Strip Failures | @ 50V | @ 100V | Comments |
SGS Thomson (~2.5 detectors measured) | 2.8% | 3.7% | Out of specification.
Those failing at 100V do not subsequently hold any voltage. See example |
Hamamatsu | <0.5% | <0.5% | We have no reason to disagree with the manufacturers own results which indicate <0.1% See example |
|
NOTE: | Some of the SGS Thompson detectors/regions studied show the very long time constant behaviour (as measured in Liverpool and also by Ronan and Tara at FNAL). For these we cannot measure the strip failures as at short times the currents are up to mA levels (these are not included in the bad-strip estimates). This behaviour needs further studies as there is clearly some associated `memory' with strips which have been held at high voltage for any length of time, subsequently showing much faster recovery from the application of high voltage. |
Strip Resistance | Total (Ohms) | Ohms/cm | Comments |
SGS Thomson | 280 | 36 | Out of specifications |
Hamamatsu | 190 | 24 |
|
I-V characteristics | Reverse current @ 350V [nA] | Reverse current @ 500V [nA] | Comments |
SGS Thomson "Type B" | ~15 | ~20 | |
Hamamatsu "Type B" | ~50 | ~50 |
|
NOTE: | SGS Thomson values look remarkably low (here you find the plot).
Anyway, after irradiation the current is dominated by the induced defects
in the substrate so starting currents are not terribly significant.
|
Bias-resistor Values | Det. #1 [kOhms] | Det. #2 [kOhms] | Det. #3 [kOhms] | Comments |
SGS Thomson | 760+/-20 | 800+/-20 | 840+/-20 | Out of specification |
Hamamatsu | 2400+/-100 | 2400+/-100 | 2400+/-100 |
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NOTE: | We measured very low resistor values on the 4th detector (30-40 kOhms).
Actually, this result was obtained after the strip quality measurement,
when a bias of -100 V was put through the coupling capacitors. Measuring
the resistors with the voltage across the oxide resulted in this low value.
Grounding the strips and repeating the measurement resulted in a resistor
value in good agreement with that reported above.
|
Interstrip Capacitance | pF cm-1 | Comments |
SGS Thomson | ~ 0.8 | See note |
Hamamatsu | ~ 1 | See note |
|
NOTE: | The interstrip capacitance is genuinely lower for the SGS Thomson at the frequencies we can study (it looks to get closer to the Hamamatsu values at higher frequency:see plot). There is voltage dependence but a resonable estimate is 1pF/cm for the Hamamatsu and 0.8pF/cm for the SGS Thomson. ATLAS results after irradiation showed that <100> material such as Thomson may be using did show a lower interstrip capacitance than the <111> used by Hamamatsu but with a very strong frequency dependence. The difference reduces with frequency and as far as the actual results with fast electronics are concerned (ie at 40MHz) no appreciable difference in noise was observable for irradiated detectors. |
Full depletion voltage: | We have not checked the depletion voltages. We know these are supposed to be well over 100V for the SGS Thomson - OUT OF SPECIFICATION, but this would not in itself constitute a major issue except that the capacitors are not rated to the required depletion voltages. For Hamamatsu all the results on strip failures are at 100V which is well above the required operating voltage of the detectors. |
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FINAL REMARKS
Further information on Liverpool studies of
Hamatsu and Micron detectors can be found here.