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23/10/2003 C. Civinini – INFN Firenze - “Hysteresis” 1

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by Anna Macchiolo

INFN and University of Florence

Test Beam MeetingTracker Week

October 23rd, 2003


Scan # 1 TIB (peak) RUNS 1196-1204, 120 GeV Muons

Scan # 2 TIB (deconvolution) RUNS 30024-30054, 120 GeV Pions RUNS 30133-30175, 120 GeV Muons

Scan # 3 TIB+TOB (deconvolution)

During the test beam in May 2003 several voltage scans have been performed (0 Vmax 0)

A hysteresis effect has been observed in the TIB modules S/N values depend on the voltages at which the modules have been biased before (memory of the recent biasing history)

Introduction


The TIB modules (equipped with sensors HPK) where the beam was impinging during the voltage scan were:

Mod #2 – IB2 302 202 261 065 24 V-depl. =180 V (substrate)=2.5 Kcm

Mod #5 – IB2 302 202 261 242 41 V-depl= 138 V (substrate)=3.2 K cm

All the 6 TOB modules (equipped with sensors OB2 STM ) were hit by the beam

Modules and sensors in the beam-test


Module # 6 TIB- Dec. Mode

In a “standard” operative procedure (bias voltage driven directly from 0 V to the working point) the expected performance have been found, both for TIB and TOB modules

Deconvolution mode

S/N (TIB)~18 @350V

S/N (TOB)~24 @350V


Scan # 1 – Peak – TIB Modules

time


Scan # 2 – Deconvolution –TIB Modules

time

S/N


Scan # 2 – Deconvolution –TIB Modules

tt

Signal Noise


Scan # 2 – Deconvolution – TIB Modules

Decreasing the bias voltage the cluster width increases

The difference in the average cluster width between the two modules are due to the different inclination wrt the beam direction

t


Scan # 3 – Deconvolution – TOB Modules

t


How the hysteresis effect shows up for the TIB modules in the beam-test data ?

For instance in deconvolution mode at 300 V:

The signal decreases (8 %)

The noise increases (9 % )

S/N decreases (17 %)

The cluster width increases (16 %)


The increase of the cluster width and of the noise can be linked to an increase in the inter-strip capacitance (C_int) of the sensors.

In the lab we studied the C_int behavior repeating bias cycles similar to those done in the beam test.

From beam-test to the lab

Lab measurementscheme (PQC)


6,00E-13

7,00E-13

8,00E-13

9,00E-13

1,00E-12

1,10E-12

1,20E-12

1,30E-12

1,40E-12

1,50E-12

0 50 100 150 200 250 300 350 400 450 500

Bias Voltage (V)

Inte

rstr

ip C

ap

ac

ita

nc

e (

F)

Series 1 - Voltage up

Series 2 - Voltage down

Series 3 - Voltage up

Series 4 - Voltage down

Inter-strip capacitance measured in the CAP-TS-AC structure

20 minutes @ 450 V

HPK


5,00E-13

7,00E-13

9,00E-13

1,10E-12

1,30E-12

1,50E-12

0 50 100 150 200 250 300 350 400 450 500

Bias Voltage (V)

Inte

rstr

ip C

apac

itanc

e (F

)

75 minutes @ 450 V

C-int (250V) = 5 %

HPK



5.00E-13

7.00E-13

9.00E-13

1.10E-12

1.30E-12

1.50E-12

0 50 100 150 200 250 300 350 400 450 500

Bias Voltage (V)

Inte

rstr

ip C

apac

itan

ce (

F)

135 m inutes @ 450 V

10 minutes @ 300 V

C-int (250V) = 10 %

HPK



C

ePePCtC PtPt ]1[)( 42 /3

/1

0.718 pF

Time dependence of the inter-strip capacitance

Measurement done @ V_bias = 250V when the structure has been kept 75 minutes @ 450V

HPK

Measurement as a function of time at constant bias

22’ 3’30”


5.00E-13

5.50E-13

6.00E-13

6.50E-13

7.00E-13

7.50E-13

0 50 100 150 200 250 300 350 400 450 500

Bias Voltage (V)

Inte

rstr

ip C

apac

itan

ce (

F)

60 minutes @ 450 V

No hysteresis effect observed in the same experimental conditions


STM


From PQC standard measurements we know a hysteresis effect that affects HPK test structures only: the interstrip resistance drops by several orders of magnitude (from hundreds of G to hundreds of M) when the substrate has been biased to high voltages

This phenomenon verifies only when the environment relative humidity is quite high (>30-40 %).

The relative humidity measured for the TIB modules during the beam test is:

A hypothesis

Scan 1 (runs 1196-1204) RH ~ 45-50 %

Scan 2 (runs 30024-30054) RH ~ 45-50 %

Scan 3 (runs 30142-30175) RH from 60 % to 4% (nitrogen flux in TIB box)

All the lab measurements shown before have been done with RH ~ 45-50 %

During all the beam test time the TOB modules have been kept under nitrogen with low relative humidity (~ 4 %)


TIB test beam relative humidity


RH < 25%

Under low humidity conditions…

HPK


At relative humidity close to 0%

from J.

C. Fon

taine

(PQC S

trasb

ourg

)

R-int before and after bringing the substrate at 700 V

IV on mini-sensor up to 700 V

360 G

147 G


At relative humidity close to 50%

from J.C

. Fontai

ne (PQC

Strasbourg)

R-int before and after bringing the substrate at 700 V.

21 G

9 G

Hysteresis


Finally…

RH ~ 50 %

Noise measurements, inv on, common mode subtracted

done with the ARC system

RH < 10 %

t

Noi

se

Noi

se


Scan 3 – Deconvolution – Module 2 TIB

During the first ramp up the TIB box has been fluxed with nitrogen, so the other measurements have been taken with a relative humidity close to 3%

Order of magnitudeof the hysteresis (15%)in the previous scan


Conclusions

The hysteresis effect observed for the TIB modules during the X5 beam test voltage scans can be related to the interstrip capacitance and resistance behaviour of the HPK sensors

PQC studies show that hysteresis effects on Cint and Rint disappear if the measurements are done at relative humidity less than 35-40%

Hysteresis free results are obtained for the TIB noise lab measurements (done after the beam test) and for the TIB S/N scan performed during the May test beam at low relative humidity

Since ST sensors don’t show any hysteresis a possible mechanism that produce this effect could be traced to the difference in the oxide thickness and composition among the two manufacturers.

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