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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

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


Consequences

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

  • Hole Mobility Enhancement(good news)

ΔEV

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)

4th

3rd

2nd

1st


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

Earth

• 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

Presently…

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

diffusion

drift

DARPA RHBD Program


Modeling Challenges

IBM SiGe 8HP

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

M/S

CSH-M/S

New Circuit

NAND

M/S

CSH-M/S

New Circuit

NAND

RAMHARD

RAMHARD

DARPA RHBD Program


8HP RHBD SR Designs

Data / Clock Buffers

No Local Sx Contact

With Local Sx Contact

Output Buffer

DARPA RHBD Program


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

Inverse

Forward

63 MeV Protons


Damage Mechanisms

  • Use DLTS to Probe the Nature of the Traps

  • Can We Meaningfully Perform DLTS Inside a Transistor?

5AM SiGe HBT

Tx Chain


Stability Issues

  • Can Irradiation Trigger Film Relaxation?

  • How is This Affected by Generational Scaling?


GT MURI Tasks

  • 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)

  • - 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


Summary

• 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

BUT …


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