Marten Bosma 1, Alex Fauler 2, Michael Fiederle 2 en Jan Visser Nikhef, Amsterdam, The Netherlands 2. FMF, Freiburg, Germany

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1 Marten Bosma 1, Alex Fauler 2, Michael Fiederle 2 en Jan Visser 1 1. Nikhef, Amsterdam, The Netherlands 2. FMF, Freiburg, Germany

electrode But: Gray-scale images Only one storage capacitor and TFT per pixel Amorphous

2 Digital Screen film Digital radiography advantages: Larger dynamic range Immediate image preview; real-time imaging Image enhancement processing Overall cost reduction X rays Bias electrode But: Gray-scale images Only one storage capacitor and TFT per pixel Amorphous selenium Storage capacitor TFT Pixel electrode M.J. Bosma at FOM, Veldhoven January 18,

X ray photon Back contact Semiconductor sensor Hybrid

pixel pitch Excellent contrast transfer: Solder bump o

Medipix readout chip 3 Medipix3 features 1080 transistors

and read-out; no dead time Colour mode: seven energy bands

3 X ray photon Back contact Semiconductor sensor Hybrid pixel detector Sensor pixel High granularity: (55 um)2 pixel pitch Excellent contrast transfer: Solder bump o Large dynamic range Pixel readout pad o Noise suppression Medipix readout chip 3 Medipix3 features 1080 transistors / pixel: Charge summing circuitry Simultaneous counting and read-out; no dead time Colour mode: seven energy bands can be resolved M.J. Bosma at FOM, Veldhoven January 18,

4 3 inch M.J. Bosma at FOM, Veldhoven January 18,

5 Direct conversion Wide band gap (1.45 ev) Short attenuation length (Z avg = 50) X ray X ray Scintillator Photo diode CdTe Read out electronics Silicon a Selenium CdTe Read out electronics Image Image M.J. Bosma at FOM, Veldhoven January 18,

6 Tellurium inclusions and sub-grain boundaries Flood ﬁeld image Te inclusions Edge eﬀects M.J. Bosma at FOM, Veldhoven Defects January 18,

3 10 3 Holes 100 ~2 10 6 2 10 4 Silicon: μτ e/h 1 Polarising detector Φ

7 Schubweg: λ e/h = μ e/h τ e/h E Mobility μ (cm 2 /Vs) Lifetime τ (s) μτ product (cm 2 /V) Electrons 1100 ~ Holes 100 ~ Silicon: μτ e/h 1 Polarising detector Φ critical 10 9 ph/mm 2 s Non polarising detector M.J. Bosma at FOM, Veldhoven January 18,

Less-deleterious dicing: o Etching o Laser dicing Design: o

8 Edge issues: Charge injection Depletion zone confinement High-field regions Reduction of inactive periphery by: Less-deleterious dicing: o Etching o Laser dicing Design: o Active edges M.J. Bosma at FOM, Veldhoven January 18,

9 500 µm 50 µm M.J. Bosma at FOM, Veldhoven January 18,

10 Sample Inactive edge (μm) I volume (na) I surface (na) I surface /I volume Edgeless Conv M.J. Bosma at FOM, Veldhoven January 18,

11 Spectral response to pion test beam M.J. Bosma at FOM, Veldhoven January 18,

;me; 50 kv; 15 ma; 0.2 mm Cu filter. 0.47 1.59 1.

12 Active edge distance of 50 μm Active edge distance of 20 μm Cu target X ray tube: 40 V bias; 3s. acq. ;me; 50 kv; 15 ma; 0.2 mm Cu filter rd 2 nd 1 st M.J. Bosma at FOM, Veldhoven January 18,

Weighting potential center edge corner Z

4% 122 kev 20 ns E pixel E pixel E pixel 1

13 Weighting potential center edge corner Z (mm) Z (mm) Z (mm) anode cathode Counts E backplane center edge corner 122 kev 122 kev FWHM = 3.7% FWHM = 4.7% FWHM = 6.4% 122 kev 20 ns E pixel E pixel E pixel 1 ns M.J. Bosma at FOM, Veldhoven January 18,

14 Pad spectral response Stand alone Closely surrounded by other detectors E backplane E backplane E pixel E pixel Counts Counts E pixel E pixel M.J. Bosma at FOM, Veldhoven January 18,

We have proven to be able to reduce the inactive periphery by more than a factor 10 while maintaining an acceptable leakage current.

