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Sensor Stability Measurements

Sensor Stability Measurements. Objective: find simple method of observing sensor stability -> measure fluctuations in overall leakage current Outline: setup and experimental method description results so far for 4 sensors (3 ST, 1 Hamamatsu) Mark Raymond, Imperial College.

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Sensor Stability Measurements

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  1. Sensor Stability Measurements Objective: find simple method of observing sensor stability -> measure fluctuations in overall leakage current Outline: setup and experimental method description results so far for 4 sensors (3 ST, 1 Hamamatsu) Mark Raymond, Imperial College CMS Tracker Week

  2. Experimental setup 100 kW => 100 mV / mA transimpedance circuit chosen to give ~ low impedance to guard ring, but could just use 100 k resistor to ground all measurements @ room temp. (24 oC (+/- ~ 1)) (RH ~ 30 – 40 %) CMS Tracker Week

  3. Experimental Setup op-amp circuit sensor CMS Tracker Week

  4. scope setup Tektronix (TDS724D) operated in peak detect mode internal sampling (Gs/s) much faster than intervals between displayed samples displayed samples alternate between highest in one interval and lowest in next allows capture of fast transients over relatively long time period (few seconds) only red samples stored and displayed CMS Tracker Week

  5. 4 sensors studied 1st ST sensor type W7B (ID 30211433739909) failed acceptance test - high leakage on one strip (and neighbours) (~ 10 mA) 2nd ST sensor type W7B (ID 30211433961106) good sensor (I think), Ileak ~ 650 nA @ 550 V 3rd ST sensor TOB (ID 30210432016302) one leaky strip (~ 6 mA) Hamamatsu type W4 (ID 3022883101103) good sensor, Ileak ~200 nA @ 800 V CMS Tracker Week

  6. Measurements – 1st ST sensor DC leakage only DC leakage measurement in close agreement with data provided (Vienna) take off at > 150V attributed to group of 3 strips only scope measurements show instability appearing for bias > 150 V, spiky transients and step changes 6.7 mA DC current measurement clean => no significant noise contribution from measuring system CMS Tracker Week

  7. Measurements – DC + AC shows relative magnitudes of DC leakage and transient behaviour for all 4 sensors studied (instability not correlated with overall leakage current magnitudes) CMS Tracker Week

  8. AC only DC leakage subtracted – baselines offset CMS Tracker Week

  9. AC only instability characteristics different to 1st ST sensor (no step changes) some evidence of instability but much better than first two CMS Tracker Week

  10. additional observations vacuum effects leakage current changes ~ randomly if vacuum to chuck turned on/off initially observed 50 Hz interference also traced to vacuum pressure variations these effects also observed on Hamamatsu sensor … not clear what’s going on here – leakage sensitive to stress? CMS Tracker Week

  11. Summary simple scope method used to monitor stability of overall sensor leakage current sensitivity at ~ few 10’s nA possible results for four sensors only – 3 ST and 1 Hamamatsu instability observable in 2 ST sensors (1 already rejected on overall leakage measurement) but instability characteristics not identical for these two probably worth looking at larger sample CMS Tracker Week

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