The future of rad-tol electronics for HEP

G.A. & A.M. - CERN

The future of rad-tolelectronics for HEP

Giovanni Anelli & Alessandro MarchioroCERN

Experimental Physics DivisionMicroelectronics Group

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What comes after

• SLHC– Luminosity: ~ 1035 fb-1

– Beam cms energy: ~ same

– Radiation levels (5 years): 200 Mrad @ 7 cm, 40 Mrad @ 20 cm

– Compensate for higher intensity through higher segmentation

– Cost: lower than current !

– Power/channel must decrease

G.A. & A.M. - CERN

What if SLHC ?

• If 5x luminosity [1] tracker would require:– 2 x speed

– 2x segmentation 20 M channels

– 25% higher occupancy

• Assuming that (magically) FE power/ch remains the same, the CMS tracker would require:– Ptot = 60 kW

– Pcables = 150 kW

– Cables : double, cooling pipes: double[1] This is purely hypothetical, actual numbers may change

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Outline

• Where is technology going (anyway)

• Problems with following technology

• What makes CMOS rad-tolerant

• Is technology all what we need ?

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Saving power: Technology

1997 1999 2001 2003 2006 2009 2012

Overall Characteristics

Transistor density (2) 3.7 M/mm2 6.2 M/mm2 10 M/mm2 18 M/mm2 39 M/mm2 84 M/mm2 180 M/mm2

Chip size (3) 300 mm2 340 mm2 385 mm2 430 mm2 520 mm2 620 mm2 750 mm2

Local clock frequency (4) 750 MHz 1.25 GHz 1.5 GHz 2.1 GHz 3.5 GHz 6 GHz 10 GHz

Power supply voltage (5) 1.8-2.5V 1.5-1.8V 1.2-1.5V 1.2-1.5V .9-1.2V .6-.9V .5-.6V

Maximum power (6) 70 W 90 W 110 W 130 W 160 W 170 W 175 W

Technology Requirements

µP channel length (1) .20 µm .14 µm .12 µm .10 µm 70 nm 50 nm 35 nm

DRAM ½ pitch (1) .25 µm .18 µm .15 µm .13 µm .10 µm 70 nm 50 nm

Tox Equivalent (7) 4-5 nm 3-4 nm 2-3 nm 2-3 nm 1.5-2 nm <1.5 nm <1.0 nm

Gate Delay Metric CV/I (7) 16-17 ps 12-13 ps 10-12 ps 9-10 ps 7 ps 4-5 ps 3-4 ps

Solutions Exist Solutions Being Pursued No Known Solution

LHC Start SLHC

Start

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Moore’s law1965: Number of Integrated Circuit components will double every year

G. E. Moore, “Cramming More Components onto Integrated Circuits”, Electronics, vol. 38, no. 8, 1965.

1975: Number of Integrated Circuit components will double every 18 monthsG. E. Moore, “Progress in Digital Integrated Electronics”, Technical Digest of the IEEE IEDM 1975.

The definition of “Moore’s Law” has come to refer to almost anything related to the semiconductor industry that when plotted on semi-log paper approximates a straight line. I don’t want to do anything to restrict this definition. - G. E. Moore, 8/7/1996P. K. Bondyopadhyay, “Moore’s Law Governs the Silicon Revolution”, Proc. of the IEEE, vol. 86, no. 1, Jan. 1998, pp. 78-81.

1996:

http://www.intel.com/

An example:

Intel’s Microprocessors

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When will it stop ?

Carver Mead’s Law

tox = 210 * L 0.77

from C. Mead, ‘Scaling of MOS Technology to Submicron Feature Sizes’, Journal of VLSI Signal Processing,July 1994

Tox

(A

)

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Why is CMOS so widespread?• IC market is driven by digital circuits (memories,

microprocessors, …)• Bipolar logic and NMOS - only logic: too high power

consumption per gate• Many improvements in the manufacturing technology made

CMOS technologies a reality• Modern CMOS technologies offer excellent performance: high

speed, low power consumption, VLSI, low cost, high yield

CMOS technology occupies a dominant position of the IC market

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Following technologies•We have no choice other than follow industry, but:

•Industry may move to SOI

•Substrates and isolation will change

•Gate oxides are going down to atomic levels

•Our volume is dangerously small

•CMOS is engineered primarily for digital applications

•VDD is going down (analog harder and harder)

•Most of our circuits are mixed signal and modeling for analog is poorer

• ¼ micron is well adapted to our designs, was it just “good luck” ?

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Constant field scaling

B. Davari et al., “CMOS Scaling for High Performance and Low Power - The Next Ten Years”, Proc. of the IEEE, vol. 87, no. 4, Apr. 1999, pp. 659-667.

