Results of 65nm pixel readout chip demonstrator array

Abderrezak Mekkaoui, Maurice Garcia-Sciveres, Dario Gnani

amekkaoui@lbl.gov

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Objectives

To explore the capabilities of advanced CMOS processes to

address future HEP needs (Upgrades, High Luminosity LHC)

Establish an analog front-end baseline

To have a feel of what is the best way these processes

should be used in order to maximize benefit

To evaluate radiation hardness

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FE-I4 : Front End chip for the IBL

• The FE-I4B chip is the production version for IBL installation

– Designed in a 130nm CMOS process

– Dimensions : 20 mm x 19 mm

– Active zone : ~ 90 % of the total area

– Respects all the specifications

– IBL Production : 1 Module = 1 Chip

• The FE-I4 pixel array is organized in Double Columns (DC)

– Double Column is divided into 2 × 2 pixel regions

– 1 région : 2×2 pixel

– Pixel size : 50 x 250 µm²

– 26880 pixels

– Radiation tolerance > 200 Mrad

• Phase I or Phase II

– New pixel detector planned

• 2 removable internal layers at radii of 3.3–10

cm

• 2-3 fixed outer layers at radii of about 15–25 cm

– The FE-I4 fits requirements for outer layers in terms

of hit occupancy and radiation hardness

– A new development (FE-I5) is required for the inner

layers

Periphery

IO pads

16

.8

mm

2 m

m

20.2 mm

336×80 pixel array

Main functional core

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Pixel region (2X2) a la FEI4 if implemented in 65nm

Region logic synthesized from FEI4 verilog.Neither 100% complete nor verified.Just to have an idea on what is possible Pixel size=50X100 (?)

~FEI4 AFE equivalent

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“FEI5” 2X2 REGION (100X200)

=> Substantial area reduction=> Ultimately the width of a pixel will limited by practical considerations (power distribution) and not the number of transistors!=> Room to add functionality

FIE4 pixel region Vs Pix65nm region (assuming y=50u)

FEI4 2X2 REGION (100X500)

If area to be kept the same as FEI4, about 4X more logic can be added

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Snapshot of submitted pixel array

25 mm y cell pitch but 50mm bump y picth. Power distribution will be major factor in the ultimate minimum dimensionsBump mask not part of the submitted layout (same size as FEI4)

Analog FE Config. Logic FutureDigitalRegion

nXm pixels

Analog FEConfig. Logic

Bump opening

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ATPIX65A FEND BLOC DIAGRAM

Inject Bloc Preamp.17fF Feedback cap.Variable “Rff”

Single to differential+Comparator “preamp”

Comparator

TDAC (+/- 4b tuning)

Passive RC: gate leakage limited

Uses only native 65nm Transistors2mA to 25mA @ 1.2V

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ATPIX65A: Atlas Pixel prototype array

Pixels withAddedsensors(row 11:31)

Pixels withAddedmimcaps(31,27,22,18)

16 X 32 array25m X 125m pixels

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Test results: front end waveforms

Preamp out

Single to Diff. out

Chan 15/32 Qin: 2ke

Chip found to work as expected!VDD=1.2VI= 5mA per pixel (can be as low as 2mA)

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Test results: front end waveforms

Qin=10ke-; 5IFF settings

Chan 15/32 Qin: 2ke to 10ke-

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Timewalk @Preamp current of 2mA and 0.2mA

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ATPIX65A: ENC for some columns

. . . .Channels withmimcaps

Channels withDiodes (3 types)

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ATPIX65: ENC Vs Preamp Bias

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ATPIX65A: Noise and Threshold distribution

Channels with caps or diodes

s > than FEI4(as expected!)

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ATPIX65A: Threshold tuning

Sigma untuned ~350e- rmsSigma Tuned < 60e- rms

---- 565e- p-p tuned ----

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Radiation effects on DC bias voltages0 rad (Chip2)

~70 Mrad (chip2)

>600 Mrad (chip3)

Vbp1 (pmos) 525 474 440 @250 nA

Vbp2 (pmos) 620 609 586 @2 uA

Vbn1 (nmos) 636 623 648 @1uA

Vbn2 (nmos) 238 237 236 @1uA

Vbn3 (nmos) 277 274 276 @0.5uA

VG of diode connected transistors at fixed current (in mV)Different size transistorsSmall/negligible change in threshold voltages of PMOSs/NMOSsPMOS threshold variation more pronounced!Some measurement errors in the low current regime (meter impedance and esd diodes leakage)

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Radiation effects: Threshold and noise

Green: chipB > 600MradBlue: chipA unirradiated

Different chips. Under same bias conditions except for VthModest ENC increase (but only 2 chips) Preliminary results!

ChipB: ENC=110e- ChipA: ENC=94e-

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Conclusions

Chip works as expected

Good results

SEU evaluation under way (See talk by Mohsine Menouni CPPM)

Promising process. It offers:Very high integration densityInherent very high radiation toleranceA reasonable number of devices types for extra design flexibilityAvailability of high quality passivesA high number of metal levels

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Backup slides

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Fe55 spectrum as detected by one of the integrated sensors

Chip2 high gain mode. Sensor@-8V

1040e- pulser injection~3.7keV. Assuming Cinjto be nominal.

2154 KeV (2.9KeV? May be partial 5.9KeV charge collection?)

5154 KeV (theory; 5.9KeV?)

For the experiment to agree with theory (for the 5.9KeV), injection cap has to be corrected by 15% . Still being reviewed!

Noi

se a

rtific

ially

Lim

ited

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65nm: Some transistor test result

M. Manghisoni et al. TWEPP 2011

Same gate capacitance No noise degradation at lower nodesNo thermal noise increase with radiation No or little 1/f noise increase with radiation

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65nm: Some radiation tolerance resultsThreshold voltage Leakage current

S. Bonacini et al. TWEPP 2011

65 nm devices seem to outperform their 130nm counterparts in theirtolerance to ionizing radiation !

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ATPIX65: ENC Vs Diode bias

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ATPIX65: Threshold Vs Preamp current

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ATPIX65: Threshold Vs feedback current

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Lower part of the Am241 spectrum as detected by one of the integrated sensors

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Chip1 low gain mode(V)

Very preliminary! Work in progress! Low statistics

?

?

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ATPIX65: ENC Vs IFF (feedback current)