Punch-through protection in ATLAS SCT sensors A.Chilingarov, Lancaster University, UK

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

A.Chilingarov, Punch-through protection in ATLAS SCT sensors

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Outline

1. Measurement method2. Main results reported in 20073. Some recent results


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A

Rb Rstr Rdyn

1. Punch-through (PT) resistance measurement method

Positive DC potential, Ustrip, varying from 0.5 to 50 V is applied to the strip implant and the resulting current, Istrip, is measured. The slope dUs/dIs gives an effective dynamic resistance, Reff, between the strip and the bias rail. Note that the PT behaviour is not necessarily polarity independent.

Reff consists of the bias resistor, Rb, with Rdyn + Rstr in parallel. Rdyn is the dynamic resistance of the 8 m punch-through gap. Above the PT onset voltage Rdyn decreases quickly with Ustrip. The Rstr is the strip implant resistance between the punch-through gap and the contact point.

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


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The punch-through protection voltage Upth was measured with the detectors biased by 100 V, which is above Ud 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.0.8 1 2 4 6 8 10 20 40

1

10

100

1000

I stri

p (A

)

Ustrip

(V)

w12-406w21-9w22-18w31-225w31-405w31-1277w32-560

Strip IV for 7 Endcap detectors under 100 V bias


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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.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

200

400

600

800

1000

1200

1400

1600

1800

dU

/dI (

k)

Ubias (V)

w12-406w21-9w22-18w31-225w31-405w31-1277w32-560

Lancaster 9-14.05.07: strips with highest Up-through

in 7 SCT sensors


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3. Some recent results

w31-2055 at 150V, 23.7.09: total strip current vs potential

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35 40 45

Ustrip, V

Cu

rren

t,

A

strip 388

strip 446

strip 360

strip 416

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.


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w31-2055: dynamic resistance vs strip potential

0.01

0.1

1

10

0 4 8 12 16 20 24 28 32 36 40 44

Ustrip, V

dU/d

I, M

strip 388

strip 446

strip 360

strip 416

For all strips the PT onset voltage is ~8.5 V and the minimum dynamic resistance is slightly above 10 k.


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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 +21oC

temperature and 30-50% relative humidity.

Documents

Punch-through protection in ATLAS SCT sensors A.Chilingarov, Lancaster University, UK