• L, W, tox, xD, V, VT, C, I, scale by 1/

• Area, Power diss. for a given circuit, Charges scale by 1/

• Power diss. per unit area, Charges per unit area do not scale

2

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Constant field scaling problem

Subthreshold slope and width of the moderate inversion region do not scale!!!

VGS

log ID

0 V

pA

nA

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Challenges for the future(See the talk by Y. Taur 9/Jul/01)

• Lithography• Leakage currents• Gate oxide (materials, tunneling, reliability)• Wiring and interconnections (materials)• Many metal layers (up to 10)• Design complexity (CAD tools)• Cost of fabs

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Power: Not only our problem…

by End of the Decade

But this is not the worst of it…But this is not the worst of it…But this is not the worst of it…

0.10.1

11

1010

100100

1,0001,000

10,00010,000

’71’71 ’74’74 ’78’78 ’85’85 ’92’92 ’00’00 ’04’04 ’08’08

PowerPower(Watts)(Watts)

4004400480088008

8080808080858085

80868086286286

386386486486

PentiumPentium®®

processorsprocessors

Power Too HighPower Too High

Source: P. Gelsinger, Intel Corp.Presentation at the ISSCC 2001

Source: P. Gelsinger, Intel Corp.Presentation at the ISSCC 2001

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Problem: device leakage

Source: P. Gelsinger, Intel Corp. Presentation at the ISSCC 2001

Source: P. Gelsinger, Intel Corp. Presentation at the ISSCC 2001

Source: D. Frank et al., Proceedings of the IEEE, 3/2001

Source: D. Frank et al., Proceedings of the IEEE, 3/2001

0.1 m technologyWill have a leakageCurrent of 100A/cm2

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Ideal “Analog Technology”

…Several considerations suggest that the 0.35 m or perhaps the 0.25 m

[BiCMOS technology] will be adequate… B. Gilbert, “Analog at Milepost 2000”, Proc. of the IEEE, 3/2001

Reasons:1. Cost of high performance technologies2. No need for extreme scaling in analog3. Limited supply voltage

• Limited topologies• Limited signal swing (dyn-range)

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Scaling impact on analog circuits

With tox reduced and for the same device dimensions:

• Threshold voltage matching improves

• 1/f noise decreases

• Transconductance increases (same current)

LW

tConst ox

Vth

⋅=Δσ

DSoxm IL

WC

ng

2 =

f

1

WLC

K

f

v2ox

a2in =

Δ

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Scaling impact on analog circuits

• New noise mechanisms

• Modeling difficulties

• Lack of devices for analog design

• Reduced signal swing (new architectures needed)

• Substrate noise in mixed-signal circuits

• Velocity saturation. Critical field: 3 V/m for electrons,

10 V/m for holes

satoxsatvelm vWCg =.._

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What makes CMOS rad-tol•Radiation tolerant design

• The Enclosed Layout Transistor (ELT)• Guard rings• SEE tests

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Transistor level leakage (NMOS)

Bird’s beak

Field oxide

Parasitic MOS

Trapped positive charge

Parasitic channel Source

Drain

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Single Event Upset (SEU)

GND

VDD

GND

VDDStatic RAM cell

1

10

00 1

Highly energetic particle

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ΔVT and tox scaling

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ΔVth tox

n+ ELT’s and

guard rings =TID

RadiationTolerance

Deep sub-m means also:

speedlow powerVLSIlow costhigh yield

Radiation tolerant layout approach

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SD

G

S D

G

Enclosed Layout Transistor (ELT)

ELTs solve the leakage problem in the NMOS transistors

At the circuit level, guard rings are necessary

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Effectiveness of ELTs

0.7 m technology - tox = 17 nm

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Effectiveness of ELTs

0.5 m technology - tox = 10 nm

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ELT & deep submicron

0.25 m technology - tox = 5 nm

Prerad and after 13 Mrad

No leakage

No VT shift

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Threshold voltage Leakage current

Output conductance

Annealing Annealing

NMOS L=0.28

PMOS L=0.28

NMOS L=2

PMOS L=2

Mobility degradation:< 6% NMOS< 2% PMOS

0.25 m technology

Total dose results up to 30 Mrad

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metal polysilicon

p+ guard ring n+ guard ring

INO

UT

VSS VDD

n+ diffusion p+ diffusion

Radiation tolerant layout approach

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Single Event Upset tests

σ= (cm2/bit)Nevents

•Nbitsσsat=2.59e-7 cm2

LETth=14.7 MeVcm2/mgW=29.9 MeVcm2/mgS=0.863

Static register, un-clocked mode

Design hardened register: LETth between 63 and 89 MeVcm2mg-1

at 89 MeVcm2mg-1, σ< 10-8 cm2/bit

F. Faccio et al., “Single Event Effects in Static and Dynamic Registers in a 0.25 m CMOS Technology”, IEEE Transactions on Nuclear Science, vol. 46, no. 6, Dec. 1999 , pp. 1434-1439.

