Substrate 170µm Submicron spatial resolution Design : ESRF (Thierry Martin) Eiroforum school on Instrumentation - 16-20 May 2011 40
Large mosaic CCD 2D X-ray detector technologies Field size 312 x 312 mm 2 Pixel size 52µm ADC range 16 bits Noise 4 ADU/pixel r.m.s Gain 2.1 ADU/10 kev X-ray DQE 0.6 @ 10 kev LSF FWHM 124 µm Frame rate 0.26 Hz (1 s exposure) Eiroforum school on Instrumentation - 16-20 May 2011 41
Large mosaic CCD : image corrections 2D X-ray detector technologies Correction - Spatial distortion - flatfield raw image Eiroforum school on Instrumentation - 16-20 May 2011 42
Hybrid photon-counting pixel detectors sensor bias 2D X-ray detector technologies SC sensor pixel ASIC chipboard PCB bump-bonding contacts wirebonds Example : Medipix2 CERN, the Medipix Collaboration http://medipix.web.cern.ch/medipix/ Llopart et al. IEEE TNS 49 ( 2002 ) 2279 Each pixel is a photon counter Eiroforum school on Instrumentation - 16-20 May 2011 43
2D X-ray detector technologies 2D photon-counting : charge sharing relative counts 1.5 1.0 0.5 pixel 170 µm pixel 55 µm q 0.0 5 10 15 20 25 30 Energy (kev) Eiroforum school on Instrumentation - 16-20 May 2011 44
MAXIPIX 256x256 Detection areas 512x512 pixel 2 1280x256 Pixel size 55 µm 2 X-ray converter Si 500 µm Counter depth 13.5 bits Frame rate 280-1400 Hz Readout dead time 0.29 ms 2D X-ray detector technologies Fast readout photon-counting detector ESRF development Based on MEDIPIX2 chip http://medipix.web.cern.ch/medipix/ Eiroforum school on Instrumentation - 16-20 May 2011 45
Other photon-counting pixel detectors PILATUS (DECTRIS) Detection areas 487x195 to pixel 2 2463x2527 Pixel size 172 µm 2 X-ray converter Si 300 µm Counter depth Frame rate Readout dead time XPAD2 (CNRS CPPM) Detection areas 120x75 mm 2 Pixel size 330 µm 2 X-ray converter Si 500 µm Counter depth Readout dead time 2D X-ray detector technologies 15 bits 2 ms 20 bits 12-200 Hz 2.7-3.6 ms Delpierre et al. NIMA 572 (2007) 250 Eiroforum school on Instrumentation - 16-20 May 2011 46
Example application : SAXS Photon-counting detector (Medipix2) Colloidal PMMA, 40% concentration, 8.33 kev 2D X-ray detector technologies data : F. Zontone (ESRF) Reduced exposure time Arbitrarily high dynamic range No profile distortion at low signal MPX2 : 1 s CCD : 100 x 1 s point detector scan : 5s/point IEEE TNS 52(5) (2005) 1760 Eiroforum school on Instrumentation - 16-20 May 2011 47
Fluorescence rejection 2D X-ray detector technologies Photon-counting detector (Medipix1) Cu foil sample, 20 kev beam threshold settings 1x10 4 ROI 1 (backgd.+ring) ROI 2 (backgd.) counts/kev 5x10 3 fluorescence background elastic scatter 0 5 10 15 20 25 30 energy threshold (kev) NIMA 510 (2003) 29 Eiroforum school on Instrumentation - 16-20 May 2011 48
Flatpanel + scintillator Main application : high energy diffraction 2D X-ray detector technologies Images : Trixell PIXIUM (Thales) Field size 407 x 296 mm 2 Pixel size 154µm Noise 0.2-2.6 ADU/pixel r.m.s Gain 0.2-1 ADU/X-ray @ 37 kev DQE 0.85 @ 37 kev LSF FWHM 210 µm Frame rate 7.5-30 Hz Energy range 30-100 kev Eiroforum school on Instrumentation - 16-20 May 2011 49
Flatpanel + semiconductor 2D X-ray detector technologies Main application : diffraction Field size 358 x 430 mm 2 Pixel size 139 µm 2 X-ray converter a-se ADC range 16 (20) bits Noise 2.8 ADU/pixel r.m.s Gain 0.6 ADU/17.4 kev DQE 0.6 @ 17.4 kev LSF FWHM ~130 µm Frame rate 0.3 Hz (1 s exposure) Eiroforum school on Instrumentation - 16-20 May 2011 50
Flatpanel + semiconductor 2D X-ray detector technologies a-se flatpanel pixel size 139 µm CCD fiberoptic pixel size 100 µm Pixel-limited spatial resolution Large uniform detection area Image afterglow Eiroforum school on Instrumentation - 16-20 May 2011 51
Image plate scanner 2D X-ray detector technologies Photostimulable luminescent screen Image : NONIUS Von Seggern et al., J. Appl. Phys. 64(3) (1988) 1405 Field size 345 mm diametre Pixel size 100µm X-ray converter BaFBr:Eu 2+ ADC range 17 bits Noise 1 ADU/pixel r.m.s Gain 1 ADU/8 kev X-ray Readout time 108s Eiroforum school on Instrumentation - 16-20 May 2011 52
Conclusion Detector parameters and characterization This lecture only pretends to be : An obviously incomplete overview of 2D X-ray detectors for synchrotrons experiments A guide to help asking oneself the right questions when having to choose or design a 2D X-ray detector A incentive to learn more about modern 2D X-ray detection technologies Thank you for your attention Eiroforum school on Instrumentation - 16-20 May 2011 53