STATUS OF MEDIPIX-3, PLANS FOR TIMEPIX-2

X. Llopart

-2- X.Llopart

Medipix 3 - reminder

• Medipix3 builds on the success of Medipix2 as a single photon counting imaging chip

• Added Features– Analogue charge summing to keep all charge information– Spectroscopic mode with 8 threshold levels– Continuous readout mode (no dead time)– Increased counter depth increasing dynamic range– Increased readout speed– Increased radiation hardness from 130nm CMOS process

-3- X.Llopart

Status

• First engineering run (12 wafers of 100 chips) delivered early this year

• Wafer probing complete

• One wafer diced and bonded to PCBs

• Using the IC Tester data transfers speeds of 1.6 Gb/s were achieved

• Initial readout system working at low speed (USB from Prague)

• Electrical characterisation is almost completed

• Medipix3 readout integration in Pixelman is underway

• First bump bonded assemblies with wafers expected soon (~1 month)

17.3

mm

14.1 mm

-4- X.Llopart

Electrical Characterisation Status

• Almost everything works as designed:– Complex pixel functionality: Charge summing, 8 independent thresholds,

programmable counter depth– Expected ENC and minimum threshold has been measured as expected

in all the different pixel modes

• Need to confirm the electrical characterisation with Medipix3 Si assemblies

• We found 2 issues with the chip– Cas and FBK DACs are not able to supply the designed nominal voltage– Continuous Read Write is not working correctly

-5- X.Llopart

The “analog switches” (problem)

Digital

Vin

R=100K

Vout

!EnablePixelCom

EnablePixelCom

EnablePixelCom

VSSA

Cascode DAC (Vcas) x65536 Pixels

75pA

75pA5A

5A

10A FS

Due to radiation and temperature an increase in the leakage current of NMOS transistors is observed

-6- X.Llopart

Temperature Measurements Setup

• The Medipix3 has an on-chip temperature sensor in the chip periphery

• At CERN we have available the Climatic Chamber ESPEC EGNX12-6CWL (-70 °C to +180 °C)

• Measurements covered the -60 °C to 60 °C range

y = 1.0555x + 24.173R² = 0.9999

-60

-40

-20

0

20

40

60

80

100

-60 -40 -20 0 20 40 60Tem

p M

edip

ix3

[ºC]

Temp In Climate Chamber [ºC]

-7- X.Llopart

Vcas and Vfbk temperature sensitivity

• Vcas is pulled low since the current leakage path goes to GND• Vfbk is pulled high• The consequence of this is effect is that the operational biasing of

the front end is not stable in temperature and it must be controlled carefully

0

0.2

0.4

0.6

0.8

1

1.2

1.4

-60 -40 -20 0 20 40 60

DAC

Out

put [

V]

Temp In Climate Chamber [ºC]

Cas @ 0xF8

Fbk @ 0x00

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Temperature effects in one pixel

• The chip is operational in all the studied temperature range• But, we observe variations on the noise, threshold position and gain

0 100 200 3000

1000

2000

3000

4000

5000

Pixel at 60CPixel at 20CPixel at -40C

THL DAC

Cou

nts

-9- X.Llopart

Pixel to pixel gain variation

• Gain variation (0.086 e-/THL DAC step) is due to the Medipix3 shaper stage

y = 0.0861x + 31.816R² = 0.9552

0

5

10

15

20

25

30

35

40

45

-60 -40 -20 0 20 40 60

Gai

n [e

-/TH

L D

AC st

ep]

Temp In Climate Chamber [ºC]

-10- X.Llopart

Overall pixel noise variation

• Noise is increasing at low temperature probably due the change in front end bias voltages Vcas and Vfbk

0

20

40

60

80

100

120

140

160

-60 -40 -20 0 20 40 60

ENC

[e-]

Temp In Climate Chamber [ºC]

-11- X.Llopart

Overall threshold position shift

• Significant effect visible in the threshold position due to the variation on Vcas

• When the shaper’s pol-zero cancellation circuit is activated the measured temperature sensitivity is 16.7 e-/°C and 3.7 e-/°C when it is switched off.

y = 0.0167x + 8.453R² = 0.9744

0

2

4

6

8

10

12

-60 -40 -20 0 20 40 60

Title

Title

-12- X.Llopart

400Mrad Irradiation

• Used a calibrated X-ray machine (Seifert RP149)• Beam profile is smaller than the Medipix3 → Two runs:

On the Pixel Matrix 60Mrad

Threshold Variation

Gain Variation

Noise Increase

On the Periphery 400Mrad

Check DACs

E-fuses

Logic functionality

60 MRad

460 MRad

400 MRad

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Performance after 460MRad

Threshold Noise

Yie

ld a

rtifa

ct

b 190.733061= σ 35.304781= Fit 0.000026=

0 2 4 6 8 10 12 14 16 18 200

200

400

600

800

THL [ke-]

Cou

nts

σ=1.72 ke-

µ=9.3 ke-

b1 8.798851= σ1 1.591887= Fit1 0.000247=

0 20 40 60 80 100 120 140 160 180 2000

2000

4000

6000

8000

10000

noise[e-]

