ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08

Electrical characteristics of un-irradiated ATLAS07 mini strip sensors

A.Chilingarov,Lancaster University

ATLAS Tracker Upgrade UK Workshop

Coseners House, 8.07.08

A.Chilingarov, ATLAS07 mini sensors2

Outline

1. Sensors2. C-V,I-V measurements3. Punch-through voltages4. Interstrip resistance5. Interstrip capacitance6. Summary7. Conclusions


Available versions (“Zones”) of the ATLAS07 mini-SSDs. Here we report the results for zone 1 (no isolation structure) and for zone 3 (baseline option) sensors. Each zone may additionally have a thin lightly p-doped layer on the surface (“p-spray”). PTP means Punch-Through Protection structure.


. . . . .

Rb Bias rail

Backplane

A

Cs

Rsto LCR meter

CV – IV measurements

Both C-V and I-V measurements are made simultaneously. The impedance is measured between the backplane and the bias rail by the LCR meter in Cs-Rs mode (standard frequency is 10kHz).

The Cs represents the total capacitance between the strips and the backplane, while the Rs is the average bias resistor divided by the number of strips.


IV for ATLAS07 minis at Lancaster

0.00

0.01

0.02

0.03

0.04

0 100 200 300 400 500 600 700 800 900 1000

Bias, V

Cur

rent

, mA

w02-BZ1-P19w04-BZ1-P7w27-BZ1-P7w28-BZ1-P19w23-BZ3-P21w04-BZ3-P3w07-BZ3-P3

CV for ATLAS07 minis at Lancaster

0

400

800

1200

1600

0 100 200 300 400 500 600 700 800

Bias, V

1/C

2 , nF-2


Rs-V for ATLAS07 minis at Lancaster

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600 700 800

Bias, V

Rs,

kO

hm


Five out of 7 sensors can withstand 1000V bias, two develop a breakdown above 800V. Typical current is below 10 nA (for ~1cm2 area). Depletion voltage values lie between 150 and 180V. Resistance agrees with expectation within a factor of ~1.5


A

Rb Rstr Rdyn

Punch-through resistance measurements

Negative DC potential, U, varying from 0.5 to 50 V is applied to a strip implant and the resulting current, I, is measured. The slope dU/dI gives the value of effective resistance, Reff, between the strip and the bias rail.

Reff represents the bias resistor, Rb, with Rdyn + Rstr in parallel. Here Rdyn is the dynamic resistance of the punch-through gap quickly decreasing with U above the break-through voltage and the Rstr is the strip implant resistance (if the punch-through gap is at the strip end opposite to the contact point).


Dynamic resitance for fresh Zone 1 sensors (no p-stops)

0.01

0.1

1

10

0 5 10 15 20 25 30

-Ustrip, V

dU/d

I, M

ohm

w27-bz1-p7w28-bz1-p19w02-bz1-p19w04-bz1-p7

with p-spray

no p-spray

Dynamic resistance for Zone 3 sensors with p-spray: fresh and after 3h at 220V bias

0.1

1

10

24 28 32 36 40 44 48 52

-Ustrip, V

dU/d

I, M

Ohm

w07-bz3-p3w04-bz3-p3w07-bz3-p3w04-bz3-p3

fresh

biased for 3h

Dynamic resitance for Zone 3 sensor w23-bz3-p21 (no p-spray) for different time @ 220V bias

0.01

0.1

1

10

24 28 32 36 40 44 48 52-Ustrip, V

dU/d

I, M

ohm

fresh1h bias2h bias3h bias

biased for 3h

fresh

As expected, zone 1 sensors have a relatively low break-through voltage of ~5 or ~15V. For zone 3 sensors the break-through is also observed above 45 V. For all sensors this voltage decreases with time under bias.

Note that the strip bias resistors can tolerate up to ~50V voltage drop across them without being burnt.


Interstrip resistance measurements

A “master” DC potential U0 is applied to a strip implant and the “slave” potential U1 induced at the neighbouring strip implant is measured by a high impedance voltmeter.

The U0 is varied by a few volts around zero and the resulting current I0 is measured. The slope dU0/dI0 gives the value of effective resistance between the strip and the bias rail, R0. The slope dU1/dU0 allows calculation of the effective interstrip resistance, Ris, using an assumption of bias resistor, Rb, being the same at both strips.

