1. Punch-through protection in ATLAS SCT sensors A.Chilingarov, Lancaster University, UK Meeting on Investigations into the effect of beam splash on SCT Modules CERN, 3.08.09

2. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 2 Outline 1.Measurement method 2.Main results reported in 2007 3.Some recent results

3. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 3 A  RbRb R str R dyn 1. Punch-through (PT) resistance measurement method Positive DC potential, U strip, varying from 0.5 to 50 V is applied to the strip implant and the resulting current, I strip, is measured. The slope dU s /dI s gives an effective dynamic resistance, R eff, between the strip and the bias rail. Note that the PT behaviour is not necessarily polarity independent. R eff consists of the bias resistor, R b, with R dyn + R str in parallel. R dyn is the dynamic resistance of the 8  m punch- through gap. Above the PT onset voltage R dyn decreases quickly with U strip. The R str is the strip implant resistance between the punch-through gap and the contact point.

4. Measurement of the punch-through protection voltage for ATLAS SCT sensors A.Chilingarov, Lancaster University, UK (extracts) Meeting on Silicon Strip Sensors for ATLAS Upgrade CERN, 2.07.07 2. Main results reported in 2007

5. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 5 The punch-through protection voltage U pth was measured with the detectors biased by 100 V, which is above U d for all detectors. The positive bias from a separate source-meter was applied to the strip implant and the resulting current was measured as a function of bias. At low volts the slope of the IV curve reflects the value of the polysilicon bias resistor. The punch- through appears as a soft breakdown in the IV.

6. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 6 Differential resistance dU/dI was calculated from the measured IV curves. It has a similar shape for all 7 detectors A non-smooth behaviour of some characteristics is an artefact related to an insufficient precision of the voltage settings in earlier measurements. This was fixed later (e.g. for the measurements with w12- 406 and w31-225). PT onset voltage lies between 8 and 14 V.

7. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 7 3. Some recent results PT operation was tested up to ~1 mA strip current with the sensor w31-2055 under 150 V bias at room temperature and ~50% RH. The measurements were performed with four different strips.

8. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 8 For all strips the PT onset voltage is ~8.5 V and the minimum dynamic resistance is slightly above 10 k .

9. A.Chilingarov, Punch-through protection in ATLAS SCT sensors 9 Concluding remarks 1.The punch-through protection in the SCT sensors seems to work as expected. 2.The PT onset voltage lies between 8 and 14 V. 3.All reported measurements were made at about +21 o C temperature and 30-50% relative humidity.