Cou

nts

σ=12.9 e-

µ=71.6 e-

Threshold can be re-tuned using 5 bit equalisation

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0 15 30 45 60 75 90 105 120 135 1500

1000

2000

3000

4000

5000

Pixel Non-IrradiatedPixel Irradiated at 460 MRad

THL [DAC step]

Pix

el c

ount

s

Performance after 460MRad

Yie

ld a

rtifa

ct

Qin=2ke-

0 100 20040

60

80

100

Row Number

Noi

se [

e-]

Row

[0:2

55]

After 460MRad there is essentially no gain variation observed

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DAC Measurement

0.5

0.525

0.55

0.575

0.6

0.625

0.65

0.675

0.7

0 10 20 30 40 50 60 70 80 90 100 110

Volt

age

[v]

Hours (1hour→ 4Mrad)

Band Gap

Accumulated dose of 396 Mrad

0.3

0.325

0.35

0.375

0.4

0.425

0.45

0.475

0.5

0 10 20 30 40 50 60 70 80 90 100 110

Volt

age

[v]

Hours (1hour→ 4Mrad)

Accumulated dose of 396 Mrad

9mV

NMOS DAC (Preamp)

0.95

0.975

1

1.025

1.05

1.075

1.1

1.125

1.15

0 10 20 30 40 50 60 70 80 90 100 110

Volt

age

[v]

Hours (1hour→ 4Mrad)

Accumulated dose of 396 Mrad

33mV

PMOS DAC

For this technology there worst threshold shifts due to radiations happen ~3Mrad

-16- X.Llopart

3MRad irradiation

3 MRad

Worst effect at 3MRad, After this the effect of further radiation is much

less.

Irradiated a small area of the chip up to 3Mrad to try and keep Cas DAC

working by only damaging a limited number of pixels

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General behavior after 3 Mrad

0 3 6 9 12 15 18 21 24 27 300

200

400

600

THL [ke-]

Cou

nts

Threshold Noise

b1 4.928843= 1 0.991838= Fit1 3508.489764=

0 20 40 60 80 100 120 140 160 180 2000

5000

10000

15000

noise[e-]

Cou

nts

Yie

ld a

rtifa

ct

-18- X.Llopart

Overall threshold position variation

0 100 200180

200

220

240

260

280

300

Row Number

TH

L [

DA

C s

teps

]

Main contributor is the protection diode. In order to minimize the pixel to pixel threshold variation Ikrum is set to 16nA which indicated that the leakage of this diode at 3Mrad is ~5 to 10 nA. This is the worst radiation operation point.

Row

[0:2

55]

-19- X.Llopart

3MRad Noise and Gain Result

Yie

ld a

rtifa

ct

0 100 20040

60

80

100

Row Number

Noi

se [

e-]

0 15 30 45 60 75 90 105 120 135 1500

1000

2000

3000

4000

5000

Pixel Non-IrradiatedPixel Irradiated at 3 MRad

THL [DAC step]

Pix

el c

ount

s

Qin=2ke-

Row

[0:2

55]

In this worst case situation the noise is

still less than 100e- and the gain variation is still

minimal

-20- X.Llopart

Wafer Probing Summary

Name # AA Bs Cs Ds E F # Chips Where

VK7DG2H 0 100 CERN/diced

VT7DCWH 1 27 10 11 45 3 4 100 CERN

VT7DEVH 2 71 17 2 2 6 2 100 Bump bonding

VV7DFAH 3 33 18 6 32 7 4 100 CERN

VN7DE0H 4 57 18 2 15 8 0 100 Bump bonding

VU7DCVH 5 18 5 1 63 10 3 100 CERN

VW7DF9H 6 36 18 4 30 6 6 100 CERN

VQ7DCZH 7 61 18 2 8 6 5 100 Bump bonding

VS7DCXH 8 6 0 1 84 9 0 100 CERN

VU7DDCH 9 47 21 2 16 12 2 100 CERN

VL7DFJH 10 33 19 7 36 5 0 100 CERN

VW7DDAH 11 48 22 5 15 9 1 100 CERN

437 166 43 346 81 27 1100

39.7% 15.1% 3.9% 31.5% 7.4% 2.5% 100.0%

-21- X.Llopart

Best and worst wafer

-22- X.Llopart

Conclusions

• The electrical characterisation of the chip is basically completed

• By monitoring the chip temperature and the radiation effects through Vcas line the chip is practically insensitive to radiation large temperature fluctuations

• Only remaining issue is to understand the failure mechanism of the CRW mode

• Yield results are very encouraging given the complexity of such chip

• First Si assemblies will be available shortly and will be use to confirm electrical measurements

-23- X.Llopart

Towards Timepix2

• In the Medipix3 collaboration there is a growing interest in Timepix2

• It might be possible to fund this development with the Medipix3 funds

• Main specs:– Pixel to measure TOT and Arrival time information simultaneously– <2ns time resolution– Triggered readout– Sparse and very fast readout

• Many building blocks used in Medipix3 can be reused for a new chip

• Start of design depends on available experienced man-power