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Radiation Effects in SiGe Technologies

John D. Cressler

MURI Kickoff: Vanderbilt, Nashville, TN, May 10, 2005

School of Electrical and Computer Engineering777 Atlantic Drive, N.W., Georgia Institute of Technology

Atlanta, GA 30332-0250 USA

cressler@ece.gatech.eduTel (404) 894-5161 / http://users.ece.gatech.edu/~cressler/

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• 21st Century Communications Market- wireless + wireline + transportation + satellites + radar + other DoD + …

frequency bands are pushing ever higher

huge market but stringent device requirements

Moral: Need High-Performance Device Technology at Low-Cost!

• The SiGe HBT- first bandgap-engineered Si transistor (nanotechnology!)- better , VA, fT, fmax, NFmin than Si BJT- III-V performance + Si fabrication yield and cost (win-win scenario!)- 200 GHz SiGe HBTs are a reality! … 300 GHz is on the way!

• SiGe HBT BiCMOS Technology- very high performance SiGe HBT + best-of-breed Si CMOS- RF/MMIC + analog + digital + passives for integrated SoC / SiP solutions- in production (e.g., IBM, Jazz, National, TI, ST, Infineon, Hitachi, etc…)

SiGe: Why The Fuss?

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SiGe Strained-Layers

The Idea: Practice Bandgap Engineering (i.e., nanotechnology) in the Si Material System!

Introduce a small amount of Ge (smaller bandgap) into a Si BJT to …

Selectively tailor the transistor for improved performance!

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• Seamless Integration of SiGe into Si

When You Do It Right …

No Evidenceof Deposition! 50 nm

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• Type-I Band Alignment (Valence Band Offset = 74 meV / 10% Ge)• Hole Mobility Enhancement (good news)

Consequences

100 meV grading across 100 nm = 10 kV/cm electric field!

Strained SiGe Si

ΔEV

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SEM of a SiGe HBT

• 120 GHz Peak fT Process (IBM)

Courtesy of IBM

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The SiGe HBT

The Idea: Put Graded Ge Layer into the Base of a Si BJT

Primary Consequences:• smaller base bandgap increases electron injection (β )

• field from graded base bandgap decreases base transit time (fT )

• base bandgap grading produces higher Early voltage (VA )

III-V HBT Properties + Si Processing Maturity!Bandgap Engineering in Si!

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Performance Trends

• Generational Evolution (full SiGe BiCMOS technology)

1st

2nd

3rd

4th

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SiGe Fab Facilities

• Many Industrial SiGe Fab Facilities Worldwide (and growing)

> 25!

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• SiGe Millimeter-wave Communications Systems

- 60 GHz ISM band (> 1Gb/sec wireless links)

- wavelength at mm-wave enables monolithic antennae integration

• SiGe Radar Systems- defense theater radar (10 GHz)

- automotive radar (24 GHz, 77 GHz, 94 GHz)

• SiGe Core Analog Functions- data converters (10Gb/sec 8 bit ADC!)

- references, op-amps, drivers, etc.

• SiGe Extreme Environment Electronics- cryogenic temperatures (e.g., to 77K or 4K)- radiation (e.g., space)- high-temperatures (e.g., to 200C or 300C)

New DoD Opportunities

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• The Holy Grail of the Space Community- IC technology space-qualified without additional hardening- high integration levels to support SoC / SiP (low cost)

Radiation Effects

SiGe Technology Offers Significant Appeal!

Earth

protons belts electron belts

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Total Dose Response

• Multi-Mrad Total Dose Hardness! (with no intentional hardening!)

• Radiation Hardness Due to Epitaxial Base Structure (not Ge)- thin emitter-base spacer + heavily doped extrinsic base + very thin base

63 MeV protons

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• Observed SEU Sensitivity in SiGe HBT Shift Registers- low LET threshold + high saturated cross-section (bad news!)

• Common Circuit-level Hardening Schemes Not Effective

P. Marshall et al., IEEE TNS, 47, p. 2669, 2000

1.6 Gb/sec

Presently…The ‘Achilles Heel’ of SiGe and Space!SiGe 5HP

SEU “Issues”

Our Goal…

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• Collector-substrate (n+/p-) Junction Is a Problem (SOI)• Lightly Doped Substrate Definitely Doesn’t Help!

Very Efficient Charge Collection!

The Intuitive Picture

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diffusion

drift

• Charge Collection Mostly Occurs Through C/Sx Junction • Long Diffusion Collection Tail for High LET Hit• Collection Depth is Approximately 16um for Vertical Strike

Charge Collection

DARPA RHBD Program

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Modeling Challenges

MURI Collaboration with Robert Reed

IBM SiGe 8HP

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RAMHARD

M/SCSH-M/SNew CircuitNAND

• Reduce Tx-Tx Feedback Coupling Internal to the Latch• Circuit Architecture Changes, Layout Changes for RHBD• Variable Substrate Bias / Contacting Can Help

Need RHBD Techniques

RAMHARD

M/SCSH-M/SNew CircuitNAND

DARPA RHBD Program

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No Local Sx Contact

With Local Sx Contact

Data / Clock Buffers

Output Buffer

8HP RHBD SR Designs

DARPA RHBD Program

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• Surface (ionization) vs. Bulk (displacement + ionization) • Gamma ∆JB larger than proton ∆JB for inverse-mode

Proton vs Gamma

63 MeV Protons

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• Damage Depends on Proton Dose Rate!• Forward Mode (EB) Is Not the Same as Inverse Mode (STI) • Very Unusual Annealing Effects!

Dose Rate Effects?!

63 MeV Protons

Damage Spontaneous Annealing

Inverse

Forward

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• Use DLTS to Probe the Nature of the Traps • Can We Meaningfully Perform DLTS Inside a Transistor?

Damage Mechanisms

5AM SiGe HBTTx Chain

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• Can Irradiation Trigger Film Relaxation?• How is This Affected by Generational Scaling?

Stability Issues

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• Many Fundamental Issues Need Attention - damage mechanisms? (need first principles calculations?)- nature of the traps? (DLTS inside the device?!)- STI vs EB damage mechanism differences?- dose rate issues? - impact on displacement damage on film stability?- improved 3D modeling for SEU understanding? (with R. Reed)- device-to-circuit coupling? (mixed mode – with R. Reed)

GT MURI Tasks

• Leverage Significant SiGe Hardware / Testing Activity - SiGe tapeouts at Georgia Tech (IBM, Jazz, NSC)- DTRA / NASA-GSFC- DARPA RHBD- NASA SiGe Code T

• Leverage MURI Team Expertise (Exciting!) - R. Reed for modeling / TCAD (use the Vandy Cluster) - theory groups

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• SiGe HBT BiCMOS Technology- bandgap engineering in Si (high speed + low cost + integration)- SiGe ideally suited for RF to mm-wave, analog, and digital circuits- SiGe technology offers many interesting DoD possibilities!

Lots to Still Be Learned in SiGe Radiation Effects!

Summary

• SiGe for Radiation-Intense Electronics Is Very Promising - epi-base structure has built-in total-dose hardness (multi-Mrad!) - SEU mitigation approaches currently being pursued

BUT …