15 Cadmium telluride hybridised to Medipix is a promising candidate as a digital radiography detector. Moderate homogeneity and resulting polarisation remain a problem. Medipix size and small single-crystal areas seamless tessellation of edgeless detectors. We have proven to be able to reduce the inactive periphery by more than a factor 10 while maintaining an acceptable leakage current. Edge effects can be reduced by proper cutting, effective passivation as well as active-edge technology. Inherent physical edge effects can be reduced by close tiling. M.J. Bosma at FOM, Veldhoven January 18,

16 Kasap, S.O.; Rowlands, J.A., "Direct-conversion flat-panel X-ray image sensors for digital radiography," Proceedings of the IEEE, vol.90, no.4, pp , Apr 2002 MARS: Medipix All Resolution System, Andreini, K. et al., Low-Signature Cadmium Zinc Telluride CZT, Defect Inspection by IR, Ultrasound, Etch Pit, Density, and X-ray Topography, 2010 IEEE NSS-MIC-RTSD Conference, 30 October 6 November 2010, Knoxville, Tennessee M J Yaffe and J A Rowlands, X-ray detectors for digital radiography, Physics in Medicine and Biology, 1997 A. E. Bolotnikov et al., Correlations between crystal defects and performance of CdZnTe detectors, 2010 IEEE NSS-MIC-RTSD Conference, 30 October 6 November 2010, Knoxville, Tennessee D. Greiffenberg et al., Characterisation of CdTe Medipix assemblies using synchrotron radiation at ANKA, MPX Meeting 09/2008 Stephen A. Soldner, Derek S. Bale & Csaba Szeles, Hole Transport and Pixel Count Variations in CdZnTe Monolithic Pixellated Detectors with Dynamic Polarization under x-ray Irradiation, 2010 IEEE NSS-MIC-RTSD Conference, 30 October 6 November 2010, Knoxville, Tennessee Rossi et al., Pixel Detectors: From Fundamentals to Applications (Particle Acceleration and Detection), Springer, March 2006 Mardor, I.; Shor, A.; Eisen, Y., "Edge and corner effects on spectra of segmented CdZnTe detectors," Nuclear Science, IEEE Transactions on, vol.48, no.4, pp , Aug 2001 Shor, A.; Mardor, I.; Eisen, Y., "Performance of 1 cm 1 cm 1 cm pixelated CdZnTe gamma detectors," Nuclear Science, IEEE Transactions on, vol.49, no.4, pp , Aug 2002 M.J. Bosma at FOM, Veldhoven January 18,

17 M.J. Bosma at FOM, Veldhoven January 18,

Excellent image contrast at low dose: High spatial resolution 55 um square pixel pitch Large dynamic range and good noise performance 13 bit deep counter and noise suppression per pixel High quantum

18 Excellent image contrast at low dose: High spatial resolution 55 um square pixel pitch Large dynamic range and good noise performance 13 bit deep counter and noise suppression per pixel High quantum efficiency and high sensitivity CdTe: Z 50; w = 4.4 ev, i.e. ~ e-h pairs / 60 kev photon Room-temperature operation CdTe: Wide band gap, i.e. high resistivity Uniformity of spatial and temporal response Defects and polarisation at high photon fluxes Full field coverage with minimum amount of dead regions 8 cm 2 Medipix module versus ~(40 x 40) cm 2 flat-panel AMA M.J. Bosma at FOM, Veldhoven January 18,

Sensor Medipix ASIC Medipix ASIC PCB Maximally, 3 inch diameter

19 Towards an edgeless module Quad Sensor with Guard Ring Medipix ASIC Medipix ASIC PCB Ball-Grid-Array Through-Silicon-Via Edgeless Quad Sensor Medipix ASIC Medipix ASIC PCB Maximally, 3 inch diameter single crystal wafers M.J. Bosma at FOM, Veldhoven January 18,

The Influence of Edge Effects on the Detection Properties of Detector Grade Cadmium Telluride

The Influence of Edge Effects on the Detection Properties of Detector Grade Cadmium Telluride M.J. Bosma a, M.G. van Beuzekom a, S. Vähänen b, J.Visser a a. National Institute for Subatomic Physics, Nikhef,