Radiation Effects                     in SiGe Technologies
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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 Engineering 777 Atlantic Drive, N.W., Georgia Institute of Technology Atlanta, GA 30332-0250 USA [email protected]

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Radiation Effects in SiGe Technologies John D. Cressler

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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 Engineering

777 Atlantic Drive, N.W., Georgia Institute of Technology

Atlanta, GA 30332-0250 USA

[email protected]

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

SiGe: Why The Fuss?

•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 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!

When You Do It Right …

  • Seamless Integration of SiGe into Si

No Evidence

of Deposition!

50 nm


  • Type-I Band Alignment(Valence Band Offset = 74 meV / 10% Ge)

  • Hole Mobility Enhancement(good news)


Strained SiGeSi

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

SEM of a SiGe HBT

•120 GHz Peak fT Process (IBM)

Courtesy of IBM

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!

Performance Trends

  • Generational Evolution (full SiGe BiCMOS technology)





SiGe Fab Facilities

  • Many Industrial SiGe Fab Facilities Worldwide (and growing)

> 25!

New DoD Opportunities

  • • 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)

Radiation Effects

protons belts electron belts


• The Holy Grail of the Space Community

- IC technology space-qualified without additional hardening

- high integration levels to support SoC / SiP (low cost)

SiGe Technology Offers Significant Appeal!

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

SEU “Issues”

  • • Observed SEU Sensitivity in SiGe HBT Shift Registers

  • - low LET threshold + high saturated cross-section (bad news!)

  • Common Circuit-level Hardening Schemes Not Effective


The ‘Achilles Heel’

of SiGe and Space!

SiGe 5HP

Our Goal…

1.6 Gb/sec

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

The Intuitive Picture

  • Collector-substrate (n+/p-) Junction Is a Problem (SOI)

  • Lightly Doped Substrate Definitely Doesn’t Help!

Very Efficient Charge Collection!

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




Modeling Challenges


MURI Collaboration with Robert Reed

Need RHBD Techniques

  • Reduce Tx-Tx Feedback Coupling Internal to the Latch

  • Circuit Architecture Changes, Layout Changes for RHBD

  • Variable Substrate Bias / Contacting Can Help



New Circuit




New Circuit





8HP RHBD SR Designs

Data / Clock Buffers

No Local Sx Contact

With Local Sx Contact

Output Buffer


Proton vs Gamma

  • • Surface (ionization) vs. Bulk (displacement + ionization)

  • Gamma ∆JBlarger than proton ∆JB for inverse-mode

63 MeV Protons

Dose Rate Effects?!

  • Damage Depends on Proton Dose Rate!

  • Forward Mode (EB) Is Not the Same as Inverse Mode (STI)

  • Very Unusual Annealing Effects!

Damage Spontaneous Annealing



63 MeV Protons

Damage Mechanisms

  • Use DLTS to Probe the Nature of the Traps

  • Can We Meaningfully Perform DLTS Inside a Transistor?


Tx Chain

Stability Issues

  • Can Irradiation Trigger Film Relaxation?

  • How is This Affected by Generational Scaling?


  • 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)

  • Leverage Significant SiGe Hardware / Testing Activity

  • - SiGe tapeouts at Georgia Tech (IBM, Jazz, NSC)



  • - NASA SiGe Code T

  • Leverage MURI Team Expertise (Exciting!)

  • - R. Reed for modeling / TCAD (use the Vandy Cluster)

  • - theory groups


• 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!

• 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


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