X-ray area detectors for synchrotron experiments Characteristics and Technologies

Transcription

1 X-ray area detectors for synchrotron experiments Characteristics and Technologies Cyril Ponchut ESRF Instrumentation Services and Development Division ESI school May 2011 X-ray area detectors for SR 1

2 Outline Introduction 2D detector parameters 2D detector principles 2D detector technologies Eiroforum school on Instrumentation May

3 Introduction The beamline user problem X-ray area detector on a SR beamline Eiroforum school on Instrumentation May

4 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 May

5 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 May

6 Detector parameters and characterization 2D detector parameters 2D detector model Gain Noise Dynamic range Eiroforum school on Instrumentation May

7 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 May

8 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 May

9 Noise Detector parameters and characterization Image noise : N o = Var( I( i, j)) ( i, j) ROI ADU/pixel r.m.s. Noise components : N = N Q + N R + N P + quantum readout proportional stochastic spatial 2 D DSNU N r.m.s. image noise quantum readout proportional DSNU total incoming photons (Poisson) electronics inhomogeneities (fixed pattern noise) dark pattern X-ray photons/pixel Eiroforum school on Instrumentation May

10 Dynamic range DR = S S 0 max 0 min DR bits = log 2 DR DR = = 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 May

11 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 May

12 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 May

13 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 Eiroforum school on Instrumentation May

14 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 May

15 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 May

16 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 May

17 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 May

18 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 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 May

19 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 May

20 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 May

21 2D X-ray detection principles Indirect conversion X-ray converters Optical coupling Direct conversion Eiroforum school on Instrumentation May

22 Indirect conversion X-ray 2D detection principles Impinging X-ray photon X-ray to light converter optical coupling image sensor Eiroforum school on Instrumentation May

23 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 = µm scintillator layer transparent substrate microscope objective α e=1 25 µm LuAG, YAG:Ce, LAG:Ce, NA=n.sin α spatial resolution = µm Martin, Koch, JSR (2006) Eiroforum school on Instrumentation May

24 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 kev Absorption efficiency / spatial resolution trade off Eiroforum school on Instrumentation May

25 Decay times 2D X-ray detection principles Afterglow depend on exposure time GGG: Eu 14 bit 80ms bit are resolved Bit depth 1 Relative amplitude s 10s 12 bit 14 bit 16 bit Data from Thierry Martin (ESRF) ms Time (ms) speed / dynamic range trade off Eiroforum school on Instrumentation May

26 Decay times Phosphors with peak emission in the nm range : 60 efficiency (ph/kev) P46 P43 P 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 May

27 Optical coupling 2D X-ray detection principles Lens Fiberoptic taper Direct coupling Eiroforum school on Instrumentation May

28 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 N (1 1/ G G = 1:1 and N = F/2 : η opt = 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 May

29 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 May

30 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 May

31 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) MPX CCD (b) IEEE TNS 52 (2005) Distance to slit centre (mm) Eiroforum school on Instrumentation May

32 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 May

33 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 May

34 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 May

35 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 May

36 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 fps Shutter type TrueSNAP Data Rate 660 Mp/s Master Clock 66 MHz Data Format 10-bit digital Eiroforum school on Instrumentation May

37 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 May

38 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 µm Converter YAG 280 µm Gain 2.4 ADU/keV LSF FWHM µm Frame rate ~10 Hz Design : ESRF manual zoom setting folding mirror screen holder with motorized focusing Eiroforum school on Instrumentation May

39 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 Phosphor screen Eiroforum school on Instrumentation May

40 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 May

41 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 10 kev LSF FWHM 124 µm Frame rate 0.26 Hz (1 s exposure) Eiroforum school on Instrumentation May

42 Large mosaic CCD : image corrections 2D X-ray detector technologies Correction - Spatial distortion - flatfield raw image Eiroforum school on Instrumentation May

43 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 Llopart et al. IEEE TNS 49 ( 2002 ) 2279 Each pixel is a photon counter Eiroforum school on Instrumentation May

44 2D X-ray detector technologies 2D photon-counting : charge sharing relative counts pixel 170 µm pixel 55 µm q Energy (kev) Eiroforum school on Instrumentation May

45 MAXIPIX 256x256 Detection areas 512x512 pixel x256 Pixel size 55 µm 2 X-ray converter Si 500 µm Counter depth 13.5 bits Frame rate Hz Readout dead time 0.29 ms 2D X-ray detector technologies Fast readout photon-counting detector ESRF development Based on MEDIPIX2 chip Eiroforum school on Instrumentation May

46 Other photon-counting pixel detectors PILATUS (DECTRIS) Detection areas 487x195 to pixel x2527 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 Hz ms Delpierre et al. NIMA 572 (2007) 250 Eiroforum school on Instrumentation May

47 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 May

48 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 energy threshold (kev) NIMA 510 (2003) 29 Eiroforum school on Instrumentation May

49 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 ADU/pixel r.m.s Gain kev DQE 37 kev LSF FWHM 210 µm Frame rate Hz Energy range kev Eiroforum school on Instrumentation May

50 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 17.4 kev LSF FWHM ~130 µm Frame rate 0.3 Hz (1 s exposure) Eiroforum school on Instrumentation May

51 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 May

52 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 May

53 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 May