1. Image quality and spectroscopic characteristics of different silicon pixel imaging systems M. G. Bisogni, D.Bulajic, M. Boscardin, G. F. Dalla Betta, P. Delogu, M. E. Fantacci, M. Novelli, C. Piemonte, M. Quattrocchi, V. Rosso*, A. Stefanini and N. Zorzi + valeria.rosso@pi.infn.it * Universita degli Studi e Sezione I.N.F.N., Pisa, Italy 14TH INTERNATIONAL WORKSHOP ON ROOM-TEMPERATURE SEMICONDUCTOR X-RAY AND GAMMA-RAY DETECTORS ROME 18-21 OCTOBER 2004

2. Outline 3 imaging systems based on different thickness Si pixel detectors were compared: Spectroscopic characteristics 109 Cd source Imaging quality contrast signal to noise ratio (SNR) Spatial resolution modulation transfer function (MTF)

3. Si detector p+ side Imaging system ITC-Irst Detector Si 300-800 m thick pixel 170 x 170 m 2 p+ side 150x150 m 2 64 x 64 chs 1.2 cm 2 area Photon Counting Chip Medipix collaboration SACMOS 1 m technology pixel: 170 x 170 m 2 64 x 64 channels area 1.7 cm 2 threshold adjust 3-bit 15-bit counter VTT Bump-bonding: http://medipix.web.cern.ch/MEDIPIX/http://medipix.web.cern.ch/MEDIPIX/

4. Spectroscopic capability 109 Cd Integral spectra 109 Cd Differential spectra

5. Thickness ratio Calculated ratio Experimental ratio 525/3001.621.61 800/5251.391.38 800/3002.252.23 109 Cd Integral spectra Wafers characteristics Thickness ( m) resistivity J (nA/cm 2 )V DEP (V)V OVER-DEP (V) 300+15 >= 6 K cm 0.53060 525+20 >= 5 K cm 1.290120 800+25 12 ÷ 30 K cm 2680200 Detection efficiencies ratio V th =11keV

6. Contrast measurements Al thickness 75 m Air X-ray (W-anode) settings : 40 kV, 25 mA, 500 ms Si detector 140 cm Collimator X-ray focus 1.5 cm Al

7. Contrast Al (E) and air (E) are the absorption coefficients at the energy E (E) is the detector efficiency at the energy E S(E) is the incident spectrum

8. Signal to Noise Ratio Thickness ratioCalculated ratioExperimental SNR ratio 525/3001.241.25 800/3001.411.42 800/5251.14 75 m Al air

9. Spatial resolution 800 m Vth=11keV Settings : 40 kV, 20 mA, 4000 ms W Slit : width: 10±1 m length: 5.5±0.1mm thikness: 1.5mm

10. Counts/row pixel number experimental finely sampled LSF 2 Boltzman functions LSF fitted fft MTF

11. MTF MTF Nyquist Freq. (2.94 lp/mm) MTF: 64 % Evaluated aperture 168 m Detector pitch 170 m V th (keV) 800 m aperture ( m) 11168 15161 19155 23146

12. Exposure condition: W anode, 40 kV, 40 mA, 630 ms 300 m525 m800 m C=4,8% C=1,2% C=2,4% C=3,7% 25 micron 50 micron 75 micron 100 micron Image of different Al thickness

13. Conclusions Increasing the detector thickness: increases the detection efficiency SNR increases contrast decrease as expected spatial resolution unchanges More information on a PCC based digital mammographic system: poster session R11-51 Thursday 11:00-12:30

15. width Electric Field and Potential

16. Photos of some details Medipix 1 Medipix 2 Pixel 150 m x 150 m Pixel 45 m x 45 m guardring multiguardrings Snake pads

17. Diffusione di carica Con la diffusione, una carica che impiega un tempo t per raggiungere lelettrodo avrà una fluttuazione sulla posizione cor rms diff 2 diff = D*t D alla mobilita dei portatori di carica. E diff