Rb

Bias rail

AVRis

U1 UoIo


-4 -2 0 2 4304

306

308

310

312

314

316

318

320

322

324

326

328

Ub=10V

Ub=20V

Usl

ave, mV

Umaster

, V

Fresh w07-bz3-p3, 13.5.08: Uslave

vs. Umaster

for different Ubias

Typical dependence of the induced voltage (Uslave) vs. the voltage applied to the neighbouring strip (Umaster). Normally the slope dU1/dU0 is ~1mV/V which means Ris ~ 106 Rbias i.e. ~1000 GOhm. The spread of the points around the linear fit determines the Ris error.


Interstrip R for Zone 3 sensor w23-bz3-p21 (no p-spray): bias ramps up and down after 3 hours at 200 V

0

200

400

600

800

1000

1200

1400

1600

1 10 100 1000Ubias, V

Ris,

GO

hm

fresh3h bias

Interstrip R for Zone 3 sensors with p-spray: bias ramps up and down after a time @ 200 V

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 10 100 1000Ubias, V

Ris

, GO

hm

w07-bz3-p3 freshw07-bz3-p3 3h biasw04-bz3-p3 freshw04-bz3-p3 10' bias

For zone 3 sensors the interstrip resistance Ris does not depend on bias in the range 10-200V and doesn’t change after sensor remaining at 200V bias during 3 hours.

Typical Ris value is ~1000 GOhm.


Interstrip R for Zone 1 sensors with p-spray: bias ramps up and down after 3 hours at 200 V

0

200

400

600

800

1000

1200

1400

1 10 100 1000Ubias, V

Ris

, GO

hm

w02-bz1-p19 freshw02-bz1-p19 3h biasw04-bz1-p7 freshw04-bz1-p7 3h bias

Interstrip R for Zone 1 sensors without p-spray: bias ramps up and down after ~3 hours at 200 V

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1 10 100 1000Ubias, V

Ris

, GO

hm

w28-bz1-p19 freshw28-bz1-p19 3h biasw27-bz1-p7 freshw27-bz1-p7 3.5h bias

fresh sensors, ramp up

after 3h bias, ramp down

For fresh zone 1 sensors with p-spray the Ris also doesn’t depend on bias in the range 10-200V but after 3 hour biasing by 200V it decreases and becomes slightly bias dependent with Ris value of ~500 GOhm above 100V bias.

For zone 1 sensors without p-spray the Ris behaviour is more complicated. Nevertheless above 100V bias the Ris remains above 100 GOhm even after 3 hours at 200V bias.


to LCR meter

Interstrip capacitance measurements

The capacitance is measured between an aluminium outer strip and two its nearest neighbours connected together. The LCR meter operates in Cp-D mode. Standard measurement frequency is 100 kHz.

The strips are grounded through ~1 M resistors to keep their DC potential fixed.


Interstrip capacitance versus bias (sensors w01-17 have p-spray)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 100 200 300 400 500 600Ubias, V

Cis,

pF

w28-bz1-p19w27-bz1-p7w02-bz1-p19w04-bz1-p7w23-bz3-p21w04-bz3-p3w07-bz3-p3KEK data

Zone 1 (no p-stop)

Zone 3 (with p-stop)

p-spray

no spray

Below 300V the Cis has a complicated behaviour with bias but above 300V it almost flattens and gradually converges to a value of ~0.6 pF for all sensor types.

Our results are in a reasonable agreement with KEK measurements.

Interstrip capacitance Cis vs. Ubias


Interstrip C vs. time at 600V (sensors w01-17 have p-spray)

0.55

0.56

0.57

0.58

0.59

0.6

0.61

0.62

0.63

0.64

0 40 80 120 160 200Time, min

Cis,

pF

w28-bz1-p19w27-bz1-p7w02-bz1-p19w04-bz1-p7w23-bz3-p21w04-bz3-p3w07-bz3-p3

Zone 1 (no p-stop)

Zone 3 (with p-stop)

Interstrip capacitance Cis vs. time at Ubias = 600V

At 600V bias the Cis further converges with time to a common value of ~0.61 pF for all sensor types.

The measurements were made at ~22oC temperature and 35-45% relative humidity.