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Comparison with the general trend

This static cell

P.E. Dodd et al., “Impact of technology trends on SEU in CMOS SRAMs”, IEEE Transactions on Nuclear Science, vol. 43, no. 6, Dec. 1996, pp. 2797-2804.

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What if deeper submicron ?

• SEU will be an even bigger problem

• Possible remedies– Triple redundant logic

– Error correcting logic

– Self-checking FSM

• Consequences– Higher power consumption

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Density and speed

A & B : 0.6 m standard

C & D : 0.25 m rad-tol

A B

C D

Area AArea C

3.2

Area BArea D

2.2

VDD [V]

Delay [ps]

Pwr [W/MHz]

Area [m2]

0.6 m

3.3

114

1.34

162

0.25 m

2

48

0.14

50

Inverter with F.O. = 1

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Is technology enough ?

• The next issue is power consumption, and not just technology– Need work at all levels

• Technology

• Circuits

• Architecture

• Algorithms

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Power in CMS Tracker: worst case 1)

• Total # channels: 75,500 FE chips x 128 = ~10M• Power/FE: 2.3 mW/channel• Pwr/ch data TX: ~0.6 mW/channel• Supply: 2.5 V and 1.25 V, Ptot= ~30 kW• Total FE currents: IDD125: ~7.5 kA, IDD250: ~6.5 kA• Remote supplies

# of service cables: 1,800• Power in the cables: > 75 kW• Cross section of power cables and cooling pipes

directly proportional to power dissipated !

1) Worst case is computed after 10 years of irradiation

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Material budget in CMS Tracker

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Saving power in VLSI circuits

• Technology scaling– Advanced technology, packaging, scaling

• Circuit and logic topologies– Device sizing, Logic optimization (digital),

Power down (sleep) mode

• Architecture (analog and digital)– Signal features (e.g. correlation), Data

representation, Concurrency, Partitioning

• Algorithms– Regularity, Data Representation, Complexity

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Designing chipsDesigning chips is very difficult

• Need clear objectives

• Errors are “unforgiving”

• Need complex tools

• Analog designers suffer of frequent technology changes

• Most HEP designs are “mixed” A-D (even worse !)

• Need large teams and large investments

• Need time and continuous training

• Need good engineers

• Need long term commitments

• Need complex infrastructure

• Need stable partnership with foundry

• Need good and supportive management

• The last 10% takes 90% of the time

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Time investment: Custom componentsMan*years Iterations

APV25 >10 many

PLL 4 3

MUX 1 3

CCU 5 2

DCU 3 3

LD 2 3

TTCrx 5 4Lib Dev 2

APV25

DetectorControlUnit(DCU)

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Example: Library development

• First approach”Well, let’s layout some gates and we are done…”

• Reality–Complete set of tools to fit library into CAD system–Simulation (timing) models of each gate under all load and operating conditions–Models for synthesis–Wire load models (small, medium, large designs)–Extraction models–Iterate with each new release of tools

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Reliability: how much risk can you take ?

• Did you simulate process corners ?• Device/technology modeling

– Did you look at electro-migration ?– Did you optimize your design for yield ?

• ESD: are you following the rules ?– How safe is your protection circuit ?

• How well was the chip characterized ?– IC Tester or application specific test-bench ?

• If the chip works ok on the ASTB, how much margin do you really have ?

– Will your users follow your application recommendation ?

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Miscellaneous issues

• Industry is moving to 12” wafers

• The total need for microelectronics for LHC in 1998 was corresponding to small % of the annual production of typical producer in industry

• We need a large number of prototyping cycles:– Do we have the money ?

– Will they care about us ?

• Do we have the structure necessary to design large chips ?

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Conclusions• Our community has no choice other than follow the

trend in industry– But we are not ‘normal’ users, need access to more info that

foundries typically give

• To adapt a technology for rad-tol requires many man-years of work: Need to work with a ‘minimum’ of technologies

• Don’t look at the cheapest (short-term) because what really matters is service and support– Our cost is dominated by design cost and not production

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Web

• Slides summarizing some of the talks organized for the microelectronics day organized by Erik Heijne at:

http://cern.ch/Snowmass2001