Performance test of STS demonstrators

1. Performance test of STS demonstrators Anton Lymanets 15th CBM collaboration meeting, April 12th, 2010

2. Outline • Demonstrators tested so far. • n-XYTER energy calibration. • ADC response. • Pedestal position and effective amplitudes of -peaks. • Pedestal profile dependence on current consumption. • Crosstalk studies.

3. The demonstrators • FEB rev. B: • Every second channel bondable. • Still good for lab tests for timing studies or • ADC response (without clustering). • FEB rev. C: • All channels are usable • But thermal stability becomes an issue. • Detector-FEB cable: • Turns out to work if shielded properly. • Detectors of CBM01 and CBM02 type • “behave” similarly (bad), poor charge • collection at n-sides. • “D boards” • FEB rev. B, C, (D) • Q boards • Detectors (CBM01B2, CBM02B2s) • FEB 4nx: • Cooling plates improve thermal stability • Problems with surviving potential of the chips • on board. • Beam time : vastly different count rates • in different stations caused by the beam. Conclusion: depletion conditions should be controlled carefully.

4. C V Q Energy calibration is important for beam time data analysis and estimates of signal-to-noise performance, charge collection efficiency, etc. Create known voltage step over known capacitance Use x-rays with Si strip detector    Q=C∙V Cons: capacitance is small => strongly depends on stray capacitance. Pros: well defined energy. Range of 59 keV electrons is ~ 15 μm => full energy is absorbed.

5. Energy calibration with 241Am Using 300 μm pitch detector => no significant charge sharing Energy gain = 110.6 e-/ADC cnt + one can obtain pedestal energy (not necessarily zero) Noise 460 e- @ 6 pF

6. Calibration line Energy calibration is obtained, but extrapolated pedestal amplitude is ~3 kElectrons. Possible reasons: non-linearity, bias due to peak detector.

7. Controlling detector depletion 241Am x-rays measured on p-side Q6 Q6 X-ray characterization: count rate vs. bias Current-voltage measurement • Method works for • p-strips before type inversion or • n-strips after type inversion

8. ADC response to the MIPs Landau + Gaussian component Landau peak with maximum corresponding to ~16.5 ke- Expectation in ~300 μm Si: 23 ke-

9. Pedestal position Measured in FEB B03, ch. #46 Pedestal position crosses zero at ~1.4 V • Dynamic range is reduced! Indirect measurement: VbiasS is measured in test channel, not in ch.46

10. Peak amplitudes Amplitude = peak position - pedestal Peak1: 7.2 ke- Peak2: 16.3 ke- Hitting the lower rail Hitting the upper rail

11. The role of peak detector in out Peak detect & hold Offset in peak detector output may cause pedestal ≠ 0 Peak detect & hold circuit “remembers” the maximum amplitude and keeps it until it is transferred to analog FIFO. Observed pedestal/peak shifts are not reproducible in device simulations

12. n-XYTER chip Power lines current Test channel Channel 0 Output pads Input pads Channel 127 current Power lines

13. Pedestal profile over channels • Pedestal “sag” is observed with maximum in channel #64 • To be addressed in the upcoming engineering run done in Heidelberg Univ. (H. K. Soltveit)

14. Crosstalk problem – looking into the test channel digital part analog part Look with scope into test channel and fire pulses in its neighbor ch. 0

15. Default chip settings, test pulses in 32 channels Questions: digital or analog pickup? dependence on channel number? local effect?

16. Part of the channels masked, pulses in 16 channels. Channels 64..127 masked Channels 0..63 masked Crosstalk is not related to activity in neighboring channel, but to number of active channels => Non-local effect

17. Does the effect have analog nature? Change test pulse height (cal setting) cal = 128 cal = 256 Very small effect of amplitude seen => Mostly digital effect

18. Crosstalk problem – using laser pulses • XT - signal transmitted in one channel creates undesired effect in another channel. • Crosstalk in detector vs. crosstalk in read-out chip. • n-XYTER review meeting: December 11th, 2009. • The way to go: create signals using laser in isolated channels, look for the response in neighboring channels. ? Advantage: Study crosstalk in the chip avoiding crosstalk in the detector. ? ? ? read-out chip detector

19. Channel hit occupancy Counts Channel number • Big laser spot - equal number of hits in each channel. • Hit count rate corresponds to pulse rate.

20. ADC distribution Using automatic baseline correction Baseline subtracted. Line shape corresponds to intensity distribution in the laser spot. Raw spectrum

21. Method: look at signal peak mean and RMS with noise present Low noise High noise With low noise in the channel of interest the observed effects are caused by increased occupancy in other channels

22. Signal mean and RMS vs. n-XYTER occupancy Channel 69 Channel 69 Signal amplitude drops down linearly with increasing total count rate. Signal peak width increases vs. total chip occupancy.

23. Conclusions I • Energy calibration has been done. Energy gain = 110 e-/ADC count. • Pedestal “amplitude” depends on VbiasS voltage. • Conditions for pedestal zero “amplitude” have been determined, but then the dynamic range is reduced.

24. Conclusions II • N-XYTER Gain depends on VbiasS voltage. • “Sag” in pedestal profile depends on chip power consumption => to be addressed in n-XYTER engineering run. • Crosstalk in the chip has digital nature and depends on overall chip activity.

25. Conclusions III – Demonstrator Systems • Problems with charge collection in CBM01 and CBM02 – need to control sensor bias. • Front-end boards: no operational 4nx-boards and few 1nx-bords are left (this poses a threat to the upcoming beam time).