Interstrip C for different sensors

0.605

0.606

0.607

0.608

0.609

0.61

0.611

0.612

0.613

0.614

0.615

0 0.5 1 1.5 2 2.5 3 3.5 4

Zone+0.5*(p-spray)

Cis,

pF

L=8060 mm

L=8000 mm

Interstrip C per unit length for different sensors

0.753

0.754

0.755

0.756

0.757

0.758

0.759

0.760

0.761

0.762

0 0.5 1 1.5 2 2.5 3 3.5 4

Zone+0.5*(p-spray)

Cis/

L, p

F/cm <C> = 0.758 +- .003 pF/cm

The strip length, L, is 8000 mm for zone 3 sensors and 8060 mm for zone 1 sensors. Assuming the whole measured capacitance being scalable with L the capacitance per unit length was calculated.

No systematic difference due to the sensor type or the p-spray presence was observed. The average Cis value is 0.758+-.003 pF/cm where the error is the points r.m.s. spread.


Interstrip capacitance per unit length versus pitch

y = -0.007x + 1.2664R2 = 0.996

0.60

0.65

0.70

0.75

0.80

0.85

60 65 70 75 80 85 90

Average pitch, um

Cis

, pF/

cm

SCT wedges/LancsAtlas07 minisSCT MPI/NIKHEF0.01 pF abs.uncertaintyLinear (SCT wedges/Lancs)

NIKHEF

w12 w31 w21 w32 w22

Comparison with the SCT sensors

The observed Cis/L agrees well with the data measured for the SCT sensors. An absolute LCR meter uncertainty of 0.01 pF is also shown in the error. Thus the Cis in ATLAS07 minis can be regarded as simply geometrical one.


Frequency dependence of the interstrip capacitance

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0 100 200 300 400 500 600 700 800 900 1000

Frequency, kHz

Cis

, pF

w23-bz3-p21/400Vw23-bz3-p21/600Vw07-bz3-p3/600Vw04-bz3-p3/600Vw02-bz1-p19/600Vw04-bz1-p7/600Vw28-bz1-p19/600Vw27-bz1-p7/600V

10 100 10000.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02

Cis/C

is(1

00kH

z)

Frequency, kHz

19.06.0825.06.08

Normalised Cis vs frequency for two measurements with w32-312

Frequency dependence of the Cis

For the frequencies above 100kHz the Cis for the mini SSDs is by ~10% higher. However for the SCT sensors there is <1% difference between the Cis values in the range from 100kHz to 1MHz. Measurements with longer strips are necessary to distinguish between the changes with frequency due to the whole strip (scalable with L) and to the strip edges (independent of L).


Sensor name p-sprayBreakdown

onset, VI, mA

at 1000VI, mA at

brkd.onset Vdep,VRbias,MOhm

InterstripR, GOhm

p-throughonset, V

InterstripC, pF

Zone 1 - PTP*, no p-stops (in fresh sensors)

w02-BZ1-P19 Yes >1000 0.0084 174 1.22 442 15 0.608

w04-BZ1-P7 Yes >1000 0.0317 174 1.32 535 15 0.613

w27-BZ1-P7 No >1000 0.0068 153 1.30 604 5.5 0.614

w28-BZ1-P19 No >1000 0.0061 159 1.25 280 4.5 0.610

Zone 3 - no PTP, p-stops

w23-BZ3-P21 No >1000 0.0071 167 1.21 890 47.5 0.607

w04-BZ3-P3 Yes 810 20.1 0.0078 183 1.23 853 48.5 0.606

w07-BZ3-P3 Yes 830 18.4 0.0078 182 1.19 1008 48.5 0.608

* PTP – Punch-Through Protection structure

Summary of the results presented in this talk

Note: the interstrip resistance values are given at 200V bias and after 3 hours where appropriate.


Conclusions

1. Typically ATLAS mini SSDs show a stable behaviour up to at least 800 V. More than a half of them can be operated up to 1000V bias. The depletion voltage values are below 200V.

2. The punch-through protection structure implemented in zone 1 sensors operates according to expectations with a break-through voltage below 15 V.

3. For all sensor types the interstrip resistance exceeds 100 GOhm for bias voltage above 100V.

4. The interstrip capacitance values for all sensor types are very similar and agree with those for ATLAS SCT sensors scaled by the length.

5. The bias resistors have the value in the range 1.2 - 1.3 MOhm. They are able to withstand up to ~50V voltage drop across them without thermal destruction.

Documents

ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08